Jamel Saadaoui

Global Imbalances and Capital Account Openness: an Empirical Analysis

Keywords: JEL Classification: F31, F41 Global Imbalances, Capital Account Openness, Chinn-Ito index

We investigate if capital account openness has played a major role in the evolution of global imbalances on the period 1980-2003. We estimate, with panel regression techniques, the impact of capital account openness on medium run current account imbalances for industrialized and emerging countries by using a de jure measure of capital account openness (the Chinn-Ito index of capital account openness, 2002, 2006) and a de facto measure of capital account openness (the gross foreign assets measured as the sum of foreign assets and foreign liabilities). By increasing the opportunities of overseas investments, the relative capital account openness has had positive impact on medium run current account balances of industrialized countries (because of downward pressures on domestic investment rates). Conversely, the relative capital account openness has had negative impact on medium run current account balances of emerging countries (because of upward pressures on domestic investment rates). The evolutions of domestic and foreign capital account openness have allowed increasing medium run current account balances in absolute value during this period.

Introduction

Current account imbalances have grown significantly the last fifteen years. Several factors have been designated, in the literature, as the main drivers of these imbalances: growth differentials, saving and investment rate differences, exchange rate misalignments and financial openness (i.e. capital account openness).

Since the middle of the 1990's, global imbalances intensify to reach a climax before the financial crisis in 2006-08. These evolutions can be considered as unsustainable and they have been one of the underlying causes of the financial crisis1 . In 2006, the main contributors of these imbalances are the United States (with a deficit of more than 1.6 percent of world GDP), China and Asian countries and the oil exporters' countries (with a joint surplus of more than 1.8 percent of world GDP) as shown in figure 1.

Global imbalances are a threat to the global macroeconomic stability. Therefore identify the main causes and drivers of these imbalances seem to be crucial. We estimate, with panel regression techniques, the impact of capital account openness on medium run current account imbalances for industrialized and emerging countries by using a de jure measure of capital account openness (the Chinn-Ito index of capital account openness, 2002, 2006) and a de facto measure of capital account openness (the gross foreign assets measured as the sum of foreign assets and foreign liabilities). The main finding is that the relative capital account openness (measured relatively to world average) has played significant role on the magnitude of medium run current account. By increasing the opportunities of overseas investments, the relative financial openness has had positive impact on medium run current account balances of industrialized countries (because of downward pressures on domestic investment rates).

Conversely, the relative financial openness has had negative impact on medium run current account balances of emerging countries (because of upward pressures on domestic investment rates).

For a number of industrialized countries, the evolution of the relative financial openness (which has dropped since the middle of the 1980's since they have already liberalized their capital account and that the world average has followed an increasing trend) has had a negative impact on medium run current account balances. For South-East Asian countries, the evolution of the relative financial openness (which has dropped since the middle of the 1980's since these countries have liberalized their capital account more slowly than the world average) has had a positive impact on medium run current account balances.

This paper is organized as follow. Section 2 presents various approaches which have been proposed to shed light on the development of global imbalances since the mid-1990's. Section 3 provides empirical results of the current account regressions. Section 4 studies in greater details the contributions of each explanatory variable to the medium run current account.

Section 5 concludes.

Various explanatory approaches of global imbalances

Various explanations have been proposed to explain the surge of global imbalances observed since the middle of the 1990's among them we find the Saving-Investment approach, the intertemporal approach, the Global Saving Glut hypothesis, Bretton-Woods II and East Asian Mercantilism versus Self-protection 2 .

 The Saving-Investment approach

From the point of view of the national account identity, the external sector balance (the current account balance) can be seen as the sum of the public sector balance and the private sector balance:

2 Chinn (2010) provides a large survey on these different approaches and the corresponding empirical findings. The issues surrounding global imbalances can be analyzed as imbalances in domestic saving rates and domestic investment rates in the main economic areas at world scale. These imbalances could have been accentuated by financial openness (i.e. openness of the capital account) which has increased on the 1980-2003 period at the world level.

 The Intertemporal approach

The intertemporal approach is based on the behavior of rational expectation agent which maximizes utility function under a budget constraint. They smooth consumption by borrowing and saving thus current consumption is equal to a discounted value of future expected net output or net wealth. Change in expectations about future growth caused by productivity shocks or reductions in investment and government spending induces change in consumption.

In this perspective, the huge deficits observed in the U.S. during the 2000's could be interpreted as an expectation of a productivity boom which will improve future growth significantly. This view could be more attractive if the GDP growth has been driven by investment rather than by consumption during this period. It seems that the profit motive was not the main reason behind the huge incoming flows in the U. S.

 The Global Saving Glut hypothesis

Introduced by [START_REF] Bernanke | The Global Saving Glut and the U.S. Current Account[END_REF], Clarida (2005a, b), the "global saving glut" hypothesis explain the surge of U.S. deficit during the 2000's by a financial underdevelopment of Asian emerging countries. These differences in financial development and financial openness have allowed Asian emerging countries to export their excess of saving (due to rising savings and dropping investments after the 1997 crisis) to the U.S. Following the oil price evolutions, the oil exporter has become an important provider of savings to international financial markets.

In this view, the U.S. external imbalance is a problem made overseas. The solution is to develop financial system of emerging market with excess saving in order to reduce the financial flow to countries with better financial system.

 Bretton-Woods II and East Asian Mercantilism versus Self-protection

The East Asian surpluses can be attributed to mercantilist behavior as an outcome of this concerted effort, the U.S. run large external have surged. Dooley, Folkerts-Landau, andGraber (2003, 2008) argue that financing of America's trade deficit is an explicit quid pro quo to continued access to American markets. The accumulation of large amount of reserve can be explained by a precautionary demand or self-insurance against volatility of capital flows and macroeconomic consequences of sudden drop for instance and notably after the East-Asian crisis of 1997.

Empirical results

As the current account equals the difference between domestic saving and investment (i.e.

the saving-investment balance), the current account developments are examined from the perspective of the medium and long run determinants of saving and investment behaviors (Faruqee andDebelle, 1998, Chinn and[START_REF] Chinn | Medium term determinants of current accounts in industrial and develloping countries: an empirical exploration[END_REF]. According to these authors, the main determinants of the current account at medium term are, inter alia, the demographic characteristics, such as, the dependency ratios of dependent populations relative to the working age population or the population growth, which is expected to exert a negative influence, with a higher dependency ratio leading to more spending; the government budget balance, with a public deficit having a negative effect on the current account, but this effect may be regarded as a simple accounting one which has not to be introduced3 . South Africa, Sri Lanka, Thailand, Tunisia and Turkey).

In the current account regressions for industrialized country group (table 1), the coefficients are significant and have the expected signs: the increase of the relative population growth (RPG) reduces the current account balance (because of a higher proportion of dependent population), the increase of the relative output gap (ROG) deteriorates the current account (via the induced imports caused by the increase of the output gap of the country relatively to world average). For industrialized countries, an increase of relative financial openness (RKAOPEN or RGFA) allows to make investment abroad more extensively. Consequently, there is a downward pressure on the domestic investment rate and so, this evolution have a positive impact on the current account5 .

The sign of this coefficient express the impact of a variation financial openness on the current account balance. This kind of relationship is connected with the extensive litterature on the capital account openness and economic growth nexus. If financial openness enhance growth then the current account deteriorates because of an increase of induced imports.

However, the survey works on this issue by [START_REF] Eichengreen | Capital Account Liberalization: What Do Cross-Country Studies Tell Us?[END_REF] and by [START_REF] Kose | Financial Globalization: A Reappraisal[END_REF] reports that the litterature failed to provide a robust and systematic (positive) evidence between growth and capital account openness.

As an illustration of this last point, two recent empirical studies (Carmignani, 2008, Quinn andToyoda, 2008) found different results on this issue. [START_REF] Carmignani | Does capital account liberalisation promote economic growth? Evidence from system estimation[END_REF] argues (thanks to a system estimation and a de jure measure of financial openness) that capital account openness stimulated growth through trade openness and financial development and that the direct effect of capital account on growth is negligeable. Quinn and Toyoda ( 2008) found empirical evidence of positive link between capital account openness and growth by using a de jure measure of capital account openness. Ordinary least square (OLS) specifications with individual fixed effects raise the coefficient of determination. The generalized method of moments panel estimator [START_REF] Arellano | Some Tests of Specification for Panel Data: Monte Carlo Evidence and an Application to Employment Equations[END_REF][START_REF] Arellano | Another Look at the Instrumental Variable Estimation of Error-Components Models[END_REF] shows that there is no problem of endogeneity for the chosen specification in the current account regressions for industrialized countries group (appendix 2).

For a number of industrialized countries, the RKAOPEN variable follows a negative trend since the beginning of the 1980's. The RKAOPEN variable describes the magnitude of financial openness relative to global average of financial openness (which corresponds to a weighted average 6 of the KAOPEN index [START_REF] Chinn | Capital account liberalization, institutions and financial development: cross country evidence[END_REF], 2006). Since the global average follows a positive trend since the middle of the 1980's and that many industrialized countries have already liberalized their capital account in early 1980's, the relative capital openness variable (RKAOPEN) dropped in these countries. These evolutions have contributed negatively to the current account since the estimated coefficient is positive and statistically significant for the industrialized countries' panel in all regressions (see appendix 3, for the linear correlation between current account and RKAOPEN).

In order to check the consistency of the results, we introduce an alternative measure of financial openness (RGFA) which corresponds to the sum of the foreign assets and foreign liabilities of the country relatively to world average in % of GDP. The coefficient of the RGFA variable7 is positive and statistically significant for the industrialized country like in regression with the RKAOPEN variable. This is reassuring about the robustness of the results (see appendix 4). 6 The weights are equals to the share of each country in world GDP in dollar PPP terms. More precisely, the more the KAOPEN index is high, the more the country is open to cross-border capital transactions. In order to avoid the complexity of interpreting the estimated coefficients, this variable (KAOPEN) is adjusted such that the minimum value is zero, i.e., they range between zero and some positive value. The demeaning of the series allows controlling for rest of the world effects (Chinn & Ito, 2007). The results of unit root tests are presented in table 2 and 4. As it can be seen, the null hypothesis of non-stationarity is rejected in all the series.

In the current account regressions for emerging country group (table 3), the coefficients are significant and have the expected signs. Once again, OLS specifications with individual fixed effects raise the coefficient of determination. GMM panel estimator shows that there is no problem of endogeneity for the chosen specification in the current account regressions (appendix 2). The main difference with the current account regression for industrialized countries group is the sign of the coefficient of the RKAOPEN variable which is negative for emerging countries group (see appendix 3 for the linear correlation between current account and RKAOPEN).

For emerging countries, an increase of relative financial openness (RKAOPEN or RGFA)

allows to receive investments from abroad more extensively. Consequently, there is an upward pressure on the domestic investment rate 8 and so, this evolution have a negative impact on the current account (Ito & Chinn, 2007).

Once again, the de facto measure of financial openness (RGFA) is statistically significant and has the same sign (i.e. negative) than that of the RKAOPEN variable for the emerging countries group (see appendix 4).

For a number of emerging countries, the RKAOPEN variable follows a negative trend since the beginning of the 1980's. The RKAOPEN variable describes the magnitude of financial openness relative to global average of financial openness (which corresponds to a weighted average9 of the KAOPEN index [START_REF] Chinn | Capital account liberalization, institutions and financial development: cross country evidence[END_REF], 2006)).

