Post-collisional Extensional Environment Research Articles

Late Magmatic Activity in the Tarim Large Igneous Province: Evidence from the Puchang Granites.

The magmatic evolution sequence and tectonic activity background of the Permian Tarim large igneous province were discussed based on the research of petrogeochemistry, chronology, and zircon Lu-Hf isotope of two types of granite distributed in the Puchang V-Ti-magnetite deposit in the northwestern margin of Tarim. The results show that the two types are characterized by high silica, alkali, and potassium content. Both types of granites are enriched with light rare earth elements, including porphyritic granites with a negative anomaly of Eu and biotite monzogranites with a weak positive anomaly of Eu. The trace elements generally show that the large-ion lithophile elements are enriched relative to the high-field-strength elements, P and Ti are obviously depleted, and Rb, U, and K are relatively enriched. The zircon U-Pb age of porphyritic granites is 275.7 ± 1.0 Ma, the εHf(t) value ranges from -6.6 to -3.3, and the tDM2 ranges from 1469 to 1684 Ma. The zircon U-Pb age of biotite monzogranites is 268.9 ± 1.4 Ma. The εHf(t) value ranges from -1.2 to 0.5, and the tDM2 ranges from 1232 to 1340 Ma. The two types of granite were formed in a postcollisional extensional environment at the end of the early Permian, which is related to the Permian Tarim mantle activity and asthenosphere upwelling. The porphyritic granite was derived from an enriched lithospheric mantle; the biotite monzogranite was formed by the melting of mantle with crust contamination; and basalt and intrusive complexes in the research area were formed in an extensional intraplate rift environment.

Early Paleozoic granitic magmatism and mineralization in the Debao Sn-Cu deposit, South China: Constraints from zircon and cassiterite U-Pb geochronology and whole-rock geochemistry

Numerous W-Sn deposits are developed in South China. While the majority of these deposits are related to the Yanshanian granites, a few of them are associated with the Early Paleozoic granites, and their geological significance is poorly understood. The Debao deposit is a typical skarn Sn-Cu polymetallic deposit that is spatially related to the Early Paleozoic Qinjia granites. Zircon U-Pb dating of three lithofacies (coarse-grained biotite granite, medium-grained porphyritic biotite granite and fine-grained porphyritic biotite granite) of the Qinjia granites yielded emplacement ages of 437.8 ± 3.0 Ma, 440.2 ± 2.0 Ma and 441.0 ± 3.0 Ma, respectively, consistent with cassiterite U-Pb ages of skarn ore (439.6 ± 2.7 Ma), indicating a close genetic relationship between the granitic magmatism and Sn mineralization. Biotite from the Qinjia granites belong to the ferro-biotite series with relatively high F contents (up to 0.70 wt. %). The Biotite compositions plot near the Ni-NiO (NNO) buffer on a Fe3+-Fe2+-Mg2+ diagram, suggesting formation under relatively low oxygen fugacity. The Qinjia granites are characterized by highly silicious (70.37–72.88 wt. %), high alkali (Na2O + K2O = 6.98–8.88 wt. %) and metaluminous to strongly peraluminous with the A/CNK ratios of 0.92–1.21, belonging to the I-S transform-type granites. They are enriched in U, Th, Zr, Nd and Hf, and depleted in Ba, Sr, Nb, Ta and Ti. They display right-declining chondrite-normalized REE patterns with significant negative Eu anomalies (EuN/Eu* = 0.33–0.66), and have low Nb/Ta and K/Rb ratios, indicating that the Qinjia granites experienced a high degree of fractional crystallization. The zircon εHf(t) values (−2.7 to +1.4), together with TDMC of 1.59 to 1.33 Ga, indicate that the granites formed via partial melting of Mesoproterozoic crustal with minor addition of mantle materials. The reduced (fO2 near NNO and Ce4+/Ce3+ ratios of zircon < 100), fractionated and volatile-rich magma facilitated the enrichment of Sn in the residual melt and hydrothermal fluids. Combined with previous studies on the Early Paleozoic magmatic rocks and tectonic activities in South China, we suggest that the Qinjia granites and associated Sn-Cu mineralization were likely formed in the post-collisional extensional environment during the Wuyi-Yunkai orogeny.

The gold mineral systems of the West Qinling orogen, central China: New insight from the Baguamiao gold deposit

The Baguamiao gold deposit is the first large deposit discovered in the West Qinling orogen in central China in the 1990 s. However, the occurrence of invisible gold in the deposit has not been reported. There is also no consensus on whether magmatic activity is involved in the gold mineralization, the style of mineralization, and the mechanism of gold precipitation. In this study, the in-situ trace elements, and chemical mapping of pyrite and pyrrhotite in the Baguamiao gold deposit were carried out for the first time. These data combined with the C-H-O isotope data of quartz, ankerite and calcite were used to determine mineralization process. In the Baguamiao gold deposit, five types of pyrite (Py0 to Py4) and pyrrhotite (Po0 to Po4) were identified, corresponding to the sedimentary-diagenetic period and four stages of mineralization (Stage I to Stage IV), respectively. From stage I to stage IV, gold mineralization in pyrite and pyrrhotite occurs as either visible or invisible crystals. The latter occurs dominantly as lattice-bound solid solutions (Au+) and is related to the content of Cu and Te. Co and Ni contents and Co/Ni ratios indicate that pyrite and pyrrhotite are magmatic-hydrothermal origin and affected by fluid-rock interaction. The change of Se and Te concentrations in pyrite and pyrrhotite indicates that oxygen fugacity (ƒO2) was increased from stage I to stage II, and then decreased during stage III and stage IV. In addition, the δ18O values of quartz, calculated δ18OH2O values of the ore-forming fluids and δ13C values range from 16.9 to 20.3 ‰, 7.7 to 12.9 ‰, and − 19.3 to + 0.2 ‰, respectively. Such isotopic signature records typical characteristics of orogenic gold deposit. The ore-forming fluid is a mixed hydrothermal solution involving metamorphic water, magmatic water, and meteoric water, and mixed with marine carbonate and sedimentary organic matter. Gold was precipitated by phase separation, fluid-rock interaction, and fluid mixing. Combined with the tectono-magmatic evolution, metamorphic deformation, and gold mineralization age of the West Qinling orogen, it can be concluded that with the closure of the Mianlue portions of the East Paleo-Tethys Ocean, the Baguamiao gold deposit was formed in the post-collisional extensional environment between the South China Block and the North China Block in the Late Triassic and is an orogenic gold deposit reference to the crustal continuum model.

