Petrochemical Characteristics and Timing of Middle Eocene Granitic Magmatism in Kooh-Shah, Lut Block, Eastern Iran

The Kooh-Shah region located in a Tertiary volcanic-plutonic belt of the Lut Block in eastern Iran comprises several subvolcanic intermediate to acidic intrusive rocks, diorite to syenite in composition, which have intruded into volcanic rocks. The Kooh-Shah granitoid rocks are characterized by enrichment in large ion-lithophile elements (LILE: e.g. Sr, Ba, Rb) and depletion in high field-strength elements (HFSE: e.g. Nb, Ta, Ti). The chondrite-normalized REE patterns are characterized by moderate LREE enrichment (La/Yb)N=6.01-10.01, medium-heavy REE enrichment, and absence of Eu anomalies. The Kooh-Shah intrusive rocks are metaluminous, shoshonitic with calc-alkaline affinity and high values of magnetic susceptibility, and classified as the magnetite-series of oxidant I-type granitoids. The age of Kooh-Shah granitoid rocks based on zircon U-Pb age dating is 39.7±0.7 Ma (=Middle Eocene) and the ranges of their initial 87Sr/86Sr and 143Nd/144Nd ratios are from 0.704812 to 0.704920 and 0.512579 to 0.512644, respectively, when recalculated to an age of 39 Ma. The initial ?Nd isotope values for the Kooh-Shah intrusive rocks range from -0.18 to 1.09. This geochemical data indicates that the Kooh-Shah granitoid rocks formed from depleted mantle in an island arc setting. The geochemical signature of the studied granitoid rocks represents a characteristic guide for future exploration of copper-gold porphyry-type deposits in the Lut block.     

Zircon U-Pb age,Lu-Hf Isotopic Characteristics and Origin of the Banshanping Granitoid Rocks in East Qinling Orogenic Belt

The Banshanping granitoid rocks distribute in the east of the North Qinling orogenic belt. It is a diorite-quartz diorite-granodiorite-granite series, spreading in a NW-SE direction, and intrudes into the Erlangping Group. The SiO2 content ranges from 57.04% to 76.56%, Na2O from 2.05% to 4.65%, K2O from 0.84% to 3.40%. Major element characteristics indicate that Banshanping granitoid rocks have properties of I type granotoids. SREE ranges from 36.51 ppm to 473.25 ppm, and LREE/HREE ratios lie between 3.95 and 22.18. Negative Eu anomalies are not obvious in most samples, though there are obvious Nb, P and Ti positive anomalies. The zircon LA-ICP-MS ages of Banshangping granitoid rocks are 496.0±8.1 Ma–486.9±9.3 Ma. Hf isotope shows that 176Hf/177Hf ratios range from 0.282721 to 0.282876, εHf(t) values from 8.5 to 14, all positive, and corresponding modal ages(TDM2) range from 559 Ma to 908 Ma. Based on Hf isotope characteristics and existing SmNd and Rb-Sr isotope data, we consider that the Banshanping granitoid rocks originate from mantlederived material, i.e. the igneous rocks that formed in Neoproterozoic, and there may be a certain amount of crust-derived material during the formation of Banshanping granitoid rocks.     

Origin of the Cenozoic–Mesozoic magnetite-series and ilmenite-series granitoids in East Asia

Among the Phanerozoic granitoids of East Asia, the most prevailing Cenozoic–Mesozoic rocks are reviewed with respect to gabbro/granite ratio, bulk composition of granitoids, redox state, and O- and Sr-isotopic ratios. Quaternary volcanic rocks, ranging from basalt to rhyolite, but typically felsic andesite in terms of bulk composition in island arcs, are oxidized type, possibly due to oxidants from subducting oceanic crust into the source regions. Miocene plutonic rocks in the back-arc of Japan could be a root zone for such volcanism but are more felsic in composition. Cenozoic–Mesozoic plutonic zones are classified by (1) the redox state (magnetite/ilmenite series), and (2) average bulk composition (granodiorite/granite). The granodioritic magnetite series occur with fairly abundant gabbro and diorite in the back-arc of island arcs (Greentuff Belt) and intercontinental rapture zones (Yangtze Block). These rocks are mostly juvenile in terms of the ⁸⁷Sr/⁸⁶SrI and δ¹⁸O values.The granitic magnetite series with some gabbroids occur in rapture zones along the continental coast (Gyeongsang Basin, Fujian Coast) and the back-arc of island arc (Sanin Belt). They were generated mostly in felsic continental crust, with the help of heat and magmas from upper mantle. The generated granitic magmas had little interaction with C- and S-bearing reducing materials, due probably to extensional tectonic settings. The δ¹⁸O value gives narrow ranges but the ⁸⁷Sr/⁸⁶SrI ratio varies greatly depending upon the age and composition of the continental crust. Granitic ilmenite-series are characterized by high δ¹⁸O values, implying much contribution of sediments. The ⁸⁷Sr/⁸⁶SrI ratios are low in island arcs but very high in continental interior settings. Amount of mafic magmas from the upper mantle seems a key to control the composition of granitoid series in island arc settings, while original composition of the protolith may be the key to control granitoid composition in continental interiors.     

