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.     

东昆仑东段三叠纪岩浆混合作用:以香加南山花岗岩基为例

香加南山花岗岩基位于东昆仑造山带东段,岩基主要岩石类型为花岗闪长岩。千瓦大桥-加鲁河一带花岗岩体为香加南山岩基的重要组成部分。香加南山花岗岩基含大量暗色微粒包体,包体中捕掳晶丰富。千瓦大桥-加鲁河一带花岗岩体寄主岩中斜长石和暗色微粒包体中捕掳晶斜长石具正常环带,An值震荡变化,角闪石和黑云母Mg O含量和Mg#值较低,具壳源特征;暗色微粒包体中基质斜长石具核边结构,核部和边部An值存在间断,角闪石和黑云母Mg O含量和Mg#值较高,具幔源特征。LA-ICP-MS锆石U-Pb同位素定年结果显示千瓦大桥花岗闪长岩、暗色微粒包体和加鲁河辉长岩的结晶年龄分别为251.0±1.9Ma、252.8±3.0Ma和221.4±3.3Ma。千瓦大桥花岗闪长岩和加鲁河花岗闪长岩富集轻稀土元素(LREE)和大离子亲石元素(LILE),亏损高场强元素(HFSE),具较低的Mg#和Nb/Ta比值;从千瓦大桥到加鲁河花岗闪长岩呈现出由准铝质中钾钙碱性系列向准铝-弱过铝质中钾-高钾钙碱性系列演化;暗色微粒包体和加鲁河辉长岩轻重稀土元素分异程度相对较低,具较高的Mg#和Nb/Ta比值。千瓦大桥花岗闪长岩和加鲁河花岗闪长岩分别为古特提斯演化俯冲阶段和后碰撞阶段幔源岩浆底侵新生地壳使其部分熔融产物。镁铁质岩浆注入长英质岩浆的混合作用形成了暗色微粒包体。岩浆混合过程中,如果岩浆不完全混合,混合岩浆中混入物质除了长英质岩浆的残留岩浆和捕掳晶,还应该有镁铁质岩浆与长英质岩浆之间的元素梯度差导致的物质扩散;如果岩浆为近完全混合,混合岩浆近似为镁铁质岩浆和长英质岩浆以一定比例二元混合。东昆仑东段晚古生代-早中生代幔源岩浆对花岗质岩浆的影响是一个持续的过程,从俯冲阶段早期流体交代地幔熔融,到俯冲阶段后期板片断离,然后同碰撞阶段板片断离的持续影响,再到后碰撞阶段加厚地壳的拆沉作用,由于地球动力学体制不同,导致幔源岩浆影响的大小和特征不同。     

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.     

Magmatic history during late Carboniferous to early Permian in the North of the central Xing’an-Mongolia Orogenic Belt: a case study of the Houtoumiao pluton,Inner Mongolia

We undertake zircon U–Pb dating, Hf isotopes, and geochemical analyses of the Houtoumiao pluton in the Xilinhot microcontinent (XLMC) in the central Inner Mongolia with an aim of determining their ages, petrogenesis, and sources, which are important for understanding the late Palaeozoic tectonic evolution of the Xing’an-Mongolia Orogenic Belt. The Houtoumiao pluton consists of medium-grained granodiorite, coarse- and medium-grained syenogranite. Mafic microgranular enclaves (MMEs) are common in the Houtoumiao pluton. Zircon U–Pb dating has yielded ages of 303 ± 2 and 301 ± 2 Ma for the granodiorite, 295 ± 2 Ma for the syenogranite, and 292 ± 1 Ma for the MMEs. The granodiorite and syenogranite have features of high-K high silica content, rich in Rb, U, and Th, but low content of HFSE, belong to calc-alkaline series. The P₂O₅ concentration decreases with the increasing SiO₂ content, suggesting I-type affinity. The MMEs, which are characterized by low SiO₂, relatively high and variable TiO₂, Al₂O₃, FeO^T, MgO, CaO, Ni, and Cr contents, also have much higher total rare earth element concentrations that the REE patterns are subparallel to those of the host rocks. Zircons from the host rocks have ε_Hf(t) values from +3.91 to +7.73 and T_DM2 values of 820–1067 Ma, suggesting that the granitoids were probably dominated by remelting of juvenile crust materials. The MMEs are of ε_Hf(t) value ranging from +6.23 to +11.04 and T_DM1 values from 490 to 693 Ma, suggesting that the primary magma probably was derived from partial melting of a depleted lithospheric mantle, the mafic mineral fractional crystallization and crustal contamination occurred during the magma evolution. Combined with previous studies on the contemporaneous magma-tectonic activities in the Uliastai Continental Margin and XLMC, we suggest that the Houtoumiao pluton formed in a post-orogenic setting.     

