Granitoid Suites Research Articles

The Basement of the Deccan Traps and Its Madagascar Connection: Constraints from Xenoliths

Paleogeographic reconstructions of India and Madagascar before their late Cretaceous rifting juxtapose the Antongil Block of Madagascar against the Deccan Traps of India, indicating that the Western Dharwar Craton extends below the Deccan lavas. Some recent studies have suggested that the South Maharashtra Shear Zone along the northern Konkan coast of India limits the northern extent of the Western Dharwar Craton, implying that the craton does not extend below the Deccan Traps, raising a question mark on paleogeographic reconstructions of India and Madagascar. The continuity of the Western Dharwar Craton north of the South Maharashtra Shear Zone below the Deccan Traps—or its lack thereof—is critical for validating tectonic models correlating Madagascar with India. In this study, zircons in tonalitic basement xenoliths hosted in Deccan Trap dykes were dated in situ, using the U-Pb isotope system. The data furnish U-Pb ages that define three populations at 2527 ± 6, 2456 ± 6, and 2379 ± 9 Ma. The 2527 ± 6 Ma ages correspond to the igneous crystallization of the tonalites, whereas the 2456 ± 6 and 2379 ± 9 Ma ages date metamorphic overprints. The results help to establish for the first time that the basement is a part of the Neoarchean granitoid suite of the Western Dharwar Craton, which extends northward up to at least Talvade in central and Kihim beach in the western Deccan. By implication, the South Maharashtra Shear Zone cannot be the northern limit of the Western Dharwar Craton. The granitoids are correlated with the Neoarchean felsic intrusions (2.57–2.49) of the Masaola suite in the Antongil Block of Madagascar, supporting the existence of a Neoarchean Greater Dharwar Craton comprising the Western Dharwar Craton and the Antongil-Masora Block.

Padrť Stock (Teplá-Barrandian Unit, Bohemian Massif): petrology, geochemistry, U-Pb zircon dating of granodiorite, and Re-Os age and origin of related molybdenite mineralization

4 �NationalMuseum,�Vaclavske�naměsti�68,�115�79�Prague�1,�CzechRepublic * Corresponding author † Deceased The Padrť Stock is a small (~5 km 2 ) intrusion located near the SE margin of the Tepla-Barrandian Unit, Bohemian Massif, several kilometers away from the NW periphery of the Central Bohemian Plutonic Complex. On outcrops, which are all located close to the contact of the stock with Neoproterozoic sedimentary rocks, two types of granitoids were detected, fine- to medium-grained hornblende-biotite Padrť granodiorite, and, along its SW margin, fine- to medium-grained partly porphyritic biotite Tesliny leucogranite. The U-Pb zircon dating of the more voluminous Padrť granodiorite by laser ablation ICP-MS yielded a magmatic age of 342.8 ± 1.1 Ma, which is slightly lower than are the published age data for the nearby Blatna suite granitoids of the Central Bohemian Plutonic Complex. The Re-Os dating of molybdenite occurring in quartz veins within a quartzite lens in close exocontact yielded ages of 337.2 ± 2.4 Ma and 339.8 ± 2.5 Ma (two samples). The data indicate that the formation of molybdenite postdated that of the magmatic rock. This is in agreement with relatively low-temperature deposition of quartz related to formation of the molybdenite, as indicated by the fluid inclusions (280 to 300 °C).

Evolution of continental crust of the Aravalli craton, NW India, during the Neoarchaean–Palaeoproterozoic: evidence from geochemistry of granitoids

Neoarchaean–Palaeoproterozoic granitoids of the Aravalli craton, represented by four plutons with different ages, viz. Gingla (2.6–2.4 Ga), Ahar River (2562 Ma), Untala (2505 Ma), and Berach (2440 Ma) granitoids, are classified into three suites: TTG-like, Sanukitoid, and High-K Granitoid suite, all exhibiting negative Nb and Ti anomalies. The TTG-like suite is characterized by high contents of SiO2, Na2O, and LREEs, high (La/Yb)N, low contents of K2O, MgO, Cr, and Ni, and low (Dy/Yb)N, suggesting that this suite formed by partial melting of a subducted basaltic slab without interacting with a mantle wedge. In contrast, the calc-alkaline Sanukitoid suite is marked by a high content of LILEs and mantle-compatible elements, which indicate that this suite formed by partial melting of a slab-fluid metasomatized mantle wedge in a subduction-related arc environment. On the other hand, the High-K Granitoid suite is characterized by high contents of SiO2 and K2O, and low contents of Na2O, MgO, Cr, and Ni with variable Eu anomaly, along with high (La/Sm)N and (La/Yb)N, and low (Dy/Yb)N and Nb/Th. Some high-K granitoids also exhibit A-type characteristics. These features indicate that the High-K Granitoid suite formed by melting of crustal rocks. Early Neoarchaean continental crust formation reflected a slab-melting-dominated magmatic process as evidenced by the TTG-like suite, whereas Palaeoproterozoic petrogenesis was governed by the interaction of slab melt with mantle wedge as demonstrated by the Sanukitoid suite. The High-K Granitoid suite formed during the waning stages of subduction. This study reveals that granitic rocks of the Aravalli craton evolved from slab melting in the Neoarchaean to melting of mantle wedge in the Palaeoproterozoic. Melting of older crust led to the formation of the High-K Granitoid suite.

