Petrological evidence of Mesozoic tectonic extension in the coastal area of SE China:The spatial-temporal distribution and geochemical constraints on the mafic rocks from Hainan,Guangdong,Fujian and Zhejiang Provinces,South China

This paper summarizes the spatial and temporal distribution and geochemical characteristics of Mesozoic mafic rocks of Hainan,Guangdong,Fujian,and Zhejiang Provinces,South China,and analyzes the regional tectonic environment and geodynamic settings.Reliable isotopic age dates indicate that Mesozoic mafic rocks in above-mentioned 4 provinces formed in six episodes during 245~230,180~175,165~142,130~115,110~101,95~85 Ma in Early Mesozoic and Late Mesozoic.The Early Mesozoic Indosinian mafic rocks(245~230 Ma,T2)occur in Hainan Island,and coexist with A-type granite and alkaline syenite.They formed in the late-collisional extensional environment.Of the Late Mesozoic mafic rocks(180~90 Ma,J2-K2),the middle-Jurassic ones with age of 180~175 Ma occurring in Nouth-western Fujian and Northern Guangdong,are associated with the tholeiite-rhyolite/gabbro-A-type granite bimodal magmatic assemblages in Hunan,South Jiangxi,and interpreted to be of rift origin.The late-Jurassic(160~142 Ma)mafic rocks mainly occured as small plutons in Northern Guangdong and Hainan Island,are also associated with A-type granite.The Cretaceous mafic rocks widely occured in the coastal region of Fujian,Zhejiang,and Hainan Provinces.The Early Cretaceous(130~115 and 110~101 Ma)mafic rocks are always mixed/mingled with high-K calc-alkaline granitic rocks,forming gabbro/basalt-granite/rhyolite composite igneous complexes.The late Cretaceous mafic rocks(95~85 Ma)mainly occured as dyke swarms,and are also associated with A-type granite.The Late Mesozoic mafic rocks formed in extension environment in paleo-Pacific tectonic regime.The Mesozoic mafic rocks were generated in response to multi-lithospheric extension events.They are petrological indictors of Mesozoic tectonic extension.