Martin Guitreau
email: martin.guitreau@uca.fr

Abdelmouhcine Gannoun

Zhengbin Deng

Marc Chaussidon

Frédéric Moynier

Bernard Barbarin

Johanna Marin-Carbonne

Stable isotope geochemistry of silicon in granitoid zircon

Keywords: Si isotopes, zircon, granite, LA-MC-ICP-MS

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

Introduction

Silicon is a major component of silicates which make up most of the terrestrial mantle and crust. This chemical element has three stable isotopes 28, 29, and 30, with respective mean abundances of 92.23%, 4.68%, and 3.09% [START_REF] Debievre | Table of the isotopic compositions of the elements[END_REF]. Although developed long ago (e.g., [START_REF] Reynolds | Natural variations in the isotopic constitution of silicon[END_REF][START_REF] Clayton | Isotopic fractionation of silicon in Allende inclusions[END_REF][START_REF] Douthitt | The geochemistry of the stable isotopes of silicon[END_REF], Si isotope measurements have been applied to high-temperature geochemistry only recently (e.g., Shahar et al., 2009;Savage et al., 2011, Zambardi and[START_REF] Zambardi | Precise silicon isotopes determination in silicate rock reference materials by MC-ICP-MS[END_REF] thanks to the advent of multicollection inductively coupled plasma mass spectrometry (MC-ICP-MS; e.g., [START_REF] Georg | New sample preparation techniques for the determination of Si isotopic compositions using MC-ICP-MS[END_REF] and optimized sample preparation procedure (i.e., alkali fusion) that allowed sufficiently high precision to observe natural variations. High-temperature Si isotope fractionation has consequently been studied in various contexts from cosmochemistry to igneous petrology allowing the establishment of bulk silicate Earth composition, which is distinct from most other planetary bodies (e.g., [START_REF] Georg | Silicon in the Earth's core[END_REF][START_REF] Savage | Silicon isotope homogeneity in the mantle[END_REF]Shahar et al., 2011;Ziegler et al., 2012;[START_REF] Zambardi | Silicon isotope variations in the inner solar system: Implications for the planetary formation, differentiation and composition[END_REF][START_REF] Moynier | Metal-silicate silicon isotopic fractionation and the composition of the bulk Earth[END_REF], and the identification of a general igneous differentiation trend towards isotopically heavy Si isotope signatures for SiO2-rich magmas (e.g., [START_REF] Savage | Silicon isotope fractionation during magmatic differentiation[END_REF][START_REF] Poitrasson | Silicon isotope geochemistry[END_REF]. In addition, it has been shown recently that granitoids -plutonic rocks formed by the slow cooling of a silica-rich magmasexhibit distinct silicon isotope signatures depending on their chemical affinity and, hence, their source (e.g., [START_REF] Savage | The silicon isotope composition of granites[END_REF][START_REF] André | Early continental crust generated by reworking of basalts variably silicified by seawater[END_REF][START_REF] Deng | An oceanic subduction origin for Archaean granitoids revealed by silicon isotopes[END_REF]Fig. 1). There are several ways to produce granitic magmas which is reflected in their chemical and isotopic compositions, ultimately responsible, together with pressure and temperature of crystallization, for the mineralogy of these plutonic rocks (e.g., [START_REF] Nédélec | Granites: Petrology, structure, geological setting, and metallogeny[END_REF]. Granites have been grouped into multiple types according to various classifications (e.g., peraluminous, metaluminous [START_REF] Shand | Eruptive rocks. Their genesis, composition, classification, and their relations to ore-deposits[END_REF]; A, I, S: [START_REF] Chappell | Two contrasting granite types[END_REF]MPG, CPG, KCG, ACG, RTG, PAG: Barbarin, 1999; Table 1) essentially based on petrological and/or geochemical criteria.

Granites, and more generally granitoids, are the major constituents of continents and it is, therefore, important to understand their formation and evolution over time because continents witnessed almost the entire Earth's evolutionary history.

Granites (sensu lato) most commonly contain zircon (ZrSiO4) but in variable quantities depending on their origin and their degree of differentiation (e.g., [START_REF] Pupin | Zircon and granite petrology[END_REF][START_REF] Moecher | Inherited, enriched, heated, or recycled? Examining potential causes of Earth's most zircon fertile magmatic episode[END_REF]. Zircon can be precisely and accurately dated using U-Th-Pb isotope systems (e.g., [START_REF] Schoene | U-Th-Pb geochronology[END_REF] while the source of its parental magma can be approached using Hf and O isotopes (e.g., [START_REF] Patchett | Importance of the Lu-Hf isotopic system in studies of planetary chronology and chemical evolution[END_REF][START_REF] Valley | Oxygen isotopes in zircon[END_REF][START_REF] Payne | Strengths and limitations of zircon Lu-Hf and O isotopes in modelling crustal growth[END_REF]. Moreover, zircon is very resistant to weathering and erosion, and most elements diffuse very slowly within its lattice (e.g., [START_REF] Lee | Pb, U, Th diffusion in natural zircon[END_REF][START_REF] Cherniak | Diffusion in zircon[END_REF] making this mineral a very efficient time-capsule. Therefore, zircon has been a very useful source of information for granite petrogenesis. It is currently used in magmatic rocks and in detrital sediments, as an archive of the crust, to reconstruct the formation and evolution of continents (e.g., Roberts and Spencer, 2015 and references therein).

Isotopic information provided by zircon should be interpreted differently for each granite type because of the distinct sources and petrogenetic processes involved in their formation (e.g., [START_REF] Barbarin | A review of relationships between granitoid types, their origins and their geodynamic environments[END_REF][START_REF] Bonin | Chemical variation, modal composition and classification of granitoids[END_REF][START_REF] Moyen | Archean granitoids: classification, petrology, geochemistry and origin. In : Archean granitoids of India: Windows into Early Earth Tectonics (Dey and Moyen Eds[END_REF]. While only a few tools exist to determine the nature of the parental rock of a detrital zircon, they remain ambiguous and not always reliable (e.g., [START_REF] Belousova | Zircon crystal morphology, trace element signatures and Hf isotopic composition as a tool for petrogenetic modelling: Examples from Eastern Australian granitoids[END_REF]. Since granites of different types (A, I, S, and TTG) can have distinct Si isotope signatures [START_REF] Savage | The silicon isotope composition of granites[END_REF][START_REF] Poitrasson | An Earth-Moon silicon isotope model to teack silicic magma origins[END_REF][START_REF] André | Early continental crust generated by reworking of basalts variably silicified by seawater[END_REF][START_REF] Deng | An oceanic subduction origin for Archaean granitoids revealed by silicon isotopes[END_REF], it is likely that these differences can be retrieved from the Si isotope signature of zircon crystallized in these rocks.

The silicon stable isotope signature of an igneous rock can be controlled by that of its source, mineralogy, and melting/crystallization history [START_REF] Savage | Silicon isotope fractionation during magmatic differentiation[END_REF][START_REF] Poitrasson | Silicon isotope geochemistry[END_REF]. In contrast, the Si isotope signature of a zircon is controlled by the degree of fractionation with its parental magma which essentially depends on the temperature of crystallization and the silica content (~degree of polymerization) of the surrounding melt that was studied theoretically and experimentally by [START_REF] Qin | First-principles calculations of equilibrium fractionation of O-and Si-isotopes in quartz, albote, anorthite and zircon[END_REF] and [START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF]. Co-precipitating phases (e.g., feldspar, quartz) can also play a role provided that they formed in equilibrium. However, post-crystallization processes (e.g., radiation-damage, metamorphic recrystallization, alteration and weathering; [START_REF] Ewing | Radiation effects in zircon[END_REF][START_REF] Vavra | Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite facies zircons: Geochronology of the Ivrea zone (Southern Alps)[END_REF][START_REF] Pidgeon | The effect of weathering on U-Th-Pb and oxygen isotope system of ancient zircons from the Jack Hills, Western Australia[END_REF][START_REF] Pidgeon | The accumulation of non-formula elements in zircons during weathering: Ancient zircons from the Jack Hills, Western Australia[END_REF] could possibly modify the Si isotope composition of a zircon. [START_REF] Trail | Origin and significance of Si and O isotope heterogenities in Phanerozoic, Archean, and Hadean zircon[END_REF] and [START_REF] Chowdhury | Geochemical and textural investigations of the Eoarchean Ukaliq Supracrustals, Northern Québec (Canada)[END_REF] already presented Si isotope data for natural zircons and illustrated the potential of such application for very old igneous rocks. However, we thought it was appropriate to present a more extensive dataset of natural zircons from a wider variety of granite types to more deeply understand the fractionation behavior between zircon and its parentalrock and, hence, complement theoretical [START_REF] Qin | First-principles calculations of equilibrium fractionation of O-and Si-isotopes in quartz, albote, anorthite and zircon[END_REF] and experimental [START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF] constraints. This, in turn, would provide a more robust reference frame for the interpretation of Si isotope data in zircon, and illustrate whether or not they can be used to discriminate granite types. Moreover, adding Si isotopes to the isotope tool-box currently applied to detrital zircons would help clarify the detrital record by better constraining the nature of zircon parental rocks and, therefore, prevent ad hoc interpretations of O and Hf isotope signatures.