Multistage evolution of the Keluo Complex in the northern Da Hinggan Mountains: Implications for the Mesozoic tectonic history of the eastern Central Asian Orogenic Belt

The Da Hinggan Mountains (DHM) are located in the eastern segment of the Central Asian Orogenic Belt (CAOB) and represent a prominent geomorphic marker of NE China, although its evolution history and exhumation/uplift mechanisms remain equivocal. Here, we present results from a comprehensive study on the field and micro-structures, kinematics, rheology, quartz EBSD fabrics, geochemistry and geochronology of the Keluo Complex (KC) exposed in the northern DHM. The KC is dominated by deformed Early Carboniferous to earliest Permian rocks (337–297.1 Ma) and is invaded by Early Mesozoic multi-stage granitic intrusions (219.8–175.5 Ma). These were further overprinted by magmatism, metamorphism, and deformation during the Late Jurassic (152.0–157.7 Ma) and late Early Cretaceous (118.3 Ma). The latest Carboniferous/earliest Permian rocks formed in a post-collisional extensional environment that might be related to the collision of the Xing'an and Songnen massifs. The Early Mesozoic rocks were derived from magma generated by partial melting of the lower continental crust within an active continental margin setting related to the subduction of the Mongol-Okhotsk Ocean. Two prominent deformation events (D1 and D2) were recognized in the KC, which occurred in Late Jurassic and late Early Cretaceous. The D1 is dominated by SW-trending sinistral ductile shearing accompanied by moderate to high-temperature deformation (500–600 °C) resulting from NW–SE compression. The D2 is a bi-directional extensional and detachment deformation corresponding to a low temperature (300–400 °C) deformation developed at a shallow-level ductile regime resulting from NW–SE extension. The D1 deformation was influenced by subduction and closure of the Mongol-Okhotsk Ocean, whereas the D2 deformation is correlated to the superposition of the extension after the closure of the Mongol-Okhotsk Ocean and the rollback of the Paleo-Pacific Plate. Our results provide new insights into the tectonic history of the DHM domain of the CAOB.

Geochronology and geochemistry of the dioritic rocks from the Inexpressible Island, Northern Victoria Land, Antarctica and their geological implications

东南极北维多利亚地沿威尔逊、鲍尔斯地体边缘发育广泛的花岗质岩浆作用。本文选取了罗斯造山带北维多利亚地难言岛古生代闪长质岩石开展了锆石U-Pb年代学、Sr-Nd-Hf同位素地质学及全岩地球化学研究，分析探讨其岩浆的源区特征和岩石成因。锆石U-Pb同位素定年结果显示，难言岛闪长质岩石形成于约500Ma，属于晚寒武世罗斯造山后岩浆活动产物。岩石地球化学特征显示的SiO₂含量变化范围为54.03%~60.10%，总碱值为5.92%~6.91%，里特曼指数σ为2.67~3.68，A/CNK值为0.77~0.85，属于高钾钙碱性、准铝质岩石。在正常洋中脊玄武岩标准化蛛网图中，样品富集大离子亲石元素（LILE），亏损Nb、Ta、Ti；在球粒陨石标准化稀土元素配分图中，难言岛闪长质岩石显示轻稀土相对富集，（La/Yb）_N=12.99~14.60，Eu弱负异常（0.62~0.71）。样品的锆石ε_Hf（t）值为-10.7~-6.3；（⁸⁷Sr/⁸⁶Sr）_i范围0.7095~0.7097，（¹⁴³Nd/¹⁴⁴Nd）_i范围0.511502~0.511629，ε_Nd（t）范围-7.1~-10.3。结合前人资料，显示难言岛闪长质岩石来自于先前富集的陆下岩石圈地幔部分熔融，在罗斯汇聚的过程中被俯冲组分进一步交代。晚寒武世罗斯造山带处于后碰撞环境，熔融可能与后碰撞伸展环境下俯冲板块回卷、撕裂过程中软流圈上涌或其他减薄机制有关。;Extensive Early Paleozoic granitic magmatism developed along the margins of the Wilson and Bowers terranes in Northern Victoria Land, Antarctica. Based on zircon U-Pb geochronology, Sr-Nd-Hf isotope geology and geochemistry of the Paleozoic Inexpressible Island dioritic rocks in the Northern Victoria Land, Ross Orogenic Belt, this paper analyzed the initial time of the post-collisional extensional environment and the characteristics of magma source region. Zircon U-Pb isotope dating reveals that the Inexpressible Island diorites were formed at about 500Ma, representing Late Cambrian Ross magmatic activity. The samples show characteristics of a high potassic and magmatic arc affinity. The contents of SiO₂ and total alkali (K₂O+Na₂O) range within 54.03%~60.10% and 5.92%~6.91%, respectively. The σ and A/CNK values vary from 2.67 to 3.68 and 0.77 to 0.85, respectively, indicating that the rocks belong to metaluminous rocks. On the normal mid-ocean ridge basalt-normalized diagram, the samples are enriched in large ion lithophilic elements (LILE) and depleted in Nb, Ta and Ti. In the chondrite-normalized REE diagram, the Inexpressible Island diorite shows a relatively rich LREE with (La/Yb)_N=12.99~14.60 and a slight negative Eu anomaly (0.62~0.71). Furthermore, zircon ε_Hf(t) and ε_Nd(t) values of the measured samples range from -10.7 to -6.3 and -7.1 to -10.3, respectively, with correspondent (⁸⁷Sr/⁸⁶Sr)_i and (¹⁴³Nd/¹⁴⁴Nd)_i ratios of 0.7095 to 0.7097 and 0.511502~0.511629. Combined with previous data, the Inexpressible Island diorites can be ascribed to the melting of previously enriched subcontinental lithospheric mantle, which further metasomatized by a subduction component before. The mechanism that triggers partial melting could be slab rollback and convective thinning and/or delamination of overthickened lithosphere during Ross orogenic belt post-collision.