Oligocene subduction-related plutonism in the Nodoushan area,Urumieh-Dokhtar magmatic belt: Petrogenetic constraints from U–Pb zircon geochronology and isotope geochemistry

Geochemical data and Sr–Nd isotopes of the host rocks and magmatic microgranular enclaves (MMEs) collected from the Oligocene Nodoushan Plutonic Complex (NPC) in the central part of the Urumieh–Dokhtar Magmatic Belt (UDMB) were studied in order to better understand the magmatic and geodynamic evolution of the UDMB. New U–Pb zircon ages reveal that the NPC was assembled incrementally over ca. 5 m.y., during two main episodes at 30.52 ± 0.11 Ma and 30.06 ± 0.10 Ma in the early Oligocene (middle Rupelian) for dioritic and granite intrusives, and at 24.994 ± 0.037 Ma and 24.13 ± 0.19 Ma in the late Oligocene (latest Chattian) for granodioritic and diorite porphyry units, respectively. The spherical to ellipsoidal enclaves are composed of diorite to monzodiorite and minor gabbroic diorite (SiO₂ = 47.73–57.36 wt.%; Mg# = 42.15–53.04); the host intrusions are mainly granite, granodiorite and diorite porphyry (SiO₂ = 56.51–72.35 wt.%; Mg# = 26.29–50.86). All the samples used in this study have similar geochemical features, including enrichment in large ion lithophile elements (LILEs, e.g. Rb, Ba, Sr) and light rare earth elements (LREEs) relative to high field strength elements (HFSEs) and heavy rare earth elements (HREEs). These features, combined with a relative depletion in Nb, Ta, Ti and P, are characteristic of subduction-related magmas. Isotopic data for the host rocks display I_Sr = 0.705045–0.707959, ε_Nd(t) = −3.23 to +3.80, and the Nd model ages (T_DM) vary from 0.58 Ga to 1.37 Ga. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition, with I_Sr ranging from 0.705513 to 0.707275 and ε_Nd(t) from −1.46 to 4.62. The MMEs have T_DM ranging from 0.49 Ga to 1.39 Ga. Geochemical and isotopic similarities between the MMEs and their host rocks demonstrate that the enclaves have mixed origins and were most probably formed by interactions between the lower crust- and mantle-derived magmas. Geochemical data, in combination with geodynamic evidence, suggest that a basic magma was derived from an enriched subcontinental lithospheric mantle (SCLM), presumably triggered by the influx of the hot asthenosphere. This magma then interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on Sr–Nd isotope data indicate that ∼50% to 90% of the lower crust-derived melt and ∼10% to 50% of the mantle-derived mafic magma were involved in the genesis of the early Oligocene magmas. In contrast, ∼45%–65% of the mantle-derived mafic magma were incorporated into the lower crust-derived magma (∼35%–55%) that generated the late Oligocene hybrid granitoid rocks. Early Oligocene granitoid rocks contain a higher proportion of crustal material compared to those that formed in the late Oligocene. It is reasonable to assume that lower crust and mantle interaction processes played a significant role in the genesis of these hybridgranitoid bodies, where melts undergoing fractional crystallization along with minor amounts of crustal assimilation could ascend to shallower crustal levels and generate a variety of rock types ranging from diorite to granite.     

The formation and rejuvenation of continental crust in the central North China Craton: Evidence from zircon U–Pb geochronology and Hf isotope

The Trans-North China Orogen (TNCO) along the central part of the North China Craton (NCC) is considered as a Paleoproterozoic suture along which the Eastern and Western Blocks of the NCC were amalgamated. Here we investigate the Precambrian crustal evolution history in the Fuping segment of the TNCO and the subsequent reactivation associated with extensive craton destruction during Mesozoic. We present zircon LA-ICP-MS U–Pb and Lu–Hf data on TTG (tonalite–trondhjemite–granodiorite) gneiss, felsic orthogneiss, amphibolite and granite from the Paleoproterozoic suite which show magmatic ages in the range of 2450–1900 Ma suggesting a long-lived convergent margin. The ε_Hf(t) values of these zircons range from −11.9 to 12 and their model ages suggest magma derivation from both juvenile components and reworked Archean crust. The Mesozoic magmatic units in the Fuping area includes granite, diorite and mafic microgranular enclaves, the zircons from which define a tight range of 120–130 Ma ages suggesting a prominent Early Cretaceous magmatic event. However, the ε_Hf(t) values of these zircons show wide a range from −30.3 to 0.2, indicating that the magmatic activity involved extensive rejuvenation of the older continental crust.     

Magma mixing origin for the post-collisional adakitic monzogranite of the Triassic Yangba pluton, Northwestern margin of the South China block: geochemistry, Sr–Nd isotopic, zircon U–Pb dating and Hf isotopic evidences