For these countries, the drop of the relative capital openness (RKAOPEN) variable means that they liberalized their capital account more slowly than the global average. These evolutions have contributed positively to the current account since the estimated coefficient is negative and statistically significant for the emerging countries' panel in all regressions.

8 In order to check this point, we replace in the regressions the current account balance by the domestic investment rate (see appendix 1 for the source of the data). We find that financial openness has a positive and statistically significant impact on the domestic investment rate for the emerging countries group.

Contributions to the medium run current account balances

As it been explained in the previous section, the drop of the RKAOPEN variable has induced an increase of the medium run deficit in a number of industrialized countries and an increase of the medium run surplus of South-East Asia's emerging countries. This section illustrates this point by studying some striking cases.

 The United States and the United Kingdom

The case of the United Stated (table 5 to 10) is very interesting because it illustrates very well the case of countries which have totally liberalized its capital account in the early 1980's (thus the KAOPEN index, which is an inverse measure of capital controls, reached its upper limit). In addition, the global average of financial openness had increase on the 1980-2003's period (see appendix 5). These two evolutions have induced a drop of the RKAOPEN variable for the United States. The medium run current account 10 , which was around -1.7 % at the beginning of the 1980's, have reached around -2.5 % at the beginning of the 2000's. In this evolution, the relative financial openness has played a negative role. In fact, the contribution of the RKAOPEN variable was near from 1.3 % in the beginning of the period was reduced to only 0.9 % because the domestic and foreign evolution of the financial openness which have been already describe and because of positive coefficients of the RKAOPEN variable in the current account regressions for industrialized countries.

The case of the United Kingdom (table 5 to 10) is very similar to that of the United States, in a smaller scale. However, the capital account was totally liberalized only at the middle of the 1980's. The medium run current account have dropped to -1.7 % at the end of the period whereas it was equal to -1 % in 1980. Once again the reduction of the relative capital openness (the RKAOPEN variable) has played a negative role in the evolution of the medium run current account from the middle of the 1980's to the end of the period.

 South-East Asian countries and India

For South-East Asian's emerging countries, the story is completely different. These countries have also seen the RKAOPEN variable decrease but for different reasons of those of the United States or the United Kingdom. The main explanation of this drop is that, globally, 10 We use the OLS individual fixed effects specification to calculate the medium-term current account (i.e. equilibrium current account) for all the countries. In order to capture medium to long run trends, we set the output gaps at zero. East Asian's emerging countries have opened they capital account more slowly than the world average (see appendix 5). For China (table 5 to 10), the medium-term current account have grown significantly from the beginning of the period (from 1% in 1980 to 2.5% in 2003) in this evolution the reduction of the relative population growth and the stability of the financial openness have played a positive role 11 .

The cases of Malaysia and Indonesia (table 5 to 10) are similar on several points. They have increased their medium run current account since the beginning of the 1980's (from around -2% in 1980 to 1 % in 2003 for Indonesia; from 0% to 2% for Malaysia). In these evolutions the reduction of the relative population growth and the drop of the relative financial openness (due to the fact that these countries have liberalized their capital account more slowly than the world average) have played a positive role.

The medium run current accounts of Thailand and the Philippines have different profiles (table 5 to 10) but, in these two countries, the stability of the relative financial openness has had a positive impact on the underlying capital flows, on the whole period. The medium run current account, which was very negative in the beginning of the sample (-4% for Thailand and -2.5 % for the Philippines), have progressively improved to reach 0 % in Thailand and -2% in the Philippines. In this evolution, the depletion of the population growth has played a positive role.

The evolution of the relative financial openness in the South-East Asian's emerging countries reflect the fact these countries have liberalized their capital account more slowly than the world average. This relative decrease has had a positive impact on the current for these countries since the coefficient associated to the RKAOPEN variable is negative for the emerging countries group.

The evolutions of the medium run current account of India and its contributions (table 5 to 10) can be compared to those of South-East Asian's emerging countries. Insofar the medium run current account has improved steadily during the whole period (from around -2% to around 0%). In addition, the stability of relative financial openness has contributed positively (about 1%) to the medium run current account and the reduction of the dependency ratio has also had a positive impact but to a lesser extent than small South-East Asian countries 11 It seems to be important to recall that the signs of the coefficients are negative and statistically significant for the RKAOPEN variable in all current account regression of the emerging countries group.

which are submitted to weaker demographic constrained (comparatively to demographic giants like China and India12 ).

 Latin American countries

The case of Latin American countries is more dispersed than those of South-East Asian countries on the 1980-2003's period. For Brazil (table 5 to 10), the evolution of the relative financial openness has had a positive impact until the end of the 2000's. At the beginning of the 2000, Brazil opened his capital account more rapidly (see appendix 5) and this evolution induced a drop in the positive contribution of relative financial openness observed earlier. In spite of this decreasing evolution of financial openness, the reduction of the population growth has had a positive impact on the medium run current account which has slowly improved (from -4% to -2%).

The case of Mexico (table 5 to 10) can be seen as the opposite of South-East Asian's emerging countries cases. Indeed, Mexico had strongly reduced its relative capital openness (see appendix 5) after the debt crisis. The RKAOPEN variable decreased until 1986 and after that the openness index increased steadily until the beginning of the 2000's. This evolution of relative financial openness has contributed negatively to the medium run current account from the middle of the 1980's to the beginning of the 2000's. In spite of this negative contribution of financial openness, the medium run current account has improved strongly (from around -4% to around 0%) mainly thanks to favorable demographic evolution.

Argentina is the country in which the medium-term current account has known the most contrasted movements (table 5 to 10) mainly due to large variation in the relative financial openness. The medium run current account has improved on the whole period (from -1.5% to -0.5%) but with large variations notably during the period of the currency board system. At the beginning of the currency board scheme, the relative financial openness has been more pronounced and, thus, the contribution of the RKAOPEN variable which has been positive

(around 1%) in 1988-1991, became negative (around -0.3%) in 1996-1999. This evolution of the relative financial openness has participated to accentuate the current account deficit during the currency board era. After the burst of the crisis in 2001, the medium run current account became less negative (about -0.5%).

For Chile, the medium run current account remains stable to around -4% (table 5 to 10).

The relative financial openness is relatively stable and contributed positively to the medium term current account until the beginning of the 2000's. At this moment, Chile has opened its capital account more rapidly13 and so the contribution to the medium run current account of the RKAOPEN variable decreased sharply.

For Colombia, the medium-term current account has steadily improved from -2% to -1% on the whole period (table 5 to 10). The stability of the relative financial openness has contributed positively (like in the case of South-East Asian's emerging countries) to the medium run current account. An impressive reduction of the relative population growth has, also, contributed to the medium run current account progression.

Conclusion

Global imbalances are a threat to the global macroeconomic stability. Therefore identify the main causes and drivers of these imbalances seem to be crucial. The objective of this paper was to investigate if financial openness has played a major role in the evolution of global imbalances on the period 1980-2003.

The main finding is that the relative financial openness (measured as the deviation relatively to world average) has played significant role on the magnitude of medium run current account. By increasing the opportunities of overseas investments, the relative financial openness has had positive impact on medium run current account of industrialized countries (because of downward pressures on domestic investment rates). Conversely, the relative financial openness has had negative impact on medium run current account of emerging countries (because of upward pressures on domestic investment rates). For a number of industrialized countries, the relative financial openness has had a negative impact on medium run current account. For South-East Asian countries, the relative financial openness has had a positive impact on medium run current account. The evolution of domestic and foreign financial openness has allowed increasing the medium run current account in absolute value.

In the recent debate on the ceiling of the current account surplus (The Economist, 2010), many observers have raised questions on how quantify the threshold from which world macroeconomic stability is assured. We argue that financial openness should be taken in account in these kinds of calculations. The evolution of domestic and foreign financial openness has allowed increasing the medium run current account in absolute value during the period 1980-2003.

United Kingdom

Relative KAOPEN (Source: author's calculations)

For a number of industrialized countries (the United States, the United Kingdom, Canada, Germany, Japan), the RKAOPEN variable follows a negative trend since the beginning of the 1980's. The RKAOPEN variable describes the magnitude of capital openness relative to global average (which corresponds to a weighted average of the KAOPEN index [START_REF] Chinn | Capital account liberalization, institutions and financial development: cross country evidence[END_REF], 2006). The weights are equal to the share of each country in world GDP in PPP terms. More precisely, RKAOPEN = KAOPEN -KAOPEN ).

Since the global average follows a positive trend since the mid-1980 and that many industrialized countries have already liberalized their capital account in early 1980's, the relative capital openness variable (RKAOPEN) dropped in these countries. These evolutions have contributed negatively to the current account since the estimated coefficient is positive and statistically significant for the industrialized countries' panel in all regressions. For a number of emerging countries (China, Malaysia, Thailand, Indonesia), the RKAOPEN variable follows a negative trend since the beginning of the 1980's. The RKAOPEN variable describes the magnitude of capital account openness relatively to global average (which corresponds to a weighted average of the KAOPEN index [START_REF] Chinn | Capital account liberalization, institutions and financial development: cross country evidence[END_REF], 2006). The weights are equal to the share of each country in world GDP in PPP terms. More precisely, RKAOPEN = KAOPEN -KAOPEN ).

For these countries, the drop of the relative capital openness (RKAOPEN) variable means that they liberalized their capital account more slowly than the global average. These evolutions have contributed positively to the current account since the estimated coefficient is negative and statistically significant for the emerging countries' panel in all regressions.

Figure 1 :

 1 Figure 1: Current account balances as percent of world GDP

Table 1 : Determinants of the current account for industrialized countries

 1

		OLS Pooled	OLS Individual Fixed Effects	OLS Time Fixed Effects
	Constant	-2.54*** (0.09)	-1.43*** (0.21)	-2.45*** (0.37)
	RPG	-3.00*** (0.28)	-1.20** (0.51)	-3.03*** (0.61)
	ROG	-0.37* (0.19)	-0.48*** (0.12)	-0.39*** (0.14)
	RKAOPEN	1.08*** (0.15)	0.92*** (0.10)	0.92*** (0.25)
	Adjusted R squared	0.40	0.77	0.36
	Number of Observations	108	108	108
	Hausman test statistic		2.60 [0.45]	

Notes: The independent and dependent variables are non-overlapping 4-year averages of the corresponding annual variables. Heteroskedasticity robust standard errors are reported in parentheses. The symbols *, **, and *** indicate statistical significance at the 10 percent, 5 percent, and 1 percent levels, respectively. The last row shows Hausman test statistics for random effects versus fixed effects specifications. P-values are reported in square brackets. Source: author's estimates.

Table 2 : Panel unit root tests for industrialized countries

 2

	Variables	CA	RPG	ROG	RKAOPEN RGFA
	Industrialized countries group	-11.01*** [0.00]	-19.49*** [0.00]	-51.20*** [0.00]	-28.83*** [0.00]	-2.50*** [0.00]

Notes: The symbols *, **, and *** indicate statistical significance at the 10 percent, 5 percent, and 1 percent levels, respectively, using the test statistic Im Pesaran Shin; the rejection of the null hypothesis (of the presence of unit root), leads to reject non-stationarity of the series. P-values are reported in square brackets. Source: author's calculations.

