Lithos 126 (2011) 341–354

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The imprint of subduction fluids on subducted MORB-derived melts(Sierra del Convento Mélange, Cuba)

C. Lázaro a,⁎, I.F. Blanco-Quintero a, C. Marchesi b,c, D. Bosch c, Y. Rojas-Agramonte d, A. García-Casco a,b

a Departamento de Mineralogía y Petrología, Universidad de Granada, Avda. Fuentenueva s/n, 18002 Granada, Spainb Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Avda. de las Palmeras 4, 18100 Armilla (Granada), Spainc Géosciences Montpellier, Equipe Manteau-Noyau, UMR 5243, CNRS-Université Montpellier II, 34095, Montpellier, Franced Institut für Geowissenschaften, Universität Mainz, 55099 Mainz, Germany

⁎ Corresponding author at: Departamento de MineraCiencias, Universidad de Granada, Avda. FuentenuevTel.: +34 958 241 795; fax: +34 958 243 368.

E-mail address: clazaro@ugr.es (C. Lázaro).

0024-4937/$ – see front matter © 2011 Elsevier B.V. Aldoi:10.1016/j.lithos.2011.07.011

a b s t r a c t

a r t i c l e i n f o

Article history:Received 25 January 2011Accepted 19 July 2011Available online xxxx

Keywords:Slab meltsFluid compositionTrondhjemiteSedimentary imprintSr–Nd–Pb isotopesTrace elements

Major and trace element signatures and Sr–Nd–Pb isotope data for muscovite (Ms)-bearing amphiboliteblocks and associated muscovite-bearing trondhjemite and quartz-muscovite rocks from the Sierra delConvento mélange (eastern Cuba) indicate that Proto-Caribbean oceanic crust underwent wet partial meltingprocesses during Mesozoic subduction and after accretion to the upper plate. Trace element normalizedpatterns of Ms-bearing amphibolites are enriched in light rare earth elements (LREE) and large-ion lithophileelements (LILE) and evidence variable trace element transfer from the Proto-Caribbean subducting slab to themantle wedge. Ms-bearing trondhjemites show LREE enrichment and HREE depletion and have geochemicalfeatures similar to adakites, including SiO2N56 wt.%, high Na2O contents (5.5–9.0 wt.%) and high Sr/Y (16–644).We consider that the trondhjemites represent primary and natural melts formed by deep partial meltingof the subducting slab which did not significantly react with the mantle wedge before intrusion in thesubduction channel. The Ms-bearing trondhjemites show different geochemical and petrological signaturescompared with theMs-free tonalites–trondhjemites from Sierra del Convento, that are interpreted as primaryslab melts. These differences support the idea that partial melting processes in the Sierra del Conventosubduction channel were triggered by the infiltration of fluids derived from three distinct subducted sources:sediments, altered mid-ocean ridge basalts (MORB), and serpentinites. In this scenario, the pegmatitic quartz-muscovite rocks, which are highly enriched in LILE, probably represent the crystallization products of fluidsderived by differentiation of the trondhjemitic melts.

logía y Petrología, Facultad dea s/n, 18002 Granada, Spain.

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1. Introduction

Different physical–chemical conditions can trigger dehydrationand/or partial melting of the slab in subduction settings. In relativelycold subduction zones the geothermal gradient in the slab may notallow the attainment of P–T conditions for melting at sub-arc depths(ca. 150 km). However, dehydration releases large ion lithophileelement (LILE)-enriched hydrous fluids that metasomatize theoverlying mantle wedge lowering its solidus temperature and causingmelting (e.g. Gill, 1981; Kushiro, 1990; Tatsumi and Kogiso, 1997). Incontrast, partial melting of the slab is inferred to occur at sub-arcdepths in many warm and hot subduction zones (Bebout, 2007). Slabmelts may eventually reach shallow depths in the volcanic arc after

infiltration through the mantle wedge (triggering its melting, Defantand Drummond, 1990; Martin, 1999; Rapp et al., 1999) or afterformation of underplated mantle wedge plumes (Castro et al., 2010;Castro and Gerya, 2008; Gerya and Yuen, 2003; Gorczyk et al., 2007).However, direct observation of processes taking place at the plateinterface in subduction zones is hampered by the scarcity of rocks thatescaped descent into the mantle.

In the Northern Caribbean realm, the presence of adakites or rockswith adakitic-affinities, have been described in several localities inHispaniola (Escuder Viruete et al., 2007) and recently in Jamaica,where Hastie et al. (2010a) identified a new sub-group of adakitelavas derived from melting of underthrusted Caribbean oceanicplateau crust in the early Tertiary. These lavas were generated byunderthrusting (or subducting) and partial melting of oceanic plateaucrust beneath Jamaica without assimilating peridotite, in a settinganalogous to proposed plate tectonic processes in the early Archean(Hastie et al., 2010b).

Down to ≤100 km depth, the dominant fluid/melt-rock interac-tion regimes involve migration of aqueous fluid rather than silicate

342 C. Lázaro et al. / Lithos 126 (2011) 341–354

melts (Bebout, 2007). Indeed, examples of primary and natural slab-derived melts that reached the Earth's surface are scarce. Only in rareoceanic subduction complexes, such as the Catalina Schist mélange(California) and the Sierra del Convento and La Corea serpentiniticmélanges (eastern Cuba), have partial melting of metabasite andmetasomatic mass-transfer processes in the slab-wedge interfacebeen described (Bebout and Barton, 1993; Blanco-Quintero et al.,2010; García-Casco et al., 2008a; Grove and Bebout, 1995; Lázaro andGarcía-Casco, 2008; Sorensen, 1988; Sorensen and Grossman, 1989).

The tonalitic–trondhjemitic rocks produced after melting of am-phibolite in the Catalina Schist and the Sierra del Convento mélangewere considered primary adakitic liquids or natural slab melts byMartin (1999) and Lázaro and García-Casco (2008), respectively. Themajor, trace element and isotopic geochemical signatures of K-poor(muscovite-free) amphibolites and associated tonalitic–trondhjemiticrocks of the Sierra del Convento mélange support the idea that thelatter constitute primary partial melts formed after fluid-fluxedmelting of the former in response to subduction of young hot oceaniclithosphere (García-Casco et al., 2008a; Lázaro and García-Casco,2008). The circulation of fluids in the Sierra del Convento mélange isalso shown by the presence of hornblendites (Lázaro and García-Casco, 2008) and veins of K-poor jadeitites (García-Casco et al., 2009),which represent metasomatic products of the residual amphiboliteand testify to the direct precipitation of fluids in deep-seated veins atca. 1.5 GPa. Geochemical arguments based on trace elements and Sr–Nd isotopes preclude a sedimentary or (altered) oceanic basalt sourcefor the fluids infiltrating the K-poor amphibolites, since these sourceswould imprint an enrichment in Rb, Cs, Ba, B, Li, Th, U, Pb and the LREEto the related arc lavas (Elliott, 2003; Tatsumi, 2005). This factsuggests, in turn, that the flux of fluids evolved from a depleted sourcesuch as dehydrating serpentinite from the downgoing slab (Lázaroand García-Casco, 2008).