Petrogenesis of high Mg# adakitic rocks in intracontinental settings is still a matter of debate. This paper reports major and trace element, whole-rock Sr–Nd isotope, zircon U–Pb and Hf isotope data for a suite of adakitic monzogranite and its mafic microgranular enclaves (MMEs) at Yangba in the northwestern margin of the South China Block. These geochemical data suggest that magma mixing between felsic adakitic magma derived from thickened lower continental crust and mafic magma derived from subcontinental lithospheric mantle (SCLM) may account for the origin of high Mg# adakitic rocks in the intracontinental setting. The host monzogranite and MMEs from the Yangba pluton have zircon U–Pb ages of 207 ± 2 and 208 ± 2 Ma, respectively. The MMEs show igneous textures and contain abundant acicular apatite that suggests quenching process. Their trace element and evolved Sr–Nd isotopic compositions [(⁸⁷Sr/⁸⁶Sr)_i = 0.707069–0.707138, and ε_Nd(t) = −6.5] indicate an origin from SCLM. Some zircon grains from the MMEs have positive ε_Hf(t) values of 2.3–8.2 with single-stage Hf model ages of 531–764 Ma. Thus, the MMEs would be derived from partial melts of the Neoproterozoic SCLM that formed during rift magmatism in response to breakup of supercontinent Rodinia, and experience subsequent fractional crystallization and magma mixing process. The host monzogranite exhibits typical geochemical characteristics of adakite, i.e., high La/Yb and Sr/Y ratios, low contents of Y (9.5–14.5 ppm) and Yb, no significant Eu anomalies (Eu/Eu* = 0.81–0.90), suggesting that garnet was stable in their source during partial melting. Its evolved Sr–Nd isotopic compositions [(⁸⁷Sr/⁸⁶Sr)_i = 0.7041–0.7061, and ε_Nd(t) = −3.1 to −4.3] and high contents of K₂O (3.22–3.84%) and Th (13.7–19.0 ppm) clearly indicate an origin from the continental crust. In addition, its high Mg# (51–55), Cr and Ni contents may result from mixing with the SCLM-derived mafic magma. Most of the zircon grains from the adakitic monzogranite show negative ε_Hf(t) values of −9.4 to −0.1 with two-stage Hf model ages of 1,043–1,517 Ma; some zircon grains display positive ε_Hf(t) of 0.1–3.9 with single-stage Hf ages of 704–856 Ma. These indicate that the source region of adakitic monzogranite contains the Neoproterozoic juvenile crust that has the positive ε_Hf(t) values in the Triassic. Thus, the high-Mg adakitic granites in the intracontinental setting would form by mixing between the crustal-derived adakitic magma and the SCLM-derived mafic magma. The mafic and adakitic magmas were generated coevally at Late Triassic, temporally consistent with the exhumation of deeply subducted continental crust in the northern margin of the South China Block. This bimodal magmatism postdates slab breakoff at mantle depths and therefore is suggested as a geodynamic response to lithospheric extension subsequent to the continental collision between the South China and North China Blocks.     

Magma mixing revealed from in situ zircon U–Pb–Hf isotope analysis of the Muhuguan granitoid pluton, eastern Qinling Orogen, China: implications for late Mesozoic tectonic evolution

In this paper, we present zircon U–Pb age and Hf isotope data to document the significance of magma mixing in the formation of Late Jurassic granitoid intrusions in the eastern Qinling Orogen, China. The Muhuguan granitoid pluton from this orogen consists of monzogranite and lesser biotite granite and granodiorite, all containing abundant hornblende-rich cumulates, dioritic xenoliths, and mafic magmatic enclaves (MMEs). The monzogranite and granodiorite are intruded by a number of lamprophyre dykes. Both a cumulate and a dioritic xenolith samples have concordant zircon U–Pb ages of ca. 161 ± 1 Ma, but possess contrasting Hf isotopic compositions. The cumulate has more radiogenic zircon Hf isotopes with negative ε _Hf(t) values (?7.9 to ?2.5) and T _DM1 ages of 0.9–1.1 Ga, indicating its derivation likely from basaltic rocks of the Neoproterozoic to early Paleozoic Kuanping Group in the area. The dioritic xenolith has much lower zircon ε _Hf(t) values of ?19.5 to ?8.8 and T _DM2 ages of 2.4–1.7 Ga, consistent with a juvenile Paleoproterozoic crust source presumably represented by the metabasic rocks of the Qinling Group in the area. Individual samples of the monzogranite, MME, and a lamprophyre dyke have U–Pb ages of 150 ± 1, 152 ± 1, and 152 ± 1 Ma, respectively, demonstrating coeval mafic and felsic magmatism in the Late Jurassic. The lamprophyre dyke has homogeneous, highly negative zircon ε _Hf(t) values (?29.8 to ?24.8) and Archean T _DM2 ages (3.0–2.7 Ga), and its genesis is interpreted as partial melting of an ancient enriched subcontinental mantle source. Zircons from the fine-grained MME show a large range of ε _Hf(t) between ?29.1 and ?9.8, overlapping values of the monzogranite and lamprophyre dyke samples. Zircon U–Pb age and Hf isotopes of the MMEs are consistent with their formation by mixing of crustal- and enriched mantle-derived magmas. The main group of zircons from the monzogranite has ε _Hf(t) values (?17.9 to ?9.3) and T _DM2 ages (2.3–1.8 Ga) that are compatible with the dioritic xenoliths, indicating that the former was produced by partial melting of Paleoproterozoic crustal source with involvement of mantle-derived magmas. Mafic magmatism revealed from the Muhuguan pluton indicates that the eastern Qinling Orogen was dominated by lithospheric extension during the Late Jurassic. Compilation of existing geological and geochronological data suggests that this extensional event started in Late Jurassic (ca. 160 Ma) and persisted into the Early Cretaceous until ca. 110 Ma. The Jura-Cretaceous extension may have resulted from the late Mesozoic westward subduction of the Pacific plate beneath the East Asian continental margin.     

