The rhyolites which are widely exposed to the northern margin of the East Kunlun orogenic belt were chosen as a research object to discern the post-orogenic tectonic evolution of the East Kunlun orogenic belt and reconstruct the post-collision orogenic processes of the Buqingshan- A’nyemaqen Ocean. We researched zircon U-Pb ages and geochemistry characteristics of the Late Triassic rhyolites in the eastern segment of the East Kunlun Orogenic Belt in the northern Tibetan Plateau. Zircon U-Pb dating yields coeval ages of 200.4 ± 1.4 Ma and 202.8 ± 1.2 Ma for the Keri rhyolites of the East Kunlun Orogenic Belt, indicating that the volcanic rocks were formed in the Late Triassic Rhaetian–Early Jurassic Hettangian. The Keri rhyolite is a product of the late magmatism of the Elashan Formation volcanic rocks. The rhyolites include rhyolitic brecciated tuff lavas and rhyolitic tuff lavas. The rhyolites are peraluminous and are high-K calc-alkaline, with high contents of SiO2, K2O, TFe2O3, and low P2O5 contents. The A/CNK ratios range from 0.97 to 1.09, indicating that the rhyolites are metaluminous to weakly peraluminous. The chondrite-normalized rare earth element (REE) distribution shows a significant negative Eu anomaly and low total REE concentrations. All samples are depleted in high field strength elements (HFSEs, e.g., Eu, Sr, Ti, and P), heavy rare earth elements (HREEs), and enriched in large ion lithophile elements (LILEs, e.g., Rb, Zr, Nd, Th, and U) and light rare earth elements (LREEs). The Keri rhyolite has the characteristics of A1-type magmatic rock, formed in an anorogenic environment after the closure of the Paleo-Tethys Ocean, and was the product of late magmatism in the Elashan Formation volcanic rocks.
Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder with strong genetic contributions. To provide a comprehensive resource for the genetic evidence of ASD, we have updated the Autism KnowledgeBase (AutismKB) to version 2.0. AutismKB 2.0 integrates multiscale genetic data on 1379 genes, 5420 copy number variations and structural variations, 11 669 single-nucleotide variations or small insertions/deletions (SNVs/indels) and 172 linkage regions. In particular, AutismKB 2.0 highlights 5669 de novo SNVs/indels due to their significant contribution to ASD genetics and includes 789 mosaic variants due to their recently discovered contributions to ASD pathogenesis. The genes and variants are annotated extensively with genetic evidence and clinical evidence. To help users fully understand the functional consequences of SNVs and small indels, we provided comprehensive predictions of pathogenicity with iFish, SIFT, Polyphen etc. To improve user experiences, the new version incorporates multiple query methods, including simple query, advanced query and batch query. It also functionally integrates two analytical tools to help users perform downstream analyses, including a gene ranking tool and an enrichment analysis tool, KOBAS. AutismKB 2.0 is freely available and can be a valuable resource for researchers.
The subduction process of the Paleo-Tethyan Ocean is still under controversy. We report zircon U-Pb ages and geochemistry (major and trace elements, and Hf isotopic compositions) for the Xiangjiananshan granitic plutons in the eastern segment of the East Kunlun Orogenic Belt, northern Tibetan Plateau, to constrain the subduction-related granitoids in its petrogenesis and to reconstruct the subduction prosess of the Buqingshan-A'nyemaqing Ocean. Zircon U-Pb dating yields coeval ages of 246.6 ± 4.1 Ma for granodiorite and 246.4 ± 3.9 Ma for biotite monzogranite of the Xiangjiananshan granitoid pluton. The granitoids include granodiorites, biotite monzogranites, and pseudo-porphyritic monzogranites. The granitoids have high contents of SiO2 (66.60–73.19 wt.%) and Al2O3 (13.28–16.38 wt.%), consistent with the high-K calc-alkaline series. The A/CNK ratios range from 0.98 to 1.02, indicating that the granodiorite is metaluminous and weakly peraluminous. The mafic microgranular enclaves (MMEs) in granodiorite and biotite monzogranite have a restricted SiO2 range (57.24–60.03 wt.%), and have higher Fe2O3T, and MgO contents than the host granitoids, as well as higher total rare earth element (REE) concentrations. All samples are depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti and P) and heavy rare earth elements (HREEs), and are enriched in large ion lithophile elements (LILEs; e.g., Rb, Nd and La) and light rare earth elements (LREEs). Zircons from the pseudoporphyritic monzogranite yield two-stage model ages of 1137.32 to 1588.12 Ma, together with εHf(t) values from −5.01 to +2.11. These results indicate that the parental magma of pseudoporphyritic monzogranite was generated by partial melting of Paleoproterozoic to Mesoproterozoic rocks of the lower crust with contamination of ancient crustal material. Field and petrological observations, together with elemental and Hf isotopic data, indicate that the Xiangjiananshan granitic plutons was formed by magma mixing of mafic and felsic magmas. The felsic magma was derived from partial melting of the lower crust, while the mafic magma was derived from partial melting of an enriched lithospheric mantle metasomatized by slab-derived fluid due to the subduction of the Buqingshan-A'nyemaqing Ocean. Therefore, we propose that the northward subduction of the Buqingshan-A'nyemaqing ocean north to the Bayan Hara block under East Kunlun initiated in the Middle Permian (ca. 270 Ma), yielding calcium metaluminous arc magmatic rocks with I-type granite characteristics at East Kunlun, including the XG pluton in this study. Subsequently, the Buqingshan-A'nyemaqing ocean closed and resulted in collision of the Bayan Hara and East Kunlun blocks from 240 to 230 Ma.