Geodynamic setting and ore formation of the Younusisayi thorium deposit in the Altyn orogenic belt, NW China

Thorium deposit related to alkaline/peralkaline magmatism is the dominant thorium source. Its ore-forming thorium mechanism has long been fascinating. The Younusisayi Th deposit, hosted in early Paleozoic alkali-feldspar granite in the South Altyn Complex, NW China, is an example to explore the Th mineralization processes in magmatic-hydrothermal systems. Zircon U-Pb dating shows that the ore-hosting alkali-feldspar granites are emplaced at 445.7–439.0 ± 1.3 Ma. The apatite that occurs concomitantly with thorite in the mineralized alkali-feldspar granites formed at are 442.0–438.0 ± 14 Ma, indicating Th mineralization temporally related to the magmatism. Four populations of fluorite exhibit distinct occurrences, the fluorite Ia and Ib are in intergrowth with thorite, but the fluorite IIa and IIb are not. Notably, four populations of fluorite are differentiated by their Th + U and HREE concentrations, fluorite Ia and Ib show higher Th + U contents and lower HREE contents than fluorite IIa and IIb. Th was extracted by magma during emplacement. As a strong incompatible element, thorium will not be enriched in rock-forming minerals. In the process of magmatic evolution, thorium is gradually enriched in the post-magmatic fluids which contains abundant volatile components. Thorium can be transported as F-Th complexes in F-rich fluids. As temperature decreased, thorium precipitated in the form of thorite, and fluorite Ia and Ib crystallized with a low HREE content. Fluorine from the decomposition of F-Th complexes, reacts with HREE in the fluids to form F-HREE complexes, which increases the HREE content in the fluid. Therefore, the fluorite IIa and IIb which formed in the late stage of mineralization have obviously higher contents of HREE. We propose that the Younusisayi deposit, with an average grade of 0.4 wt% ThO2, formed in a post-collisional extensional environment during the early Paleozoic. The Younusisayi deposit is best classified as a magmatic-hydrothermal deposit. Our results demonstrate the usefulness of geochemistry of fluorite for tracing the ore-forming process, thus establishing the ore formation model.

Sericite 40Ar/39Ar dating and S-Pb isotope composition of the Kanggur gold deposit: Implications for metallogenesis of late Paleozoic gold deposits in the Tianshan, central Asian Orogenic Belt

The Tianshan is one of the largest gold provinces on Earth and hosts several giant gold deposits, while most giant gold deposits are distributed in the western and central segments of the Tianshan (i.e., the Western Tianshan) but not in Chinese Tianshan. Thus, the differences for metallogenesis of gold deposits between the Western and Chinese Tianshan attract intensive interest but remain ambiguous. Here we present sericite 40Ar/39Ar ages and S–Pb isotope compositions of pyrite from the Kanggur gold deposit, the largest shear zone-related gold deposit in the Chinese Tianshan. By integrating new sericite 40Ar/39Ar plateau ages (262.71 ± 2.95 Ma and 263.40 ± 2.94 Ma) with previous geochronological results, three peaks in gold mineralization are identified for the entire Tianshan: an early peak at ca. 330 Ma during which time subduction–accretion-related porphyry-type and orogenic gold deposits formed, a middle peak at ca. 290 Ma during which time post-collisional magmatism-related orogenic gold deposits formed in a collisional compressional to post-collisional extensional environment, and a late peak at ca. 260 Ma during which time strike–slip shear zone-related orogenic gold deposits formed in a post-collisional extensional environment. The sulfur (δ34SV-CDT of −1.0 to +2.5‰ for pyrite from ores and −1.9 to +2.6‰ for pyrite from wall rocks) and lead (18.199–18.231 for 206Pb/204Pb, 15.585–15.624 for 207Pb/204Pb, 38.104–38.229 for 208Pb/204Pb for pyrite from ores, and 18.176–18.244 for 206Pb/204Pb, 15.583–15.611 for 207Pb/204Pb, 38.090–38.205 for 208Pb/204Pb for pyrite from wall rocks) isotope compositions of pyrite indicate that the metals in gold deposits throughout the Tianshan were sourced from different reservoirs. In the Western Tianshan, the ore-forming metals for the deposits southwest of longitude 70°E were mainly sourced from upper crustal reservoirs, whereas those east of longitude 70°E were mainly sourced from lower crustal reservoirs. In the Chinese Tianshan, however, the ore-forming metals were dominantly sourced from lower crustal and/or mantle reservoirs. These different reservoirs were likely responsible for the distinct characteristics of the gold deposits located in the Western and Chinese Tianshan.