Magmatic and metamorphic history of Paleoarchean tonalite–trondhjemite–granodiorite (TTG) suite from the Singhbhum craton, eastern India

Texturally controlled dating of zircon from Paleoarchean tonalite–trondhjemite–granodiorites of the Older Metamorphic Tonalitic Gneisses and the Singhbhum Granite batholith (Phases I, II, and III) from the Singhbhum craton in eastern India reveals a polycyclic evolution of the Archean crust. The granitoid suites were emplaced in two pulses at 3.45–3.44Ga and 3.35–3.32Ga. Tonalites and trondhjemites of the Older Metamorphic Tonalitic Gneisses were emplaced at ca. 3.45–3.44Ga together with Phase III of the Singhbhum Granite pluton while granites belonging to the Older Metamorphic Tonalitic Gneisses were emplaced at ca. 3.35–3.32 together with Phase I and Phase II of the Singhbhum Granite pluton. Both crustal units underwent an early phase of relatively high-grade metamorphism at 3.30–3.28Ga followed by extensive fluid-induced alteration during low-grade metamorphism at 3.19–3.12Ga, and 3.02–2.96Ga. The two units have also been marginally affected at ca. 2.52Ga and 1.06Ga by major metamorphic events in the North Singhbhum Mobile Belt and the Singhbhum shear zone at the northern margin of the craton. The zircon grains in granites have inherited cores with ages of ca. 3.61Ga and 3.46–3.41Ga and with well-developed oscillatory growth zonation which suggests the granitic magmas were derived by partial melting of an igneous precursor or sedimentary rocks derived from an igneous source. The emplacement of the expansive granitoids belonging to the Older Metamorphic Tonalitic Gneisses and the Singhbhum Granite was synchronous with the amphibolite-facies metamorphism (ca. 3.32Ga) of older meta-igneous and metasedimentary rocks belonging to the Older Metamorphic Group. Major felsic crust formation in the craton occurred in a narrow time interval between 3.46 and 3.32Ma with minor contributions of material as old as 3.6Ga. The complex polycyclic evolution of the Paleoarchean crust in the Singhbhum craton can account for the wide range of often disparate ages obtained using whole rock isochron dating techniques with some of the isochron dates being geologically meaningful while others representing mixing lines or disturbance of the isotopic systems during metamorphism.

From passive margin to volcano–sedimentary forearc: The Tonian to Cryogenian evolution of the Anosyen Domain of southeastern Madagascar

The Anosyen Domain of southeastern Madagascar represents a part of a vast sequence of predominantly siliciclastic and carbonaceous sedimentary and felsic volcanic rocks that can be traced from Madagascar through southern India, Sri Lanka, and into East Antarctica. We present new age and geochemical data from the Iakora and Horombe groups: units that represent the sedimentary and volcanogenic components of the Anosyen Domain. Our data demonstrate that the siliciclastic sedimentary rocks of the Iakora Group contain predominantly 2400–1600Ma aged detrital zircon with a modal age peak at approximately 1850Ma. This age spectrum is comparable to those reported from the majority of the other sedimentary rocks exposed in Madagascar. The felsic volcanic rocks of the Horombe Group are of both metaluminous and peraluminous composition and have a similar chemistry and the same age as the Imorona–Itsindro Suite (840–700Ma), a voluminous suite of continental arc-related granitoids that intrude central and northern Madagascar.Taken together we interpret the strata of the Anosyen Domain to have been deposited in an expansive continent margin basin that existed on the western ocean-facing margin of the Indo-Antarctic Craton. We infer this basin records both passive margin and forearc phases of deposition and, on the basis of the regional similarities in detrital zircon spectra and cross-cutting relationships, suggest the older passive margin phase of deposition occurred after c. 980Ma. The younger forearc phase of deposition occurred in the Cryogenian synchronous with the development of the Imorona–Itsindro magmatic arc (840–700Ma). This suite reflects east-dipping subduction beneath the western margin of the Indo-Antarctic Craton and defines a linear belt of intrusions that, similar to the forearc sediments of the Anosyen Domain, can be traced from East Antarctica through Madagascar and potentially into East Africa, regions we take to have been continuous within the pre-Gondwana Indo-Antarctic plate. The volcanic and plutonic rocks of the Malani Igneous Suite (780–730Ma) may represent the coeval backarc basin.

Geochronology and petrogenesis of granitoid rocks from the Goryczkowa Unit, Tatra Mountains (Central Western Carpathians)

Abstract The geochemical characteristics as well as the LA-MC-ICP-MS U-Pb zircon age relationship between two granitoid suites found in the Goryczkowa crystalline core in the Western Tatra Mountains were studied. The petrological investigations indicate that both granitoid suites were emplaced at medium crustal level, in a VAG (volcanic arc granites) tectonic setting. However, these suites differ in source material melted and represent two different magmatic stages: suite 1 represents a high temperature, oxidized, pre-plate collision intrusion, emplaced at ca. 371 Ma while suite 2 is late orogenic/anatectic magma, which intruded at ca. 350 Ma. These data are consistent with a period of intensive magmatic activity in the Tatra Mountain crystalline basement. The emplacement of granitoids postdates the LP-HT regional metamorphism/ partial melting at ca. 387 Ma and at 433-410 Ma, imprinted in the inherited zircon cores.

