粤东北基底变质岩的组成和形成时代

Compositions and Formation History of the Basement Metamorphic Rocks in Northeastern Guangdong Province

基底变质岩的成分和形成时代对揭示地壳演化至关重要．利用锆石U-Pb-Hf研究和全岩成分分析,发现粤东北及邻区的许多基底变质岩是晚新元古代形成的沉积岩,它们具有高的SiO2、Rb、Zr、Y和过渡金属元素含量以及相对低的 Al2O3、CaO、Na2O、Sr、Nb含量．它们沉积于活动大陆边缘环境．盆地的形成与Rodinia超大陆裂解时的张性背景相关．粤东北龙川地区新元古代沉积岩主要由新太古代和中元古代碎屑物质组成,并含少量中太古代和新元古代物质,明显不同于闽西南和粤北地区新元占代沉积岩．粤东北这些变质岩没有受到加里东运动的强烈影响,而是在印支期发生变质-重熔作用．

The compositions and formation history of basement metamorphic rocks are the key to understanding crust evolution. Based on zircon U-Pb-Hf isotopic studies and the compositions of basement metamorphic rocks in northeastern Guangdong Province and southern Jiangxi Province, this paper indicates that the protoliths of these metamorphic rocks are sedimentary rocks deposited in the Late Neoproterozoic. They have high SiO2, Rb, Zr, Y and transitional metal concentrations and relatively low Al2O3, CaO, Na2O, Sr and Nb contents. They were deposited in an active continental margin basin near a volcanic arc. The basin formation was closely related with the extensional regime during the breakup of the supercontinent Rodinia. Neoproterozoic sediments in the Longchuan area of northeastern Guangdong Province are mainly composed of Neoarchaean and Mesoproterozoic clastic constituents with small amounts of Mesoarchaean and Neoproterozoic fragments, quite distinct from those in southwestern Fujian Province and northern Guangdong Province, showing different provenances. The basement metamorphic rocks in northeastern Guangdong Province were not influenced by the Early Paleozoic Caledonian movement, hut underwent strong Indosinian metamorphism and anatexis.