A Lopez-Carmona

P Pitra

I Abati

Blueschist-facies metapelites from the Malpica-Tui Unit (NW Iberian Massif): phase equilibria modelling and H20 and Fe203 influence in high-pressure assemblages

Keywords: blueschist-facies metapelites, H20 content, Iberian Massif, MnNCKFMASHTO, Variscan subduction

The Malpica-Tui Unit (Galicia, NW Spain) records eclogite-and blueschist-facies metamorphism during the onset of the Variscan orogeny in Europe. Petrological analysis involving pseudo sections calculated using THERMOCALC shows that the Upper Sheet of this unit, the Cean Schists, recorded a three stage metamorphic evolution involving (i) Early subduction-related medium-pressure/low-temperature metamorphism (M!) constrained at �350-380 cC, 12-14 kbar, which is only recorded in the basal part (lower metapelites, LM) of the Cean Schists. (ii) Subduction-related blueschist facies prograde metamorphism (M,) going from �19 kbar, 420 cC to 21 kbar, 460 cC in the LM, and from 16 kbar 430 cC to 21-22 kbar, 520 cC in the structurally upper metapelites (UM). (iii) Exhumation-related metamorphism (M3) is characterized by a decompression to 8-10 kbar, 470-490 cC in the LM. This decompression is also recorded in the UM, but it was not possible to estimate precise P-T conditions.

The calculations indicate that (i) the prograde evolution in subduction zones may occur in f l uid undersaturated conditions due to the crystallization of lawsonite, even in metapelitic rocks. This signifi cantly inf l uences phase equilibria and hence the P-T estimates. (ii) The proportion of ferric iron also has a strong inf l uence on phase equilibria, even in metapelites. However, the analysed values of Fe203 may not ref l ect the oxidation state during the main metamorphic evolution and are probably easily modifi ed by superfi cial alteration even in apparently fresh samples. The use of P-T-X(Fe203) pseudo sections together with petrographic 0 bservations is then necessary to estimate the real oxidation state of the rocks and correctly evaluate the P-T conditions.

INTRODUCTION

Sinking of cold, dense lithosphere in subduction zones is the principal plate-driving force, causing orogenesis along continental margins. The descent of a relatively cold crustal slab to mantle depths leads to the fonnation of high-pressure (HP) and low-(L 1) to medium-temperature (MT) metamorphic rocks, like blueschists and eclogites, frequently found in the suture zones of orogenic belts (e.g. [START_REF] Miyashiro | Evolution of metamorphic belts[END_REF][START_REF] Ernst | Metamorphic zonations on presumably sub ducted lithospheric plates from Japan, California and the Alps[END_REF][START_REF] Maruyama | Blueschists and eclogites of the world[END_REF]. Blueschist-and eclogite-facies assemblages, as markers of fossil and active subduction zones, store much infonnation concerning processes at convergent plate boundaries, and provide important clues to the understanding of the thermal history of the evolving Earth (e.g. [START_REF] Ernst | Blueschists metamorphism and P TRegimes in active subduction zones[END_REF][START_REF] Ernst | Subduction, ultrahigh-pressure metamor phism, and regurgitation of buoyant crustal slices implica tions for arcs and continental growth[END_REF][START_REF] Platt | Exhumation of high-pressure rocks: a review of concepts and processes[END_REF][START_REF] Stern | Evidence from ophiolites, blueschists, and ul tra high pressuremetamorphic terranes that the modern epi sode of subduction tectonics began in Neoproterozoic time[END_REF].

Data about the metamorphic evolution of subducted terranes, obtained through petrological analysis and thermodynamic modelling, are fundamental to geo dynamic models and palaeogeographical reconstruc tions of the lithospheric plates. In this context, the northwest section of the Iberian Massif provides infonnation that helps to understand the evolution of the European Variscan belt. This region comprises exotic terranes forming a huge and complex allochth onous sheet emplaced upon the sequences deposited on the passive margin of north Gondwana (Martinez Catalin et al., 2009). They include a HP and LT MT belt that can be discontinuously traced throughout the Variscan belt, located below several rock units with ophiolitic associations, probably having originated in the Rheic Ocean. This HP belt is a coherent piece of continental crust fonned by different rock units known in the NW Iberian Massif as the Basal Units (Fig. 1). The goal of this work is to analyse phase equilibria of blueschist-facies metapelites (Cean Schists) from the upper sequence of the westernmost basal unit, the Malpica Tui Unit (MTU; Fig. 1), with particular attention to the effects of H20 and Fe203' This lithology preserves the chloritoid glaucophane para genesis (L6pez-Carmona et al., 2010), which is one of the classic HP indicators in metapelites (e.g. [START_REF] Kienast | Le chloritolde dans les parageneses a glaucophane, albite ou paragonite[END_REF][START_REF] Katagas | Ferroglaucophane and chloritoid bearing metapelites from the phyllite series, southern Peloponnes, Greece[END_REF][START_REF] Chopin | Talc Phengite: a widespread assemblage in high-grade pelitic Blueschists of the Western Alps[END_REF][START_REF] El-Shazly | Glaucophane chloritoid bearing assemblages from NE Oman: petrologic signifi cance and a petrogenetic grid for high P metapelites[END_REF][START_REF] Wei | Chloritoid glaucophane schist in the north Qilian orogen, NW China: phase equilibria and P T path fr om garnet zonation[END_REF]. Phase equilibria of pelitic rocks at high pressures do not attract as much attention as metabasic rocks, probably because the mineral associations are less spectacular. Yet, metapelitic rocks are common in HP terranes (e.g. [START_REF] Bosse | Ductile thrusting re corded by the garnet isograd from blueschist-facies metape lites of the He de GrODe, Armorican Massif, France[END_REF]Wei & Pow ell, 2003 and references therein), and are suitable for con straining P Tevolution. However, similar to metabasic rocks, the assemblages are sensitive to the amount of available H20 and Fe203 (cf. Korhonen et al., 2012).

HIGH-PRESSURE ROCKS IN THE BASAL UNITS OF NW IBERIA

Pods and relicts of HP rocks, well preserved in the NW Iberian massif, with widespread distribution along the so-called Basal Units, are the best record of the Vari scan subduction of the north Gondwana margin dur ing the Late Devonian. Their petrological and structural study has constrained the P T paths and the kinematics of the subduction (e.g. Martinez Catalin et al., 1996;[START_REF] Arenas | P T evolution of eclogites fr om the Ag ualada Unit (Ordenes Complex, northwest Iberian Massif, Spain): implications for crustal subduction[END_REF]L6pez-Carmona et al., 2010;Diez Fernindez et al., 2011), concluding that Basal Units formed part of a subducting slab buried beneath Laurussia at the onset of the Variscan colli sion [START_REF] Arenas | High-pressure micro inclusions and development of an inverted metamorphic gradient in the Santiago Schists (Ordenes Complex, NW Iberian Massif, Spain): evidence of subduction and syncollisional decom pression[END_REF][START_REF] Arenas | P T evolution of eclogites fr om the Ag ualada Unit (Ordenes Complex, northwest Iberian Massif, Spain): implications for crustal subduction[END_REF][START_REF] Santos Zalduegui | Isotope constraints on the age and origin of magmatism and metamorphism in the Malpica Tuy allochthon, Galicia, NW Spain[END_REF][START_REF] Rodriguez Aller | Strain partitioning and preservation of 4o Ar/ 3 9 Ar ages during Variscan exhumation of a subduct ed crust (Malpica Tui complex, NW Spain)[END_REF][START_REF] Abati | Mag matism and early Variscan continental subduction in the northern Gondwana margin recorded in zircons from the Basal Units of Galicia, NW Spain[END_REF]. They were rapidly exhumed by crustal-scale thrusting accompanied by recumbent folding and tectonic denudation (Martinez Catalin et al., 1996, 1997;Diez Fernandez & Martinez Catal<in, 2009;Diez Fernandez et al., 2011). The original polarity of the subducting slab was reconstructed on the basis of the palaeo-pressures inferred from metamorphic parageneses, indicating that the subduction had a signifi cant westward com ponent in present coordinates (Martinez Catal<in et al., 1996). Kinematic indicators in HP fabrics are in agreement with this reconstruction, indicating top to the northwest movement [START_REF] Fernandez | The onset of the assembly of Pangaea in NW Iberia: constraints on the kinematics of continental subduc tion[END_REF].

According to their metamorphism and tectonostra tigraphy, the Basal Units can be separated into two sheets (Fig. I). In the MTU: (i) a Lower Sheet of continental affi nity, where felsic orthogneisses and turbiditic metasedimentary rocks predominate; and (ii) an Upper Sheet that represents a volcano-sedimentary sequence viewed as a more distal part of the same continental margin, extremely attenuated and transi tional to an oceanic domain [START_REF] Rodriguez Aller | Recristalizacion y deformacion de lit ologias supracorticales some tidas a metamor jismo de alta presion (Complejo de Malpica Tui[END_REF]. The Upper Sheet is preserved in a small synformal structure (the Pazos Synform) and is formed by a basal layer of fi nely foliated amphibolites and greenschists with N-MORB chemistry (Cambre Amphibolites), and an overlying sequence of pelitic schists (Cein Schists) with minor intercalations of bituminous schist, cherts and carbonates. The mafi c rocks are strongly retro gressed blueschists that locally preserve lawsonite pesudomorphs dominated by epidote/clinozoisite and paragonite [START_REF] Rodriguez Aller | Strain partitioning and preservation of 4o Ar/ 3 9 Ar ages during Variscan exhumation of a subduct ed crust (Malpica Tui complex, NW Spain)[END_REF]L6pez-Car mona et al., 2010). The contact between the Upper and the Lower Sheets is marked by a several metres thick layer of mylonites and ultramylonites located at the base of the Cambre Amphibolites (Diez Fernindez, 2011). Another layer of mylonites occurs in the middle of the Upper Sheet, within the Cein Schists, separating them in a lower and an upper part (Fig.

Previous P-T estimates

The metamorphic evolution of the Cein Schists has been previously studied by conventional thermobarometric techniques, multiequilibrium thermobarometry (THER MOCALC average P T) and thermodynamic modelling, usmg pseudosections m the KFMASH and MnNCKFMASH chemical systems (L6pez-Carmona et al., 2010). Conventional thermobarometry calcula tions using micro inclusion compositions indicate peak conditions of � 19 22 kbar and 500°C. The same cal culations using the matrix minerals yield approximate values of 16 20 kbar and 440 515°C. P Tvalues ob tained with the average P T multiequilibrium ther mobarometry are compatible with the conventional thermobarometry results, but show signifi cantly lower pressures for the matrix foliation (13 14 kbar and 495 500°C). Petrological modelling in the MnNCKF MASH system provided a minimum pressure limit for the paragenesis chloritoid + glaucophane at � 17 kbar, confi rming the HP stability of this assemblage.

SAMPLE DESCRIPTION AND MINERAL

CHEMISTRY

The deformation in the Cein Schists is relatively het erogeneous, with irregular development of foliations and deformation phases in different domains. Their deformation history includes several compressive, extensional and strike-slip phases (Diez Fernandez et al., 2011). However, only three of the deformation phases have a direct link with relevant metamorphic associations. Two blueschist facies defonnation phases have been identifi ed (Dj D2), followed by the devel opment of the main foliation in blueschist-amphibolite facies conditions (D3) and an amphibolite greenschist facies overprint (POSt-D3) (Fig. 2). The fabric from the showing the mineral assemblages predicted in the metamorphic events. *Inferred phases that have not been observed petrographi cally. The dominant rock type of the Cean series is a typical pelite (e,g, Atherton & Brotherton, 1982), However, to the base of the sequence, metapelitic rocks are interbedded with the Cambre Amphibolites and most samples show compositions that move away from the fi eld of pure pelites in the direction of N-MORB, indicating either some mixing between both lithologies during primary volcano-sedimentary processes, or mechanical assimilation during the deformation. The different whole-rock chemistry between the samples selected for this study results in slightly different mineral associations (Table 1),

The Cein Schists show a medium-grained por phyro lepidoblastic texture and a well-developed pla nar to planar linear fabric (Fig, 3), White mica and quartz constitute> 50%, and locally up to 80%, of the modal proportion of each sample, The alternation of both minerals defi nes a banding preserved between extensional shear bands, The foliation is defi ned by the shape preferred orientation of phengitic muscovite, paragonite and chlorite, and is parallel to the banding, Quartz grains commonly show undulate extinction, subgrain boundaries and recrystallization to smaller grain aggregates (Fig, 3), Two representative samples of the Cean Schists from the Upper Sheet of the MTU (Fig, 1) were studied, Sample 106340, referred to hereafter as LM (for lower metapelites), is located at the base of the synformal structure, and interbedded within the Cambre Amphibolites. The presence of numerous garnet porphyroblasts rich in Sj and S2 inclusions makes this sample ideal to study the fi rst subduction related deformation phases. Sample 108289, referred to hereafter as UM (for upper metapelites), is located structurally above the sample 106340, in the middle part of the synformal structure, in an upper structural domain separated from the fi rst by a mylonitic band (Fig. la).

