Geochemical constraints on the petrogenesis of the Paleozoic granitoids of the Sierra de San Luis,Sierras Pampeanas,Argentina

The Paleozoic granitoids of the Sierra de San Luis comprise the Ordovician tonalite suite (OTS; metaluminous to mildly peraluminous calcic tonalite–granodiorites) and granodiorite–granite suite (OGGS; peraluminous calcic to calc-alkaline granodiorite–monzogranites), as well as the Devonian granite suite (DGS; peraluminous alkali-calcic monzogranites) and monzonite–granite suite (DMGS; metaluminous alkali-calcic quartz monzonite–monzogranite ± granodiorite, mildly peraluminous alkalicalcic monzogranites). The OTS has relatively high K₂O, CaO, and Yb_N and low Cr, Ni, Ba, Sr, Rb/Sr, Sr/Y, and (La/Yb)_N, as well as negative Eu/Eu¹, high ⁸⁷Sr/⁸⁶Sr (0.70850–0.71114), and unradiogenic ε_Nd(470Ma) (−5.3 to −6.0), which preclude an origin of variably fractionated mantle melts and favour a mafic lower crustal source. The OGGS consists of two granitoids: (1) high-temperature characterized by low Al₂O₃/TiO₂, Rb/Sr, and (La/Yb)_N, a smooth negative Eu/Eu¹, and relatively high CaO and (2) low-temperature with high Al₂O₃/TiO₂ and Rb/Sr, low CaO, (La/Yb)_N, and Sr/Y, and negative Eu/Eu¹. Melting of metagreywackes at pressures below 10 kbar with a variable supply of water could account for the chemistry of the high-T OGGS, whereas dehydration melting of biotite-bearing metasedimentary sources at low pressures is proposed for the low temperature OGGS. Melting of crustal sources relates to a contemporaneous mafic magmatism.Devonian magmatism is characterized by high Ba, Sr, K₂O, Na₂O, Sr/Y, and (La/Yb)_N. Sources for the DGS include metasedimentary or metatonalitic protoliths. Biotite dehydration melting triggered by the addition of heat, supplied by mantle-derived magmas, is proposed. High Ba, Sr, LREE, MgO, Cr, Ni, Zr, and V of the monzonites suggest an enriched lithospheric mantle source. Low Yb and Y and high Sr and (La/Yb)_N indicate a garnet-rich residual assemblage (P ⩾ 10 kbar). Melts for the peraluminous rocks may have derived from a metasedimentary or metaigneous source at lower pressures in a process dominated by biotite consumption and plagioclase in the residue.The Ordovician granitoids are synkinematic with compressive deformation related to the early stages of Famatinian convergence. The Devonian magmatism is synkinematic with a system of shear zones that were active during the Achalian cycle.     

Magma sources and petrogenesis of the early–middle Paleozoic backarc granitoids from the central part of the Qilian block,NW China

The petrology, geochemistry, geochronology, and Sr–Nd–Hf isotopes of the backarc granitoids from the central part of the Qilian block are studied in the present work. Both S- and I-type granitoids are present. In petrographic classification, they are granite, alkali feldspar granite, felsic granite, diorite, quartz diorite, granodiorite, and albite syenite. The SHRIMP ages are 402–447 Ma for the S-type and 419–451 Ma for the I-type granitoids. They are mostly high-K calc-alkaline granitoids. The S-type granitoids are weakly to strongly peraluminous and are characterized by negative Eu anomalies (Eu/Eu* = 0.18–0.79). The I-type granitoids are metaluminous to weakly peraluminous and are characterized mostly by small negative to small positive Eu anomalies (Eu/Eu* = 0.71–1.16). The initial (⁸⁷Sr/⁸⁶Sr) values are 0.708848–0.713651 for the S-type and 0.704230–0.718108 for the I-type granitoids. The ε_Nd(450 Ma) values are − 8.9–−4.1 and − 9.7–+ 1.9 for the S-type and I-type granitoids, respectively. The T_DM values are 1.5–2.4 Ga for the S-type and 1.0–2.3 Ga for the I-type granitoids. For the Qilian block, the backarc granitoid magmatism took place approximately 60 million years after the onset of the southward subduction of the north Qilian oceanic lithosphere and lasted approximately 50 million years. Partial melting of the source rocks consisting of the Neoproterozoic metasedimentary rocks of the Huangyuan Group and the intruding lower Paleozoic basaltic rocks could produce the S-type granitoid magmas. Partial melting of basaltic rocks mixed with lower continental crustal materials could produce the I-type granitoid magmas. Major crustal growth occurred in the late Archean and Meso-Paleoproterozoic time for the Qilian block. The magma generation was primarily remelting of the crustal rocks with only little addition of the mantle materials after 1.0 Ga for the Qilian block.     

