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The Khanka Massif forms the easternmost part of the Central Asian Orogenic Belt (CAOB) and represents an ideal location for examination of the timing and processes involved in the transition from the Palaeo-Asian to Palaeo-Pacific Ocean tectonic systems. However, it is obstructed because the late Palaeozoic tectonic attributes of the eastern margin of this massif remain unclear. In this paper, we provide zircon U-Pb ages and Hf isotopic, as well as the whole-rock Sr-Nd-Pb-Hf isotopic data for Permian granitic and volcanic rocks within the eastern margin of the Khanka Massif, with the aim of exploring the petrogenesis and their geodynamics significance. These data suggest that the Permian magmatism within the eastern margin of the Khanka Massif, composed of monzogranites and rhyolites, can be split into two stages; i.e. middle (ca. 264 to ca. 263 Ma) and late (ca. 252 Ma) Permian. The highly fractionated middle Permian monzogranites are formed in an N-S extensional setting and represent the magmatic response to the amalgamation of the Khanka and Jiamusi massifs. Middle-late Permian rhyolites with decoupled Nd-Hf isotopic compositions were derived from partial melting of metasedimentary crustal rocks. Their moderate-high zircon saturation temperatures (796–817°C) are thought to represent the involvement of ridge subduction of the Palaeo-Asian Ocean beneath the western margin of the Khanka Massif. Our findings further reinforce the existence of the ridge subduction of the Palaeo-Asian Ocean at the western margin of Khanka Massif in the Permian, while excluding the possibility of Permian Palaeo-Pacific oceanic plate subduction occurred beneath the eastern margin of the Khanka Massif in the Permian. [ABSTRACT FROM AUTHOR]

Reconstructing the tectonic architecture of the southern Altaids is of great importance to piece together the continental growth history of the Central Asian continent. In this paper, we address the subduction‐accretion process of the Paleo‐Tianshan Ocean, one branch of the South Tianshan Ocean, in the southern Altaids, through a detailed geological and geochemical investigation of the Wulanmoren Accretionary Complex (WAC). The WAC is composed of ophiolitic mélanges, ocean plate stratigraphy mélanges, and turbiditic coherent units. In this study, we present key geological, petrological, and geochemical evidence indicating back‐arc and ocean island affinity of the igneous rocks of the WAC. Zircon U‐Pb dates of these rocks ages range between 380.2 ± 1.3 and 302.0 ± 5.3 Ma. The sedimentary matrix units of the mélanges were deposited in the Early Devonian (∼405 Ma) to the Late Triassic (∼222 Ma), rather than Silurian strata as previously thought. However, the ages of some detrital zircons in the sedimentary matrix are Precambrian, pointing to a complex evolution involving multiple ocean island terrains and island arcs of different ages that accreted from the mid‐Paleozoic to the Early Mesozoic. Plain Language Summary: Well‐exposed rock outcrops of the Wulanmoren Accretionary Complex (WAC) offer an ideal opportunity to solve the enigma of the evolutionary history of the Paleo‐Tianshan Ocean (PTO) of Central Asia. We report field observations, geochemistry, and geochronology of the WAC in the southern Altaids, pointing to multiple tectonic settings of ages spanning from the Early Devonian (∼405 Ma) to the Late Triassic (∼222 Ma). These reconstructions suggest closure time of the PTO occurred post‐Triassic. Based on detrital zircons provenance analysis, we propose a multi‐island ocean model to explain the tectonic evolution of the PTO in the time period studied. Key Points: The Wulanmoren Accretionary Complex was composed of ophiolitic mélanges, ocean plate stratigraphy mélanges, and coherent unitsThe Late Paleozoic MORB‐like and OIB‐type basalts, and ∼222 Ma coherent units indicate closure of the Paleo‐Tianshan Ocean occurred post‐TriassicThe southern Paleo‐Asian Ocean was an archipelago with several subduction systems which is similar to the modern southwest Pacific [ABSTRACT FROM AUTHOR]