Mineral analyses and elemental X-ray maps have been performed with a JEOL-Superprobe JXA-8900M microprobe equipped with fi ve spectrometers at the lCTS-National Electronic Microscopy Centre at the Complutense University of Madrid (Spain; http:// www .cnme.es). The operating parameters for punctual analyses were 15 kV accelerating voltage, 20 nA beam current, between 1 and 5 !ffi1 beam diameter (1 !ffi1 for the microinclusions) and 10 s counting time. X-ray maps were operated at 20 kV and 150 nA. Represen tative analyses of selected minerals are listed in Tables 2 and3. Mineral abbreviations are those used by THERMOCALC (Holland & Powell, 1998): albite (ab), biotite (bi), chlorite (chI), chloritoid (ctd), clinozoisite (cz), epidote (ep), garnet (g), glaucophane (gl), ilmenite (ihn), jadeite (id), lawsonite (law), muscovite (mu), omphacite (0), paragonite (pa), plagioclase (PI), quartz (q), rutile (ru) and titanite (sph). Other abbreviations: apatite (ap), barroisite (bar), carbonates (carb), Fe/Ti bearing oxides (FelTi-ox), hornblende (hb), sericite (ser), stilpnomelane (stp), sulphides (suI), tschermakite (ts), tourmaline (tur) and winchite (win Prp � Mg/(Fe + Mg + Ca + Mn), Grs � Ca/(Fe + Mg + Ca + Mn), Sps � Mn/(Fe + Mg + Ca + Mn); per formula unit (pfu); weight per cent (wt%); , --7 ' denotes core-to-rim evolution, and ,* , indicates phases inferred from the petrological modelling that have not been identifi ed petrographically. Holland, 2002). For amphibole, the Fe3 + content corresponds to the average from minimum and maximum constraints [START_REF] Holland | Non-ideal interactions in calcic amphiboles and their bearing on amphibole-plagioclase thermometry[END_REF].

Table 3. Representative microprobe analyses fr om sample UM. groups}hollandjax). The amount of ferrlc iron was calculated from stolchiometric constraints using the programme AX [START_REF] Powell | Course Notes for THER MOCALC Workshop 2002: Calculating Metamorphic Phase Equilibria[END_REF]. For amphibole, the Fe3 + content corresponds to the average from minimum and maximum constraints [START_REF] Holland | Non-ideal interactions in calcic amphiboles and their bearing on amphibole-plagioclase thermometry[END_REF].

Structurally lower metapelites

Sample LM is a micaschist that contains a main foli ation (S3) defi ned by white mica (type 3 phengite with 3.40-3.45 Si pfu, XNa � 0.04 and paragonite, XNa � 0.81), biotite (XF' � 0.47), epidote (type 3; XF,3 + � 0.55), minor chlorite (type 3; XF, � 0.60) and quartz. The dominant Ti-bearing minerals in the matrix are Mn-rich ilmenite (MnO = 3.7 wt%, i.e. �9'10 pyrophanite) and titanite (type 3), which con tains up to 1.8 wt% A1203, up to 1.2 wt% FeO and up to 0.4 wt% F. S3 parageneses also include minor pro portions of bluish Ca Na amphiboles such as winchite (Si � 7.4 pfu; XNa � 0.30 0.32; XF, � 0.51 0.52) and barroisite (Si � 6.9 pfu; XNa � 0.33 0.36; XF, � 0.45 0.5), and relatively abundant small crys tals of dravite-rich tourmaline and apatite (Fig. 3a; Table 2). This foliation wraps around subhedral crystals of garnet (0.5 4 mm) concentrated in the micaceous do mains of the matrix, and locally included in albite porphyroblasts. Garnet is rich in inclusions, which commonly display a concentric arrangement (Figs 3a &4a). Locally, however, they defi ne curved or sig moidal patterns or, more rarely, markedly rotational paths arranged as spirals (snowball garnet). Large garnet crystals display an optical zoning. The cores, referred to as garnet 1 (g I), usually lack fractures and contain very fi ne-grained inclusions « 0.06 mm) of epidote (type I, XF,3 + � 0.60), titanite (type I), rutile needles and quartz (Fig. 3a; Table 2). In general, the inclusions defi ne a very fi ne foliation, SI. The outer parts of large garnet, referred to as garnet 2 (g2), are commonly fractured and rich in coarser-grained (up to 0.7 mm) inclusions of glaucophane (Si � 7.8 pfu; XNa � 0.97; XF'�O.4; XF,3 + � 0.05 0.1), chloritoid (XF' � 0.80), phengitic muscovite (type 2, Si up to 3.5 pfu) that is locally also included in chloritoid (an inclusion m an inclusion), chlorite (type 2, XF, � 0.43), rutile (locally partly replaced by ilmen ite), ilmenite and quartz (Fig. 3a; Table 2). In most cases, these inclusions defi ne a curved or sigmoidal foliation (S2) discordant with the external foliation, S3. The optical zoning can be correlated with the chemical zoning (Fig. 4a). Type 1 garnet core displays zoning characterized by an increase in almandine and pyrope (Alm51 --760, Prp2 --7 3) and a decrease in spessartine (Spsl8 --7 9). XF, remains constant (XF' � 0.96) and the proportion of grossular varies irregularly between 28 and 31 %. The apparent absence of zoning in garnet I core in Fig. 4a is caused by the profi le running slightly off the centre of the crystal; the core values were obtained by point analysis (Table 2). The garnet I zoned rim (Fig. 4a; profi le I) is characterized by an increase in the amount of both grossular and spessartine, compensated by the decrease of the pro portion of almandine (Grs28 --7 32, Sps9 --7 11, Ahn61 --7 55). In type 2 garnet, the rimward evolution is characterized by a decrease in grossular, spessartine and XF, (Grs31 --7 19, Sps11 --7 I, XF, � 0.96 --7 0.93), accompanied by an increase in ahnandine and pyrope (Ahn55 --7 73, Prp3 --7 6).

Finally, post-S3 minerals are locally present around garnet and are commonly composed by inter growths of chlorite (type 3b), albite and quartz. Garnet rim is nearby replaced by chlorite flakes (type 3b; XF, � 0.56). Rare bluish-green Ca-amphibole such as Fe/Mg-hornblende (Si � 6.5 6.8 pfu; XNa � 0.17 0.22; XF, � 0.51 0.38; XFd+ � 0.07 0.22) and tschermakite (Si � 6.9 pfu; XNa � 0.24 0.25; XF, � 0.36 0.37; XF,3 + � 0.21) grow in optical continuity on the rims of the Na Ca amphibole. Lo cally, hornblende develops large crystals (> 0.3 mm long), which are arranged parallel to type 3b chlorite (Fig. 3a; Table 2). Minor proportions of sericite, stil pnomelane, carbonates and sulphides are commonly concentrated along the extensional shear planes and in some samples a pervasive growth of albite porphyro blasts occurs.

In summary, three metamorphic stages (Ml M3) can be distinguished in the evolution of this sample (Fig. 2). Evidence for Ml is recorded by aligned inclusions (ep, ru, sph, q) in the cores of large garnet (gl) (Fig. 3a). M2 is characterized by the inclusions of ctd, chI, gl, ru, ilm, mu, q preserved in garnet 2. The third stage (M3) is recorded by the matrix foliation (S3), comprising the assemblage chl-ep-mu-pa-bi rulihn-sph-q ± g ±winlbar (Figs 2a & 3a). Finally, post-M3 crystallization includes post-S3 phases such as chI, hb/ts, ab, ser, stp, carb, suI.

Structurally upper metapelites

Sample UM consists essentially of quartz, white mica, chloritoid porphyroblasts and garnet. It displays layers dominated by quartz and white mica respectively. Chloritoid and garnet are concentrated in the mica ceous domains. The matrix foliation (S3) is parallel to the layering and contains quartz, muscovite (type 3, 3.06 3.08 Si pfu, XNa � 0.06), paragonite (type 3; XNa � 0.93), chlorite (type 3; XF, � 0.60), garnet (0.1 0.4 mm in average, locally up to I mm), ilmenite (MnO � 3.11 wt%, i.e. �9'10 pyrophanite) and rare elongated crystals of chloritoid (type 3; 0.5 I mm long, XF, � 0.81 0.82). It is not clear whether these chloritoid crystals really belong to the foliation or represent reoriented crystals of an older generation of chloritoid (type 2). Small crystals of tourmaline are relatively widespread in the foliation. The foliation wraps around clusters containing abundant large stubby crystals of chloritoid (type 2; up to 4 mm long, XF, � 0.80 0.84), commonly lacking a preferred ori entation. Garnet, white mica and minor chlorite, quartz, rutile and ilmenite are also present in these clusters. Chloritoid porphyroblasts contain numerous tiny inclusions of tourmaline, rutile, phengitic musco vite (type 2; Si � 3.33 3.34 pfu, XNa � 0.04), parag onite (type 2; XNa � 0.95), garnet and locally ilmenite (2) that defi ne an internal foliation, S2' Garnet inclusions are euhedral and signifi cantly smaller (0.02 0.06 mm) than the matrix crystals (Fig. 3b). Chemical zoning of garnet (Fig. 4; profi le 2) is characterized, from core to rim, by a decrease in spessartine (Sps38 --7 5), balanced by an increase in ahnandine (Ahn41 --773) and pyrope (Prp2 --7 9). XPe decreases regularly from 0.96 to 0.93. The grossular content varies irregularly between Grs20 and Grs16, with a tendency to decrease towards the rim. Finally, an increase in spessartine (Sps5 --7 7) and XPe (0.90 --7 0.93) is observed in the outermost rim, together with an inversion of the general zoning pat tern of pyrope (Prp9 --7 8) and ahnandine (Alm73 --7 70). Garnet inclusions in chloritoid display the same type of zoning. However, the rims lack the reversal in spessartine zoning and their composition (Alm61 Prp4 Grsl8 20 Spsl8) suggests that they cor respond to the matrix crystals, the growth of which was arrested by the inclusion in the chloritoid (type 2). Finally, post-S3 phases include tiny crystals of chlorite (type 3b; XPe � 0.58) and Fe Ti-bearing oxides and hydroxides concentrated along the shear planes

1 0.8 o Fe/(Fe+Mg} • XA1m • • • 0.1 • • o XSPII • • • • • 0.6 0.5 0.4 0.3 0.2 • • • • • XGrto • XPrp -.. . • ••• • DOD O D D C C o 0 • • C O • • •• 0 •• • • •• • •• • • • 0 • • • ••• •• (] 0 0.1 . 0 .O� . � D ••O 0.0 DD • ••••• •••••••• • •
(Figs 2b & 3b).
In summary, it is inferred that the preserved mineral assemblages correspond to the sequence of two meta morphic stages, named M2 and M3, according to their textural position. The Ml event (recorded in the LM) was not identifi ed as inclusions in garnet cores in sample UM. This event represents the early stages of subduction, and it is not possible to infer if it was not preserved in these rocks, or if they never recorded it. Evidence for M2 is achieved by the assemblage g-ctd mu-pa-ru ± ilm. These minerals occur preserved as inclusions in garnet and in chloritoid porphyroblasts (type 2), and defi ne the internal fabric S2. M3 corre sponds to the matrix foliation S3 and is composed of g-chl-mu-pa-ru-ilm-q ± ctd. The post-M3 event in cludes post-S3 phases such as chlorite and Fe/Ti-oxide.