Incremental growth and origin of the Cretaceous Renjiayingzi pluton,southern Inner Mongolia,China: Evidence from structure,geochemistry and geochronology

The Renjiayingzi intermediate-acid pluton is located along a pre-existing ENE–WSW-trending dextral shear zone that forms part of the Xar Moron suture zone that marks the final closure of the Paleo-Asian Ocean. The pluton is composed of three small intrusions, which from northwest to southeast, are named the Shuangjianshan (SI), the Qianweiliansu (QI) and the Xingshuwabeishan (XI) intrusions. LA-ICPMS zircon U–Pb dating of a pyroxene diorite from the SI yields an age of 138 ± 1 Ma; the SHRIMP zircon U–Pb age of a tonalite from the QI records an age of 134 ± 2 Ma, whereas LA-ICPMS zircon U–Pb dating of a monzogranite from the XI has an age of 126 ± 1 Ma, suggesting the entire pluton was built up by three separate emplacement events that young to the ESE: this is further supported by the contact relations. Incremental growth of plutons by amalgamation of repeated small magma pulses is the most viable emplacement model. The pluton was probably emplaced by updoming of the roof along previous tensile fractures and by upward stacking of the three intrusions. The SI and QI have similar U–Pb ages and geochemical characteristics, and most likely had the same magma source and underwent similar petrogenetic processes. They have high MgO concentrations at low silica contents, are enriched in large ion lithophile elements, depleted in high field strength elements, have negative ε_Nd(t) values of −1.8 to −3.7, with Nd model ages of 1.07–1.19 Ga. Pyroxene diorites of the SI also have variable zircon ε_Hf(t) values (from −0.8 to +6.1), indicating that they were mainly derived from juvenile crust with minor crustal contamination and clinopyroxene-dominated fractional crystallization. The late monzogranites from the XI show weak negative ε_Nd(t) values of −2.3 to −2.5, young Nd model ages of 0.99–1.00 Ga, positive zircon ε_Hf(t) values (+1.3 to +4.6) and higher SiO₂ and K₂O contents, with strong depletion in Eu, P and Ti, indicating derivation from a distinct petrogenetic process from the two earlier intrusions. The monzogranites were the result of partial melting of juvenile crust in response to mantle-derived magma underplating, together with plagioclase-dominated fractional crystallization.     

U–Pb dating,geochemistry, and Sr–Nd isotopic composition of a granodiorite porphyry from the Jiadanggen Cu–(Mo) deposit in the Eastern Kunlun metallogenic belt,Qinghai Province,China

The Jiadanggen porphyry Cu–(Mo) deposit is newly discovered and located in the Eastern Kunlun metallogenic belt of Qinghai Province, China. Here, we present a detailed study of the petrogenesis, magma source, and tectonic setting of the mineralization causative granodiorite porphyry. The new data indicate that the granodiorite porphyry is characterized by high SiO₂ (68.21–70.41 wt.%) and Al₂O₃, relatively high K₂O, low Na₂O, and low MgO and CaO concentrations, and is high-K calc-alkaline and peraluminous. The granodiorite porphyry has low Mg^# (38–46) values that are indicative of no interaction between the magmas and the mantle. The samples that we have examined have low Nb/Ta (9.17–10.3) and Rb/Sr (0.28–0.39) ratios, which are indicative of crustal-derived magmas. Source region discrimination diagrams indicate that the magmas that formed the granodiorite porphyry were derived from melting of a mixed amphibolite source in the lower crust. The samples have I_Sr values of 0.70954–0.70979, ε_Nd(t) values of − 8.3 to − 7.9, and t_2DM ages ranging from 1644 to 1677 Ma. These indicate that the magmas that formed this intrusion were generated by melting of Mesoproterozoic lower crustal material. Higher K(Rb) contents of the samples indicate that the magma source is high potassium basaltic material in the lower crust, which could be derived from an enriched mantle source. LA-ICP-MS zircon U–Pb dating of the granodiorite porphyry yields a late Indosinian age (concordia age of 227 ± 1 Ma; MSWD = 0.31), which is close to the molybdenite Re–Os isochron age (227.2 ± 1.9 Ma), indicating further the close relationship between the granodiorite porphyry and the Cu–(Mo) mineralization. These samples are LREE and LILE (e.g., Rb, K, Ba, and Sr) enriched, and HFSE (e.g., Nb, Ta, P, and Ti) depleted, especially in P and Ti, similar to the characteristics of volcanic arc magmas. This intrusion most likely formed during the later stage of Indosinian deep subduction of oceanic slab. This was associated with underplating of mantle-derived magmas, which provided heat for crustal melting. Similar to the Jiadanggen granodiorite porphyry, Indosinian hypabyssal intermediate-felsic intrusive rocks, formed under subduction tectonism or a transitional regime from subduction to syn-collision, make up the most important targets for porphyry Cu(Mo) deposits in the Eastern Kunlun metallogenic belt.     