Petrogenesis and tectonic implications of early Palaeozoic igneous rocks of the western South Qilian Belt,central China

Early Palaeozoic granitoids in the South Qilian Belt, central China, record details of the tectonic evolution and crustal growth of the Qilian orogenic belt. Five representative granitoids from the western South Qilian Belt were sampled for zircon LA-ICPMS U–Pb dating, Lu–Hf isotopes, and whole-rock geochemical analyses. Zircon U–Pb dating of two porphyritic granodiorites and a porphyritic monzogranite yielded ages of 442.7 ± 3.5, 441.8 ± 4.3, and 435.4 ± 3.5 Ma, respectively. These granitoids exhibit a geochemical affinity to I-type granite, are metaluminous with a low aluminium saturation index (A/CNK = 0.75–1.15), have moderate Al₂O₃ and low MgO contents, high La/Yb and low Sr/Y ratios, and are depleted in Nb, Ta, P, and Ti, which suggests a subduction zone magmatic arc affinity, with mixing between a primary mantle-derived magma with lesser continental crustal material. The syenogranite and monzogranite from the South Qilian Belt, which yield U–Pb zircon ages of 440.4 ± 9.0 and 442.3 ± 1.2 Ma, respectively, have pronounced S-type geochemical affinities, are peraluminous with A/CNK values of 1.07–1.16, have relatively high SiO₂, Al₂O₃, K₂O, and Rb contents, low Y and Yb, low Sr/Y and La/Yb ratios, positive Th, U, and light Rare Earth Element (REE) anomalies, and depletions in Nb, Ta, Sr, and Ti. Their geochemical signature suggests derivation from partial melting of continental crust in a syn-collisional setting. The Hf isotopic data of zircons from the granitoids show a significant input of Paleoproterozoic crust in the crustal formation of the western South Qilian Belt in Palaeozoic. Compare the ε_Hf(t) value of S-type granite with that of I-type granite, the former may have a comparatively homogeneous source. Together with regional evidence, it is proposed that a collisional event occurred between the South Qilian Belt and the Central Qilian Belt at ca. 442–435 Ma.     

Constraints on Variscan granite emplacement in north-east Bavaria,Germany: further clues from a petrogenetic study of the Mitterteich granite

Petrochemical and Rb-Sr, K-Ar and Sm-Nd isotopic data presented for the Mitterteich granite provide information on whole rock and mineral compositional characteristics, intrusion and cooling history, and protolith nature and put further constraints on the Variscan magmatic evolution in north-east Bavaria.The compositional characteristics classify the Mitterteich granite as a peraluminous (monzo-)granite (SiO₂ 67.3–73.5 wt.% ). Values for K₂O/Na₂O (> 1.2 and Al₂O₃/(CaO + N₂O + K₂O) (>1.1) are in the range of S-type granites. The rare earth elements show fractionated chondrite-normalized patterns (La _N /Yb _N =24–19) with negative Eu anomalies (Eu _N /Eu _N ^*=0.35–0.19). The micas have restricted ranges of major element composition, but reveal notable variations in trace element concentrations. Different biotite fractions of single specimens show a trend to lower concentrations of compatible elements in the finer fraction which can be explained as a result of asynchronous growth during the fractionation process. The PT conditions of crystallization of the magma based on muscovite and biotite is 600–640°C at 3 kbar. Regression of the whole rock samples gives an isochron corresponding to a ⁸⁷Rb-⁸⁷Sr age of 310 ± 7 Ma, initial ⁸⁷Sr/⁸⁶Sr of 0.7104±0.0010 (2 errors) and MSWD =0.03. Muscovite and biotite yield concordant K-Ar ages between 310 and 308 Ma, indicating a fast cooling rate of the granite intrusion. _{Nd T310}values average –4.2±1.0. Nd model ages of 1.4 Ga suggest a source region of mid-Proterozoic age.The Rb-Sr isochron age and initial Sr ratio of the Mitterteich granite are indistinguishable from those of the adjacent Falkenberg granite, establishing a genetic link. However, the K-Ar mica ages suggest that the Mitterteich granite must have undergone a faster uplift or cooling history than Falkenberg. Confronted with the geochronological record of granite emplacement in north-east Bavaria, the new results substantiate the view of three key periods of magmatic activity around 330–325, 315–305 and 290 Ma.     

Geochemistry and Nd–Sr isotopic studies of Late Mesozoic granitoids in the southeastern Hubei Province, Middle–Lower Yangtze River belt, Eastern China: Petrogenesis and tectonic setting

A geochemical and isotopic study was carried out for the Mesozoic Yangxin, Tieshan and Echeng granitoid batholiths in the southeastern Hubei Province, eastern China, in order to constrain their petrogenesis and tectonic setting. These granitoids dominantly consist of quartz diorite, monzonite and granite. They are characterized by SiO₂ and Na₂O compositions of between 54.6 and 76.6 wt.%, and 2.9 to 5.6 wt.%, respectively, enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), and relative depletion in Y (concentrations ranging from 5.17 to 29.3 ppm) and Yb (0.34–2.83 ppm), with the majority of the granitoids being geochemically similar to high-SiO₂ adakites (HSA). Their initial Nd (ε_Nd = − 12.5 to − 6.1) and Sr ((⁸⁷Sr/⁸⁶Sr)_i = 0.7054–0.7085) isotopic compositions, however, distinguish them from adakites produced by partial melting of subducted slab and those produced by partial melting of the lower crust of the Yangtze Craton in the Late Mesozoic. The granitoid batholiths in the southeastern Hubei Province exhibit very low MgO ranging from 0.09 to 2.19 wt.% with an average of 0.96 wt.%, and large variations in negative to positive Eu anomalies (Eu/Eu = 0.22–1.4), especially the Tieshan granites and Yangxin granite porphyry (Eu/Eu = 0.22–0.73). Geochemical and Nd–Sr isotopic data demonstrate that these granitoids originated as partial melts of an enriched mantle source that experienced significant contamination of lower crust materials and fractional crystallization during magma ascent. Late Mesozoic granitoids in the southeastern Hubei Province of the Middle–Lower Yangtze River belt were dominantly emplaced in an extensional tectonic regime, in response to basaltic underplating, which was followed by lithospheric thinning during the early Cretaceous.     