An exotic Mesoarchean microcontinent: The Coorg Block, southern India

Sandwiched between the Dharwar Craton in the north and the Neoarchean–Proterozoic crustal blocks to the south, the Coorg Block in southern India is composed dominantly of a suite of arc magmatic rocks including charnockites, TTG (tonalite–trondhjemite–granodiorite)-related granitoid suite and felsic volcanic tuffs together with minor accreted oceanic remnants along the periphery of the block. Coeval mafic and felsic magmatism with magma mixing and mingling in an arc setting is well represented in the block. Here we present the petrology, geochemistry, zircon U–Pb geochronology and Lu–Hf isotopes of all the major lithologies from this block. Computation of metamorphic P–T conditions from mineral chemical data shows consistent granulite-facies P–T conditions of 820–870°C and up to 6kbar. Our geochemical data from major, trace and REE on representative samples of the dominant rock types from the Coorg Block corroborate an arc-related signature, with magma generation in a convergent margin setting. The zircon data yield weighted mean 207Pb/206Pb ages of 3153.4±9 to 3184.0±5.5Ma for syenogranites, 3170.3±6.8Ma for biotite granite, 3275±5.1Ma for trondhjemite, 3133±12 to 3163.8 ±6.9Ma for charnockites, 3156±10 to 3158.3±8.2 for mafic enclaves, 3161±16Ma for diorite and 3173±16Ma for felsic volcanic tuff. An upper intercept age of 3363±59Ma and a lower intercept age of 2896±130Ma on zircons from a charnockite, as well as an evaluation of the Th/U values of the zircon domains against respective 207Pb/206Pb ages suggest that the Mesoarchean magma emplacement which probably ranged from >3.3 to 3.1Ga was immediately followed by metamorphism at ca. 3.0 to 2.9Ga. The ages of magmatic zircons from the charnockites and their mafic granulite enclaves, as well as those from the volcanic tuff and biotite granite, are all remarkably consistent and concordant marking ca. 3.1Ga as the peak of subduction-related crust building in this block, within the tectonic milieu of an active convergent margin. The majority of zircons from the Coorg rocks show Hf isotope features typical of crystallization from magmas derived from juvenile sources. Their Hf crustal model ages suggest that the crust building might have also involved partial recycling of basement rocks as old as ca. 3.8Ga. The crustal blocks in the Southern Granulite Terrane in India preserve strong imprints of major tectonothermal events at 2.5Ga, 2.0Ga, 0.8Ga and 0.55Ga associated with various subduction–accretion–collision or rifting events. However, the Coorg Block is exceptional with our data suggesting that none of the above events affected this block. Importantly, there is also no record in the Coorg Block for the 2.5Ga pervasive regional metamorphism that affected all the other blocks in this region. The geochronological data raise the intriguing possibility that this block is an exotic entity within the dominantly Neoarchean collage in the northern domain of the Southern Granulite Terrane of India. The Mesoarchean arc-related rocks in the Coorg Block suggest that the magma factories and their tectonic architecture in the Early Earth were not markedly different from those associated with the modern-style plate tectonics.

Carboniferous U–Pb zircon age for S-type Karamea Suite Redjacket Granite, Paparoa Metamorphic Core Complex lower plate, northern Westland

Laser-ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS) U–Pb zircon dating combined with whole-rock geochemical analysis indicate that the Redjacket Granite was emplaced at 350.9±2.3 Ma (2σ) and belongs to the S-type Karamea Suite. This is the first report of Karamea Suite-type magmatism occurring after 368 Ma in the Nelson block and the first confirmation of Karamea Suite granitoids in the lower-plate of the Paparoa Metamorphic Core Complex.

Mesoproterozoic arc magmatism in SE India: Petrology, zircon U–Pb geochronology and Hf isotopes of the Bopudi felsic suite from Eastern Ghats Belt

The southern segment of the Eastern Ghats Mobile Belt (EGMB) in India was an active convergent margin during Mesoproterozoic, prior to the final collision in Neoproterozoic during the assembly of the Rodinia supercontinent. Here we present mineralogical, whole-rock geochemical, zircon U–Pb and Hf isotopic data from a granitoid suite in the Bopudi region in the EGGB. The granitoid complex comprises quartz monzodiorite with small stocks of rapakivi granites. The monzodiorite, locally porphyritic, contains K-feldspar megacrysts, plagioclase, quartz, biotite and ortho-amphibole. The presence of mantled ovoid megacrysts of alkali feldspar embaying early-formed quartz, and the presence of two generations of the phenocrystic phases in the rapakivi granites indicate features typical of rapakivi granites. The K-feldspar phenocrysts in the rapakivi granite are mantled by medium-grained aggregates of microcline (Ab7 Or93), which is compositionally equivalent to the rim of Kfs phenocryst and Pl (An23–24 Ab75). The geochemistry of both the granitoids shows arc-like features for REE and trace elements. LA-ICP-MS zircon analyses reveal 207Pb/206Pb ages of 1582 (MSWD=1.4) for the rapakivi granite 1605±3Ma (MSWD=3.9) for the monzodiorite. The zircons from all the granitoid samples show high REE contents, prominent HREE enrichment and a conspicuous negative Eu anomaly, suggesting a common melt source. The zircons from the monzodiorite have a limited variation in initial 176Hf/177Hf ratios of 0.28171–0.28188, with εHf(t) values of −2.2 to +2.8. Correspondingly, their two-stage Hf isotope model ages (TDM2) ranging from 2.15 to 2.47Ga probably suggest a mixed source for the magma involving melting of the Paleoproterozoic basement and injection of subduction-related juvenile magmas. The prominent Mesoproterozoic ages of these granitoids suggest subduction-related arc magmatism in a convergent margin setting associated with the amalgamation of the Columbia-derived fragments within the Neoproterozoic Rodinia assembly.