Table 3 : Determinants of the current account for emerging countries

 3

		OLS Pooled	OLS Individual Fixed Effects	OLS Time Fixed Effects
	Constant	-0.97** (0.40)	-0.30 (0.50)	-1.19** (0.52)
	RPG	-1.94*** (0.36)	-3.21*** (0.41)	-1.66*** (0.43)
	ROG	-0.44*** (0.06)	-0.35*** (0.06)	-0.33*** (0.10)
	RKAOPEN	-0.47** (0.17)	-0.63** (0.23)	-0.45* (0.18)
	Adjusted R squared	0.47	0.68	0.35
	Number of Observations	126	126	126
	Hausman test statistic		9.51** [0.02]

 Notes: The independent and dependent variables are non-overlapping 4-year averages of the corresponding annual variables. Heteroskedasticity robust standard errors are reported in parentheses. The symbols *, **, and *** indicate statistical significance at the 10 percent, 5 percent, and 1 percent levels, respectively. The last row shows Hausman test statistics for random effects versus fixed effects specifications. P-values are reported in square brackets. Source: author's estimates.

Table 4 : Panel unit root tests for emerging countries

 4

	Variables	CA	RPG	ROG	RKAOPEN RGFA
	Emerging countries group	-5.88*** [0.00]	-6.19*** [0.00]	-27.17*** [0.00]	-4.74*** [0.00]	-4.74*** [0.00]

Notes: The symbols *, **, and *** indicate statistical significance at the 10 percent, 5 percent, and 1 percent levels, respectively, using the test statistic Im Pesaran Shin; the rejection of the null hypothesis (of the presence of unit root), leads to reject non-stationarity of the series. P-values are reported in square brackets. Source: author's calculations.

Table 5 : Contribution to the medium run current account on the 1980-1983 period (in % of GDP)

 5

		Actual current account	Medium run current account	Population Growth	Kaopen	Intercept	Individual fixed effect
		[1]	[2]	[3]	[4]	[5]	[6]
	Industrial
	United States	-0.26	-1.77	0.06	1.33	-1.44	-1.73
	Japan	0.45	2.07	0.34	0.96	-1.44	2.20
	Germany	-0.28	0.94	1.20	1.33	-1.44	-0.16
	France	-1.09	-0.60	0.59	-1.34	-1.44	1.59
	United Kingdom	0.96	-1.08	1.17	0.96	-1.44	-1.76
	Italy	-2.38	-2.14	1.08	-1.90	-1.44	0.11
	Canada	-1.65	-1.39	-0.22	1.33	-1.44	-1.07
	Developing
	China	1.06	0.79	-1.16	1.74	-0.30	0.52
	Brazil	-6.65	-3.64	-4.23	1.84	-0.30	-0.95
	India	-1.54	-1.91	-3.88	1.41	-0.30	0.86
	Mexico	-2.64	-4.21	-4.26	0.17	-0.30	0.20
	Korea	-4.97	-1.05	-1.71	1.08	-0.30	-0.12
	Indonesia	-2.31	-1.96	-3.54	-0.51	-0.30	2.39
	Argentina	-2.60	-1.62	-1.64	1.08	-0.30	-0.75
	Thailand	-5.92	-3.48	-2.46	0.75	-0.30	-1.47
	Colombia	-3.72	-2.40	-3.82	1.84	-0.30	-0.12
	Malaysia	-8.89	-0.33	-4.79	-0.51	-0.30	5.28
	Chile	-8.99	-4.14	-1.70	1.30	-0.30	-3.44
	Philippines	-5.51	-2.49	-4.80	1.41	-0.30	1.21

Note: The independent and dependent variables are non-overlapping 4-year averages of the corresponding annual variables. Source: author's calculations.

Table 6 : Contribution to the medium run current account on the 1984-1987 period (in % of GDP)

 6

		Actual current account	Medium run current account	Population Growth	Kaopen	Intercept	Individual fixed effect
		[1]	[2]	[3]	[4]	[5]	[6]
	Industrial
	United States	-2.97	-1.88	0.03	1.26	-1.44	-1.73
	Japan	3.58	2.43	0.40	1.26	-1.44	2.20
	Germany	3.05	0.88	1.22	1.26	-1.44	-0.16
	France	-0.10	-0.40	0.62	-1.17	-1.44	1.59
	United Kingdom	-0.80	-1.09	0.86	1.26	-1.44	-1.76
	Italy	-0.54	-1.41	1.09	-1.17	-1.44	0.11
	Canada	-2.05	-1.41	-0.16	1.26	-1.44	-1.07
	Developing
	China	-1.37	0.10	-1.68	1.57	-0.30	0.52
	Brazil	-0.61	-3.11	-3.75	1.90	-0.30	-0.95
	India	-1.75	-1.81	-3.83	1.46	-0.30	0.86
	Mexico	1.13	-2.18	-3.67	1.60	-0.30	0.20
	Korea	2.30	0.71	-0.33	1.46	-0.30	-0.12
	Indonesia	-2.93	-1.97	-3.20	-0.86	-0.30	2.39
	Argentina	-2.45	-1.43	-1.84	1.46	-0.30	-0.75
	Thailand	-2.29	-2.72	-1.75	0.80	-0.30	-1.47
	Colombia	-1.64	-2.23	-3.70	1.90	-0.30	-0.12
	Malaysia	0.25	-1.95	-6.07	-0.86	-0.30	5.28
	Chile	-7.45	-4.22	-2.38	1.90	-0.30	-3.44
	Philippines	1.46	-2.59	-4.79	1.30	-0.30	1.21

Note: The independent and dependent variables are non-overlapping 4-year averages of the corresponding annual variables. Source: author's calculations.

Table 7 : Contribution to the medium run current account on the 1988-1991 period (in % of GDP)

 7

		Actual current account	Medium run current account	Population Growth	Kaopen	Intercept	Individual fixed effect
		[1]	[2]	[3]	[4]	[5]	[6]
	Industrial
	United States	-1.38	-2.05	-0.09	1.20	-1.44	-1.73
	Japan	2.07	2.74	0.77	1.20	-1.44	2.20
	Germany	2.57	-0.01	0.39	1.20	-1.44	-0.16
	France	-0.55	-0.39	0.49	-1.04	-1.44	1.59
	United Kingdom	-3.63	-1.11	0.89	1.20	-1.44	-1.76
	Italy	-1.76	-1.23	1.13	-1.04	-1.44	0.11
	Canada	-3.51	-1.88	-0.57	1.20	-1.44	-1.07
	Developing
	China	1.10	0.58	-1.56	1.94	-0.30	0.52
	Brazil	0.08	-1.74	-2.42	1.94	-0.30	-0.95
	India	-2.29	-1.26	-3.32	1.50	-0.30	0.86
	Mexico	-2.85	-1.84	-2.89	1.16	-0.30	0.20
	Korea	1.64	0.45	0.03	0.84	-0.30	-0.12
	Indonesia	-2.34	-0.93	-2.20	-0.82	-0.30	2.39
	Argentina	0.80	-0.88	-1.33	1.50	-0.30	-0.75
	Thailand	-5.49	-1.72	-0.79	0.84	-0.30	-1.47
	Colombia	1.14	-1.74	-3.03	1.72	-0.30	-0.12
	Malaysia	-1.20	-1.70	-5.86	-0.82	-0.30	5.28
	Chile	-1.29	-4.19	-2.38	1.94	-0.30	-3.44
	Philippines	-2.69	-1.97	-4.38	1.50	-0.30	1.21
	Note: The independent and dependent variables are non-overlapping 4-year averages of the corresponding annual
	variables. Source: author's calculations.

Table 8 : Contribution to the medium run current account on the 1992-1995 period (in % of GDP)

 8

		Actual current account	Medium run current account	Population Growth	Kaopen	Intercept	Individual fixed effect
		[1]	[2]	[3]	[4]	[5]	[6]
	Industrial
	United States	-1.33	-2.59	-0.35	0.92	-1.44	-1.73
	Japan	2.72	2.46	0.83	0.86	-1.44	2.20
	Germany	-1.16	-0.09	0.59	0.92	-1.44	-0.16
	France	0.50	1.33	0.74	0.44	-1.44	1.59
	United Kingdom	-1.55	-1.39	0.88	0.92	-1.44	-1.76
	Italy	0.46	0.27	1.15	0.44	-1.44	0.11
	Canada	-2.63	-1.63	-0.05	0.92	-1.44	-1.07
	Developing
	China	0.24	1.50	-0.51	1.80	-0.30	0.52
	Brazil	-0.34	-0.88	-1.75	2.13	-0.30	-0.95
	India	-0.97	-0.44	-2.69	1.69	-0.30	0.86
	Mexico	-4.73	-2.31	-2.63	0.43	-0.30	0.20
	Korea	-0.91	0.47	-0.14	1.03	-0.30	-0.12
	Indonesia	-1.98	-0.22	-1.68	-0.63	-0.30	2.39
	Argentina	-3.12	-1.80	-1.08	0.33	-0.30	-0.75
	Thailand	-5.95	-1.24	-0.50	1.03	-0.30	-1.47
	Colombia	-2.53	-1.14	-2.73	2.02	-0.30	-0.12
	Malaysia	-6.31	-0.07	-5.02	-0.03	-0.30	5.28
	Chile	-3.07	-4.45	-2.46	1.76	-0.30	-3.44
	Philippines	-3.61	-2.45	-4.07	0.72	-0.30	1.21
	Note: The independent and dependent variables are non-overlapping 4-year averages of the corresponding annual
	variables. Source: author's calculations.

Table 9 : Contribution to the medium run current account on the 1996-1999 period (in % of GDP)

 9

		Actual current account	Medium run current account	Population Growth	Kaopen	Intercept	Individual fixed effect
		[1]	[2]	[3]	[4]	[5]	[6]
	Industrial
	United States	-2.24	-2.57	-0.32	0.92	-1.44	-1.73
	Japan	2.34	2.24	0.80	0.67	-1.44	2.20
	Germany	-0.76	0.25	0.93	0.92	-1.44	-0.16
	France	2.41	1.76	0.69	0.92	-1.44	1.59
	United Kingdom	-0.91	-1.53	0.75	0.92	-1.44	-1.76
	Italy	2.08	0.65	1.05	0.92	-1.44	0.11
	Canada	-0.43	-1.65	-0.07	0.92	-1.44	-1.07
	Developing
	China	2.31	1.61	-0.29	1.69	-0.30	0.52
	Brazil	-3.64	-1.27	-1.93	1.91	-0.30	-0.95
	India	-1.20	-0.42	-2.67	1.69	-0.30	0.86
	Mexico	-2.16	-1.64	-1.76	0.23	-0.30	0.20
	Korea	2.84	1.50	0.23	1.69	-0.30	-0.12
	Indonesia	0.75	0.40	-1.59	-0.09	-0.30	2.39
	Argentina	-3.91	-2.21	-0.86	-0.29	-0.30	-0.75
	Thailand	3.25	-1.35	-0.61	1.03	-0.30	-1.47
	Colombia	-3.18	-1.40	-2.67	1.69	-0.30	-0.12
	Malaysia	4.62	0.46	-5.12	0.60	-0.30	5.28
	Chile	-3.32	-3.32	-1.59	2.02	-0.30	-3.44
	Philippines	-2.81	-2.10	-3.89	0.89	-0.30	1.21
	Note: The independent and dependent variables are non-overlapping 4-year averages of the corresponding annual
	variables. Source: author's calculations.