Petrography and geochemistry of the Ngaoundéré Pan-African granitoids in Central North Cameroon: Implications for their sources and geological setting

The Nagoundéré Pan-African granitoids in Central North Cameroon belong to a regional-scale massif, which is referred to as the Adamawa-Yade batholith. The granites were emplaced into a ca. 2.1 Ga remobilised basement composed of metasedimentary and meta-igneous rocks that later underwent medium- to high-grade Pan-African metamorphism. The granitoids comprise three groups: the hornblende–biotite granitoids (HBGs), the biotite ± muscovite granitoids (BMGs), and the biotite granitoids (BGs). New Th–U–Pb monazite data on the BMGs and BGs confirm their late Neoproterozoic emplacement age (ca. 615 ± 27 Ma for the BMGs and ca. 575 Ma for the BGs) during the time interval of the regional tectono-metamorphic event in North Cameroon. The BMGs also show the presence of ca. 926 Ma inheritances, suggesting an early Neoproterozoic component in their protolith.The HBGs are characterized by high Ba–Sr, and low K₂O/Na₂O ratios. They show fairly fractionated REE patterns (La_N/Yb_N 6–22) with no Eu anomalies. The BMGs are characterized by higher K₂O/Na₂O and Rb/Sr ratios. They are more REE-fractionated (La_N/Yb_N = 17–168) with strong negative Eu anomalies (Eu/Eu^* = 0.2–0.5). The BGs are characterized by high SiO₂ with K₂O/Na₂O > 1. They show moderated fractionated REE patterns (La_N/Yb_N = 11–37) with strong Eu negative anomalies (Eu/Eu^* = 0.2–0.8) and flat HREE features (Gd_N/Yb_N = 1.5–2.2). In Primitive Mantle-normalized multi-element diagrams, the patterns of all rocks show enrichment in LILE relative to HFSE and display negative Nb–Ta and Ti anomalies. All the granitoids belong to high-K calc-alkaline suites and have an I-type signature.Major and trace element data of the HBGs are consistent with differentiation of a mafic magma from an enriched subcontinental lithospheric mantle, with possible crustal assimilation. In contrast, the high Th content, the LREE-enrichment, and the presence of inherited monazite suggest that the BGs and BMGs were derived from melting of the middle continental crust. Structural and petrochemical data indicate that these granitoids were emplaced in both syn- to post-collision tectonic settings.     

Geochronology and geochemistry of Cretaceous–Eocene granites,Tengchong Block (SW China): Petrogenesis and implications for Mesozoic-Cenozoic tectonic evolution of Eastern Tethys

The Early Cretaceous–Early Eocene granitoids in the Tengchong Block record the evolutionary history of the Mesozoic-Cenozoic tectono-magmatic evolution of Eastern Tethys. (a) The Early Cretaceous granitoids with relatively low (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7090–0.7169 and ε_Nd(t) values of ?9.8 to ?7.8 display metaluminous, calc-alkaline dominated by I-type granite affinity and hybrid mantle–crust geochemical signatures. They may have been derived from melting of the subducted Meso-Tethyan Bangong-Nujiang oceanic crust with terrigenous sediments in an arc-continent collisional setting. (b) The Late Cretaceous–Paleocene granitoids with relatively high (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7109–0.7627, and ε_Nd(t) values of ?12.1 to ?7.9 exhibit metaluminous to peraluminous, calc-alkaline dominated by S-type granite affinity and hybrid Lower–Upper crust geochemical signatures, which may be originated from partial melting of the Meso-Proterozoic continental crust in the collision setting between the Tengchong Block and Baoshan Block. (c) The Early Eocene granitoids have metaluminous, calc-alkaline I-type and S-type granites dual affinity, with relatively high (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.711–0.736, ε_Nd(t) values of ?9.4 to ?4.7, showing crust-mantle mixing geochemical signatures. They may have been originated from partial melting of the late Meso-Proterozoic upper crustal components mixed with some upper mantle material during the ascent process of mantle magma caused by the subduction of the Neo-Tethyan Putao–Myitkyian oceanic crust, and collision between the Western Burma Block and the Tengchong Block. It is these multi-stage subductions and collisions that caused the spatial and temporal distribution of the granitic rocks in the Tengchong Block.     