P-T ESTIMATES

Pseudosections were calculated for the P T domain of interest, between 350 and 600°C and 5 25 kbar. The diagrams have been computed using THERMOCALC 3.33 3.35 [START_REF] Powell | An internally consistent dataset with uncertainties and correlations: 3. Applications to geobarometry, worked examples and a computer program[END_REF] and the internally consistent thermodynamic data set 5.5 (Holland & Powell, 1998;updated Nov. 2003). References of the mixing models for solid solutions of the phases con sidered in the calculations are amphibole [START_REF] Diener | A new thermodynamic model for clino and orthoamphiboles in the system Na20 CaO FeO MgO Ab03 Si02 H20 O[END_REF], clinopyroxene [START_REF] Green | An order disorder model for omphacitic pyroxenes in the system jadeite diop side hedenbergite acmite, with applications to eclogitic rocks[END_REF], chloritoid (Mahar et The rock slab of each sample used to make the thin section was crushed and analysed by XRF to obtain the bulk composition. FeO (v. Fe203) was analysed by wet chemical titration. Phase relations were modelled in the chemical system MnO Na20 CaO K20 FeO MgO Al203 Si02 H20 Ti02 Fe203 (MnNCKFMASHTO). The original compositions of the studied rocks were simplifi ed to fi t this system (Table 1). Bulk-rock com positions indicated in brackets in fi gure captions are those recalculated using THERMOCALC. The fluid phase was fixed as pure H20, initially in excess. The diagrams are shown in Figs 5 &6. Thick lines indicate the stability fi eld of diagnostic phases, and the thickest semitrans parent lines represent the proposed P T paths. White fi elds are divariant and increasing variance is shown with progressively darker shades. Mineral abbreviations are those used by THERMOCALC (see above).

Lower metapelites AP T pseudosection calculated in the system MnNCKFMASHTO for the analysed bulk composi tion with H20 considered in excess is presented in Fig. Sa. The stability domains corresponding to the observed relicts of mineral assemblages Ml (g, ep, sph, ru, q) and M2 (g, ctd, chI, gl, nI, ilm, mu, q) are modelled in the HP and LT part of the pseudosec tion. However, most assemblages containing these phases are predicted to also contain lawsonite, which has not been observed either as inclusions in garnet or in the matrix. This hydrous mineral is stable over a wide P T range in the LT blueschist facies, but rarely preserved. Pseudo morphs of this mineral can be found in the interbedded mafi c rocks, so it seems possible that some of the abundant crystals of epidote present in the matrix of the schists could be the product of destabilization of lawsonite, although unquestionable pseudomorphs of this mineral were not found.

The ctd + gl paragenesis, preserved in the second generation of garnet (g2), and characteristic of this lithology, is present in the uppermost part of the dia gram between 20 and 22 kbar, and 400 and 500°C. However, in this fi eld, the calculated composition of garnet does not correspond to that observed in g2. The isopleth values corresponding to type 2 garnet cores (g2c) (Grs � 28 32% and Sps � 5 11 %) intersect in the lower pressure chloritoid-absent fi eld (at 18 kbar and 470°C; see shaded star (I) in Fig. Sa). The isop leths that represent the garnet rim (g2R) (Grs � 28 19% and Sps � 5 1 %) intersect in the same fi eld at higher pressures (�20 kbar and 490°C; see shaded star (2) in Fig. Sa). Therefore, it is not possible to infer a reasonable P T evolution for this sample because garnet zoning does not fi t with the petrographic observations.

Although considering water in excess for the petro logical modelling is a good approximation in most metapelites along the prograde path, crystallization of strongly hydrous minerals, like lawsonite, at high pressures and low temperatures may lead to H20undersaturation as metamorphism progresses (e.g. [START_REF] Guiraud | H20 in metamor phism and unexpected behaviour in the preservation of metamorphic mineral assemblages[END_REF][START_REF] Ballevre | Lawsonite growth in the epidote blueschists from the Ile de GrODe (Armorican Massif, France): a potential geobarometer[END_REF][START_REF] Clarke | The lawsonite paradox: a comparison of field evidence and mineral equilibria modelling[END_REF]. The available amount of H20 also has an influence on the position of the compositional isopleths. To estimate the amount of H20 available in the system at peak conditions, a P X(H20) pseudosection has been calculated at 480°C (Fig. 5b). The temperature corresponds to that estimated for the peak conditions from pseudosection approach (Fig. 5). However, other temperature values have been tested and the exact value does not have a signifi cant effect on the result. The assemblage corresponding to the crystallization of the second generation of garnet (g-ctd-chl-gl-law*-ru ihn +mu,q) is stable between 21 and 23 kbar under H20-saturated conditions, but extends to slightly lower pressures (down to 20.5 kbar) with the decreas ing amount of H20. In this four-variant fi eld, the isopleths corresponding to the composition of the outer part of garnet 2 (g2IJ (Grs � 28 19%, Sps � 5 1 %) intersect between XH,00f 13.75 and 15%. Therefore, the available amount of H20 was set to 14.375 mol. % (�14.4 mol. %), corresponding to the average of these values (see shaded area in Fig. 5b). In addition, with the estimated amount of water (14.4 mol. %), a P X (Fe203) pseudosection at 480°C has been calculated to explore the effect of varying the Fe203 content for sample LM (Fig. Se). According to this diagram, the isopleths of interest intersect in a wide area between the Fe203 values analysed and the double of it (see shaded area in Fig. Se). Therefore, this diagram yields no constraints on the amount of Fe203 present in the rock, although it excludes values sig nifi cantly lower than the analysed one. A new P T pseudosection has been computed m the MnNCKFMASHTO system for the analysed bulk composition and the amount of H20 fi xed at 14.4% (Fig. 5d; Table 1 b). The diagram shows that the rock is water saturated at LPs and HTs, but fluid absent under HP LT conditions. The HP part of the diagram (> 18 kbar) is characterized by the presence of gl + ctd and the absence of epidote (stable at < 18 kbar). Titanite is present at pressures lower than � 15 kbar and temperatures lower than 480°C. Rutile is stable at pressures higher than �12 kbar or tem peratures in excess of 470 QC. Biotite is stable in the LP, HT part of the diagram. The stability of parago nite is modelled only at > 470°C and < 11 kbar (Fig. 5d).

The type 1 garnet inclusions (ep, sph, ru, q) are in ferred to represent relicts of the former full assemblage g-chl*-ep-gl*-law*-ru-sph-mu*-q, suggesting that the rock passed through the corresponding stability fi eld at 350 380°C, 12 14 kbar. Garnet 2 cores equilibrated then in the fi eld g-ctd-chl-gl-Iaw*-ru-ihn +mu,q. This area is a relatively wide fi eld at �360 480°C, 18 22 kbar. P T conditions corresponding to the growth of garnet 2 have been refi ned based on the intersection between different isopleths. The isopleths correspond ing to the composition of type 2 garnet core (g2c) (Sps5-11, Grs28-32) and muscovite inclusions (mu2, Si � 3.45 3.50 pfu) intersect between �18 and 19 kbar, and �400 and 420°C (shaded star (I) in Fig. 5d). Continuous decrease in grossular and spessartine towards garnet 2 rims (g20 (Grs28 ---7 19; SpsS ---7 1) suggests further heating at increasing pressure up to �460 QC, 21 kbar (shaded star (2) in Fig. Sd). The matrix foliation (M3) assemblage is defi ned by the occurrence of muscovite, paragonite, biotite, chlorite, epidote, Na Ca amphibole, ilmenite and titanite, and the absence of chloritoid. The appearance of epidote indicates < 18 kbar for the M3 event. Biotite is stable at < 16 kbar, ihnenite and paragonite at < 11 kbar. The presence of paragonite suggests temperatures higher than 470°C, whereas titanite is stable at < 480°C. Although all these phases are not stable together in a single fi eld of the pseudo section, their stability domains are extremely close in the region '""'-' 8 10 kbar, 470 490°C, which is inferred to represent the approximate conditions of development of the main foliation S3 (green ellipse in Fig. Sd). This point is further discussed below. In any case, this suggests signifi cant subisothennal decompression between M2 and M3. Finally, the late crystallization of albite (post M3) indicates pressures lower than �8 kbar and a probable further evolution towards lower P T (Fig. Sd). Although this pseudosection accounts quite well for the petrographic evolution of sample LM in general terms, the modelled composition of amphibole along the post-M2 path does not agree with that of the observed Na Ca amphiboles. This issue will also be discussed below.

Upper metapelites AP T pseudosection has been calculated in the MnNCKFMASHTO model system for the bulk com position obtained by XRF and the amount of FeO (v.

Fe203) obtained by titration (Fig. 6). To check that the bulk composition does not reach H20-undersaturated conditions during the pro grade evolution, the amount of H20 was set so that the rock is just fluid saturated in the HP part of the fi eld ctd-chl-pa-ep-ilm-ru + q,ms, along the LP stability limit of lawsonite. This fi eld corresponds to aP T domain through which the rock would pass, when following a hypothetical, but prob able P T path, before entering the stability domain of lawsonite. Indeed, as discussed above (see also [START_REF] Ballevre | Lawsonite growth in the epidote blueschists from the Ile de GrODe (Armorican Massif, France): a potential geobarometer[END_REF][START_REF] Clarke | The lawsonite paradox: a comparison of field evidence and mineral equilibria modelling[END_REF], the formation of lawsonite commonly leads to H20 undersaturation. However, in this low-Ca metapelite, the modelled modal amount of lawsonite is very low. As a result, using this approach, the assemblages are H20 under saturated at low pressures and temperatures, with aqueous fluid stabilized at higher conditions (Fig. 6b). Consequently, the entire prograde evolution of this rock occurs under H20-saturated conditions and water is considered in excess in the following calculations.

In this P T pseudosection (Fig. 6a), garnet is stable at > 500°C, epidote is stable at < 520°C and < 18 kbar and glaucophane is predicted to be stable from 15 to 21 kbar, at < 590°C. Epidote and glau cophane have not been found either as inclusions or in the matrix. Therefore, based on the petrographic observations the four-variant fi eld g-ctd-chl-pa-ihn ru+q,ms located between 12 and 15 kbar and at > 510 QC reflects the paragenesis corresponding to the matrix foliation. However, this pseudosection cannot be used to infer the equilibration conditions of the garnet core, as the observed amount of spessartine in the garnet core (Sps38-40; Fig. 4b) is not modelled anywhere in the diagram. The maximum values pre dicted in the diagram are SpslS. One reason may be the relatively high amount of Fe203 analysed in this sample, uncommon in typical pelites. Although sample UM does not appear to be altered in hand specimen or in thin section, the concentration of Fe-bearing oxides/hydroxides along shear planes (Fig. 3b) sug gests that the Fe203 proportion in the original rock may have been signifi cantly lower compared with the result of the analysed bulk composition, possibly due to the circulation of oxidizing fluids. A series of pseudosections was recalculated with progressively lower amounts of Fe203 ('0' in the bulk composition), with signifi cant changes only being observed when the amount of Fe203 was close to zero. The highest values predicted in the diagram for the spessartine and gros sular isopleths calculated for the garnet core compo sition intersect at � 16 kbar in the three-variant fi eld g-ctd-pa-ep-gl-ihn-ru + q,ms (shaded star in Fig. 6a). Therefore, this domain seemed the most suitable for obtaining spessartine values closer to the observed ones by modifying the amount of Fe203 in the bulk composition. Trying to estimate a reliable amount of Fe203 for this sample, a T X(Fe203) pseudosection was calculated at 16 kbar (Fig. 6c). This diagram shows that the isopleths corresponding to the compo sition of the garnet core intersect between 425 and 440°C in the four-variant fi eld g-ctd-chl-pa-gl-law ru + q,ms for Fe203 � 0.05 (shaded star in Fig. 6c). Consequently, aP T pseudosection has been recalcu lated with this value, 0 � 0.05 (Fig. 6d; Table 1

b).