The Cida complex is situated in the Panxi region and is predominantly composed of mafic-ultramafic and syenitic rock units; minor amounts of intermediate rocks occupy the contact zone between the two major rock types. The intermediate unit is mineralogically heterogeneous and typically exhibits a mottled structure. Laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) U–Pb zircon dating shows that the mafic-ultramafic rocks and syenitic rocks formed almost coevally (243 ± 0.77 Ma and 240.5 ± 0.76 Ma, respectively). These ages may represent the end phase of the Emeishan large igneous province (ELIP) magmatism. Most of these three rock types possess alkaline and metaluminous affinities. The mafic-ultramafic, syenitic, and intermediate units have K2O + Na2O contents of 1.85–5.16, 6.55–10.46, and 9.55–11.54 wt.%, and SiO2 contents of 40.06–46.70, 61.74–68.54, and 51.57–54.13 wt.%, respectively. The mafic-ultramafic unit displays ocean-island basalt (OIB)-like primitive-mantle-normalized incompatible element patterns, coupled with low initial 87Sr/86Sr ratios (0.7048–0.7064), positive ϵNd(t) (0.32–2.23), and zircon ϵHf(t) (4.53–14.17) values, consistent with a mafic plume-head origin, whereas one exceptional sample with negative ϵNd(t) (–0.22) can be interpreted as due to the involvement of considerable amounts of enriched subcontinental lithospheric mantle. The relatively low (La/Yb) N ratios (3.40–7.69) reflect a spinel-facies lherzolite source. The syenitic unit is characterized by enrichment in large ion lithophile elements (e.g. Rb, K, Pb) and light rare earth elements (LREEs), relative to high field strength elements (e.g. Nb, Ta, P, Ti) and heavy rare earth elements (HREEs), respectively. These features, together with their metaluminous affinities, low SiO2 contents, lower initial 87Sr/86Sr ratios (0.7043), positive ϵNd(t) (0.18), and zircon ϵHf(t) (2.63–10.09) values as well as modelling of REEs, can be plausibly explained by crustal partial melting of juvenile basic materials beneath the Yangtze Block. In contrast, the field, petrographic observations, and geochemical signatures (e.g. the linear correlations between FeO* and MgO, K/Ba and Rb/Ba ratios) suggest that the intermediate unit may have resulted from magma mixing between the syenitic and basaltic magmas that in turn had evolved from a parental mafic-ultramafic liquid. Thus, the formation of the Cida complex can be attributed to the plume–lithosphere interaction plus partial melting of juvenile basic lower crust in response to heating of underplated plume-derived basaltic magma.
<p>The Central Asian Orogenic Belt (CAOB), also known as the Altaids, is one of the world's largest accretionary orogen and it is estimated that ca. 50% of the present crust in Central Asia is juvenile. However, some researchers argued that the amount of continental growth in the CAOB was overestimated. One evidence is that many intra-arc sediments and accretionary wedges in the CAOB contain heterogeneous sources (large proportion of detritus from basement rocks), and no examples from the CAOB where the sediment mainly derived from erosion of juvenile crust has been reported. Here, we conducted geochemistry and Nd isotope study on the turbidites from the North Tianshan Accretionary Complex (NTAC) in the Chinese West Tianshan orogen, which might be an good example of sediment derived from juvenile materials. The turbiditess in the NTAC are mainly composed of fine-grained sandstone, siltstone and argillaceous siliceous rocks. In the southern part near the North Tianshan Fault, the turbidites were deformed and metamorphosed into slate. Geochemically, all the collected rocks (sandstoen/siltstone and slates) have relatively low CIA (Chemical Index of Alteration) values (35 to 63) and PIA (plagioclase index of alteration ) values (34 to 68), indicating that their source rocks experienced relatively weak weathering before erosion and deposition. Both the sandstone/siltstone and slate samples display high ICV (Index of Compositional Variability) values of 0.89 to 1.50 and 0.89 to 0.93, higher than the PAAS, suggesting a relatively immature source. Based on geochemical data, it is suggested that the sandstone/siltstone were mainly derived from intermediate and felsic igneous rocks, while the slates were mainly derived from felsic igneous rocks, and their source rocks were most likely formed in oceanic/continental arc settings. Most of the samples from the NTAC display high positive &#949;<sub>Nd</sub>(t) values (+5.5 to +7.9) with only one exception of +0.8, and the Nd model ages (cluster between 672 Ma and 522 Ma, with one exception of 1.1 Ga) are only slightly older than their depositional age (Carboniferous). Our previous study has revealed that the detrital zircons from the turbidites display unimodal age patterns with peaks at 320 to 310 Ma, and have high positive &#949;<sub>Hf</sub>(t) values (+2.9 to +15.8, mostly greater than +10). These results indicate that the turbidites in the NTAC were mainly derived from intermediate to felsic igneous rocks with juvenile arc signature. The northern Chinese West Tianshan is a typical site with significant Phanerozoic continental growth, and the mechanism needs further study.</p>
