Adakitic-like magmatism in western Ossa–Morena Zone (Portugal): Geochemical and isotopic constraints of the Pavia pluton

Lithos 160–161 (2013) 98–116

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Adakitic-like magmatism in western Ossa–Morena Zone (Portugal): Geochemical and isotopic constraints of the Pavia pluton S.M. Lima a, c,⁎, A.M.R. Neiva a, c, J.M.F. Ramos b a b c

Geosciences Center, University of Coimbra, Largo do Marquês de Pombal, 3000-272 Coimbra, Portugal LNEG, Rua da Amieira, Apartado 1089, 4466-901, S. Mamede de Infesta, Portugal Department of Earth Sciences, University of Coimbra, Largo do Marquês de Pombal, 3000-272 Coimbra, Portugal

a r t i c l e

i n f o

Article history: Received 26 March 2012 Accepted 11 November 2012 Available online 29 November 2012 Keywords: Ossa–Morena Zone Pavia pluton Adakitic rocks Geochemistry Sr–Nd–O isotopic compositions

a b s t r a c t Granitic rocks are a major component of the Earth's continental crust and occur in a wide variety of tectonic settings. Their chemical and isotopic characterization is crucial to the recognition of the potential sources and mechanisms involved in their generation. In this study, we present the first whole rock chemical and isotopic (Sr–Nd–O) data for the Pavia pluton (328–317 Ma), located near the western border of the Ossa–Morena Zone (Évora Massif, Portugal). Major and trace element geochemistry suggests that the different granitic phases composing this intrusive body (enclaves, granites (s.l.) and crosscutting dikes) represent independent magma pulses and the majority is similar to TTGs and adakites. The little Sr–Nd–O isotopic variation, with (87Sr/86Sr)328 = 0.70428–0.70560, εNd328 ranging between −3.4 and + 0.4 and δ18O varying from + 5.6‰ to + 8.4‰ implies an isotopically similar protolith for all phases. The most viable mechanism for the generation of the Pavia pluton adakitic-like magmatism is assimilation–fractional crystallization of a mantlederived magma. This mechanism was also invoked to explain the genesis of other plutons within the Évora Massif but they have a distinct chemistry (typical arc calc-alkaline rocks). The chemical differences between them and the Pavia pluton granitic rocks are interpreted as the result of lower degrees of crustal assimilation and higher degrees of contamination of mantle-derived magmas by the sinking slab (after subduction blocking and subsequent slab break-off). © 2012 Elsevier B.V. All rights reserved.

1. Introduction The origin and analogy of Archean TTGs and modern adakites are still the center of passionate debate (e.g. Castillo, 2012; Condie, 2005; Hastie et al., 2010; Hoffman et al., 2011; Martin, 1999; Martin et al., 2005; Moyen, 2009, 2011; Moyen and Martin, 2012; Rapp et al., 2010; Smithies, 2000). Both terms are commonly used not only for the characteristic chemical composition (high-silica and sodic igneous rocks with high Sr/Y and LaCN/YbCN ratios), but also for their petrogenetic connotation. Adakites usually occur in subduction-related environments resulting from partial melting of hot, hydrated and young (b25 m.y.) oceanic crust metabasalts (Defant and Drummond, 1990; Martin, 1999; Martin et al., 2005) later modified by interaction with peridotitic mantle wedge (e.g. Lázaro et al., 2011) or melting of mantle peridotite metasomatized by slab-melts (e.g. Mahlburg Kay et al., 1993). The first model is directly associated with subduction and is responsible for the formation of high-silica adakites (HSA), whereas the second model is indirectly related to subduction and is responsible for the formation of ⁎ Corresponding author at: Geosciences Center, University of Coimbra, Largo do Marquês de Pombal, 3000-272 Coimbra, Portugal. Tel.: +351 239860521; fax: +351 239860501. E-mail addresses: [email protected] (S.M. Lima), [email protected] (A.M.R. Neiva), [email protected] (J.M.F. Ramos). 0024-4937/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.lithos.2012.11.020

low-silica adakites (LSA) (Martin et al., 2005). However, Danyushevsky et al. (2008) are of the opinion that the distinction between the low-silica and high-silica varieties is not straightforward and that the primitive magnesian andesites are parental to evolved adakites, which is consistent with the previous line of thoughts (Yogodzinski and Kekemen, 1998). Adakitic-like melts can also be produced by assimilation and fractional crystallization (AFC) of parental basaltic magmas (e.g. Bourdon et al., 2002; Castillo et al., 1999; Macpherson et al., 2006), partial melting of delaminated lower crust (e.g. Karsli et al., 2010; Wang et al., 2006) or partial melting of thickened lower crust (e.g. Guan et al., 2012; Karsli et al., 2011; Muir et al., 1995; Petford and Atherton, 1996; Xiong et al., 2003; Yu et al., 2012). The Iberian Massif (IM) corresponds to the southwestern extension of the European Variscan Belt. Based on differences in the Lower Paleozoic sedimentary record, which are interpreted to reflect their relative proximity to the Gondwana margin (Fernández-Suárez et al., 2011), structure, magmatism and metamorphism, the IM is divided into six main units (Fig. 1a). The Ossa–Morena Zone (OMZ; Fig. 1b) is one of these tectonostragraphic divisions and corresponds to a part of a continental magmatic arc (Armorica) accreted to the Iberian Autochthon (outer continental margin of Gondwana) near the West African Craton (Sánchez-García et al., 2008). The time of accretion is still debated. Some authors (e.g. Quesada, 2006; Ribeiro et

S.M. Lima et al. / Lithos 160–161 (2013) 98–116

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Fig. 1. a) Zonal division of the Iberian Massif: CZ — Cantabrian Zone; WALZ — West Asturian Leonese Zone; GTMZ — Galicia–Trás-os-Montes Zone; CIZ — Central Iberian Zone; OMZ — Ossa–Morena Zone; SPZ — South Portuguese Zone. b) Simplified geological map of the Ossa–Morena Zone. The location of the studied area is given in both figures. Panel a is redrawn from Sánchez-García et al. (2008). Panel b is modified after Etxebarria et al. (2006).

al., 2007) defend that Armorica was accreted to Gondwana during the Cadomian Orogeny (650–550 Ma), whereas others (e.g. GómezPugnaire et al., 2003; Simancas et al., 2001) argue that the suture is Variscan in age. To the south, the OMZ contacts with the South Portuguese Zone (SPZ) which corresponds to the Avalonia or Meguma terrane (e.g. Murphy et al., 2011 and references therein) already accreted to Laurussia during the Caledonian Orogeny. The SPZ collided against Armorica (plus Gondwana), as the result of the Rheic Ocean closure, during the Variscan Orogeny (480–290 Ma). The OMZ is characterized by polyphase ductile deformation and metamorphism related to a complex evolution that includes two major tectonothermal episodes of Cadomian and Variscan ages. The Variscan orogenic events affected both the Cadomian basement and the Paleozoic cover. Magmatism is characterized by the small size of plutonic rocks, common appearance of basic (gabbroic) rocks, frequent time–space association of basic and acid rocks (bimodal magmatism) and important volcanic and subvolcanic events (Sanchez-Carretero et al., 1990). Jesus et al. (2007) suggest the occurrence of three main magmatic events: 1) early mantle-derived orogenic magmatism triggered by subduction (ca. 370–360 Ma); 2) intense magmatism both in the SPZ and OMZ southern border as the result of subduction blocking and subsequent (inferred) slab break-off (~355–345 Ma) and; 3) late collisional magmatism involving mixing of mantle and crust-derived melts as the result of rapid crustal uplift/erosion near the OMZ/SPZ

suture (~330–325 Ma). Care must be taken when considering the age intervals above as they were defined using a limited number of analyses (35) from the Ossa–Morena southern border and some have a large error, up to ±18 m.y. In this paper we characterize the Pavia pluton, which is part of the Évora Massif and is located in the western limit of the OMZ (Portugal), using whole rock major and trace element geochemistry and Sr–Nd–O isotopic data. The integration of the data allows us to confirm that this pluton was constructed by the amalgamation of several batches of magma, as suggested by the geochronological data (Lima et al., 2012a), and identify, for the first time, rocks with a chemical signature similar to adakites that contrasts with the typical arc calc-alkaline signature observed in other plutons of the Évora Massif (Antunes et al., 2010, 2011a, 2011b; Moita, 2008; Moita et al., 2005, 2009). 2. Geological setting The Pavia pluton is located in the western part of the OMZ, in the Évora Massif (sensu Carvalhosa, 1983). The Évora Massif was mainly affected by a clockwise metamorphic path with distinct series of metamorphic facies indicative of a complex distribution of tectonic processes involving crustal extension under transcurrent regime of deformation. Based on structural, metamorphic and lithological criteria, this massif is divided into three sectors (Montemor-o-Novo

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Shear Zone (MNSZ), Évora High-grade Metamorphic Terrain (EHMT) and Évora Medium-grade Metamorphic Terrain (EMMT); Fig. 1b). The three sectors are bounded by transcurrent faults (Pereira et al., 2007). The EHMT constitutes the central sector of the Évora Massif and is partially composed by high-amphibolite and amphibolite–granulite facies rocks exhumed, during the Early Carboniferous, as the result of orogenparallel movements. The uplift and decompression of this high-grade unit may be on the origin of the observed voluminous magmatism along the EHMT–EMMT boundary (Pereira et al., 2012). The Pavia pluton is located near this limit. It is a Carboniferous intrusive body elongated E–W and, although mainly granitic (s.s.) in composition, comprises rocks ranging from tonalite to two-mica granite (Fig. 2). The elliptical shape, the almost parallel E-trending lithological contacts and the occurrence of two main dike systems orientated perpendicularly (predominantly NE–SW and NW–SE) and with high length/width ratios indicate emplacement under stress. It intruded the Neoproterozoic Gneiss–Migmatite Complex, metamorphosed in the Early Carboniferous, and Middle/Upper Cambrian–Lower Ordovician (?) schists, metabasites and metapelites (Moura and Carvalhal Formations; Pereira et al., 2007). Based on ID-TIMS U–Pb ages, the Pavia pluton is divided into two domains. Domain I is constituted by tonalite (G1), trondhjemite (G2T) and granodiorite (G2G) emplaced in the inner part of the pluton at 328 Ma and domain II is constituted by the flanking granodiorites (G3, G4 and G5) and contemporaneous and widespread two-mica granite (G6) emplaced at ~324 Ma (Lima et al., 2012a). Amphibolites/metabasites occur as an approximately 800 meter-thick band mixed with G1 and G2, marking the contact between these rocks and mainly within G6. Meter-sized enclaves of tonalitic (Enc.4) and granodioritic (Enc.5, 6) compositions occur within G4 and G5, respectively (Table 1). They are petrographically and mineralogically distinct from the host rocks and from the other Pavia pluton outcropping tonalite and granodiorites and thus were distinguished in the field. The chemical and isotopic data (this study) and ID-TIMS U–Pb dating (Lima et al., 2012a) support the distinction. Their limits were not observed due to the absence of continuous non-altered outcrops in the region. Fine-grained dioritic (Enc.1) and quartz-dioritic (Enc.2, 3) mesocratic (M≈50%) enclaves (Table 1), with ovoid shapes and sharp, although lobated, contacts with the host rocks and lenticular to ovoid surmicaceous enclaves were rarely observed. Several rhyodacitic porphyries, microgranitic dikes (Table 1), pegmatites and quartz dikes cut the different lithologies. They are