Recently, we have identified K-rich muscovite-bearing trondhje-mitic rocks in the Sierra del Convento and La Corea mélanges (Blanco-Quintero et al., 2011a). These rocks formed by partial melting ofMORB-derived amphibolite and crystallized at depth in the subduc-tion environment, similar to the K-poor trondhjemites described byLázaro and García-Casco (2008), but richer in LREE and LILE (K, Ba, Rb)compared to the K-poor samples, suggesting a different source for theinfiltrating fluids. In this paper, we characterize the major, traceelement and Sr–Nd–Pb isotope geochemistry of these muscovite-bearing rocks and interpret them as primary melts (muscovite-bearing trondhjemites), residual rocks (muscovite-bearing amphibo-lites) and hydrothermal rocks (quartz–muscovite rocks) producedduring subduction of the Sierra del Convento mélange. These data areused to obtain insights into the source and role of slab-derived fluidsin the generation of primary slab magmas and to infer how theirresidues were affected by fluid circulation at depth. We show thatfluids derived from sediments and/or altered oceanic basaltseffectively transferred LILE and other elements from the slab to themagmas generated by partial melting of subducted MORB, producinggeochemical and petrological variability of primary slab melts andtheir residues.

2. Geological setting

The Greater Antilles constitute an orogenic belt located at thenorthernmargin of the Caribbean plate (Fig. 1a) which documents thecollision of theMesozoic–Tertiary volcanic arc with themargins of theNorth American plate (Pindell et al., 2006). The orogenic belt is mainlycomposed of oceanic material, including ophiolites and intra-oceanicvolcanic arc complexes, as well as continental rocks derived from thesouthern borderlands of North America (Bahamas platform and theMaya block) and the Mesozoic sedimentary Caribeana terrane(García-Casco et al., 2008b). All these terrains are well exposed inCuba (Fig. 1b), where the oceanic material includes the northern and

eastern ophiolite belts and the Cretaceous and Palaeogene volcanicarcs (Iturralde-Vinent, 1998 and references therein).

In eastern Cuba, the ophiolitic belt is formed by two large bodiesnamed Mayarí-Cristal and Moa-Baracoa. The elemental and isotopiccompositions of these complexes indicate a supra-subduction origin(Marchesi et al., 2006, 2007; Proenza et al., 2006). The ophioliticbodies constitute the highest structural complexes in the region, andoverride the volcanic-arc rocks of the Santo Domingo (to the NW) andthe Purial (to the S–SE) complexes, which have been classicallyconsidered the eastern continuation of the western and central CubanCretaceous volcanic arc complex (Fig. 1b; Iturralde-Vinent et al., 1996,2006). The ophiolites are composed of tholeitic and calc-alkalinevolcanic arc sequences (Gyarmati et al., 1997). The Purial complexwas partially metamorphosed at greenschist and blueschist facies(Cobiella et al., 1984; Millán, 1996; Millán and Somin, 1985; SominandMillán, 1981) during the latest Cretaceous (70–75 Ma) (Iturralde-Vinent et al., 2006; Somin et al., 1992).

Mélange complexes, principally made up of serpentinitic matrixenclosing high pressure metamorphic exotic blocks, are occasionallysandwiched between the ophiolitic bodies and the volcanic arccomplexes. The most significant serpentinite mélanges are the Sierradel Convento and La Corea mélanges (Fig. 1b), which have similarlithological assemblages (Blanco-Quintero et al., 2010; García-Cascoet al., 2006, 2008a; Hernández and Canedo, 1995; Kulachkov andLeyva, 1990; Leyva, 1996; Millán, 1996; Somin and Millán, 1981). TheSierra del Convento mélange overrides the Purial complex from thesouth (Fig. 1b, c), while the La Corea mélange is located in the Sierrade Cristal and is associated with the Mayarí-Cristal ophiolitic body(Fig. 1b). The serpentinitic matrix of these mélanges consists ofantigoritite, which formed at ca. 1.3–1.5 GPa (~50 km) in thesubduction environment after hydration of harzburgite in the upperplate (Blanco-Quintero et al., 2011b). These mélanges have beeninterpreted as portions of the subduction channel, the few km-thickzone characterized by visco-plastic rheology and located between theslab and the overriding plate, related to the south-westwardsubduction of the Proto-Caribbean plate beneath the Caribbeanplate in the Cretaceous (Blanco-Quintero et al., 2010, 2011b; García-Casco et al., 2006, 2008a,b; Lázaro et al., 2009).

3. The subduction-related mélanges in Eastern Cuba

The main type of exotic block in the Sierra del Convento and LaCorea mélanges is epidote±garnet amphibolite spatially andgenetically associated with centimeter to meter-sized leucocratictonalite–trondhjemite veins, pods or isolated blocks. Minor bodies ofquartz–muscovite (Qtz–Ms) rocks, of variable size, from centimeterto meter, and geometry, from veins to isolated blocks, have beenoccasionally observed cross-cutting the other rock-types. Theamphibolites show variable grain size and extent of deformationand recrystallization (García-Casco et al., 2008a). They are foliatedand mainly composed of amphibole+epidote±quartz±garnet andusually have major and trace element N-MORB compositions (Lázaroand García-Casco, 2008). Leucocratic tonalitic–trondhjemitic rocksconstitute the partial melting product of amphibolites at ca. 700–750 °C and 1.5 GPa (Blanco-Quintero et al., 2010; García-Casco, 2007;García-Casco et al., 2008a; Lázaro et al., 2009; Lázaro and García-Casco, 2008). They are formed by primary (magmatic) plagioclase+quartz+epidote±paragonite±pargasite, have variable grain size,and show minor deformation.

Muscovite-bearing amphibolites and trondhjemites constitutedifferent varieties of exotic blocks associated with the previouslydescribed Ms-free lithologies. Normally, the Ms-bearing and Ms-freevarieties of the same lithology (for example, Ms-bearing and Ms-freeamphibolites) are not in contact; but comprise separate blocks in thesame field areas. The counterclockwise P–T–t paths and crystallizationages inferred for both varieties of samples are similar (Blanco-

Fig. 1. (a) Plate tectonic configuration of the Caribbean region, with location of the main geological features including ophiolitic bodies (black), the Caribbean–Colombian OceanicPlateau and the Cretaceous–Present volcanic arc complex (compiled by García-Casco et al., 2006). (b) General geological map of Cuba (Iturralde-Vinent, 1998) showing its maintectonic units. (c) Geological map of Sierra del Convento (Kulachkov and Leyva, 1990) with location of the sample sites (black circles).

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Quintero et al., 2010; Lázaro et al., 2009). Moreover, geochronologicalanalyses carried out on both Ms-free and Ms-bearing samplesalso have similar ages. U–Pb single zircon data indicates that meltscrystallized at 114–105 Ma (Lázaro et al., 2009; Blanco-Quintero,unpublished data) and Ar/Ar amphibole dating yield two groups ofcooling ages at 106–97 Ma (interpreted as cooling of metamorphic/-magmatic pargasite) and 87–83 Ma (interpreted as growth/cooling ofretrograde overprints). These ages, and the inferred P–T–t paths,allow determination of the onset of subduction at ~119 Ma and themelting of amphibolites (metamorphic peak conditions) at ~114 Ma(Lázaro et al., 2009).

In this paper we present geochemical data of Ms-bearing amphib-olites (samples CV139a, CV140a, CV230a, CV230c), Ms-bearing trondh-jemites (SC-20, CV230e, CU-72-I, CU-72), locally with pegmatitic

texture (CV201a, CV201g, CV201h), and Qtz–Ms rocks (CV201d,CV201f, CV53e-I, CV53e-II). Preliminary mineral and whole-rockelemental data of samples CV201a, CV201f and CV53e were providedby Blanco-Quintero et al. (2011a). In addition, we present new Pbisotopic data of the Ms-free varieties of amphibolite, trondhjemite–tonalite and hornblendite studied previously by Lázaro and García-Casco (2008).