In order to address these issues, this article presents Si isotope data obtained by laser-ablation multicollection inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) and solution multicollection inductively coupled plasma mass spectrometry (S-MC-ICP-MS) for zircons from various granite types (4 A-type, 9 tonalitetrondhjemite-granodiorite: TTGs, 10 I-type, and 3 S-type; Tables 1 andS1), together with LA-ICP-MS trace element concentrations, U-Pb ages, and LA-MC-ICP-MS Lu-Hf isotope data for a subset of these zircons. We acknowledge that the A-I-S classification does not encompass the entire diversity of granites (e.g., [START_REF] Barbarin | Genesis of the two main types of peraluminous granitoids[END_REF][START_REF] Barbarin | A review of relationships between granitoid types, their origins and their geodynamic environments[END_REF][START_REF] Bonin | Chemical variation, modal composition and classification of granitoids[END_REF][START_REF] Moyen | Collision vs. Subduction-related magmatism: two contrasting ways of granite formation and implications for crustal growth[END_REF][START_REF] Moyen | Archean granitoids: classification, petrology, geochemistry and origin. In : Archean granitoids of India: Windows into Early Earth Tectonics (Dey and Moyen Eds[END_REF] but have decided to use it in the present study because it has the advantage of being widely used. Our new results

show that Si isotopes in zircon display a fractionation behavior that complies very well with theory and experiment but, as suspected, secondary processes (e.g., weathering and metamorphism) can compromise the Si isotope signature of zircon. However, trace element signatures can help filter out altered compositions. Once fractionation behavior is understood and alteration filtered out, zircon Si isotope signatures are consistent with those in bulk-rocks.

Material and Methods

Samples

Zircon crystals studied here are from felsic igneous rocks of various affinities (e.g., A, I, S, TTG; Table 1) and correspond to separate minerals mounted in epoxy. The A-type granites analyzed in this study are from the Pikes Peak batholith, the Colorado Front Range (USA; [START_REF] Guitreau | Pikes Peak batholith (Colorado, USA) revisited: A SIMS and LA-ICP-MS study of zircon U-Pb ages combined with solution Hf isotope composition[END_REF] and the Skjoldungen complex (Greenland; [START_REF] Nutman | SHRIMP U-Pb zircon geochronology of the late Archaean Ruinnaesset syenite, Skjoldungen alkaline province, southeast Greenland[END_REF] but we also analyzed a detrital zircon megacryst (1.5 cm long) from Tambani (Malawi) that derives from nepheline-bearing gneiss [START_REF] Ashwal | Geochronology of zircon megacrysts from nepheline-bearing gneisses as constraints on tectonics setting: implications for resetting of the U-Pb and Lu-Hf isotopic systems[END_REF].

Granites of I-type affinity analyzed here are from the Skellefte district (Sweden; Guitreau et al., 2014a and references therein), the Acasta Gneiss Complex (Canada; Guitreau et al., 2014b), and the French Massif Central (France; Barbarin, 1988a). Note that some of the Skellefte samples are not granites but sub-volcanic or porphyritic eruptive products that are chemically akin to and coeval with I-type granites with which they are associated. S-type granites are from the French Massif Central (Barbarin, 1988b) and correspond to cordierite granite (CPG) and two-mica granite (MPG; [START_REF] Barbarin | A review of relationships between granitoid types, their origins and their geodynamic environments[END_REF]. TTG studied here are from the Acasta Gneiss Complex (Canada), Barberton Greenstone Belt (South Africa), the Karelian craton (Finland), the Sharyzalgai uplift (Siberia), and the Napier Complex (East Antarctica). More information about these samples can be found in [START_REF] Guitreau | Hafnium isotope evidence from Archean granitic rocks for deep-mantle origin of continental crust[END_REF] and references therein.

Zircon imaging and analysis

Zircon CL and BSE imaging

Zircon cathodoluminescence (CL) and back-scattered electron (BSE) imaging was done at Laboratoire Magmas et Volcans (LMV, France) using a Jeol JSM-5910LV scanning electron microscope. Image acquisition was done using an acceleration voltage of 15 kV. Zircon imaging revealed internal textures which served as a tool to interpret zircon crystallization conditions (e.g., mafic or felsic igneous, metamorphic) as well as radiation damage accumulation and alteration effects (e.g., [START_REF] Corfu | Atlas of zircon textures[END_REF]. This ultimately guided elemental and isotopic measurements that were located as much as possible in igneous domains (based on texture), except in the case of the zircon megacryst from Malawi in which domains corresponding to various crystallization conditions were purposely analyzed. Zircon crystals from TTGs and some I-and A-type granites were already imaged using CL/BSE technique and analyzed for Lu-Hf isotopes and U-Pb ages [START_REF] Guitreau | Hafnium isotope evidence from Archean granitic rocks for deep-mantle origin of continental crust[END_REF](Guitreau et al., , 2014a[START_REF] Guitreau | Pikes Peak batholith (Colorado, USA) revisited: A SIMS and LA-ICP-MS study of zircon U-Pb ages combined with solution Hf isotope composition[END_REF][START_REF] Guitreau | Crystallization and disturbance histories of single zircon crystals from Hadean-Eoarchean Acasta gneisses examined by LA-ICP-MS U-Pb traverses[END_REF](Guitreau et al., , 2019)).

Si isotope measurements by LA-MC-ICP-MS

Laser-ablation multicollection inductively coupled plasma mass spectrometry measurements were conducted at LMV using a Resonetics Resolution M-50E coupled to a Thermo Scientific Neptune Plus MC-ICP-MS, and followed closely the analytical protocol of [START_REF] Guitreau | Silicon isotope measurement in zircon by laser ablation multiple collector inductively coupled plasma mass spectrometry[END_REF]. Analytical conditions are provided in Table 2. Si isotopes were measured as traverses and the international zircon standard 91500 (from a syenite; [START_REF] Wiedenbeck | Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses[END_REF] was used as a bracketing standard. The zircon standards MudTank (from a carbonatite; [START_REF] Black | The age of the Mud Tank Carbonatite, Strangways Range, Northern Territory[END_REF], KIM (from a kimberlite ;[START_REF] Trail | Origin and significance of Si and O isotope heterogenities in Phanerozoic, Archean, and Hadean zircon[END_REF], AS3 (from a gabbro; [START_REF] Paces | Precise U-Pb ages of Duluth complex and related mafic intrusion, Northeastern Minnesota: Geochronological insights to physical, petrogenetic, paleomagnetic, and tectonomagmaitc processes with the 1.1 Ga midcontinent rift system[END_REF], Plešovice (hyperpotassic granulite; [START_REF] Sláma | Plešovice zircon -A new natural reference material for U-Pb and Hf isotopic microanalysis[END_REF], and the synthetic standards MUN from the Memorial University of NewFoundland [START_REF] Fisher | Synthetic zircon doped with hafnium and rare earth elements: A reference material for in situ hafnium isotope analysis[END_REF] were used for quality check. Silicon isotope results are reported in Tables S2,S3, and 3 in delta notation, δ 29 Si and δ 30 Si, which express per mil deviations from a reference (quartz NBS 28), and are calculated using the following equations. δ X Si = [( X Si/ 28 Sisample)/ ( X Si/ 28 Sistandard)-1] x 1000 where X is either 29 or 30.

Throughout the manuscript, analytical uncertainty (i.e., within-run precision) is reported as 2 standard-errors (2SE) whereas external reproducibility (e.g. average of multiple analyses of the same zircon) is reported as 2 standard-deviations (2SD).

Silicon isotope data for AS3 zircon analyzed by LA-MC-ICP-MS in this study gave a δ 30 Si of -0.47 ± 0.20‰ (2SD; Table 3), coherent with the value of -0.36 ± 0.35‰ (2SD obtained by [START_REF] Trail | Origin and significance of Si and O isotope heterogenities in Phanerozoic, Archean, and Hadean zircon[END_REF] using SIMS and the value of -0.44 ± 0.23‰ (2SD) obtained by [START_REF] Guitreau | Silicon isotope measurement in zircon by laser ablation multiple collector inductively coupled plasma mass spectrometry[END_REF] using the same LA-MC-ICP-MS set-up as the present study. KIM zircon returned a LA-MC-ICP-MS δ 30 Si of -0.41 ± 0.19‰ which is identical to the S-MC-ICP-MS value of -0.41 ± 0.01‰ [START_REF] Trail | Origin and significance of Si and O isotope heterogenities in Phanerozoic, Archean, and Hadean zircon[END_REF]) and the LA-MC-ICP-MS δ 30 Si of -0.40 ± 0.23‰ from [START_REF] Guitreau | Silicon isotope measurement in zircon by laser ablation multiple collector inductively coupled plasma mass spectrometry[END_REF]. MudTank zircon analyzed in this study exhibit a LA-MC-ICP-MS δ 30 Si of -0.38 ± 0.23‰ which is consistent, within error, with the S-MC-ICP-MS value of -0.34 ± 0.03‰ from [START_REF] Trail | Origin and significance of Si and O isotope heterogenities in Phanerozoic, Archean, and Hadean zircon[END_REF] and the δ 30 Si of -0.47 ± 0.17‰ obtained by [START_REF] Guitreau | Silicon isotope measurement in zircon by laser ablation multiple collector inductively coupled plasma mass spectrometry[END_REF]. Plešovice zircon gave a δ 30 Si of -0.44 ± 0.21‰ which is consistent with S-MC-ICP-MS data of -0.39 ± 0.06‰ from [START_REF] Guitreau | Silicon isotope measurement in zircon by laser ablation multiple collector inductively coupled plasma mass spectrometry[END_REF]. The synthetic MUN zircons analyzed in this study exhibited δ 30 Si of -1.61 ± 0.21‰ for MUN-0 and -2.02 ± 0.27‰ for MUN-1, which agree with values of -1.67 ± 0.14‰ and -2.08 ± 0.17‰, respectively, reported in [START_REF] Guitreau | Silicon isotope measurement in zircon by laser ablation multiple collector inductively coupled plasma mass spectrometry[END_REF].