contemporaneous (emplaced at 328 Ma and 324 Ma) to late intrusions (319–317 Ma, Lima et al., 2012a, 2012b). The study and characterization of the pegmatite and quartz dikes are beyond the scope of this paper and for this reason their genetic link with the main granitic phases will not be addressed. The main characteristics and mineralogical association of the different granitic phases are presented in Table 1. 3. Materials and methods Whole rock chemical analyses were determined at Actlabs, Canada. The majority of the analyzed elements were determined by a fusion process that uses lithium metaborate and lithium tetraborate and analyzed in a Perkin Elmer Sciex ELAN 6000 for major elements, Sc, V, Ba and Sr and in a 9000 ICP-MS for trace and rare earth elements. Lithium and nickel were determined by multi-acid digestion and analyzed using a Varian Vista 735 ICP. Chromium and chlorine were determined by instrumental neutron activation analysis and measured in a high purity Ge detector. Sulfur was determined by combustion infrared detection (IR) and measured as sulfur dioxide in a Leco CNS 2000. Fluorine was determined by ion selective electrode technique and an automated fluoride analyzer from Mandel Scientific was used for the analysis. FeO was determined by titration with a standardized KMnO4 solution at the Chemical Laboratory of the Department of Earth Sciences, University of Coimbra. Precision calculation was based on replicate analysis of 15 samples and, in the course of this study, it was generally better than 1% for major elements, 3% for FeO, 6% for loss on ignition (LOI), 5% for trace elements, TiO2 and P2O5 and 3% for rare earth elements. Rubidium–strontium isotopic ratios were measured using a Thermo Fisher Scientific Instrument (MC-ICP-MS) at SGIker facility, University of the Basque Country/EHU (Spain). Raw ratios were processed in a similar way to that of Balcaen et al. (2005). Instrumental mass bias was corrected using an 88Sr/86Sr ratio of 8.375209 (Steiger and Jäger, 1977) and the exponential law. The presence of trace amounts of Rb was monitored at the 85Rb mass and the 87Rb interference on 87Sr was subtracted considering an 85Rb/87Rb ratio of 2.59265 (Steiger and Jäger, 1977) and assuming for Rb the same mass bias as for Sr. 86Sr was also corrected for interference of 86Kr that comes as impurities in the Ar gas (Rosman and Taylor, 1998). The accuracy and reproducibility of the method were verified by periodic determinations under the same conditions of

Fig. 2. Geological map of the Ciborro–Aldeia da Serra area (SW border of the Pavia pluton) showing the location of representative samples given in Tables 2 and 3. Modified from Carvalhosa (1999), Carvalhosa and Zbyszewski (1994) and Zbyszewski et al. (1979, 1980).

Table 1 Main macroscopic characteristics and constituent minerals of Pavia pluton granitic phases.

Reference

Rock

Characteristics

Mineralogical Association

G1

Tonalite

Coarse-grained, foliated

Qz, Kfs, Pl, Amp, Bt, Ttn, Grt, Ep, Ap, Fe-Ti, Zrn

Enc.1

Diorite (enclave)

Elliptical shape (18/9.5 cm), very-fine grained, mesocratic, sharp limits with the host. Its orientation and foliation is concordantto the host foliation

Qz, Kfs, Pl, Amp, Bt, Ttn, Ep, Grt, Ap, Fe-Ti, Zrn

Fine-grained, porphyritic, sharp contacts with the host, usually not foliated

Qz, Pl, Amp, Bt, Fe-Ti, Mnz, Zrn

Very fine-grained, porphyritic, sharp contacts with the host, usually not foliated

Qz, Kfs, Pl, Bt, Ttn, Ep, Ap, Fe-Ti, Zrn

Domain I

P1 P2

Rhyodacite porphyry Rhyodacite-Dacite porphyry

Microgranodiorite dike

Very-fine grained, sharp limits with the host. Both concordant and discordant bodies occur. They are usually foliated

Qz, Pl, Bt, Ep, Ttn, Fe-Ti, Ap, Zrn

G2T

Trondhjemite

Medium-grained, foliated

Qz, Pl, Bt, Ttn, Fe-Ti, Ap, Zrn

G2G

Granodiorite

Medium-grained, foliated

Qz, Kfs, Pl, Bt, Ep, Ms, Ap, Fe-Ti, Mnz, Zrn

P3

Rhyodacite porphyry

Similar to P1 dikes

Qz, Kfs, Pl, Bt, Ep, Fe-Ti, Sil

G3E

Granodiorite

Qz, Kfs, Pl, Bt, Ep, Ms, Ap, Fe-Ti, Mnz, Zrn

G3W

Granodiorite

Enc.2

P4

Quartz-diorite (fine-grained mesocratic enclave) Quartz-diorite (fine-grained mesocratic enclave) Tholeiite dike

Fine to medium-grained, slightly porphyritic. Abundant fine-grained, mesocratic enclaves occur in the easternmost outcrops Medium-grained, containsrare surmicaceous enclaves and shows variations in grain size and color Lenticular to elliptical shapes (maximum 57/11 cm), very-fine grained, sharp and irregular limits with the host Lenticular to elliptical shapes (maximum 90/10 cm), fine-grained, the limits with the host are sharp but more regular than in Enc.2 Fine-grained, green colored. Itcuts discordantly the host foliation

G4

Granodiorite

Medium-grained, porphyritic

Qz, Kfs, Pl, Bt, Ms, Ttn, Ap, Fe-Ti, Mnz, Zrn

Enc.4

Tonalite (enclave)a

Coarse-grained. Macroscopicallyis very distinct from G1and G4

Qz, Kfs, Pl, Amp, Bt, Ep, Ttn, Grt, Ap, Mag, Zrn

G5

Granodiorite

Medium-grained, slightly porphyriticand intensely foliated

Qz, Kfs, Pl, Bt, Ep, Ms, Ap, Fe-Ti, Mnz, Zrn

Enc.5

Tonalite (enclave)a

Medium-grained, gneissic

Qz, Kfs, Pl, Bt, Ep, Ms, Ap, Fe-Ti, Zrn

Enc.6

Granodiorite (enclave)a

Qz, Kfs, Pl, Amp, Bt, Ep, Ttn, Ap, Fe-Ti, Zrn

M2

Microgranite dikea

Medium-grained, foliated. It is cut by a pegmatitic vein concordant with the foliation Fine-grained, intensely foliated

G6

Granite

Coarse-grained, porphyritic. Several surmicaceous enclaves and amphibolite xenoliths/restites were observed

Qz, Kfs, Pl, Bt, Ep, Ms, Ap, Fe-Ti, Mnz, Zrn Qz, Pl, Amp, Bt, Ep, Ttn, Grt, Ap, Fe-Ti, Zrn Qz, Pl, Amp, Bt, Ep, Ttn, Ap, Fe-Ti, Zrn

−

S.M. Lima et al. / Lithos 160–161 (2013) 98–116

M1

Enc.3

Domain II

Symbol

Qz, Kfs, Pl, Bt, Ap, Ilm, Mnz, Zrn Qz, Kfs, Pl, Bt, Ep, Ms, Fe-Ti, Mnz, Zrn

Domains I and II were distinguished geochronologically (Lima et al., 2012a). Mineral abbreviations as in Whitney and Evans (2010): Amp — amphibole; Ap — apatite; Bt — biotite; Ep — epidote; Fe–Ti — iron and titanium oxides; Grt — garnet; Ilm — ilmenite; Kfs — K-feldspar; Mag — magnetite; Mnz — monazite; Ms — muscovite; Pl — plagioclase; Qz — quartz; Sil — sillimanite; Ttn — titanite; Zrn — zircon. a Due to the absence of continuous outcrops, the contacts of enclaves with their host rock were not observed. For this reason, the exact dimensions are unknown, but they are at least metric.

101

102

Table 2 Representative chemical analyses of the Pavia pluton granitic rocks, western Ossa–Morena Zone. Unit

Domain I

Domain II Enc.1

P1

P2

M1

G2T

G2G

C69B

C16

C20P

C24A

C11

C30

Major elements (wt.%) 61.31 65.17 SiO2 0.82 0.67 TiO2 17.31 16.84 Al2O3 Fe2O3 1.75 1.11 FeO 3.70 2.95 MnO 0.10 0.07 MgO 2.74 1.94 CaO 5.26 4.60 4.03 4.30 Na2O 2.17 1.81 K2O P2O5 0.26 0.21 Cl 0.05 0.03 F 0.06 0.05 S 0.02 0.01 LOI 0.97 0.74 TOTAL 100.6 100.5

52.67 1.20 18.60 2.77 5.06 0.13 3.78 5.33 4.20 2.94 0.40 b.d. 0.05 b.d. 1.72a 98.9

71.56 0.28 15.76 0.29 1.53 0.03 0.79 2.47 5.37 1.78 0.09 0.01 0.03 0.02 0.60 100.6

66.01 0.54 17.26 1.19 1.92 0.06 1.25 3.74 4.95 2.03 0.18 b.d. 0.04 0.02 0.91 100.1

65.56 0.58 17.39 0.69 2.34 0.05 1.31 3.99 4.44 1.87 0.23 0.02 0.03 b.d. 0.77 99.3

65.70 0.64 17.00 1.03 2.74 0.07 1.84 4.44 4.27 1.97 0.20 0.01 0.04 0.03 0.74 100.7

