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During the Late Carboniferous to Early Permian, a rift was formed by post‐collisional extension after ocean closure or an island arc‐related basin formed by Paleo‐Asian Ocean (PAO) subduction in the Xi Ujimqin area. Nevertheless, the closure time of the PAO is still under debate. Thus, to identify the origin of the PAO, the geochemistry and U‐Pb age of zircons were analyzed for the extra‐large deep marine, polymict clastic boulders and sandstones in the Shoushangou Formation within the basin. The analyses revealed magmatic activity and tectonic evolution. The conglomerates include megaclasts of granite (298.8 ± 9.1 Ma) and granodiorite porphyry (297.1 ± 3.1 Ma), which were deposited by muddy debris flow. Results of this study demonstrated that the boulders of granitoids have the geochemistry of typical I‐type granite, characterized by low Zr + Nb + Ce + Y and low Ga/Al values. The granitoid boulders were formed in island arc setting, indicating the presence of arc magmatism in the area that is composed of the Late Carboniferous to Early Permian subduction‐related granitoid in southern Xi Ujimqin. Multiple diagrams for determining sedimentary provenance using major and trace elements indicate that Shoushangou sediments originated from continental island arc‐related felsic rocks. Detrital zircon U‐Pb age cluster of 330‐280 Ma was obtained, indicating input from granite, ophiolite, Xilin Gol complex, and Carboniferous sources to the south. The basin was geographically developed behind the arc during the Early Permian period because the outcropped intrusive rocks in the Late Carboniferous to Early Permian form a volcanic arc. The comprehensive analyses of source areas suggest that Shoushangou sediments developed in a backarc basin in response to the northward subduction of the PAO. The backarc basin and intrusive rocks, in addition to previously published Late Carboniferous to Early Permian magmatic rocks of arc unit in Xilin Gol, confirm the presence of an Early Permian trench‐arc‐basin system in the region, represented by the Baolidao arc and Xi Ujimqin backarc basin. This study highlights the importance and potential of combined geochemical and geochronological studies of conglomerates and sandstone for reconstructing the geodynamic setting of a basin. [ABSTRACT FROM AUTHOR]

The Early–Middle Devonian Shugouzi Formation in the Quruqtagh block consists mainly of clastic rocks. However, their provenance has been scarcely studied since it was named. Geochemistry of clastic rocks was commonly used to interpret the provenance. Detrital heavy mineral analyses help frame the U‐Pb age from zircon grains, integrated with geochemical data from detrital tourmaline and spinels. These techniques were used to characterize components of the sediment flux and define erosion areas in the Qurugtagh block, further providing evidence about the tectonic evolution of the South Tianshan and Tarim plate. The maximum depositional age constrained by detrital zircon dating was Early–Middle Devonian. Multiple diagrams for sedimentary provenance using major and trace elements indicate that continental island arc‐related felsic rocks were the major source rocks for the Shugouzi Formation. Detrital tourmalines are dravite and schorl. The results of detrital tourmaline electron probe microanalysis (EPMA) show that the source rocks are mainly metasedimentary rocks and granitoids. The detrital chromian spinels within the sediments are characterized by high chroumium (Cr#) and varying magnesium (Mg#). The discrimination plots reveal that these spinels were sourced from island arc magmatic rocks. The laser ablation inductively‐coupled plasma mass spectrometry (LA‐ICP‐MS) U‐Pb chronology of detrital zircons suggests that the sediments were derived mainly from 414–491 Ma and 744–996 Ma magmatic rocks. Paleocurrent restoration, sandstone geochemistry, EPMA, and detrital zircon geochronology indicate that the source rocks were predominantly derived from Late Ordovician and Devonian magmatic rocks and subordinately from recycled Neoproterozoic magmatic rocks. Comprehensive analyses of the source areas suggest that a remnant arc still existed in the Early Devonian and the Shugouzi Formation was deposited in a passive continental margin. [ABSTRACT FROM AUTHOR]