SIMS zircon U–Pb and mica K–Ar geochronology, and Sr–Nd isotope geochemistry of Neoproterozoic granitoids and their bearing on the evolution of the north Eastern Desert, Egypt

Granitic rocks are commonly used as means to study chemical evolution of continental crust, particularly, their isotopic compositions, which reflect the relative contributions of mantle and crustal components in their genesis. New SIMS and K–Ar geochronology, isotope, geochemical, and mineral chemistry data are presented for the granitoid rocks located in and around Gabal Dara in the Northern Eastern Desert of Egypt. The granitoid suite comprises quartz diorites, Muscovite (Mus) trondhjemites, and granodiorites intruded by biotite-hornblende (BH) granites and alkali feldspar (AF) granites. Mus trondhjemite, granodiorite and BH granite exhibit I-type calc alkaline affinities. Mus trondhjemite and granodiorite show medium-K calc-alkaline and metaluminous/mildy peraluminous affinities, whereas BH granites have high-K calc-alkaline and metaluminous character. Concordant 206Pb/238U weighted mean ages together with geochemical peculiarities suggest that Mus trondhjemites (741Ma) followed by granodiorites (720Ma) are genetically unrelated, and formed in subduction-related regime by partial melting of lower oceanic crust together with a significant proportion of mantle melt. The genesis of Mus trondhjemites is correlated with the main event in the evolution of the Eastern Desert, called “~750Ma crust forming event”.The field and geochemical criteria together with age data assign the high-K calc-alkaline BH granites (608–590Ma) and alkaline AF granites (600–592Ma) as post-collisional granites. The differences in geochemical traits, e.g. high-K calc-alkaline versus alkaline/peralkaline affinities respectively, suggest that BH granites and AF granites are genetically unrelated. The age overlap indicating coeval generation of calc-alkaline and alkaline melts, which in turn suggests that magma genesis was controlled by local composition of the source. The high-K calc-alkaline BH granites are most likely generated from lithospheric mantle melt which have been hybridized by crustal melts produced by underplating process. AF granites exhibit enrichment in K2O, Rb, Nb, Y, and Th, and depletion in Al2O3, TiO2, MgO, CaO, FeO, P2O5, Sr, and Ba as well as alkaline/peralkaline affinity. These geochemical criteria combined with the moderately fractionated rare earth elements pattern (LaN/YbN=9–14) suggest that AF granite magma might have been generated by partial melting of Arabian–Nubian Shield (ANS) arc crust in response of upwelling of hot asthenospheric mantle melts, which became in direct contact with lower ANS continental crust material due to delamination. Furthermore, a minor role of crystal fractionation of plagioclase, amphibole, biotite, zircon, and titanomagnetite in the evolution of AF granites is also suggested. The low initial 87Sr/86Sr ratios (0.7033–0.7037) and positive εNd(T) values (+2.32 to +4.71) clearly reflect a significant involvement of depleted mantle source in the generation of the post-collision granites and a juvenile nature for the ANS.

High-T–low-P thermal anomalies superposed on biotite-grade rocks, Wongwibinda Metamorphic Complex, southern New England Orogen, Australia: heat advection by aqueous fluid?

The Wongwibinda Metamorphic Complex is characterised by ∼400 km2 of biotite-grade rocks with irregular, km-scale zones of cordierite-bearing high-T rock (T > 550°C). Cordierite-bearing rocks include different textures: (i) cordierite–K-feldspar–spotted hornfels; (ii) sheared cordierite–K-feldspar–augen schists; and (iii) migmatites with or without comparatively coarse garnet poikiloblasts. Integrated petrography, mineral chemistry and mineral equilibria modelling indicate metamorphic peak conditions in samples of hornfels of approximately P ≤ 250 MPa and T = 570–620°C. Two samples of sheared rock preserve peak conditions of approximately T = 670–690°C or T < 600°C and P ≤ 200 MPa, consistent with rapid cooling or variable thermal structure in the Glen Mohr Shear Zone. Electron microprobe U–Th–Pb monazite data indicate a date of 291.5 ± 1.8 Ma for the shear zone, indistinguishable from the age of Hillgrove Plutonic Suite granitoids in the complex. Monazite ages are complex in the hornfels samples that were likely, on the basis of structural relationships, metamorphosed early in the history of the Wongwibinda Metamorphic Complex (ca 300 Ma). Previous monazite dating of migmatite samples (ca 297 Ma) suggests that the metamorphic cycle was short-lived, lasting less than ca 10 m.y. Metamorphic field gradients are <15–23°C km−1 across much of the complex but locally steep (>50–100°C km−1) around the high-T rocks. Rejection of most heat sources leaves regional conductive heating as the most plausible explanation for the smooth, broad and shallow metamorphic field gradient in the biotite-grade rocks. Another mechanism of heat transfer is required to explain the local, steep metamorphic field gradients and development of high-T cordierite-bearing rocks. The spatial association of quartzite units centred within two cordierite-bearing high-T domains and an increased abundance of quartz veins above the cordierite isograd suggests heat advection by aqueous fluid locally perturbed the broad conductive heating. Fluid was channelled within shear zones and locally infiltrated nearby rocks. Variable fluid flux and strain have produced the range of different textures in cordierite-bearing rocks of the Wongwibinda Metamorphic Complex.