Petrogenesis and tectonic setting of granitic plutons in the Guaizihu region, North Alxa Block, China: constraints from whole-rock geochemistry, zircon U–Pb ages and Hf isotope compositions

To better constrain the petrogenesis and tectonic setting of the granitic plutons in the Guaizihu region, NW China, this study presents a new analysis of zircon U–Pb ages, whole-rock geochemistry and Hf isotopes of syenogranites. The syenogranites are medium- to coarse-grained, with moderate to high SiO2 (72.55–74.27 wt%) and Al2O3 (13.02–13.75 wt%) contents and moderate total alkalis (Na2O + K2O, 7.58–7.98 wt%), which indicate that the syenogranites exhibit calc-alkaline and peraluminous characteristics. The low Ce, 10 000 Ga/Al, and A/CNK values and the negative correlation of SiO2 and P2O5 confirm that the syenogranites are of I-type origin. The whole-rock geochemistry demonstrates that the magma was generated by partial melting and experienced fractional crystallisation. Specifically, the correlations of Rb with Ba and Sr and the weak negative Eu anomalies indicate that the plagioclase has undergone fractional crystallisation. In addition, Eu anomalies and La/Sm–La relations show that both fractional crystallisation and partial melting contributed to the magmatic process. The positive εHf(t) values (0.11–9.78); enrichments in Rb, Th and other LILEs; depletions in Nb, Sr and other HFSEs; and the ratios of geochemical elements indicate that the syenogranites were generated from the partial melting of juvenile crust. The granites are inferred to have formed in a post-collisional extensional environment. Additionally, the U–Pb zircon ages (284.6 ± 0.84 Ma and 269.4 ± 1.2 Ma) of syenogranites suggest that final closure of the Paleo-Asian Ocean occurred before 285 Ma. KEY POINTS Granites in the Guaizihu region are dated at 284.6 ± 0.84 Ma and 269.4 ± 1.2 Ma, and the Paleo-Asian Ocean, where the Engger Us Ophiolite Belt is located, closed before 285 Ma. Granites are medium- to coarse-grained and highly fractionated I-type syenogranites. Granites have been derived from magma generated by the partial melting of juvenile crust followed by fractional crystallisation. Granites were formed in an intraplate extensional environment related to a post-collisional event.

Timing of formation and cause of coloration of brown nephrite from the Tiantai Deposit, South Altyn Tagh, northwestern China

The world’s largest and economically valuable nephrite deposits are distributed along the Western Kunlun Orogen in northwestern China. During the past 20 years, extensive white and brown nephrite deposits have been discovered in both China and Russia, and several of these deposits have been found in South Altyn Tagh in the eastern part of the Western Kunlun Orogen. However, the timing of formation, genesis, petrographic characteristics, mineralogical composition, and reasons for the white–brown color of the nephrite remain unclear. We analyzed 50 samples of white, brown, and white–brown nephrite from the Tiantai nephrite deposit in Qiemo County with the aim of understanding the processes of formation, age, and diversity of these nephrites. Three main types of nephrite can be distinguished: white, brown, and dark brown. X-ray diffraction and petrographic studies indicate that the brown and dark-brown nephrite samples have fewer mineral inclusions compared with the white nephrites. The nephrite formed during early retrogression through the sequence of diopside skarn → coarse-grained tremolite skarn and coarse-grained tremolite → fine-grained tremolite. The higher bulk Fe content of the white nephrite (0.76 wt% FeO) relative to the brown nephrite (0.39 wt%), and the uniform, very low Fe2O3 contents of both of these color varieties (<0.15 wt%), suggest that the brown coloration is unrelated to Fe content and oxidation state. The white nephrite is characterized by a wide range of SiO2 contents (49.6–56.7 wt%), in contrast to the brown nephrites, which are characterized by nearly constant SiO2 contents (~58 wt%), close to the ideal content for tremolite. On average, the white nephrite is enriched in Al2O3 (3.22 wt%) and water (3.96 wt% loss on ignition) and depleted in CaO (12.35 wt%) relative to the brown nephrite (0.80 wt% Al2O3, 2.23 wt% loss on ignition, 12.95 wt% CaO). These characteristics, combined with greater transparency and higher Al and water contents in the chlorite formula relative to that of tremolite, as well as a near-absence of Ca in the chlorite formula, can explain the lower transparency and associated more intense coloration (i.e., yellow to brown) of the brown nephrite in terms of the lower modal abundance of chlorite. The spatial distribution of selected elements agrees with this hypothesis, whereby the brown-colored zones are dominated by Ca- and Sr-rich (substituting Ca) domains reflecting the highest modal volume of the tremolite. In contrast, the white zones are characterized by a substantially higher volumetric ratio of Al-rich domains, reflecting the higher chlorite content. Thus, the different coloration is not caused by specific elements, but by modal proportions of tremolite and chlorite. The slightly higher average Cr (10.1 ppm) and Ni (6.4 ppm) contents of brown nephrite, relative to white nephrite (8.7 ppm Cr and 5.5 ppm Ni), might also contribute to the color intensity and brown coloration. Ore-forming fluids involved in the formation of the studied nephrite have isotopic compositions of δ18O = 1.5‰ to 9.4‰ (330–430 °C) and δD = −87‰ to −50‰ (330–450 °C), suggesting that the formation of the Mg-skarn deposit was related to metasomatism of dolomite by fluids derived from local granite/granodiorite intrusions. Zircons from three brown–white samples yield concordant SHRIMP ages of 438 ± 14 Ma (2σ, MSWD=10.4), 916 ± 10 (2σ, MSWD = 1.5), 438 ± 9 Ma (2σ, MSWD = 5.3), and 431.1 ± 2.5 Ma (2σ, MSWD = 2.4). The younger ages (ca. 430 Ma) are close to those for placer nephrite from the Yurungkash and Karakash rivers, as well as those for Yecheng, Alamas, and Buya granodiorites, and probably represent the primary formation ages of nephrite within the Hetian Nephrite Belt. Overall, these ages indicate that the primary deposits formed during pre- or post-orogenic stages in the Western Kunlun Orogen. 40Ar/39Ar dating of hydrothermal muscovite and phlogopite intergrown with tremolite in the nephrite yielded ages of 418.8 ± 3.4 Ma (2σ, MSWD = 0.65), 379.5 ± 3.0 Ma (2σ, MSWD = 0.81), and 354.5 ± 3.6 Ma (2σ, MSWD = 0.71), which suggest multiple metasomatic activity. The similar formation ages of nephrites from Altyn Tagh (433 Ma) and from the previously studied areas of West Kunlun (441–378 Ma) and East Kunlun (416 Ma) indicate that these nephrites formed during the closure of the Proto-Tethys and in the accompanying post-collisional extensional environment.

