Abstract Amphibolites and metapelites exposed in the Zanhuang metamorphic complex situated in the south-middle section of the Trans-North China Orogen (TNCO) underwent upper-amphibolite-facies metamorphism and record clockwise P – T paths including retrograde isothermal decompression. High-resolution zircon U–Pb geochronological analyses indicate that the metamorphic peak occurred during ~ 1840–1860 Ma, which is in accordance with the ubiquitous metamorphic ages of ~ 1850 Ma retrieved by miscellaneous geochronologic methods throughout the metamorphic terranes of the northern TNCO, confirming that the south-middle section of the TNCO was involved in the amalgamation of the Eastern and Western Blocks of the North China Craton during the Palaeoproterozoic.
Eclogites have provided important constraints on the processes of plate subduction, collision and the overall tectonic evolution of orogens. The Gubaoquan eclogite is the only one identified in the Beishan Orogenic Belt, which constitutes the southernmost part of the Central Asian Orogenic Belt. The protolith age and tectonic setting of the eclogite and associated rock units remain ill-constrained. U–Pb dating of the eclogite indicates a Neoproterozoic age of 887 ± 7 Ma for its protolith age and an Ordovician age of 461 ± 15 Ma for the eclogite facies metamorphism. Detailed U-Pb ages of zircons, monazites, rutiles and apatites from the eclogite and country rocks suggest that they have experienced multiple metamorphic events in the Neoproterozoic and Paleozoic, which are inferred to correlate with retrograde metamorphism during the later exhumation. The protoliths of the Gubaoquan eclogite are of continental origin, and along with the extensive distribution of the Neoproterozoic arc-related rocks probably resulted from assembly of Rodinia. This work was financially supported by the National Natural Science Foundation of China (41730213 and 41890831), Hong Kong RGC GRF grants (17307918), HKU Internal Grants for Member of Chinese Academy of Sciences (102009906) and for Distinguished Research Achievement Award (102010100), Northwest University Excellent Doctoral Thesis Cultivation Program (YB2023003), and from the Australian Research Council (FL160100168).
Late Ordovician–Early Silurian intermediate igneous rocks have been detected in the Dunhuang Block, NW China. These igneous rocks help to constrain the tectonic evolution of the Dunhuang Block and the southern Central Asian Orogenic Belt in the early Paleozoic. We carried out zircon U–Pb dating, whole-rock geochemistry and zircon Hf isotope analyses for the early Paleozoic gneissic diorites from the Sanweishan and northern Huangshuihou areas in the Dunhuang Block. The zircon U–Pb geochronology shows that the emplacement ages of the gneissic dioritic rocks were c. 443–440 Ma. The dioritic rocks show varying SiO 2 (48.1–63.1 wt%) and MgO (1.87–3.52 wt%) contents, with high Mg# (46–52) values and negative Eu anomalies (Eu/Eu* = 0.62–0.94). Zircons in the gneissic diorites from the northern Huangshuigou and Sanweishan areas yield variable ε Hf ( t ) values of −4.4 to +10.4 and −8.6 to −6.2, respectively, coupled with low Rb/Sr (0.04–0.34), Rb/Ba (0.06–0.31) and Al 2 O 3 /(MgO + FeO T ) (0.72–1.47) ratios, indicating that they were predominately generated by disequilibrium melting of the juvenile crust and mixed with ancient crustal and minor mantle melts. In conjunction with previously published data, we propose that the early Paleozoic gneissic dioritic rocks were formed in a continental margin arc setting related to the southward subduction of the Palaeo-Asian Ocean. Our findings suggest that the Dunhuang Block was modified and reactivated by the Paleozoic orogenic events related to the evolution of the Palaeo-Asian Ocean, resulting in extensive Paleozoic magmatism–metamorphism over the whole Dunhuang area. Supplementary material: Analytical methods, U-Pb geochronological data, zircon trace element data, zircon Lu-Hf isotopic compositions, and geochemical data for analysed samples, and additional figures are available at https://doi.org/10.6084/m9.figshare.c.6174601