4. Analytical techniques

4.1. Major and trace elements

Sixteen whole-rock powders were obtained by grinding largeamounts of each sample in a tungsten carbidemill. Major element and

Fig. 2. Plane-polarized (a), and crossed-polarized (b) photomicrographs of Ms-bearing amphibolite composed of amphibole (Amp), epidote (Ep), garnet (Grt), mica (phengite) (Ms)and titanite. Plane-polarized (c), and crossed-polarized (d) photomicrographs of Ms-bearing trondhjemite bearing plagioclase (Pl), muscovite (Ms), quartz and clinozoisite–epidote(Ep). Outcrop pictures of quartz (Qtz)–muscovite(Ms) rock (e) and Garnet(Grt)-bearing Qtz–Ms rock (f). The scale bar is 1500 μm in (a) and (b), and 500 μm in (c) and (d). Mineralabbreviations after Kretz (1983).

344 C. Lázaro et al. / Lithos 126 (2011) 341–354

Zr compositions were determined on glass beads, made up of ~0.6 gpowdered sample diluted in 6 g of Li2B4O7, by a PHILIPS Magix Pro(PW-2440) X-ray fluorescence (XRF) equipment at the University ofGranada (Centro de Instrumentación Científica, CIC). Precision isbetter than ±1.5% for an analyte concentration of 10 wt.%. Precisionfor Zr and LOI is better than ±4% at 100 ppm concentration. Theanalyses were recalculated to an anhydrous 100 wt.% basis, and thesedata are used in the text and figures. The Mg number (Mg#) wascalculated as (100*molar MgO/(MgO+FeOtot)).

Trace elements, except Zr, were determined at the University ofGranada (CIC) by ICP-Mass Spectrometry (ICP-MS) after HNO3+HFdigestion of ~100 mg of sample powder in a Teflon-lined vessel at

~180 °C and ~200 p.s.i. for 30 min, evaporation to dryness, andsubsequent dissolution in 100 ml of 4 vol.% HNO3. Procedural blanksand international standards PMS, WSE, UBN, BEN, BR, and AGV(Govindaraju, 1994) were run as unknowns during analytical ses-sions. Precision was better than ±2% and ±5% for analyte concen-trations of 50 and 5 ppm, respectively.

4.2. Sr–Nd–Pb isotopes

Sixteen whole rock samples were processed for Sr–Nd isotopicanalyses at the CIC (University of Granada). Samples were digested inthe same way as for ICP-MS and were analyzed by a Finnigan Mat 262

Fig. 3. Zr/TiO2–Nb/Y diagram with classification fields of volcanic rocks (Winchesterand Floyd, 1977). Ms-bearing amphibolites: white circles, Ms-bearing trondhjemites:black triangles, Qtz–Ms rocks: grey squares.

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thermal ionization mass spectrometer (TIMS) after chromatographicseparation by ion exchange resins. Isotopic data were normalized to86Sr/88Sr=0.1194 and 146Nd/144Nd=0.7219. Procedural blanks were0.6 and 0.09 ng for Sr and Nd, respectively. The external precision(2σ), estimated by 10 replicate analyses of the WSE internationalstandard (Govindaraju, 1994), was better than 0.003% for 87Sr/86Srand 0.0015% for 143Nd/144Nd. The long-term 87Sr/86Sr value of theNBS 987 international standard measured at the CIC is 0.710250±4(n=106). Long-term measurements of the La Jolla Nd internationalstandard in this lab yield 143Nd/144Nd=0.511844±7 (n=49).

Ten and twenty-three whole rock samples were processed for Sr–Nd and Pb isotopic analyses, respectively, at the GéosciencesMontpellier laboratory (CNRS-Université Montpellier 2, France).Before acid digestion, all whole rock powders were leached for50 min with 6 N HCl at 80 °C. After leaching, the residues were rinsedthree times with purified milli-Q H2O. Pb chemical separation wascarried out using the AG1X8 anion exchange resin washed in 0.5 NHBr and 6 N HCl. Nd and Sr were separated following an extractionchromatographic method modified from Pindell et al. (2006). Sr, Ndand Pb concentrations in procedural blanks were less than 65, 30 and35 pg, respectively. Nd and Pb isotopic compositions were measuredby a Nu 500 MC-ICP-MS at the Ecole Normale Supérieure in Lyon(France), and Sr isotopic ratios by a ThermoFinnigan Triton T1 TIMS atthe LABOGIS of the Centre Universitaire de Formation et de Recherchein Nimes (France). Further details on the sample digestion, isotopechemical separations and analytical measurements including repro-ducibility, accuracy and values of the international standards arereported in Bosch et al. (2008).

All the measured isotopic data have been corrected for radioactivedecay from the inferred crystallization age at 114 Ma, according to theP–T–t path presented by Lázaro et al. (2009), based on SHRIMPanalyses of zircons in the Sierra del Convento trondhjemites, Ar–Arages of several minerals from different rock types from this complex,and calculated rates of subduction, cooling and exhumation.

5. Petrography

The peak metamorphic mineral assemblage of the studied Ms-bearing amphibolite samples consists of pargasitic amphibole,epidote, garnet, phengite, rutile, titanite and accessory apatite andquartz (Fig. 2a; Table S1). This assemblage defines a crude foliationmainly marked by phengite and pargasite crystals. Quartz appearsas small dispersed grains in the matrix, but quartz-free samplesare common. Garnet has been observed in all the studied samples(Table S1). It forms large porphyroblasts containing inclusions ofamphibole and epidote (Fig. 2a). Phengitic mica appears as idiomor-phic and medium-grained crystals. Titanite forms idiomorphiccrystals elongated along the foliation, but it also replaces rutile.Retrograde overprints consist of glaucophane, actinolite, (clino)zoisite, chlorite, pumpellyite, and, less abundantly, albite andparagonite. All these retrogrademinerals are fine-grained and corrodethe peak-metamorphic minerals, but they are also dispersed in thematrix or located in fractures. Retrograde glaucophane is typicallyfound in aggregates with actinolite, chlorite and albite, and commonlyoverprints peak amphibole (Fig. 2a,b). Chlorite and pumpellyitereplace garnet and pargasite. Retrograded crystals of amphiboleusually contain small needles of exsolved rutile or titanite.

The magmatic mineral assemblage of the Ms-bearing trondhje-mites (including the pegmatitic variety) is composed of medium-grained plagioclase, quartz and phengite, with subordinate epidote,plus accessory apatite, titanite and rutile (Fig. 2c,d; Table S1). Garnetis present in some samples. Epidote and garnet are idiomorphic andmedium-grained. Phengite is idiomorphic and has a medium-grainsize. Retrograde mineral assemblages overprint the magmatic ones.Magmatic plagioclase appears generally transformed to retrogradealbite plus fine-grained (clino)zoisite, paragonite, saussurite, phengite

and, locally, lawsonite. Magmatic epidote is overprinted by fine-grained overgrowths of (clino)zoisite. Titanite replaces rutile. Smallamounts of retrograde K-feldspar and celsian are present in somesamples (Blanco-Quintero et al., 2011a).

The Qtz–Ms rocks are pegmatitic, they are essentially composed ofmedium to coarse size crystals of quartz and phengite (Fig. 2e, TableS1) and scarce fine-grained albitized plagioclase. Sample CV278a-Ialso has coarse garnet crystals (Fig. 2f). The mineralogy andpegmatitic microstructures of these rocks suggest a hydrothermalorigin.

6. Results

The mobility of several elements (e.g., Rb, Ba, K, Sr and LREE) atmetamorphic conditions similar to those attained by the Sierra delConvento rocks during exhumation, needs to be assessed, asretrograde metamorphism or later alteration may have affected themineralogical and geochemical compositions of the samples. Howev-er, we note that mineral analyses carried out by laser ablation ICP-MSshow enrichments of Cs, Rb, Ba, Nb, Pb and Sr in the core of primaryphengite in these samples (Blanco-Quintero et al., 2011a). Thisobservation strongly suggests that the trace element budget in theSierra del Convento rocks mainly records geochemical processesoccurring at the peak metamorphic conditions (i.e., at high P–T) andnot during retrograde events.