Si isotope measurements by S-MC-ICP-MS

We analyzed some of the zircons by S-MC-ICP-MS for the sake of comparison with LA-MC-ICP-MS measurements. Solution-MC-ICP-MS measurements were conducted during the same analytical sessions as zircon standard data from [START_REF] Guitreau | Silicon isotope measurement in zircon by laser ablation multiple collector inductively coupled plasma mass spectrometry[END_REF] which used a technique modified after [START_REF] Deng | An oceanic subduction origin for Archaean granitoids revealed by silicon isotopes[END_REF]. Results for basalt reference material BHVO-2 normalized to quartz reference NBS28 analyzed using MC-ICP-MS alongside unknowns comply well with consensus values as we obtained δ 29 Si and δ 30 Si values of -0.14 ± 0.09‰ and -0.28 ± 0.15‰ (n = 60; 2SD) for BHVO-2 (δ 30 Si = -0.29 ± 0.05‰; [START_REF] Schuessler | Testing the limits of micro-scale analyses of Si stable isotopes by femtosecond laser ablation multicollector inductively couple plasmla mass spectrometry with application to rock weathering[END_REF].

Trace element measurements in zircon

Trace element measurements were done at LMV by LA-ICP-MS using the same laser as for Si isotopes but coupled to a Thermo Scientific Element XR ICP-MS. Analytical spots were located on shallow lines formed by Si isotope analyses. Information regarding analytical conditions are given in Table 2. We used 28 Si as an internal standard and the synthetic glass standard SRM NIST 610 [START_REF] Jochum | Determination of reference values for NIST SRM 610-617 glasses following ISO guidelines[END_REF] as a bracketing standard, whereas SRM NIST 612 [START_REF] Jochum | Determination of reference values for NIST SRM 610-617 glasses following ISO guidelines[END_REF], 91500 [START_REF] Wiedenbeck | Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses[END_REF][START_REF] Wiedenbeck | Further characterization of the 91500 zircon crystal[END_REF], MudTank [START_REF] Gain | Mud Tank zircon: Long-term evaluation of a reference material for U-Pb dating, Hf isotope analysis and trace element analysis[END_REF], and AS3 [START_REF] Takehara | New insights into disturbance of U-Pb and trace-element systems on hydrothermally altered zircon via SHRIMP analyses of zircon form the Duluth gabbro[END_REF] zircon standards were analyzed for quality check. Batches of 6 unknowns and 3 quality-control standards were bracketed by 2 analyses of NIST 610. We used published Si concentration data when available but, otherwise, used stochiometric values to convert ICP-MS counts/second into concentrations. Results are presented in Table S4. Elemental concentrations obtained for SRM NIST 612 were all consistent with published values within ≤ 7% [START_REF] Jochum | Determination of reference values for NIST SRM 610-617 glasses following ISO guidelines[END_REF]. Data for zircon standards analyzed in this study complied well with available published values for most elements (Table S4; Fig. S1). Note, however, that some elemental concentrations fall within the range of published values or close in the case of zircon reference materials that exhibit compositional differences between batches (MudTank and AS3) and/or because of alteration (e.g., Ca, Al, K, La contents).

U-Pb geochronology in Malawi zircon

The megacrystic zircon from Malawi was the only crystal studied for U-Pb and Lu-Hf in this work because its size allowed spatial resolution on various domains such as magmatic, metamorphic, and altered ones, and we wanted to investigate possible relationship between geochemical signatures within these domains. The regular size of normal zircons (~100-200 µm) does not allow these domains to be individualized. Therefore, this zircon was the appropriate candidate to test the effect of magmatic and metamorphic growth as well as secondary alteration on the geochemistry of zircon. In addition, a fair number of other zircons studied in this study were previously analyzed for U-Pb and Lu-Hf isotope systematics in earlier studies [START_REF] Guitreau | Hafnium isotope evidence from Archean granitic rocks for deep-mantle origin of continental crust[END_REF](Guitreau et al., , 2014b(Guitreau et al., , 2019)). U-Th-Pb isotope measurements were done at LMV by LA-ICP-MS using the same instruments as for trace elements. Analytical spots were located next to lines formed during Si isotope analyses. Information regarding analytical conditions are given in Table 2. The zircon standard 91500 (1065.4 ± 0.3 Ma;[START_REF] Wiedenbeck | Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses[END_REF] was used for bracketing whereas AS3 (1099.1 ± 0.5 Ma; [START_REF] Paces | Precise U-Pb ages of Duluth complex and related mafic intrusion, Northeastern Minnesota: Geochronological insights to physical, petrogenetic, paleomagnetic, and tectonomagmaitc processes with the 1.1 Ga midcontinent rift system[END_REF] and Plešovice (337.13 ± 0.37 Ma;[START_REF] Sláma | Plešovice zircon -A new natural reference material for U-Pb and Hf isotopic microanalysis[END_REF] were analyzed as unknowns for quality check. Data were acquired as batches of 6 unknowns bracketed by 4 measurements of 91500. Zircon U-Th-Pb data were processed using Glitter software [START_REF] Van Achterbergh | LaserAblation -ICP-Mass Spectrometry in the Earth Sciences: Principles and Applications[END_REF] and age calculations were done using a present-day 238 U/ 235 U of 137.818 [START_REF] Hiess | 238 U/ 235 U systematics in terrestrial uranium-bearing minerals[END_REF] and decay constants of 1.55125.10 -10 , 9.8485.10 -10 , and 4.9475.10 -11 yr -1 for 238 U, 235 U and 232 Th, respectively [START_REF] Jaffey | Precision measurement of half-lives and specific activities of 235U and 238[END_REF]LeRoux and Glendenin, 1963). Concordia plots were built using the Isoplot software [START_REF] Ludwig | User's Manual for Isoplot 3.6, a Geochronological Toolkit for Microsoft Excel[END_REF]. Finally, semi-quantitative concentrations of U, Th, and Pb were determined by external normalization to 91500 as an additional means for interpreting U-Pb ages, notably to detect correlation between ages and U concentrations potentially arising from alteration facilitated by radiation-damage accumulation.

We obtained a Concordia age of 1097.5 ± 4.5 Ma (2SE; n = 7; MSWD = 0.52) and weighted average 206 Pb/ 238 U and 207 Pb/ 206 Pb ages of 1096.9 ± 6.6 Ma (2SE; n = 7; MSWD = 0.24), and 1097.3 ± 7.7 Ma (2SE; n = 7; MSWD = 0.24,) respectively, for AS3, and a Concordia age of 338.2 ± 2.9 Ma (2SE; n = 7; MSWD = 0.11), as well as 338.1 ± 2.9 Ma (2SE; n = 7; MSWD = 0.14) and 343 ± 22 Ma (2SE; n = 7; MSWD = 0.06), respectively, for Plešovice, which agree well with consensus ages [START_REF] Wiedenbeck | Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses[END_REF][START_REF] Sláma | Plešovice zircon -A new natural reference material for U-Pb and Hf isotopic microanalysis[END_REF]. All results are available in Tables S5.

Lu-Hf isotope measurements in Malawi zircon

Lu-Hf isotope measurements were done at LMV by LA-MC-ICP-MS using the same instruments as for Si isotopes. Details regarding operating conditions can be found in Table 2. Measurements were done next to traces of U-Pb and Si isotope analyses.

Zircons were analyzed as batches of 10 unknowns (4 standards and 6 samples) bracketed by REE-absent MUN zircon standard (MUN-0; [START_REF] Fisher | Synthetic zircon doped with hafnium and rare earth elements: A reference material for in situ hafnium isotope analysis[END_REF].

Standards analyzed as unknowns (91500, MudTank, and two MUN zircons with low and high Yb/Hf ratios) were used to monitor data quality. Yb and Hf instrumental mass biases were determined using 173 Yb/ 171 Yb normalized to the value of 1.129197 [START_REF] Vervoort | Isotopic composition of Yb and the determination of Lu concentrations and Lu/Hf ratios by isotope dilution using MC-ICPMS[END_REF]) and 179 Hf/ 177 Hf normalized to 0.7325 [START_REF] Stevenson | Implications for the evolution of continental crust from Hf isotope systematics of Archean detrital zircons[END_REF]. Lu fractionation was assumed to follow that of Yb [START_REF] Fisher | Guidelines for reporting zircon Hf isotopic data by LA-MC-ICP-MS and potential pitfalls in the interpretation of these data[END_REF]. Values of 0.793045 for 176 Yb/ 173 Yb [START_REF] Vervoort | Isotopic composition of Yb and the determination of Lu concentrations and Lu/Hf ratios by isotope dilution using MC-ICPMS[END_REF] and 0.02655 for 176 Lu/ 175 Lu [START_REF] Fisher | Guidelines for reporting zircon Hf isotopic data by LA-MC-ICP-MS and potential pitfalls in the interpretation of these data[END_REF] were used to correct isobaric interferences of 176 Yb and 176 Lu at mass 176.

Since standards showed a slight shift, though reproducible, in 176 Hf/ 177 Hf after mass bias correction, we have used MUN-0 to determine an offset factor (i.e., difference between consensus and measured value) and correct all LA-MC-ICP-MS Lu-Hf analyses accordingly.

Malawi zircons were measured during two separate analytical sessions. The first session gave average 176 Hf/ 177 Hf measured in 91500 and MudTank of 0.282312 ± 0.000014 (2SD; n = 3) and 0.282508 ± 0.000023 (2SD; n = 2), respectively, and the second session gave 0.282315 ± 0.000057 (2SD; n = 4) for 91500 and 0.282511 ± 0.000023 (2SD; n = 4) for MudTank. These values compare well with consensus values of 0.282308 ± 0.000008 (Blichert-Toft, 2008) and 0.282507 ± 0.000006 [START_REF] Woodhead | A preliminary appraisal of seven natural zircon reference materials for in situ Hf isotope determination[END_REF]. The average 176 Hf/ 177 Hf measured during the first session in MUN_1-2b and MUN_4-2b were 0.282139 ± 0.000037 (2SD; n = 5), and 0.282131 ± 0.000034 (2SD; n = 5), respectively. The average 176 Hf/ 177 Hf measured during the second session in MUN_1-2b and MUN_3-2b were 0.282124 ± 0.000029 (2SD; n = 4), and 0.282127 ± 0.000034 (2SD; n = 4), respectively. Therefore, our results on MUN zircons are fully consistent with the value of 0.282135 ± 0.000007 reported in [START_REF] Fisher | Synthetic zircon doped with hafnium and rare earth elements: A reference material for in situ hafnium isotope analysis[END_REF] which shows that our Lu-Hf data are accurately corrected for isobaric interferences created by 176 Yb and 176 Lu. We used the 176 Lu decay constant of 1.867.10 -11 yr -1 from [START_REF] Scherer | Calibration of the lutetium-hafnium clock[END_REF]Sӧderlund et al. (2004) to calculate initial Hf isotopic compositions.