Table 10 : Contribution to the medium run current account on the 2000-2003 period (in % of GDP)

 10

		Actual current account	Medium run current account	Population Growth	Kaopen	Intercept	Individual fixed effect
		[1]	[2]	[3]	[4]	[5]	[6]
	Industrial
	United States	-4.30	-2.45	-0.21	0.92	-1.44	-1.73
	Japan	2.70	2.47	0.78	0.92	-1.44	2.20
	Germany	0.59	0.20	0.87	0.92	-1.44	-0.16
	France	1.44	1.33	0.26	0.92	-1.44	1.59
	United Kingdom	-2.01	-1.69	0.58	0.92	-1.44	-1.76
	Italy	-0.67	0.28	0.68	0.92	-1.44	0.11
	Canada	1.98	-1.64	-0.06	0.92	-1.44	-1.07
	Developing
	China	2.06	2.48	0.57	1.69	-0.30	0.52
	Brazil	-2.18	-1.89	-1.86	1.23	-0.30	-0.95
	India	0.56	-0.25	-2.34	1.53	-0.30	0.86
	Mexico	-2.21	-0.40	-0.85	0.56	-0.30	0.20
	Korea	1.75	1.44	0.67	1.20	-0.30	-0.12
	Indonesia	4.14	0.77	-1.54	0.23	-0.30	2.39
	Argentina	2.67	-0.50	-0.48	1.03	-0.30	-0.75
	Thailand	4.77	-0.65	0.09	1.03	-0.30	-1.47
	Colombia	-0.72	-1.04	-2.31	1.69	-0.30	-0.12
	Malaysia	9.21	2.07	-3.94	1.03	-0.30	5.28
	Chile	-1.18	-4.40	-0.99	0.34	-0.30	-3.44
	Philippines	-1.35	-2.20	-3.99	0.89	-0.30	1.21

Note: The independent and dependent variables are non-overlapping 4-year averages of the corresponding annual variables. Source: author's calculations.

Table A4 .1: Determinants of the current account with a de facto measure of financial openness for industrialized countries

 A4

		OLS Pooled	OLS Individual Fixed Effects
	Constant	-2.03*** (0.13)	-0.96*** (0.23)
	RPG	-2.57*** (0.52)	-0.89** (0.39)
	ROG	-0.56** (0.17)	-0.55*** (0.11)
	ΔRGFA	0.01*** (0.00)	0.007*** (0.00)
	Adjusted R squared	0.43	0.92
	Number of Observations	90	90

Notes: The independent and dependent variables are non-overlapping 4-year averages of the corresponding annual variables. Heteroskedasticity robust standard errors are reported in parentheses. The symbols *, **, and *** indicate statistical significance at the 10 percent, 5 percent, and 1 percent levels, respectively. Source: author's estimates.

Table A4 .2: Determinants of the current account with a de facto measure of financial openness for emerging countries

 A4

				Figure A5.1: Relative KAOPEN for Industrialized Countries
			World weighted average									United States
	3.6												1.6
	3.4												1.4
	3.2												1.2
	3.0												1.0
													0.8
	2.8												0.6
	2.6												0.4
	2.4												0.2
	2.2												0.0
	1980	1982	1984	1986	1988	1990	1992	1994	1996	1998	2000	2002		1980	1982	1984	1986	1988	1990	1992	1994	1996	1998	2000	2002
					KAOPEN WORLD									Relative KAOPEN
						Japan											Germany
	1.6												1.6
	1.4												1.4
	1.2												1.2
	1.0												1.0
	0.8												0.8
	0.6												0.6
	0.4												0.4
	0.2												0.2
	0.0												0.0
	1980	1982	1984	1986	1988 Relative KAOPEN 1990 1992 1994 1996	1998	2000	2002 OLS Pooled	1980	1982	1984	1986	1988 Relative KAOPEN 1990 1992 1994 1996 OLS Individual 1998 2000 2002 Fixed Effects
	0.0 0.5 1.0 1.5	Constant RPG ROG		France					-0.67 (0.48) -1.20*** (0.46) (0.11) 1.0 -0.43*** 1.2 1.4 1.6								-0.71** (0.34) -1.53*** (0.05) -0.34*** (0.38)
	-1.0 -0.5	ΔRGFA								(0.00) -0.02** 0.6 0.8								(0.00) -0.02***
	Adjusted R squared -2.0 -1.5						0.23	0.2 0.4									0.70
	Number of Observations -2.5					105	0.0									105
	1980	1982	1984	1986	1988	1990	1992	1994	1996	1998	2000	2002		1980	1982	1984	1986	1988	1990	1992	1994	1996	1998	2000	2002
					Relative KAOPEN

Notes: The independent and dependent variables are non-overlapping 4-year averages of the corresponding annual variables. Heteroskedasticity robust standard errors are reported in parentheses. The symbols *, **, and *** indicate statistical significance at the 10 percent, 5 percent, and 1 percent levels, respectively. Source: author's estimates.

Servén and Nguyen (2010) examine the different views on the role of the global imbalances before and after the crisis.

There are other variables, such as the openness ratio, which plays negatively, a higher openness meaning a greater possibility of assuring the debt service in the future, or the relative real GDP per capita, which exerts a non-linear influence according to stages of development. The results were not significant enough. Moreover, relative GDP per capita is evaluated non stationary by most of tests.

We introduce a panel GMM panel estimator in order to cope with eventual problems of endogeneity.

In order to check this point, we replace in the regressions the current account balance by the domestic investment rate (see appendix 1 for the source of the data). We find that financial openness has a negative and statistically significant impact on the domestic investment rate for the industrialized countries group.

The RGFA variable is not stationary in level so we use the variation, to avoid fallacious regressions' problems, of this variable but the interpretation remains basically the same than for the RKAOPEN variable.

See note 4.

In spite of similar demographic profiles, China and India have had different policy of fertility. The 'one-child policy' has allowed an impressive reduction of the population growth and dependency ratios in China.

Interestingly, Brazil and Chile have opened more rapidly their capital account at the beginning of the 2000's whereas Argentina has known the inverse evolution.

Fund. Quinn, D.P., Toyoda, A.M., 2008. Does Capital Account Liberalization Lead to Growth?, Review of Financial Studies, 21(3), pp. 1403-1449. Servén, L., Nguyen, H., 2010. Global Imbalances Before and After the Global Crisis, Policy Research Working Paper 5354, The World Bank.

The Economist, 'Finally, a talking-shop worth having', November 4, 2010.

The KAOPEN index is a measure of financial openness (i.e. openness of the capital account).

Introduced for the first time by [START_REF] Chinn | Capital account liberalization, institutions and financial development: cross country evidence[END_REF] this index aims to measure the extensity of the capital controls (as it is an inverse measure of the intensity of capital controls) based on the information of the IMF's Annual Report on Exchange Rate Arrangements and Exchange Restrictions (AREAR).

The KAOPEN index is computed from binary dummy variables. These dummy variables are used to codify the restrictions on cross border financial transaction reported in the AREAR.

Until 1996, the AREAR assign dummy variables for the four major categories on the restriction on the capital account (the existence of multiple exchange rates (k 1 ), restrictions on current account transactions (k 2 ), restrictions on capital account transactions (k 3 ) and requirement of the surrender of export proceeds (k 4 )). In order to understand the complexity of capital control policies, these four categories have been more disaggregated in 1996 (the variables indicating restrictions on current account transactions have been divided into thirteen categories).

Since they are focused on the effect of financial openness, Chinn and Ito reverse these binary variables. When variables are equal to zero, the capital account restrictions exist. In addition for the k 3 category, they used a five-year window where capital controls where not in effect (SHAREk 3 ).

  

Then, they construct their index for capital account 'openness', which the first standardized principal component of k 1t , k 2t , SHAREk 3t , k 4t [START_REF] Chinn | Current account balances, financial development and institutions: Assaying the world ''saving glut[END_REF]. The more the country is open to cross-border capital flows, the more the KAOPEN index is high. This index has the merit to try to measure the intensity of capital restriction. The index was firstly designed to measure the extensity of capital controls, but as it incorporates various kinds of restrictions it may be a good proxy to gauge the intensity of capital account restrictions. Note that the KAOPEN index is highly correlated with other measures of financial openness [START_REF] Chinn | Current account balances, financial development and institutions: Assaying the world ''saving glut[END_REF].


Valenti Sallarès
email: vsallares@cmima.csic.es

Audrey Gailler

Marc-André M-A Gutscher

David Graindorge

Rafael Bartolomé

Eulalia Gracia

Jordi Diaz

Juan José Dañobeitia

Nevio Zitellini

Jordi Díaz

Valentí Sallarès

Seismic evidence for the presence of Jurassic oceanic crust in the central Gulf of Cadiz (SW Iberian margin)

établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The region offshore SW Iberia lies at the eastern end of the Azores-Gibraltar fracture zone (AGFZ), and is part of the complex plate boundary between the African and Eurasian plates (Figure 1). The tectonic behavior along the AGFZ is complex, varying from extensional in the West, close to the Mid-Atlantic Ridge, strike-slip in the center, along the Gloria fault, and mostly compressional in the East, from cape São Vicente to the Strait of Gibraltar. The regional tectonic history has been dominated by the long-term evolution of the triple junction between the North-American, African and Eurasian plates, as well as the interaction with other smaller blocks such as the Iberian plate (e.g. [START_REF] Srivastava | Iberian plate kinematics: a jumping plate boundary between Eurasia and Africa[END_REF][START_REF] Olivet | La cinématique de la Plaque Ibérique[END_REF]. Plate kinematic models and GPS observations show that Africa is currently moving in a NW-WNW direction with respect to Iberia at 4-5 mm/yr [START_REF] Argus | Closure of the Africa-Eurasia-North America plate motion circuit and tectonics of the Gloria fault[END_REF][START_REF] Nocquet | Geodetic measurements of crustal deformation in the Western Mediterranean and Europe[END_REF]. This plate boundary is fairly diffuse, marked by an E-W trending band of seismicity about 100-200 km wide (e.g. [START_REF] Buforn | Seismotectonics of the Ibero-Maghrebian region[END_REF]. Moderate to strong earthquakes have struck here in the past, with a combination of compressional and strike-slip focal mechanisms [START_REF] Grimison | The Azores Gibraltar plate boundary: Focal mechanisms, depths of earthquakes, and their tectonic implications[END_REF][START_REF] Stich | Moment-tensor solutions for small and moderate earthquakes in the Ibero-Maghreb region[END_REF][START_REF] Gràcia | Earthquake and Tsunami Hazards in the Southwest Iberian Margin: High-resolution imaging of active faults and paleoseismic signature at the external part of the Gulf of Cadiz[END_REF]. In addition to this continuous, moderate magnitude seismic activity, the region has been also struck by large historical earthquakes, most notably the catastrophic Great Lisbon earthquake of 1755 (Mw=8.5-8.6) [START_REF] Johnston | Seismic moment assessment of earthquakes in stable continental regions -III New Madrid 1811-1812, Charleston 1886 and Lisbon 1755[END_REF].