Pan-African Magmatism, and Sedimentation in the NW Himalaya

Correlation of early Palaeozoic, Pan-African (500 ± 50 Ma) granites that intruded the Chail, Salkhala, Haimanta Formations in the Lesser Himalaya, Zanskar crystallines, and Lower Taglang La of Tso-Morari crystallines in the northwestern Himalaya, is based on the field relationship, tectonic setting, mineralogical, and geochemical characteristics, and isotope dating of the granites. These granite plutons exhibit identical petrographical, and geochemical character. The mineralogical composition of the granites is quite similar, consisting of quartz, K-feldspar, plagioclase feldspar, biotite, muscovite, garnet, tourmaline, ± cordierite, andalusite, and sillimanite fibrolite. The granite which are massive, and inequigranular in the core of the plutons, show strongly foliated character indicating development of ductile shear zone at the margins. These are peraluminous S-type granites having high A/CNK value (> 1). Presence of normative corundum, rounded shape of zircon, and high initial Sr ratio suggest crustal source of the granites. Mantle normalized spider-diagram exhibits similar characters for all these granitoids. The intrusion of the Pan-African granites mark an abrupt end of the sedimentation that continued virtually uninterrupted from Palaeoproterozoic. The sudden break in sedimentation towards the terminal phases of the Lower Cambrian has been observed in almost all parts in Lesser as well as the Tethys Himalaya. Occurrences of large number of plutons along different tectonic belts of northwestern Himalaya are indicative of widespread tectono-thermal event during early Palaeozoic (500 ± 50 Ma). The bracketing of the two features like, the break in sedimentation during post-Late Cambrian, and the intrusion of granites around 500 ± 50 Ma, is considered to be the result of a strong diastrophic orogenic event correlatable to the late phases of the Pan-African Orogeny in Africa.     

Early Palaeozoic crustal melting in an extensional setting: petrological and Sm–Nd evidence from the Izera granite-gneisses, Polish Sudetes

The Izera Block in the West Sudetes, which is composed of granites, gneisses (and transitional granite-gneisses) and minor mica schists, is one of the largest outcrops of Early Palaeozoic (ca. 500 Ma) metagranitoid rocks in the basement units of the Variscides of Central Europe. The Izera granites show S-type features: magmatic cordierite, relict garnet and sillimanite, lack of mafic enclaves, and absence of coexisting tonalites and diorites. The paucity of pegmatites indicates that the granitic magma was relatively dry. The S-type character of these granites is further supported by their peraluminous character (A/CNK 1.0–1.63), high content of normative corundum (up to 3.5%) and relatively high ⁸⁷Sr /⁸⁶Sr initial ratio. The chemical variation of these rocks was controlled by the fractional crystallization of plagioclase (CaO, Sr, Eu/Eu*), biotite and cordierite (Al₂O₃, MgO, FeO), zircon (Zr, Hf) and monazite (REE). Initial Nd values range from –5.2 to –6.9 (mean: –5.9, SD=0.6). These largely negative Nd values imply that the granitic magmas emplaced ca. 500 Ma were extracted from a source reservoir that was strongly enriched in LREE (i.e., with low Sm/Nd ratio) on a time-integrated basis. The relatively consistent depleted mantle model ages (1,730–2,175 Ma; mean: 1,890 Ma) is in agreement with the earlier reported presence of ca. 2.1 Ga old inherited Pb component in zircon from the closely related Rumburk granite. This points to an old (Early Proterozoic) crustal residence age of the inferred metasedimentary protoliths of the Izera granitoids, with only minor contribution to their protoliths of juvenile components of Late Proterozoic/Early Palaeozoic age. Although the Izera granites show some trace element features reminiscent of syn-collisional or post-collisional granitoids, they more likely belong to the broad anorogenic class. Our data corroborate some previous interpretations that granite generation was connected with the Early Palaeozoic rifting of the passive margin of the Saxothuringian block, well documented in the region by bimodal volcanic suites of similar age (Kaczawa Unit, eastern and southern envelope of the Karkonosze–Izera Block). In this scenario, granite magmatism and bimodal volcanism would represent two broadly concomitant effects of a single major event of lithospheric break-up at the northern edge of Gondwana.     

Geochemical and mantle-like isotopic (Nd, Sr) composition of the Baklan Granite from the Muratdağı Region (Banaz, Uşak), western Turkey: Implications for input of juvenile magmas in the source domains of western Anatolia Eocene–Miocene granites

The (late syn)- post-collisional magmatic activities of western and northwestern Anatolia are characterized by intrusion of a great number of granitoids. Amongst them, Baklan Granite, located in the southern part of the Muratdağı Region from the Menderes Massif (Banaz, Uşak), has peculiar chemical and isotopic characteristics. The Baklan rocks are made up by K-feldspar, plagioclase, quartz, biotite and hornblende, with accessory apatite, titanite and magnetite, and include mafic microgranular enclaves (MME). Chemically, the Baklan intrusion is of sub-alkaline character, belongs to the high-K, calc-alkaline series and displays features of I-type affinity. It is typically metaluminous to mildly peraluminous, and classified predominantly as granodiorite in composition. The spider and REE patterns show that the rocks are fractionated and have small negative Eu anomalies (Eu/Eu^* = 0.62–0.86), with the depletion of Nb, Ti, P and, to a lesser extent, Ba and Sr. The pluton was dated by the K–Ar method on the whole-rock, yielded ages between 17.8 ± 0.7 and 19.4 ± 0.9 Ma (Early Miocene). The intrusion possesses primitive low initial ⁸⁷Sr/⁸⁶Sr ratios (0.70331–0.70452) and negative ε_Nd(t) values (−5.0 to −5.6). The chemical contrast between evolved Baklan rocks (SiO₂, 62–71 wt.%; Cr, 7–27 ppm; Ni, 5–11 ppm; Mg#, 45–51) and more primitive clinopyroxene-bearing monzonitic enclaves (SiO₂, 54–59 wt.%; Cr, 20–310 ppm; Ni, 10–70 ppm; Mg#, 50–61) signifies that there is no co-genetic link between host granite and enclaves. The chemical and isotopic characteristics of the Baklan intrusion argue for an important role of a juvenile component, such as underplated mantle-derived basalt, in the generation of the granitoids. Crustal contamination has not contributed significantly to their origin. However, with respect to those of the Baklan intrusion, the generation of the (late syn)- post-collisional intrusions with higher Nd(t) values from the western Anatolia require a much higher amount of juvenil component in their source domains.     