Origin of the Newly Discovered Zhunuo Porphyry Cu-Mo-Au Deposit in the Western Part of the Gangdese Porphyry Copper Belt in the Southern Tibetan Plateau, SW China

The newly discovered Zhunuo porphyry Cu-Mo-Au deposit is located in the western part of the Gangdese porphyry copper belt in southern Tibet, SW China. The granitoid plutons in the Zhunuo region are composed of quartz diorite porphyry, diorite porphyry, granodiorite porphyry, biotite monzogranite and quartz porphyry. The quartz diorite porphyry yielded zircon U-Pb ages of 51.9±0.7 Ma(Eocene) using LA-ICP-MS, whereas the diorite porphyry, granodiorite porphyry, biotite monzogranite and quartz porphyry yielded ages ranging from 16.2±0.2 to 14.0±0.2 Ma(Miocene). CuMo-Au mineralization is mainly hosted in the Miocene granodiorite porphyry. Samples from all granitoid plutons have geochemical compositions consistent with high-K calc-alkaline series magmatism. The samples display highly fractionated light rare-earth element(REE) distributions and heavy REE distributions with weakly negative Eu anomalies on chondrite-normalized REE patterns. The trace element distributions exhibit positive anomalies for large-ion lithophile elements(Rb, K, U, Th and Pb) and negative anomalies for high-field-strength elements(Nb and Ti) relative to primitive mantlenormalized values. The Eocene quartz diorite porphyry yielded εNd(t) values ranging from-3.6 to-5.2,(~(87)Sr/~(86)Sr)i values in the range 0.7046–0.7063 and initial radiogenic Pb isotopic compositions with ranges of 18.599–18.657 ~(206)Pb/~(204)Pb, 15.642–15.673 ~(207)Pb/~(204)Pb and 38.956–39.199 ~(208)Pb/~(204)Pb. In contrast, the Miocene granitoid plutons yielded ε_(Nd)(t) values ranging from-6.1 to-7.3 and(87Sr/86Sr)i values in the range 0.7071–0.7078 with similar Pb isotopic compositions to the Eocene quart diorite. The Sr-Nd-Pb isotopic compositions of the rocks are consistent with formation from magma containing a component of remelted ancient crust. Zircon grains from the Eocene quartz diorite have ε_(Hf)(t) values ranging from-5.2 to +0.9 and two-stage Hf model ages ranging from 1.07 to 1.46 Ga, while zircon grains from the Miocene granitoid plutons have ε_(Hf)(t) values from-9.9 to +4.2 and two-stage Hf model ages ranging from 1.05–1.73 Ga, indicating that the ancient crustal component likely derives from Paleo- to Mesoproterozoic basement. This source is distinct from that of most porphyry Cu-Mo-Au deposits in the eastern part of the Gangdese porphyry copper belt, which likely originated from juvenile crust. We therefore consider melting of ancient crustal basement to have contributed significantly to the formation Miocene porphyry Cu-Mo-Au deposits in the western part of the Gangdese porphyry copper belt.     

The ubiquitous nature of accessory calcite in granitoid rocks: Implications for weathering, solute evolution, and petrogenesis

Calcite is frequently cited as a source of excess Ca, Sr and alkalinity in solutes discharging from silicate terrains yet, no previous effort has been made to assess systematically the overall abundance, composition and petrogenesis of accessory calcite in granitoid rocks. This study addresses this issue by analyzing a worldwide distribution of more than 100 granitoid rocks. Calcite is found to be universally present in a concentration range between 0.028 to 18.8 g kg⁻¹ (mean = 2.52 g kg⁻¹). Calcite occurrences include small to large isolated anhedral grains, fracture and cavity infillings, and sericitized cores of plagioclase. No correlation exists between the amount of calcite present and major rock oxide compositions, including CaO. Ion microprobe analyses of in situ calcite grains indicate relatively low Sr (120 to 660 ppm), negligible Rb and ⁸⁷Sr/⁸⁶Sr ratios equal to or higher than those of coexisting plagioclase. Solutes, including Ca and alkalinity produced by batch leaching of the granitoid rocks (5% CO₂ in DI water for 75 d at 25°C), are dominated by the dissolution of calcite relative to silicate minerals. The correlation of these parameters with higher calcite concentrations decreases as leachates approach thermodynamic saturation. In longer term column experiments (1.5 yr), reactive calcite becomes exhausted, solute Ca and Sr become controlled by feldspar dissolution and ⁸⁷Sr/⁸⁶Sr by biotite oxidation. Some accessory calcite in granitoid rocks is related to intrusion into carbonate wall rock or produced by later hydrothermal alteration. However, the ubiquitous occurrence of calcite also suggests formation during late stage (subsolidus) magmatic processes. This conclusion is supported by petrographic observations and ⁸⁷Sr/⁸⁶Sr analyses. A review of thermodynamic data indicates that at moderate pressures and reasonable CO₂ fugacities, calcite is a stable phase at temperatures of 400 to 700°C.     