Petrogenesis of mafic microgranular enclaves (MMEs) in the oligocene-miocene granitoid plutons from northwest Anatolia, Turkey

Mafic microgranular enclaves (MMEs) in host granitoids can provide important constraints on the deep magmatic processes. The Oligocene-Miocene granitoid plutons of the NW Anatolia contain abundant MMEs. This paper presents new hornblende Ar-Ar ages and whole-rock chemical and Sr-Nd isotope data of the MMEs from these granitic rocks. Petrographically, the MMEs are finer-grained than their host granites and contain the same minerals as their host rocks (amphibole + plagioclase + biotite + quartz + K-feldspar), but in different proportions. The Ar-Ar ages of the MMEs range from 27.9 ± 0.09 Ma to 19.3 ± 0.01 Ma and are within error of their respective host granitoids. The MMEs are metaluminous and calc-alkaline, similar to I-type granites. The Sr-Nd isotopes of MMEs are 0.7057 to 0.7101 for 87Sr/86Sr and 0.5123 to 0.5125 for 143Nd/144Nd, and are similar to their respective host granitoids. These lithological, petrochemical and isotopic characteristics suggest that the MMEs in this present study represent chilled early formed cogenetic hydrous magmas produced during a period of post-collisional lithospheric extension in NW Anatolia. The parental magma for MMEs and host granitoids might be derived from partial melting of underplated mafic materials in a normally thickened lower crust in a post-collisional extensional environment beneath the NW Anatolia. Delamination or convective removal of lithospheric mantle generated asthenospheric upwelling, providing heat and magma to induce hydrous re-melting of underplated mafic materials in the lower crust.

Petrogenesis and tectonic setting of the Chaheilingashun pluton, North Alxa Block, NW China: constraints from whole-rock geochemistry, zircon U–Pb ages, and Hf isotope compositions

To better constrain the petrogenesis and tectonic setting of the Chaheilingashun pluton in the southern Ya-Gan Fault, North Alxa Block, NW China, this study presents new zircon U–Pb ages, whole-rock geochemistry, and Hf isotopes of diorites from the Chaheilingashun pluton. The Chaheilingashun pluton is composed of medium- to coarse-grained monzonitic diorite, with moderate to high SiO2 contents (58.22–62.77 wt.%), moderate total alkali contents (Na2O + K2O, 5.72–7.66 wt.%), and high Al2O3 contents (14.26–17.69 wt.%), which indicate that the diorite exhibits calc-alkaline to alkaline and metaluminous to peraluminous series. The correlations of SiO2 with oxides and the right-dipping oblique trends of rare earth elements (REEs) demonstrate that the magma experienced fractional crystallization. In particularly, the correlations of Rb with Ba and Sr, and the weak negative Eu anomalies indicate that the plagioclase has undergone fractional crystallization. In addition, this paper has shown that both fractional crystallization and partial melting also contributed to the magmatic process through the Eu anomalies and La/Sm-La diagram. The positive eHf(t) values (2.2–4.6) and low Mg#, Cr, and Ni indicate that diorite was generated from the partial melting of juvenile mafic crust. Together with previous results, the diorites are inferred to have formed in an post-collisional extensional environment. The zircon U–Pb age of diorite from the Chaheilingashun pluton is dated at 289.3 Ma, suggesting that the final closure time of the Paleo-Asian Ocean was might before 289.3 ± 2.3 Ma.