Uncertainties associated with the radiogenic-ingrowth correction were propagated using the algorithms of [START_REF] Ickert | Algorithms for estimating uncertainties in initial radiogenic isotope ratios and model ages[END_REF] and ɛHf values were calculated using CHUR values provided in [START_REF] Iizuka | Meteorite zircon constraints on the bulk Lu-Hf isotope composition and early differentiation of the Earth[END_REF]. Results can be found in Table S6. Overall, zircon δ 30 Si values are the highest in A-type granites (up to -0.13 ‰) and the lowest in S-type granites (down to -1.19 ‰), with an overall decrease forming the sequence A-type > TTG > I-type > S-type. However, there is too much overlap between the data to give confidence to this pattern as is.

Results

Si isotopes in zircon

Zircons from A-type granites have δ 30 Si values that vary from -0.67 to -0.11‰ (average = -0.39‰; Fig. 1; Tables 3 andS3), which translate into apparent fractionation factors between zircon and whole-rock (∆ 30 SiWR-Zrc = δ 30 SiWR -δ 30 Sizrc) of -0.04 to 0.52‰ (average = 0.24‰) when A-type bulk-rock δ 30 Si of -0.15‰ is used [START_REF] Savage | The silicon isotope composition of granites[END_REF]. Zircons from TTGs have δ 30 Si values that range from -0.83 to -0.29‰ (average = -0.50‰; Fig. 1; Tables 3 andS3), which translate into apparent fractionation factors (∆ 30 SiWR-Zrc) of 0.29 to 0.83‰ (average = 0.50‰) when TTG bulk-rock δ 30 Si of 0.0‰ is used [START_REF] Deng | An oceanic subduction origin for Archaean granitoids revealed by silicon isotopes[END_REF]. Zircons from I-type granites have δ 30 Si values that vary from -0.91 to -0.27‰ (average = -0.52‰; Fig. 1; Tables 3 andS3), which translate into apparent fractionation factors (∆ 30 SiWR-Zrc) of 0.07 to 0.71‰ (average = 0.32‰) when I-type bulk-rock δ 30 Si of -0.2‰ is used [START_REF] Savage | The silicon isotope composition of granites[END_REF]. Zircons from Stype granites have δ 30 Si values that range from -1.19 to -0.47‰ (average = -0.77‰; Fig. 1; Tables 3 andS3), which translate into apparent fractionation factors (∆ 30 SiWR-Zrc) of 0.17 to 0.89‰ (average = 0.46‰) when S-type bulk-rock δ 30 Si of -0.3‰ is used [START_REF] Savage | The silicon isotope composition of granites[END_REF]. Si isotope data obtained in this study and calculated apparent fractionation factors are consistent with theoretical (∆ 30 SiWR-Zrc = 0.1 at 1300°C for an andesitic melt and 0.45‰ at 600°C for a rhyolitic melt; [START_REF] Qin | First-principles calculations of equilibrium fractionation of O-and Si-isotopes in quartz, albote, anorthite and zircon[END_REF] and experimental results (∆ 30 SiWR-Zrc = 0.32 to 0.56‰ at 700°C; [START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF], as well as with available Si isotope data on minerals (zircon δ 30 Si = -1.5 to 0.0‰; [START_REF] Trail | Origin and significance of Si and O isotope heterogenities in Phanerozoic, Archean, and Hadean zircon[END_REF].

Trace element concentrations

Results for trace elements are presented in Table S4 and Figures 2 and3, which is organized according to 4 groups (A-type, TTG, I-type, and S-type), and in Figures S3 andS4, which presents the same data but for each sample separately. Trace element patterns in Figures 2 andS3 are normalized to chondrites [START_REF] Mcdonough | The composition of the Earth[END_REF] and data for zircons from each granite type are reported with AS3 data for comparison.

In contrast, Figures 3, S2 and S4 are normalized to AS3. Analyzed zircons exhibit trace element patterns that are consistent with that of AS3 (Fig. 2), though with two kinds of variations. The first one is "coupled variation" which means that all trace element contents vary coherently with each other, and this results in a vertical shift of the entire pattern without changing its shape (Fig. 2). This is precisely the case for rare earth elements (REE) from Gd to Lu. The second kind is "decoupled variation" which corresponds to an increase in a chemical element content that is independent from the pattern. This increase is, however, often correlated between several elements such that when one element content increases the content of other elements increase too but to different extents. The best example corresponds to light REE (LREE) which show that when La content increases both Ce, Pr, Nd, and Sm increase but to a lesser extent as REE mass increases (Fig. 2). These two kinds of variations are visible in all groups but not in all zircon crystals. Decoupled variation describes the behavior of elements that are the most incompatible in zircon lattice (e.g., Al, Ca, Ga, Ba, LREE; [START_REF] Hoskin | The composition of zircon and igneous and metamorphic petrogenesis[END_REF][START_REF] Pidgeon | The accumulation of non-formula elements in zircons during weathering: Ancient zircons from the Jack Hills, Western Australia[END_REF], whereas coupled variation corresponds to the behavior of least incompatible elements (e.g., Y, HREE, Hf, U). These two kinds of variations in trace element contents are shared by all granite types (Fig. 2). Zircon chemistry is very similar between all granite types which makes it difficult to use in granite-host identification as it was also acknowledged by [START_REF] Belousova | Zircon crystal morphology, trace element signatures and Hf isotopic composition as a tool for petrogenetic modelling: Examples from Eastern Australian granitoids[END_REF].

However, a few differences can be noted such as higher HREE content in S-type, an overall shallower REE pattern in A-type, and higher Nb and Ta contents in A-type zircons that create shoulders in the patterns visible in Figure 2. Zircon patterns reveal no or various extent of negative Eu and positive Ce anomalies, the latter being also blurred by an increase in La contents in some cases. Due to the size of the laser-beam and the scale of analyzed zircon crystals, variations in trace element contents and/or specific anomalies could not be associated with peculiar textural features, except in the Malawi zircon in which domains of different origins could be identified more readily (Figure 4). Figure 3 presents the same trace element data as in Figure 2 but normalized to AS3 which allows to more precisely observe the variation of chemical elements around igneous values, represented by AS3, within each granite type as well as between granite types.

We determined Ti-in-zircon temperatures following the method of [START_REF] Ferry | New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers[END_REF]. Activities of SiO2 (aSiO2) and TiO2 (aTiO2) play a fundamental role in the validity of these temperature estimates which is why we used the software Rhyolite-MELTS [START_REF] Gualda | Rhyolite-MELTS: a modified calibration of MELTS optimized for silica-rich, fluid-bearing magmatic systems[END_REF] to determine the appropriate activities at the zircon saturation temperature (TZr, [START_REF] Watson | zircon saturation revisited: temperature and composition effects in a variety of crustal magma types[END_REF][START_REF] Miller | Hot and cold granites? Implications of zircon saturation temperatures and preservation of inheritance[END_REF][START_REF] Boehnke | Zircon saturation re-revisited[END_REF], according to suggestions of [START_REF] Schiller | Application of Ti-in-zircon thermometry to granite studies: problems and possible solutions[END_REF]. We used TZr from both [START_REF] Watson | zircon saturation revisited: temperature and composition effects in a variety of crustal magma types[END_REF] and [START_REF] Boehnke | Zircon saturation re-revisited[END_REF] calibrations as well as TZr/2 (i.e., TZr at half of the whole-rock Zr content; [START_REF] Schiller | Application of Ti-in-zircon thermometry to granite studies: problems and possible solutions[END_REF] but this only resulted in temperature variations within a narrow range of about 20°C.

Similarly, changing the activity values within the main range of variation displayed in [START_REF] Schiller | Application of Ti-in-zircon thermometry to granite studies: problems and possible solutions[END_REF] does not drastically change the temperature estimates.