Zircon U–Pb ages and Sr–Nd isotope ratios for the Sirstan granitoid body,NE Iraq: Evidence of magmatic activity in the Middle Cretaceous Period

The Sirstan granitoid (SG), comprising diorite and granodiorite, is located in the Shalair Valley area, in the northeastern part of Iraq within the Sanandaj–Sirjan Zone (SSZ) of the Zagros Orogenic Belt. The U–Pb zircon dating of the SG rocks has revealed a concordia age of 110 Ma, which is interpreted as the age of crystallization of this granitoid body during the Middle Cretaceous. The whole-rock Rb–Sr isochron data shows an age of 52.4 ± 9.4 Ma (MSWD = 1.7), which implies the reactivation of the granitoid body in the Early Eocene due to the collision between the Arabian and Iranian plates. These rocks show metaluminous affinity with low values of Nb, Ta and Ti compared to chondrite, suggesting the generation of these rocks over the subduction zone in an active continental margin regime. The SG rocks are hornblende-bearing I-type granitoids with microgranular mafic enclaves. The positive values of ?_Nd (t = 110 Ma) (+0.1 to +2.7) and the low (⁸⁷Sr/⁸⁶Sr)_i ratios (0.7044 to 0.7057) indicate that the magma source of the SG granitoids is a depleted subcontinental mantle. The chemical and isotope compositions show that the SG body originated from the metasomatic mantle without a major role for continental contamination. Our findings show that the granitoid bodies distributed in the SSZ were derived from the continuous Neo-Tethys subduction beneath the SSZ in Mesozoic times and that the SSZ was an active margin in the Middle Cretaceous.     

Age, composition, sources, and geodynamic environments of the origin of granitoids in the northern part of the Ozernaya zone, western Mongolia: Growth mechanisms of the Paleozoic continental crust

The paper presents data on the structure, composition, and age of granitoid associations (Tokhtogeshil’skii Complex) composing the Kharanur and Sharatologoi polychronous plutons in the northern part of the Ozernala zone in western Mongolia. The Tokhtogeshil’skii Complex was determined to consist of a number of independent magmatic associations, which were formed at 540–450 Ma, within three age intervals (540–520, 510–485, and 475–450 Ma), have different composition, were derived from different sources, and were emplaced in different geodynamic environments. During the first, island-arc stage (540–520 Ma), high-Al plagiogranites were produced, which belong to tonalite-plagiogranite (531 ± 10 Ma) and diorite (529 ±6 Ma) associations in the Kharanur pluton, low-Al plagiogranites of the tonalite-plagiogranite association (519 ± 8 Ma) in the Sharatologoi pluton, and rocks of the Khirgisnur peridotite-pyroxenite-gabbronorite complex (Kharachulu and Dzabkhan massifs). The rocks of the diorite and plagiogranite associations of the Kharanur pluton have ɛ_Nd(T) from +7.9 to +7.4, T_Nd(DM) = 0.65 Ga, and (⁸⁷Sr/⁸⁶Sr)₀ = 0.7038–0.7039. The plagiogranites of the Sharatologoi pluton (tonalite-plagiogranite association) are characterized by ɛ_Nd(T) from +6.5 to +6.6, T_Nd(DM) = 0.73–0.70 Ga, and (⁸⁷Sr/⁸⁶Sr)₀ = 0.7038–0.7039, which suggest predominantly juvenile subduction sources of the parental melts at a subordinate role of ancient crustal material. During the second, accretionary stage (510–485 Ma), low-Al plagiogranites of the diorite-tonalite-plagiogranite association of the Sharatologoi pluton (494 ± 10 Ma, M type) were formed. The Sr-Nd isotopic characteristics of these rocks ɛ_Nd(T) = +6.6, (⁸⁷Sr/⁸⁶Sr)₀ = 0.7039 are analogous to those of the plagiogranitoids of the early type. This suggests that the melted sources were similar in composition. During the third, postcollisional stage (475–450 Ma), rocks of the diorite-granodiorite-granite association were formed (459 ± 10 Ma, type I) in the Kharanur pluton. These rocks have ɛ_Nd(T) = +5.1, T_Nd(DM) = 0.74 Ga, and (⁸⁷Sr/⁸⁶Sr)₀ = 0.7096. The parental melts were supposedly derived by means of partial melting of “the Caledonian” juvenile crust with the addition of more ancient crustal material.     