Juvenile vs. recycled crust in NE China: Zircon U–Pb geochronology, Hf isotope and an integrated model for Mesozoic gold mineralization in the Jiaodong Peninsula

The continental crust of the North China Craton (NCC) is a major reservoir of mineral resources with imprints of secular changes in tectonics and metallogeny. The Jiaodong Peninsula, located in the eastern margin of the North China Craton (NCC), is currently one of the largest gold producers over the globe, and preserves the records of multiple magmatic and metamorphic events. Here we characterize the timing and tectonics of the major Mesozoic magmatism and the associated gold metallogeny in this region through a comprehensive U–Pb geochronological and Hf isotope investigation of zircons in a suite of granitoids, mafic magmatic enclaves, melanocratic dikes and melted basement rocks.The Linglong granite, hosting one of the major gold deposits in Jiaodong, shows emplacement ages between 150 and 160Ma, and the dominantly negative εHf (t) values (−34.0 to −23.8) of zircons from this intrusion suggest magma derivation from recycled components in the Archean basement. The Guojialing granodiorite and its mafic magmatic enclaves show similar ages between 123 and 127Ma, with negative εHf (t) values (−19.3 to −16.8), corresponding to crustal magma source. The melanocratic dikes, belonging to pre- and syn-mineralization stages, with U–Pb age range of 126 to 166Ma display large variation in their zircon εHf (t) values (−25.7 and 2.3) suggesting the involvement of both recycled crustal and juvenile mantle components. Zircons in the melted basement rocks with ages in the range of ca. 127–132Ma also display both positive and negative εHf (t) values (−44.6 and 9.8) indicating a mixture of recycled ancient crust and juvenile magmas. Our study shows that although the peak of gold metallogeny coincided with the tectonics associated with Pacific plate subduction which mobilized and concentrated the ores, the source materials of gold mineralization and magmatism had multiple origins including from the Precambrian basement rocks, Mesozoic granitoids and mantle-derived mafic magmas with extensive mixing of crustal, lithosphere mantle and asthenospheric components. A combination of delamination, mantle upwelling, subduction-related metasomatic enrichment and recycling of ancient components facilitated the gold metallogeny in this region. Our study provides a typical case of juvenile and recycled components in the formation and evolution of continental crust and associated mineral resources.

The Paleozoic evolution of Central Tianshan: Geochemical and geochronological evidence

A suite of Paleozoic granitoids in Central Tianshan was studied for both geochemistry and geochronology in an effort to constrain their origin and tectonic setting. We combined LA-ICP-MS dating of zircon, standard geochemical analyses and Hf-isotopic studies of zircon to develop our tectonic model. Based on our analysis, the granitoids formed in three distinctive stages: ~450–400Ma, ~370–350Ma and ca. 340Ma. The first stage (450–400Ma) granitoids exhibit metaluminous, magnesian, high-K to shoshonitic characteristics of I-type granitoids (arc-setting), that are enriched in LREE relative to HREE with high (La/Yb)CN values, show negative Eu anomaly and are depleted in Nb, Ta and Ti. This phase of granitoid emplacement was most likely related to the southward subduction of the Paleo-Tianshan Ocean beneath the Tarim block and the subsequent Central Tianshan arc. In contrast, the second stage granitoids (370–350Ma) are distinctly different and are classified as calc-alkaline or shoshonitic plutons with a weak positive Eu anomaly. Within the second stage granitoids, it appears that the earlier (~365Ma) granitoids fit within the A-type field whereas the younger (~352Ma) granitoids plot within the post-collisional potassic field. These granitoids formed during collisions between Central Tianshan and the Tuha terrane that occurred along the northern margin of Central Tianshan. Lastly, the ca. 340Ma granitoids are typical of volcanic arc granitoids again that probably formed during the northward subduction of the South Tianshan Ocean beneath the Central Tianshan landmass or the subsequent southward subduction of the residual Paleo-Tianshan Ocean.The Hf isotopic data of zircons from all the studied granitoids were pooled and yielded three prominent Hf TDMC model age populations: ca. 2400Ma, ca. 1400Ma and ca. 1100Ma. The Hf-data shows a significant input of juvenile crust in addition to crustal recycling. We interpret these three phases of juvenile crustal addition to phases of global growth of continental crust (~2400Ma), the addition of juvenile crust during the breakup of the Columbia supercontinent (~1400Ma) and the assembly of Rodinia (~1100Ma).