Trace elements (ppm) Cr 52 39 Ni 32 25 Sc 14 9 V 99 69 Co 14 11 Cu 34 4 Rb 94 64 Cs 3.10 1.80 Ba 433 511 Sr 454 515 Tl 0.92 0.36 Nb 6.7 6.5 Ta 0.41 0.45 Hf 4.8 5.0 Zr 212 231 Y 15.1 13.0 Th 8.55 7.18 U 1.84 1.31 Li 41 30

55 30 18 139 22 330 118 5.50 739 493 0.54 11.9 0.39 7.3 361 16.4 2.13 1.11 48

37 36 4 27 4 4 43 1.10 368 596 0.39 2.6 0.16 3.1 120 8.2 3.80 1.13 22

19 21 5 44 7 3 96 5.80 609 644 0.97 4.0 0.14 4.6 217 7.4 10.20 1.22 25

23 15 4 48 7 10 72 2.60 348 567 0.32 11.8 0.78 6.1 310 12.8 10.80 3.19 43

51 30 7 68 9 8 71 2.30 473 526 0.48 7.8 0.79 4.4 193 16.0 7.53 1.56 29

Sample

C17

C27

P3

G3E

Enc.2

Enc.3

P4

G4

C66

C10

C5

C55

G3W C14

C63

C55F

C55E

C6B

C73

C75

72.94 0.25 15.02 – 1.60 0.03 0.59 1.92 4.14 3.38 0.13 0.02 0.02 0.01 0.63 100.7

68.29 0.44 16.62 0.30 2.41 0.05 1.12 3.12 4.40 2.14 0.16 0.03 0.03 b.d. 0.82 99.9

71.75 0.25 15.78 0.31 1.42 0.03 0.75 2.51 5.52 1.34 0.07 0.03 0.02 0.03 0.80 100.6

67.54 0.21 18.12 1.02 0.35 0.03 0.44 3.46 5.87 1.43 0.08 b.d. 0.02 0.02 0.60 99.2

69.07 0.27 17.76 1.55 0.24 0.05 0.65 3.56 5.72 1.09 0.07 b.d. 0.03 b.d. 0.67 100.7

69.01 0.44 16.57 0.73 2.16 0.05 1.04 3.05 4.70 2.12 0.17 0.02 0.04 0.02 0.61 100.7

69.17 0.38 16.33 2.46 0.17 0.06 0.91 2.80 4.44 2.07 0.08 b.d. 0.03 b.d. 0.82 99.7

48.13 1.05 18.56 6.44 2.81 0.19 6.13 9.12 3.07 1.78 0.30 0.06 0.06 0.01 1.80 99.5

51.12 0.91 17.61 5.56 2.81 0.18 6.22 8.87 2.99 1.60 0.33 0.04 0.06 b.d. 1.37 99.7

54.15 1.40 11.30 4.42 1.62 0.15 7.92 10.14 2.90 2.08 1.64 0.04 0.21 0.03 1.45 99.5

66.98 0.47 15.86 2.69 0.11 0.06 1.21 3.22 4.28 2.28 0.16 b.d. 0.02 b.d. 0.87a 98.2

68.19 0.41 16.52 1.90 0.54 0.04 0.98 3.15 4.92 1.64 0.16 0.02 0.03 b.d. 0.73 99.2

15 11 4 17 2 b.d. 98 3.00 526 278 0.74 5.7 0.57 2.6 97 9.9 5.79 1.82 19

22 20 6 38 5 b.d. 82 2.70 308 337 0.37 10.3 0.92 4.7 222 14.3 9.32 1.64 23

125 148 4 23 3 3 31 0.90 413 536 0.12 2.4 0.14 2.6 98 6.9 2.69 0.82 20

14 6 2 16 2 1 35 1.40 296 939 0.33 2.0 0.13 2.3 93 5.1 4.15 0.73 35

51 77 3 15 3 8 49 4.20 255 908 0.59 3.6 0.28 2.6 109 7.3 4.40 0.74 35

23 8 5 33 6 2 92 3.30 259 365 0.71 8.7 0.61 4.7 192 19.5 10.50 1.53 32

24 21 6 27 4 b.d. 97 3.40 221 297 0.46 13.8 1.07 3.9 181 24.0 11.60 30.5 40

85 27 34 255 30 60 56 2.30 511 668 0.27 10 0.42 3.0 127 27.5 1.01 0.58 35

152 47 32 219 27 110 50 2.60 369 568 0.23 10.3 0.41 3.9 176 30.5 0.94 0.60 33

296 156 28 146 24 b.d. 47 0.30 745 740 0.35 12.6 0.65 4.6 196 22.8 8.27 3.84 7

49 29 5 43 6 b.d. 69 1.50 629 456 0.32 5.1 0.39 3.6 168 5.1 6.93 0.87 22

26 39 4 35 4 b.d. 50 1.50 487 598 0.23 4.8 0.31 3.8 180 7.0 5.51 0.67 27

Enc.4

G5

Enc.5

Enc.6

M2

G6

C77

C1

C80

C2E

C79

C59

C61

64.61 0.27 20.11 – 1.59 0.03 0.65 5.11 5.79 1.16 0.11 b.d. 0.01 b.d. 0.70 100.1

69.29 0.36 16.66 0.72 1.67 0.05 0.88 2.82 5.14 1.99 0.13 0.01 0.05 0.02 0.64 100.4

61.86 0.81 17.87 1.21 3.38 0.07 2.12 4.66 4.17 2.01 0.21 0.02 0.07 b.d. 0.80 99.3

67.14 0.54 16.36 1.95 1.44 0.07 1.56 3.83 4.37 1.67 0.18 b.d. 0.06 0.01 0.71 99.9

68.78 0.39 15.88 1.48 0.51 0.03 0.56 2.17 4.19 4.19 0.12 0.02 0.04 0.01 0.61a 99.0

73.28 0.19 15.40 0.73 0.51 0.04 0.35 1.85 4.56 3.10 0.09 0.01 0.06 b.d. 0.66 100.8

72.39 0.15 15.15 0.73 0.40 0.03 0.32 1.84 4.51 3.06 0.10 b.d. 0.05 0.01 0.71 99.5

24 20 4 24 2 b.d. 24 1.30 226 1310 0.11 3.0 0.21 2.9 128 6.1 2.84 1.52 25

41 55 5 32 4 b.d. 84 2.30 418 617 0.78 5.9 0.44 3.7 144 8.4 11.50 1.60 36

32 28 16 109 13 b.d. 94 2.5 416 911 0.50 6.9 0.55 2.1 88 15.9 4.59 1.04 23

28 20 10 60 8 b.d. 79 2.70 462 491 0.57 7.7 0.75 3.4 144 15.2 6.49 2.02 42

44 59 2 40 3 b.d. 93 1.60 2424 2154 0.44 4.2 0.17 6.2 301 4.6 29.50 1.29 22

23 35 3 16 2 b.d. 100 2.50 661 629 0.68 4.8 0.50 3.0 110 9.6 7.70 1.69 47

24 33 2 12 2 1 100 4.60 461 529 0.87 3.4 0.41 1.9 67 6.7 3.84 0.82 66

S.M. Lima et al. / Lithos 160–161 (2013) 98–116

G1

Unit

Domain I G1

Domain II Enc.1

P1

P2

M1

G2T

G2G

C27

C69B

C16

C20P

C24A

C11

C30

Rare earth elements La 28.8 Ce 56.4 Pr 6.77 Nd 21.6 Sm 4.13 Eu 1.18 Gd 3.39 Tb 0.50 Dy 2.70 Ho 0.51 Er 1.44 Tm 0.20 Yb 1.23 Lu 0.18