Magma mixing origin for the Aolunhua porphyry related to Mo–Cu mineralization,eastern Central Asian Orogenic Belt

Many Cu–Mo–Au deposits are considered to be related to adakitic porphyries formed in non-arc settings, e.g., in collisional orogenic zones and intra-plate environments, but their genesis is still under discussion. The Aolunhua porphyry complex and its related Mo–Cu deposit from the eastern Central Asian Orogenic Belt (CAOB) provide important insights into this issue. The porphyries are characterized by high Sr (496–705 ppm) and Sr/Y and La/Yb ratios similar to those of typical adakitic rocks, and low I_Sr ratios (0.7049–0.7052) and positive ε_Nd(t) (+ 0.5 to + 1.4) and ε_Hf(t) (+ 3.5 to + 9.8) values. These features, along with the occurrence of mafic microgranular enclaves (MMEs), compositional and textural disequilibrium of plagioclase phenocrysts and relatively high Mg# values (45–52), indicate that they were derived from mixing of felsic magma from partial melting of a juvenile arc-type lower crust and mafic magma from a lithospheric mantle previously metasomatized by subduction zone fluids/melts. High Sr/Y and La/Yb ratios are indicative of contribution from enriched mantle-derived materials (with high LILEs; e.g., Sr, La), which were strengthened by subsequent fractionation of ferromagnesian phases such as pyroxene and hornblende. MMEs hosted by the ore-bearing porphyry have zircon U–Pb ages of ca. 132 Ma, similar to those of the host rocks. The enclaves have elevated Mg^# (56–63), LILEs (e.g., Sr = 660–891 ppm), LREE (La_N = 68–150, (La/Sm)_N = 3.0–4.0, (La/Yb)_N = 12.0–19.6) and ratios of radiogenic isotopes of Nd- and Hf (ε_Nd = + 0.7 to + 1.6; ε_Hf = + 3.3 to + 10.9), suggesting that their parental magmas were derived from the metasomatized mantle source. The Mo–Cu mineralization was probably related to the high water content, high oxygen and sulfur fugacity of hybrid magma. Formation of the adakitic porphyries and related Mo–Cu deposits of the eastern CAOB could be related to the Early Cretaceous lithospheric extension, caused by the subduction of the Paleo-Pacific plate and its induced reactivation of juvenile arc-type lower crust.     

Geology and geochemistry of the Triassic Wenquan Mo deposit and Mo-mineralized granite in the Western Qinling Orogen,China

The recently-discovered Wenquan porphyry Mo deposit hosted in the Wenquan granite of the West Qinling Orogen has been recognized as a product of the Indosinian metallogenesis. Three generations of mineral assemblage for the deposit are identified as follows: (1) quartz–biotite–K-feldspar; (2) quartz–sulfide and (3) sulfide–calcite. Geochemical study shows that the mafic microgranular enclaves (MMEs) in the ore-bearing Wenquan granite have lower SiO₂, and higher Mg# and Nb/Ta ratios than the host granite itself. Different from the granite which have zircon ε_Hf(t) values of − 3.6–3.0 and T_DM2 of 1234–890 Ma, the MMEs are characterized by the ε_Hf(t) values of − 10.1–10.8 and T_DM1 of 865–441 Ma. This can be interpreted to indicate a mixture origin of the Meso- and Neoproterozoic crust-derived component and Neoproterozoic SCLM-derived materials for the formation of the Wenquan granite, which played an essential role in the Mo mineralization. Comparative Pb isotopic data between ores and K-feldspar suggest that the Wenquan granitic magma originated from the middle-lower crust of the South China Block and the ore-forming materials were incorporated by hydrothermal fluid differentiated from the Triassic magmatic system, with minor contribution of sedimentary rocks. The δ³⁴S values of 5.0–11.7‰ with a pronounced mode at 5.0 to 6.1‰ for the ores probably represent the sulfur incorporation of a typical magmatic hydrothermal fluid contaminated by heavy sulfur of Devonian sediments. The granite yielded the zircon U–Pb ages of 218 ± 2.4 Ma and 221 ± 1.3 Ma, as the same as the ages of 217 ± 2.0 Ma and 218 ± 2.5 Ma obtained for the MMEs. These ages are indistinguishable with the molybdenite Re–Os isochron age of 219 ± 5.2 Ma which is the timing for the Mo mineralization. Tectonically, the magmatic mixture processes of the Wenquan granite and the Mo mineralization to form the Wenquan Mo deposit contemporaneously occurred during the transition of tectonic regime from syn- to post-collision orogeny in the Qinling Orogen in the Late Triassic.     

