华南沿海地区中生代岩石圈伸展的岩石学制约:琼粤闽浙镁铁质岩时空分布与地球化学研究

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

系统总结了华南沿海琼、粤、闽、浙4省中生代镁铁质岩的时空分布与地球化学特征，分析讨论了华南中生代区域构造环境和地球动力学背景．区内主要发育6期镁铁质岩石，分别形成于早中生代和晚中生代，即245～230、180～175、165～142、130～115、110～101和95～85Ma．旱中生代印支期（245～230Ma）镁铁质岩，出露在海南岛，伴有A型花岗岩和碱性正长岩产出，形成于印支运动后的伸展环境．在晚中生代（180～90Ma）的镁铁质岩中，中侏罗世（i80～175Ma）的镁铁质岩石集中出露在粤北、闽西南一带，与湖南、赣南拉斑玄武岩／辉长岩一流纹岩／正长岩和A型花岗岩一起构成双峰式火成岩组合，具有裂谷型火成岩特征．晚侏罗世（165～142Ma）镁铁质岩，主要有海南、广东一些小的辉长岩等，也与A型花岗岩、碱性正长岩等伴生．白垩纪的镁铁质岩广泛出露在福建、浙江和海南沿海地区．其中，早白垩世（130～115、110～101Ma）的镁铁质岩常与高钾钙碱性花岗质岩混合，构成辉长岩／玄武岩一花岗岩／流纹岩等复合火成岩；晚白垩世（95～85Ma）的镁铁质岩，在华南沿海地区形成壮观的镁铁质岩墙群，并伴有A型花岗岩产出．晚中生代镁铁质岩形成于古太平洋构造域伸展环境．华南中生代镁铁质岩石的形成，对应于华南岩石圈多期伸展事件，是华南岩石圈伸展的重要岩石学标志．

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 2454230, 180-175, 165-142, 130-115, 110-101, 95-85 Ma in Early Mesozoic and Late Mesozoic. The Early Mesozoic Indosinian marie 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 marie 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 （1604142 Ma） mafic rocks mainly occured as small plutons in Northern Guangdong and Hainan Is- land, are also associated with A-type granite. The Cretaceous mafic rocks widely occured in the coastal region of Fu- jian, Zhejiang, and Hainau 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 re- gime. The Mesozoic mafic rocks were generated in response to multi-lithospheric extension events. They are petrological indictors of Mesozoic tectonic extension.