29.5 57.7 6.84 22.5 4.11 1.19 3.09 0.44 2.34 0.43 1.19 0.16 0.98 0.14

16.0 28.9 4.23 18.4 4.60 0.85 4.50 0.65 3.27 0.57 1.53 0.20 1.29 0.21

14.4 28.9 3.21 11.1 2.24 0.69 1.89 0.25 1.34 0.24 0.69 0.10 0.64 0.10

37.0 69.5 7.64 23.7 4.05 1.20 2.53 0.28 1.20 0.20 0.53 0.07 0.45 0.07

42.2 81.1 8.60 30.1 5.38 1.38 3.88 0.51 2.58 0.45 1.21 0.17 1.09 0.18

28.2 55.7 6.43 22.6 4.78 1.35 4.04 0.57 3.00 0.55 1.50 0.21 1.28 0.16

Sr/Y Rb/Sr Nb/Ta La/Ybb Gd/Ybb Eu/Eua Tzrc °C

39.6 0.12 14.4 20.3 2.56 0.98 856

30.1 0.24 30.5 8.4 2.83 0.57 879

72.7 0.07 16.3 15.2 2.39 1.00 806

87.0 0.15 28.6 55.6 4.56 1.07 854

44.3 0.13 15.1 26.2 2.88 0.88 893

32.9 0.13 9.9 14.9 2.56 0.92 841

Sample

C17

30.1 0.21 16.3 15.8 2.23 0.94 840

P3

G3E

C66

C10

C5

17.7 35.9 4.40 14.8 2.99 0.70 2.41 0.33 1.71 0.31 0.87 0.13 0.78 0.11

27.1 52.7 5.76 20.7 4.34 0.99 3.62 0.54 2.77 0.49 1.35 0.20 1.36 0.23

11.5 23.5 2.63 9.1 1.82 0.57 1.52 0.20 1.05 0.19 0.54 0.08 0.49 0.07

15.4 29.8 3.17 10.3 1.92 0.78 1.46 0.17 0.84 0.15 0.42 0.06 0.39 0.06

28.1 0.35 10.0 15.3 2.50 0.78 790

23.6 0.24 11.2 13.5 2.16 0.74 865

77.7 0.06 17.1 15.9 2.51 1.02 789

184.1 0.04 15.4 26.7 3.03 1.37 780

G3W

Enc.2

Enc.3

P4

G4

Enc.4

G5

Enc.5

Enc.6

M2

G6

C14

C63

C55F

C55E

C6B

C73

C75

C77

C1

C80

C2E

C79

C59

C61

16.2 31.9 3.92 12.8 2.42 0.82 1.83 0.25 1.26 0.24 0.68 0.10 0.61 0.09

32.0 64.2 7.03 23.4 4.64 1.06 3.81 0.50 2.52 0.45 1.22 0.17 1.01 0.14

36.7 69.8 7.58 26.6 5.02 0.88 4.16 0.71 3.96 0.78 0.20 0.32 2.01 0.31

38.5 86.8 10.9 41.8 7.40 1.94 5.61 0.86 4.81 0.94 2.76 0.43 2.96 0.49

28.1 71.9 9.57 38.2 7.78 1.94 6.37 0.97 5.40 1.04 3.05 0.47 3.19 0.53

121.0 240.0 28.30 85.3 14.20 4.19 9.45 1.04 4.76 0.76 2.00 0.26 1.52 0.21

31.5 53.0 5.84 18.8 2.77 0.69 1.43 0.17 0.88 0.16 0.47 0.08 0.50 0.08

27.6 47.9 5.37 18.7 3.10 0.89 2.12 0.26 1.29 0.23 0.64 0.09 0.54 0.09

11.8 22.1 2.52 9.6 2.08 0.80 1.83 0.24 1.19 0.22 0.61 0.09 0.62 0.10

39.7 77.1 8.26 25.3 4.48 1.01 2.86 0.33 1.51 0.25 0.66 0.09 0.59 0.09

14.0 32.2 3.80 15.9 4.27 1.07 4.18 0.61 3.24 0.58 1.53 0.21 1.28 0.19

27.5 53.8 6.15 21.6 4.36 1.24 3.62 0.49 2.57 0.48 1.33 0.19 1.22 0.18

130.0 234.0 26.50 79.1 9.64 1.80 2.76 0.21 0.87 0.15 0.40 0.06 0.39 0.06

22.8 45.3 5.36 16.3 3.01 0.68 2.02 0.30 1.63 0.31 0.88 0.13 0.78 0.11

12.6 25.7 3.08 10.2 2.02 0.55 1.55 0.21 1.13 0.21 0.57 0.08 0.55 0.08

124.4 0.05 10.0 17.9 2.43 1.14 795

18.7 0.25 14.3 21.4 3.06 0.75 849

12.4 0.33 12.9 12.3 1.68 0.57 847

24.3 0.08 23.8 8.8 1.54 0.89 754

18.6 0.09 25.1 6.0 1.62 0.82 786

32.5 0.06 19.4 53.8 5.04 1.04 727

89.4 0.15 13.1 42.6 2.32 0.95 832

85.4 0.08 15.5 34.5 3.18 1.00 842

214.8 0.02 15.0 12.9 2.39 1.22 803

73.5 0.14 13.4 45.5 3.93 0.81 822

57.3 0.10 12.6 7.4 2.65 0.77 769

32.3 0.16 10.3 15.2 2.40 0.93 818

468.3 0.04 24.7 225.2 5.74 0.82 893

65.5 0.16 9.6 19.8 2.10 0.80 802

79.0 0.19 8.3 15.5 2.28 0.92 759

C55

S.M. Lima et al. / Lithos 160–161 (2013) 98–116

Rock references as in Table 1; b.d. — below the detection limit. a LOI values of samples with the total of major elements below 99% were corrected using the equation: LOI (corrected) = ((1.11 × FeO) − FeO) + LOI (measured) of Lechler and Desilets (1987). b Chondrite-normalized ratios (Taylor and McLennan, 1985); Eu* = (SmN + GdN) / 2. c Zircon solubility geothermometer of Watson and Harrison (1983): TZr = 12,900 / [2.95 + 0.85[(Na + K + 2Ca) / (Al× Si)] + ln(496,000 / Zrmelt)].

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S.M. Lima et al. / Lithos 160–161 (2013) 98–116

the NBS-987 strontium standard. In the first session, 8 samples were measured and the average 87Sr/86Sr ratio of this standard for 3 determinations was 0.710284±0.000012 (2σ). In the second session 23 samples were measured and the average 87Sr/86Sr ratio of this standard for 17 determinations was 0.710281±0.000020 (2σ). Samarium–neodimium isotopic ratios were measured by thermal ionization mass spectrometry (TIMS) using a Finnigan MAT-262 with 8 Faraday cups and 1 secondary electron multiplier at SGIker facility, University of the Basque Country/EHU (Spain). Possible interferences were monitored using 147Sm. The values obtained were corrected using the exponential law, taking as constant the relation 146 Nd/ 144Nd = 0.7219 (Thirlwall, 1991; Wasserburg et al., 1981). The correction of the mass fractionation and of the isotopic composition of the tracer ( 150Nd/ 149Sm) was done offline using specially written software. The accuracy and reproducibility of the method were verified by periodic determinations under the same conditions of the La Jolla neodymium standard. The average 143Nd/ 144Nd ratio for 7 determinations of this standard during the course of this study was 0.511861 ± 0.000011 (2σ). Whole rock δ 18O compositions were measured at the Laboratory for Stable Isotope Science (LSIS) at the University of Western Ontario (Canada). The analyses were done following the method of Clayton and Mayeda (1963) as modified by Borthwick and Harmon (1982) for use with ClF3. Procedure details can be found in Potter et al. (2008a, 2008b). The samples were analyzed using an Optima dual inlet-mass spectrometer whose performance is daily checked using a laboratory reference carbon-dioxide gas with known values calibrated using the accepted values of VSMOW (Vienna Standard Mean Ocean Water) and SLAP (Standard Light Antarctic Precipitation). NBS-28, NBS-30 and an internal laboratory quartz standard (calibrated to the accepted values of NBS-30 and NBS-28) were used for accuracy. During the course of this study, NBS-28 (+9.6‰), NBS-30 (+ 5.11‰), the laboratory quartz standard (+11.5‰) and the reference carbon-dioxide gas (+ 10.18‰) yielded averages values which compare very well with the accepted values for each standard. The standard deviation of replicate analyses is generally better than ± 0.2‰.

affinity between these rocks and typical calc-alkaline magmatism (Martin, 1999), although all of them plot in the “volcanic arc granite field” of Harris et al. (1986) and Pearce et al. (1984) diagrams (Fig. 4). In domain I (emplaced at 328 Ma), the SiO2 content varies from 61 to 67 wt.% in G1, from 66 to 73 wt.% in G2 and from 65 to 72 wt.% in the cutting dikes (P1, P2, P3 and M1) (Table 2). The fine-grained dioritic mesocratic enclave (Enc.1) hosted in G1 has the lowest SiO2 content. In domain II (emplaced at ~ 324 Ma), the SiO2 content ranges between 66 and 72 wt.% in the granodiorites (G3, G4 and G5), 71–74 wt.% in G6 and is equal to 69 wt.% in the microgranite dikes (M2) cutting G5. The lowest values of both SiO2 and Na2O occur in the fine-grained quartz-dioritic mesocratic enclaves (Enc.2, 3) and in the tholeiitic dike (P4) cutting G3. With the exception of these units, all granitic rocks from the Pavia pluton have 4–6 wt.% of Na2O and Al2O3 > 15 wt.%. Selected oxide and trace element diagrams versus Mg# (molar MgO/(MgO + 0.9 total Fe2O3)) are presented in Fig. 5 (domain I) and in Fig. 6 (domain II). In order to maintain the chemical variations between the different lithological units as perceptible as possible, Enc.2, Enc.3 and P4 are not represented in Fig. 6. The low Rb and Y and high Sr and Ba contents (Table 2) show that these rocks are poorly differentiated. They also present enrichment in light over heavy rare earth elements and slightly negative to slightly positive Eu anomalies (Fig. 7). 4.2. Sr–Nd–O isotopic signature

Major and trace elements were determined in a total of 56 samples comprising enclaves, granites (s.l.) and crosscutting dikes. Representative analyses are given in Table 2. Rb–Sr and δ 18O isotopic compositions were determined in 31 samples and Sm–Nd in 23 samples (Table 3).

In spite of the rocks' compositional diversity, initial 87Sr/ 86Sr and εNdt ratios, calculated to the age of emplacement of each rock (Table 3), show little variation. The ( 87Sr/ 86Sr)i ranges from 0.70428 to 0.70560 and εNdt varies between − 3.4 and +0.4. The small variation in the isotopic ratios is independent of the crystallization age and thus, distinction between rocks from domain I and rocks from domain II is not possible. One rhyodacite porphyry (P1, sample C16) has the same isotopic composition as the bulk earth and the microgranodiorite dike (M1, sample C24A) is the only sample with slightly positive εNdt. Whole rock δ18O values range between 5.6‰ in Enc.1 and 8.4‰ in M2 (Table 3). With the exception of G5 and crosscutting microgranite dike (M2) and G6, which present δ18O > 8‰ (mixed origin) and Enc.1, which has δ18O b 6‰ (altered), all the samples are derived from a mantle-like source (Taylor, 1968, 1978). Small intra-granite (s.l.) δ18O variations (b1.0‰) are observed (Table 3). These can result from closed-system fractional crystallization (e.g. Muehlenbachs and Byerly, 1982) or secondary alteration (e.g. Muehlenbachs and Clayton, 1980).

4.1. Major and trace geochemistry

5. Discussion

The granitic rocks are metaluminous to slightly peraluminous with the ASI (Alumina Saturation Index) values ranging from 0.94 to 1.14. Smaller values are observed in the fine-grained quartzdioritic mesocratic enclaves hosted in G3 (Enc.2, 3) and in the tholeiitic dike cutting the same unit (P4). All the studied rocks are magnesian, with the exception of diorite Enc.1 (alkalic), quartz-diorite Enc.2 and microgranite dike M2 (alkali-calcic), and show moderate to strong enrichment in alkalis (Fig. 3a). The majority belongs to medium-K calc-alkaline series (Fig. 3b). These units, like adakites, have more calcic compositions than the TTGs of Martin (1994) (Fig. 3c). G6, two samples of G2G and the microgranite dikes (M2) cutting G5 are very distinct from the other samples showing besides an enrichment in Na, enrichment in K relative to the TTGs of Martin (1994) and plotting in the granite field of Barker's (1979) Ab–An– Or ternary diagram (Fig. 3c, d). The remaining samples are concentrated near the trondhjemite–tonalite–granodiorite joint. These follow a trondhjemitic differentiation trend (Fig. 3c) which is a reflection of their high Na2O and low K2O/Na2O contents suggesting no

5.1. Multi-phasic construction of the Pavia pluton

4. Results

Geochronological data (Table 3) show that the Pavia pluton resulted from the amalgamation of two major and some subsidiary magmatic pulses over a period of ~ 11 m.y. Magmatism trends towards more felsic compositions through time, from tonalite to granodiorite and then granite, with rocks of granodioritic composition being injected and emplaced sequentially for about 5 m.y. Each magmatic episode was interspersed with periods of quiescence without intrusive activity. It was suggested that the cyclic character of these phenomena (magma injection versus magma storage) and the geometry of the various intrusive phases may have been a response to the prevailing transtensional tectonic regime (Lima et al., 2012a). Major and trace element variation diagrams confirm that the different granitic phases correspond to discrete magmatic pulses. In domain I, the compositional gap between tonalite G1 and granodiorite G2G and the distinct behavior of Rb and Sr with decreasing Mg# show that they are unrelated (Fig. 5). Also, the trondhjemite (G2T), although

Table 3 Whole rock Rb–Sr, Sm–Nd and δ18O isotopic data from the granites (s.l.), enclaves and crosscutting veins from the Pavia pluton, western Ossa–Morena Zone. Unit

Sample

Domain II G3E C5 C55 G3E aver. G3W C14 C62 C63 C70 G3W aver. Enc.3 C55E G4 C52 C73 C74 C75 C83 G4 aver. G5 C1 Enc.6 C2E M2 C79 G6 C49 C59 C61 G6 aver.