Geochemistry and petrogenesis of Mashhad granitoids: An insight into the geodynamic history of the Paleo-Tethys in northeast of Iran

Mashhad granitoids in northeast Iran are part of the so-called Silk Road arc that extended for 8300km along the entire southern margin of Eurasia from North China to Europe and formed as the result of a north-dipping subduction of the Paleo-Tethys. The exact timing of the final coalescence of the Iran and Turan plates in the Silk Road arc is poorly constrained and thus the study of the Mashhad granitoids provides valuable information on the geodynamic history of the Paleo-Tethys. Three distinct granitoid suites are developed in space and time (ca. 217–200Ma) during evolution of the Paleo-Tethys in the Mashhad area. They are: 1) the quartz diorite–tonalite–granodiorite, 2) the granodiorite, and 3) the monzogranite. Quartz diorite–tonalite–granodiorite stock from Dehnow–Vakilabad (217±4–215±4Ma) intruded the pre-Late Triassic metamorphosed rocks. Large granodiorite and monzogranite intrusions, comprising the Mashhad batholith, were emplaced at 212±5.2Ma and 199.8±3.7Ma, respectively. The high initial 87Sr/86Sr ratios (0.708042–0.708368), low initial 143Nd/144Nd ratios (0.512044–0.51078) and low εNd(t) values (−5.5 to −6.1) of quartz diorite–tonalite–granodiorite stock along with its metaluminous to mildly peraluminous character (Al2O3/(CaO+Na2O+K2O) Mol.=0.94–1.15) is consistent with geochemical features of I-type granitoid magma. This magma was derived from a mafic mantle source that was enriched by subducted slab materials. The granodiorite suite has low contents of Y (≤18ppm) and heavy REE (HREE) (Yb<1.53ppm) and high contents of Sr (>594ppm) and high ratio of Sr/Y (>35) that resemble geochemical characteristics of adakite intrusions. The metaluminous to mildly peraluminous nature of granodiorite from Mashhad batholiths as well as its initial 87Sr/86Sr ratios (0.705469–0.706356), initial 143Nd/144Nd ratios (0.512204–0.512225) and εNd(t) values (−2.7 to −3.2) are typical of adakitic magmas generated by partial melting of a subducted slab. These magmas were then hybridized in the mantle wedge with peridotite melt. The quartz diorite–tonalite–granodiorite stock and granodiorite batholith could be considered as arc-related granitoid intrusions, which were emplaced during the northward subduction of Paleo-Tethys Ocean crust beneath the Turan micro-continent. The monzogranite is strongly peraluminous (Al2O3/(CaO+Na2O+K2O) Mol.=1.07–1.17), alkali-rich with normative corundum ranging between 1.19% and 2.37%, has high initial 87Sr/86Sr ratios (0.707457–0.709710) and low initial 143Nd/144Nd ratios (0.512042–0.512111) and εNd(t) values (−5.3 to −6.6) that substantiate with geochemical attributes of S-type granites formed by dehydration-melting of heterogeneous metasedimentary assemblages in thickened lower continental crust. The monzogranite was emplaced as a consequence of high-temperature metamorphism during the final integration of Turan and Iran plates. The ages found in the Mashhad granites show that the subduction of Paleo-Tethys under the Turan plate that led to the generation of arc-related Mashhad granites in late-Triassic, finally ceased due to the collision of Iran and Turan micro-plates in early Jurassic.

The U-Pb age, geochemistry and tectonic significance of granitoids in the Soursat Complex, Northwest Iran

The Soursat Complex in northwestern of Iran is part of the Sanandaj-Sirjan metamorphic belt. Three granitoid suites are present: Type I- syenogranite and deformed syenogranite; Type II- Turkeh Dare and Pichagchi plutons; and Type III- quartz porphyry. The granites can be assigned to a medium-K calc-alkaline to high-K calc-alkaline series. The Type I granitoids are weakly to strongly peraluminous and belong to a S-type suite, whereas Type II plutons are metaluminous to weakly peraluminous with I-type character. Type III granitoids are weakly peraluminous and can be labelled as a highly fractionated I-type suite. U/Pb zircon dating of the syenogranite and deformed syenogranite from Type I and Type II granitoids by laser inductively coupled plasma mass spectrometry (LA-ICP-MS) yielded ^{238}U/^{206}Pb emplacement ages of ~540 Ma (543±6 Ma and 537±8 Ma) and 59.0±2.7 Ma, respectively. Rare Earth Elements in the Type I granitoids are strongly fractionated with (La/Lu)_N= 32 to 52 and negative Eu anomalies (Eu/Eu*= 0.09-0.72), typical for plagioclase fractionation; the primitive mantle-normalized element patterns are homogeneous with marked negative Ba, Nb, Ta, Sr and Eu anomalies. Based on geochemical data, Type I granitoids are formed in a continent-continent collision, which could be related to Cadomian collision along the northern margin of Gondwana after its final amalgamation. Types II and III granitoids have I-type affinities and show homogeneous and moderately fractionated REE patterns with (La/Lu)_N= 17-34. Primitive mantle-normalized element patterns are homogeneous with marked negative Nb, Ta, Sm and Ti anomalies. The Soursat Complex is shown to contain early- to syn-collisional granitoid magmatism of Ediacaran-Cambrian age and a subsequent group of Palaeocene I-type granitoids that are syn- to post-collisional with respect to the Arabia-Eurasia collision and are interpreted to represent roll-back during the closure of Neotethys, pre-dating the Arabia-Eurasia collision.