A major limit exists in the Gulf of Cadiz between the Central Atlantic domain, which opened in the Early Jurassic, and the Northern Atlantic domain, which opened in the Upper Cretaceous (e.g., [START_REF] Roest | Kinematics of the plate boundaries between Eurasia, Iberia, and Africa in the North Atlantic from the Late Cretaceous to the present[END_REF][START_REF] Olivet | La cinématique de la Plaque Ibérique[END_REF][START_REF] Rovere | Seismic images and magnetic signature of Late Jurasic to Early Cretaceous Africa-Eurasia plate boundary off SW Iberia[END_REF]Sahabi et al., 2004). Available plate reconstruction models suggest that the region might have been the site of limited amounts of oceanic spreading due to the ESE migration of the African plate with respect to Iberia during this period of time (e.g. [START_REF] Stampfli | A Plate Tectonic Model for the Paleozoic and Mesozoic[END_REF][START_REF] Schettino | Tectonic history of the western Tethys since the Late Triassic[END_REF]. The possible presence of an oceanic basin of Jurassic age in this area is a largely debated question that has profound implications in the geodynamic evolution of the Western Mediterranean, and most specifically the Alboran basin system (e.g. [START_REF] Lonergan | Origin of the Betic-Rif mountain belt[END_REF]Gutscher et al., 2002;[START_REF] Faccenna | Lateral slab deformation and the origin of the western Mediterranean arcs[END_REF]. Unfortunately, the nature of the crust in the deep oceanic domains offshore SW Iberia is unknown and difficult to determine because there are few recognizable magnetic anomaly patterns [START_REF] Verhoef | Magnetic anomalies off West-Africa[END_REF], and the seafloor is covered by a thick layer of Mesozoic to recent sediments, thus basement samples are difficult to obtain. The only deep sea drilling in the region that penetrated to the basement was the DSDP site 120 on Gorringe Bank (Figure 1), where serpentinized peridotite corresponding to exhumed mantle, gabbro, and extrusive rocks were sampled [START_REF]Gorringe Bank -Site 120[END_REF]. Similar rocks were also recovered during dredging and deep-sea submersible expeditions [START_REF] Auzende | Intraoceanic tectonism on the Gorringe Bank: Observations by submersible, in Ophiolites and Oceanic Lithosphere[END_REF][START_REF] Girardeau | Extensional tectonics in the Gorringe Bank rocks, eastern Atlantic ocean: Evidence of an oceanic ultra slow mantellic accreting centre[END_REF]. DSDP site 135 Southwest of the Coral Patch Ridge (Figure 1) penetrated Jurassic sediments (Aptian) but did not reach the basement (Hayes et al., 1972). Finally, continental rocks of Paleozoic age have been also sampled at the Guadalquivir Bank in the Iberian margin [START_REF] Malod | L'histoire géologique néogène du Golfe de Cadix[END_REF].

Because of the lack of basement samples, current knowledge of the crustal domains in the Gulf of Cadiz is based almost exclusively on geophysical data. Available multi-channel seismic (MCS) data [START_REF] Sartori | Eastern Segment of the Azores-Gibraltar Line (Central-Eastern Atlantic): An Oceanic Plate Boundary with Diffuse Compressional Deformation[END_REF][START_REF] Banda | Iberian Atlantic Margins Group Investigates Deep Structure of Ocean Margins, a Multichannel Seismic Survey[END_REF][START_REF] Torelli | The giant chaotic body in the Atlantic off Gibraltar: new results from a deep seismic reflection survey[END_REF][START_REF] Gràcia | Earthquake and Tsunami Hazards in the Southwest Iberian Margin: High-resolution imaging of active faults and paleoseismic signature at the external part of the Gulf of Cadiz[END_REF], as well as refraction and wide-angle reflection (WAS) data [START_REF] Purdy | The Eastern end of the Azores-Gibraltar plate boundary[END_REF][START_REF] González | Crustal thinning in the southwestern Iberia margin[END_REF]Gutscher et al., 2002) and models based on potential field data (e.g. Gràcia et al., 2003;[START_REF] Fullea | The structure and evolution of the lithosphere -asthenosphere boundary beneath the Trans-Mediterranean region[END_REF], globally highlight the eastward increase in sediment thickness, depth to basement, and depth to Moho [START_REF] Iribarren | The structure of the Atlantic-Mediterranean transition zone from the Alboran Sea to the Horseshoe Abyssal Plain (Iberia -Africa plate boundary)[END_REF]Gutscher et al., 2009b), but do not provide information on the crustal nature across the different tectonic boundaries.

In fall 2008, in the framework of the EU-funded NEAREST (NEAR shore sourcES of Tsunamis: towards an early warning system) project, the NEAREST-SEIS WAS survey was performed in the Gulf of Cadiz. During that survey, two long profiles using Ocean Bottom Seismometers (OBS) and land stations were acquired to probe the deep structure of the SW Iberian margin and adjacent oceanic areas (Figure 1). One of the profiles was mainly designed to shed light on the unresolved question of the crustal nature in the central Gulf of Cadiz (N-S profile in figure 1). The interpretation of the modeling results obtained along this profile, which begins in the Seine Abyssal Plain, crosses the Gulf of Cadiz imbricated wedge (GCIW) and several of the "SWIM" lineaments [START_REF] Zitellini | The quest for NWAfrica-SW Eurasia plate boundary west of Gibraltar[END_REF], the Portimao bank, and continues up onto the Portuguese continental shelf until the Variscan Iberian domain, are the main goals of the work presented in this paper.

Data acquisition

The WAS data were acquired onboard the Spanish R/V Hesperides. Fifteen OBS were deployed along a 257-km-long shooting line reaching from the southern tip of the GCIW into the Portimao Canyon (Figure 1). Four of the OBS were L-Cheapo 4x4 instruments, designed by the Scripps Institution of Oceanography, and belonging to the Spanish OBS pool operated by the UTM-CSIC. The other eleven OBS were from the joint IFREMER-IUEM pool [START_REF] Auffret | MicrOBS: A new ocean bottom seismometer generation[END_REF]. The profile was extended on land in Portugal by 7 land-stations. Due to timing problems we used only 3 of these stations in the modelling, giving a total recording length of 342 km. The source was composed of 7 airguns organized in two arrays, providing a total volume of 4320 c.i. The arrays were deployed at a depth of 12 m, and the shot interval was set to 90 s (∼210 m) to avoid noise generated by previous shots. Pre-processing of the OBS data included calculation of the clock-drift corrections and instrument relocation for spatial drift during their fall to the seafloor.

Most of the WAS data have a good quality, showing clear sedimentary (Ps) and intra-crustal refracted phases (Pg), reflections at the sediment-basement interface (PsP) and crustmantle boundary (PmP), and deeper arrivals refracted in the upper mantle (Pn) up to 100 km offset in some OBS, and to more than 150 km in the land stations. Five of the record sections at OBS and land stations are displayed in figure 2.

Seismic sections of the instruments located on the top of the GCIW show clear lowvelocity sedimentary refractions (Ps) and reflections at the top of the basement (PsP).

Significant variations are observed between record sections of the southern instruments, located towards the frontal part of the GCIW, and those located northward in the Algarve basin area (Figure 2d). Seismic sections from OBS located close to the Portimao canyon in very shallow water have limited quality. Conversely, long offset PmP and Pn phases can be clearly traced on the record sections of all the land stations (Figure 2e). Instruments located southward, in deeper water show clearer arrivals, including sediment and crustal arrivals (Figure 2a). In the modelling of the crustal structure we used data recorded at all the OBS and at the three land stations located the closest to the coast (Figure 1).

Travel-time picking and modelling approach

A total of 4003 picks, including first arrivals (Ps, Pg, Pn) and secondary reflections (PsP and PmP) were identified in the record sections. Picking was done manually on unfiltered data where possible and if needed, a deconvolution whitening, band-pass filtering (4-16 Hz) and Automatic Gain Correction were applied to improve lateral coherence and increase signal-to-noise ratio. Ps and PsP phases were observed and picked in all the OBS located on top of the sedimentary wedge, and Pg was also observed to variable offset in all the OBSs. PmP and Pn's could not be identified in all the record sections, especially in the two shallowest, northernmost OBSs. A picking uncertainty was assigned to the different picks taking into account the quality of the phase, individual picking errors, and a possible systematic shift, of the order of half of the dominant period of the dominant signal, in the arrival identification. For Ps and near-offset Pg phases the average assigned uncertainty was 40-50 ms, while it was 60-70 ms for far-offset Pg's and 70-80 ms for Pn's. For PsP reflections it was 50-60 ms, and 70-80 ms for PmP's.

The 2-D velocity-depth model was obtained using the tomo2d joint refraction and reflection travel-time inversion code described in [START_REF] Korenaga | Crustal structure of the southeast Greenland margin from joint refraction and reflection seismic tomography[END_REF]. The method allows inverting simultaneously and independently travel-times from first arrivals and from a reflected phase, to obtain a velocity model and the geometry of a floating reflector. Traveltimes and ray paths are calculated using a hybrid ray-tracing scheme based on the graph method [START_REF] Moser | Shortest path calculation of seismic rays[END_REF] and a local ray bending refinement. Smoothing constraints for predefined correlation lengths and optimized damping for the model parameters are used to regularize the iterative linearized inversion (see Korenaga et al., 2000, for details).

To perform the inversion we employed an original multi-step, hybrid inversion strategy consisting of (1) splitting the data into two subsets, one for instruments located on the sedimentary wedge, and the other for those in the continental margin, and (2) adding the data sequentially, starting from the shortest offsets/uppermost levels, and finishing with the longest offsets/deepest levels.

The velocity model for the southern part of the profile was constructed in two steps, corresponding to the inversion of the sediments and crust. The Ps and PsP phases were used to invert for the velocities and thickness of the sedimentary wedge, and hence the geometry of the sediment-basement boundary (Figure 3a and3b). The starting model was a laterallyextended "minimum 1-D velocity model", which is the one that fits the best the Ps traveltimes (e.g. [START_REF] Sallarès | Seismic structure of Malpelo and Cocos Volcanic Ridges and implications for hotspot-ridge interaction[END_REF]. The top of the basement reflector was initially set at 7 km.

The inverted velocity model of the sediments was included as a priori information in the second inversion step, in which Ps, Pg and PmP arrivals were used to obtain the crustal velocity distribution and Moho geometry. The sediment velocity parameters were overdamped by a factor of 20 to 1 to let the inversion modify the model preferably within the crust. The starting velocity model below the sediment layer was a 1-D model varying uniformly from 4.5 km/s at the sediment-basement boundary to 7.2 km/s 7 km below, simulating an Atlantic oceanic crust older than 140 m.y. [START_REF] White | Oceanic crustal thickness from seismic measurements and rare earth element inversions[END_REF]. The initial Moho reflector was set 7 km below the sediment-basement boundary. The corresponding 2-D crustal velocity model, obtained after 8 iterations, is shown in figures 3c and 3d.

The velocity model for the northern part of the profile was inverted in a single step, since no clear Ps or PsP phases were identified in the record sections. Consequently, sediments and crust were inverted together using the Pg and PmP phases to model the crustal velocity field and Moho geometry. The 2-D starting velocity model was constructed combining a 1-D model for the offshore section (i.e., the model that best fits Pg arrivals from the OBS located in the Algarve basin), and a second one for the onshore section, which was extracted from an onshore WAS profile acquired nearby (Palomeras et al., 2009). At the landsea transition, the seismic velocities of the reference model were calculated by linear interpolation of these two 1-D velocity-depth models. The 2-D crustal velocity model for the northern section obtained after 8 iterations is shown in figures 3e and 3f.