Late Paleozoic igneous rocks in the Xing’an Massif and its amalgamation with the Songnen Massif, NE China

We present new zircon U–Pb–Hf isotopic and whole-rock geochemical data for late Paleozoic igneous rocks from the Xing’an Massif, Northeast China, to further our understanding of the amalgamation of the Xing’an and Songnen massifs. Zircon laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) U–Pb ages indicate that late Paleozoic magmatism occurred in the Xing’an Massif over three stages: during the early Carboniferous (359–352 Ma), early late Carboniferous (327–320 Ma), and late Carboniferous–early Permian (307–295 Ma). The early Carboniferous igneous rocks are mainly quartz diorite, granodiorite, monzogranite, syenogranite, and rhyolite, and formed in an active continental margin setting related to the westward subduction of the Heihe–Nenjiang oceanic plate. The early late Carboniferous monzogranites are medium-K calc-alkaline I-type granitoids, with zircon εHf(t) values of +5.6 to +13.0 and TDM2 ages of 973–502 Ma, suggesting that the primary magma was derived from the partial melting of newly-accreted crust. The early late Carboniferous igneous rocks formed in collisional setting, marking the amalgamation of the Xing’an and Songnen massifs. The late Carboniferous–early Permian intrusive rocks are dominated by diorite, monzogranite, syenogranite, alkali-feldspar granite, and granite porphyry. The large volume of alkali feldspar granites and A-type granites suggested that they formed in a post-collisional extensional environment.

Petrogenesis of Permo-Triassic intrusive rocks in Northern Liaoning Province, NE China: implications for the closure of the eastern Paleo-Asian Ocean

ABSTRACT The Changchun-Yanji belt recorded widespread Permo-Triassic magmatism, but their origins remain unclear, inhibiting a comprehensive understanding of the magmatic response to the final closure of the Paleo-Asian ocean in the eastern Central Asian Orogenic Belt (CAOB). Here, we present new geochronological, geochemical, and Hf isotopic data for the Permo-Triassic plutons from Northern Liaoning province, NE China. Combined the published ages with our new data, the Permo-Triassic magmatism in the eastern CAOB can be divided into five episodes: early Permian (293–274 Ma), middle–late Permian (270–257 Ma), latest late Permian–Middle Triassic (255–242 Ma), Late Triassic (240–215 Ma), and latest Late Triassic (209–200 Ma). The middle Permian and Late Triassic mafic plutons (i.e. ~266 Ma Mengjiagou gabbro–diorite, ~240 Ma Jiancaicun gabbro and ~224 Ma Shudetun gabbro-diorite) contain relatively high TFe2O3, MgO, Cr and Ni contents with positive εHf(t) values (+1.2 to +7.2), suggesting a depleted mantle origin. These mafic rocks together with the coeval granitoids make up typical bimodal associations, suggesting that they were formed under an extensional environment. The conclusions are also supported by occurrence of A-type granites during 270–257 Ma and 240–215 Ma. By contrast, the granitoids of 255–242 Ma in the eastern CAOB, including the Jianshanzi (~251 Ma) and Daganhe (~242 Ma) monzogranites, show typical geochemical features of adakitic granites, with high Sr/Y ratios and negative εHf(t) values (–8.6 to – 22.0), suggesting that the magmas were generated through partial melting of thickened ancient lower crust. Combined with previous studies, a four-stage tectonic evolution scenario was proposed: (1) active continental margin stage during 293–274 Ma; (2) continuing subduction resulted in the initiation collision, moderate crustal thickening, and slab break-off during 270–257 Ma; (3) final closure of the Paleo-Asian Ocean associated with continued crustal thickening occurred during 255–242 Ma; (4) lithospheric delamination in a post-collisional extensional environment occurred during 240–215 Ma.

Geochemistry, Geochronology, and Hf-S-Pb Isotopes of the Akechukesai IV Mafic-Ultramafic Complex, Western China

The Akechukesai IV mafic–ultramafic complex, located in the western segment of the eastern Kunlun orogenic belt (EKOB), represents a newly-discovered complex, containing Ni ores at grades of up to 0.98% Ni. It is dominated by olivine pyroxenite, pyroxenite, and gabbro units. The gabbros are enriched in lithophile elements (e.g., Rb, U, and K) and light rare-earth elements (LREE), with negative anomalies in high field-strength elements, except Zr, Ta. Nb/Ta(∼5) and Zr/Hf (∼10) ratios lower than the primitive mantle and chondrites, respectively, indicate the influence of the mantle metasomatic process or fractionation of accessory mineral phases. Zircon U–Pb dating of the gabbro yielded an age of 423.9 ± 2.6 Ma, indicating that the complex formed contemporaneously with the Xiarihamu Ni deposit (423 ± 1 Ma). The gabbro has negative εHf(t) values (−11.3 to −1.2) with corresponding TDM1 ages of 1535–1092 Ma. The vein-like and disseminated mineralization (i.e., pyrite and pyrrhotite) have δ34S values of 13.1‰–13.4‰ and 5.0‰–8.5‰, respectively, suggesting that the magmas that formed the complex assimilated crustal sulfur. They yield 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of 17.323–18.472, 15.422–15.626, and 37.610–38.327, respectively, indicating Pb derived from multiple sources (i.e., mantle crustal sources). Geochemical and Hf–S–Pb isotopic characteristics suggest that the complex formed from a primitive magma derived by partial melting of a spinel- and garnet-bearing lherzolite mantle at variable degree of 5%–10%. This source region was geochemically enriched by previous interaction with slab-related fluids. Tectonic reconstruction suggests that the Akechukesai IV complex was generated in a post-collisional extensional environment.