The evolution of two petrogenesis-mineralization series of granites in Southern China

In this paper, the authors have proposed two distinct series of petrogenesis and mineralization: Series I and Series II. Series I (the Nanling Series) has a sequence of petrogenesis and mineralization: monzonitic granite or granodiorite → biotite granite → leuco-granite → granoporphyry or quartz porphyry → intermediate-basic dikes; REE → Nb, Ta (Li, Rb, Cs), Be, Sn, W, Mo, Bi, As → Cu, Zn, Pb → Sb, Hg, U. Series II (the Yangtze Series): Pyroxene diorite (or gabbro) → diorite or quartz diorite → granodiorite (quartz monzonite or monzonitic granite → granite → K-feldspar granite → granoporphyry or quartz porphyry (syenitic porphyry or quartz syenitic porphyry) → intermediate-basic dikes; Fe → Cu(Au) → Mo(W) → Zn, Pb → Pb (Ag). Obvious differences have been recognized between Series I and II. As for Series II, the bulk composition is close to that of andesite. Relatively high temperatures of formation (980°–1,140°C) petrochemical enrichment in Mg and Ca, the composition of biotite characterized by high magnesium, assemblages of accessory minerals (magnetite-sphene-apatite or magnetite-ilmenite-REE-rich zireon), trace elements predominated by Cl and Sr with ΣCe>ΣY in the rocks and accessory minerals, relatively high σEu(0.74–0.99) without depletion, δ¹⁸O<10‰ δ³⁴S close to that of meteorite sulfur, relatively high content of platinum metals (>10 times) characteristic of mantle origin, vory low⁸⁷Sr/⁸⁶Sr (0.7036–0.7085) and the occurrence of intermediate-basic dikes (similar to basaltic composition) in the final evolutionary stage are sufficiently enough to show that Series II has a material source in the lower crust or in the upper mantle. The fact that⁸⁷Sr/⁸⁶Sr>0.7037 in most cases implies a partial incorporation of crust materials. As for Series I, the bulk composition is consistent with that of normal granites. Relatively low temperatures of formation (600°–680°C), chemical composition noted for high SiO₂ and K₂O, complicated accessory mineralogy and assemblages (magnetiteilmenite-zircon, or monazite-xenotime-zircon), biotite with high content of iron, trace elements predominated by F, Li, Rb (Cs) and Be, relatively low δEu with distinct depletion, δ¹⁸O>10‰ greatly varying δ³⁴S, low content of platinum metals typical of mantle derivation, high⁸⁷Sr/⁸⁶Sr (0.7112–0.7360), in conjunction with the consideration of mineralizations of REE, Nb, Ta, Sn, Be, W, Bi, etc. of crust origin, indicate that the continental crust is the main material source for Series I. The possibility, however, cannot be ruled out that a small amount of upper mantle-derived material took part in this process, as has been indicated by lower⁸⁷Sr/⁸⁶Sr (≈0.7100), part of δ³⁴S close to that of meteorite sulfur and the occurrence of intermediate-basic dikes (similar to basalts in composition) as the end products of magmatic evolution. It is of interest to note that granitoid rocks of these two series in southeast China show considerable dissimilarities with those in Japan and Australia in⁸⁷Sr/⁸⁶Sr, δ¹⁸O and δ³⁴S.     

陕西柞山盆地池沟铜钼矿区含矿岩体的锆石U-Pb年龄和岩石成因

秦岭造山带柞山盆地多处发育与晚中生代中酸性小岩体有关的铜钼矿床(点),最近在池沟深部发现了厚大的斑岩型铜矿体,但对这些小岩体的形成时代和成因的研究很少。本文选择池沟地区不同类型的花岗质岩石开展地球化学特征和锆石U-Pb测年的研究。结果表明:该区小岩体主要为闪长岩、石英闪长岩和斑状花岗岩,它们为钾质钙碱性Ⅰ型花岗质岩石。矿物学、地球化学和Sr-Nd同位素特征均暗示它们是上地幔和下地壳同熔的深熔岩浆产物。与成矿密切相关的含矿岩体LA-MC-ICPMS锆石U-Pb谐和年龄为~145Ma,结合区域地质资料和成岩成矿关系的研究,认为池沟含矿岩体形成于晚侏罗世-早白垩世,柞水盆地存在一期重要的晚侏罗世-早白垩世中酸性岩浆岩和相应的斑岩-矽卡岩铜钼金矿化,与华北地块南缘晚中生代岩体和相关的钼铅锌矿床形成于同一地质事件。     

Petrogenesis of Middle-Eocene granitoids and their Mafic microgranular enclaves in central Urmia-Dokhtar Magmatic Arc (Iran): Evidence for interaction between felsic and mafic magmas