Rb (ppm)

Sr (ppm)

87

Rb/86Sr

87

Sr/86Sr

±2σ

(147Nd/144Nd)i

εNdt

TDMb (Ga)

δ18O (‰)

n.d. 0.512466 0.5123980

n.d. 5 6

n.d. −0.3 −0.6

n.d. 1.05 1.01

0.1473 0.1121 0.0913 0.1055 0.1177 0.1109 0.1194 0.1170 n.d. n.d.

0.512494 0.512455 0.512349 0.512466 0.512446 0.512325 0.512300 0.512391 n.d. n.d.

6 8 6 6 5 7 7 5 n.d. n.d.

n.d. 0.51220 0.51218 0.51219 0.51218 0.51221 0.51215 0.51224 0.51219 0.51209 0.51204 0.51214 n.d. n.d. 0.51212

−0.7 0.0 −1.2 +0.4 −0.4 −2.5 −3.4 −1.5 n.d. n.d.

1.50 1.04 1.00 0.96 1.12 1.22 1.37 1.20 n.d. n.d.

6.9 6.6 6.9 6.8 5.6 7.3 7.5 7.2 7.5 7.2 7.9 7.6 7.4 7.5 7.5

1.83 n.d.

0.1029 n.d.

0.512417 n.d.

7 n.d.

0.51220 n.d.

−0.4 n.d.

1.01 n.d.

28.02 17.47 n.d. 25.47

5.06 3.03 n.d. 4.23

0.1091 0.1049 n.d. 0.1004

0.512335 0.512385 n.d. 0.512292

5 6 n.d. 5

−2.3 −1.1 n.d. −2.8

1.19 1.07 n.d. 1.15

−0.3 +6.9 +8.6 +9.6 +7.8 +6.8

42.11 n.d. 19.49 n.d. 19.95 15.20

8.07 n.d. 2.75 n.d. 3.26 2.79

0.1158 n.d. 0.0854 n.d. 0.0988 0.1108

0.512409 n.d. 0.512384 n.d. 0.512378 0.512416

7 n.d. 5 n.d. 7 5

−1.0 n.d. −0.3 n.d. −1.0 −0.8

1.15 n.d. 0.91 n.d. 1.02 1.09

+13.5 +8.7 +14.9 +11.5 +12.2 +10.0

28.32 24.40 82.05 18.22 n.d. 110.2

4.41 4.52 9.60 3.06 n.d. 20.8

0.0942 0.1120 0.0707 0.1015 n.d. 0.1142

0.512327 0.512424 0.512287 0.512322 n.d. 0.512316

6 6 5 6 n.d. 7

0.51210 0.51216 n.d. 0.51208 0.51211 0.51216 n.d. 0.51220 n.d. 0.51217 0.51218 0.51218 0.51213 0.51218 0.51214 0.51211 n.d. 0.51207 0.51209

−1.8 −0.6 −1.8 −2.2 n.d. −2.9

1.05 1.09 0.92 1.12 n.d. 1.28

±σ

(87Sr/86Sr)i

εSri

Nd (ppm)

Sm (ppm)

147

0.70508 0.70502 0.70490 0.70500 0.70495 0.70430 0.70452 0.70460 0.70502 0.70503 0.70483 0.70520 0.70494 0.70526 0.70505

+11.0 +10.1 +8.5

n.d. 24.98 29.38

n.d. 4.54 4.86

n.d. 0.1098 0.0999

+9.1 0.0 +3.0 +4.1 +10.2 +10.2 +7.4 +12.7 +9.0 +13.5

19.44 12.32 28.11 32.21 26.46 25.46 17.59 22.70 n.d. n.d.

4.74 2.29 4.24 5.62 5.15 4.67 3.48 4.39 n.d. n.d.

0.70456 0.70468 0.70462 0.70496 0.70490 0.70560 0.70538 0.70521 0.70428 0.70479 0.70491 0.70499 0.70486 0.70479 0.70487 0.70526 0.70492 0.70537 0.70512 0.70517 0.70502 0.70510

+3.6 +5.3

10.73 n.d.

+9.3 +8.4 +18.3 +15.2

328.6 ± 0.7

93 64 65

450 515 504

0.5979 0.3595 0.3730

0.707876 0.706697 0.706646

3 5 5

328.5 ± 0.8 329.2 ± 0.8 327.4 ± 1.2 323.6 ± 0.4 327.6 ± 0.6 328.2 ± 0.6

118 43 96 72 71 81 98 82 76 60

493 596 644 567 526 380 278 337 294 351

0.6924 0.2087 0.4312 0.3673 0.3904 0.6166 1.0200 0.7039 0.7479 0.4945

0.708184 0.705278 0.706526 0.706288 0.706845 0.707907 0.709590 0.708488 0.708431 0.707598

4 6 5 5 5 7 7 8 3 4

324.6 ± 0.6

35 49

939 908

0.1078 0.1561

0.705057 0.705403

6 3

92 85 97 101

365 485 297 362

0.7292 0.5070 0.9450 0.8072

0.708332 0.707246 0.709965 0.709111

5 5 3 5

334.5 ± 0.5 325.4 ± 0.8

50 59 69 66 50 55

568 523 456 457 598 452

0.8072 0.3263 0.4377 0.4178 0.2418 0.3520

0.705492 0.706303 0.706942 0.706922 0.705977 0.706417

4 3 5 3 6 5

323.2 ± 0.5 327.4 ± 0.4 317.2 ± 0.6 324.4 ± 0.5

84 79 93 113 100 100

617 491 2154 562 629 529

0.3938 0.4654 0.1249 0.5817 0.4599 0.5468

0.707073 0.707085 0.705929 0.707802 0.707294 0.707540

3 6 5 6 3 5

Sm/144Nd

147

Nd/144Nd

7.9 8.2 8.1 7.8 7.4 7.6 7.8 7.7 7.2 7.3 7.2 7.6 7.7 7.3 7.4 8.3 7.9 8.4 8.1 8.2 8.2 8.2

S.M. Lima et al. / Lithos 160–161 (2013) 98–116

Domain I G1 C17 C27 C51 G1 aver. Enc.1 C69B P1 C16 P2 C20P M1 C24A G2T C11 G2G C29 C30 C66 C67 C68 G2G aver.

Agea (Ma)

Rock references are as in Table 1. a Emplacement ages determined by U–Pb ID-TIMS on zircon, monazite and titanite (Lima et al., 2012a). b TDM ages were calculated using 143Nd/144Nd = 0.51315 and 147Sm/144Nd = 0.2137 for the depleted mantle (DePaolo, 1981).

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S.M. Lima et al. / Lithos 160–161 (2013) 98–116

Fig. 3. Chemical discrimination of the different granitic phases constituting the Pavia pluton: a) Na2O + K2O–CaO vs. SiO2 diagram that allows the distinction of rock suites based on their alkalis and calcium contents into alkalic (a), alkali-calcic (a-c), calc-alkalic (c-a) and calcic (c) (Frost et al., 2001); b) K2O vs. SiO2 diagram of Peccerillo and Taylor (1976) discriminating tholeiitic (low-K), calc-alkaline (medium and high-K) and shoshonitic suites; c) Na–K–Ca ternary plot showing the field of Archean tonalite–trondhjemite–granodiorite (TTG) suites (from Martin, 1994) and typical calc-alkaline and trondhjemitic differentiation trends (from Barker and Arth, 1976); d) normative Ab–Or–An ternary plot (Barker, 1979). Rock references are as in Table 1.

Fig. 4. Tectonomagmatic discrimination diagrams: a) Rb vs. Y+Nb of Pearce et al. (1984); b) Hf-3Ta-Rb/30 of Harris et al. (1986). WPG — within plate granites; syn-COLG — syncolisional granites; post-COLG — post-collisional granites; and VAG — volcanic arc granites; ORG — ocean ridge granites. Symbols are as in Fig. 3 and rock references are as in Table 1.

spatially associated with the biotite>muscovite granodiorite (G2G), in chemical-based diagrams (Figs. 3, 5) is always plotted far from this granodiorite and close to the tonalite (G1), revealing that G2 was built up by, at least, two coeval but chemically distinct magmatic pulses. Chondrite-normalized REE patterns are in good agreement with the above as both G1 and G2T have higher ΣREE compared to G2G (Fig. 7a). The fine-grained dioritic mesocratic enclave (Enc.1) and its host (tonalite G1) are coeval (Table 3), proving the interaction of two magmas. These are characterized by similar Mg#, CaO and Sr contents (Fig. 5). Significant differences between them include the lower SiO2 content and the existence of small negative anomalies of Ce and Eu in Enc.1, not observed in G1 (Fig. 7a). The microgranodiorite dike (M1) cutting G1 is the only dated rock from domain I whose emplacement is contemporaneous of the second magmatic event, at ~324 Ma, and consequently is genetically unrelated with its host. Two petrographically and chemically distinct groups of rhyodacite porphyries cutting G1 were recognized (P1 and P2). Although both have identical Mg#, P1 is richer in SiO2 and poorer in all the other oxides and trace elements plotted in Fig. 5 and has lower LREE and MREE but similar HREE contents to those of P2. Consequently, P1 is characterized by lower LaCN/YbCN and a flatter REE pattern (Fig. 7b), indicating that P1 and P2 are unrelated. Compared to P1, the rhyodacitic porphyry (P3) cutting G2 has identical amounts of all oxides and V, slightly lower contents of Rb and Sr (Fig. 5) and subparallel REE pattern (Fig. 7b), demonstrating that they are similar. In domain II, the mineralogical and geochemical differences observed between G3 samples collected from the west (G3W) and those from the east (G3E) suggest that the two-mica granodiorite G3 was built up by, at least, two discrete pulses of magma. No trends, with decreasing Mg#, are observed between the two groups (Fig. 6), showing their independence. Although the biotite granodiorite G4 presents slightly higher Mg# than G3E, they have similar CaO and Rb