Compared with the original diagram, in this P T pseudosection, garnet stability increases notably towards lower temperatures (from 510 to 420°C) and glaucophane is stable at pressures higher than 11 kbar. The syn-S3 matrix assemblage, g-ctd-chl-pa-ihn ru + mU,q is modelled in the relatively LP and HT part of the diagram. The analysed composition of muscovite (Si < 3.1 pfu) is compatible with the equilibration of the matrix in the LP part « 11 kbar) of this fi eld. The isopleths corresponding to the proportions of grossular and spessartine in the garnet cores (18 20 and 38 40% respectively) intersect in the four-variant fi eld g-ctd chl-pa-gl-law-ru + q,ms at � 15 16 kbar, 430°C (shaded star (1) in Fig. 6d). One of the principal characteristics of the garnet zoning observed in the sample is a continuous decrease of spessartine, whereas the grossular content remains at an approximately stable value. This evolution may only be explained if a Ca-rich phase like epidote or lawsonite coexists with garnet (shaded star (2) in Fig. 6d). Beyond, both "-' �����--����-r--, 2 5 ������--���------, . (e) P T pseudosection calculated for the bulk-rock composition after fr actionation of garnet and chloritoid. (t) P T pseudosection calculated in the CKFMASH system for the bulk-rock composition after fr actionation. The star (2)* is inferred from (e). See text and Table 1 for details.

isopleths become nearly parallel and a decrease in spessartine is accompanied by a decrease in grossular, which is not observed in the sample. However, at the lawsonite-out line of the fi eld g-ctd-pa-gl-law ill + q,ms, for grossular contents between 15 and 20%, corresponding to those observed in the sample, the spessartine content is '""'-' 15%, whereas the value ob served in the garnet rim is �3'10 (Fig. 4b).

As Mn is mostly stored in garnet cores during pro grade metamorphism, this inconsistency could be re lated to the fractionation of whole-rock composition due to the garnet growth. However, progressive re moval of even all crystallizing garnet from the bulk composition does not reproduce the observed garnet rim compositions. Although much poorer in Mn than garnet, chloritoid does contain Mn and is present in signifi cant quantities in the sample (and the model pseudo section). Furthermore, clusters of large chlori toid crystals in the sample appear shielded from the deformation associated with the development of the main foliation and could be effectively inert during the recrystallization of the rock matrix (and the crystalli zation of the rims of matrix garnet). Progressive frac tionation of garnet and the removal of 95% of chloritoid at the point when the modelled crystallizing garnet has the composition of the rims of the garnet inclusions in chloritoid results in a Mn-poor bulk composition (Table 1 b) and a corresponding P T pseudo section depicted in Fig. 6e. This model repro duces the observed garnet zoning, with the garnet rims crystallizing at the lawsonite-out limit of the fi eld g-ctd-pa-gl-law-ru + q,mu at �21.5 kbar, 510 520°C.

The composition of muscovite (Si �3.3 pfu) mod elled along the path iuferred for the garnet growth is compatible with the values observed in the muscovite inclusions in the chloritoid porphyro blasts. Conse quently, the preserved garnet zoning constrains the prograde P T evolution of the sample from � 16 kbar and 430°C to �21 kbar and 510°C.

The lack of further garnet growth suggests that the subsequent evolution must have occurred at constant or decreasing garnet mode. Indeed, partial garnet resorp tion is suggested by the local increase of spessartine at the very rim of the matrix crystals (Fig. 4). The isop leths of garnet mode (not represented) are essentially parallel to the isopleths of the spessartine content. Their position suggests an evolution dominated by decom pression at approximately constant or decreasing tem perature. Nevertheless, in Fig. 6e, such an evolution systematically passes through fi elds containing glauco phane, which is not present in sample UM. Glauco phane disappears from the model mineral assemblages at pressures lower than 8 kbar (not represented). But, all fi elds at pressures lower than 10 13 kbar contain biotite, which is not present in the sample either (Fig. 6e). However, it cannot actually be excluded that the rock passed although biotite-bearing fi elds because during cooling rocks become dry and diffusion ineffi cient (e.g. [START_REF] Guiraud | H20 in metamor phism and unexpected behaviour in the preservation of metamorphic mineral assemblages[END_REF]. Consequently, it is not possible to interpret the formation of the matrix assemblage using this pseudosection.

Trying to overcome these problems, the chemical system was simplifi ed to CKFMASH using the fol lowing assumptions based on the petrographic obser vations. Sodium was removed from the bulk composition in the form of paragonite (which is the only Na-bearing mineral in the matrix), MnO was subtracted in the form of ihnenite containing 10% pyrophanite and the remaining Ti02 was removed as 40% rutile and 60% ihnenite (according to the modal proportions observed in thin section). These minerals are therefore considered de facto in excess. The resulting P T pseudo section (Fig. 61) has chloritoid in the HP LT corner of the diagram, whereas biotite is stable in the LP HT part. The stability fi eld that ap proaches best the observed matrix assemblage is g-chl (+mu-q; +pa-ilm-ru), stable at temperatures between 460 and 560°C and 13 < P < 23 kbar. The P T conditions of the formation of the matrix remain therefore largely unconstrained.

DISCUSSION

The two samples representative, respectively, of the lower and upper level of the Cein Schists in the Upper Sheet of the MTU have recorded similar P T evolu tions characterized by a prograde P T path in blues chist facies conditions, peaking at 21 22 kbar. The temperatures recorded in the UM are slightly higher than those from the LM (Fig. 7a). Both samples could have experienced a slightly different evolution due to their different position in the orogenic wedge (Fig. 7b). In the LM, the blueschist facies assemblages were overprinted by the regional foliation developed at signifi cantly lower pressures (8 10kbar, 470 490°C). Whereas the calculated phase diagrams and the proposed metamorphic evolution account reason ably well for the fi rst-order petrographic observations, and are in agreement with the mineral chemistry in both the LM and the UM, several details need to be discussed.

Phase diagrams

For both rock types, the fi rst step was to calculate a P T pseudosection using the water-saturated analysed bulk composition. Coufronted with the lack of com patibility between the observations and the modelling results, various compositional parameters that may signifi cantly modify the appearance of the pseudo sec tion have been investigated (calculating parts of P T or PIT X pseudo sections), to obtain coherent results. For the LM, the H20 content appeared to be the critical factor. Fe 3 + appeared to play the major role for UM, whereas the low mode of lawsonite in this low-Ca pelite did not lead to H20-depletion and the rock remained H20 saturated during the prograde evolution. In both samples, the modelling accounts quite well for the observed paragenetic sequence. It can be ob jected that all the phases inferred to be stable during the prograde part of the P T evolution, in particular lawsonite and glaucophane, are not observed in the thin sections (with the exception of the M2 glauco phane inclusion in garnet of the LM). However, inclusions typically only represent remnants of the initial full assemblages. In more detail, in the LM, the absence of lawsonite has already been discussed above and can be explained by the classic replacement by epidote during decompression. In the UM, the mod elled proportion of both lawsonite and glaucophane is very low (max. 0.9 and 3 5% respectively) making their preservation improbable.

In the LM, no stability fi eld can account for the presence of all the M3 minerals in the S3 foliation. The stability domains of the M3 minerals, in particular paragonite, chlorite and titanite are extremely close to one another in the topologically complex region at around 8 kbar, 470°C, but do not overlap. Never theless, it can be argued that along a P Tpath crossing this region, a rock could develop these minerals sequentially, giving the impression of an equilibrium assemblage. Alternatively, minor changes in the parameters of the mixing models for solid solutions could change the topology suffi ciently to obtain the observed assemblage in one fi eld in this P T domain .

Similarly, only small and scattered crystals of chemically heterogeneous Na Ca amphibole are ob served in the matrix foliation. However, the amphibole predicted in the pseudosection has systematically a high-glaucophane content and is relatively abundant (18 14 moL%) down to pressures of �8 kbar, when albite becomes stable. When reaching the fi eld g-chl ep-gl-sph-bi-ab + q,ms at 7 kbar, an abrupt decrease in the mode of amphibole (from 14 to 3 moL %) coincides with an increase of the proportion of hornblende. This increase is compatible with the presence of Ca amphiboles, such as hornblende and tschermakite, observed in the post-S3 textural position. Although the amphibole chemical composition along the proposed P T path never coincides with the analysed composi tions, this qualitative evolution is compatible with the crystallization of the post-S3 phases under relatively LP conditions, of the order of 7 8 kbar, < 480°C.

In sample UM, it is difficult to estimate reliably the equilibration conditions of the matrix foliation (S3). In the P Tpseudosection calculated for the analysed bulk composition (Fig. 6a,b), the syn-S3 matrix assemblage, g-ctd-chl-pa-ilm-ru + q,ms and the composition of the matrix muscovite (Si < 3.1 pfu) suggest equilibration of the matrix in the LP and HT part of the diagram « 11 kbar, > 480°C). However, this diagram does not account for the observed garnet zoning. This can only be explained if signifi cant fractionation of garnet and chloritoid takes place (Fig. 6e). Then, however, any reasonable P T evolution systematically passes through fi elds containing glaucophane, which is not present in the sample, unless paragonite is forced in excess in a model system reduced effectively to CKF MASH (Fig. 61).

The fi rst reason for this can be a problem with the solid-solution models. Unfortunately, even using the most recent glaucophane [START_REF] Diener | Revised activity composition models for clinopyroxene and amphibole[END_REF] and white mica (Smye et ai., 2010) models only results in minor differences in the pseudosection and does not solve the problem. It appears that glaucophane is 'too stable', in particular with respect to paragonite. A second reason may be related to problems with the identifi cation of the effective bulk composition. This can be related to the deformation-enhanced fraction ation of the bulk composition in a layered rock. In certain layers, the initial bulk composition undergoes fractionation during the growth of garnet and chlori toid porphyroblasts. During the subsequent defonna tion, a certain proportion of these porphyroblasts is preserved in undeformed domains, forming the ob served chloritoid + garnet-rich clusters (Fig. 3b). Other layers and a part of the garnet chloritoid clus ters recrystallize during the fonnation of the S3 foliation.

For these domains, the unfractionated composition and hence the original pseudosection (Fig. 6a,b) is still applicable. Alternatively, problems may also be related to the presence in the sample of some minerals that should have been removed from the effective bulk composition, like tourmaline. However, the crystalli zation of such minerals is generally related to fluid circulation, which may occur at different stages of the metamorphic evolution, resulting in the modifi cation of the bulk composition at a point that may be difficult to estimate. Finally, a major change in the oxidation conditions during the evolution of the rock cannot be excluded, with important consequences on the stable mineral assemblages, as discussed before.

Fluid-ab sent prograde metamorphism

The possibility of reduced water availability in certain geodynamic scenarios allows rocks to experience a fluid-absent prograde evolution during subduction. A vast majority of metamorphic reactions have a dehy dration character and produce H20 fluid when crossed upon heating, during the prograde evolution. Accordingly, most rocks are saturated in H20, which is then commonly considered in excess for petrological modelling. Whereas this approach yields correct results in most cases, several exceptions merit highlighting: polycyclic evolution, partial melting, retrograde evo lution and subduction metamorphism. The latter is the one that concerns this study. Metamorphism in sub duction zones is characterized by low geothermal gradients (steep in aP T diagram). Rocks following these gradients may cross some dehydration reactions in the 'wrong', H20-consuming direction. This is the case of the reactions involving lawsonite, which have a relatively 'flat' slope with lawsonite being stable at the HP, LT side. Consequently, rocks become H20 undersaturated with important implications for the phase relations and mineral assemblages encountered in such environments (e.g. [START_REF] Ballevre | Lawsonite growth in the epidote blueschists from the Ile de GrODe (Armorican Massif, France): a potential geobarometer[END_REF][START_REF] Clarke | The lawsonite paradox: a comparison of field evidence and mineral equilibria modelling[END_REF]. Unlike their metabasic counterparts, pe litic rocks are depleted in Ca and can only form limited quantities of lawsonite. It is then not common for a metapelite to experience a fluid-absent prograde metamorphism, which can be expected in metabasic rocks. Sample LM, with a composition intennediate between a pelitic and a basic one, is more likely to have undergone a fluid-absent prograde metamorphism than a pure pelite. On the contrary, sample UM, with a true pelitic composition, experienced a fluid-bearing prograde metamorphism.