Whole rock major and trace element geochemistry together with zircon U-Pb ages and Sr-Nd isotope compositions for the Middle Eocene intrusive rocks in the Haji Abad region are presented. The granitoid hosts, including granodiorite and diorite, yielded zircon U-Pb ages with a weighted mean value of 40.0 ± 0.7 Ma for the granodiorite phase. Mafic microgranular enclaves(MMEs) are common in these plutons, and have relatively low SiO_2 contents(53.04-57.08 wt.%) and high Mg#(42.6-60.1), probably reflecting a mantle-derived origin. The host rocks are metaluminous(A/CNK = 0.69-1.03), arc-related calc-alkaline, and I-type in composition, possessing higher SiO_2 contents(59.7-66.77 wt.%) and lower Mg#(38.6-52.2); they are considered a product of partial melting of the mafic lower crust. Chondritenormalized REE patterns of the MMEs and granitoid hosts are characterized by LREE enrichment and show slight negative Eu anomalies(Eu/Eu* = 0.60-0.93). The host granodiorite samples yield(⁸⁷Sr/⁸⁶Sr);ratios ranging from 0.70498 to 0.70591,positive eNd(t) values varying from +0.21 to +2.3, and TDM2 ranging from 760 to 909 Ma, which is consistent with that of associated mafic microgranular enclaves(⁸⁷Sr/⁸⁶Sr)i = 0.705111-0.705113, ε_Nd(t)= +2.14 to +2.16, T_DM2 = 697-785 Ma). Petrographic and geochemical characterization together with bulk rock Nd-Sr isotopic data suggest that host rocks and associated enclaves originated by interaction between basaltic lower crust-derived felsic and mantlederived mafic magmas in an active continental margin arc environment.     

东秦岭杨斜金矿区石英闪长玢岩锆石U-Pb年代学、地球化学特征及地质意义

杨斜中型金矿床是东秦岭杨斜-丰北河地区典型的石英脉型金矿床,成矿与区内石英闪长玢岩密切相关,具中高温蚀变特征及矿物组成。LA-ICP-MS锆石U-Pb测年结果表明,石英闪长玢岩锆石²⁰⁶Pb/²³⁸U加权平均年龄为149.5±2.7 Ma,谐和年龄为149.5±2.1 Ma,属晚侏罗世。岩石地球化学研究显示,石英闪长玢岩具有高SiO₂(65.53%~65.76%)、高Al₂O₃(15.65%~15.87%)、富碱(N₂O+K₂O=8.07%~8.30%)及贫MgO(1.37%~1.40%)特征,属于高钾钙碱性准铝质系列岩石;相对富集Rb、Ba、K、Pb、Sr等大离子亲石元素和LREE,亏损Nb、Ta、Ti等高场强元素和HREE;其高Sr、高Sr/Y、低Y和低Yb值及正Eu异常等特征参数,与典型埃达克质岩一致,岩浆应起源于加厚下地壳的部分熔融。综合研究认为,杨斜金矿属岩浆期后热液型金矿床,成岩成矿时代一致,形成于秦岭造山带晚侏罗世-早白垩世陆内俯冲向伸展转换的构造环境。     

Carboniferous porphyry Cu (-Au) mineralization of the West Junggar region,NW China: the Shiwu example

ABSTRACT

The West Junggar region, located in the Central Asian Orogenic Belt (CAOB), is characterized by extensive Carboniferous magmatism and porphyry Cu (-Au) deposits. The Shiwu porphyry Cu-Au deposit, located in the east of the Barluk Mountains, the West Junggar region, is not only a newly discovered deposit but also a representative porphyry Cu-Au deposit in this area. The volcanic rocks (including andesite and tuff) and intrusive rocks (including diorite, quartz diorite, quartz diorite porphyry, and tonalite porphyry) occurred in the Shiwu area and the mineralization associated with the quartz diorite porphyry. The secondary ion mass spectrometry (SIMS) zircon U–Pb ages of quartz diorite porphyry and tonalite porphyry are 310.4 ± 2.3 Ma and 310.1 ± 2.4 Ma, respectively, indicating that the Shiwu deposit is related to the Late Carboniferous magmatism. Intrusive rocks, which were characterized by the enrichment of large ion lithophile elements (LILEs) and pronounced negative high field strength elements (HFSEs), belong to the calc-alkaline or tholeiitic series. Their (⁸⁷Sr/⁸⁶Sr)_i, (¹⁴³Nd/¹⁴⁴Nd)_I, and εNd(t) values range from 0.703569 to 0.704311, 0.512488 to 0.512512, and 4.9 to 5.3, respectively. Volcanic rocks, which belong to the calc-alkaline series, have similar geochemical features as the intrusive rocks, and their (⁸⁷Sr/⁸⁶Sr)_i, (¹⁴³Nd/¹⁴⁴Nd)_i, and εNd(t) values, respectively, are 0.703704–0.704071, 0.512520–0.512542, and 5.49–5.92. These characters indicate that the igneous rocks in the Shiwu area derived dominantly from the mantle and formed in an island arc setting. These characters also further confirmed that the Barluk Mountains is still in an island arc setting in the Late Carboniferous and the accretionary orogenesis can exist until 310 Ma at least.     