The Lower Jurassic clastic rocks in the Qiangtang Basin, northern Tibet, are generally regarded as the early sediments of the new Mesozoic Qiangtang Basin (Late Triassic to Early Cretaceous). However, little attention has been paid to the palaeoenvironment, provenance, and tectonic setting of this unit. The QZ‐16 well, located in the east of the northern Qiangtang Basin, firstly recovered the Lower Jurassic strata (Quemo Co Formation) in the Qiangtang Basin. In this paper, the whole‐rock major‐trace elemental characteristics of 34 mudstone samples and detrital zircon geochronology of one sandstone, collected from the Quemo Co Formation of the QZ‐16 well, are reported in order to infer the palaeoenvironment, provenance, and tectonic setting. Quemo Co mudstones are dominated by SiO2 and Al2O3, while Fe2O3, CaO, K2O, and MgO are the second most abundant oxides. They are generally characterized by high REE concentrations, enrichment in light rare earth elements (LREEs), marked negative Eu and Ce anomalies. The REE contents of the mudstones are mainly controlled by terrigenous detrital minerals input. The Lower Jurassic mudstones have relatively high chemical index of alteration (79.1–83.6) values, indicating moderate to high degree of chemical weathering conditions of the source area. Sr/Ba and Rb/K ratios reflect that the marine transgression impact was limited and the mudstones were generally deposited in a brackish water environment. Major, trace, and REE contents indicate that the mudstones were mainly derived from intermediate igneous rocks with subordinate felsic igneous rocks. Prominent age peaks at ca. 200 ~ 400 Ma, 700 ~ 970 Ma, 1,700 ~ 1,900 Ma, and 2,100 ~ 2,700 Ma of the detrital zircon grains suggest that the Lower Jurassic clastic rocks were derived from the Central Qiangtang and Songpan–Ganzi complex. Moreover, tectonic discrimination diagrams based on major and trace elements show that the source of the Lower Jurassic sediments were most likely derived from a collision tectonic setting. [ABSTRACT FROM AUTHOR]

This paper presents new zircon U-Pb geochronological, Hf isotopic and whole-rock geochemical data for the granitic plutons in the Xing'an Massif, Northeast China, to constrain the Late Mesozoic tectonic evolution of the Mongol-Okhotsk Ocean and the Paleo-Pacific Ocean. The zircon U-Pb ages indicate that the granitoids emplaced during the Late Jurassic-Early Cretaceous. The granodiorites show an adakitic affinity with high Sr/Y ratios and low Yb (< 1.30 μg/g) contents. The monzogranites exhibit high SiO2, low MgO contents, enrichment in LILEs (Rb, K, and Th), and depletion in HSFEs (Ta, Nb, Zr, P, and Ti). Petrological and geochemical features of these monzogranites suggest that they are highly fractionated I-type granitoids. In addition, the zircon εHf(t) values and two-stage model ages (TDM2) are in the range of +2.6 to +8.1 and 669-1011 Ma, respectively, indicating that primary magma was generated by partial melting of juvenile lower-crustal materials, and there was a significant crustal growth in the Phanerozoic in the Northeast China. Combined with the coeval granitoids widely exposed in the Xing'an Massif, we conclude that the Late Jurassic magma in Northeast China was generated in an extensional setting related to the closure of the Mongol-Okhotsk Ocean, but the Early Cretaceous magma was related to the subduction of the Paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

