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The Suizhou-Zaoyang Belt (SZB, southern Tongbaishan Orogen), which was least affected by Triassic HP-UHP metamorphism, preserves the Precambrian basement of the northern Yangtze Craton and exposes voluminous Neoproterozoic ultramafic-mafic sill swarms. These sills, together with the dyke/sill swarms of the Wudang Block, southern Qinling orogen, stretch up to ca. 800 km.
The sills are predominantly composed of two-pyroxene troctolites with minor gabbronorites. In this work, we acquired zircon U-Pb SHRIMP data and major, trace element and Sr-Nd isotopic analyses on whole-rocks (WR) and minerals, Pb isotopic analyses on plagioclase and O isotopic analyses on olivine in order to gain systemic geochronological and geochemical signatures to constrain their genesis, mantle source characteristics and emplacement ages. The results are as follows: (1) The emplacement ages of the two-pyroxene troctolites and the gabbronorites are 633±5 Ma and 619±5 Ma respectively, which is the first reported data regarding Ediacaran magmatism in the Yangtze craton. (2) Major and trace element characteristics suggest that the SZB sills show a tholeiitic continental affinity in composition and that the evolution of the magmas was controlled by olivine and plagioclase crystallization/accumulation, with little crustal contamination. (3) Nd and Sr isotopic compositions of whole-rocks, Pb isotopic compositions of plagioclase samples, O isotopic compositions of olivine samples, combining with trace element distribution patterns define an enriched subcontinental lithospheric mantle for the northern Yangtze Craton, similar to EM1.
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