In the third and last step, the southern and northern crustal models were merged together and a new inversion was performed using the whole set of refractions (Ps, Pg,and Pn) together with PmP's, to obtain a complete model including sediments, crust and uppermost mantle along the entire profile. As in the previous steps, the velocity nodes above the basal reflector were over-damped to favour model changes below the Moho. Beneath the Moho, a laterally-extended 1-D velocity-model with velocity varying uniformly from 7.5 km/s below the Moho to 8.3 km/s at 35 km depth, although alternative models with higher velocity beneath the Moho were also tested. The 2-D velocity model obtained after 7 iterations is shown in figure 4. The final rms for this model is 65 ms (χ 2 =1.02), with an rms of 61 ms for first arrivals and 72 ms for PmP's. The derivative weight sum (DWS), which is the column sum vector of the velocity kernel [START_REF] Toomey | Tomographic inversion of local earthquake data from the Hengill-Grensdalur central volcano complex, Iceland[END_REF]) and provides information on the linear sensitivity of the inversion, is shown in figure 5a.

Results

Seismic structure

The final velocity model in figure 4 shows marked differences between the sedimentary and crustal structures from south to north, with a marked transition zone between 160 and 210 km distance along the profile where the crust thins sharply. The southern part of the model (0-160 km along profile), which runs across the GCIW, shows a ~5 km thick layer corresponding to the sedimentary cover, with velocities ranging from ~1.8 km/s at the top to ∼3.5 km/s at the base. This layer can in turn be subdivided in an upper layer of 2-3 km with velocity between ~1.6 km/s and 3.0 km/s, and a bottom one of 1-2 km with velocity between 2.8 km/s and 4.0 km/s. This sedimentary unit exhibits a quite uniform thickness along the southern 120 km of the profile, then thins progressively to the north, and more abruptly landward from ~125 km (between OBS37 and 38).

The crust below the sedimentary units shows a rather uniform thickness of ∼7.0 km between 0 km and 160 km. Crustal velocities vary from 4.6-4.8 km/s at the top to 6.9-7.1 km/s at the base. The vertical velocity gradient is steeper in the uppermost crust (∼0.45 s -1 in the upper 2 km) than in the lower part (∼0.14 s -1 in the lower 5 km) (Figure 4). The Moho depth and geometry is constrained by PmP reflections, and it follows the basement topography along most of the section. The long-wavelength crustal velocity field is rather uniform laterally, except for a pronounced anomaly centred at 130-145 km (between OBS38 and 39), as indicated by the depression of the velocity contours observed in this area (Figure 4) that gets down to the Moho but does not affect the sediments. The anomaly is clearly imaged in figure 6 representing the negative anomalies with respect to a laterally-smoothed velocity average along the profile. As it is observed in this figure, the corresponding anomaly (f1) has an amplitude of -0.5 km/s, dips to the south, and is >10 km-wide. A second crustalscale low-velocity anomaly with similar geometry but lower amplitude (~-0.15 km/s) was also detected at ~90 km (f0 in figure 6).

The profile section between 160 and 210 km (between OBS41 and 44) corresponds to the rough topographic region between the GCIW and the Algarve Basin. This segment accommodates almost all the crustal thickening. Within ~60 km, the Moho deepens from ~14 km to ∼25 km depth (corresponding to a slope of ∼12-13°), so the crust thickens drastically from ~7 km to ∼24 km. Northward from 210 km the vertical velocity gradient decreases (∼0.05 s -1 ), reaching maximum velocities of 6.9-7.0 km/s just above the crust-mantle boundary. The Moho geometry in this section is mainly constrained by PmP arrivals (OBS44 in figure 2d). The shallow velocity field at the transition zone from the oceanic domain towards the continent indicates the presence of a thin sediment cover on top of the basement, so that Ps/PsP phases are not distinguished in the record sections, so that the structure of the sedimentary layers and the sediment-basement interface could not be properly defined. In this area, two bathymetric highs are present, one located at ~180 km (the Portimao Bank) and the other one located at 200-210 km (a spur bounding the Portimão canyon). The isovelocity contour of 4.0 km/s reaches there almost the surface, indicating that the basement is possibly outcropping here (BH in Figure 1). Two zones of relatively low crustal velocity, similar to that described in the southern part of the model, can be seen at [180][181][182][183][184][185][186][187][188][189][190]) and ~225 km (around OBS44) (Figure 5). Both features are also reflected as pronounced, south-dipping, negative velocity anomalies of up to -0.7 km/s that seem to start at the seafloor and reach a maximum depth of 13-14 km (f2 and f3 in figure 6). Similarly to f1, f2 and f3 extend laterally to >10 km in the model and show dip angles of 35-45º.

The northernmost part of the model, between 210 km and the end of the profile (Figure 4), corresponds to the upper part of the contouritic drift and shelf and the Algarve Basin, characterized by the Variscan basement. It shows only a residual sedimentary cover that is less than 1 km-thick. In this area the Moho gently deepens from ~25 km at 210 km along profile (between OBS43 and 44) to ~29 km at 260 km (north from OBS45 in figure 1).

A maximum crustal thickness of 29 km is obtained at the coastline, where crustal velocity ranges from ~4.8 km/s and ~7.1 km/s. The velocity field in this area is mainly constrained by the PmP phases recorded in the land stations, so there is a trade-off between lower crustal velocity and Moho location. The upper mantle is sampled by Pn phases only a few kilometres below the Moho, and the obtained velocity appears to be considerably low for upper mantle (7.6-7.7 km/s).

Uncertainty analysis

In order to estimate model parameters uncertainty owing to a combination of data picking errors and other non-linear effects related to the theoretical approximations made, the starting model selected, and the experiment geometry, we performed a Monte Carlo-type stochastic error analysis. The approach followed is similar to that described in Sallarès et al. (2005) and [START_REF] Gailler | Segmentation of the Nazca and South American plates along the Ecuador subduction zone from wide-angle seismic profiles[END_REF], which is a modified version of that of [START_REF] Korenaga | Crustal structure of the southeast Greenland margin from joint refraction and reflection seismic tomography[END_REF], and consists of: (1) generating a set of 250 2-D starting models by randomly perturbing velocity and reflector depth in the initial models within reasonable bounds, which are chosen according to a priori lithological information. In our case we have used the resulting model shown in figure 4 as reference. Velocities have been varied within ±0.35 km/s in crust and mantle, and Moho geometry within ±1.25 km in the oceanic domain and within ±2.5 km in the continent. In addition, 250 noisy data sets have been generated by adding random timing errors of ±60 ms, including common phase errors (±30 ms), common receiver errors (±10 ms), and individual picking errors (±20 ms), to the reference data set, constituted by first arrivals and PmPs. Then, we repeated the inversion for 250 randomly selected perturbed velocity models-noisy data set pairs, using the same inversion parameters as with the model shown in figure 4. According to [START_REF] Tarantola | Inverse problem theory: Methods for data fitting and model parameter estimation[END_REF], the mean deviation of all realizations of such an ensemble can be interpreted as a statistical measure of the model parameters uncertainty. The mean deviation of model parameters is shown in figure 5b. The average rms of all the Monte-Carlo realizations diminishes from 361 ms (χ 2 =36.2) before the inversion, to 63 ms (χ 2 =1.1) after the inversion.

Uncertainty within the sedimentary layer is low (≤0.1 km/s), increasing to ∼0.15 km/s near the top of the basement, due to the sharp velocity contrast between sediments and basement and to the strong velocity gradient in the upper part of the crust (e.g. [START_REF] Calahorrano | Structure and physical properties of the subduction channel off the Gulf of Guayaquil (Ecuador) from seismic reflection data[END_REF]. Velocity uncertainty within the oceanic crust is also low (≤0.1 km/s), confirming that the crustal velocity field obtained in the oceanic domain of the model is remarkably well constrained by the data. The Moho geometry in this oceanic domain has an average uncertainty of less than ±0.5 km (Figure 5b).

The transitional and continental domains (between 160 km and the end of the model) also display rather low crustal velocity uncertainty, increasing from ≤0.15 km/s in average in the upper third of the crust to ~0.20 km/s near the Moho boundary. This locally high uncertainty reflects the lack of multi-fold ray coverage in this area, especially in the deep part of the model sampled only by PmP phases, which are subject to trade-off between the reflector location and the velocity field above it (e.g. [START_REF] Korenaga | Crustal structure of the southeast Greenland margin from joint refraction and reflection seismic tomography[END_REF]Sallarès et al., 2005). Interestingly, Moho depth uncertainty in the continental domain is reasonably low, varying between ±1.0 km in the transition zone, and ±1.5 km beneath the coast line, in the deepest part of the model (Figure 5b).

The worst-resolved part of the model corresponds to the upper mantle, where uncertainty is locally ≥0.2 km/s. A common problem in WAS experiments is that the low mantle velocity gradient makes that Pn phases do not dive deep into the mantle (see DWS plot in figure 5a), so they only carry limited information on the velocity structure of the uppermost few km of the mantle (e.g., [START_REF] Sallarès | Structure and tectonics of the erosional convergent margin off Antofagasta, North Chile (23˚30' S)[END_REF]. In order to test the reliability of the obtained upper mantle velocity, we performed two additional inversions using the same reference crustal velocity model and data set, but including two end-member uppermost mantle velocities of 7.4 km/s and 8.1 km/s. Both models converged to low mantle velocity ranging between ~7.5 km/s and ~7.8 km/s, respectively. Given that the upper mantle is covered only by Pn to a few km below the Moho, which have a very limited azimuthal coverage and have a limited penetration, the model parameter resolution at the upper mantle is low, so that the velocity represents an average along the ray path.

Discussion

Nature of the crustal domains offshore SW Iberia

The final velocity model of figure 4 reveals the presence two distinct crustal domains (labelled 1 and 2 in our interpretative model of figure 7, summarizing our main structural interpretations), with a transition zone in between. In domain 1 the crust is ~7.0 km thick. It is overlain by a 1-2 km of high-velocity sediments, and by other 3-4 km of lower-velocity sediments. These two sedimentary units had been previously identified in different local MCS profiles over the GCIW [START_REF] Tortella | Geodynamic evolution of the eastern segment of the Azores-Gibraltar Zone: the Gorringe Bank and Gulf of Cadiz region[END_REF][START_REF] Torelli | The giant chaotic body in the Atlantic off Gibraltar: new results from a deep seismic reflection survey[END_REF]Gràcia et al., 2003;Gutscher et al., 2009a). According to these authors the lower unit is constituted by Mesozoic to Eocene sedimentary rocks, whereas the upper one includes the GCIW, mainly emplaced during Late Miocene, and a thin layer of Upper Miocene to plio-Quaternary sediments that overlay the GCIW. However, the interpretations regarding the evolution and tectonic behavior of both units differ in several aspects. A number of authors have suggested that the GCIW is an allocthonous body emplaced tectonically by the westward migration of the Gibraltar arc between ~15 Ma and ~8 Ma (e.g. [START_REF] Torelli | The giant chaotic body in the Atlantic off Gibraltar: new results from a deep seismic reflection survey[END_REF]Gràcia et al., 2003;[START_REF] Medialdea | Structure and evolution of the "Olistostrome" complex of the GibraltarArc in theGulf ofCadiz (eastern CentralAtlantic): evidence from two long seismic cross-sections[END_REF]Iribarren, 2009), whereas Gutscher et al. (2009b) consider that this unit is as an actively deforming accretionary prism on top of an eastward--subducting oceanic slab, source of the largest earthquakes having occurred in the region. There is however overall agreement in that the lowermost unit covering the basement is Mesozoic in age (e.g. Sartori et al., 1993;[START_REF] Torelli | The giant chaotic body in the Atlantic off Gibraltar: new results from a deep seismic reflection survey[END_REF][START_REF] Tortella | Geodynamic evolution of the eastern segment of the Azores-Gibraltar Zone: the Gorringe Bank and Gulf of Cadiz region[END_REF]Gràcia et al., 2003), giving an upper bound for the age of the basement below. Domain 2 corresponds to the stable continental Variscan margin of SW Iberia, and consists of a continental crust (27-30 km thick) overlain by a poorly contrasted sedimentary layer made of Mesozoic units [START_REF] Terrinha | Tsunamigenic-seismogenic structures, neotectonics, sedimentary processes and slope instability on the Southwest Portugese Margin[END_REF]. The velocity structure and crustal thickness are very similar to that modelled along the on-shore IBERSEIS WAS transect (Palomeras et al., 2009), and it is also consistent with that of [START_REF] González | Crustal thinning in the southwestern Iberia margin[END_REF], which is based on land recordings of the IAM data. The transition zone in between both domains is roughly 60 km-wide, across which occurs an abrupt lateral variation in crustal thickness between the continental margin and the central Gulf of Cadiz. The sharpest transition takes place at km 160-170 (marked by "COB" in figure 7).