In order to classify variably altered igneous rocks and circumventthe possible influence of alteration on major elements and inparticular in alkalis, we have classified the samples using the diagramof Winchester and Floyd (1977) (Fig. 3) that is based on ratios ofrelatively immobile incompatible elements. In this diagram the Sierradel Convento Ms-bearing amphibolites show sub-alkaline basalticsignatures, whereas the Ms-bearing trondhjemites and Qtz–Ms rocksrange from trachyandesitic to rhyolitic compositions (Fig. 3).

6.1. Major elements

The SiO2 contents of Ms-bearing amphibolites range from 42.1 to46.5 wt.%, and those of Ms-bearing trondhjemites and Qtz–Ms rocksfrom 65.6 to 81.2 wt.%, thus indicating their respective basaltic andacidic affinities (Table 1). Ti content is a useful parameter in order todiscriminate between mid-ocean ridge (MOR) and island arc (IA)basalts, as IAB generally have lower TiO2 values than MORB (Kelemen

Table 1Major (wt.%) and trace element (ppm) composition of Ms-amphibolites, Ms-trondhjemites and Qtz–Ms rocks from the Sierra del Convento mélange.

Rocktypesample

Ms-amphibolites Ms-trondhjemites Qtz–Ms rocks

CV139a CV140a CV230c CV230a CV201a CV201g SC-20 CV201h CV230e CU-72-I CU-72 CV201d CV201f CV278a-I CV53e-I CV53e-II

SiO2 46.3 46.5 42.1 44.2 75.6 73.8 73.1 65.6 72.7 73.4 73.2 81.2 77.1 77.9 71.5 71.8TiO2 1.66 2.31 2.34 1.39 0.03 0.05 0.04 0.06 0.07 0.02 0.03 0.08 0.13 0.02 0.08 0.12Al2O3 17.5 19.7 17.3 15.8 15.7 16.4 16.0 21.5 16.4 15.9 16.2 12.3 14.1 15.1 18.3 17.6Fe2O3tot 11.1 9.4 12.8 13.5 0.28 0.40 0.61 0.51 0.59 0.98 1.03 0.73 0.84 0.76 0.78 0.72MnO 0.21 0.22 0.19 0.11 0.03 0.05 0.04 0.01 0.01 0.04 0.03 0.01 0.01 0.29 0.02 0.01MgO 6.71 7.08 7.90 9.7 0.05 0.25 0.05 0.38 0.31 0.19 0.17 0.93 1.11 0.16 1.05 1.06CaO 11.8 7.95 14.0 11.0 0.87 0.34 2.28 0.21 1.73 1.49 1.60 0.14 0.15 0.17 0.19 0.16Na2O 1.32 3.02 1.21 1.65 5.93 6.92 5.74 9.01 5.77 5.50 5.40 0.54 0.48 1.66 0.48 0.43K2O 1.08 1.33 0.67 1.21 0.77 0.95 0.78 1.74 1.08 0.97 1.12 2.80 3.98 1.69 5.14 5.07P2O5 0.13 0.52 0.54 0.15 0.03 0.05 0.04 0.07 0.05 0.09 0.10 0.03 0.03 0.06 0.01 0.02LOI 1.68 2.15 0.77 1.14 0.50 0.67 1.73 0.85 1.22 1.19 0.94 1.38 1.83 1.61 2.37 2.89Total 99.55 100.20 99.79 99.83 99.73 99.88 100.38 99.94 99.92 99.78 9.82 100.10 99.79 99.43 99.85 99.88Zr (XRF) 99 212 202 62 17.8 13.8 25 71 47 21 23 43 19.3 26 42 32Li 7.4 49 7.4 10.0 0.42 2.5 0.00 4.6 0.64 1.06 0.64 6.9 6.3 2.7 4.7 4.6Rb 15.8 20.1 10.4 22 12.3 16.1 15.1 31 20.4 15.7 15.1 57 79 41 88 85Cs 0.17 0.43 0.11 0.17 0.100 0.23 0.63 0.16 0.30 00 0.0181 0.30 0.45 1.18 0.32 0.33Be 0.71 1.77 1.19 1.29 1.00 7.9 0.77 1.02 0.50 0.93 0.89 1.96 2.4 3.6 2.4 2.2Sr 510 458 531 259 192 86 389 97 410 150 132 21 24 187 100 99Ba 1022 157 574 1267 4460 5063 759 4220 1095 647 504 9040 11810 833 6882 6329Sc 38 27 45 51 0.70 7.7 0.36 0.37 b.d.l. b.d.l. b.d.l. 1.56 4.6 3.7 5.7 4.8V 280 185 322 350 3.7 20 3.0 15.0 5.9 2.6 3.1 38 52 5.3 20 18.2Cr 333 293 405 545 39 34 129 119 165 28 136 40 35 26 54 40Co 49 48 53 63 36 29 0.00 0.99 0.87 29 118 45 37 23 25 31Ni 78 192 146 154 2.77 3.8 1.33 12.9 18.7 0 10.9 13.4 18.4 1.66 23 18.8Cu 14.2 64 10.2 5.8 3.4 10.7 5.4 3.3 7.0 7.1 5.2 3.3 2.5 5.7 2.9 2.4Zn 109 73 146 159 7.3 3.5 20 12.4 9.2 23 19.3 18.9 21.8 29 8.0 7.9Ga 20 16.3 23 19.8 13.6 18.3 11.1 16.8 9.9 18.3 16.9 13.2 20 21 22 20Y 29 32 45 23 10.7 5.4 0.74 3.3 0.64 1.32 1.47 1.80 4.1 17.4 5.3 5.4Nb 7.6 21 30 4.9 2.5 12.2 0.55 1.95 0.29 1.22 2.7 4.2 8.2 7.4 5.6 4.5Ta 0.74 1.64 2.3 0.32 0.56 1.30 0.02 0.26 0.030 0.104 0.45 0.99 0.65 0.86 0.45 0.47Hf 0.96 0.37 1.27 0.86 0.37 0.27 0.20 2.6 0.139 0.053 0.082 0.20 0.36 0.44 0.95 0.50Mo 2.5 1.87 1.67 0.65 7.3 6.6 0.20 0.91 1.17 4.1 6.6 8.8 7.6 4.7 4.7 4.9Sn 1.95 1.27 4.2 2.1 0.67 10.6 0.00 0.89 0.21 0.43 1.03 1.14 4.4 5.0 3.3 2.5Tl 0.113 0.036 0.100 0.22 0.120 0.120 0.180 0.28 0.21 0.155 0.144 0.47 0.64 0.24 0.60 0.57Pb 11.3 1.55 6.6 5.4 20 13.9 3.1 6.7 4.8 9.0 8.2 2.3 3.0 10.2 5.4 5.0U 0.40 0.78 1.06 0.61 0.63 1.54 0.115 3.1 0.055 0.23 0.52 0.90 2.6 10.4 0.77 1.01Th 0.63 3.1 3.3 0.84 0.93 1.57 0.22 2.6 0.035 0.27 0.46 1.55 6.4 2.3 4.3 3.6La 8.3 22 28 6.6 3.1 1.31 0.77 1.80 0.72 4.2 5.7 3.7 10.7 1.26 3.0 3.2Ce 19.8 48 54 12.8 4.4 2.4 1.13 2.6 0.54 9.0 12.0 4.5 15.1 2.6 5.8 6.1Pr 3.0 5.6 7.1 1.92 0.65 0.35 0.177 0.34 0.095 1.25 1.64 0.74 2.1 0.45 0.65 0.68Nd 14.2 23 30 8.7 2.6 1.63 0.72 1.37 0.38 5.0 6.9 2.6 8.4 2.2 2.8 2.8Sm 4.4 5.4 7.4 2.6 0.95 0.58 0.168 0.50 0.093 1.25 1.59 0.66 1.95 0.99 0.79 0.76Eu 2.1 1.71 2.9 1.35 0.63 0.40 0.085 1.13 0.32 0.51 0.51 0.72 1.08 0.23 0.65 0.65Gd 4.9 5.2 7.2 3.1 1.32 0.81 0.164 0.56 0.101 0.89 1.17 0.60 1.81 1.72 0.83 0.99Tb 0.85 0.90 1.25 0.57 0.23 0.139 0.026 0.094 0.017 0.101 0.101 0.076 0.23 0.36 0.129 0.153Dy 5.2 5.5 7.8 4.0 1.53 0.88 0.155 0.58 0.095 0.30 0.30 0.37 1.06 2.5 0.89 0.94Ho 1.11 1.15 1.63 0.88 0.29 0.172 0.028 0.105 0.020 0.034 0.036 0.060 0.162 0.58 0.180 0.180Er 3.1 3.1 4.5 2.4 0.77 0.48 0.080 0.23 0.051 0.057 0.069 0.140 0.36 1.62 0.53 0.47Tm 0.45 0.46 0.66 0.35 0.110 0.070 0.0120 0.030 0.0070 0.0006 0.0072 0.020 0.050 0.26 0.080 0.070Yb 2.6 2.9 4.1 2.0 0.73 0.44 0.102 0.159 0.051 0.063 0.063 0.130 0.29 1.90 0.54 0.39Lu 0.37 0.43 0.63 0.30 0.110 0.080 0.010 0.024 0.0080 0.0052 0.0020 0.020 0.040 0.28 0.090 0.050Mg # 54 60 55 59 26 55 13.7 60 51 28 25 72 72 29 73 74(La/Yb)n 2.1 5.1 4.6 2.2 2.9 2.02 5.1 7.7 9.6 45 62 19.4 25 0.45 3.7 5.6