The age of young intrusions of Tsana Complex (Greater Caucasus) and isotope-geochemical evidence for their origin from hybrid magmas

This paper presents isotope-geochronological and petrological study of granitoids of the potentially ore-bearing (Au–As–Sb–Sn–Mo) Early Pliocene Tsana Complex, which are confined to the Main Caucasus fault zone (upthrow fault) in the central part of the Greater Caucasus Range. The Tsurungal and Karobi groups of magmatic bodies are distinguished based on spatial criterion. The Tsurungal group includes three small granite—granodiorite massifs (Tsurungal, Chorokhi, and Toteldash) and numerous acid and intermediate dikes in the upper reaches of the Tskhenistsqali River (Kvemo Svaneti, Georgia). The Karobi group comprises three subvolcanic rhyodacite bodies located in the upper reaches of the Chashuri River (Zemo Racha, Georgia) and numerous N–S-trending trachyandesite dikes near the axial zone of the Main Caucasus Range. The K-Ar and Rb-Sr isotope dating shows that the granitoid massifs and dike bodies of the Tsana Complex were formed in two different-age pulses of the Pliocene magmatism: phase I at 4.80 ± 0.15 and phase II at 4.15 ± 0.10 Ma. All hypabyssal rocks of the Karobi group, unlike those of the Tsurungal Group, were formed during the first pulse. Petrographic studies in combination with geochemical data indicate that most of the granitoids of the Tsana Complex are hybrid rocks (I-type post-collisional granites) and were derived through mixing of deep-seated mantle magmas with acid melts obtained by the upper crustal anatectic melting in the Main Caucasus fault zone. The granitoids of the Tsurungal Group define basic to acid evolution (diorite–granodiorite–granite–two-mica granite) possibly caused by both crystallization differentiation and increasing role of crustal contamination in the petrogenesis of the parental magmas of these rocks. This conclusion is also confirmed by the differences in the Sr isotope composition between granitoids of the early (⁸⁷Sr/⁸⁶Sr = 0.7053) and late (⁸⁷Sr/⁸⁶Sr = 0.7071) phases of the Tsana Complex. Main trends in spatiotemporal migration of magmatic activity in the central part of the Greater Caucasus in the Pliocene–Quaternary time were established using obtained and earlier published isotope-geochronological data.     

Petrogenesis and tectonic implications of early Paleozoic granitoids in East Kunlun belt: Evidences from geochronology,geochemistry and isotopes

The East Kunlun Orogenic Belt(EKOB) provides an important link to reconstruct the evolution of the Proto-Tethys and Paleo-Tethys realm. The EKOB is marked by widespread Early Paleozoic magmatism.Here we report the petrology, bulk geochemistry, zircon Ue Pb dating and, Lue Hf and SreN d isotopic data of the Early Paleozoic granitic rocks in Zhiyu area of the southern EKOB. Based on the zircon U-Pb dating, these granitoids, consisting of diorite, granodiorite and monzogranite, were formed during 450 -430 Ma the Late Ordovician to Middle Silurian. The diorite and granodiorite are high Sr/Y ratio as adakitic affinities, and the monzogranite belongs to highly fractionated I-type. Their(~(87)Sr/~(86)Sr)ivalues range from 0.7059 to 0.7085, εNd(t) values from -1.6 to -6.0 and the zircon εHf(t) values show large variations from +9.1 to -8.6 with Hf model ages(T_(DM2)) about 848 Ma and 1970 Ma. The large variations of whole-rock Nd and zircon Hf isotopes demonstrate strong isotopic heterogeneity of the source regions which probably resulted from multi-phase underplating of mantle-derived magmas. Geochemical and isotopic studies proved that the diorite and granodiorite had been derived from partial melting of heterogeneous crustal source with variable contributions from ancient continental crust and juvenile components, and the monzogranites were representing fractional crystallization and crustal contamination for arc magma. The Early Paleozoic adakitic rocks and high-K calc-alkaline granitoids in the southern EKOB were likely emplaced in a continental marginal arc setting possibly linked to the southwards subduction of the Paleo Kunlun Ocean and the magma generation is linked to partial melting of thickened continental crust induced by underplating of mantle-derived magmas.     

