Geochronology,geochemistry and tectonic setting of Late Triassic diabase in buried hills of Qiongdongnan Basin
The buried hills containing Mesozoic igneous rocks in the Qiongdongnan Basin are a major site for offshore oil and gas exploration.However,owing to a lack of systematic chronology and geochemical research,the petrogenesis and tectonic setting of the basement rocks remain unclear,hindering further exploration of oil and gas reservoirs in these buried hills.Here,we comprehensively investigate the petrology,zircon geochronology,whole-rock geochemistry,and zircon Lu-Hf isotopes of diabase collected by drilling in the Qiongdongnan Basin to determine its petrogenesis and tectonic setting.The results of LA-ICP-MS zircon U-Pb geochronology reveals a crystallization age of(236±3)Ma for the diabase,indicating that it formation during the Late Triassic.The diabases have low contents of SiO2(47.96％～49.97％)and Al2O3(13.16％～13.68％),but are enriched in MgO(6.02％～7.49％)and Mg#(58～61).The sampled rocks exhibit right-sloping rare earth elements pattern and positive Eu anomalies,and are enrich in large ion lithophile elements and depletion in high field strength elements.They are also enrich in zircon Hf isotopes(eHf(t)=-9.08～—4.70).The results of petrogenesis analysis indicates that the diabases had originated from the melting of enriched mantle which was metasomatized by early subducted sediments-derived aqueous melts.The results of this study reveals that diabases in the Qiongdongnan Basin formed in a post-collision extension setting,and are products of the Paleo-Tethyan orogeny.
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