b.d.l. = below detection limit.

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et al., 2004). In Fig. 4 the Ms-bearing amphibolites show TiO2 andAl2O3 contents similar to, or higher than, MORB, although with lowerSiO2 contents. On the other hand, Ms-bearing trondhjemites overlapthe compositions of slab-derived melts and Jamaican-type adakites,and the Qtz–Ms rocks are even more evolved (i.e., richer in SiO2) thanthe latter (Table 1).

Like MORB, the Ms-bearing amphibolites have metaluminoussignatures (Fig. 5), but, owing to their variable Na2O contents (1.17–4.17 wt.%) possibly influenced by secondary mobilization, two sampleshave higher inverse agpaitic index (molar Al2O3/Na2O+K2O).

Importantly, the Ms-bearing trondhjemites have a peraluminousaffinity (i.e.; ASI=molar Al2O3/CaO+Na2O+K20=1.11–1.29) andoverlap the compositions of the primary slab melts and the Jamaican-type adakites (Fig. 5). On the other hand, the Qtz–Ms rocks plot along

the alkali feldspar-white mica mixing line (Fig. 5), accordingly theirmineralogy is dominated by quartz+phengite+plagioclase.

In the CIPW normative anorthite–albite–orthoclase (An–Ab–Or)diagram of O'Connor (1965) modified by Barker (1979), generallyused to classify acid and intermediate rocks, the Ms-bearingtrondhjemites plot in the same trondhjemitic field as the primaryand natural slab melts and the Jamaican-type adakites (Fig. 6),whereas the Qtz–Ms rocks show granitic affinity.

6.2. Rare earth elements

TheMs-bearingamphibolites are slightly enriched in LREE relative toHREE (Fig. 7a). These HREE concentrations are higher than in IAB andare similar to those of N-MORB. On the other hand, the relative LREE-

Fig. 4. Anhydrous TiO2 vs. SiO2 and Al2O3 vs. SiO2 (wt.%) diagrams. Symbols as in Fig. 3.Subducted oceanic crust-derived adakites (compilation of Wang et al., 2006, andreferences therein), primary and natural slab melts (Kepezhinskas et al., 1995, Lázaroand García-Casco, 2008, and Sorensen and Grossman, 1989), Jamaican-type adakites(Hastie et al., 2010a), MOR basalts (Arevalo and McDonough, 2010; Hofmann, 1988;Houghton R.L., 1979; Kelemen et al., 2004; Staudigel et al., 1996, Sun and McDonough,1989) and Island Arc Basalts (Kelemen et al., 2004) are shown for comparison.

Fig. 6. Molecular normative (CIPW) diagram (O'Connor, 1965), modified by Barker(1979) showing typical calc-alkaline and trondhjemite differentiation trends of acidrocks (gray lines). Symbols as in Fig. 3. Subducted oceanic crust-derived adakites,natural slab melts and Jamaican-type adakites are shown for comparison (sources as inFig. 4).

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enrichment of these patters (La/Ybn=2.1–5.1) is similar to thatobserved in island arc basalts (IAB) thus differing from normal MORBcompositions (Fig. 7a). The positive Eu anomaly (Eu/Eu*=0.98–1.45;Eu/Eu*=Eun(Smn*Gdn)1/2) in some sample can be explained by thepresence of epidote that preferably incorporates this element comparedwith Sm and Gd.

Fig. 5. IAI (inverse agpaitic index = molar Al2O3/Na2O+K2O)-ASI (alumina saturationindex =molar Al2O3/CaO+Na2O+K2O) diagram with the projections of alkali-feldspar and white mica compositions plotted for reference. Symbols as in Fig. 3.Compositional fields from the same references as in Fig. 4.

The Ms-bearing trondhjemites are slightly enriched in LREErelative to HREE (Fig. 7b). The normalized patterns are slightly tostrongly fractionated (La/Ybn=2 to 62), show positive Eu anomalies(Eu/Eu*=1.1–10) and are very similar to those of primary and naturalslab melts (Fig. 7b).

The REE concentrations in Qtz–Ms rocks are similar to those in Ms-bearing trondhjemites, except for slightly higher LREE abundances insome samples and higher HREE contents CV278a-I (Fig. 7c) due to thepresence of garnet (Fig. 2d). The chondrite-normalized REE patterns ofthese rocks are fractionated (La/Ybn=4 to 25, except in CV278a-I thathas La/Ybn=0.45, again due to the presence of garnet, see Fig. 2)(Fig. 7c).

6.3. Other lithophile trace elements

The distribution of lithophile trace elements in Ms-bearingamphibolites indicates important deviations from N-MORB composi-tion, with significant enrichments in Rb, Ba, Nb, Ta, Pb and Sr (Fig. 8a).On the other hand, concentrations of Th, Zr, and Y are homogeneousand comparable to those in N-MORB (Fig. 8a).

The Ms-bearing trondhjemites have abundances of Th, Nb, Ta, Sr,Hf and Zr very similar to those of primary slab melts, but compared tothe latter they are enriched in Rb, Ba, Pb and K, similar to oceaniccrust-derived adakites (Fig. 8b). The Qtz–Ms rocks are even moreenriched in LILE (Rb, Ba, K) compared with Ms-bearing trondhjemites(Fig. 8c).

In the Nb vs. Y and Ta vs. Yb diagrams (Pearce et al., 1984) the Ms-bearing acid rocks from Sierra del Convento plot in the field ofvolcanic arc rocks, thus ruling out an origin of subducted oceanicplagiogranite (Fig. 9). In these diagrams, Cenozoic adakites from anumber of localities worldwide (including Jamaica) and primary slabmelts from the Catalina Schist and Sierra del Convento mélanges arecompositionally similar to the studied Ms-bearing trondhjemitic andQtz–Ms rocks.