Spatial variations of Sr and Nd isotope ratios of Cretaceous-Paleogene granitoid rocks,Southwest Japan Arc

Cretaceous-Paleogene granitoid rocks and contemporaneous volcanic rocks are widely distributed in the Inner Zone of Southwest Japan. This intense intermediate to felsic magmatism is considered to have taken place on the eastern margin of the Eurasian Continent, before the Southwest Japan Arc drifted away from the continent in the middle Miocene, resulting in the opening of the Japan Sea. The granitoid rocks show regional variations in terms of their radiometric age, petrography, Sr, Nd and O isotope ratios. Based on Sr and Nd isotope ratios, granitoid rocks can be divided into three zones (South, Transitional and North) between the Median Tectonic Line and the Japan Sea. Granitoid rocks and associated gabbros of the North Zone have low initial Sr isotope ratios (0.7048 to 0.7068) and high initial Nd values (+3 to-2.2), whereas granitoid rocks and gabbros from the South Zone have high initial Sr isotope ratios (0.7070 to 0.7088) and low initial Nd values (-3.0to-8.0). Most granitoid rocks from the Transitional Zone have Sr and Nd isotope ratios that lie between those of the North and South Zones, although there is some overlap. Contamination of magmas by upper crust cannot explain this geographical variation in Sr and Nd isotopes. Instead, the regional variation is attributed to compositionally different, magma sources (probably upper mantle and lower crust), beneath the North and South Zones. This is supported by the Sr and Nd isotopic ratios of upper mantle and lower crustal xenoliths included in Cenozoic volcanic rocks in the North and South Zones. These ratios are similar to those of the granitoid rocks in the respective zones. It is suggested that a micro-continent or island arc consisting of continental crust was underthrust beneath the South Zone before or during the Cretaceous, resulting in compositionally distinct sources for granitoid rocks of the North and South Zones. The large variation observed in Sr and Nd isotope ratios for Transitional Zone granitoid rocks is explained by variable proportions of the two different crustal and upper mantle components.     

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.     

Sr,Nd, and Hf Isotope Composition of Rocks of the Reft Gabbro–Diorite–Tonalite Complex (Eastern Slope of the Middle Urals): Petrological and Geological Implications

This paper reports Rb–Sr and Sm–Nd isotope data on the gabbro–diorite–tonalite rock association of the Reft massif (eastern margin of the Middle Urals) and Lu–Hf isotope data on zircon populations from these rocks. In terms of Nd and Hf isotope composition, the rocks of the studied association are subdivided into two distinctly different groups. The first group consists of gabbros and diorites, as well as plagioclase granites from thin dikes and veins cutting across the gabbros. In terms of ⁴³Nd/¹⁴⁴Nd _i = 0.512518–0.512573 (ε_Nd(T) = +8.6...+9.7) and ¹⁷⁶Hf/¹⁷⁷Hf _i = 0.282961–0.283019 (ε_Hf(T) = +15.9...+17.9), these rocks are practically identical to depleted mantle. Their Nd and Hf model ages show wide variations, but in general are close to their crystallization time. The second group is represented by tonalites and quartz diorites, which compose a large body occupying over half of the massif area. These rocks are characterized by the lower values of ¹⁴³Nd/¹⁴⁴Nd _i = 0.512265–0.512388 (ε_Nd(T) = +3.7...+6.0) and ¹⁷⁶Hf/¹⁷⁷Hf _i = 0.282826–0.282870 (ε_Hf(T) = +11.1...+12.7). The T_DM values of the second group are much (two–three times) higher than their geological age (crystallization time), which indicates sufficiently long crustal residence time of their source. The initial ⁸⁷Sr/⁸⁶Sr in the rocks of both the groups varies from 0.70348 to 0.70495. This is likely explained by the different saturation of melts with fluid enriched in radiogenic Sr. The source of this fluid could be seawater that was buried in a subduction zone with oceanic sediments and released during slab dehydration. Obtained data make it possible to conclude that the formation of the studied gabbro–diorite–tonalite association is a result of spatially and temporally close magma formation processes in the crust and mantle, with insignificant contribution of differentiation of mantle basite magma.     