Early Proterozoic postcollisional granitoids of the Biryusa block of the Siberian craton

Comprehensive geochemical and geochronological studies were carried out for two-mica granites of the Biryusa block of the Siberian craton basement. U-Pb zircon dating of the granites yielded an age of 1874 ± 14 Ma. The rocks of the Biryusa massif correspond in chemical composition to normally alkaline and moderately alkaline high-alumina leucogranites. By mineral and petrogeochemical compositions, they are assigned to S-type granites. The low CaO/Na₂O ratios (< 0.3), K₂O - 5 wt.%, CaO < 1 wt.%, and high Rb/Ba (0.7-1.9) and Rb/Sr (3.9-6.8) ratios indicate that the two-mica granites resulted from the melting of a metapelitic source (possibly, the Archean metasedimentary rocks of the Biryusa block, similar to the granites in £_Nd(t) value) in the absence of an additional fluid phase. The granite formation proceeded at 740-800 °C (zircon saturation temperature). The age of the S-type two-mica granites agrees with the estimated ages of I- and A-type granitoids present in the Biryusa block. Altogether, these granitoids form a magmatic belt stretching along the zone of junction of the Biryusa block with the Paleoproterozoic Urik-Iya terrane and Tunguska superterrane. The granitoids are high-temperature rocks, which evidences that they formed within a high-temperature collision structure. It is admitted that the intrusion of granitoids took place within the thickened crust in collision setting at the stage of postcollisional extension in the Paleoproterozoic. This geodynamic setting was the result of the unification of the Neoarchean Biryusa continental block, Paleoproterozoic Urik-Iya terrane, and Archean Tunguska superterrane into the Siberian craton.     

Rb-Sr Isotope Dating of Neoproterozoic (Malani Group) Magmatism from Southwest Rajasthan, India: Evidence of Younger Pan-African Thermal Event by Ar-Ar Studies

This paper reports Rb-Sr isotope ages of the Neoproterozoic volcanics, and associated granitoids of the trans-Aravalli belt of northwestern India. All these rocks along with the earlier reported 779±10 Ma old felsic volcanics from Diri, and Gurapratap Singh of Pali district, Rajasthan, constitute the Malani Group. The study indicates that different rock suites belonging to the Malani Group represent a polyphase igneous activity which spanned for about 100 Ma ranging from 780 to 680 Ma. The granitoids of the Malani Group, i.e. peraluminous Jalore type, and peralkaline Siwana type, were emplaced around 730, and 700 Ma ago, respectively. These plutonic suites represent two different magmatic episodes within a short time interval. The initial Sr ratios of these granitoids suggest lower crustal derivation of the magma. The peralkaline granitoids, and the associated peralkaline rhyolites (pantellerites) are coeval, and cogenetic. The ultrapotassic rhyolite exposed at Manihari of Pali district represents the youngest magmatic activity at 681±20 Ma, having a very high initial Sr ratio of 0.7135±0.0033. The high initial Sr ratio of these rocks may be due to incorporation of radiogenic ⁸⁷Sr from the country rock, by assimilation or fusion, into the residual fraction of the magma in the crust which gave rise to other differentiated rocks of the Group.⁴⁰Ar³⁹Ar studies of two Jalore granite samples indicate presence of post crystallisation thermal disturbance between 500550 Ma ago. The timing of this thermal overprinting on the Malani rocks is related to the widespread Pan-African thermo-tectonic event which is witnessed, and magmatically manifested in different part of the Indian shield.     

Diversity of late Neoarchean K-rich granitoid rocks derived from subduction-related crust/mantle interactions in the Jiaobei terrane,North China Craton