In the classic Sr/Y vs. Y diagram of Defant and Drummond (1990)the Ms-bearing trondhjemites and Qtz–Ms rocks plot in field of the(Jamaican-type) adakites and primary and natural slab melts

Fig. 7. Chondrite (McDonough andSun, 1995) normalizedREEpatterns of: (a)Ms-bearingamphibolites, (b) Ms-bearing trondhjemites and (c) Qtz–Ms rocks from the Sierra delConvento mélange. Compositional fields shown for comparison are from the samereferences as in Fig. 4.

Fig. 8. N-MORB (Sun and McDonough, 1989) normalized trace elements patterns of:(a) Ms-bearing amphibolites, (b) Ms-bearing trondhjemites and (c) Qtz–Ms rocks fromSierra del Convento mélange. Compositional fields shown for comparison are from thesame references as in Fig. 4.

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(Fig. 10a). Similar observations can be drawn from the (La/Yb)n vs.(Yb)n diagram (Martin, 1986), in which Ms-bearing trondhjemitesand Qtz–Ms rocks mostly coincide with the compositions of adakitesand primary and natural slab melts (Fig. 10b).

6.4. Sr–Nd–Pb isotopes

Age-corrected (114 Ma) 87Sr/86Sr ratios of Ms-bearing amphibolites(0.70354–0.70551) overlap with those of Ms-free amphibolites andhornblendites (0.70310–0.70470) but are rather more radiogenic thanthe latter. Similarly, Ms-bearing trondhjemites have age-corrected87Sr/86Sr (0.70337–0.70552) higher than Ms-free trondhjemites(0.70308–0.70322). Initial 87Sr/86Sr of Qtz–Ms rocks vary between0.70412 and 0.70569, and coincide with the values in Ms-bearingtrondhjemites (Fig. 11a).

Age-corrected 143Nd/144Nd ratios in Ms-bearing amphibolitesrange from 0.51278 to 0.51288 and are lower than in Ms-freeamphibolites and hornblendites (0.51279 to 0.51300). Initial143Nd/144Nd range from 0.51258 to 0.51304 in Ms-bearing trondhje-mites and from 0.51281 to 0.51296 in Ms-free trondhjemites. Qtz–Msrocks have initial 143Nd/144Nd ranging from 0.51242 to 0.51247(Fig. 11a).

Ms-free amphibolites and hornblendites have initial Pb isotoperatios that overlap but are generally lower than those of Ms-bearingamphibolites (Table 2). A similar relationship exists between the Pbisotopic ratios of Ms-free trondhjemites and the more radiogenic Ms-bearing trondhjemites (Fig. 11b, c). We note that the Pb isotopiccompositions ofMs-free andMs-bearing trondhjemites overlap those ofthe respective amphibolitic variety. Finally, 206Pb–207Pb–208Pb/204Pb inQtz–Ms rocks range from 18.18 to 18.70, from 15.52 to 15.61 and from37.76 to 38.33, respectively (Fig. 11b, c).

Fig. 9. Ms-bearing trondhjemites and Qtz–Ms rocks plotted in discrimination diagramsfor granitic rocks (Pearce et al., 1984) showing the fields of ocean ridge, volcanic arc(VA), syn-collisional, and within-plate (WP) granitic rocks. Symbols as in Fig. 3.Compositional fields shown for comparison are from the same references as in Fig. 4.

Fig. 10. (Sr/Y) vs. Y (a) and (La/Yb)n vs. Ybn (b) diagrams for Ms-bearing trondhjemitesand Qtz–Ms rocks with the adakite and calc-alkaline arc fields defined by Defant andDrummond (1990) andMartin (1986), respectively. Symbols as in Fig. 3. Compositionalfields shown for comparison are from the same references as in Fig. 4.

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7. Discussion

7.1. Petrogenesis of muscovite-bearing rocks from the Sierra delConvento mélange

7.1.1. Ms-bearing amphibolitesLázaro and García-Casco (2008) concluded that the protoliths of

the Ms-free amphibolites from the Sierra del Convento mélange arebasaltic rocks of N-MORB composition derived from a depletedmantle source. These authors interpreted the Ms-free amphibolites asmetamorphosed MOR basalts that underwent low degrees (~10%)partial melting during subduction. In this scenario, the associatedK-poor tonalites–trondhjemites constitute natural and primary slabmelts formed by amphibolite melting during the initial stages ofsubduction of young oceanic lithosphere at ca. 1.5 GPa and 750 °C(García-Casco et al., 2008a; Lázaro et al., 2009).

The compositions of Ms-bearing amphibolites are relativelyenriched in LREE and several LILE compared with the Ms-free varietyand N-MORB but nevertheless present similar Ti and HREE concen-trations (Figs. 7a and 8a).This suggests that the petrogenesis of theMs-free andMs-bearing amphibolite blocks in the Sierra del Conventomélange are linked but that the compositions of the latter wereprobably modified during moderate to high temperature metamor-phism in the subduction zone. The presence of primary muscovite(Fig. 2a), the enrichment in LREE, Rb, Ba and Sr (Figs. 7a and 8a) andthe higher Sr–Pb and lower Nd radiogenic isotopic ratios (Fig. 11)support the idea that the Ms-bearing amphibolites interacted withfluids derived from sediments and/or altered MORB during subduc-

tion/accretion in the subduction channel. The Ms-bearing amphibo-lites are also relatively enriched in Nb and Ta compared to N-MORB(Fig. 8a).The high-field strength elements (HFSE=Nb, Ta, Zr, Hf, Ti)have generally been assumed to be immobile during subduction zonemetamorphism and slab dehydration reactions (Pearce, 1983).However, more recently several authors have demonstrated therelative mobility of HFSE by high T fluids/melts (Elliott, 2003; Schmidtet al., 2009). In particular, our data support the conclusions ofWoodhead et al. (2001), who showed that in island arc systems HFSEmay be transported by aqueous fluids derived from the dehydratingslab.

We thus infer that the Ms-bearing amphibolites acquired theirpetrographic and geochemical characteristics during high grademetamorphism and partial melting triggered by the infiltration ofslab fluids derived by dehydration of subducted sediments and/oraltered MORB.

7.1.2. Ms-bearing trondhjemitesField relations, major, trace element and isotopic compositions of

the Ms-bearing trondhjemites are similar to those of primary slabmelt, Ms-free (K-poor) trondhjemites described in the Sierra delConvento mélange (Figs. 4, 5, 6, 7b, 8b, 9, 10 and 11), and point to asimilar origin for these rocks. Based on trace element and Sr–Ndisotopic data, Lázaro and García-Casco (2008) showed that the Ms-free trondhjemites in the Sierra del Convento mélange weregenerated by low degrees of partial melting of Ms-free amphibolites,Ms-bearing trondhjemites were thus most likely generated by similarprocesses, i.e., partial melting of Ms-bearing amphibolite or of Ms-free

Fig. 11. Whole rock Sr–Nd (a) and Pb (b, c) isotopic ratios of samples from the Sierra delConvento mélange corrected to 114 Ma. Symbols as in Fig. 3. CrossedWhite circles: (Ms-free) amphibolites and hornblendites; crossed black triangles: (Ms-free) trondhjemites.Other symbols as in Fig. 3. Field of age-corrected isotopic ratios of Atlantic marinesediments (dashed line) fromBenOthmanet al. (1989) and Jolly et al. (2006). Field of age-corrected isotopic ratiosofCenozoicadakites (linefilledfield) is fromAguillón-Robles et al.(2001), Defant et al. (1992), Kay et al. (1993), Samaniego et al. (2005) and Stern and Kilian(1996). Field of altered MORB (gray area), from Staudigel et al. (1996). Mixing linesbetween the isotopic compositions of the most depleted trondhjemite (SC-21) and thoseof different Atlantic sediments (white stars) are shown. Mixing wasmodeled between anN-MORB amphibolite (Pb = 0.489 ppm, Nd= 11.179 ppm, Sr = 113.2 ppm, Hofmann,1988), assumed tohave the isotopic composition of SC-21, andfluidsderived fromAtlanticsediments (Pb = 280 ppm, Nd = 171 ppm, Sr = 2734 ppm, and Pb = 280 ppm,Nd = 747 ppm, Sr = 2648 ppm, Straubet al. 2004 and references therein). Labels indicatethe percentages of fluid contribution.