Rhenium in porphyry copper deposits of the urals

The overwhelming majority of porphyry Mo-Au-Cu deposits in the Urals are related to the low-K quartz diorite minor intrusions of the island-arc type, which were formed from Silurian Middle-Late Carboniferous. In the South Urals, the Cu/Mo ratio of ore decreases eastward along with enrichment in Re. At the same time, molybdenite is depleted in this metal in compliance with more sialic crust and potassium content in ore-bearing dioritic rocks. Quartz diorites at the highest-Re deposits contain 1–2 wt % K₂O. At most Early-Middle Devonian deposits and occurrences of the western Tagil-Magnitogorsk-West Mugodzhary femic megazone, molybdenite is sporadic. The Re content in rocks was mainly determined using the kinetic method and to a lesser extent with ICP-MS. A Cameca SX-100 microprobe was also used for study of molybdenite. The Cu/Mo ratio of ore exceeds 600; the Mo content is commonly 1–15 ppm (occasionally up to 30 ppm and higher); the Re content is up to 0.01–0.04 ppm, sporadically increasing to 0.08–0.17 ppm. At the same time, the Re content in molybdenite often reaches 0.2–0.4 wt %. The highest Re concentration was established in the ore of the largest Mikheevsky deposit formed in the Late Devonian-Early Carboniferous and localized in the easternmost part of the East Ural sialic-femic megazone. The Re content in the orebodies of this deposit often reaches 0.2–0.5 ppm (up to 1.4–2.7 ppm) and 0.21 wt % in molybdenite. The average Mo grade of ore is 80 ppm and Cu/Mo ratio is 66. These data and Sr isotopic composition of ore-bearing granitoid and metasomatic rocks [(⁸⁷Sr/⁸⁶Sr)_t = 0.7038–0.7051; (?_Nd)_t = 3–7] testify to the mantle source of matter with insignificant admixture of crustal material. The same is apparently valid for Re and Cu in contrast to Mo. This statement is corroborated by the inverse correlation between Cu/Mo and Mo/Re ratios in the ore. Fluid-crystal fractionation of ore-bearing dioritic rocks is accompanied by enrichment of ore in Mo and by decrease in Re content in molybdenite. In the Tarutino ore field, the pyrite-chalcopyrite mineralization gives way to the molybdenite mineralization in line with in-sequence intrusion of diorite with quartz-bearing groundmass and granodiorite porphyry. Because of increasing silica content in granitoids, the Re concentration in molybdenite commonly remains below 0.07 wt % as is noted at the rare deposits localized in the sialic megazones.     

Evidence for mass-dependent isotopic fractionation of strontium in a glaciated granitic watershed

The stable isotope composition of strontium (expressed as δ^88/86Sr) may provide important constraints on the global exogenic strontium cycle. Here, we present δ^88/86Sr values and ⁸⁷Sr/⁸⁶Sr ratios for granitoid rocks, a 150 yr soil chronosequence formed from these rocks, surface waters and plants in a small glaciated watershed in the central Swiss Alps. Incipient chemical weathering in this young system, whether of inorganic or biological origin, has no resolvable effect on the ⁸⁷Sr/⁸⁶Sr ratios and δ^88/86Sr values of bulk soils, which remain indistinguishable from bedrock in terms of Sr isotopic composition. Although due in part to the chemical heterogeneity of the forefield, the lack of a resolvable difference between soil and bedrock isotopic composition indicates that these soils have thus far witnessed minimal net loss of Sr; a low degree of chemical weathering is also implied by bulk soil chemistry. The isotopic composition of Sr in streamwater is more radiogenic than median soil, reflecting the preferential weathering of biotite in the catchment; streamwater δ^88/86Sr values, however, are indistinguishable from bulk soil δ^88/86Sr values, implying that no resolvable fractionation of Sr isotopes takes place during release to the weathering flux in the Damma forefield. Analyses of plant tissue reveal that plants (Rhododendron and Vaccinium) preferentially assimilate the lighter isotopes of Sr such that their δ^88/86Sr values are significantly lower than those of the soils in which they grow. Additionally, δ^88/86Sr values of foliar and floral tissues are lower than those of roots, contrary to observations for Ca, for which Sr is often used as an analogue in weathering studies. We suggest that processes that discriminate against Sr in favour of Ca, due to the different nutritional requirement of plants for these two elements, are responsible for the observed contrast.     

Strontium isotopic and chemical variations of the granitic rocks in the Tsukuba district,Japan

Initial ⁸⁷Sr/⁸⁶Sr ratios, major and trace element compositions have been determined for the Paleogene granitic rocks in the Tsukuba district, Japan. Isotopic ages strongly suggest that the granitic rocks (seven units) were continuously emplaced and solidified during a short time interval. Initial ⁸⁷Sr/⁸⁶Sr ratios for seven granitic units vary from 0.7082 to 0.7132, while sedimentary and metasedimentary country rocks have ratios at the time of granitic magma emplacement ranging from 0.7149 to 0.7298. Continuous linear arrays for the granitic rocks in the diagrams of initial ⁸⁷Sr/⁸⁶Sr ratios versus some chemical parameters can be explained by either of following two processes. One is the assimilation — fractional crystallization (AFC) process between the parental magma (SiO₂ of 68% and initial ratio of 0.7078) and sedimentary country rocks, and the other is magma mixing process between above parental magma and sediment derived acidic magma (melt) (SiO₂ of 75%). The high initial ratios (0.7078–0.7098) for basic rocks such as gabbro or diorite in the Tsukuba district and the similar characteristics observed in the rocks of Ryoke belt (SW Japan) suggest that the parental magma had the same source region as the basic rocks, probably the lower crustal source.