The appearance of voluminous K-rich granitoids within nearly all ancient cratons represents one major characteristic of late Archean Earth, which hold the key to understand the transitional geodynamic regimes globally during this period. The genetic regimes and links among different K-rich granitoids and their implications for crustal growth and evolution remain controversial. A series of late Neoarchean K-rich granitoids, including quartz dioritic, granodioritic, and monzogranitic gneisses, occur in the Jiaobei terrane of North China Craton. Zircon U-Pb isotopic data reveal that they emplaced during ~2544–2494 Ma, coeval with regional ~2530–2470 Ma high-grade metamorphism.The quartz dioritic-granodioritic gneisses are magnesian rocks, and they show low Si and Ti, but high K and Mg, similar to Archean low-Ti sanukitoids. The Sr/Y and (La/Yb)_N are high (mostly 59.99–119.32 and 8.56–61.42), with moderate to high Nb (up to 11.79 ppm). Geochemical modeling, combined with depleted zircon εHf(t₂) (+0.5 − +7.2) and the presence of minor xenocrystic zircons, indicate that these low silica samples were derived from a metasomatized depleted mantle source with inputs of slab-derived fluids and melts, and minor contamination by ancient crustal materials. The monzogranitic rocks are ferroan rocks showing high Si, K, and Fe, but low Mg. They are divided into two subgroups: the first displays low TREE of 44.00–127.00 ppm and positive Eu anomalies (Eu_N/Eu*_N = 1.06–1.60), whereas the second shows high TREE of 85.76–819.02 ppm but negative Eu anomalies (Eu_N/Eu*_N = 0.51–0.62). Geochemical modeling and depleted zircon εHf(t₂) of +2.6 − +8.4 suggest their formation by partial melting of juvenile crustal sources involving tonalitic and some metasedimentary rocks at diverse crustal levels.Combined with regional geological data, these late Neoarchean K-rich granitoids were generated by coupled melting of metasomatized depleted mantle and dominantly juvenile crustal materials during crustal stabilization. Furthermore, the Jiaobei terrane experienced ~2.6–2.5 Ga crustal growth under a subduction-accretion setting.     

Petrogenesis of Rabor-Lalehzar magmatic rocks (SE Iran): Constraints from whole rock chemistry and Sr-Nd isotopes

The Urumieh-Dokhtar magmatic arc (UDMA) of Central Iran has been formed during Neotethyan Ocean subduction underneath Eurasia. The Rabor-Lalehzar magmatic complex (RLMC), covers an area ～1000?km² in the Kerman magmatic belt (KMB), SE of UDMA. RLMC magmatic rocks include both granitoids and volcanic rocks with calc-alkaline and adakitic signatures but with different ages.Miocene adakitic rocks are characterd by relatively enrichmented in incompatible elements, high (Sr/Y)_(N) (>40), and (La/Yb)_(N) (>10) ratios with slightly negative Eu anomalies (Eu_N/Eu*≈ 0.9), depletion in HFSEs, and relatively non-radiogenic Sr isotope signatures (⁸⁷Sr/⁸⁶Sr?=?0.7048–0.7049). In contrast, the Oligocene granitoids exhibit low Sr/Y (<20) and La/Yb (<9) ratios, negative Eu anomalies (Eu_N/Eu*?≈?0.5), and enrichment in HFSEs and radiogenic Sr isotope signatures (⁸⁷Sr/⁸⁶Sr?=?0.7050–0.7052), showing affinity to the island arc rocks. Eocene volcanic rocks which crusscut the younger granitoid rocks comprise andesites and dacites. Geochemically, lavas show calc-alkaline character without any Eu anomaly (Eu_N/Eu*?≈?1.0). Based on the geochemical and isotopic data we propose that melt source for both calc-alkaline and adakitic rocks from the RLMC can be related to the melting of a sub-continental lithospheric mantle (SCLM). Basaltic melts derived from a metasomatized mantle wedge might be emplaced at the mantle-crust boundary and formed the juvenile mafic lower crust. However, some melts fractionated in the shallow magma chambers and continued to rise forming the volcanic intermediate-mafic rocks at the surface. On the other hand, the assimilation and fractional crystallization in the shallow magma chambers of may have been responsible for the development of Oligocene granitoids with calc-alkaline affinity. In the mid-Late Miocene, following the collision between Afro-Arabia and Iranian block the juvenile mafic crust of UDMA underwent thickening and metamorphosed into garnet-amphibolites. Subsequent upwelling of a hot asthenosphere during Miocene was responsible for partial melting of thickened juvenile crust of the SE UDMA (RLM complex). The adakitic melts ascended to the shallow crust to form the adakitic rocks in the KMB.     

Geochemistry of the Bafoussam Pan-African I- and S-type granitoids in western Cameroon

The Bafoussam area in western Cameroon is part of the Central African Orogenic Belt. It is dominated by granitoids which belong to the Pan-African syn- to post-collisional post-650 Ma group. Syenogranites are predominant, but alkali-feldspar granite, monzogranite, quartz-monzonite and quartz-monzodiorite occur as well. Four granitoid suites, biotite granitoids and deformed biotite granitoids with amphibole, megafeldspar granitoids with megacrysts and two-mica granitoids with primary muscovite and igneous garnet are distinguished. The granites can be assigned to high-K calc-alkalic to shoshonitic series. The partly shoshonitic biotite granitoids are metaluminous to weakly peraluminous and can be labelled as a highly fractionated I-type suite. The megafeldspar granitoids are weakly peraluminous with I-type character whereas the two-mica granitoids are weakly to strongly peraluminous and belong to an S-type suite. Emplacement ages at 558–564 Ma for the two-mica granitoids have been dated from monazite by the EMP Th–U–Pb method.The REE in the biotite granitoids are moderately fractionated with (La/Lu)_N = 23–38. Enrichment of Nb and Ta varies by one order of magnitude. The megafeldspar granitoids show homogeneous and strongly fractionated REE patterns with (La/Lu)_N = 27–42. The primitive mantle-normalized element patterns are homogeneous with marked negative Ba, Nb, Ta, Sr, Eu and Ti anomalies. The two-mica granitoids are characterized by low to moderate total REE contents with strongly fractionated REE expressed by (La/Lu)_N ranging from 7 to 59. The negative Nb and Ta anomalies are less significant. Nd and Sr whole-rock isotope data confirm different sources for the granitoid suites. The source of the I-type biotite granitoids was probably a juvenile mantle which has been variably metasomatized. The source of the I-type megafeldspar granitoids is characterized by juvenile mantle and lower crust components. Anatectic melts of the upper continental crust with variable contribution of lower continental crust or mantle melts can explain the heterogeneous isotopic signatures of the S-type two-mica granitoids. It is suggested that the melting of these sources was successively initiated by the rising isotherms during a syn- to post-collisional setting which followed a subduction.     