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amphibolite fluxed by a fluid enriched in LILE (e.g., Rb, Ba) probablyderived from sediments and/or altered MORB.

The genetic relationship betweenMs-free amphibolites and trondh-jemites is reinforced by the similarity of the Pb isotope compositions ofthese rock-types (Fig. 11b, c). The Ms-bearing amphibolites andtrondhjemites also have overlapping isotopic compositions but gener-ally have more radiogenic Sr–Pb and less radiogenic Nd isotopic ratiosthan the muscovite-free samples (Fig. 11). This suggests that the Sierradel Convento mélange records partial melting events triggered byagents (i.e., fluids) with originally different isotopic compositions.

The isotopic signature of theMs-bearing rocks canbe explainedby theinteraction between a MORB-like amphibolite (whose isotopic compo-sition is typified by that of the most depleted trondhjemite, SC-21) and afluid derived from Atlantic sediments which may be used as a proxy ofpotential subducted sediments. In particular, the contribution of up to 2%of this fluid to the Sr–Nd–Pb isotopic budgets of the amphibolitic sourceexplains the composition of the Ms-bearing amphibolites and trondhje-mites (Fig. 11).We thus conclude thatwhile thepartialmeltingofMs-freeamphibolites was probably triggered by the flux of fluids fromdehydration of the subducted oceanic serpentinized mantle (Lázaro andGarcía-Casco, 2008), that of Ms-bearing amphibolites was probablycaused by a flux of fluids derived from subducted sediments and alteredbasaltic crust.

7.1.3. Qtz–Ms rocksBlanco-Quintero et al. (2011a) considered two hypotheses for the

origin of the Qtz–Ms rocks: they crystallized either from (1)hydrothermal fluids that evolved from the differentiation of trondhje-mitic–pegmatitic melts, or (2) from fluids produced exclusively by thedehydrationof subducted sediments. Although the trace elementdata ofBlanco-Quintero et al. (2011a) do not clearly discriminate betweenthese hypotheses, these authors infer that the Ba-enrichment of theQtz–Ms rocks supports a sediment-related origin of their parentalfluids.However, the Sr–Nd–Pb isotopic data presented here (Fig. 11) indicatethat:

(a) The Qtz–Ms rocks were not formed by precipitation of fluidsexclusively derived from sediments, as their isotopic compo-sitions are variable and show different contributions of asedimentary component;

(b) The parental fluids of these rocks are derived from differentsources (principally MORB-related amphibolites and sub-ducted metasediments) that contributed to their trace elementbudgets in different proportions. In particular, the unradiogenicPb isotopic signatures of two Qtz–Ms samples (Fig. 11b, c)agree with the evidence that Pb in arc-related rocks is mainlyderived from the subducted oceanic igneous crust (Regelouset al., 2010). On the other hand, Ba was most likely transportedby fluids mainly released by dehydration of metasediments(Blanco-Quintero et al., 2011a);

(c) The Qtz–Ms rocks probably crystallized from fluids derived fromdifferentiation of trondhjemitic–pegmatitic melts. The isotopiccompositions of these rocks reflect the composite source of theirparental melts, i.e., MORB-related amphibolites fluxed by fluidsderived from sediments and/or altered basaltic crust.

7.2. Implications for fluid circulation in serpentinitic subduction channels

The petrological and geochemical characteristics of theMs-bearingand Ms-free rocks studied here provide evidence for three differentsources of fluids in the subduction environment. As established byLázaro and García-Casco (2008), the main agent influencing thepetrogenesis of the Ms-free rocks is a depleted serpentinite-derivedfluid (dark gray arrows in Fig. 12). On the other hand, for the Ms-bearing rocks, either altered MORB-derived fluid (light gray arrows inFig. 12), or sediment-derived fluid (black arrows in Fig. 12) may have

Table 2Sr, Nd and Pb radiogenic isotope compositions of samples from the Sierra del Convento mélange. Ratios corrected for radioactive decay since 114 Ma are also shown. Elemental concentrations by ICP-MS are from Lázaro and García-Casco(2008) and unpublished data.

Sample Rock-type 87Sr/86Sr ± Rb(ppm)

Sr(ppm)

87Sr/86Sr(114 Ma)

143Nd/144Nd

± Sm(ppm)

Nd(ppm)

143Nd/144Nd(114 Ma)

206Pb/204Pb

± 207Pb/204Pb

± 208Pb/204Pb

± U(ppm)

Th(ppm)

Pb(ppm)

206Pb/204Pb(114 Ma)

207Pb/204Pb(114 Ma)

208Pb/204Pb(114 Ma)

CV53x-1 Amphibolite 0.703277 28 1.3 272 0.703254 0.513091 10 5.4 16 0.512940 18.7307 11 15.5604 10 38.086 3 0.51 0.20 1.5 18.3371 15.5412 38.036CV62b-1 Amphibolite 0.703317 14 1.4 169 0.703277 0.513105 10 3.3 9.1 0.512941 18.4095 11 15.5286 9 37.921 3 0.082 0.11 0.76 18.2899 15.5228 37.867CV62a Amphibolite 0.703155 56 1.6 130 0.703096 0.513170 10 2.7 7.1 0.513000 18.6123 6 15.5667 6 38.192 2 0.029 0.061 0.52 18.5507 15.5637 38.149CV230b Amphibolite 0.704724 3 2.2 426 0.704699 0.513133 2 4.4 13 0.512977 18.5446 3 15.5849 4 38.289 1 0.20 0.17 7.5 18.5143 15.5834 38.281CV228e Amphibolite 0.703171 21 2.0 165 0.703115 0.513109 15 5.1 15 0.512949 b.d.l. b.d.l. b.d.l. - - - – – –