Reconstruction of periods and sources of continental arc magmatism provides critical insights for deciphering the thermal evolution and geodynamics of the continental lithosphere and unveiling subduction-related episodes of accretion and orogeny. The Dunhuang Block, located in the southern Central Asian Orogenic Belt, is built upon a Precambrian metamorphic crystalline basement that is intruded by numerous Paleozoic granitoids. In this paper, we present new zircon U-Pb ages, whole-rock geochemistry and Sr-Nd-Pb-Hf isotopes from the Hanxiakouzi and Shuangta granodiorite plutons outcropped in the central and northern Dunhuang Block, respectively. The U-Pb zircon dating indicate that the Hanxiakouzi and Shuangta granodiorites were emplaced at ca. 366–363 Ma, i.e., in the late Devonian. Geochemically, the Hanxiakouzi granodiorites are medium- to high-K, I-type granites possessing high Sr and Sr/Y, i.e., similar to adakites. The Hanxiakouzi granodiorites show negative εNd(t) values (−8.2 to −6.6), significant positive εHf(t) values (+0.7 to +8.1), and evolved Pb isotope features suggesting their derivation by melting of subducted terrigenous sediments, interaction of melts with mantle peridotite, and assimilation of ancient crust during magma ascent. The Shuangta granodiorites belong to high-K calc-alkaline I-type granites with medium Sr and low Sr/Y. The Shuangta granodiorites yield negative εNd(t) values (−2.9 to −3.1) and negative to positive zircon εHf(t) values (−1.8 to +3.6), suggesting their formation by partial melting of ancient mafic crust with addition of minor mantle-derived melt and subducted terrigenous sediments. In general, Hf-in-zircon isotopes characteristics of the late Paleozoic granitic rocks in the Dunhuang Block indicate that the southern Dunhuang area carries more ancient crust materials than the central and northern Dunhuang areas, indicating a lateral heterogeneity of the middle Paleozoic crust. Conclusively, the middle Paleozoic granitoids of the Dunhuang Block were emplaced at an active continental margin of the southern Paleo-Asian Ocean.
Eclogites provide important constraints on the processes of plate subduction, collision, and the overall tectonic evolution of orogens. The Gubaoquan eclogite is the only one identified in the Beishan Orogenic Belt, which constitutes the southernmost part of the Central Asian Orogenic Belt. U-Pb dating of the eclogite indicates a Neoproterozoic metamorphic age of 887 ± 7 Ma and an Ordovician age of 461 ± 15 Ma for the eclogite-facies metamorphism. Multi-proxy (zircon, monazite, rutile, and apatite) U/Th-Pb geochronology and trace element geochemistry reveal that they have experienced multiple tectonothermal events in the Neoproterozoic and Paleozoic. The protolith of the Gubaoquan eclogite is of continental origin, and along with the extensive distribution of the Neoproterozoic arc-related rocks probably formed near the periphery of Rodinia. Given the continental setting of the protolith of the Gubaoquan eclogite, we suggest that eclogite-facies metamorphism at ca. 461 Ma was due to subduction under the Shuangyingshan-Huaniushan arc, which is manifested as an arc-continental collision process.
The Altun mountains is a collisional orogenic belt strongly modified by strike-slip-faults,constituting the current northern tectonic boundary of Qinghai-Tibet Plateau.Its uplift is remarkable part of the Cenozoic uplift of Qinghai-Tibet Plateau.This contribution presents LA-ICP-MS U-Pb dating results of detrital zircons,together with heavy mineral assemblages from sandstones of the Xiaganchaigou Formation(E13) and lower segment of the Xiayoushashan Formation(N12) from northwest Qaidam Basin.Our results show that there are significant Indosinian and Caledonian age populations in all samples.However,significant differences in age spectrums exist between the samples from Xiaganchaigou Formation ages and those from Xiayoushashan Formation.Indosinian peaks in the age spectrums of Xiaganchaigou samples are stronger than those of Xiaganchaigou,whereas the Caledonian peak gradually become stronger in Xiayoushashan samples.The stability coefficients of heavy mineral assemblages decrease rapidly from the Xiaganchaigou Formation to the Xiayoushashan Formation,indicating that their debris changed from a high maturity into a low maturity level and that provenance area for the Xiaganchaigou Formation is much farther than that of the Xiayoushashan Formation.All these results imply that the Altun had experienced significant uplift from early Oligocene to early Pliocene.Although the subduction-collision orogenes is of Altun orogenic belt was completed in the early Paleozoic,the currently exposed Altun mountains was primarily formed by much late tectonic movement,i.e.uplifting associated with strike-slip faulting in Cenozoic.This work also confirms the U-Pb age spectrum of detrital zircon,associated with heavy mineral assemblage analysis,is an effective tool in research of stratum provenance and basin-mountain coupling.
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