Archean geodynamics in the Central Zone, North China Craton: constraints from geochemistry of two contrasting series of granitoids in the Fuping and Wutai complexes

The Archean to Paleoproterozoic Central Zone of the North China Craton is situated between the Eastern and Western Archean continental blocks and contains two contrasting series of Neoarchean granitoids: the 2523–2486 Ma tonalite−trondhjemite–granodiorite (TTG) gneisses in the Fuping Complex, and the 2555–2525 Ma calc-alkaline granitoids (tonalite, granodiorite, granite and monzogranite) in the Wutai Complex. The Fuping TTG gneisses most likely formed from partial melting of 2.7 Ga basalts at >50 km, with an involvement of 3.0 Ga crustal material. The Wutai granitoids have higher K₂O, LILE and Rb/Sr, but lower Sr/Y and La_N/Yb_N than the Fuping TTG gneisses, are characterized by Nd T_DM from 2.5 to 2.8 Ga and _Nd(t) from 0.49 to 3.34, and are derived from partial melting of a juvenile source at <37 km.The geochemistry of these two contrasting series of Neoarchean granitoids provides further evidence that the Wutai Complex originated and evolved separately from the Fuping Complex. The Wutai Complex most likely formed as an oceanic island arc with volcanism and synvolcanic granitoid intrusions at 2555–2525 Ma. The Wutai Complex was subsequently accreted onto the Eastern Archean Continental Block, and was probably responsible for crustal thickening and TTG magmatism at 2523–2486 Ma in the Fuping Complex (as part of the Taihangshan–Hengshan block), at the western margin of the Eastern Archean Continental Block.     

Hydrogeochemical Characterization and Groundwater Quality of Jamshedpur Urban Agglomeration in Precambrian Terrain,Eastern India

This paper reports petrography, geochemistry and Rb-Sr age data on the rare metal bearing Neoarchean fertile (Nb-Ta) granite at Allapatna and elucidates its petrogenesis and role in Nb-Ta-Li-Be mineralization. The Allapatna granite (AG) intrudes the Tonalitic-Trondhjemitic - Granodioritic (TTG) Peninsular Gneiss and analysed SiO₂ (72.3-75.6 wt%), K₂O (4.0-5.7wt%), Na2O (3.0-4.4wt%), CaO (0.7-1wt%), MgO (0.13-0.25wt%) and K₂O/Na₂O (>1) indicating evolved nature. The presence of muscovite, biotite and garnet in the mode, peraluminous nature and high initial ⁸⁷Sr/⁸⁶Sr ratio (0.7284±0.0083) attest to their S-type characteristics. Varying Nb/Ta ratio and high Li with moderate abundance of Cs further indicate affinity to Li-Cs-Ta (LCT) type granite-pegmatite system. TheAG showing whole rock Rb-Sr isochron age of 2803± 68 Ma, is the oldest reported fertile granite in India parental to rare metal pegmatites hosting Nb-Ta, Be, and Li resources. Partial melting of a mixed source consisting of both basement TTG rocks and metapelites has generated such type of granitic magma. Fractionation of such granitic magma possibly has given rise to the rare metal (Ta-Nb-Li-Be) bearing pegmatites intruding the nearby schist belt.     

The granite problem as exposed in the southern Snake Range,Nevada

A geochemically and mineralogically diverse group of granitoids is present within an area of 900 km² in the southern Snake Range of eastern Nevada. The granitoids exposed range in age from Jurassic through Cretaceous to Oligocene and include two calcic intrusions, two different types of two-mica granites, and aplites. The younger intrusions appear to have been emplaced at progressively more shallow depths. All of these granitoid types are represented elsewhere in the eastern Great Basin, but the southern Snake Range is distinguished by the grouping of all these types within a relatively small area. The Jurassic calcic pluton of the Snake Creek-Williams Canyon area displays large and systematic chemical and mineralogical zonation over a horizontal distance of five km. Although major element variations in the pluton compare closely with Daly's average andesite-dacite-rhyolite over an SiO₂ range of 63 to 76 percent, trace element (Rb, Sr, Ba) variations show that the zonation is the result of in situ fractional crystallization, with the formation of relatively mafic cumulates on at least one wall of the magma chamber. Models of trace element and isotopic data indicate that relatively little assimilation took place at the level of crystallization. Nonetheless, an initial ⁸⁷Sr/⁸⁶Sr value of 0.7071 and δ ¹⁸O values of 10.2 to 12.2 permil suggest a lower crustal magma that was contaminated by upper crustal clastic sedimentary rocks before crystallization. The involvement of mantle-derived magmas in its genesis is difficult to rule out. Two other Jurassic plutons show isotopic and chemical similarities to the Snake Creek-Williams Canyon pluton. Cretaceous granites from eastern Nevada that contain phenocrystic muscovite are strongly peraluminous, and have high initial Sr-isotope ratios and other features characteristic of S-type granitoids. They were probably derived from Proterozoic metasediments and granite gneisses that comprise the middle crust of this region. Another group of granitoids (including the Tertiary aplites) show chemical, mineralogic, and isotopic characteristics intermediate between the first two groups and may have been derived by contamination of magmas from the lower crust by the midcrustal metasediments.     