Furthermore, propagating all sources of uncertainty arising from the calibration curve for Ti-in-zircon temperature [START_REF] Ferry | New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers[END_REF], that of zircon saturation [START_REF] Watson | zircon saturation revisited: temperature and composition effects in a variety of crustal magma types[END_REF][START_REF] Boehnke | Zircon saturation re-revisited[END_REF], the input parameters and calculations behind the Rhyolite-MELTS model [START_REF] Gualda | Rhyolite-MELTS: a modified calibration of MELTS optimized for silica-rich, fluid-bearing magmatic systems[END_REF], and the uncertainty on zircon Ti concentrations, we think that it seems unrealistic to expect a Ti-in-zircon temperature more precise than ~50°C. Consequently, we have finally used values of 0.95 for aSiO2 and 0.45 aTiO2, which are coherent conservative estimates of the true activities [START_REF] Schiller | Application of Ti-in-zircon thermometry to granite studies: problems and possible solutions[END_REF], to determine zircon crystallization temperatures and have considered these values with a 50°C uncertainty. The Ti-inzircon temperatures obtained for zircon standards MudTank and AS3 comply well with independent estimates from previous studies (Tables 3 andS4; [START_REF] Currie | The Mud Tank carbonatite complex, central Australia -An example of metasomatism at mid-crustal levels[END_REF][START_REF] Leu | Geology and Petrology of the Wilder Lake Intrusion[END_REF]. Measured Ti-in-zircon temperatures gave 572-937°C for A-type granites (one extreme at 1508°C), 716-974°C for TTGs (two extremes at 1107 and 1337°C), 758-970°C for I-type (two extremes at 1033 and 1312°C), and 776-1015°C for S-type granites (Table S4). These temperatures usually vary within a range of ≤ 100°C in each sample, except for S-type granites in which determined temperatures vary by up to ~250°C. Ti-in-zircon temperatures, therefore, vary from one sample to the other but without systematic difference between granite types. Temperature extremes mentioned above always have Ti concentrations that correlate with Al, and/or K, and/or Ca, which reach high values (e.g., 500-3000 ppm Al) that are inconsistent with elemental substitution during magmatic growth [START_REF] Hoskin | The composition of zircon and igneous and metamorphic petrogenesis[END_REF][START_REF] Bouvier | Li isotopes and trace elements as a petrogenetic tracer in zircon: insights from Archean TTGs and sanukitoids[END_REF]. Some Ti-in-zircon temperatures are consistent with zircon-saturation temperatures (Tzr) whereas other disagree by more than 100°C (Table 3).

Malawi zircon

A back-scattered electron map of the megacrystic zircon (length = 1.5 cm) from Malawi reveals a very well-defined oscillatory zoning from core to rim (Figure 4), nevertheless, with visible concentric and radial fractures as well as metamorphic domains (dark grey zones) and biotite inclusions (black rounded areas). Various types of domains, labeled MZ1-MZ7, have been analyzed to track possible δ 30 Si variations and link them to independent parameters such as crystallization (magmatic vs metamorphic) and alteration conditions, chemical composition, age, Hf isotope signature, and crystallization temperature. Traverses for Si isotope measurements by LA-MC-ICP-MS were done parallel to the magmatic zoning. Magmatic and metamorphic domains returned identical U-Pb dates (Table S5) which gave a Concordia age of 726.6 ± 2.3 Ma (2SE; MSWD = 0.92), identical to that of 730 Ma reported by [START_REF] Ashwal | Geochronology of zircon megacrysts from nepheline-bearing gneisses as constraints on tectonics setting: implications for resetting of the U-Pb and Lu-Hf isotopic systems[END_REF] for megacrystic zircons from nepheline-bearing gneisses from Malawi. Metamorphic and magmatic domains display sharp differences in Th/U and U concentrations, which is also visible in176 Lu/177 Hf ratios, but more importantly in 176 Hf/ 177 Hf and δ 30 Si although differences are subtler in these isotopic systems (Figure 4). The chemical distinction between magmatic and metamorphic domains also translates into an overall downward shift of trace element patterns to lower concentrations in Figure 2, and in Tiin-zircon temperatures change from 627-743°C for magmatic to 572-602°C for metamorphic domains (Table S4). The megacrystic zircon gave present-day 176 Hf/ 177 Hf from 0.282464 ± 0.000018 (2SE) to 0.282560 ± 0.000024 (2SE; Table S6) regardless of the domain analyzed, and 176 Lu/ 177 Hf from 0.0017 to 0.00004 with a sharp difference between magmatic and metamorphic domains, the latter having the smallest 176 Lu/ 177 Hf (Figure 4). Our new Lu-Hf isotope data are consistent with bulk-zircon solution data from [START_REF] Ashwal | Geochronology of zircon megacrysts from nepheline-bearing gneisses as constraints on tectonics setting: implications for resetting of the U-Pb and Lu-Hf isotopic systems[END_REF] that gave present-day 176 Hf/ 177 Hf of 0.282454 ± 0.000037 (2SE), 0.282466 ± 0.000057 (2SE), and 0.282475 ± 0.000057 (2SE) on three different zircon megacrysts for which the authors, however, did not measure 176 Lu/ 177 Hf. δ 30 Si for magmatic domains gave an average value of -0.43 ± 0.15‰ (2SD; average of individual analyses) identical to the S-MC-ICP-MS value of -0.46 ± 0.10‰ (2SD;

Table 3), whereas metamorphic zones returned an average δ 30 Si of -0.26 ± 0.19‰ (2SD; average of individual analyses). Note that δ 30 Si are very reproducible within each magmatic domain and more variable in metamorphic domains (Figs 1 and4). It should also be noted that slight variations in δ 30 Si are visible between some of the magmatic domains. In fact, MZ2 has lower δ 30 Si than MZ1, MZ3, and MZ4 but similar to MZ5 which is patchy-looking in BSE but does not have metamorphic signatures as in MZ6 and MZ7 (Figs. 2 and4). Interestingly, magmatic domains have very variable

Discussion

As presented in the result section, Si isotope signatures in zircon can be either reproducible or variable within a zircon population, hence, at the sample scale (Fig. 1).

Before interpreting zircon δ 30 Si in terms of fractionation behavior between crystals and their parental melts (primary processes), we need to, first, evaluate the effects of secondary processes such as metamorphic recrystallization and alteration/weathering, which can be assessed using zircon internal texture and chemical composition.

Secondary causes of δ 30 Si variations at the sample scale

The megacrystic zircon from Malawi (MZ; Fig. 4) presents good evidence for secondary modification of δ 30 Si because metamorphic domains within this crystal display a distinct δ 30 Si value (-0.26‰) compared to magmatic domains (-0.46‰).

Metamorphic parts of MZ have typical characteristics of metamorphic zircons because they appear dark and homogeneous in BSE images (Fig. 4; [START_REF] Corfu | Atlas of zircon textures[END_REF], have very low Th/U (e.g., [START_REF] Vavra | Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite facies zircons: Geochronology of the Ivrea zone (Southern Alps)[END_REF] and low Lu/Hf ratios, together with low trace element contents [START_REF] Hoskin | The composition of zircon and igneous and metamorphic petrogenesis[END_REF]. In addition, their estimated Ti-inzircon temperature (~580°C) is lower than that of magmatic domains by about 100°C, and in itself low for a magmatic zircon. Given that the degree of fractionation between zircon and its parental melt/fluid increases as temperature decreases, the fact that metamorphic domains have higher δ 30 Si than magmatic ones is good evidence for the formation of metamorphic zircon domains from high-δ 30 Si medium, possibly crustal fluids (e.g., [START_REF] Kleine | Silicon and oxygen isotopes unravel quartz formation processes in the Icelandic crust[END_REF].

Metamorphism may also be responsible for the low δ 30 Si of AG09-016 (TTG) zircons (Fig. 5A) which exhibit a well-defined positive correlation between Th/U ratios and δ 30 Si values. Zircons from this 3947 Ma sample are known for having been affected by metamorphism (e.g., [START_REF] Guitreau | Crystallization and disturbance histories of single zircon crystals from Hadean-Eoarchean Acasta gneisses examined by LA-ICP-MS U-Pb traverses[END_REF] but the ones analyzed for Si isotope were selected to be the most pristine according to CL and BSE images, as well as U-Th-Pb ages. This illustrates that metamorphism cannot always be straightforwardly detected in zircon and each isotope system has its own sensitivity to metamorphism. When considering the AG09-016 zircon that is least affected by metamorphism (i.e., with highest Th/U), its δ 30 Si is very consistent with that of other TTG samples that have reproducible zircon δ 30 Si (Figs 1 and5A). Metamorphism appears to have opposite effects on δ 30 Si values between MZ and AG09-016 zircons, which is likely controlled by local factors (e.g., nature of fluids, temperature, water-rock ratio in crustal fluids) as well as what actually happens during metamorphism (i.e., recrystallization or enhanced diffusion). The influence of metamorphism should therefore be evaluated on case-bycase basis.

Diffusion is a process known to possibly influence crystal elemental and isotope chemistry (e.g., [START_REF] Watson | Dissolution, growth and survival of zircons during crustal fusion: kinetic principles, geological models and implications for isotopic inheritance[END_REF][START_REF] Albarède | The thermal history of leaky chronometers above their closure temperature[END_REF][START_REF] Cherniak | Diffusion in zircon[END_REF] and we can, therefore, wonder if Si diffusion can play a role in the observed variability in zircon δ 30 Si values (Fig. 1). [START_REF] Cherniak | Si diffusion in zircon[END_REF] conducted diffusion experiments in zircon and concluded that Si diffuses in zircon lattice at rates similar to those for Ti, which are faster than those for U, Th, and Hf that are known to be essentially immobile in pristine zircon (e.g., [START_REF] Cherniak | Diffusion in zircon[END_REF], but slower than those for O. For example, it would take 1.7 Ma for a silicon atom to diffuse over a radius of 1 µm at 650°C. The same distance would be reached after 12 Ga at 500°C. As a consequence, diffusion cannot account for Si isotope variations in studied zircon crystals.