Concerning the nature of the crust in domain 1, there are in principle three possible interpretations; namely thinned continental crust, exhumed mantle or oceanic crust. Available heat flow data above the GCIW indicate values from 59-45 mW/m 2 [START_REF] Grevemeyer | Heat flow anomalies in the Gulf of Cadiz and off Cape San Vicente, Portugal[END_REF], values that are consistent with old lithosphere but do not help constraining the crustal type. Some ENE-WSW trending magnetic anomalies are also present in the internal Gulf of Cadiz [START_REF] Verhoef | Magnetic anomalies off West-Africa[END_REF][START_REF] Dañobeitia | An interpretation of a prominent magnetic anomaly near the boundary between the Eurasian and African plates (Gulf of Cadiz, SW margin of Iberia)[END_REF], but these are too subdued and sparse to be identified as seafloor spreading anomalies. In the absence of direct basement samples or well-defined magnetic anomalies, the best available indicator on the nature of the crust is the velocity structure and crustal thickness provided by offshore WAS data. Figure 8 shows a comparison of 1-D velocity-depth profiles representative of the two crustal domains and the transition zone with compilations made for: (1) exhumed mantle sections along the western Iberian margin [START_REF] Srivastava | Magnetic evidence for slow seafloor spreading during the formation of the Newfoundland and Iberian margins[END_REF], (2) >140 m.y.-old Atlantic oceanic crust [START_REF] White | Oceanic crustal thickness from seismic measurements and rare earth element inversions[END_REF], (3) continental crust (Christensen and Mooney, 1995), and (4) altered oceanic crust near subduction trenches [START_REF] Meléndez | Seismic structure of the Nicaraguan convergent margin by travel time tomographic inversion of wide-angle seismic data in the area of the 1992 Nicaragua slow earthquake[END_REF]. A comparison of the velocities obtained in domain 1 to velocities of exhumed/serpentinized upper mantle (Figure 8a) show that crustal velocities are far too slow and velocity gradients too smooth to correspond to exhumed mantle. In contrast, the obtained velocities are too high to correspond to extended continental crust (Figure 8a). An additional observation that helps to rule out this option of continental crustal affinity is that all the continental thinning occurs in domains 2 and 3, and there is no thinning at all in domain 1 for more than 150 km, an observation that is hardly compatible with an extended continental nature.

The comparison with the velocity structure for >140 m.y.-old Atlantic oceanic crust [START_REF] White | Oceanic crustal thickness from seismic measurements and rare earth element inversions[END_REF] is shown in figure 8b. The velocity structure in domain 1 is closer to oceanic crust than to the two options shown in figure 8a, but it is near the lower velocity bound. This atypical velocity profile may be the result of fault-related rock fracturing and subsequent alteration by fluids percolating through faults at this anomalously old (probably of Jurassic age, see introduction and explanation below), and hence cold and brittle crust. The presence of low velocity anomalies that spatially coincide with two of the long, N120°E trending strike-slip "SWIM lineaments", interpreted by [START_REF] Zitellini | The quest for NWAfrica-SW Eurasia plate boundary west of Gibraltar[END_REF] as crustal-scale faults, would support this hypothesis. Anomaly f1 (figure 6) corresponds to the location of the northernmost lineament (LN in figure 1), whereas f0 is located next to the southern one (LS in figure 1). Additionally, the uppermost mantle velocity is low, which might be indicative of mantle serpentinization, probably by means of fluids percolating through the aforementioned faults crossing the Moho. The low crustal and upper mantle velocity is a common feature in the oceanic plate at subduction zones. It has been described for the incoming plate in Chile [START_REF] Ranero | Geophysical evidence for alteration of the crust and mantle of the Nazca Plate during bending at the north Chile trench[END_REF][START_REF] Lefeldt | Intraplate seismicity and releated mantle hydration at the Nicaraguan trench outer rise[END_REF] and Middle America (Ivandic et al., 2009;[START_REF] Meléndez | Seismic structure of the Nicaraguan convergent margin by travel time tomographic inversion of wide-angle seismic data in the area of the 1992 Nicaragua slow earthquake[END_REF]. It has been associated to the presence of pre-existing lithosphericscale normal faults that are reactivated by flexure at the outer rise allowing the water to percolate through the crust well into the upper mantle [START_REF] Ranero | Bending, faulting and mantle serpentinization at the Middle America Trench[END_REF]. To check this hypothesis, we have included in figure 8b a 1-D velocity-depth profile extracted from a WAS profile acquired in the outer rise area of the Nicaraguan margin [START_REF] Meléndez | Seismic structure of the Nicaraguan convergent margin by travel time tomographic inversion of wide-angle seismic data in the area of the 1992 Nicaragua slow earthquake[END_REF].

Clearly, this is the velocity profile that fits the best our model, suggesting that the crust in the central Gulf of Cadiz could well be a fragment of fractured, altered and serpentinized oceanic lithosphere. As expected, domains 2 and 3 (Figure 8c and8d) show 1-D velocity-depth profiles that fit well within the range of extended and normal continental crust velocities (Christensen and Mooney, 1995). According to these observations continent-ocean boundary (COB) is located at the northern limit of domain 1, some 100 km south from the coast line (Figure 7).

Origin and tectonics of the SW Iberian and NW African margins

The study area is located at the intersection of the NW African and the SW Iberian continental margins. The NW African margin developed during Triassic-Jurassic times (Le [START_REF] Roy | Triassic-Liassic western Moroccan synrift basins in relation to the central Atlantic opening[END_REF], as the Central Atlantic formed by the rifting of Africa from North America at the southern end of the modern day Grand Banks of Newfoundland by extension by transcurrent motion along the current southern Grand Banks fault [START_REF] Bill | Radiolarite ages in Alpine-Mediterranean ophiolites: Constraints on the oceanic spreading and the Tethys-Atlantic connection[END_REF][START_REF] Stampfli | A Plate Tectonic Model for the Paleozoic and Mesozoic[END_REF] (Figure 9). The SW Iberian margin and the Gulf of Cádiz domain developed at the intersection of a N-S trending margin, between the West Iberia and the Flemish Cap -Grand Banks Margin of Newfoundland (Canada), and the Grand Banks transform referred to above [START_REF] Roest | Kinematics of the plate boundaries between Eurasia, Iberia, and Africa in the North Atlantic from the Late Cretaceous to the present[END_REF]. According to reconstructions based on available plate tectonic models [START_REF] Stampfli | A Plate Tectonic Model for the Paleozoic and Mesozoic[END_REF][START_REF] Schettino | Tectonic history of the western Tethys since the Late Triassic[END_REF] this domain may have been the site of limited amounts of oblique seafloor spreading that accommodated the ~N-S component of the migration of Africa with respect to Eurasia during the Jurassic. This spreading could have opened a narrow oceanic basin separating southern Iberia from NW Africa (Figure 9). These reconstructions indicate that the oceanic spreading between Africa and Iberia would have been coeval with the opening of the Central Atlantic, starting in the Bajocian (Middle Jurassic) at ~180 Ma [START_REF] Roeser | Structural development of the Jurassic Magnetic Quiet Zone off Morocco and identification of Middle Jurassic magnetic lineations[END_REF] and finishing with the onset of rifting at the North Atlantic in the Tithonian (latest Jurassic), some 145 Ma [START_REF] Stampfli | A Plate Tectonic Model for the Paleozoic and Mesozoic[END_REF][START_REF] Schettino | Tectonic history of the western Tethys since the Late Triassic[END_REF].

Our work provides the first direct evidence for the presence of oceanic crust between North Africa and SW Iberia. According to this interpretation, the oceanic crustal section imaged in figure 4 would represent the westernmost segment of the Alpine-Tethys ocean, the pre-Alpine oceanic domain that opened between NW Africa and Eurasia in the Jurassic and closed during the Alpine orogeny [START_REF] Stampfli | A Plate Tectonic Model for the Paleozoic and Mesozoic[END_REF][START_REF] Schettino | Tectonic history of the western Tethys since the Late Triassic[END_REF][START_REF] Handy | Reconciling plate-tectonic reconstructions of Alpine Tethys with geological-geophysical record of spreading and subductions in the Alps[END_REF]. A south-eastern branch of this oceanic domain is the true Tethys, which was consumed by north-dipping subduction as Africa converged northward with Europe, a process which continues today beneath the Hellenic and Calabrian arcs (e.g. [START_REF] Faccenna | History of subduction and back-arc extension in the Central Mediterranean[END_REF]. Therefore, the Alpine-Tethys domain represented the boundary zone between the Atlantic and Tethys domains during the Jurassic and the Mesozoic (Figure 9). According to these reconstructions, the oceanic crustal segment that we have identified in the Gulf of Cadiz would represent the last remnant of the western Alpine-Tethys lithosphere and, therefore, it would be one of the oldest oceanic crustal fragments currently preserved on Earth. It is interesting to note that the oceanic spreading would have mainly occurred during the so-called "Jurassic Quiet Zone" [START_REF] Larson | A Revised Time Scale of Magnetic Reversals for the Early Cretaceous and Late Jurassic[END_REF], which would also explain the absence of a clear magnetic anomaly pattern in the area (e.g. [START_REF] Verhoef | Magnetic anomalies off West-Africa[END_REF] despite its oceanic crustal nature.

In this context, we suggest that the large, prominent, south-dipping, low-velocity anomalies of figure 6 could be related with the presence of faults created during this rifting episode. Our interpretation is that they represent a smeared, coarse image of either the fractured, altered and fluid-saturated zone surrounding the fault area, or the contrast between rocks with different properties at both sides of the faults. According to our interpretation, f2 and f3 would correspond to extensional faults generated during this phase, whereas f1 (and possibly f0) could represent either normal faults created during oceanic spreading or fracture zones. As we explained above, f0 and f1 coincide spatially with the two northernmost "SWIM lineaments", whereas f2 coincides with a south-dipping fault reaching the seafloor that spatially coincides with the one imaged along MCS profile Voltaire-3 in the southern flank of the "Guadalquivir basement high" (see figure 9 in [START_REF] Terrinha | Morphotectonics and Strain Partitioning at the Iberia-Africa plate boundary from multibeam and seismic reflection data[END_REF]. To our knowledge, there are no MCS data crossing the f3 anomaly (figure 6), so there is no link between this anomaly and other faults in the area. Finally, it is worth noting that f2 and f3 are imaged up to 13-14 km and no deeper, this is near the base of the upper crust in the Variscan belt (Palomeras et al., 2009). This depth corresponds to the maximum expected depth for continental earthquakes, which is believed to be associated with a thermal limit that marks the transition between "brittle" upper crust and "ductile" lower crust (e.g. [START_REF] Scholz | The brittle-plastic transition and the depth of seismic faulting[END_REF].