Petrogenesis and tectonic significance of Early Cretaceous high-Zr rhyolite in the Dazhou uranium district, Gan-Hang Belt, Southeast China

Early Cretaceous felsic intrusions and volcanic rocks are widespread in the Gan-Hang Belt, SE China. In this study, we report a distinctive high-Zr rhyolite (802–1145ppm Zr) from the Dazhou uranium district in the eastern Gan-Hang Belt. SHRIMP zircon U–Pb dating shows that the Dazhou rhyolite erupted at 127.3±1.7Ma. Geochemical data indicate A-type characteristics for the Dazhou rhyolite, such as high contents of alkali elements, high Fe2O3∗/MgO and high Ga/Al ratios, enrichment in some LILEs, HFSEs, and REEs, and depletion in Sr, Ba, P, and Ti. Compared to other A-type granitoids reported previously in the same belt, the Dazhou high-Zr rhyolite shows only a slight enrichment in other HFSE elements and LREE, but has similar whole-rock Nd and zircon Hf isotopic compositions to those A-type granitoids with relatively lower Zr concentrations, indicating that all these A-type rocks may have similar magma sources. Hence, the difference of Zr contents in these rocks is not due to their different source rocks. We found that zircon grains in the Dazhou high-Zr rhyolite are generally inheritance-poor, and the calculated zircon saturation temperatures are extremely high at ∼1000°C. It is therefore suggested that the distinctive high-Zr characteristic of the Dazhou rhyolite was a result of high-temperature suppression of zircon crystallization by ambient mafic magmas correlative with the upwelling of the asthenospheric mantle. The fundamental difference in magma temperature and magmatic evolution mechanism between the Dazhou high-Zr rhyolite and other A-type granitoid suites in the eastern Gan-Hang Belt brought about their different Zr concentrations.

High pressure rocks of the Acatlán Complex, southern Mexico: Large-scale subducted Ordovician rifted passive margin extruded into the upper plate during the Devonian–Carboniferous

High pressure (HP) rocks in the Paleozoic Acatlán Complex of southern Mexico occur in a median belt extruded into the complex, which is the root zone of a klippe to the west. These HP rocks are predominantly clastic metasedimentary rocks and include a bimodal suite of amphibolites and granitoids. U–Pb LA-ICPMS zircon dating indicates that one of the amphibolites was intruded at or before 461±2Ma, and a megacrystic granitoid yielded an intrusive age of 488 +8/−7Ma, which is within the 490–450Ma range of other dated HP megacrystic granitoids. The amphibolites have a tholeiitic (transitional to alkalic), within-plate chemistry derived from a heterogeneous mantle by various degrees of partial melting. The host metasedimentary rocks contain detrital zircons derived both from the Acatlán granitoids and the ca. 1.0–1.3Ga Oaxacan Complex, and are inferred to represent rifted passive margin sediments. An age of 348 +4/−1Ma from zircons in a migmatized amphibolite is interpreted as the time of migmatization and dates decompression melting following peak pressure at depths of 45–55km. Retrogression from 530°C to 370°C occurred between 343 and 335Ma. The predominance of reasonably coherent, rifted passive margin rocks over a surface area of 10×90km suggests removal of a large slice of the upper plate during flat slab subduction. This slice was subducted to depths of ca. 45–55km where it was underplated and transferred to the overriding plate. The absence of Oaxacan Complex rocks in the HP belt suggests the Oaxacan basement was subducted to greater depths. Underplating was followed by extrusion facilitated by extension in the upper plate that produced Mississippian rift basins east of the median HP belt. Westward overthrusting of the HP rocks produced a klippe that overrode Mississippian clastic wedge sediments.

The origin of Eo- and Neo-himalayan granitoids, Eastern Tibet

Two distinctive modes of post-collisional magmatism are evident along a transect through the eastern Himalaya at ca. 92°E. The first comprises Eocene igneous complexes emplaced into the central Tethyan Himalaya Series (THS) (Dala granitoids, 44.1±1.2Ma) and the core of the Yala-Xiangbo dome (Yala-Xiangbo granitoids, 42±5Ma). Trace element characteristics and Rb–Sr and Sm–Nd isotopes indicate that the Dala granitoids formed from sub-equal mixtures of Gangdese-type magmas and rocks of the Greater Himalayan Crystallines and/or THS. The Yala-Xiangbo granitoids are geochemically complex but interpreted to be evolved equivalents of the Dala granitoid suite. The undeformed Dala plutons constrain the timing of deformation of THS metasediments to be >44Ma and their compositions indicates that components of the Indian foreland sequences had been accreted to the hanging wall of the main Himalayan decollement by that time. The second magmatic mode comprises Miocene intrusions (Arunachal- and Tsona-types) similar in most respects to the High Himalayan Leucogranites documented throughout the range. Although fluid-absent melting of metapelites appears to be the dominant origin of Miocene Himalaya leucogranites, thermometry and trace element data for the Arunachal-type intrusions suggest that they formed under fluid-present conditions. Sr and Nd-isotopes indicate that Lesser Himalayan metasediments were involved during the partial melting that produced the Arunachal-type leucogranites.