Origin of the Heping granodiorite pluton: Implications for syn-convergent extension and asthenosphere upwelling accompanying the early Paleozoic orogeny in South China

We present geochemical and geochronological data of host granodiorites and mafic microgranular enclaves (MMEs) from the Heping pluton, which is situated in the central part of the Wuyi-Yunkai Orogen (WYO) in the South China Block (SCB), and reveal syn-convergent extension and asthenosphere upwelling during the early Paleozoic intracontinental orogeny. Two host and two MME samples from the Heping pluton yield LA-ICP-MS zircon UPb ages of ca. 445 Ma, coincident with the peak magmatism-metamorphism of the WYO. The host granodioritic samples are metaluminous (A/CNK = 0.68–0.91) and have abundant amphibole and low-moderate SiO₂ (59.1 to 67.3 wt%), belonging to high-K calc-alkaline I-type granite, whereas the MMEs are more basic with SiO₂ of 56.3 to 59.6 wt%. Both the host and MME samples display weakly negative Eu anomalies and distinctly relative depletions of Ta, Nb, and Ti, and most of them share similar initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7089–0.7112 and ε_Nd(t) values of −6.52 to −7.12, except one MME sample with a lower initial ⁸⁷Sr/⁸⁶Sr of 0.70758 and a higher ε_Nd(t) of −4.33. The zircon ε_Hf(t) values exhibit a wide range from −13.68 to −0.87. Petrological, geochemical, and chronological data suggest that the Heping pluton were generated by mingling of mafic and felsic magmas. The mafic endmember magma was originated mainly from the enriched subcontinental lithosphere mantle at the spinel–garnet transitional zone (~70 km), subsequently underplated/intraplated into the lower-middle crust resulting in the melting of the intermediate rock at pressure < 8 kbar to produce the felsic endmember magma. We proposed a new tectonic model “syn-convergent extension and asthenosphere upwelling during the intracontinental orogeny”. The syn-convergent extension zones, which include a series of NW-trending transverse faults and the NE-trending reactivated pre-exsiting suture and rift zone (i.e. Shaoxing-Jiangshan -Pingxiang- Chenzhou fault) within the WYO, are in favor of asthenosphere upwelling leading to intensive crust-mantle interaction.     

Formation and evolution of Precambrian continental lithosphere in South China

An overview is presented for the formation and evolution of Precambrian continental lithosphere in South China. This is primarily based on an integrated study of zircon U–Pb ages and Lu–Hf isotopes in crustal rocks, with additional constraints from Re–Os isotopes in mantle-derived rocks. Available Re–Os isotope data on xenolith peridotites suggest that the oldest subcontinental lithospheric mantle beneath South China is primarily of Paleoproterozoic age. The zircon U–Pb ages and Lu–Hf isotope studies reveal growth and reworking of the juvenile crust at different ages. Both the Yangtze and Cathaysia terranes contain crustal materials of Archean U–Pb ages. Nevertheless, zircon U–Pb ages exhibit two peaks at 2.9–3.0 Ga and ~ 2.5 Ga in Yangtze but only one peak at ~ 2.5 Ga in Cathaysia. Both massive rocks and crustal remnants (i.e., zircon) of Archean U–Pb ages occur in Yangtze, but only crustal remnants of Archean U–Pb ages occur in Cathaysia. Zircon U–Pb and Lu–Hf isotopes in the Kongling complex of Yangtze suggest the earliest episode of crustal growth in the Paleoarchean and two episodes of crustal reworking at 3.1–3.3 Ga and 2.8–3.0 Ga. Both negative and positive ε_Hf(t) values are associated with Archean U–Pb ages of zircon in South China, indicating both the growth of juvenile crust and the reworking of ancient crust in the Archean. Paleoproterozoic rocks in Yangtze exhibit four groups of U–Pb ages at 2.1 Ga, 1.9–2.0 Ga, ~ 1.85 Ga and ~ 1.7 Ga, respectively. They are associated not only with reworking of the ancient Archean crust in the interior of Yangtze, but also with the growth of the contemporaneous juvenile crust in the periphery of Yangtze. In contrast, Paleoproterozoic rocks in Cathaysia were primarily derived from reworking of Archean crust at 1.8–1.9 Ga. The exposure of Mesoproterozoic rocks are very limited in South China, but zircon Hf model ages suggest the growth of juvenile crust in this period due to island arc magmatism of the Grenvillian oceanic subduction. Magmatic rocks of middle Neoproterozoic U–Pb ages are widespread in South China, exhibiting two peaks at about 830–800 Ma and 780–740 Ma, respectively. Both negative and positive ε_Hf(t) values are associated with the middle Neoproterozoic U–Pb ages of zircon, suggesting not only growth and reworking of the juvenile Mesoproterozoic crust but also reworking of the ancient Archean and Paleoproterozoic crust in the middle Neoproterozoic. The tectonic setting for this period of magmatism would be transformed from arc–continent collision to continental rifting with reference to the plate tectonic regime in South China.     

