The Early Paleozoic Subashi ophiolite in the West Kunlun Orogenic Belt (northwestern Tibetan Plateau): Implication for the tectonic evolution of the Proto-Tethys
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<p>Figure S1: Discrimination diagrams for the granite dikes in the Monhhan ophiolite. Table S1: Major and trace element compositions of the Monhhan ophiolite and intruding granite. Table S2: LA-ICP-MS zircon U-Pb analytical data for the gabbro, intruding granite, and associated sandstone in the Monhhan ophiolite. Table S3: Lu–Hf data for zircons from the gabbro and intruding granite in the Monhhan ophiolite.</p>
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LA-ICPMS Zircon U-Pb Dating of Gabbro from the Bayingou Ophiolite in the Northern Tianshan Mountains
A LA-ICPMS zircon U-Pb dating of gabbro from the Bayingou ophiolite in the northern Tianshan Mountains indicates that the magmatic age of the gabbro is 342.6±2.2 Ma (2σ), which shows the ocean basin represented by the Bayingou ophiolite was formed in the Early Carboniferous. Combined with studies of other geologists, we suggest that the Bayingou ophiolite occurred in a transition tectonic setting from continental rifting to ocean rifting.
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The westward extension of the Shangdan suture (SDS) in the West Qinling is marked by the exposure of the Guanzizhen ophiolite in the Tianshui area. The age of this ophiolite is a key to understanding the tectonic framework and evolution of the Qinling orogenic belt. Based on a field investigation and geochemical analysis, some zircons were selected from gabbro of the ophiolite. The study of zircon CL images and U and Th contents indicate that the zircons used for dating are of magmatic origin. Zircon LA-ICP-MS dating of gabbro yields a U-Pb age of 471±1.4 Ma (MSWD=1.03,2σ), representing the time of crystallization of the gabbro. This age also constrains the age of the Guanzizhen ophiolite. According to this age, combined with the available regional geological and geochemical data, it is suggested that the time span for the existence of the Shangdan paleo-ocean between the North China block and Yangtze block continued till 470 MaBP at least. The determination of this age provides new evidence for an in-depth study and understanding of the tectonic framework and evolution of the Qinling orogenic belt.
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The eastern Mediterranean region within the Tethyan realm shows a high concentration of ophiolites with contrasting times of formation and emplacement along the belt: In the Balkans, the ophiolites formed during the early to medial Jurassic, and were obducted during the late Jurassic, whereas in Turkey and farther east, structurally intact Jurassic ophiolites are rare and Jurassic ophiolite obduction is unknown. Here we report a structurally intact, large ophiolite body of early Jurassic age from NE Turkey, the Refahiye ophiolite, located close to the suture zone between the Eastern Pontides and the Menderes-Taurus block. The Refahiye ophiolite forms an outcrop belt, 175 km long and 20 km wide, and is tectonically bound by the late Cretaceous ophiolitic mélange to the south, and by the North Anatolian Transform Fault against the Triassic low-grade metamorphic rocks to the north. Early to medial Jurassic very low- to low-grade metamorphic rocks, interpreted as intraoceanic subduction-accretion complexes, occur either beneath the ophiolite or as thrust slices within it. The ophiolite body within the studied section is made up of mantle peridotite (clinopyroxene-bearing harzburgite and minor dunite) crosscut by up to 20 cm thick veins of clinopyroxenite and later dikes/pods/stocks of gabbro ranging in size from 2 m to several hundreds of meters. The gabbro is represented by two distinct types: (i) cumulate gabbro, and (ii) non-cumulate gabbro with locally well-developed igneous foliation. Within the non-cumulate gabbro or enclosing peridotite, there are up to 5 m and 50 cm-thick veins of trondhjemite and pegmatitic gabbro, respectively. LA-ICP-MS dating on zircons from two trondhjemite samples yielded weighted mean ages of ∼184 ± 4 Ma and 178 ± 4 Ma (2σ), respectively, suggesting formation during early Jurassic time. Formation in a suprasubduction-zone forearc setting is inferred from (i) wide-ranging pyroxene and spinel compositions in the peridotites as documented in most suprasubduction-zone ophiolites, (ii) arc tholeiitic signature of the non-cumulate gabbros, and (iii) association of the ophiolite with the coeval subduction-accretion complexes. Emplacement of a trapped forearc ophiolite above its own subduction-accretion complex as a backstop is proposed based on a series of field relationships such as (i) intimate association of the unsubducted suprasubduction-zone ophiolite with coeval accretionary complexes, (ii) absence of unambiguous relationship to the southern Atlantic-type continental margin, and (iii) absence of any stratigraphic indications for the ophiolite obduction in the southern Atlantic-type continental margin during Jurassic time. This is a clear difference from the Jurassic ophiolites in the Balkans that were obducted over the Atlantic-type continental margin. This difference in mode of emplacement is most probably related to the greater distance of the intra-oceanic subduction zone to the Atlantic-type continental margin than it was in the Balkans, which is commensurate with the greater width of the Tethys in the east during Jurassic time.
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<p>Figure S1: Discrimination diagrams for the granite dikes in the Monhhan ophiolite. Table S1: Major and trace element compositions of the Monhhan ophiolite and intruding granite. Table S2: LA-ICP-MS zircon U-Pb analytical data for the gabbro, intruding granite, and associated sandstone in the Monhhan ophiolite. Table S3: Lu–Hf data for zircons from the gabbro and intruding granite in the Monhhan ophiolite.</p>
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