Tectonic implications inferred from garnet zoning

The zoning of type 1 garnet in sample LM is not ac counted for satisfactorily by the phase diagrams, as the predicted garnet composition does not match the ob served one in the appropriate assemblage fi elds. This may have several reasons including problems with activity composition relations in Mn-bearing systems, inappropriate estimation of the effective bulk compo sition or the oxidation state of the rock, or problems with the degree of H20 (under)saturation of the min eral assemblages. However, the preserved zoning can be used to draw some qualitative inferences about the evolution of the rock. Whereas the core of garnet 1 displays a decrease in spessartine (Spsl8 --7 09), the rim displays a reverse trend (Sps9 --7 11) to reach values characteristic of the core of garnet 2 (Sps 11) (Fig. 4). Because of the strong fractionation of Mn into garnet, garnet growth is systematically associated with the decrease in the proportion of spessartine. Similarly, an increase of spessartine is typically related to a decrease in pressure and/or temperature (cf. Fig. 5). Consequently, the decrease of spessartine in the garnet 1 core can be interpreted in terms of a pro grade growth. Higher spessartine content preserved in the core of garnet 2 suggests that it began to crys tallize at P T conditions lower than those reached by the rim of garnet 1. This suggests a slightly more complex metamorphic evolution characterized by a stage of partial exhumation during the subduction process (Fig. 7a). The reverse zoning in the garnet 1 rim may be related either to partial resorption or to a diffusional reequilibration with the garnet 2 core (e.g. [START_REF] Banno | A model to explain the Mn enrich ment in the rim of zoned garnet[END_REF][START_REF] Tracy | Compositional zoning and inclusions in me tamorphic minerals[END_REF]. Moreover, type 1 garnet contains the earliest foliation (S)) preserved in the Cean Schists, which is not observed in samples from the higher structural levels. Therefore, the M) event was recorded at least by the LM and the fi rst subduction-related stage is only preserved in the lower structural levels of the series (Fig. 7a).

Implications for the Variscan subduction in NW Iberia

The P T results obtained from pseudosection calcu lations yield fi rst-order constraints for geodynamic models: the maximum depth reached by the Upper Sheet of the MTU during subduction and the geo thermal gradient. P T conditions of 21 22 kbar and 460 and 520°C in the lower and UM, respectively, correspond to an approximate depth of �76 80 km and a geothermal gradient of 67 °C km -) , typical of relatively cold subduction zones (Fig. 7a). Martinez Catalin et al., 1996). The important relative movements between the Upper and the Lower Sheet, reflected by their tectonic extensional contact, produced the superposition of sheets located at different depths in the subduction complex, but their relative position in the subducting slab was probably not altered. The differences in the P T paths (Fig. 7a) between the MTU and the Agualada Unit can be explained on a schematic cross-section of the subduc tion zone at the moment when peak pressures were reached (Fig. 7b). The blueschist sheet of this study (Cein Schists) is sandwiched between two eclogitic units: the Lower Sheet of MTU below and the Agua lada Unit above. The highest temperatures during subduction are found in Agualada, where the temper ature peak is �720 °C and pressure is > 14 kbar [START_REF] Arenas | P T evolution of eclogites fr om the Ag ualada Unit (Ordenes Complex, northwest Iberian Massif, Spain): implications for crustal subduction[END_REF]. The fact that highest tempera tures have been recorded on the top of the subducting slab demonstrates the existence of an inverted meta morphic gradient at the top of the subducting slab. The presence of a blueschist sheet sandwiched between two eclogite facies sheets is interpreted as a consequence of the geometry of the isotherms (Fig. 7b).

CONCLUSIONS

From this study we can conclude that:

1 The Upper Sheet of the MTU recorded a three-stage metamorphic evolution involving (i) Early subduc tion-related medium-pressure/LT metamorphism (Mj) roughly constrained at � 350 380°C, 12 14 kbar, which is only preserved in the basal part (LM) of the Cein Schists. (ii) Subduction-related blueschist facies prograde metamorphism (M2) going from �19 kbar, 400°C to 21 kbar, 460°C in the structurally LM, and from 16 kbar 430°C to 21 22 kbar, 520°C in the UM. (iii) Exhumation related metamorphism (M3) is characterized by a decompression to 8 10 kbar, �470 490°C in the LM. This decompression is also recorded in the UM, but it was not possible to estimate precise P T conditions. 2 The pseudosection calculations indicate that the prograde evolution in subduction zones may occur in H20-undersaturated conditions due to the crys tallization of lawsonite, even in metapelitic rocks. This signifi cantly influences phase equilibria and hence the P T estimates. 3 The proportion of ferric iron has a strong influ ence on the phase equilibria of HP metapelites. However, the analysed values of Fe203 may not reflect the oxidation state during the main meta morphic evolution and are probably easily modi fi ed by superfi cial alteration even in apparently fresh samples. The use of PIT X(Fe203) pseudo sections together with petrographic observations is then necessary to estimate the real oxidation state of the rocks and correctly evaluate the P T con ditions. 4 The Basal Units of the NW Iberian Massif formed part of a slab subducted beneath Laurussia at the onset of the Variscan collision. The units are sepa rated and displaced by tectonic contacts. However, the succession of the P T conditions recorded by the different basal units preserves the original thermal structure of the subduction zone in the northern margin of Gondwana.

Figure 1 .

 1 Figure 1. (a) Cross-section for the Upper Sheet (pazos Synfonn) of the Malpica Till Unit. The gradation of colours indicates the decrease in the metamorphic grade. Sample locations are indicated. Modified from Diez Fernandez (2011). (b) Geological map of the Allochthonous Complexes of the NW Iberian Massif. A B and B C correspond to cross-sections along the different units. US, upper sheet; LS, lower sheet; AG, Agualada Unit. Modified from Martinez Catahin et al. (2009).

  ). Peak metamorphic conditions in the Lower Sheet of the MTU are in the intermediate temperature eclogite facies (Rodriguez et al., 2005), with a progressive transition to the blueschist facies in the eastern sections of the same units in the remaining allochthonous complexes (Martinez Catalin et al., 1996; Rubio Pascual et al., 2002). The Upper Sheet can be consid ered as a highly condensed metamorphic sequence with a lower part in the blueschist facies and an uppermost part without HP relicts (Fig. la). The signifi cant dif ference in metamorphic grade between the Upper and the Lower Sheets, and between the upper and lower part of the Upper Sheet suggests that the mylonites that mark the contacts are related to extensional deformation (L6pez-Carmona et al., 2007; Fig. I).

Figure 2 .

 2 Figure 2. Diagram showing the crystalliza tion deformation relations of the Cean Schists in the lower (a) and upper metapel ites (b). (c) Summary of the modelling results showing the mineral assemblages predicted in the metamorphic events. *Inferred phases that have not been observed petrographi cally.

  (a) Bulk-rock composition from XRF analyses of samples LM and UM expressed in wt%. (b) Bulk-rock compositions normalized with THERMOCALC expressed in mol. %. F e203(T) was measured by the XRF and F eO by wet chemical titration. The amount Fe203 is calculated stoichiometrically as: [total iron/ I.43 (FeO/l.286)' 1.43]. Studied samples MnNCKFMASHTO CKFMASHtectonics. The effects of POSt-S3 defonnations associ ated with vertical folding are particularly evident in the core of the synformal structure, where an axial planar foliation S4 is usually developed, In these areas, the schists are highly altered and the main foliation consists of alternations of quartz and phyllosilicate rich layers,

Figure 3 .

 3 Figure 3. Microphotographs of the Cean Schists. Photomontages of thin-section images displaying the porphyro lepidoblastic texture and the highly deformed fabrics. (a) Sample LM showing garnet porphyroblasts fi lled with concentric inclusions. (b) Sample UM cluster of highly pleochroic chloritoid porphyroblasts and numerous small garnets. Sample locations are indicated in Fig. 1. Mineral abbreviations are after Holland & Powell (1998). Other abbreviations: tur, tourmaline; Fe/Ti-ox, Fe/Ti-bearing oxides.

( 1 )

 1 1 dJ I:PDJDoca:o cPI:QcDJDCCOQJctI.oc OOCQJroODo ••• � . ........ . . .. .. . ... ' . .. ..... . . 0.2 • • -"

Figure 4 .

 4 Figure 4. X-Ray maps and chemical profi les illustrating zoning of garnet porphyroblasts from the Cean Schists. (a) Types 1 2 garnet from the lower metapelites (profile 1). (b) Garnet fr om the upper metapelites (profile 2). Tbick dashed lines on the X-ray maps indicate the position of the profi les. The location of each garnet is indicated in Fig. 3.

Figure 5 .

 5 Figure 5. Sample LM [Si02:66.15; Ti02:O.87; AI203:11.55; FeO:7.72; 0:0.60; MnO:O. 17; MgO:5.00; CaO:3.16; Na20:1.40; K20:3.37]. (a) P Tpseudosection with H20 in excess. (b) P X(H20) pseudosection calculated at 480°C. White box in the left shows a detail of the area of interest. (c) P Tpseudosection with H20 = 14.4%. (d) P X(Fe203) pseudosection calculated at 480 QC with H20 = 14.4%. WRA original whole-rock analysis from XRF. See text andTable 1 for details.

  .-. (b) MnNCKFMASHTO ( ... 'l> m u) 20 ctdogllawilmru 1 9 ctd � 9[ II� a� wQn � m [ ' B"�.; , ::: ::: 51i'J', § 18 gctdpagllawilmru ctd pa gl law ilm ru L , .... ... ,. ., ... -,.�,c n:I :. �"'''' .fI_'''''',o .J:::io :1."",. .,.."', .. .... ",0 64 ... . . <*1,..,." .... ",0 Q.. ' ..... ,..,."..., .. .. ",,0 ..... . ,. ..... .. .. ".0 ...... . " ... .... ",0 21 � .... . tI .... H"O 90 .... ... "''T (°C) 5M 600

Figure 6 .

 6 Figure 6. Sample UM [Si02:68.63; Ti02:O.66; AI203:14.70; FeO: 7.68; 0:0.89; MnO:0.26; MgO:3.05; CaO:0.24; Na20:0.98; K20:2.91] (a) P Tpseudosection with H20 in excess. (b) P Tpseudosection calculated for the analysed bulk-rock composition showing dehydration along the stability limit of lawsonite. (c) T X(Fe203) pseudosection calculated at 16 kbar between 420 and 520 QC; WRA original whole-rock analysis from XRF. (d) P Tpseudosection with Fe203 = 0.05 mol. %. The star (2)* is inferred from Fig. 6e. (e) P T pseudosection calculated for the bulk-rock composition after fr actionation of garnet and chloritoid. (t) P T pseudosection calculated in the CKFMASH system for the bulk-rock composition after fr actionation. The star (2)* is inferred from (e). See text and Table1for details.

  Figure 7. (a) P T diagram showing the metamorphic paths of the Cean Scmsts (LM and UM). The P T paths for the Lower Sheet of the Malpica Till Unit (unpublished data) and for the Agualada Unit (Arenas et aI., 1997) are also included. Meta morphic facies field abbreviations: as, greenschist facies; EA, epidote, amphibolite facies; AM, amphibolite facies; LB, laws onite bluescmst facies; EB, epidote bluescmst fa cies and AEC, amphibole eclogite facies (Evans, 1990 (dashed line); Maruyama et aI., 1996). (b) Schematic cross-section of the subduction zone operating in the NW Iberian Massif at 370 360 Ma. US, upper sheet; LS, lower sheet; AG, Agualada Unit. Based on Martinez Catalim et al. (1996).