This paper presents the results of combined studies of geochronology, geochemistry, whole rock Sr‐Nd and zircon Hf‐O isotopes carried out upon the rhyodacite and ignimbrite of Shangshu village, Shangyu town and Shanghupeng village of Jiangshan City in Zhejiang Province, along the northwestern side of the Jiangshan–Shaoxing suture. SHRIMP zircon U‐Pb dating of samples in the three areas yielded weighted mean 206Pb/238U ages of 842.8 ± 6.9 Ma and 850.0 ± 7.3 Ma, 839 ± 9 Ma and 832.2 ± 8.1 Ma, 828.3 ± 8.5 Ma and 836.9 ± 9.9 Ma, respectively. These ages are older than the volcanic rocks of the Shangshu Formation dated at around 780 Ma distributed in Fuyang City, Hangzhou City, Kaihua County, etc. The volcanic rocks generally have high SiO2 (54.08–76.80 wt%) and Al2O3 (12.40–21.31 wt%), low Fe2O3 (0.68–8.92 wt%), MgO (0.29–2.49 wt%), CaO (0.12–2.86 wt%), TiO2 (0.10–1.59 wt%) and P2O5 (0.01–0.39 wt%), with variable total alkalis (K2O + Na2O =5.42–8.29 wt%). There exists a clear negative correlation between SiO2 and P2O5. The volcanic rocks have A/CNK ratios of 1.03–2.77 and thus are peraluminous. They are characterized by enrichment in LREE, Rb, Ba, Zr, Hf, K, Th, La, U and depletion in Nb, Sr, P, Ti, with distinct LREE and HREE fractionation of (La/Yb)N values of 5.68–11.67, and with a moderate negative Eu anomaly (&Eu=0.58–0.89). Whole‐rock geochemical data shows that the Jiangshan volcanic rocks are possibly I‐type granitic rocks, even though they have some characteristics of A&S‐type granites due to the magma fractional crystallization and water‐rock interaction. Zircon δ18O values are 3.97‰–5.49‰ (average 4.50‰), 2.90‰–5.21‰ (average 4.32‰) for ignimbrite from Shangshu village section, and Shanghupeng village section, respectively. They are slightly lower than the average δ18O values of igneous zircons in equilibrium with mantle magmas (5.3 ± 0.6‰ (2σ)), the lower δ18O value also demonstrating the presence of high temperature water‐rock interactions. The ignimbrite rocks have positive ∊Nd(t) (4.02, 3.37, 3.91, 4.74, 2.85, 4.39, totals from the three areas) and ∊Nd(t) (in‐situ zircon) (4.3–14.6, a weighted mean of 8.4; 6.6–12.7, a weighted mean of 9.0; 8.1–12.0, a weighted mean of 9.5, respectively, from the three areas). In conjunction with the trace element studies, they indicate that the source region of the Jiangshan volcanic rocks was mainly composed of juvenile lower crustal material, mixed with some mantle‐sourced magma. Detailed elemental and isotopic data suggest that the Jiangshan volcanic rocks were formed in a continental arc setting. There is a series of ca. 860–830 Ma volcanic rocks formed in a back‐arc extensional setting in the southern margin of the eastern Jiangnan Orogen, along the northwest side of the Jiangshan–Shaoxing suture. The first stage rift‐related anorogenic magmatism may have occurred as early as ca. 860 Ma in the eastern Jiangnan Orogen. [ABSTRACT FROM AUTHOR]

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The Eastern Kunlun Orogenic Belt (EKOB) in Northwest China, is an ideal area for understanding the tectonic evolution of the Palaeo-Tethys Ocean. The EKOB is marked by widespread Palaeozoic to Early Mesozoic magmatism. However, the Late Permian–Early Mesozoic tectonic evolution of the Palaeo-Tethys Ocean tectonic regime is poorly understood. Here, we report new zircon LA-ICP-MS U–Pb dating and geochemical analyses of Late Permian–Early Triassic intrusive rocks in the Xiangyanggouxi and Dageledong areas in the EKOB, Northwest China, to discuss their petrogenesis and geodynamic setting and reconstruct the tectonic evolution of Palaeo-Tethys oceanic tectonic regime. Zircon U-Pb dating results indicate that these granitoids crystallized during ca. 256–248 Ma, i.e. the Late Permian to Early Triassic. These granitoids are mainly comprised of granodiorites and monzonitic granites that possess high concentrations of SiO2 (66.81–75.98 wt.%), K2O+Na2O (6.21–7.92 wt.