S.M. Lima et al. / Lithos 160–161 (2013) 98–116

107

Fig. 5. Selected oxide and trace element variation diagrams of the granitic rocks constituting the inner part of the Pavia pluton and field associated phases (domain I). Symbols are as in Fig. 3 and rock references are as in Table 1.

contents thus these two granodiorites cannot be related. Furthermore, G4 and G3W are also unrelated (Fig. 6). Biotite granodiorite G5 is the youngest granodiorite and does not seem to be related to granodiorites G3E, G3W and G4 (Fig. 6), which is also supported by the crosscutting chondrite normalized REE patterns (Fig. 7d) and by their emplacement ages that although close are different within error (Table 3). Granite G6 is the most evolved rock and represents a distinct magmatic pulse, as suggested by Figs. 6 and 7. One of the two fine-grained quartz-dioritic mesocratic enclaves (Enc.3) found in G3E was dated and is ~ 10 m.y. older than its host (Table 3). Thus, in spite of its mafic composition and small grain size it is not a mafic microgranular enclave (s.s.). It must have been incorporated by the rising magma, representing an earlier and widely recognized magmatic/metamorphic event in the Ossa–Morena Zone (Antunes et al., 2011a, 2011b; Azor et al., 2008; Jesus et al., 2007; Pereira et al., 2009; Pin et al., 2008; Ribeiro et al., 2007). Enc.4 and its host (G4) do not define fractionation trends (Fig. 6), indicating that they are also not cogenetic. Enc.5 and Enc.6, hosted in granodiorite G5, have higher Mg#, TiO2 and CaO and similar Rb, Zr and Nb contents to those of their host (Fig. 6). One of these enclaves (Enc.6) was dated and its older age (327.41 ± 0.40 Ma; Table 3) coupled with the crosscutting normalized REE patterns (Fig. 7f) points, once again, towards the absence of a genetic relation between the enclaves and the host. It is possible that in a scenario where the entire pluton was constructed by the emplacement of multiple magma pulses, these meter-sized enclaves with tonalitic and granodioritic compositions found within granodiorites, represent a previously emplaced, already crystallized, batch of magma.

Microgranite dikes (M2) have higher Zr content (Fig. 6d) and Sr/ (K+Ca) value (Fig. 6f) than their host (G5) and present very distinct chondrite normalized REE profiles (Fig. 7f). One of these dikes was dated and is 317.24±0.57 Ma (Table 3). The younger age and trace element behavior indicate that dikes and the host are genetically independent. 5.2. Lower Carboniferous magmatism in the Évora Massif Detailed chemical and isotopic studies from other granitic bodies located within the Évora Massif were performed in the last few years (see locations in Fig. 1b). The same mechanism was invoked to explain the genesis of the Hospitais tonalite and associated granitic facies (HT) (Moita, 2008; Moita et al., 2005), the calc-alkaline magmatism in the Alto de São Bento area (ASB) (Moita, 2008; Moita et al., 2009) and the Reguengos de Monsaraz Massif (RM) (Antunes et al., 2010, 2011a, 2011b). They were all interpreted as the result of fractional crystallization of mantle-derived magmas followed by mixing with variable proportions of crustal melts. There are substantial differences between these granitic bodies and the Pavia pluton. First, the Pavia pluton has the most primitive Sr–Nd isotopic signature (Fig. 8a); second, whereas the HT, ASB and RM have a typical arc calc-alkaline signature (Fig. 8b), several chemical features of the Pavia pluton granitic rocks, like high Na2O, Sr, Eu, Sr/Y and LREE and low K2O/Na2O, HREE and Y contents, strongly fractionated REE patterns (LaCN/YbCN = 18–43, average ratios in the main granitic phases) and the lack of a pronounced Eu anomaly (Table 2; Fig. 7), suggest

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Fig. 6. Selected oxide and trace element variation diagrams of the granitic rocks constituting the flanking units of the Pavia pluton and field associated phases (domain II). Symbols are as in Fig. 3 and rock references are as in Table 1.

that the Pavia pluton granitic rocks are chemically distinct from typical calc-alkaline arc rocks and are more similar to Archean tonalite– trondhjemite–granodiorite series (TTGs) and modern adakites (Table 4; Figs. 3c, 8b; e.g. Castillo, 2006; Martin, 1999; Martin et al., 2005). Using the compositional criteria of Defant and Drummond (1990), an evolution towards “slab-melt” compositions is observed within the Pavia pluton, whereas the rocks from the other granitic bodies clearly represent “non-slab melts” (Fig. 8c, d). An amphibole Ar–Ar cooling age of 323.0 ± 5.2 Ma was obtained for the HT (Moita, 2008; Moita et al., 2009), but precise zircon ID-TIMS U–Pb ages for the RM reveals that it was emplaced at 337–335 Ma (Antunes et al., 2011a, 2011b), showing the contemporaneity of mafic and felsic magmatism and favoring the hybridization model proposed for this pluton by these authors. Whole rock δ18O data range from 8.1 to 8.8‰ (Silva and Pinto, 2006) also favoring a mixed origin (interaction of mantle and crustal melts) for RM. No geochronological data is available for the ASB. The Pavia pluton is younger than RM and, based on the chemical differences discussed above, we suggest that, at least, two chemically distinct magmatic events, one with a typical arc calc-alkaline signature (337–335 Ma) followed by another with a clear adakitic signature (328–317 Ma) occurred in the Évora Massif. 5.3. Geochemical and isotopic constraints on the origin of magma(s) The chemical composition of adakitic suites is considered to reflect partial melting of basaltic or amphibolitic sources at elevated P–T conditions with residual garnet (explaining the impoverishment in HREE (Fig. 7) and Y and GdCN/YbCN ratios above 1 (Table 2); Martin et al.,

2005) and little or no residual plagioclase (explaining the lack of significant Eu anomalies and Sr enrichment; Defant and Drummond, 1990; Martin, 1999). Moreover, the main granitic phases show weak to distinct concave MREE patterns (Fig. 7), low to moderate Rb/Sr ratios (Table 2) and low, usually subchondritic Nb/Ta values (b 17.4; Foley et al., 2002), which are commonly considered as indicators of the presence of amphibole as a residual phase (Gómez-Tuena et al., 2003; Gromet and Silver, 1987; Petford and Atherton, 1996). The composition of the granitic phases presented in this study compares very well with the composition of liquids obtained by experimental melting of basalts and amphibolites (Fig. 9), suggesting that these are potential protoliths. The exceptions are the quartz-dioritic enclaves (Enc.2, 3), which crystallized during the previous, typical arc calc-alkaline, magmatic event (334.5± 0.5 Ma, Table 3), and the tholeiitic dike (P4), which is always plotted outside the experimental field. The dioritic enclave (Enc.1) shows abnormal Nb content (Fig. 9b) and the microgranite dike (M2) presents the highest Sr/Y ratio (Fig. 9c). Deviations from experimental liquids are usually interpreted as resulting from interaction with the mantle peridotite in different degrees (Martin et al., 2005 and references therein). The small variations on the Sr–Nd–O isotopic compositions (Table 3; Fig. 8a) reveal that all the Pavia pluton granitic phases have an isotopically similar and fairly homogeneous protolith. The obtained Sr–Nd signatures point towards a mantle source or juvenile crust origin. Crustal residence ages range between 0.91 and 1.50 Ga (Table 3), with an average value of 1.1 Ga. These values are within the interval defined for the pre-Permian subcontinental lithospheric mantle under Iberia (Gútierrez-Alonso et al., 2011). Excluding Enc.1 and G1, all the other

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Fig. 7. Chondrite normalized REE patterns (Taylor and McLennan, 1985) of granitic rocks constituting the Pavia pluton. Domain I: a) main granitic phases and microgranular enclave hosted in G1; b) rhyodacitic (P1) and rhyodacitic to dacitic (P2) porphyries and microgranodiorite dike (M1) cutting G1 and rhyodacite porphyries (P3) cutting G2. Domain II: c) discrimination between G3 samples collected from the east and west and their quartz-dioritic microgranular enclaves and tholeiitic porphyry (P4); d) main granitic phases; e) comparison between the tonalitic enclave and its host (G4); f) comparison between tonalitic and granodioritic enclaves, their host (G5) and crosscutting microgranite dikes (M2).

units have δ 18O > 7‰ (Table 3). This means that although mostly lying within the known range for granitic rocks derived from mantle-like sources, they cannot be derived directly from the depleted mantle or mantle wedge and a contribution from crustal materials, with higher δ18O, is required (e.g. Whalen et al., 2002 and references therein). This is consistent with the markedly negative Nb anomalies in primitive mantle normalized patterns (not shown) and εNdt values below +1 (Gútierrez-Alonso et al., 2011; Table 3; Fig. 8a). Mixing between the subcontinental lithospheric mantle (Downes and Dupuy, 1987) and the lower crust (Villaseca et al., 1999) was tested using the isotopic ratios recalculated to 328 Ma and the parent/daughter ratios for the Rb–Sr and Sm–Nd systems. Based on the isotopic ratios, a contribution of only 2% to 5% of metapelitic lower crust could account for the Sr–Nd signature of the Pavia pluton granitic rocks (Fig. 10a). The

metapelitic lower crust of Villaseca et al. (1999) is isotopically similar to the Ediacaran basement of the Ossa–Morena Zone, the so-called Série Negra (Chichorro et al., 2008; López-Guijarro et al., 2008; Pereira et al., 2006). According to Langmuir et al. (1978) mixing has to be substantiated by all the plots of appropriate elements and isotopes and individual samples should maintain the same relative relationship to one another on all plots (as the order of the data points is a function of the extent of mixing which is the same regardless of the plot used). We further tested mixture between these two end-members using the parent/daughter ratios for the Sr–Nd isotopic system (Fig. 10b). Almost all the Pavia pluton samples have lower Rb/Sr and Sm/Nd compared to the lower crust end-members and, as a result, they do not conform to the calculated mixing curves nor maintain the same relative positions.