Despite zircon being very resistant to most geological processes, radioactive element decay (e.g., U and Th) can significantly damage its lattice over time which can lead to metamictization of growth bands or domains (e.g., [START_REF] Holland | The effect of nuclear radiation on the structure of zircon[END_REF][START_REF] Murakami | Alpha-decay event damage in zircon[END_REF] and formation of cracks [START_REF] Lee | Self-induced fracture generation in zircon[END_REF], altogether making zircon sensitive to secondary alteration (e.g., [START_REF] Corfu | Atlas of zircon textures[END_REF][START_REF] Guitreau | Record of low-temperature aqueous alteration of Martian zircon during the late Amazonian[END_REF][START_REF] Pidgeon | The accumulation of non-formula elements in zircons during weathering: Ancient zircons from the Jack Hills, Western Australia[END_REF]. Since alteration and weathering can influence zircon chemical and isotopic compositions (e.g., [START_REF] Bouvier | Li isotopes and trace elements as a petrogenetic tracer in zircon: insights from Archean TTGs and sanukitoids[END_REF][START_REF] Pidgeon | The effect of weathering on U-Th-Pb and oxygen isotope system of ancient zircons from the Jack Hills, Western Australia[END_REF][START_REF] Pidgeon | The accumulation of non-formula elements in zircons during weathering: Ancient zircons from the Jack Hills, Western Australia[END_REF][START_REF] Guitreau | Record of low-temperature aqueous alteration of Martian zircon during the late Amazonian[END_REF] and that it has an effect on rocks and minerals (e.g., [START_REF] Ziegler | δ30Si systematics in a granitic saprolite, Puerto Rico[END_REF][START_REF] Opfergelt | Silicon isotopes and the tracing of desilication in volcanic soil weathering sequences[END_REF], we used trace element contents (i.e. non-formula elements) to assess zircon pristineness. The measured elevated contents of non-formula elements (e.g., Ca, K, Al) and their possible co-variation in some zircon crystals (Figs. 2 andS3; Table S4) testify that alteration/weathering occurred in some of the studied crystals [START_REF] Pidgeon | The accumulation of non-formula elements in zircons during weathering: Ancient zircons from the Jack Hills, Western Australia[END_REF]. However, most zircon populations displayed no relationship whatsoever between δ 30 Si values and the concentration of alteration/weathering proxies. The 1.94 Ga (I-type) sample Knaften is one of the rare examples in which alteration/weathering seems to have potentially influenced the δ 30 Si value of one zircon which is associated with a high Ca concentration (Fig. 5B). It is also evident in this sample that alteration/weathering is responsible for the high Ti concentration of the same zircon as illustrated by the positive correlation between Ca and Ti (Fig. 5C). This, in turn, means that the calculated Ti-in-zircon temperature for this crystal is over-estimated and no longer represents that of igneous crystallization. This testifies to the spurious nature of the extreme Ti-in-zircon temperatures mentioned in the result section as in all these cases Ti content correlates with that of light elements such as Al, Ca, K, (Table S4; Figs 2 andS3) which is diagnostic of external material input into zircon (e.g., [START_REF] Pidgeon | The accumulation of non-formula elements in zircons during weathering: Ancient zircons from the Jack Hills, Western Australia[END_REF].

As a consequence, alteration/weathering can affect zircon chemistry but does not always lead to modifications of zircon Si isotope signatures. However, this assertion should be regarded with some caution because Si isotopes were measured using traverses, that covered a significant portion of each crystal, whereas trace element measurements were done using spots that were located unto the marks left by Si isotope analyses. Therefore, measurements were performed sequentially and on distinct material although spatially related. This is the major limitation of our approach and it is why the absence of significant influence of alteration/weathering on Si isotopes should not be considered as a firm conclusion. Nevertheless, our data still allow a fairly good understanding of the relationship between δ 30 Si and trace elements since most of the analyzed zircons were pre-selected based on pristine-looking internal textures (fine oscillatory zoning) and existing chemical and/or isotopic data. It is, consequently, possible that a crystal was locally altered, which was detected by trace elements, although overall essentially pristine thereby giving non-altered Si isotope signatures that we can further discuss in an igneous context.

Primary causes of δ 30 Si variations at the sample scale

Silicon isotope fractionation between zircon and its parental melt mostly depends on the temperature of zircon crystallization (∆ 30 SiWR-Zrc ∝ 10 6 /T 2 ), and the degree of polymerization of SiO4 in the melt (e.g., [START_REF] Grant | The geological significance of variations in the abundances of the isotopes of silicon in rocks[END_REF][START_REF] Poitrasson | An Earth-Moon silicon isotope model to teack silicic magma origins[END_REF], which can be approached by the NBO/T parameter (Mysen et al., 1985) and SiO2 content (e.g., [START_REF] Qin | First-principles calculations of equilibrium fractionation of O-and Si-isotopes in quartz, albote, anorthite and zircon[END_REF][START_REF] Poitrasson | Silicon isotope geochemistry[END_REF][START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF]. Ti-in-zircon temperature [START_REF] Ferry | New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers[END_REF] offers a good proxy for the crystallization temperature of zircon crystals and the vast majority of our samples have Ti-in-zircon temperatures that vary within ~100°C. According to experimental calibrations from [START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF], δ 30 Si variation only related to 100°C drop would go from 0.07‰ between 900° and 800°C to 0.14‰ between 700° and 600°C. This is in the case of zircon-quartz equilibration (SiO2 concentration of ~100 wt%) for which the A value of the fractionation equation (i.e., ∆ 30 SiQz-Zrc = A x 10 6 /T 2 ) is 0.53 ± 014 [START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF].

These fractionation values of 0.07 and 0.14‰ should, therefore, be regarded as maximum since the degree of fractionation between zircon and melt would be smaller for lower SiO2 contents [START_REF] Qin | First-principles calculations of equilibrium fractionation of O-and Si-isotopes in quartz, albote, anorthite and zircon[END_REF][START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF]. These variations are smaller or equivalent to the analytical uncertainty of our analyses and would, hence, be undetected. Consequently, samples that display reproducible zircon δ 30 Si associated with narrow Ti-in-zircon temperatures very likely formed from magmas with homogeneous SiO2 contents (e.g., SKJ, 40-03, Klodden; Figs. 1 and6) and homogeneous Si isotope compositions.

In contrast, samples with variable zircon δ 30 Si can be due to crystallization over large temperature windows (>100°C) and/or from melts with variable SiO2 contents either locally (e.g., mingling effects) or temporal (e.g., fractional crystallization effects). Figure 5D presents the only relationship between Ti-in-zircon temperatures and δ 30 Si values visible in our dataset. It likely comes from the fact that this sample, MARG -a cordierite-bearing (S-type) graniteis the only sample that has a Ti-inzircon temperature range of ~250°C (1015-775°C; Table S4). The relationship between δ 30 Si values and temperature complies with theory and experiments but the degree of fractionation (0.72‰) is too large because a maximum δ 30 Si variation of 0.16‰ should be expected if only temperature controlled the fractionation (Figs. 5D and 6D;[START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF]. In order to account for the excess fractionation, we can invoke a change in SiO2 content of the parental melt but it does not entirely solve the problem (Figure 6D) because the degree of fractionation of these zircons, expressed as ∆ 30 SiWR-Zrc, exceed plausible values when a δ 30 Si of -0.3‰ is assumed for S-type granites [START_REF] Savage | Silicon isotope fractionation during magmatic differentiation[END_REF]. A way to account for this strong evolution of MARG zircon δ 30 Si is a source control because this granite is a crust-reworking product that involved clastic sediments (e.g., [START_REF] Couturié | Le massif granitique de la Margeride (Massif Central Français[END_REF], and low-temperature alteration of crustal rocks to form clay minerals result in the development of low δ 30 Si signatures down to -2‰ (e.g., [START_REF] Ziegler | δ30Si systematics in a granitic saprolite, Puerto Rico[END_REF][START_REF] Opfergelt | Silicon isotopes and the tracing of desilication in volcanic soil weathering sequences[END_REF], opposite from what is seen with O isotopes (e.g., [START_REF] Valley | Oxygen isotopes in zircon[END_REF][START_REF] Bindeman | Oxygen isotopes in mantle and crustal magmas as revealed by single crystal analysis[END_REF]. An additional consideration to account for the very large spread in δ 30 Si and Ti-in-zircon temperature is to consider that some of the analyzed zircons, or some parts of these zircons, could be inherited since this is a common feature of crustally-derived granitoids (e.g., [START_REF] Villaros | Isotopic variations in S-type granites: an inheritance from a heterogeneous source? Contrib[END_REF][START_REF] Couzinié | When zircon drowns: Elusive geochronological record of water-fluwed orthogneiss melting in the Velay dome (Massif Central, France)[END_REF]. This would, in turn, account for the very high temperature of 1015°C, which is hard to reconcile with the S-type nature of the Margeride granite.

The remaining samples with variable zircon δ 30 Si have narrow Ti-in-zircon temperatures (e.g., Pikes Peak, Kristineberg; Figs. 1 and6) which, therefore, cannot account for this within-zircon-population variability. The most likely explanation is local heterogeneities in SiO2 concentrations and/or temperatures coming from magma mingling and/or mixing, or simply fractional crystallization. At 800°C, the difference between the δ 30 Si of zircons formed from mafic (SiO2 = 50 wt%) and felsic magmas (SiO2 = 70 wt%) would be ~0.3‰ (Figure 6; [START_REF] Qin | First-principles calculations of equilibrium fractionation of O-and Si-isotopes in quartz, albote, anorthite and zircon[END_REF]. These melts would most likely have distinct temperatures which would further increase the variability in δ 30 Si values. One would have wished that zircon chemistry could help further support this hypothesis. However, trace element contents in zircon do not always significantly vary between crystals derived from mafic and felsic melts (e.g., [START_REF] Hoskin | The composition of zircon and igneous and metamorphic petrogenesis[END_REF], despite strong elemental variations between these two magma types. This, unfortunately, makes zircon a poor indicator of magma origin, except perhaps for Atype (Fig. S5), and account for the general absence of correlation between elemental concentrations and δ 30 Si values. Interestingly, magma mingling has been reported for some of the samples exhibiting variations in zircon δ 30 Si values. This is the case for Kristineberg that belongs to the well-studied Jörn granitoid group for which [START_REF] Wilson | Jörn: an early Proterozoic intrusive complex in a volcanic-arc environment, north Sweden[END_REF] described multiple magma sources and interactions. Similarly, St-Julien-la-Vêtre granite is also known for obvious magma mingling between mafic and felsic endmembers (Barbarin, 1988a).