As one of the major subduction-accretionary systems in the southeastern Central Asian Orogenic Belt, the Bainaimiao arc presents a valuable opportunity for investigating the subduction–accretion process of accretionary orogens. It is located adjacent to the northern margin of the North China Craton and developed arc-related deposits during the Silurian–Devonian period. In this paper, we employed heavy mineral geochemistry and U–Pb ages of zircon and rutile, to determine the provenance of the Silurian–Devonian deposits and reconstruct the paleogeography of the source area. The stratigraphic units involved include the Xuniwusu Formation of Early Silurian and the Xibiehe Formation of Early Devonian. Both the Xuniwusu and Xibiehe formations exhibit heavy mineral assemblages dominated by zircons and tourmalines. Nevertheless, the Xibiehe Formation contains Cr-spinels and garnets which are absent in the Xuniwusu Formation. Geochemical analyses of the detrital Cr-spinels exhibit characteristics of a supra-subduction zone ophiolite. The garnets originated from middle- to high-grade metamorphic rocks, as well as mafic and felsic rocks. The tourmalines in both formations primarily indicate a metasedimentary rock source, with a small percentage of Li-poor granitoid species in the Xuniwusu Formation. The U–Pb age spectra of both detrital zircon and rutile in the Xuniwusu Formation show multiple peaks. The age spectra consist of Precambrian ages, indicative of a recycled origin, as well as Paleozoic ages, suggesting a magmatic origin. In contrast, the U–Pb age spectra of zircon and rutile in the Xibiehe Formation display a unimodal age peak at ca. 455 and 490 Ma, respectively. These differences suggest a provenance shift from the Xuniwusu to Xibiehe formations. The Xuniwusu Formation was sourced from the Bainaimiao arc itself, whereas the Xibiehe Formation has a mixed origin of the Bainaimiao arc and Ondor Sum accretionary complex. The provenance change correlates with the unconformity between the two formations, suggesting a forearc uplift event. In combination with the previous research on the Tulinkai ophiolite, it can be inferred that the forearc uplift was triggered by ridge subduction of the Paleo-Asian Ocean plate at ca. 450–430 Ma. This research provided a new perspective on the ridge subduction of the oceanic slab in fossil orogens. • The Xuniwusu Formation was derived from the Bainaimiao arc. • The Xibiehe Formation was sourced from the Bainaimiao arc and Ondor Sum complex. • A provenance shift between the two formations was identified. • The presence of Cr-spinels and garnets indicates a forearc uplift event. • The forearc uplift is related to ridge subduction of the Paleo-Asian Ocean plate. [ABSTRACT FROM AUTHOR]

The Langao area in South Qinling consists of a poorly dated sequence of volcano-sedimentary units (Taohekou Formation). This study focuses on volcanic edifice of Taohekou Formation. Detailed field mapping, section facies analysis, geochemistry, and Ar–Ar geochronology is presented here to develop a more accurate understanding of the tectonic evolution of the Qinling Orogen. Detailed field mapping and section facies analysis reveals the presence of a seamount volcanic edifice in western Xiaozhen area. Ar–Ar dating of alkaline basalts in the sequence indicates an Early Devonian magmatic age. Whole rock geochemistry of these alkaline basalts indicates that both potassic and sodic basalts were erupted respectively in the eastern and western areas. Both types of samples are typically characterized by high concentrations of TiO2, Nb, Ta, and Zr. Ocean-island basalt (OIB)-like rare earth element distribution patterns, trace element spider diagrams, and similar Sr and Nd isotopic compositions (i.e. relatively low Sr and moderate Nd isotopic ratios) likely indicate that the samples were comagmatic but have experienced varying degrees of fractional crystallization. In addition, the samples appear to have all originated from the asthenospheric mantle and undergone mantle metasomatism, ultimately resulting in an OIB-type provenance. Most importantly, in combination with its regional tectonic evolution, the Taohekou Formation is constrained to a seamount environment. This formation does not represent a plume but, rather, an extensional fracture zone related to subduction. Thus, this geologic interpretation generates pivotal evidence for accurately investigating the properties and temporal constraints of the Mianlue oceanic basin. [ABSTRACT FROM AUTHOR]

The Xuhe mafic rocks, located in Ziyang county of Shaanxi Province, are dominated by diabase-porphyrite, gabbro-diabase, diabase, and pyroxene diorite. Primitive mantle-normalized multi-element patterns show that, the Xuhe mafic rocks are enriched in large ion lithophile elements (LITE ), such as Ba and Pb, depleted in K and Sr for basic rocks, and are depleted in Sr, P and Ti for pyroxene diorite. Chondrite-normalized REE patterns display LREE enrichment (LaN/YbN = 9.34-13.99) and have normalized patterns for trace element and REE similar to that of typical OIB. Detailed SUMS zircon U-Pb dating yields emplacement ages of 438.4 ± 3.1 Ma for Xuhe mafic rocks. The relatively low MgO (basic rock: 3.11-7.21 wt%; pyroxene diorite: 0.89-1.21 wt% ) and Mg# (0.20-0.49) for Xuhe mafic rocks suggest that they were possibly originated from an extremely evolved magma. The rising parental mafic magmas underwent pyroxene and plagioclase fractionation. Crustal contamination of pyroxene diorite before emplacement occurred at a higher crustal level compared to other lithology in Xuhe mafic rocks. The degree of partial melt was low (5%-10%) and in garnet-spinel transition facies. Sr-Nd isotope of pyroxene diorite and enrichment mantle characteristics for Xuhe mafic rocks suggest that mafic rocks in the North Daba Mountains were derived from a mixture of HIMU, EMn and small amount of EMI components. Furthermore, this study discusses mantle geodynamic significance of Xuhe mafic rocks in the Silurian, which indicates subduction and uplift of magma caused back-arc extension. [ABSTRACT FROM AUTHOR]