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Fig. 8. Comparison of the data presented in this study (Pavia pluton) with the data of other Évora Massif granitic bodies: a) εNdT vs. (87Sr/86Sr)i, calculated for 328 Ma; b) LaCN/YbCN vs. YbCN diagram discriminating the adakites and Archean TTG field from the normal arc andesite and dacite field; c) Sr vs. Sr/Y; d) (La/Yb)CN vs. Sr/Y. Fields for “slab melts” and “non-slab melts” are based on the compositional criteria of Defant and Drummond (1990) and Drummond and Defant (1990). HT — Hospitais tonalite and associated granitic rocks (HT1) and their enclaves (HT2) (Moita, 2008); ASB — Alto de São Bento granodiorite and associated two-mica leucogranite (ASB1) and their enclaves (ASB2) (Moita, 2008; Moita et al., 2009); RM — undifferentiated rocks from the Reguengos de Monsaraz Massif (Antunes et al., 2010). Panel b is taken from Wang et al. (2006). Panels c and d are taken from Whalen et al. (2002).

5.4. The origin of the Pavia pluton adakitic-like signature It is fairly accepted that the closure of Rheic (results from Laurussia and Gondwana collision) began in the Devonian (~415 Ma; Murphy et al., 2011) and was largely completed in the Mississippian (~350 Ma; Ribeiro et al., 2007). Excluding the younger microgranite dikes (M2), the Pavia pluton granitic phases chemically resemble HSA. Partial melting of the oceanic lithosphere (N-MORB) with 20% of the sediment was modeled following the principles and methodology of Guo et al. (2007). The best fit results suggest a modal mineralogy of 8% garnet + 67.9% clinopyroxene+ 23% amphibole + 0.1% rutile + 1% apatite. The calculations suggest that a melt with trace elements similar to those of the Pavia pluton main granitic phases could have been generated by ~5% slab melting with ~20% subducted sediment in the slab (Table 5; Fig. 11a). However, partial melting of the subducted oceanic crust is unlikely because, at the beginning of subduction, the Rheic lithosphere was already too old (>25 m.y.; see Defant and Drummond, 1990) and consequently too cold for melting prior to dehydration. They most probably released fluids that rehydrated the overlying mantle wedge and induced partial melting. This mechanism may have been responsible for the generation of typical arc calc-alkaline magmatism (Martin, 1987), but cannot explain the chemical characteristics of the studied granitic rocks, excluding Enc.2 and Enc.3 hosted in G3E. The emplacement of the Pavia pluton began at ~ 328 Ma, approximately 20 m.y. after the end of the Rheic subduction, already during

the late stages of a continent–continent collisional setting, according to the limits defined by Jesus et al. (2007). This is not supported by the tectonic discriminating diagrams (Fig. 4). However, it is necessary to bear in mind that these are chemical-based diagrams and the chemistry of the studied rocks is similar to adakites, whose genesis is related to subduction processes. Melts with this composition (adakitic-like) can, however, be generated by other mechanisms such as: partial melting of delaminated lower crust (e.g. Karsli et al., 2010; Wang et al., 2006), partial melting of thickened lower crust (e.g. Guan et al., 2012; Karsli et al., 2011; Muir et al., 1995; Petford and Atherton, 1996; Xiong et al., 2003: Yu et al., 2012) or AFC of a parental basaltic magma (e.g. Bourdon et al., 2002; Castillo et al., 1999; Macpherson et al., 2006). The oblique collision of OMZ–SPZ caused crustal thickening (Eguíluz et al., 2000), forcing the lower crustal rocks to higher temperatures and pressures. The rapid exhumation of migmatites and gneisses from the Coimbra–Córdoba Shear Zone, at 340–330 Ma, and of migmatites from the Campo Maior unit from more than 40 km (Pereira et al., 2012) supports a minimum crustal thickness of 40 km, which is ~ 10 km more than the minimum depth to reach garnet amphibolite P–T conditions (Macpherson et al., 2006). It was suggested that the episodic character of the magmatic activity for over 35 m.y. in the western Ossa–Morena Zone (e.g. Antunes et al., 2011a, 2011b; Jesus et al., 2007; Lima et al., 2012a, 2012b; Pereira et al., 2009; Pin et al., 2008) is the result of subduction blocking at ca.

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Table 4 Average contents of the elements used in the definition of adakites and adakitic rocks. SiO2

Al2O3

MgO

Sr

Y

Yb

63.97 65.70 71.00 69.69 68.60 68.75 69.57 72.72 52.67 49.63 64.61 61.86 67.14 71.26 65.26 71.75 54.15 65.56 69.13

16.88 17.00 15.59 17.02 16.26 16.22 15.86 15.16 18.60 18.09 20.11 17.87 16.36 15.79 17.88 15.78 11.30 17.39 16.09

2.23 1.84 0.80 0.63 0.99 1.02 0.74 0.37 3.78 6.18 0.65 2.12 1.56 0.80 1.35 0.75 7.92 1.31 0.57

489 526 368 759 377 498 636 582 493 618 1310 911 491 607 683 536 740 567 2164

15.5 16.0 9.9 5.3 15.4 7.5 8.2 7.9 16.4 29.0 6.1 15.9 15.2 7.8 7.3 6.9 22.8 12.8 5.3

1.20 1.28 0.84 0.48 1.12 0.58 0.67 0.62 1.29 3.08 0.62 1.28 1.22 0.65 0.54 0.49 1.52 1.09 0.38

Other plutons in the Évora Massif HT 63.32 ASB 71.17 RM 57.19

17.50 14.54 16.33

1.94 0.86 4.42

327 167 184

18.4 18.9 31.0

1.81 2.00 2.99

Pavia pluton G1 G2T G2G G3E G3W G4 G5 G6 Enc.1 Enc.2, 3 Enc.4 Enc.5 Enc.6 P1 P2 P3 P4 M1 M2

Major elements in weight % and trace elements in ppm. According to the definition of adakites: SiO2 > 56%; Al2O3 > 15%; MgO b 3% (rarely above 6%); Sr typically > 400 ppm; Y b 18 ppm; Yb b 1.9 ppm (Defant and Drummond, 1990). In bold are the values above or below the typical values for adakites.

355 Ma and consequent slab break-off (Jesus et al., 2007; Pin et al., 2008). This mechanism explains the typical LP–HT metamorphism and the underplating of basaltic magmas (355–345 Ma, due to astenospheric upwelling). Under such scenario (where the temperature increase in the overlying material can be more than 500 °C; Pin et al., 2008 and references therein), partial melting of the asthenosphere and overriding lithosphere occurs for a time span of a few m.y. Melting temperatures, inferred from zircon saturation temperatures (TZr; Watson and Harrison, 1983), of all granitic phases presented in this study are generally above 800 °C (Table 2). The Iberian Reflective Body (IRB), located at mid-crustal depths, is the evidence that underplating of mafic magmas has indeed occurred in the OMZ during the Carboniferous. It extends from near the southern end of the OMZ to the CIZ (140 km) and presents variable lateral thickness (maximum 5 km) (e.g. Carbonell et al., 2004; Flecha et al., 2009; Simancas et al., 2003). On the basis of lithological modeling and laboratory measurements, Brown et al. (2012) suggested that the IRB consists of mafic rocks such as gabbro with, possibly, interlayers of metasediment. As noted in Section 5.3, the trace element characteristics of the adakites provide some useful insights on the mineralogy of the source. Other than garnet and amphibole (see Section 5.3), residual rutile and apatite, as suggested by the negative Nb–Ta, P and Ti anomalies in N-MORB (Fig. 11) normalized patterns are present in the source region. Plagioclase is absent or occurs in trace amounts. The only rocks we found in the western OMZ with a similar mineralogy were mafic granulites (Grt + Cpx + Pl + Qtz + Amp+ Rt) and high-grade amphibolites (Amp+ Grt + Pl + Qtz + Ilm; Pereira et al., 2010), but their chemical or modal analyses are not given. Metabasites/amphibolites were found mainly within G6 and marking the contact between G1 and G2 and may represent remnants of non-melted protolith. A good compilation of chemical (but not mineralogical) data from metabasites/ amphibolites from the western OMZ can be found in Pereira et al. (2007) and Pin et al. (2008). The chemistry of these metabasites is consistent with the derivation from subalkaline basalts and gabbros (Chichorro et al., 2008). They were divided into three groups: group I (“VAB-like”), group II (E-MORB) and group III (N-MORB). We used the average composition of the Évora Massif group II metabasites (Chichorro et al., 2008) to

model partial melting of lower crustal rocks. Group I (“VAB”-like) and group III (N-MORB) metabasites were not used because they present, for the same degree of partial melting and modal mineralogy, melting model compositions with NbN-MORB >TaN-MORB, which is opposite to that obtained using group II metabasites and to the N-MORB normalized patterns of average compositions of the studied rocks. The mineralogy of these metabasites is not published, so we adopted a mineral assemblage involving garnet + clinopyroxene + amphibole + rutile + apatite, as suggested by the trace element characteristics of the Pavia pluton granitic rocks. Our modeling (non-batch partial melting) follows the same principles and methodology presented in Guo et al. (2007). The proportions of each mineral were obtained by progressively changing the proportions of each mineral until we obtained the best fit to the MORB-normalized patterns of the Pavia pluton main granitic phases (G1 to G6). The best fit model results (Table 5; Fig. 11b) suggest that the studied rocks could have been generated by partial melting of a metabasite with 10% garnet, 65% clinopyroxene, 18% amphibole, 5% rutile and 2% apatite. The calculated degree of partial melting of the lower crust is 5%. However, these metabasites have consistently positive εNdT values (Chichorro et al., 2008; Gómez-Pugnaire et al., 2003; Pin et al., 2008) and thus, such a low degree of partial melting cannot explain, by itself, the bulk earthlike isotopic signature of the Pavia pluton. Although fractional crystallization may be important within the same rock type, no differentiation trends between the different granitic rocks are observed (Figs. 5–7). This process may have been obscured by assimilation of crustal material during ascent and emplacement (as suggested by δ18O data; Table 3) and by the multiphase incorporation, in an evolving magma, of new and chemically distinct batches of magma (as suggested by the geochronological data; Lima et al., 2012a). The presence of scarce and genetically unrelated enclaves (namely the considerably older Enc.2, 3) suggests that assimilation may have played an important role in the formation of the Pavia pluton. Moreover, there is a general decrease in εNd328 with increasing SiO2 (Fig. 12a) and decreasing MgO (Fig. 12b) contents, which is consistent with the assimilation of crustal material during the evolution of mafic magmas (e.g. Verma, 2001). As no Rb–Sr isotopic data is available for group II metabasites, we selected one banded amphibolite sampled within the Moura Schists Formation (Pin et al., 2008) to represent the parental magma and

