非保守元素在苏鲁超高压榴辉岩退变质作用中有限迁移和近原地重新分布

中国大陆科学钻探工程主孔揭露的基性岩石包括新鲜榴辉岩和角闪岩.角闪岩是榴辉岩在折返过程中不同程度退变质作用的产物.全岩主量和痕量元素地球化学数据表明它们不仅在高场强元素(Ti,Zr,Nb,Ta),而且在高度活动元素(Rb,Cs,Sr,Ba)上化学特征相似.尽管从榴辉岩向角闪岩的退变质作用需要流体的参与,上述地球化学特征表明在榴辉岩快速折返过程中,流体仅仅有限地存在,在流体中高度活动的碱性元素仅作有限迁移和近乎原地重新分布.流体可能以高度局域化的管道流形式出现,是导致榴辉岩退变质作用和剪切变形高度局域化的主要因素.

Limited migration and nearly in-situ redistribution of non-conservative elements in retrograde Sulu ultrahigh pressure eclogites

Mafic rocks from the Chinese Continental Scientific Drilling(CCSD)project consist of fresh eclogites as well as amphibolites.These amphibolites were resulted from various degrees of retrograde metamorphic reactions of fresh eclogites during their en route to the surface.Bulk major and trace element data show that they have similar geochemistry in Rb,Cs,St,and Ba,even though these elements are extremely mobile in the presence of aqueous fluids.Such fluids were essential to retrograde reactions that led to the transformation of fresh eclogites into amphibolites.The nearly identical geochemical nature in these non-conservative elements between these mafic rocks demonstrates that(1)limited and restricted fluids during the exhumation of UHP eclogites in the Sulu UHP metamorphic belt;and(2)nearly in-situ redistribution of highly mobile elements.This conclusion is also in good agreement with those reached from studies on the stable isotope geochemistry,fluid inclusion,and structure of Sulu UHP rocks.