Mineralization age and geodynamic background for the Shangjiazhuang Mo deposit in the Jiaodong gold province,China

The Shangjiazhuang Mo deposit is located on the Jiaodong Peninsula in eastern China, which is famous for the ca. 120 Ma “Jiaodong-type” Au deposits with total Au endowment of over 3000 t. In this paper, we discuss the deposit geology, mineralization age, and geochemical features of the host granodiorite of the Shangjiazhuang Mo orebody. Using this information, we aim to clarify the time and geodynamic mechanism for the Mo deposit, which is another constraint to understand the genesis of Au deposits. The Mo mineralization generally occurs as quartz–sulfide veins within the medium-grained Yashan granodiorite. The alteration consists of potassic alteration, silicification, sericitization, chloritization, and carbonatization with a weak unclear zonation. The ore minerals mainly include molybdenite, chalcopyrite, and pyrite. We measured Re–Os isotopes of molybdenite grains, which yielded a weighted mean model age of 116.9 ± 0.81 (MSWD = 1.03) and a well-constrained ¹⁸⁷Re–¹⁸⁷Os isochron age of 117.1 ± 1.4 Ma (MSWD = 1.6). These ages are slightly younger than the age of Au mineralization on the Jiaodong Peninsula. Rhenium contents of 5.84–29.99 ppm with an average of 16.4 ppm in molybdenites indicate a crustal source. Whole-rock geochemical compositions show that the granodiorite is high-K calc-alkaline and metaluminous to peraluminous. The samples show low Y contents from 8.2 to 10.5 ppm and Sr/Y ratios from 48.2 to 58.8, displaying an adakitic affinity. The Yashan granodiorite has high initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7101 to 0.7104, low ε_Nd(t) values of − 17.6 to − 16.7, and zircon ε_Hf(t) values from − 24.8 to − 17.1, with corresponding Hf model ages of 2.7 to 2.2 Ga. These isotopic data, together with the adakitic affinity of the granodiorite, indicate that the parental magma was derived from ancient crust. Mafic microgranular enclaves (MME) that are contemporaneous with the host granodiorite show SiO₂ contents of 57.98–58.41 wt% and depletion in Nb–Ta. The MMEs show enriched initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7102 to 0.7106 and low ε_Nd(t) values of − 17.3 to − 16.3. The MMEs are the products of mixing between the metasomatized lithospheric mantle-derived mafic magma and the ancient crust-derived felsic magma. The Early Cretaceous Mo mineralization (120–110 Ma) is slightly younger than the peak time of Au mineralization (126–120 Ma) on the Jiaodong Peninsula, but have a different spatial distribution which suggests different sources of Au and Mo. The “Jiaodong-type” Au deposits were probably related to the upwelling of metasomatized lithospheric mantle, while the Mo mineralization on the Jiaodong Peninsula may delineate a 120–110 Ma Mo metallogenic belt along the southern margin of the North China Craton with the East Qinling, which is related to the melting of ancient crustal sources. The subduction of the Paleo-Pacific slab and accompanying asthenospheric upwelling triggered upwelling of metasomatized lithospheric mantle, forming “Jiaodong-type” Au deposits. Subsequently, the ponding of mantle-derived magmas resulted in partial melting of ancient crust and associated Mo deposits.     

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 (741 Ma) followed by granodiorites (720 Ma) 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 “~750 Ma crust forming event”.The field and geochemical criteria together with age data assign the high-K calc-alkaline BH granites (608–590 Ma) and alkaline AF granites (600–592 Ma) 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 (La_N/Yb_N = 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 ε_Nd(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.     

Geochemistry,geochronology and Sr–Nd–Pb–Hf isotopic compositions of Middle to Late Jurassic syenite–granodiorites–dacite in South China: Petrogenesis and tectonic implications

In situ zircon U–Pb ages and Hf isotope data, major and trace elements and Sr–Nd–Pb isotopic compositions are reported for coeval syenite–granodiorites–dacite association in South China. The shoshonitic syenites are characterized by high K₂O contents (5.9–6.1 wt.%) and K₂O/Na₂O ratios (1.1–1.2), negative Eu anomalies (Eu/Eu* = 0.65 to 0.77), enrichments of Rb, K, Nb, Ta, Zr and Hf, but depletion of Sr, P and Ti. The adakitic granodiorite and granodiorite porphyry intrusions are characterized by high Al₂O₃ contents (15.0–16.8 wt.%), enrichment in light rare earth elements (LREEs), strongly fractionated LREEs (light rare earth elements) to HREEs (heavy rare earth elements), high Sr (438–629 ppm), Sr/Y (29.2–53.6), and low Y (11.7–16.8 ppm) and HREE contents (e.g., Yb = 1.29–1.64 ppm). The calc-alkaline dacites are characterized by LREE enrichment, absence of negative Eu anomalies, and enrichment of LILEs such as Rb, Ba, Th, U and Pb, and depletion of HFSEs such as Nb, Ta, P and Ti.Geochemical and Sr–Nd–Hf isotopic compositions of the syenites suggest that the shoshonitic magmas were differentiated from parental shoshonitic melts by fractional crystallization of olivine, clinopyroxene and feldspar. The parent magmas may have originated from partial melting of the lithospheric mantle with small amount contribution from crustal materials. The adakitic granodiorite and granodiorite porphyry have Sr–Nd–Pb isotopic compositions that are comparable to that of the mafic lower crust. They have low Mg# and MgO, Ni and Cr contents, abundant inherited zircons, low ε_Nd(t) and ε_Hf(t) values as well as old whole-rock Nd and zircon Hf model ages. These granodiorites were likely generated by partial melting of Triassic underplated mafic lower crust. The Hf isotopic compositions of the dacites are relatively more depleted than the Cathaysia enriched mantle, suggesting those magmas were derived from the partial melting of subduction-modified mantle sources. The coeval shoshonitic, high-K calc-alkaline and calc-alkaline rocks in Middle to Late Jurassic appear to be associated with an Andean-type subduction. This subduction could have resulted in the upwelling of the asthenosphere beneath the Cathaysia Block, which induced partial melting of the mantle as well as the mafic lower crust, and formed an arc regime in the coastal South China during Middle to Late Jurassic.     