%), and low contents of MgO, CaO, Cr, Ni, and Mg# (<0.44). They are classified as medium- to high-K calc-alkaline and metaluminous I-type granitoids. These granitoids are rich in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and are depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs) with arc affinity. In addition, combined with the εHf(t) values of −2.4 to +2.4 with two-stage model ages ranging from 1409 Ma to 1027 Ma, and the εNd(t) values from −3.73 to −2.95, it is suggested that the primary magma of these granitoids was derived from the partial melting of the Late Meso–Proterozoic mafic lower crust. These findings, combined with spatio-temporal distributions of regional magmatism, reveal that the Late Permian and Early Triassic granitoids formed in a continental magmatic arc setting related to the northward subduction of the Palaeo-Tethys Ocean plate beneath the EKOB-Qaidam terrane. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Mafic dyke swarm is widely developed in Proterozoic continental lithosphere. The Gangou diabase dyke from the Xixia area, intruded into the Douling complex of the South Qinling belt, yields zircon UPb age of 731 Ma. It has low SiO2 content (49.02 wt.%-49.37 wt.%) and Mg# (34.0–37.7) and shows characteristics of subalkaline tholeiite series. They show high ΣREE (155.5×10 6–184.7×106), weak negative Eu anomaly (SEu=0.88-0.93), slight depletion of Nb and Ta, and enrichment of LILE. Their major and trace element, Sr-Nd-Pb isotope and clinopyroxene compositions indicate that it originated from the partial melting of the asthenospheric mantle within-plate extension setting and was slightly contaminated by crust compositions. The similarities of formation age, petrogenesis, source characteristic and tectonic setting for Gangou diabase with mafic dykes in Wudang Block and mafic volcanic rocks in Yaolinghe Group indicate that the South Qinling belt underwent strong continental extension in Neoproterozoic during 796–685 Ma most likely correspondence to the breaking-up of the Rodinia supercontinent. [ABSTRACT FROM AUTHOR]

Detailed geochronological, geochemical, and Sr-Nd-Hf isotopic data are presented for early Paleozoic volcanic rocks in the Karadaban area from the northern Altyn region, NW China, with the aim to constrain their petrogenesis and tectonic implications. The Karadaban volcanic rocks show a bimodal distribution in composition, with rhyolite and basalt. The LA-ICP-MS zircon U-Pb age indicates that the volcanic rocks were erupted at 512 Ma. The mafic rocks are calc-alkaline, enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE; Ba and U) and depleted in high-field strength elements (HFSE; Nb and Ta). These features together with their depleted isotopic signature (initial 87Sr/86Sr=0.70413–0.70817, εNdt=2.7 to 3.7) suggest that they were likely derived from a depleted mantle source but mixed with crustal components while upwelling. The felsic rocks show an A-type affinity, with high alkalis and Rb/Sr and Ga/Al ratios; enriched in LILE (e.g., Rb, K, Th, U, and REE) and depleted in Ba, Sr, Nb, P, and Ti; and with fractionated REE patterns with strong negative Eu anomalies. The combination of the decoupling of εNdt values (−2.5 to −6.3) and εHft values (+5.5 to +14.7) in the setting of subduction indicates that the felsic rocks were generated by partial melting of the juvenile crustal as a result of magma upwelling. The geochemical and Sr-Nd-Hf isotopic characteristics, coupled with regional geology, indicate that the formation of the Karadaban bimodal volcanic rocks involves an extensional regime associated with a subduction-related environment. The rifting of the back arc in response to the retreat of the subducting northern Altyn oceanic lithosphere may account for the Karadaban bimodal volcanic rocks. [ABSTRACT FROM AUTHOR]