Mechanism of emplacement and origin of the Ildır lava dome in the Karaburun Peninsula, western Anatolia (Turkey)

The Karaburun Peninsula, which is considered to be a part of the Anatolide-Tauride Block, is situated between western Anatolia and the eastern part of the Aegean Sea, in a post-collisional extensional environment, and is located within the Izmir-Balıkesir Transfer Zone. The Paleozoic – Mesozoic basement rocks of the peninsula are cut and covered by Miocene volcanic successions, comprising mostly andesitic lavas and volcanoclastic deposits that interfinger with detrital lacustrine deposits. A NW-SE elongated andesitic exogenous composite lava dome structure (major axis is 4 km and minor axis is 1 km) was identified and dated to be 16.39 ± 0.34 Ma in age. It cuts and covers the Alaçatı andesitic pyroclastic and epiclastic deposits of the Ildır peninsula. Internal structures and igneous fabrics indicate a composite exogenous lava dome structure with short distance lava flows over a flat floor of Alaçatı ignimbrite. Emplacement of this Ildır composite lava dome was controlled by fissure-like volcanic activity along multiple fault lineaments as a result of extensional duplex – negative palm-tree lineaments which are related to the Miocene NW-SE directed sinistral strike-slip transtensional fault zone of the Karaburun peninsula. Comparison of the andesitic Ildır lava dome to all volcanic rocks of the Karaburun peninsula implies that the parental (more mafic) magma which formed the lava dome was generated by partial melting of a highly contaminated mantle source which had been modified by subduction-derived fluid/melt components. The Ildır melts were subsequently differentiated by fractional crystallization and crustal assimilation processes in the crust.

Geochronology and Geochemistry of the Granites from the Longtoushan Hydrothermal Gold Deposit in the Dayaoshan Area, Guangxi: Implication for Petrogenesis and Mineralization

The gold mineralization in the Longtoushan hydrothermal gold deposit is concentrated within the contact zone of the granitic complex. Whole rock geochemistry and in-situ U-Pb and Hf isotopic data were used to constrain the genesis and age of the granites and related Cu-Au mineralization in the Longtoushan Deposit. The granites mainly consist of the granite porphyry, rhyolite porphyry, porphyritic granite and quartz porphyry. LA-ICP-MS U-Pb dating of zircons from the granite porphyry, rhyolite porphyry and quartz porphyry indicates that they intruded from ca. 94 to 97 Ma. These intrusions exhibit similar trace element characteristics, i.e., right-dipping REE patterns, depletion of Ba, Sr, P and Ti, and enrichment of Th, U, Nd, Zr and Hf. The eHf (t) values of zircons from the granite porphyry, rhyolite porphyry and quartz porphyry range from −26.81 to −8.19, −8.12 to −5.33, and −8.99 to −5.83, respectively, suggesting that they were mainly derived from the partial melting of the Proterozoic crust. The Cu-Au mineralization is mainly related to the rhyolite porphyry and porphyritic granite, respectively. The Longtoushan granites were most likely formed in a post-collisional extensional environment, and the deposit is a part of the Late Yanshanian magmatism related mineralization in the Dayaoshan area and its adjacent areas.

Petrology, mineral chemistry, and geochemistry of Late Triassic Ni–Cu ore-bearing mafic–ultramafic intrusions, Hongqiling, northeastern China: petrogenesis and tectonic implications

The Hongqiling magmatic Ni–Cu sulfide deposit, situated on the southern margin of the eastern Central Asian Orogenic Belt (CAOB), is composed of over 30 mafic–ultramafic intrusions. These ore-bearing intrusions are composed mainly of harzburgite, lherzolite, websterite, orthopyroxenite, and norite (gabbro). The constituent minerals are olivine, diopside, bronzite, calcic-hornblende, plagioclase, and spinel with orthopyroxene as a dominant mineral in these intrusions. These ore-bearing intrusions are not Alaskan-type complexes. Spinel and clinopyroxene both exhibit different chemical compositions from those in the Alaskan-type complexes. The rocks that make up the intrusions have high contents of MgO (average value = 25.20 wt.%) and low TiO2 (average value = 0.58 wt.%). The high MgO contents of the minerals and the high Mg# (71) of the calculated melt in equilibrium with olivine demonstrate that the parental magma of the Hongqiling mafic–ultramafic intrusions was a high-Mg tholeiitic magma. The Hongqiling ore-bearing mafic–ultramafic intrusions and the calculated “trapped liquids” for the olivine-orthopyroxene cumulate rocks are all enriched in large-ion lithophile elements and depleted in high field strength elements. The Ce/Pb, Ta/La, Th/Yb, and (La/Sm)PM values and the depletion of Nb and Ta suggest that the magma experienced crustal contamination. The Hongqiling ore-bearing intrusions display many similarities with mafic–ultramafic intrusions that formed in a post-collisional extensional environment in the western CAOB (e.g., Huangshanxi). Common features include their whole-rock compositions and mineral chemistry. Combined with the evolutionary history of the eastern segment of the CAOB, we believe that the Late Triassic Hongqiling mafic–ultramafic intrusions formed in a post-collisional extensional environment.

Timing and tectonic settings of the Late Paleozoic intrusions in the Zhusileng, northern Alxa: implication for the metallogeny

The Zhusileng–Hangwula tectonic zone, located in the northern Alxa area, is a key site for understanding the evolution of the Paleo-Asian Ocean (PAO) and related mineral formation. We report the major and trace elements and zircon U-Pb ages of newly discovered mafic and intermediate to felsic intrusive rocks in the Zhusileng area. LA-ICP-MS zircon U-Pb analyses of the Echenghei diabase and Haierhan and Heipingshan granites yielded crystallization ages of 305 Ma, 284 Ma, and 271 Ma, respectively. The Late Carboniferous mafic rocks have high MgO and Fe2O3T contents and low K2O and TiO2 contents, and are characterized by depletion of HREEs and notably negative Nb-Ta anomalies, with enrichment of Rb, Ba, and U, which indicate an enriched mantle source. The Early Permian granites of the Zhusileng area are highly differentiated I-type granitoids sourced from mixing of mantle and crust, are high-K calc-alkaline and enriched in LREEs, and exhibit moderately to strongly negative Eu anomalies. All the intrusive rocks formed in a post-collisional extensional environment, which indicates that the branch of the PAO in the northern Alxa area had closed before the Early Permian. The Cu-Mo/Au mineralization in the Zhusileng area formed in the Middle to Late Permian and is genetically linked to the Late Paleozoic post-collisional rifting magmatism from after the closure of the Paleo-Asian Ocean.