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portion of melt remaining (F, values in gray in Fig. 12c) and the emplacement age of the main granitic phases, but this is probably due to periodic recharges of the magma chamber. Taking into account the δ 18O mantle-like and bulk-earth isotopic signature of the studied granitic rocks and the geodynamic scenario of the OMZ at the moment of their emplacement, the AFC of a mantle-derived magma seems the most viable mechanism for its generation. The fractional crystallization of a mantle-derived magma and the assimilation of crustal material were also invoked to explain the genesis of other plutons located in the Évora Massif (Antunes et al., 2010, 2011a, 2011b; Moita, 2008; Moita et al., 2005, 2009;). However, these have a clearly distinct chemical signature (Section 5.2). Jesus et al. (2007) suggested that ~330–325 Ma magmatism resulted from mixing of mantle and crust-derived melts as the result of rapid crustal uplift/erosion. However, this mechanism is not supported by our data (Table 3; Fig. 10). So, if the source and mechanism are the same, why does the Pavia pluton have such a different chemical signature (Fig. 8c, d)? First, compared to the other granitic bodies, the isotopic data suggest lower degrees of crustal assimilation for the Pavia pluton (Fig. 8a). Second, after slab detachment, the old oceanic lithosphere continues to sink in the upper mantle (Pin et al., 2008 and references therein) and thus, until complete consumption of the oceanic lithosphere, the degree of mantle contamination is expected to increase over time. We suggest that the younger age of the Pavia pluton (328–317 Ma), compared to the RM (337–335 Ma), presupposes a derivation from a mantle-derived magma that is more metasomatized by the sinking oceanic lithosphere. This is supported by Fig. 8, where a chemical evolution from non-slab melts (normal arc rocks) to slab-melts (adakites) with decreasing emplacement age is observed and by the occurrence, in the Pavia pluton, of xenoliths (Enc.2, 3) with ~335 Ma and with a typical arc calc-alkaline signature. Also, the microgranite dike (M2) cutting G5 is the youngest dated rock (ca. 317 Ma; Table 3) and has extremely high Sr and LREE contents (Table 2), within the range of LSA, which are usually interpreted as derived from a mantle peridotite intensely metasomatized by slab-melts (e.g. Mahlburg Kay et al., 1993; Martin et al., 2005). 6. Conclusions Fig. 9. Selected plots comparing experimental melt compositions of basalts and amphibolites (dashed field; Martin et al., 2005) and rock compositions presented in this study (Pavia pluton, Ossa–Morena Zone) with most rocks plotting within the dashed field: a) MgO vs. SiO2; b) Nb vs. SiO2 and; c) Sr/Y vs. Y. Symbols are as in Fig. 3 and rock references are as in Table 1.

test the effects of assimilation of lower crust metapelitic material (Fig. 12c). We used the best fit mineral proportions obtained for partial melting of group II amphibolites (Fig. 11b). There are substantial deviations from the AFC curve and there is no relation between the

The chemical and isotopic data presented in this study show, on the one hand, the genetic independence of each granitic phase and, on the other hand, their derivation from an isotopically similar protolith. In addition, the occurrence of slightly older meter-sized tonalite and granodiorite xenoliths within compositionally similar host rocks, probably representing previously emplaced and partially crystallized batches of magma, favors the idea that the Pavia pluton results from the amalgamation of multiple batches of magma (cf. Lima et al., 2012a). The majority of the Pavia pluton granitic rocks are chemically similar to TTGs and adakites and fulfills the chemical criteria defined by Defant and Drummond (1990) for classification of these rocks

Fig. 10. Comparison between the data presented in this study and mixing between the subcontinental lithospheric mantle (Downes and Dupuy, 1987) and the lower crust (Villaseca et al., 1999) model curve using: a) Sr–Nd isotopic ratios; b) parent–daughter ratios. Numbers along the curves correspond to the percentage of mantle involved in the mixture. Symbols are as in Fig. 3 and rock references are as in Table 1.

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Table 5 Results of trace element modeling (values in ppm) for partial melting of subducted slab and group II amphibolites.

Subducted slaba — 5% PM Amphiboliteb — 5% PM Aver. G1 G2T Aver. G2G Aver. G3E Aver. G3W Aver. G4 Aver. G5 Aver. G6

Subducted slaba — 5% PM Amphiboliteb – 5% PM Aver. G1 G2T Aver. G2G Aver. G3E Aver. G3W Aver. G4 Aver. G5 Aver. G6

Rb

Ba

Th

U

Ta

Nb

K2O

La

Ce

Pb

Sr

77.14 47.70 73.13 71.00 80.00 46.75 93.75 60.33 77.67 108.20

491.79 314.36 482.33 473.00 365.57 259.75 305.25 510.22 689.33 614.00

9.86 4.3 8.31 7.53 8.10 4.53 9.24 5.84 11.89 6.70

2.10 1.32 1.87 1.56 1.73 0.88 1.73 0.78 1.85 1.48

0.54 0.37 0.39 0.79 0.68 0.20 0.87 0.34 0.46 0.45

5.16 4.14 8.12 7.80 6.56 2.38 9.55 5.09 6.90 4.04

1.73 1.57 1.92 1.97 2.31 1.35 2.21 1.98 2.39 3.25

18.99 13.66 31.48 28.20 24.91 16.25 31.55 25.37 41.87 20.92

30.09 25.06 60.75 55.70 49.56 31.33 60.93 46.22 78.07 41.31

5.86 NA 12.67 12.00 21.71 14.75 15.25 14.67 24.67 28.00

331.71 394.08 488.83 526.00 341.86 759.00 377.25 498.22 635.67 582.20

P2O5

Nd

Zr

Hf

Sm

Eu

Ti

Dy

Y

Yb

Lu

0.30 0.13 0.22 0.20 0.10 0.07 0.15 0.15 0.12 0.09

26.83 23.43 23.08 22.60 19.26 11.41 22.85 17.12 27.13 15.20

142.03 134.98 204.83 193.00 147.93 116.00 178.75 161.33 163.00 107.80

4.03 3.42 4.62 4.40 3.57 2.95 3.98 3.68 3.83 2.88

1.85 2.08 4.34 4.78 3.86 2.12 4.22 2.99 4.51 2.8

0.79 1.01 1.24 1.35 0.88 0.73 0.95 0.83 1.01 0.67

0.75 0.78 0.71 0.64 0.31 0.28 0.41 0.40 0.33 0.18

1.00 1.03 2.66 3.00 1.96 0.92 2.46 1.35 1.60 1.34

7.33 7.78 14.50 16.00 10.16 5.30 15.38 7.47 8.17 7.90

0.86 0.76 1.2 1.28 0.87 0.48 1.12 0.58 0.67 0.62

0.12 0.11 0.17 0.16 0.14 0.08 0.17 0.09 0.11 0.09

NA — not analyzed. a After Guo et al. (2007). b Average composition of group II (E-MORB) amphibolites (Chichorro et al., 2008).

Fig. 11. Comparison between the data presented in this study and partial melting model curves of a) subducted slab (Guo et al., 2007 and references therein); b) group II amphibolites (Chichorro et al., 2008). Data were normalized for the N-MORB composition of Sun and McDonough (1989). Symbols are as in Fig. 3 and rock references are as in Table 1.

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Fig. 12. Variation of εNd328 with: a) whole rock SiO2 content; b) whole rock MgO content; c) comparison between the data presented in this study and the AFC model curve using a banded amphibolite (Pin et al., 2008) as the potential parental magma and metapelic lower crust (Villaseca et al., 1999) as the assimilant. Numbers along the curve correspond to the portion of melt remaining (F; at start F = 1). Symbols are as in Fig. 3 and rock references are as in Table 1.

(SiO2 =61.86–72.72%, Al2O3 =15.16–20.11%, MgO=0.37–2.23%; Sr= 368–2164 ppm; Y=5.3–16.0 ppm; and Yb=0.38–1.28 ppm). Although resembling HSA, partial melting of the subducted slab is rejected because, at the onset of subduction, the Rheic lithosphere was already too cold for melting prior to dehydration. Moreover, the Pavia pluton age (328–317 Ma) suggests that its emplacement occurred during the late stages of a continent–continent collisional setting. The comparison with previously published data from other Évora Massif plutons suggests that at least two chemically distinct magmatic events occurred in the Évora Massif, one with a typical arc calc-alkaline signature (337–335 Ma) followed by another with a clear adakitic signature (328–317 Ma). All the intrusive bodies, including the one in this study, are interpreted as derived from a mantle-derived magma that interacted, in different degrees, with crustal melts (AFC). We suggest that the chemical differences between the Pavia pluton and the other bodies resulted from a lower contribution of crustal material and a higher degree of contamination of mantle-derived magmas by the sinking slab (after subduction blocking and subsequent slab break-off). This can also explain the increasing similarity of the granitic rocks with “slab-melts” with decreasing age. Acknowledgments We thank Ricardo L. Silva for the help in sampling, Prof. Manuel Machado Leite for the access to the crushing laboratory at LNEG (Portugal) and for the polished thin sections, António Rodrigues and António Santos for the support in FeO determinations, Prof. José Gil Ibarguchi for whole rock Sr and Nd analyses and Prof. Frederick Longstaffe for whole rock oxygen data. We appreciate constructive reviews by Zhengfu Guo, an anonymous reviewer and Nelson Eby. The first author benefited from the Ph.D grant SRFH/BD/39948/2007 sponsored by FCT — Foundation for Science Technology (Portugal) and financial support from the Geosciences Center. References Antunes, A., Santos, J.F., Azevedo, M.R., Mendes, M.H., Ribeiro, S., 2010. New petrographical, geochemical and geochronological data for the Reguengos de Monsaraz pluton (Ossa–Morena Zone, SW Iberian Massif, Portugal). Estudios Geológicos 66 (1), 25–34. Antunes, A., Santos, J.F., Azevedo, M.R., Corfu, F., 2011a. New U–Pb zircon age constraints for the emplacement of the Reguengos de Monsaraz Massif (Ossa Morena Zone). In: Molina, J.F., Scarrow, J.H., Bea, F., Montero, P. (Eds.), VII Hutton Symposium on Granites and Related Rocks. Universidade de Granada, Granada, pp. 9–10. Antunes, A., Santos, J.F., Azevedo, M.R., Corfu, F., 2011b. Geochronology and Isotope geochemistry of felsic marginal facies of the Reguengos de Monsaraz Massif (OMZ). In: Antunes, I.M.H.R., Almeida, J.P.F., Albuquerque, M.T.D. (Eds.), Livro de

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