  The relative present-day tectonostratigraphic position of the MTU (blueschist facies Upper Sheet and eclogite facies Lower Sheet) and the Basal Units of the neighbouring Ordenes Complex (Agualada Unit in Fig. I) suggests that the original position of the different units during subduction was preserved despite the subsequent post HP history (see e.g.

  \Vhite, R.W.,Powell, R., Holland, T.J.B. & Worley, B., 2000. The effect of Ti02 and Fe203 on metapelitic assemblages at greenschist and amphibolite facies conditions: mineral equi libria calculations in the system K20 FeO MgO Ah03 Si02 H20 Ti02 Fe203. Journal of Metamorphic Geology, 18, 497 511. \Vhite, R.W., Powell, R. & Clarke, G.L., 2002. The interpreta tion of reaction textures in Fe rich metapelitic granulites of the Musgrave Block, central Australia: constraints from mineral equilibria calculations in the system K20 FeO MgO Ah03 Si02 H20 Ti02 Fe203. Journal of Metamorphic Geology, 20, 41 55. \Vhite, R.W., Pomroy, N.E. & Powell, R., 2005. An in-situ metatexite diatexite transition in upper amphibolite fa cies rocks from Broken Hill, Australia. Journal of Metamorphic Geology, 23, 579 602.

Table 1 .

 1

Table 2 .

 2 Representative microprobe analyses fr om sample LM.

			S,					S,								S,
	Mineral	ep 1	sph 1	g le	g 1R		ctd	mu 2 ch1 2	g2e	g2R	ilm	ep 3	mu 3	hi	pa	ch] 3 sph 3	win	bar	ch] 3b	hb
	Analysis			2	196	2		160	43	179	183	l S	18	4	13		67		11	26		17	24	85
	Si01	38.13 30.46 36.98 37.36 56.79 23.81 51.29 25.93 37.47 37.92	0.05 38.04	50.92 36.54 46.70 24.61 30.16	53.96 46.75	24.52	44.94 47.23 67.25
	Ti01	0.04 35.81	0.31	0.05	0.03	0.02	0.15	0.07	0.12	0.09 53.38	0.15	0.19	1.55	0.07	0.06 35.51	0.14	0.10	0.09	0.26	0.23	0.00
	A110J	26.26	1.41 20.81 22.08 11.78 39.06 24.73 21.23 22.16 22.01	0.34 26.68 27.44 16.71 39.38	23.15	1.83	13.28	9.43	22.50	12.74 10.40 19.87
	Cr10J	0.11	0.03	0.01	0.05	0.01	0.05	0.06	0.04	0.00	0.03	0.08	0.09	0.05	0.10	0.00	0.00	0.00	0.04	0.00	0.01	0.04	0.12	0.00
	Fe10J	11.07	0.00	0.82	0.00	0.98	1.97	1.19	0.00	0.00	0.00	0.00	9.75	0.00	0.00	0.08	0.00	0.00	3.61	6.05	0.00	5.61	4.51	0.03
	FeO	0.10	0.76 22.46 27.51 11.86 22.27	3.17 21.82 23.61 27.06 42.24	0.09	3.51 18.36	1.09 29.14	1.23	14.01 11.99	27.72	11.63 11.93	0.00
	MnO	0.19	0.18	7.95	2.46	0.04	0.36	0.00	0.15	4.55	1.66	3.75	0.08	0.03	0.18	0.01	0.41	0.32	0.47	0.42	0.26	0.45	0.51	0.03
	MgO	0.00	0.00	0.54	0.88 10.04	3.20	3.33 16.44	0.56	0.80	0.00	0.04	2.35 11.57	0.25 10.84	0.00	7.32 11.29	12.00	10.74 11.20	0.00
	CaO	22.21 30.06 10.03	8.37	0.41	0.01	0.03	0.04 10.24	9.36	0.00 23.20	0.00	0.00	0.08	0.00 29.40	6.14	8.88	0.08	10.19	9.80	0.06
	Na10	0.00	0.02	0.05	0.03	6.43	0.03	0.22	0.03	0.00	0.03	0.00	0.Q2	0.28	0.02	6.02	0.01	0.04	1.63	2.40	0.01	1.59	1.77 10.92
	K10	0.00	0.02	0.00	0.00	0.Q2	0.00	9.73	0.02	0.00	0.01	0.01	0.Q2 10.20	9.79	2.23	0.01	0.00	0.62	0.25	0.06	0.37	0.30	0.03
	Total	98.11	98.75	99.96 98.8	98.39	90.78 93.90 85.77 98.71 98.97	99.85 98.16 94.97 94.82 95.91 88.23 98.49 101.2	97.56	87.25	98.56 98.00 98.19
	Si	2.99	1.01	2.97	3.00	7.81	1.00	3.48	2.74	3.00	3.03	0.00	2.98	3.42	2.79	2.99	2.63	1.25	7.42	6.88	2.63	6.54	6.88	2.98
	Ti	0.00	0.90	0.02	0.00	0.00	0.00	0.01	0.01	0.01	0.01	1.01	0.01	0.01	0.09	0.00	0.00	0.00	0.01	0.01	0.01	0.03	0.03	0.00
	A1	2.43	0.06	1.97	2.09	1.91	1.94	1.98	2.64	2.09	2.07	0.01	2.46	2.17	1.50	2.97	2.91	0.84	2.15	1.62	2.85	2.19	1.79	1.04
	Cr	0.01	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.01	0.00
	FeH Fe 1 '"	0.65 0.01	0.00 0.02	0.05 1.51	0.00 1.85	0.10 1.37	0.06 0.78	0.06 0.18	0.00 1.93	0.00 1.58	0.00 1.81	0.00 0.89	0.57 0.01	0.00 0.19	0.00 1.17	0.00 0.06	0.00 2.60	0.89 0.00	0.37 1.61	0.67 1.4S	0.00 2.49	0.61 1.42	0.49 1.45	0.00 0.00
	Mu	0.01	0.01	0.54	0.17	0.01	0.01	0.00	0.01	0.31	0.11	0.08	0.01	0.00	0.01	0.00	0.04	0.05	0.06	0.05	002	0.06	0.06	0.00
	MS	0.00	0.00	0.06	0.11	2.06	0.20	0.34	2.59	0.07	0.10	0.00	0.00	0.23	1.32	0.02	1.72	O.rB	1.50	2.45	192	2.33	2.43	0.00
	C.	1.87	1.07	0.86	0.72	0.06	0.00	0.00	0.01	0.88	0.80	0.00	1.95	0.00	0.00	0.00	0.00	0.20	0.91	1.38	0.01	1.59	1.52	0.00
	N.	0.00	0.00	0.01	0.01	1.72	0.00	0.03	0.01	0.00	0.01	0.00	0.00	ON	0.00	0.75	0.00	0.00	0.44	0.68	0.00	0.45	0.50	0.94
	K	0.00	0.00	0.00	0.00	0.00	0.00	0.84	0.00	0.00	0.00	0.00	0.00	0.87	0.95	0.18	0.00	0.00	0.11	0.05	0.01	0.Q7	0.06	0.00
	S=	7.97	3.06	8.00 7.95	15.04	3.99	6.92	9.94	7.94	7.93	1.99	7.99	6.93	7.83	6.97	9.90	3.33	14.58 15.26	9.94	15.29 15.22	4.96
	Xc, XN. XFeJ ...	0.60		0.96	0.95	0.40 0.97 0.05	0.80 0.03	0.35 0.03	0.43	0.96	0.95		0.55	0.45 0.04	0.47	0.75 0.81	0.60		0.52 0.32 0.15	0.38 0.33 0.29	0.56	0.38 0.22 0.22	0.37 0.25 0.21

C, core; R, rim. Data C:J.lcu1ated using AXsoftware

(Holland &Powell, 2000 inPowell & Holland 2002 http:jwww.esc.cam.ac.ukjresearchjresearch•groupsjhollandjax)

. The amount of ferrlc iron was calculated from stolchiometric constraints using the programme AX (powell &

  al., 1997; White et ai., 2000), chlorite (Le Bayon et al., 2006; based on Holland et al., 1998), white mica (Coggon & Holland, 2002), plagioclase (Holland & Powell, 2003), epidote (Holland & Powell, 1998), magnetite (White et al., 2002), garnet, biotite, ilmenite and hematite (White et al., 2005).

ACKNOWLEDGEMENTS

This work was fi nancially supported by the Spanish Project CGL2007-65338-C02-01 (Ministerio de Cien cia e Innovaci6n). We thank A. Fernandez Larios and J. Gonzilez del Tanago from the Spanish National Electronic Microscopy Centre (ICTS/CNME-UCM), and P. Lozano from the UCM, for their technical support. We are grateful to M. Ballevre for stimulating discussions. This manuscript was signifi cantly im proved by the careful and constructive reviews from F. Korhonen and an anonymous referee. Editorial handling by R. Powell is gratefully appreciated.


Carmen Corada-Fernández

Joaquín Jiménez-Martínez

Lucila Candela

Eduardo González-Mazo

Pablo A Lara-Martín
email: pablo.lara@uca.es

J De Boer

Occurrence and spatial distribution of emerging contaminants in the unsaturated zone. Case study: Guadalete River basin (Cadiz, Spain)

Keywords:

Irrigation with reclaimed water is becoming a common practice in arid-and semi-arid regions as a 32 consequence of structural water resource scarcity. This practice can lead to contamination of the vadose 33 zone if sewage-derived contaminants are not removed properly. In the current work, we have character-34 ized soils from the Guadalete River basin (SW Spain), which are often irrigated with reclaimed water from 35 a nearby wastewater treatment plant and amended using sludge. Physico-chemical, mineralogical and 36 hydraulic properties were measured in soil samples from this area (from surface up to 2 m depth). 37 Emerging contaminants (synthetic surfactants and pharmaceutically active compounds, or PhACs) were 38 also determined. Synthetic surfactants, widely used in personal care products (PCPs), were found in a 39 wide range of concentrations: 73-1300 lg kg À1 for linear alkylbenzene sulfonates (LAS), 120-40 496 lg kg À1 for alkyl ethoxysulfates (AES), 19-1090 lg kg À1 for alcohol polyethoxylates (AEOs), and 41 155-280 lg kg À1 for nonylphenol polyethoxylates (NPEOs). The presence of surfactant homologues with 42 longer alkyl chains was predominant due to their sorption capacity. A positive correlation was found 43 between LAS and AEOs and soil organic carbon and clay content, respectively. Out of 64 PhACs analyzed, 44 only 7 were detected occasionally (diclofenac, metoprolol, fenofibrate, carbamazepine, clarithromycin, 45 famotidine and hydrochlorothiazide), always at very low concentrations (from 0.1 to 1.3 lg kg À1 ).