CV61 Hornblendite 0.703871 49 3.0 74 0.703683 0.513046 10 1.6 4.4 0.512878 18.5870 7 15.6013 6 38.410 2 0.038 0.19 0.77 18.5323 15.5987 38.321CV139b Hornblendite 0.704570 14 9.7 202 0.704344 0.512930 10 3.4 11 0.512792 18.4283 22 15.5323 19 37.975 5 0.14 0.50 2.7 18.3701 15.5294 37.908CV230c Ms-amphibolite 0.705548 3 10 531 0.705456 0.512987 3 7.4 30 0.512877 18.7278 4 15.6023 4 38.528 1 1.1 3.3 6.6 18.5475 15.5935 38.345CV139a Ms-amphibolite 0.705481 14 16 510 0.705335 0.512921 10 4.4 14 0.512781 18.9822 4 15.6223 4 38.732 1 0.40 0.63 11 18.9420 15.6203 38.711CV140a Ms-amphibolite 0.703745 42 20 458 0.703540 0.512931 10 5.4 23 0.512823 19.0314 3 15.5677 4 38.702 1 0.78 3.1 1.5 18.4597 15.5398 37.951CV230a Ms-amphibolite 0.705905 14 22 259 0.705506 0.512997 10 2.6 8.7 0.512861 18.7336 5 15.6092 5 38.477 1 0.61 0.84 5.4 18.6073 15.6030 38.419SC-22 Trondhjemite 0.703266 3 7.6 708 0.703215 0.513080 7 0.43 1.6 0.512960 18.7558 10 15.5732 11 38.172 3 0.59 0.32 1.9 18.4013 15.5559 38.109CV53c Trondhjemite 0.703168 13 2.3 733 0.703153 0.512925 36 1.4 7.2 0.512839 18.6037 4 15.5640 5 38.204 1 0.30 0.58 2.2 18.4494 15.5565 38.106CV227b Trondhjemite 0.703132 2 0.80 605 0.703126 0.513004 8 0.26 1.3 0.512915 18.5426 5 15.5624 5 38.153 1 0.079 0.16 1.6 18.4872 15.5597 38.117SC-21 Trondhjemite 0.703088 14 1.3 648 0.703079 0.513022 20 0.82 3.8 0.512923 18.2701 7 15.4973 5 37.732 1 0.18 0.43 1.7 18.1543 15.4916 37.641CV228a Trondhjemite 0.703096 21 1.1 619 0.703088 0.512920 10 0.54 2.2 0.512808 18.5542 4 15.5726 4 38.212 1 0.18 0.38 1.4 18.4126 15.5657 38.112CV201h Ms-trondhjemite 0.706294 4 31 97 0.704809 0.513203 7 0.50 1.4 0.513040 n.a. n.a. n.a. - - - – – –

CV201g Ms-trondhjemite 0.706007 3 16 86 0.705132 n.a. - - – 18.6622 4 15.6103 4 38.401 1 1.5 1.6 14 18.5380 15.6043 38.359CV230e Ms-trondhjemite 0.703834 6 20 410 0.703601 n.a. - - – 18.6465 3 15.6023 3 38.502 1 0.055 0.035 4.8 18.6337 15.6017 38.499cSC-20 Ms-trondhjemite 0.703549 5 15 389 0.703367 0.513133 2 0.17 0.72 0.513028 18.5947 6 15.5791 5 38.217 1 0.12 0.22 3.1 18.5536 15.5770 38.192CV201a Ms-trondhjemite 0.705817 14 12 192 0.705517 0.512745 31 1.0 2.6 0.512578 18.5890 3 15.5929 3 38.343 1 0.63 0.93 20 18.5538 15.5912 38.326CV201d Qtz-Ms rock 0.716958 5 57 21 0.704120 n.a. - - – 18.6826 7 15.5414 6 38.196 2 0.90 1.6 2.3 18.2474 15.5202 37.949CV201f Qtz-Ms rock 0.720487 7 79 24 0.705211 n.a. - - – 19.1461 5 15.6174 5 38.563 2 2.6 6.4 3.0 18.1778 15.5702 37.760CV53e-1 Qtz-Ms rock 0.708927 14 88 100 0.704785 0.512550 10 0.79 2.8 0.512422 18.8645 5 15.6146 6 38.625 2 0.77 4.3 5.4 18.7046 15.6068 38.331CV 278-a Qtz-Ms rock 0.706729 28 40 181 0.705692 0.512709 21 1.0 1.9 0.512466 n.a. n.a. n.a. - - - – – –

n.a. = not analyzed; b.d.l. = below detection limit.

351C.Lázaro

etal./

Lithos126

(2011)341

–354

Fig. 12. Schematic model for a serpentinite subduction channel (modified from Bebout, 2007 and Guillot et al., 2009.). The serpentinite subduction channel consists of a melange ofexotic metabasalts, metasediments and metaperidotite blocks derived from the slab and the mantle wedge included in a serpentinitic matrix. The paths of fluids derived fromsubducted serpentinites (dark gray arrows), oceanic basalts (light gray arrows) and sediments (black arrows) are depicted.

352 C. Lázaro et al. / Lithos 126 (2011) 341–354

triggered partial melting of Ms-bearing amphibolites producing theMs-bearing trondhjemites, as indicated by the petrological andgeochemical characteristics of these rocks presented in this work.These three fluid sources can interact and modify the composition ofthe protoliths, melts and residual rocks in the subduction channelproducing variable geochemical signatures.

Elevated concentrations of LILE (e.g., Ba, K, Rb, Cs, Sr), U, and Pbrelative to HFSE (e.g., Nb, Ta, Zr, Hf, Ti) in arc magmas are considered keyindicators of fluid addition to theirmantle sources (Breeding et al., 2004).These fluids are mainly released by dehydration of subducting alteredMORB and sediments of the slab (Pearce, 1983). Transfer of LILE-, U-, andPb-enriched fluids to the mantle wedge at sub-arc depths may triggerpartial melting of peridotite and generate basaltic magmas withcharacteristic geochemical composition (e.g., Breeding et al., 2004;Pearce, 1983). However, these enriched fluids may also react with theoceanic crust incorporated in the subduction channel at the plateboundaries interface triggering its partial melting upon appropriate P–Tconditions, and forming melts derived from a MORB source but having asedimentary geochemical imprint (e.g., Gao et al., 2007).

We interpret the petrogenesis of theMs-bearing andMs-free rocksfrom the Sierra del Convento mélange in a subduction channel sce-nario where different type of fluids, evolved from different sources,interact between them and with the rocks present.

Due to the low viscosity and density of the serpentinite in thesubduction channel and its triangular shape, the accreted highpressure blocks are progressively exhumed during on-going subduc-tion and may crop out in subduction-related complexes (Gerya et al.,2002). Exhumation of subduction-related mélanges in eastern Cubawas facilitated by fluid fluxes that produced large scale convectiveflow (Blanco-Quintero et al., in press).

8. Conclusions

Major, trace element and Sr–Nd–Pb isotopic compositions of Ms-bearing amphibolites from the Sierra del Convento mélange indicatetheir originalMORBaffinity subsequentlymodifiedbyfluidsfluxed from

subducted sediments and/or altered basalts. Fluid availability was thekey factor controlling the melting process. P–T conditions experiencedby these rocks and fluid availability during subduction/accretion to themantle wedge caused their partial melting and the related crystalliza-tion of Ms-bearing (K-rich) trondhjemitic melts. The trondhjemiticmelts did not escape the subducted slab but represent natural andprimary slab melts crystallized at depth in the subduction zone. Thepetrographic and geochemical differences between Ms-free and Ms-bearing trondhjemites in the Sierra del Conventomélange are a result ofthedifferent sources offluids (subducted serpentinites vs. alteredMORBand sediments) that interacted with their amphibolitic sources and thedegree of interaction. The hydrothermal Qtz–Ms rocks associated withMs-bearing trondhjemites have a greater sedimentary imprint than thelatter as shown by their higher concentrations of fluid mobile elements(Rb, K, Ba) andmore enriched Sr–Nd isotopic compositions. These rocksprobably crystallized from fluids derived by the differentiation oftrondhjemitic–pegmatitic melts.

Supplementarymaterials related to this article can be found onlineat doi:10.1016/j.lithos.2011.07.011.

Acknowledgments

The authors thank Javier Escuder-Viruete, David Buchs and theeditor Andrew Kerr for their useful comments and suggestions, whichsubstantially improved the paper. Jane H. Scarrow is also thanked forher comments, suggestions and general revision of this paper. Weappreciate financial support from Spanish MEC and MICINN pro-jectsCGL2006-08527/BTE and CGL2009-12446. C.M.'s research hasbeen supported by a Marie Curie Intra-European Fellowship withinthe 7th European Community Framework Programme. This is acontribution to IGCP-546 “Subduction zones of the Caribbean”.

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