内蒙古科尔沁右翼中旗地区孟恩陶勒盖岩体成因研究

内蒙古东部科尔沁右翼中旗地区孟恩陶勒盖岩体由二长花岗岩、 花岗闪长岩、 英云闪长岩组成,属于高钾钙碱性岩系。岩石具有SiO₂较高（平均为72.03%）,富碱并相对富K₂O（K₂O/Na₂O平均为1.08）,Mg^#较低（平均为0.30）,铝饱和指数（A/CNK）较高（平均为1.08）的特点。在ACF图解中,岩石投影在S型花岗岩中,标准矿物中普遍出现刚玉分子,岩石中可见白云母,个别可见石榴石,应属S型花岗岩范畴。岩石稀土总量较低（∑ REE平均为120.76×10^-6）,轻、 重稀土分馏明显（（La/Yb）_N=3.2～32.5）,有变化较大的负铕异常（0.2～0.8）;在微量元素蜘蛛网图上,强烈富集大离子亲石元素（如Rb、 Ba）,高场强元素（如Ti）强烈亏损,在微量元素与上陆壳标准化及（La/Yb）_N-δEu图解中,物源属于壳源。岩体Sr的含量平均为176.57×10^-6,小于300×10^-6,Yb含量平均为1.3×10^-6,小于2×10^-6,属于喜马拉雅型花岗岩,源岩可能为含石榴石和斜长石的高压麻粒岩相,形成于加厚地壳部分熔融的结果,其形成的压力可能为0.8～1.5 GPa。在R₁-R₂图解、 Yb-Ta图解中,岩石均投影在同碰撞环境。因此,该岩体是中三叠世挤压背景下同碰撞壳源S型花岗岩,为华北板块与西伯利亚板块碰撞上限的约束提供了资料。     

Multiple sources for the origin of granites: Geochemical and Nd/Sr isotopic evidence from the Gudaoling granite and its mafic enclaves, northeast China

Geochemical and Sr- and Nd-isotopic data have been determined for mafic to intermediate microgranular enclaves and host granitoids from the Early Cretaceous Gudaoling batholith in the Liaodong Peninsula, NE China. The rocks include monzogranite, porphyric granodiorite and quartz diorite. Monzogranites have relatively high ⁸⁷Rb/⁸⁶Sr ratios (0.672-0.853), low initial ⁸⁷Sr/⁸⁶Sr ratios (0.7052-0.7086) and ε _Nd(t) values (−18.5 to −20.9) indicating that they were mainly derived from a newly underplated crustal source with a short crustal residence time. Quartz diorites have high initial ⁸⁷Sr/⁸⁶Sr ratios (0.7118-0.7120) and negative ε _Nd(t) values (−13.2 to −18.1) coupled with high Al₂O₃ and MgO contents, indicating they were derived from enriched lithospheric mantle with contributions of radiogenic Sr from plagioclase-rich metagreywackes or meta-igneous rocks, i.e., ancient lower crust. Two groups of enclaves with igneous textures and abundant acicular apatites are distinguished: dioritic enclaves and biotite monzonitic enclaves. Dioritic enclaves have low Al₂O₃ (13.5-16.4 wt%) and high MgO (Mg# = ∼72.3) concentrations, low initial ⁸⁷Sr/⁸⁶Sr ratios (0.7058-0.7073) and negative ε _Nd(t) values (∼−7.2), and are enriched in LILEs and LREEs and depleted in HFSEs, suggesting they were derived from an enriched lithospheric mantle source. Biotite monzonitic enclaves have Sr and Nd isotopic compositions similar to the monzogranites, indicating they were crystal cumulates of the parental magmas of these monzogranites. Granodiorites have transitional geochemistry and Nd- and Sr-isotopic compositions, intermediate between the monzogranites, quartz diorites and the enclaves.Geochemical and Sr- and Nd-isotopic compositions rule-out simple crystal-liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks. Instead, magma mixing of mafic mantle-derived and juvenile crustal-derived magmas, coupled with crystal fractionation and assimilation of ancient lower crust, is compatible with the data. This example shows that at least some calc-alkaline granitoids are not produced by pure intracrustal melting, but formed through a complex, multi-stage hybridization process, involving mantle- and crustal-derived magmas and several concomitant magmatic processes (crystal fractionation, crustal assimilation and crustal anatexis).