Implications for regional geodynamic models

Different models have been proposed to date to explain the different geological, geophysical and geochemical observations of the Gibraltar arc-Alboran basin system, including past or present collision of continental lithosphere combined with lithospheric recycling either by convective removal [START_REF] Platt | Extensional collapse of thickened continental lithosphere: A working hypothesis for the Alboran Sea and Gibraltar arc[END_REF][START_REF] Calvert | Geodynamic Evolution of the Lithosphere and Upper Mantle Beneath the Alboran Region of the Western Mediterranean: Constraints from Travel Time Tomography[END_REF], delamination [START_REF] Seber | Geophysical evidence for lithospheric delamination beneath the Alboran Sea and Rif-Betic mountains[END_REF], or slab break-off [START_REF] Zeck | Mantle peridotites outlining the Gibraltar Arc: Centrifugal extensional allocthons derived from the earlier Alpine, westward subducted nappe pile[END_REF]; together with a variety of models of either continental or oceanic subduction with southward (Sanz de [START_REF] Sanz De Galdeano | Geologic evolution of the Betic Cordilleras in the Western Mediterranean, Miocene to the present[END_REF][START_REF] Morales | Active continental subduction beneath the Betic Cordillera and the Alboran Sea[END_REF], northward [START_REF] Torres-Roldan | An early Miocene arc-tholeiitic magmatic dyke event from the Alboran Sea. Evidence for precollisional subduction and back-arc crustal extension in the westernmost Mediterranean[END_REF][START_REF] Mauffret | The Alboran Sea (Western Mediterranean) revisited with a view from the Moroccan Margin[END_REF], westward [START_REF] Docherty | Evidence for the eastward migration of the Alboran Sea based on regional subsidence analysis: A case for basin formation by delamination of the subcrustal lithosphere?[END_REF][START_REF] Zeck | Mantle peridotites outlining the Gibraltar Arc: Centrifugal extensional allocthons derived from the earlier Alpine, westward subducted nappe pile[END_REF], or eastward dips [START_REF] Lonergan | Origin of the Betic-Rif mountain belt[END_REF]Gutscher et al., 2002). The nature of the crust in the Gulf of Cadiz has important implications for these competing geodynamic models proposed for the SW Iberia region, especially for those proposing rollback of an eastward dipping subducted slab as the main driving force for the formation of the Alboran basin [START_REF] Lonergan | Origin of the Betic-Rif mountain belt[END_REF]Gutscher et al., 2002;[START_REF] Duggen | Magmatic evolution of the Alboran Region: The role of subduction in forming the western Mediterranean and causing the Messinian Salinity Crisis[END_REF][START_REF] Faccenna | Lateral slab deformation and the origin of the western Mediterranean arcs[END_REF]. Some authors had previously suggested the presence a 10-15 km-thinning of the Variscan continental crust in the central Gulf of Cadiz, based on land recordings of marine seismic data [START_REF] González | Crustal thinning in the southwestern Iberia margin[END_REF], modelling of gravity data (Gràcia et al., 2003), combined modelling of potential field data [START_REF] Medialdea | Structure and evolution of the "Olistostrome" complex of the GibraltarArc in theGulf ofCadiz (eastern CentralAtlantic): evidence from two long seismic cross-sections[END_REF][START_REF] Zeyen | Lithospheric structure under the western African-European plate boundary: a transect across the Atlas Mountains and the Gulf of Cadiz[END_REF], and joint geophysical and petrological modelling (e.g. [START_REF] Fullea | The structure and evolution of the lithosphere -asthenosphere boundary beneath the Trans-Mediterranean region[END_REF]. In contrast, our current findings evidencing the presence of oceanic crust in the central Gulf of Cadiz are fully compatible with the presence of a narrow, east-dipping, fast retreating oceanic slab beneath the Gibraltar arc. Our model and interpretation is also in agreement with available seismological data suggest the presence of a continuous, 150-200 km-wide slab that dips from the Gulf of Cadiz towards Gibraltar, reaching the 660 km-discontinuity beneath the Alboran basin. These data include the global tomography images showing a narrow subducted slab beneath Alboran and Gibraltar (e.g. [START_REF] Spakman | A tomographic view on Western Mediterranean Geodynamics[END_REF], the dispersion analysis of body waves from the deep mantle indicating the presence of a steeply eastward dipping low P-wave waveguide within a high velocity slab (Bokelmann and Mauffroy, 2007), and the recent shear-wave splitting measurements indicating a semicircular mantle flow pattern beneath the Gibraltar arc (Díaz et al., 2010).

Conclusions

Our WAS modelling results indicate the presence of three crustal domains in the SW Iberian margin. In the north, a 28-30 km-thick Variscan continental crust that gently thins to ~25 km beneath the coastline. Immediately South from it, a ~60 km-wide zone where almost all the crustal thinning (from ~25 km to ~7 km), concentrates. In the Southernmost part of the profile, a 150 km-wide segment of ~7 km-thick crust, overlain by a 1-2 km-thick lower unit of consolidated Mesozoic to Eocene sediments, and a 3-4 km-thick upper unit of sediments corresponding to the Upper Miocene GCIW that is covered in turn by a thin layer of plio-Quaternary sediments. The velocity gradient and crustal thickness in the southern section strongly suggests that the lithosphere is oceanic in nature, although absolute velocities are somewhat lower than "normal" probably due to fault-related rock fracturing and alteration and mantle serpentinization. The abrupt ocean-continent transition is suggested to be the result of the initial tectonics of the margin setting during the Triassic-early Jurassic as a transform margin, followed by oblique seafloor spreading between southern Iberia and northwestern Africa during the Middle-Late Jurassic (roughly 180-145 Ma). According to our interpretation, the oceanic spreading that took place in the Jurassic would have generated a ~150 km-wide oceanic basin that would be part of the system that have once connected the Atlantic and Tethyan oceanic domains. Based on the spatial coincidence with previously identified active faults, we suggest that the wide, crustal-scale, south-dipping, low-velocity anomalies imaged in the velocity model are the tomographic expression of the area affected by crustal-scale faults, some of which could have been created during this rifting period. The fragment of oceanic crust identified in the velocity model would therefore constitute the only remnant of the western Alpine-Tethys ocean and one of the oldest oceanic crustal fragments currently preserved on Earth. The presence of a narrow oceanic basin in the Gulf of Cadiz agrees with recent seismological observations, and it is consistent with the geodynamic models proposing roll-back of an eastward dipping slab as the main driving force for the opening of the Alboran Sea within the Betic-Rif system. including the two profiles that were acquired. Yellow circles display OBS and land stations locations along the N-S profile presented in this paper. The multi-beam bathymetry is a combination of the SWIM compilation [START_REF] Zitellini | The quest for NWAfrica-SW Eurasia plate boundary west of Gibraltar[END_REF] and GEBCO digital atlas [START_REF] Ioc | International Hydrographic Organization as part of the General Bathymetric Chart of the Oceans[END_REF]. The different faults are taken from the NEAREST active faults map (Zitellini et al., 2009) The initial model used in the inversion is a combination of the models displayed in figure 3 (see text for details). [START_REF] Srivastava | Magnetic evidence for slow seafloor spreading during the formation of the Newfoundland and Iberian margins[END_REF], extended continental crust (ECC, brown area) (Christensen and Mooney, 1995), (b) 1-D velocity-depth profile extracted at 60 km along profile (P2, black line) and corresponding uncertainty bar (grey band), velocity profiles from Atlantic oceanic crust older than 140 m.y. (AOC, blue area) [START_REF] White | Oceanic crustal thickness from seismic measurements and rare earth element inversions[END_REF] and fractured, altered oceanic crust and serpentinized mantle at the outer rise of the Nicaragua subduction zone (FOC, dark blue line with error band) [START_REF] Meléndez | Seismic structure of the Nicaraguan convergent margin by travel time tomographic inversion of wide-angle seismic data in the area of the 1992 Nicaragua slow earthquake[END_REF]

Figure 1 .

 1 Figure 1.-Location map of the study area of the NEAREST-SEIS wide-angle seismic survey,

  . White stars mark the location of DSDP sites 120 and 135. Inset: Global map including the major tectonic plates. Abbreviations: AB: Alboran Basin; AGFZ; Açores-Gibraltar Fault Zone; EUR: Eurasian plate, AFR: Africa/Nubia plate, IB: Iberia, BH: Basement High; CPS: Coral patch ridge, CPRF: Coral Patch Ridge fault, GF: Gloria Fault; GO: Gorringe bank, HAP: Horseshoe Abyssal Plain, HF: Horseshoe fault, LN: North SWIM lineament, LS: South SWIM lineament, PC: Portimao Canyon; SAP. Seine Abyssal plain, TAP: Tagus Abyssal Plain.

Figure 2 .-

 2 Figure 2.-Recorded seismic sections (up) and record sections with corresponding observed

Figure 3 .-

 3 Figure 3.-Partial results at the different steps of the tomographic inversion procedure and ray

Figure 4 .

 4 Figure 4.-2-D final velocity model obtained by tomographic inversion of the whole data set,

Figure 5 .

 5 Figure 5.-(a) Derivative weight sum (DWS), and (b) Velocity and Moho depth uncertainty

Figure 6 .-

 6 Figure 6.-Map of negative velocity anomalies along the velocity profile, which correspond to

Figure 7 .-

 7 Figure 7.-Interpretative model of the structure and tectonics of the SW Iberian margin along

Figure 8 .

 8 Figure 8.-1-D P-wave velocity/depth profiles shown at three different locations along the

  , (c) 1-D velocity-depth profile extracted at 190 km along profile (P2, black line) and corresponding uncertainty bar (grey band), velocity profiles from AOC and ECC (see definition above), (d) 1-D velocity-depth profile extracted at 190 km along profile (P2, black line) and corresponding uncertainty bar (grey band), velocity profiles from non-extended continental crust (CC, brown area) (Christensen and Mooney, 1995).

Figure 9 .-

 9 Figure 9.-Sketch summarizing our interpretation of the geodynamic and tectonic evolution

Acknowledgments

We thank the captain and crew of the research vessel BIO Hesperides, as well as the UTM and IFREMER technicians that were in charge of the airguns and OBS data acquisition. The NEAREST project has been funded by the the EU Programme "Integrating and Strengthening the European Research Area" of FP6, Sub-Priority 1.1.6.3, Global Change and Ecosystems", contract n. 037110, and the NEAREST -SEIS survey was funded by the Complementary Action # CGL2006-27098-E/ BTE of the Spanish MICINN. Additional funds were obtained from the MICINN project MEDOC (CTM2007-66179-C02-02/MAR). We also acknowledge funding from MICINN through the Ramon y Cajal programme (R. Bartolomé). We finally acknowledge the collaboration of our research partners at Grup de Recerca de la Generalitat de Catalunya Barcelona Centre of Subsurface Imaging (B-CSI) ref. 2009 SGR 146 and funding support from Repsol-YPF.