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Slab-derived fluids play a key role in mass transfer and elemental/isotopic exchanges in subduction zones. The exhumation of deeply subducted crust is achieved via a subduction channel where fluids from various sources are abundant, and thus the chemical/isotopic compositions of these rocks could have been modified by subduction-zone fluid–rock interactions. Here, we investigate the Mg isotopic systematics...
The paleo-Moho transition zone (MTZ) of the Kop ophiolite in NE Turkey is mainly composed of dunites, which are locally interlayered with chromitites and contain minor relics of harzburgites. Large Fe isotopic variations were observed for magnesiochromite (−0.14 to 0.06‰) and olivine (−0.12 to 0.14‰) from the MTZ rocks. In individual samples, magnesiochromite has lighter Fe isotopic compositions than...
The Kop ophiolite in NE Turkey is a forearc fragment of Neo-Tethys ocean, consisting mainly of a paleo-Moho transition zone (MTZ) and a harzburgitic upper mantle unit. Locally, the Kop MTZ contains cumulate dunites and high-Cr chromitites (Cr# up to ca. 79), which are cut by pyroxenites. Dunites and chromitites in the MTZ have REE concentrations that are 1–2 orders of magnitude lower than those of...
The petrogenesis of high Sr/Y-type magmas is still open to debate. Usually, such magmas could result from melting under high-pressure settings (>12kbar). In this paper, we gave an example that some high Sr/Y-type magmas could originate from melting of crustal materials at pressure of 10–12kbar. We carried out a study of petrogenesis for Devonian high Sr/Y granites from the Beidashan batholith (397–411Ma),...
Mafic intrusive rocks are widely exposed in the Motuo tectono-magmatic belt, southeast Lhasa terrane. LA–ICP-MS U–Pb zircon dating shows that they have magma crystallization ages of 69 and ca. 50Ma. These mafic intrusive rocks are characterized by variable SiO2 (44.60–57.60wt.%), high Al2O3 (17.19–20.86wt.%), and low MgO (1.85–5.38wt.%) with Mg# of 31–55. Their chemical composition is comparable with...
The Late Paleozoic tectonic evolution of the Lhasa terrane remains poorly understood due to the paucity of the Late Paleozoic magmatic rocks exposed at the surface. Detrital zircons in the sedimentary rocks can provide a record of magmatic rocks that have been eroded. Here we report detrital zircon U-Pb ages, trace-element and Hf isotopic data of metasedimentary rocks from the Nyingchi Complex in...
Late Cretaceous (~106–76Ma) adakite-like intrusive rocks in the middle-eastern Gangdese belt occur in an E–W trending belt paralleling the Indus–Yarlung suture, south Tibet. Their petrogenesis and geodynamic processes have been a subject of debate. We report here U–Pb zircon ages, geochemical and Sr–Nd–Hf isotopic data for adakite-like intrusive rocks as well as the normal arc rocks (gabbros and gabbroic...
The southwestern Tianshan orogenic belt hosts one of the Earth’s rare occurrences of ultrahigh-pressure (UHP) metamorphic rocks derived from subducted oceanic crust. To address its poorly constrained and controversial P-T-t evolution, for this study, three representative samples, two paragonite-epidote eclogites (H505-26 and H76-10) and one glaucophane-phengite eclogite (H711-1) are selected, and...
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