46

Introduction

Groundwater contamination is often the result of human activities. This is a rising issue as the worldwide population density is increasing and the use of land is becoming more intensive. One of the clearest examples is contamination by pesticides, which are directly applied to crops. These compounds are now frequently measured for monitoring the quality of soils and aquifers [START_REF] Hildebrandt | Impact of 500 pesticides used in agriculture and vineyards to surface and groundwater quality 501 (North Spain)[END_REF]. There are, however, hundreds of other chemicals that are not considered in routine sampling campaigns and have potential to jeopardize groundwater resources. Among these contaminants, there has been a growing interest over the last decade in pharmaceuticals and personal care products (PPCPs), a wide group that includes therapeutic drugs, antimicrobials, fragrances, sun-screen agents, insect repellents, surfactants and some polymers. PPCPs have been dumped into the environment for as plants and (4) surface flooding with waters containing appreciable proportions of treated wastewater [START_REF] Oppel | Leaching behaviour of pharmaceuticals in soil-testing-systems: a part of an environmental risk assessment for groundwater protection[END_REF]. Other sources include industrial production of pharmaceuticals, residues from hospitals [START_REF] Thiele-Bruhn | Pharmaceuticals antibiotic compounds in soils -a review[END_REF], and the use of antibiotics in animal farms. Later, these contaminated soils are a potential source of surface and groundwater pollution by runoff [START_REF] Oppel | Leaching behaviour of pharmaceuticals in soil-testing-systems: a part of an environmental risk assessment for groundwater protection[END_REF] and leaching [START_REF] Candela | Assessment of soil 482 and groundwater impacts by treated wastewater reuse. A case study: 483 Application in a golf course (Girona, Spain)[END_REF][START_REF] Xu | Leachability of some emerging contaminants in reclaimed municipal wastewater-irrigated turf grass field[END_REF]. Other PPCPs considered in this work, such as surfactants and their degradation products (main ingredients in detergents, cleaning products, shampoos, or lotions), unlike many PhACs, show high removal efficiencies in WWTPs (95-99%) [START_REF] Matthijs | Environmental monitoring for linear alkylbenzene sulfonates, alcohol ethoxylates, alcohol ethoxysulfate, alcohol sulfate and soap[END_REF]. Their presence in aquatic and terrestrial ecosystems, where they have been detected in a wide range of concentrations [START_REF] Lara-Martín | 522 Seasonal changes in the concentration of anionic surfactants in estuarine 523 sediments from the River Guadalete (Cadiz, Spain)[END_REF], 2013), is mostly related to their extended use and high consumption. In fact, surfactants and their metabolites constitute, by far, the organic contaminants showing the highest concentrations in untreated wastewaters [START_REF] Kolpin | Pharmaceuticals, hormones, and other organic wastewater 516 contaminants in US streams, 1999-2000: a national reconnaissance[END_REF]. Other sources include the use of these compounds in pesticide formulations as emulsifiers, dispersing and spreading agents [START_REF] Carlsen | Linear alkylbenzene sulfonates (LAS) in 480 the terrestrial environment[END_REF].

The behavior and fate of most PPCPs still remains unclear, especially in soils and aquifers. There are only a few studies focusing on the transport of these compounds from soils to surface waters and groundwater [START_REF] Oppel | Leaching behaviour of pharmaceuticals in soil-testing-systems: a part of an environmental risk assessment for groundwater protection[END_REF][START_REF] Topp | Runoff of pharmaceuticals and personal care products following application of biosolids to an agricultural field[END_REF]. Due to their wide structural diversity, understanding the different sorption mechanisms of PPCPs in soils is determinant for predicting their mobility and leaching to the groundwater. Their persistence is also another key aspect as the main route for disappearance of PPCPs from contaminated soils is biodegradation. Degradation in soils can be a relatively fast process for some surfactants such as linear alkylbenzene sulfonates (LAS) (half-life = 3-33 d), the most common anionic surfactant (Linear Alkylbenzene Sulfonate, Environmental Risk Assessment, 2013), and pharmaceuticals, but extend over long periods of time for many other PPCPs. As an example, amoxicillin, sulfamethazine and trimethoprim, three antibiotics, show half-lives in soils of 1, 18.6 and 103 d, respectively [START_REF] Boxall | Fate and transport of veterinary medicines in the soil 477 environment[END_REF]. Both sorption and degradation processes are also strongly influenced by environmental conditions such as 121 temperature, redox potential, pH, soil type, organic carbon content, 122 clay minerals and soil bacteria [START_REF] Topp | Runoff of pharmaceuticals and personal care products following application of biosolids to an agricultural field[END_REF].

123

The current work has been carried out in the Guadalete River 124 basin (Cadiz, Spain), a region where reclaimed water from WWTPs 125 is occasionally used for irrigation due to water scarcity. Other 126 issues include severe pollution episodes in some areas of the basin 127 due to uncontrolled sewage spills and the use of digested sludge as 128 a fertilizer [START_REF] Lara-Martín | Sources, transport and reactivity of anionic and non-ionic surfactants in several aquatic ecosystems from SW of Spain: a comparative study[END_REF][START_REF] Lara-Martín | 522 Seasonal changes in the concentration of anionic surfactants in estuarine 523 sediments from the River Guadalete (Cadiz, Spain)[END_REF], 129 2013;[START_REF] Perez-Carrera | Multiresidue method for the determination of 32 human and veterinary pharmaceuticals in soil and sediment by pressurized-liquid extraction and LC-MS/MS[END_REF]. Our main objectives were: (a) to

Results and discussion

3.1. Distribution of synthetic surfactants in surface soil samples Fig. 2 shows concentrations of anionic (LAS and AES) and nonionic surfactants (AEOs and NPEOs) in surface soil samples. Values of target compounds ranged from less than 20 lg kg À1 to 1200 lg kg À1 . Maximum concentrations were measured for LAS (from 290 to 1183 lg kg À1 ) and AES (from 120 to 496 lg kg À1 ), two anionic surfactants mainly used in household detergents and personal care products (e.g., shampoos). AEOs and NPEOs, nonionic surfactants mostly used for industrial applications and some specific uses (e.g., wetting agents, dispersers and emulsifiers), were detected at lower concentrations, between 19 and 140 lg kg À1 , and between 57 and 280 lg kg À1 , respectively. NPEOs were banned for household applications a few years ago in the EU due to the estrogenic properties of their degradation metabolites [START_REF] Jobling | Inhibition 512 of testicular growth in rainbow trout (Oncorhynchus mykiss) exposed to 513 estrogenic alkylphenolic chemicals[END_REF]. They were only detected in soil samples from the Guadalete alluvial aquifer, where agriculture and farming are predominant. The main source of NPEOs in this area is probably the application of pesticides to crops as this surfactant is as adjuvant in pesticide formulation [START_REF] Krogh | Environmental 519 properties and effects of nonionic surfactants adjuvants in pesticides: a review[END_REF]. Regarding LAS, the most abundant contaminant in soils, maximum concentrations (around 1 mg kg À1 ) were found at sampling points 25, 19, and 2, within the Jerez de la Frontera aquifer and surrounding urban areas. Here, treated and untreated wastewater is discharged (WWTP El Portal, Fig. 1) and represents the main source of this surfactant. The occurrence of these discharges has been confirmed in previous works reporting highly polluted sediments and surface waters within the same study area [START_REF] Corada-Fernández | 486 Tracking sewage derived contamination in riverine settings by analysis of 487 synthetic surfactants[END_REF], 2013;[START_REF] Lara-Martín | Sources, transport and reactivity of anionic and non-ionic surfactants in several aquatic ecosystems from SW of Spain: a comparative study[END_REF], 2010). Briefly, they measured average values for surfactants between 0.1 and 3.7 mg kg À1 in surface sediments from Guadalete River, and between 0.2 and 37 mg L À1 in surface water. In this study, maximum concentrations for anionic surfactants were observed in two hot spots corresponding to the outlet of WWTP El Portal (89.4 mg kg À1 ) and a small creek (Salado Stream) that collects untreated wastewater from small villages in rural areas (242.6 mg kg À1 ) [START_REF] Corada-Fernández | 486 Tracking sewage derived contamination in riverine settings by analysis of 487 synthetic surfactants[END_REF]. On the other hand, the highest values for nonionic surfactants were measured by the mouth of the river (14.9 mg kg À1 ) and were related to industrial and seaport activity in that area [START_REF] Lara-Martín | Sources, transport and reactivity of anionic and non-ionic surfactants in several aquatic ecosystems from SW of Spain: a comparative study[END_REF].

The distribution of organic contaminants in terrestrial environments is affected by their physico-chemical properties, and this is especially relevant for surfactants, which are often sold in commercial formulations as a complex mixture of homologues and ethoxymers (occasionally, formed by more than 100 individual components) with different solubility and sorption capacity. Fig. 3 shows the average homologue percentages of LAS, AES, and AEOs in surface soil samples. It is noticeable that, for AES and AEOs, only homologues with an even number of carbon atoms (C 12 , C 14 and C 16 for AES, and C 12 , C 14 , C 16 and C 18 for AEOs) in their alkyl chain were detected. This fact can be explained because most of them are derived from vegetable and/or animal fatty acids instead from petrochemical feedstocks (which contain not only even but also oddcarbon numbered homologues). Differential sorption can be observed by examining the homologue distributions represented in Fig. 3. In general, those homologues having longer alkyl chains have higher sorption capacity on soils. This is especially evident for AEO components, which are usually more hydrophobic than the rest of surfactants. Regarding AES, highlights C 12 AES, also known as lauryl ether sulfate, which is one of the main ingredients in shampoos, soaps, toothpastes, etc., as it is one of the cheapest and more effective foaming agents. It is the main homologue also in AES commercial mixtures (see data in Supplementary Information respect to the composition of the standard used), the main reason why this homologue is always the most abundant in the environment, in agreement with results reported by [START_REF] Lara-Martín | Determination and 526 distribution of alkyl ethoxysulfates and liner alkylbenzene sulfonates in coastal 527 marine sediments from the bay of Cadiz (southwest of Spain)[END_REF] for these compounds in aquatic systems. Similar trends regarding the homologue distribution of LAS, AEOs, and AES have been previously reported for river and marine sediments [START_REF] Corada-Fernández | 486 Tracking sewage derived contamination in riverine settings by analysis of 487 synthetic surfactants[END_REF][START_REF] Lara-Martín | Determination and 526 distribution of alkyl ethoxysulfates and liner alkylbenzene sulfonates in coastal 527 marine sediments from the bay of Cadiz (southwest of Spain)[END_REF][START_REF] Boxall | Fate and transport of veterinary medicines in the soil 477 environment[END_REF] from this and/or nearby sampling areas. Toxicity of these compounds has been addressed in Supplementary Information.

