琼西抱板群变质沉积岩地球化学研究

Geochemical characteristics of Baoban Group metasedimentary rocksin western Hainan, China

琼西中元古代抱板群变质沉积岩可分为白云母石英片岩组和石英二云母片岩组,其原岩为砂岩质泥质沉积岩夹火山物质。白云母石英片岩组和石英二云母片岩组在地球化学成分上的差异是原始沉积化学分异作用的结果。对主元素、微量元素(含稀土元素)及Sm-Nd同位素的综合研究表明,海南岛存在古元古代或更早的古老基底,抱板群变质沉积岩一部分来源于成熟度较低的古老地壳物质,另一部分来源于含地幔火山物质较多的初生地壳,或与研究区大规模造山运动、构造-岩浆活动所伴生的地幔物质加入有关。初步研究显示,琼西抱板群变质沉积岩可能是造山带岛弧和活动大陆边缘区(扩张弧后或弧间盆地)大地构造环境下的沉积产物。

The Baoban Group metasedimentary rocks are composed of muscovite quartz schist and quartz two mica schist. Their protoliths are sandy and argillaceous sediments intermingled with volcanic materials. The difference of geochemical compositions between the two schists is due to the chemical differentiation of the original sediments. The evidence of major and trace elements (including REE) as well as Sm Nd isotope of the rocks shows that there existed an early or earlier than Palaeoproterozic crust in western Hainan, and that the Baoban Group metasedimentary rocks partly originated from antiquity crust materials, and partly from new born crust with more mantle volcanic materials or was related with the largescale orogenic event and the tectonic magmatic activity following the addition of mantle materials. It is deposited under a tectonic setting of island arc and active continental margin (back arc or within arc spreading basin) during orogeny according to the primary research.