The formation of highly evolved, dacitic magmas has been attributed to various processes, including crystal fractionation, partial melting of overlying crust, and/or assimilation of crustal material into an evolving magma chamber. These processes are undoubtedly primary processes involved in the formation of dacites, but they may not be the only mechanism involved in the formation of high-silica dacites. For instance, mafic magma replenishment has been proposed as an additional mechanism but has not been assessed, and thus, its role has not been well-constrained. The Daliuchong volcano is the result of one of the largest eruptive events within the Tengchong Volcanic Field (TVF) in southwest China during the Early-Middle Pleistocene. Here, we conducted detailed mineral textures, mineral chemistry, and geochemical studies on Daliuchong pyroclastic rocks to explore the pre-eruptive storage conditions and evolution processes of the magma. The Daliuchong pyroclastic rocks are dacitic in composition. The samples show porphyritic textures characterized by phenocrysts of plagioclase, amphibole, clinopyroxene, orthopyroxene, and Fe-Ti oxides. Additionally, two distinct types of glomerocryst are identified: a gabbroic glomerocryst containing plagioclase + clinopyroxene + orthopyroxene ± Fe-Ti oxides assemblage and a dioritic glomerocryst containing plagioclase + amphibole ± pyroxene ± Fe-Ti oxides assemblage. Both phenocryst and glomerocryst show rich micro-textures. The Daliuchong dacite exhibits bulk compositional heterogeneity. Analysis of bulk-rock data suggests that this heterogeneity may arise from both the differentiation of the dacite itself and the injection of mafic magma. The compositional similarity between the Daliuchong dacite and experimentally produced partial melts of metamorphic basalt supports that the Daliuchong dacite was predominantly formed through the partial melting of the mafic lower crust. Thermobarometry estimation indicates that clinopyroxenes with high Mg# crystallized at 560–870 MPa, whereas amphibole and clinopyroxenes with low Mg# crystallized at 185–300 MPa. Based on the observed phase relations and the calculated crystallization conditions, we propose that during the differentiation of the Daliuchong dacite, heterogeneous dacitic magma formed by partial melting accumulated in a deep magma reservoir (21–32 km) before subsequently ascending toward shallower depths. Crystallization of plagioclase, amphibole, Fe-Ti oxides, and small amounts of pyroxene and apatite occurred at a shallower depth (7–10 km). The presence of coarse-sieve texture, fine-sieve texture, and oscillatory zoning with high amplitude in plagioclase suggests intermittent injection of mafic magma into the shallow magma reservoir, with the eruption of dacitic magma occurring after the final mafic magma replenishment. The petrological evidence above advocates that primitive magma replenishment could have been involved in the formation and triggered the eruption of dacite in the Daliuchong volcano.
Abstract High-pressure (HP) granulites exposed within the eastern Himalayan syntaxis are dominantly felsic rocks. They were displaced southward over the Pei sequence by the NW-dipping Upper Thrust. Twenty-three SHRIMP U/Pb analyses of zircons from one HP sample demonstrate that this rock was derived from Proterozoic sedimentary rocks that underwent high-temperature metamorphism or partial melting to form granitoids or paragneisses at about 500 Ma. During Oligocene collision between India and Asia, these crystalline rocks were buried beneath south Tibet, recrystallizing to form HP felsic granulites at 30-33 Ma, with a metamorphic retrogression at about 23 Ma. Evidently the south Tibetan crust was thickened, and then uplifted at this time.
Abstract Sediments within accretionary complexes, preserving key information on crust growth history of Central Asian Orogenic Belt, did not get enough attention previously. Here, we conduct comprehensive geochemical study on the turbidites from the North Tianshan Accretionary Complex (NTAC) in the Chinese West Tianshan orogen, which is a good example of sediments derived from juvenile materials. The turbidites, composed of sandstone, siltstone, and argillaceous siliceous rocks, are mainly Carboniferous. All the investigated samples have relatively low Chemical Index of Alteration values (35–63) and Plagioclase Index of Alteration values (34–68), indicating relatively weak weathering before erosion and deposition. The sandstone and siltstone, and slate samples display high Index of Compositional Variability values of 0.89–1.50 and 0.89–0.93, suggesting a relatively immature source. The sandstones and siltstones were mainly derived from intermediate igneous rocks, and the slates from felsic igneous rocks, formed in oceanic/continental arc settings. The investigated samples roughly display high positive εNd(t) values (mainly at +5.5 to +7.9, except one spot at +0.8), with corresponding Nd model ages at 672 Ma–522 Ma (except one at ∼1.1 Ga). Combined with the previous studies, we suggest that the turbidites in the NTAC were mainly derived from intermediate to felsic igneous rocks with juvenile arc signature, and thus the northern Chinese West Tianshan is a typical site with significant Phanerozoic crust growth.
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