Apart from the physico-chemical properties of their molecules, the distribution and behavior of surfactants may be also correlated to the properties of the environment, which may differ greatly from one sampling area to another. That makes that sorption mechanisms for anionic and non-ionic surfactants on soils and other solid phases (e.g., sludge and sediments) are still not fully understood [START_REF] Rodríguez-Cruz | A comparative study of adsorption of an anionic and a non-ionic surfactant by soils based on physicochemical and mineralogical properties of soils[END_REF]. Some authors have reported the existence of a positive relationship between sorption coefficients and the organic carbon content in soils [START_REF] Litz | The behaviour of linear alkylbenzene sulfonate in different soils. A comparison between field and laboratory studies[END_REF][START_REF] Fytianos | Behaviour and fate of linear 492 alkylbenzene sulfonate in different soils[END_REF], whereas other have found a similar relationship but considering the clay content and/or specific surface instead [START_REF] Ou | Adsorption of alkylbenzene sulfonate (LAS) on soils[END_REF][START_REF] Brownawell | Sorption of non-ionic 475 surfactants on sediment materials[END_REF][START_REF] Shen | Sorption of non-ionic surfactants to soil: the role of soil mineral composition[END_REF]. Sorption can occur in multiple ways in the environment as both hydrophobic and hydrophilic moieties in the molecular structure of surfactants can interact with soil surfaces. Table 1S (see Supplementary Information) shows the main physico-chemical and hydraulic properties of surface soil samples in the Guadalete River basin. These soils are characterized by low organic matter content (<2.5%) and low percent of clay (<3.8%). These values, however, are high enough to influence the sorption and, therefore, the distribution of surfactants in the area. LAS concentrations were positively correlated (r 2 = 0.6, p = 0.002213) with organic matter content in soils (Fig. 4a), suggesting hydrophobic interactions between the alkyl chain of LAS homologues and the organic 303 carbon content in soils (e.g., [START_REF] Litz | The behaviour of linear alkylbenzene sulfonate in different soils. A comparison between field and laboratory studies[END_REF]Fytianos et al., 304 1998). No influence of the soil clay content was observed for this 305 surfactant (Fig. 4b) at a p-value of 0.05. On the other hand, AEO 306 concentrations in soil did not seem to be affected by the organic 307 carbon content in soil (Fig. 4c) at a p-value of 0.05, but were weakly 308 positively correlated (r 2 = 0.5, p = 0.02148) with the presence of 309 clays in soil (Fig. 4d). This was especially true for those AEO eth-310 oxymers with higher molecular weight, as polar interactions such 311 as hydrogen bonding may occur [START_REF] Brownawell | Sorption of non-ionic 475 surfactants on sediment materials[END_REF]Shen, 312 2000; [START_REF] Krogh | Environmental 519 properties and effects of nonionic surfactants adjuvants in pesticides: a review[END_REF]. 2S, see Supplementary Information). The vertical dis-338 tribution of surfactants seems to be related to changes in the phys-339 icochemical and hydraulic properties of soils. Thus, the maximum 340 values for AEOs were measured in those soil sections with higher 341 clay content, as we could observe in surface soil samples. LAS con-342 centrations decreased with depth, which was also the trend 343 observed for organic carbon content in soil. This decrease in the 344 organic carbon content, combined with an increase in pH, may 345 reduce the sorption capacity of this surfactant on soils. Overall, 346 there was a decrease in the concentration of surfactants towards 347 deeper layers in the soil column, although an exception was 348 observed at sampling point 40, between 1.25 and 1.75 m depth 349 (Fig. 5a), where an increase in the concentrations of LAS and AEOs 350 was detected. This may be related to the presence of the capillary 351 fringe (fully saturated conditions were found at 1.75 m depth). We Table 1 shows concentrations of PhACs at specific layers (Table 2S) in the soil, as well as some physicochemical properties (log K ow and pK a ) of these compounds. The selected pharmaceuticals belong to different therapeutical classes -analgesics and anti-inflammatories, antihypertensives, lipid regulators, psychiatric drugs, and antibiotics -and are among the most used. Only 7 out of 64 target compounds (diclofenac, metoprolol, fenofibrate, carbamazepine, clarithromycin, famotidine and hydrochlorothiazide) were occasionally detected at very low concentrations (from 0.1 to 1.3 lg kg À1 ) in soil samples. Additionally, 5 pharmaceuticals (ketoprofen, acetaminophen, atenolol, clofibric acid and sulfamethazine) were detected in some samples but always below the limits of quantification (<0.1 lg kg À1 ). The compounds showing the highest concentrations were metoprolol (up to 1.5 lg kg À1 ), an antihypertensive, and clarithromycin (1.3 lg kg À1 ), an antibiotic. The rest of pharmaceuticals were always at concentrations lower than 0.4 lg kg À1 . Although some of these compounds showed relatively high log K ow values (over 4), such as fenofibrate, ketoprofen and diclofenac, this may be not the best indicator to evaluate the presence of PhACs in terrestrial environments. Many of these chemical can be either in ionic or neutral form depending on the pH of the soil and, therefore, their sorption capacity may change and better be evaluated by D ow (pH-dependent n-octanol-water distribution ratio) [START_REF] Wells | Log Dow: key to understanding and regulating wastewaterderived contaminants[END_REF]. Thus, some of the PhACs identified in this study may show log D ow values that are from similar (0.33-0.34 for acetaminophen) to very different (0.16-0.67 for sulfamethazine) from those for log K ow (Table 1). Additionally, hydrophilic interactions between ionic compounds and soils also occur. It has been observed for AEOs, which were positively correlated to the amount of clays in soil (Fig. 4d), but also for metoprolol and clarithromycin, both positively charged at environmental conditions and the two most predominant PhACs in the sampling area in spite of their relatively low log K ow values (1.88-3.16). This kind of interactions has been previously foreseen from very recent laboratory experiments [START_REF] Schaffer | Role of cation exchange processes on the sorption influenced transport of cationic b-blockers in aquifer sediments[END_REF] and field data from other aquatic systems [START_REF] Lara-Martín | Occurrence, distribution and partitioning of nonionic surfactants and pharmaceuticals in the urbanized Long Island Sound Estuary (NY)[END_REF]. 1 can be complemented with those from a previous study carried out in the same study area, where 21 surface soil samples were screened for 32 specific PhACs [START_REF] Perez-Carrera | Distribution and reactivity of regulated and emerging organic pollutants in surface and groundwater systems[END_REF][START_REF] Perez-Carrera | Multiresidue method for the determination of 32 human and veterinary pharmaceuticals in soil and sediment by pressurized-liquid extraction and LC-MS/MS[END_REF]. Eleven target compounds were detected at concentrations ranging from below limits of detection (0.3-7.1 lg kg À1 ) up to 24.3 lg kg À1 . Omeprazole, used for treating peptic ulcers and not analyzed in the present work, was the most commonly detected pharmaceutical (>50% of soil samples), although we did not include it in this sampling campaign as we used a different analytical methodology [START_REF] Jelic | Multi-residue method for trace level 505 determination of pharmaceuticals in solid samples using pressurized liquid 506 extraction followed by liquid chromatography/quadrupole-linear ion trap mass 507 spectrometry[END_REF]. The rest of compounds showed a low detection frequency (only 1-2 positive samples) [START_REF] Perez-Carrera | Distribution and reactivity of regulated and emerging organic pollutants in surface and groundwater systems[END_REF][START_REF] Perez-Carrera | Multiresidue method for the determination of 32 human and veterinary pharmaceuticals in soil and sediment by pressurized-liquid extraction and LC-MS/MS[END_REF]. As most of the pharmaceuticals detected in the sampling area are only for human consumption, their occurrence in agricultural soils may be related to irrigation of crops with either recycled wastewater (e.g., golf courses) or with river water, which is sometimes mixed with treated/untreated wastewater. Application of sludge from the WWTP El Portal over soils as a fertilizer cannot be discarded as a source either. A few compounds (e.g., sulfamethazine) are also for veterinary use, so they could be released into the environment by disposal of manure residues and/or by leaching from animal excrements [START_REF] Halling-Sörensen | Occurrence, fate and effects of pharmaceutical 498 substances in the environment -a review[END_REF].

Results in Table

Conclusions

Data on the occurrence, reactivity and behavior of PPCPs in solid matrices is severely limited in comparison with aqueous matrices.

In that sense, this work shows some of the first data available on the areal and vertical distribution of surfactants and pharmaceuti-

  Fig. 1. Map of the Guadalete River basin showing the location of sampling stations and nearby populations. Textural class for the three soil cores is also displayed.

Fig. 2 .

 2 Fig.2. Surfactant concentrations (lg kg À1 ) in surface soil samples.

  Vertical profiles of PPCPs in soils 314 Three different sampling points (2, 12 and 40) were selected to 315 study the vertical distributions of contaminants in the vadose zone. 316 We considered not only LAS but also the total concentration of sur-317 factants (LAS + AES + NPEO + AEO) in surface soil samples taken in 318 2006, as well as other criteria like land use/cover, for collection soil 319 core samples later in 2008. We decided to choose the 3 most pol-320 luted stations, which were 25, 19 and 2, having a total concentra-321 tion of surfactants of 1506, 1436 and 1888 lg kg À1 , respectively. 322 However, stations 25 and 19 were altered due to construction 323 works after two years, so we decided to sampling station 40 and 324 12 instead. Station 40 is less than 1 km away from station 25 325 (Fig. 1), whereas station 12 is the next one having higher levels 326 of LAS (and a total surfactant concentration of 1096 ng g À1 ) after 327 stations 25, 19 and 2. Fig. 5 shows concentrations of synthetic sur-328 factants, the most commonly detected target compounds, in these 329 soil sediment cores. Surfactant levels ranged from 73 to 330 1300 lg kg À1 for LAS, and from 329 to 1090 lg kg À1 for AEOs. 331 Nonylphenol polyethoxylates (NPEOs) were also detected in some 332 samples, although at much lower concentrations than the rest 333 (<200 lg kg À1 ) probably due to their lower use. According to the 334 USDA textural classification system, the three soil cores were 335 characterized by loamy sand, sandy loam and silt loam textures, 336 with low levels of organic matter (<2%) and a low clay fraction 337 (<4%) (Table

Fig. 3 .

 3 Fig.3. Average homologue distribution (%) of surfactants in surface soil samples.

Fig. 4 .

 4 Fig. 4. Concentration of LAS and AEOs (lg kg À1 ) as a function of organic carbon content (%) (a and c) and clay content (%) (b and d) in soils.

Fig. 5 .

 5 Fig. 5. Vertical concentration profiles (lg kg À1 ) for selected surfactants in three soil cores: sampling points 40, 2 and 12.

  436 cals in sewage affected soils. Their occurrence in the vadose zone 437 can be explained by several sources, including the direct (or indi-438 rect) use of treated and untreated wastewater for crop irrigation, 439 the application of sewage sludge and manure residues as fertilizer, 440 and the use of pesticides. Synthetic surfactants were detected in all 441 soil samples, and their distribution was related to the presence of 442 local sewage sources, as well as to the physico-chemical properties 443 of the soils. In this sense, LAS concentrations were positively corre-444 lated with organic matter content in soils, suggesting hydrophobic 445 sorption mechanisms. AEO concentrations, on the other hand, were 446 positively correlated with the presence of clays, especially for 447 those ethoxymers having longer ethylene oxide chains. Presence 448 of PhACs in soils was scarce. Only 7 out of 64 compounds analyzed 449 could be measured, most of them showing high log K ow values 450 (>4.45) (e.g., diclofenac, fenofibrate and ketoprofen) or being posi-451 tively charged at environmental conditions (e.g., atenolol, meto-452 prolol, clarithromycin). Our data suggest a low exposure level for 453 pharmaceuticals in terrestrial environments if we compare their 454 occurrence and concentrations with those measured for surfac-455 tants in the same soil samples. 456 5. Uncited references 457 Chemspider (xxxx), Jensen and Folker-Hansen (1995). and to E. de Miguel (SCCYT UCA) for his technical support with 462 the LC-MS system. Thanks to Dr. Ignasi Queralt from the Labora-463 tory of X-ray Analytical Applications (ICTJA-CSIC) too. This research 464 has been funded by the CICYT project CGL2008-05598 and a FPI 465 fellowship from the Spanish Ministry of Education and Science. 2014.04.098.

Table 1

 1 Chemical properties and concentrations (lg kg À1 ) of PhACs in three soils cores (12, 40 and 2). Concentration (lg kg À1 ); -, not detected; n.q., detected, not quantified. a Baccar et al. (2012). b Vazquez-Roig et al. (2010). c Morais et al. (2013). d Chemspider (www.chemspider.com/chemical-structure). e Gong et al. (2012).

	Compound	pK a	Log K ow	12-A	12-B	40-A	40-B	2-B	2-C	2-D
	Ketoprofen	3.12 a	4.45 a	-	-	n.q.	n.q.	-	-	-
	Diclofenac	4.15 b	4.51 b	0.3	0.1	0.2	0.2	-	0.1	0.1
	Acetaminophen	9.38 b	0.46 b	n.q.	n.q.	-	-	-	-	-
	Atenolol	9.6 c	À0.03 d	n.q.	n.q.	n.q.	n.q.	n.q.	n.q.	n.q.
	Metoprolol	9.7 b	1.88 b	0.5	0.1	0.6	0.6	0.1	1.5	0.6
	Clofibric acid	3.46 b	2.58 b	n.q.	n.q.	n.q.	n.q.	n.q.	n.q.	n.q.
	Fenofibrate	-	5.19 b	0.4	0.3	0.4	0.2	0.4	0.4	0.2
	Carbamazepine	13.9 b	2.45 b	n.q.	n.q.	0.1	0.1	0.1	n.q.	n.q.
	Clarithromycin	8.89 c	-	0.5	0.5	1.3	0.5	0.3	0.6	0.7
	Sulfamethazine	7.4 c	0.89 e	n.q.	0.1	1.2	n.q.	n.q.	n.q.	n.q.
	Famotidine	-	-	0.3	0.2	n.q.	0.2	0.2	0.3	0.3
	Hydrochlorothiazide	7.9 c	À0.07 d	0.1	0.2	0.2	0.2	0.2	0.2	0.2

Please cite this article in press as: Corada-Fernández, C., et al. Occurrence and spatial distribution of emerging contaminants in the unsaturated zone. Case study: Guadalete River basin (Cadiz, Spain). Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.04.098

Acknowledgements

459

We express our gratitude to J.J. Montes de Oca and 460 J.M. Traverso-Soto for their help during the sampling campaigns

Appendix A. Supplementary material 467 Supplementary data associated with this article can be found, in 468 the online version, at http://dx.doi.org/10.1016/j.chemosphere.