西秦岭德乌鲁岩体成因及地质意义——来自岩石地球化学的证据

西秦岭德乌鲁岩体位于夏河-合作断裂和力士山-围当山断裂之间,寄主岩石以花岗闪长岩为主,石英闪长岩和石英二长闪长岩次之,并含有大量暗色微粒包体(MMEs).对德乌鲁岩体开展了年代学研究,获得的花岗闪长岩的LA-ICP-MS锆石U-Pb年龄为225.9±1.3 Ma,表明该岩体形成于晚三叠世早期,可能与扬子板块与华北板块陆...     

Crust-derived felsic magmatism in the Emeishan large igneous Province: New evidence from zircon U-Pb-Hf-O isotope from the Yangtze Block,China

Numerous intrusive bodies of mafic–ultramafic to felsic compositions are exposed in association with volcanic rocks in the Late Permian Emeishan large igneous province (ELIP), southwestern China. Most of the granitic rocks in the ELIP were derived by differentiation of basaltic magmas with a mantle connection, and crustal magmas have rarely been studied. Here we investigate a suite of mafic dykes and I-type granites that yield zircon U-Pb emplacement ages of 259.9 ± 1.2 Ma and 259.3 ± 1.3 Ma, respectively. The ε_Hf(t) values of zircon from the DZ mafic dyke are –0.3 to 9.4, and their corresponding T_DM1 values are in the range of 919–523 Ma. The ε_Hf(t) values of zircon from the DSC I-type granite are between –1 and 3, with T_DM1 values showing a range of 938–782 Ma. We also present zircon O isotope data on crust-derived felsic intrusions from the ELIP for the first time. The δ¹⁸O values of zircon from the DSC I-type granite ranges from 4.87‰ to 7.5‰. The field, petrologic, geochemical and isotopic data from our study lead to the following salient findings. (i) The geochronological study of mafic and felsic intrusive rocks in the ELIP shows that the ages of mafic and felsic magmatism are similar. (ii) The DZ mafic dyke and high-Ti basalts have the same source, i.e., the Emeishan mantle plume. The mafic dyke formed from magmas sourced at the transitional depth between from garnet-lherzolite and spinel-lherzolite, with low degree partial melting (<10%). (iii) The Hf-O isotope data suggest that the DSC I-type granite was formed by partial melting of Neoproterozoic juvenile crust and was contaminated by minor volumes of chemically weathered ancient crustal material. (iv) The heat source leading to the formation of the crust-derived felsic rocks in of the ELIP is considered to be mafic–ultramafic magmas generated by a mantle plume, which partially melted the overlying crust, generating the felsic magma.     

同源岩浆不同期次之间混合产生的暗色包体——以北拉萨地块中部晚白垩世桑心日岩体为例

本文在研究西藏北拉萨块体中段桑心日岩体中的暗色包体时发现了一种具有特殊岩石成因的暗色包体。暗色包体呈椭球状,在暗色包体和寄主岩的接触面上通常形成一个明显的可能由风化作用造成的间隙面。暗色包体为二长玢岩-花岗闪长玢岩,寄主岩为花岗岩,暗色包体明显较寄主岩更基性,更富Na_2O、CaO、MgO和Fe_2O_3~T。暗色包体和寄主岩具有明显不同的稀土元素特征,暗色包体的稀土元素含量变化较大,最基性样品具有最高的稀土含量,随着基性程度的降低稀土元素含量明显下降。随着岩浆的进一步演化,岩浆向花岗岩方向演化,稀土含量又逐步升高。寄主岩和暗色包体具有基本一致的微量元素组成,具有典型的弧岩浆岩的特征,富集Rb、Cs、K等大离子亲石元素和Th、U,亏损Nb、Ta、Ti等高场强元素。此外,暗色包体和寄主岩具有明显的Ba、Sr的负异常。暗色包体成岩年龄为75. 6±1. 2Ma,寄主岩的成岩年龄为71. 8±0. 6Ma,暗色包体成岩年龄较寄主岩早约4Myr。两者具有一致的锆石原位Lu-Hf同位素特征。综合以上岩相学、年代学、元素地球化学和同位素地球化学证据,我们认为桑心日暗色包体和寄主岩来源于同源母岩浆,初始岩浆在母岩浆房中经历了不同程度的含钾角闪石结晶分离作用,并沿早期较弱的构造裂隙侵入到地壳的某一层位,随着构造活动进一步加剧,经过进一步分异母岩浆大规模上侵,并将早先侵位处于半塑性状态的暗色包体侵吞、裹挟至近地表。桑心日暗色包体最可能的成因模式可以解释为同源岩浆不同期次间的物理混合。