Origin of the Haobugao skarn Fe-Zn polymetallic deposit, Southern Great xing’an range, NE China: Geochronological, geochemical, and Sr-Nd-Pb isotopic constraints

The Haobugao skarn Fe-Zn polymetallic deposit is located in the Southern Great Xing’an Range, northeastern China, and hosted in the Lower Permian carbonates. Laser ablation inductively coupled plasma mass spectrometer zircon U-Pb dating constrains the crystallization of the granite and feldspar-phyric diorite at 139 ± 2 Ma and 134 ± 2 Ma, respectively. According to the geological investigation, the Haobugao ore bodies are cut by the feldspar-phyric diorite emplaced along the post-mineralization fault, indicating that the mineralization occurred between 134 Ma and 139 Ma. Five molybdenite samples from skarn-type ores yield a Re-Os isochron age of 138 ± 3 Ma, agree with the crystallization age of the granite, indicating the Early Cretaceous magmatism and mineralization events. The enrichment of Zr, Y and Ga in the Haobugao granite suggest its A-type granite affinity. The positive εNd(t) values, young TDM2 ages and low initial 87Sr/86Sr values for the granite potentially reveal significant amount of juvenile material contributing to the parental magma. Based on Sr-Nd isotopic two-component mixing model, the Haobugao A-type granite was derived by magma mixing between mantle-derived juvenile component (∼80%) and the lower crust component (∼20%), also supported by the Pb isotopic compositions. The geochemical and isotopic signatures indicate that the Haobugao granite are derived from a post-collisional extensional setting. A high oxidation state between Ni-NiO and Fe2O3-Fe3O4 buffer could be predicted by the assemblage of quartz-magnetite-titanite-amphibole-biotite in the granite. Hence, sulfur would have been present as sulfates (SO2-4) in such highly oxidized magmas, and the chalcophile elements (Zn, Pb, Cu, Mo) were retained as incompatible elements in the melt, facilitating subsequent mineralization. A compilation of existing data reveals that the skarn Fe-Zn polymetallic mineralization from the Haobugao and other areas along the Southern Great Xing’an Range metallogenic belt took place coevally in the Early Cretaceous and was related to a post-collisional extensional environment. This significantly differs from the typical porphyry-skarn related deposits that are commonly formed under the arc-compressive setting (e.g., the Pacific Rim).

Geochronology and geochemistry of Late Devonian-Carboniferous igneous rocks in the Songnen-Zhangguangcai Range Massif, NE China: Constraints on the late Paleozoic tectonic evolution of the eastern Central Asian Orogenic Belt

This paper presents new zircon U–Pb ages and Hf isotopic data, and whole–rock geochemical data for Late Devonian–Carboniferous igneous rocks from the Songnen–Zhangguangcai Range Massif (SRM), NE China, to constrain the late Paleozoic tectonic evolution of the eastern Central Asian Orogenic Belt and the nature of the crust beneath the SRM. LA–ICP–MS zircon U–Pb dating reveals two stages of magmatism in the Late Devonian (366Ma) and Carboniferous (325–313Ma). The Late Devonian magmatic event produced alkali feldspar granites with high SiO2 and total alkali contents, as well as pronounced negative Eu anomalies, similar to A-type granites. Based on these features, their high zircon εHf(t) values (+9.6 to +13.0), and the early Paleozoic tectonic evolution of the eastern SRM, we conclude that the primary magma for the Late Devonian granites was generated by partial melting of juvenile lower crust in a post-collisional extensional environment. The Carboniferous magmatic event produced a suite of intermediate–felsic igneous rocks. The intermediate rocks, including basaltic andesite, andesite, and quartz monzodiorites, have low SiO2 contents, high Mg#, high Cr, Co, and Ni contents, and display arc-like trace element characteristics. Based on these observations and their high zircon εHf(t) values (+5.8 to +10.7), we suggest their primary magma was derived from partial melting of depleted mantle, metasomatized by subduction-related fluids. The felsic rhyolites and monzogranites have high SiO2 contents, low Mg#, extremely low Cr, Co, and Ni contents, and zircon εHf(t) values of +10.5 to +13.7 and +4.2 to +6.9, respectively. These results indicate that the primary magma for the felsic rocks was derived from partial melting of heterogeneous juvenile crust. The Carboniferous igneous rock assemblages, together with coeval carbonate sedimentary formations, record an intra-plate extensional setting. The zircon εHf(t) data of Paleozoic igneous rocks from the eastern SRM define a temporal trend that is consistent with tectonic evolution. The increase in εHf(t) values during the early late Paleozoic age mirrors changes in magma source, corresponding to a switch from subduction–collision to post-collision tectonic regimes in the SRM. The zircon Hf isotopic compositions of the studied Late Devonian–Carboniferous igneous rocks record crustal accretion in the eastern SRM during the Neoproterozoic–early Paleozoic. Reworking of these crustal materials occurred in a post-collisional extensional environment during the late Paleozoic.