A source control can also be invoked to account for some zircon δ 30 Si variations, for example in S-type MARG (already discussed above), I-type Knaften and Kristineberg (Figure 6). In fact, [START_REF] Wasström | The Knaften granitoids of Västerbotten County, northern Sweden[END_REF] described Knaften granitoids as subvolcanic plutons that intruded into mafic rocks and a supracrustal sequence containing greywacke, turbidite, and graphite-bearing argillites. If these supracrustals interacted with Knaften magmas, it would have lowered melt δ 30 Si which could account for the sharp increase in Knaften ∆ 30 SiWR-Zrc below 850°C that fall slightly above maximum fractionation (SiO2 ~100 wt%; Fig. 6C) as calculated using a I-type bulkrock δ 30 Si value of -0.2‰. The typical A-type Pikes Peak granite involved both mantlederived and crustally-derived, though not sedimentary, components [START_REF] Smith | A review of the Pikes Peak Batholith, Front Range, central Colorado: A "type example" of A-type granitic magmatism[END_REF][START_REF] Guitreau | Pikes Peak batholith (Colorado, USA) revisited: A SIMS and LA-ICP-MS study of zircon U-Pb ages combined with solution Hf isotope composition[END_REF] which likely resulted in magmas with variable SiO2 contents, though with similar δ 30 Si values. Silicon isotope composition of zircon, therefore, appears to be sensitive to complex magma evolution and track source changes and magma interactions.

Returning to the Malawi zircon example, magmatic domains MZ1, MZ3 and MZ4 have identical δ 30 Si values, whereas MZ2, also magmatic, has a lower δ 30 Si value (Figs. 1 and4) despite MZ2 being located between growth bands MZ4 (innermost) and MZ3-MZ1 (outermost and being from the same growth bands but located in opposite parts of the zircon; Fig. 4). Our results also show that MZ2 crystallized at higher temperature than MZ3 and from a magma with apparently higher SiO2 content (Table 3; Fig. 6). In addition, the central domain of the zircon (MZ5) that was analyzed but interpreted as intermediate between magmatic and metamorphic because of patchylooking internal texture (Figs. 1 and4), has similar δ 30 Si value as MZ2, and most of the trace element patterns, alongside Ti-in-zircon temperatures, are magmatic-looking (Fig. 2; Table 3). Therefore, MZ5 can be interpreted as the oldest magmatic growth zone of MZ and the coupled δ 30 Si-temperature evolution from core (MZ5) to borders (MZ1-MZ3) reveal cycles of temperature increase and decrease associated with fluctuations in SiO2 content over the course of zircon crystallization, possibly accounting for the large size of this crystal. These changes in magma composition, and/or crystallization temperature are consistent with the fact that 176 Lu/ 177 Hf ratio vary significantly between growth zones but this could also reveal equilibration with co-precipitating phases that changed during zircon growth.

Zircon δ 30 Si variations within and between granite types

So far, our results combined with theoretical and experimental studies [START_REF] Qin | First-principles calculations of equilibrium fractionation of O-and Si-isotopes in quartz, albote, anorthite and zircon[END_REF][START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF] allowed us to demonstrate that secondary processes, such as metamorphism and alteration/weathering, can modify zircon δ 30 Si values, which could lead to an erroneous interpretation of the zircon parental melt composition, and that zircon-melt isotope fractionation is sensitive to crystallization temperature and magma silica content. Therefore, variations of zircon δ 30 Si between samples of the same granite type as visible in Figure 1 can be accounted for by differences in zircon crystallization temperatures, whole-rock SiO2 contents, and magma heterogeneities (i.e., Si elemental and isotopic compositions) linked to fractional crystallization and/or magma mingling and/or source controls as illustrated in Figure 6 and Table 3. This is for example the case between SKJ and Malawi magmatic domains because the former is higher temperature than the latter, though they have almost identical parental magma SiO2 content (Fig. 6A; Table 3). Inversely, Pikes Peak granite has higher whole-rock SiO2 content than SKJ, though similarly high temperatures (Fig. 6A). Klodden and Kristineberg belong to the same type of pluton (Jörn-type; [START_REF] Billström | Age and provenance of host rocks and ores in the Paleoproterozoic Skellefte district, northern Sweden[END_REF] and have overlapping zircon δ 30 Si values but they extend to lower values in Kristineberg (Figs 1 and6C). This is well explained by the fact that Klodden has lower SiO2 content than Kristineberg, in which zircon likely crystallized from evolving melts, hence, with changing SiO2 content (Fig. 6C). Vargfors shows lower zircon crystallization temperatures and higher SiO2 content than Klodden, which accounts for the differences in zircon δ 30 Si (Table 3; Figs 1 and6C). In contrast, differences visible between TTG zircon δ 30 Si values are mostly due to metamorphic imprints because Steynsdorp (Stp) zircons exhibit similar relationship between δ 30 Si values and Th/U ratios as AG09-016 zircons (Fig. 5A; Tables S3 andS4). Moreover, Napier zircons (78285007 and 78285013) are known for having been severely affected by metamorphism (e.g., Guitreau et al., 2019). It should also be noted that TTG samples studied in this contribution are the same, or equivalents from the same outcrops/plutons, as those analyzed for bulk-rock Si isotope compositions in [START_REF] Deng | An oceanic subduction origin for Archaean granitoids revealed by silicon isotopes[END_REF], except Napier samples 78285007 and 78285013, and they all gave a very consistent average bulk-rock δ 30 Si value of -0.01 ± 0.02‰ (2 SD). When all factors controlling zircon δ 30 Si values are considered, one can understand why data from various granite types overlap in Figure 1. It is in fact because the range of zircon δ 30 Si arising from fractionation related to melt composition (SiO2 and δ 30 Si ) and temperature variation could be larger than the difference between bulkrock δ 30 Si values. This is also close to the analytical precision and/or reproducibility of Si isotope measurements by LA-MC-ICP-MS and S-MC-ICP-MS (Table 3) which tends to increase natural variations. Yet, once all sources of variations are controlled and secondary signatures corrected for, zircon δ 30 Si values comply relatively well with bulk-rock δ 30 Si pattern, as illustrated in Figure 7. This figure also reveals that the current analytical precision achieved by LA-MC-ICP-MS does not prevent this technique to be used but is a limiting factor that should be improved in the future.

A very good illustration of the misleading interpretation possibly arising from interpreting Si isotopes in zircon at face value is given by the two non-coeval Acasta samples AG09009 and AG09008g. The former and the latter belong to TTG (bulk-rock δ 30 Si of 0.0‰; [START_REF] André | Early continental crust generated by reworking of basalts variably silicified by seawater[END_REF][START_REF] Deng | An oceanic subduction origin for Archaean granitoids revealed by silicon isotopes[END_REF] and I-type (bulk-rock δ 30 Si of -0.2‰; [START_REF] Savage | The silicon isotope composition of granites[END_REF][START_REF] Poitrasson | An Earth-Moon silicon isotope model to teack silicic magma origins[END_REF], respectively, which is visible from both their bulk-rock chemical composition [START_REF] Mojzsis | Component geochronology in the polyphase ca. 3920 Ma Acasta Gneiss[END_REF] and their bulk-rock δ 30 Si value [START_REF] Deng | An oceanic subduction origin for Archaean granitoids revealed by silicon isotopes[END_REF]. Despite these differences, they exhibit identical (and reproducible) zircon δ 30 Si values of approximately -0.4‰ (Fig. 1; Table 3). This is well accounted for by the fact that AG09-009 has higher SiO2 content than AG09-008g and its zircons have lower Ti-in-zircon (crystallization) temperatures than those from AG09-008g. These two factors together result in an increase of the isotope fractionation between zircons and their parental melt (∆ 30 SiWR-Zrc) in AG09-009 compared to AG09-008g. Consequently, without knowledge of SiO2 content and crystallization temperatures, it is virtually impossible to discriminate these Acasta samples from each other. In order for Si isotopes in zircon to be used effectively in outof-context zircons (i.e., detrital crystals), a proxy for SiO2 content or of the nature of the zircon parental melt should be used, as also pointed out in [START_REF] Qin | First-principles calculations of equilibrium fractionation of O-and Si-isotopes in quartz, albote, anorthite and zircon[END_REF][START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF].

We took advantage of our dataset to calibrate the relationship between SiO2 content and the A value, which was done indirectly by comparison with O isotopes in [START_REF] Qin | First-principles calculations of equilibrium fractionation of O-and Si-isotopes in quartz, albote, anorthite and zircon[END_REF] and using data from [START_REF] Trail | Origin and significance of Si and O isotope heterogenities in Phanerozoic, Archean, and Hadean zircon[END_REF] [START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF]. Figure 8 presents the relationship between A value (∆ 30 SiWR-Zrc/10 6 /T 2 ) as a function of melt SiO2 content that can be tentatively used to build more accurate figures such as those in Figure 6. We obtain the following relationship:

∆ 𝑆𝑖 𝑊𝑅-𝑍𝑟𝑐 30 = 10 6 𝑇 2 × 0.00545𝑥
With 𝑥 being the whole-rock SiO2 content in wt%, supposedly equivalent to that of the parental melt, and T the temperature in Kelvin (Fig. 8). Zircon crystallization temperature can be either obtained from Ti-in-zircon thermometer [START_REF] Ferry | New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers[END_REF] or possibly from zircon-saturation [START_REF] Watson | zircon saturation revisited: temperature and composition effects in a variety of crustal magma types[END_REF][START_REF] Miller | Hot and cold granites? Implications of zircon saturation temperatures and preservation of inheritance[END_REF]. However, we observed in this study that Ti-in-zircon temperatures are quite consistent with zircon-saturation temperatures (Tzr; Table 3) in some cases (e.g., TTGs, MZ), uncertainty considered, but are quite different in others (e.g., SKJ, Klodden, Kristineberg). This mismatch is strongest in studied I-type granites, which illustrates the subjective character of Tzr that most likely come from the fact that granites do not often represent actual magmatic liquids. Therefore, Ti-in-zircon temperatures should be preferred because, contrary to Tzr, they can actually track zircon parental magma evolution.