Metamorphic evolution of the Chotanagpur Granite Gneiss Complex of the East Indian Shield: current status

Abstract Geological information on the Chotanagpur Granite Gneiss Complex (CGGC) has been reviewed with a view to: (a) identifying the different metamorphic episodes; (b) developing an event stratigraphy in the high-grade blocks; and (c) correlating the different metamorphic episodes with the globally extensive orogenic processes. Integrating the existing geological information, the geological evolution of the high-grade block of the CGGC has been divided into four stages associated with four distinct metamorphic events ( M I − M IV ). The earliest metamorphic event ( M I ) that is recorded in granulite enclaves in the regionally extensive felsic gneisses culminated in ultrahigh temperatures (&gt;900 °C at c . 5–8 kbar) at around 1.87 Ga. In the second stage, voluminous felsic magmas were intruded – the M I granulites – and were metamorphosed to form migmatitic felsic gneisses ( M II ) within about 1.66–1.55 Ga. The third stage witnessed intrusions of a suite of anorthosite and porphyritic granitoids ( c . 1.55–1.51 Ga), followed by high-grade metamorphism (700±50 °C, 6.5±1 kbar, M III ) during approximately 1.2–0.93 Ga. The fourth stage ( M IV ) is marked by the intrusion of a suite of mafic dykes, followed by infiltration-driven metamorphism (600–750 °C at 7±1) during 0.87–0.78 Ga. The proposed metamorphic events have been correlated with the supercontinental cycles in the Proterozoic time.

Timing the structural events in the Palaeoproterozoic Bolé–Nangodi belt terrane and adjacent Maluwe basin, West African craton, in central-west Ghana

The Maluwe basin, north-adjacent to the Sunyani basin, is the northernmost of the northeast-trending Eburnean volcaniclastic depositories in Ghana. These basins are separated from one another by remnants of Eoeburnean crust, all formed during the evolution of an arc-backarc basins complex in a Palaeoproterozoic intraoceanic environment. The Bolé–Nangodi belt terrane to the northwest, of mostly Eoeburnean crust is fault bounded with the Maluwe basin along the northeast-trending Bolé–Navrongo fault zone. The stratigraphic sequence, which was the key to unravelling the structural evolution of the study area, was established by means of field observations aided by precision SHRIMP geochronology. The quartzitic, pelitic, quartzofeldspathic and granitic gneisses of the Eoeburnean crust (>2150Ma) experienced complex metamorphic mineral growth and migmatitization, mostly under static crustal conditions and were subjected to several deformation episodes. The foliated mafic and metasedimentary enclaves within the Ifanteyire granite establish deformation to have taken place prior to ∼2195Ma, while the tectonically emplaced Kuri amphibolites within the 2187-Ma gneissic Gondo granite indicate a stage of rifting followed by collision. Deformation of granite dykes in the Gondo granites at ∼2150Ma concluded the development of the Eoeburnean orogenic cycle (DEE).The Sawla Suite, contemporaneous with the deposition of the Maluwe Group, intruded the tectonic exhumed Bolé–Nangodi terrane during extension between ∼2137 and 2125Ma. The rifting separated the Abulembire fragment from the Bolé–Nangodi terrane. During subsequent northwestward subduction of young back-arc basin oceanic crust the volcaniclastic strata of the Maluwe Group and Sawla granitoids were deformed (DE1) under chlorite/sericite greenschist-grade conditions. The NE-trending folds had subhorizontal axes and subvertical axial planes. Simultaneous to the DE1 orogenesis the molasses of the Banda Group was deposited concordantly on the submerged Sunyani strata after a hiatus of 20 million years. After cessation of the NW–SE-directed compression the early Tanina Suite intruded as batholiths, dykes and sheets and produced garnet, staurolite, sillimanite and kyanite in their thermal aureoles. Docking of the Sunyani basin produced the DE2 thrust related folding and stacking in the deformed and granitoid invaded Maluwe basin as well as the single stage sin- and anticlinoria in the Sunyani and Banda Groups. In the Maluwe basin the Abulembire fragment acted as a resistor and the approaching front rotated anticlockwise and clockwise around the barrier to form west- and north-directed piggy-back thrust-stacking and deformation of the Tanina Suite granitoids. Due to the low metamorphic conditions the DE2 fabric is limited to crenulation cleavages in the more psammitic and pelitic units. The fold axes are double plunging (N–S and E–W) up to 60° with the axial planar fabric subvertical. Post-D2 tectonic relaxation has allowed the emplacement of the last Tanina Suite calc-alkaline melts and was succeeded by N–S extension fracturing (DE3) along which mantle derived Wakawaka gabbroids and syenite intruded. The DE1 folding occurred between 2125 and 2122Ma and DE2 before 2119Ma. The tectonic relaxation occurred at 2118Ma. Around 2100Ma, NE–SW directed strike-slip shearing (DE4), fractured the Bolé–Nangodi terrane and enhanced the basin-belt boundary. Along the boundary, the displacement was dextral along vertical faults but, southward, it became more east-over-west thrust related. Associated tension gashes are filled with vein quartz and pegmatite and typical of the brittle sector of the crust. Tectonism in this part of the intraoceanic accretionary arc back-arc complex was concluded by limited, right-lateral strike-slip (DE5) movement which formed some breccias.