Conclusions

This study focuses on the Si isotope composition of zircons from various granite types.

We show that zircon δ 30 Si can vary significantly at the sample scale (i.e., within a zircon population) but also between granites of the same type and between granite types. These variations are due to differences in zircon crystallization temperatures and parental magma SiO2 contents, which makes zircon δ 30 Si a good proxy for magma evolution.

However, secondary processes, such as metamorphism and alteration/weathering, can affect zircon δ 30 Si values but they can be readily identified on the basis of zircon internal textures, as revealed by BSE/CL images, and trace-element geochemistry.

Therefore, Si isotopes in zircon have promising applications to deciphering granitic magma evolution as well as granite-type discrimination that can be improved even further by reducing analytical uncertainty which is currently the major limitation of this technique. Color-coding is the same as in Figure 1. Data for AS3 zircon are from this study (Table S4) and given for comparison. The AS3 elemental values used to normalize zircon data are averages of measurements from this study for which Al concentration was below 1 ppm in order to obtain a least altered and representative igneous composition. Figure 6. Silicon isotope fractionation between zircon and melt, expressed as ∆ 30 SiWR-Zrc, as a function of Ti-in-zircon temperature (T°C) and 10 6 /T 2 (in Kelvin). We only plotted samples for which we analyzed trace elements and that were not affected by secondary processes (see text fo details). Also indicated are SiO2 contents of corresponding whole-rock (WR) samples ( [START_REF] Ziegler | δ30Si systematics in a granitic saprolite, Puerto Rico[END_REF][START_REF] Opfergelt | Silicon isotopes and the tracing of desilication in volcanic soil weathering sequences[END_REF][START_REF] Trail | Origin and significance of Si and O isotope heterogenities in Phanerozoic, Archean, and Hadean zircon[END_REF]. Color-coding is the same as in Figure 1.

Figure 7. Silicon isotope signatures of analyzed zircons filtered for secondary processes and grouped according to major granite types. Color-coding is the same as in Figure 1.

Each circle corresponds to the average zircon δ 30 Si obtained from one sample. Also indicated are the values for the various granite types [START_REF] Savage | The silicon isotope composition of granites[END_REF][START_REF] Poitrasson | An Earth-Moon silicon isotope model to teack silicic magma origins[END_REF][START_REF] Deng | An oceanic subduction origin for Archaean granitoids revealed by silicon isotopes[END_REF] and the within-run precision of LA-MC-ICP-MS analyses. Note the similar pattern between zircon and whole-rock δ 30 Si. et al. (2019). Compared to this study, slopes (i.e., A values) derived from theory [START_REF] Qin | First-principles calculations of equilibrium fractionation of O-and Si-isotopes in quartz, albote, anorthite and zircon[END_REF] seem to under-estimate Si isotope fractionation between zircon and high-SiO2 melts, whereas slopes from experiments tend to under-estimate Si isotope fractionation between zircon and low-SiO2 melts [START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF]. However, note that uncertainties on A values are similar to those on δ 30 Si, and hence on ∆ 30 SiWR-Zrc, that vary between 0.1 and 0.2 (2SD absolute values) which is not shown in (B).

Moreover, the fit in (A) is linear but the actual relationship between A value and SiO2

may not be linear as noted in [START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF] and could instead require a polynomial fit such as the modeling of fractionation behavior done in [START_REF] Qin | First-principles calculations of equilibrium fractionation of O-and Si-isotopes in quartz, albote, anorthite and zircon[END_REF]. This study [START_REF] Qin | First-principles calculations of equilibrium fractionation of O-and Si-isotopes in quartz, albote, anorthite and zircon[END_REF][START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF]

Figure 1

 1 Figure 1 presents all Si isotope data in the form of δ 30 Si values for zircon crystals

Figure 2 .

 2 Figure 2. Chondrite-normalized (McDonough and Sun, 1995) multi-element plots for

Figure 3 .

 3 Figure 3. Zircon reference AS3-normalized multi-element plots for granitic zircons.

Figure

  Figure Click here to access/download;Figure;Figures-All.pdf

  Figure Click here to access/download;Figure;Figures-All.pdf

Figure 4 .

 4 Figure 4. Back-scattered electron (BSE) image of the megacrystic zircon from Malawi

Figure 5 .

 5 Figure 5. Composite figure that presents zircon δ 30 Si and chemical data from TTGs (A),

Figure 8 .

 8 Figure 8. Binary plot showing the relationship between A value and whole-rock SiO2

Table 1 .

 1 Sample details

Table 2 .

 2 LA-ICP-MS and LA-MC-ICP-MS operating conditions

Table 3 .

 3 Average Si isotope signatures of zircons analyzed in this study

Table

  Click here to access/download;Table;Tables.docxFiguresFigure1. Si isotope results for zircon crystals analyzed in this study by S-MC-ICP-MS (black spots) and LA-MC-ICP-MS (colored squares) in the form of δ 30 Si values. Also indicated are the average δ 30 Si for mantle zircon (-0.38 ± 0.04 ‰; 2SD; Trail et al., 2018) together with bulk-rock average δ 30 Si values for major granite types (A-, I-, S-

and TTGs;

[START_REF] Savage | The silicon isotope composition of granites[END_REF][START_REF] Poitrasson | An Earth-Moon silicon isotope model to teack silicic magma origins[END_REF][START_REF] Deng | An oceanic subduction origin for Archaean granitoids revealed by silicon isotopes[END_REF]

.

  Table3). The solid and dashed lines with associated SiO2 contents are from[START_REF] Trail | Experimentally determined Si isotope fractionation between zircon and quartz[END_REF]. ∆ 30 SiWR-Zrc were calculated assuming bulk-rock A-type granite δ 30 Si of -0.15‰, TTG δ 30 Si of -0.0‰, I-type δ 30 Si of -0.20‰, and S-type granite δ 30 Si of -0.30‰[START_REF] Deng | An oceanic subduction origin for Archaean granitoids revealed by silicon isotopes[END_REF]. Note the general

	good consistency between zircon group positions and WR SiO2 contents for samples
	with simple distribution (e.g., SKJ = 58 wt% SiO2; Klodden = 58 wt% SiO2; 40-03 =
	71 wt% SiO2; AG09-009 = 72 wt% SiO2; Meymac = 70 wt% SiO2). Also note the
	spread in ∆

30

SiWR-Zrc values for other samples (e.g., Pikes Peak granite, Knaftern, MARG) that indicate heterogeneous SiO2 that most likely arise from fractional crystallization, magma mingling, and/or change in the source of parental magma, or crustal assimilation. In fact, clay-rich sediments can have δ 30 Si down to approximately -2‰, thereby artificially increasing the ∆ 30 SiWR-Zrc

Lu/

Hf ratios that are, however, reproducible within each zone (Fig.4).

Acknowledgements

We are grateful to Samuel B. Mukasa and Kjell Billström for providing Pikes Peak batholith and Skellefte samples, respectively. We are also grateful to Sam Broom-Fendley for providing the megacrystic Malawi zircon and to Dustin Trail for providing KIM and KL zircons as well as for stimulating discussions. Ken Koga and Fernando Corfu are thanked for help with Rhyolite-MELTS software and for sharing a fragment of 91500 zircon, resepctively. Jean-Luc Devidal is thanked for technical advice with trace element analysis by LA-ICP-MS. Martin Guitreau acknowledges financial support from the Région Auvergne through the Auvergne Fellowship program, LabEx ClerVolc (ANR-10-LABX-0006) and the French Agence Nationale de la Recherche through funded ANR-JC project Zircontinents (ANR-17-CE31-0021). This is Laboratory of Excellence ClerVolc contribution number 502. F.M. acknowledges funding from the European Research Council under the H2020 framework program/ERC grant agreement #637503 (Pristine). F.M. and M.C. thank the financial support of the UnivEarthS Labex programme at Université de Paris (ANR-10-LABX-0023 and ANR-11-IDEX-0005-02). Finally, we thank Jeffrey G Catalano and Helen M. Williams for handling our manuscript as well as Paul Savage and Franck Poitrasson for helpful and constructive reviews.

 204, 206, 207, 208, 232, 238 27-29, 39, 43, 44, 49, 51, 66, 71, 85, 88-91, 93, 96, 137, 139-141, 146, 147, 153, 157, 159, 163, 165, 166, 169, 172, 175, 178, 181, 206, 232∆ 30 SiWR-zrc is calculated using δ 30 SiWR of -0.15‰ for A-type, 0.0‰ for TTG, -0.2‰ for I-type, -0.3‰ for S-type, and -0.29‰ for AS3, KIM and MudTank.

Tzr calculated using the calibration of [START_REF] Boehnke | Zircon saturation re-revisited[END_REF] whereas Tzr* was calculated using the original calibration of [START_REF] Watson | zircon saturation revisited: temperature and composition effects in a variety of crustal magma types[END_REF] Zircon T°C is the average Ti-in-zircon temperature determined for each sample Temperature is expressed in Kelvin in 10 6 /T 2 A is the constant in the fractionation law: ∆ 30 SiWR-zrc = A*10 6 /T 2

Supplementary Material

Click here to access/download Supplementary Material Supplementary Material.pdf

Stable isotope geochemistry of silicon in granitic zircon

Highlights :

-Zircons from various granite types were analyzed for Si isotopes -Si isotopes were measured using laser-ablation and solution MC-ICP-MS -Metamorphism and alteration can modify zircon Si isotope composition -Si isotope fractionation in zircon is controlled by temperature and melt SiO2 wt% -Si isotopes in zircon can discriminate granite types and track magma evolution

Highlights

Declaration of interests

☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: