徐州—宿州地区中生代埃达克质岩石岩浆起源深度的限定——深源捕掳体温度—压力条件证据

Determination of the Magma Depth of the Mesozoic Adakitic Rocks in the Xuzhou—Suzhou Area: Evidence from p-T Estimation of Deep-seated Xenoliths

徐州—宿州地区中生代侵入杂岩主要由二长闪长斑岩—闪长岩—二长岩组成 ,属钙碱性系列。岩石地球化学特征与典型埃达克岩极为相似 ,可称之为埃达克质岩石。该类侵入杂岩中含有较多的榴辉岩类和石榴片麻岩类深源岩石捕虏体及石榴子石残留晶。深源岩石捕虏体的岩相学研究表明 ,榴辉岩类捕虏体在遭受榴辉岩相变质之后 ,又经历了角闪岩相退变质 ,然后被寄主岩浆所捕获。矿物平衡温压计算结果表明 ,榴辉岩相变质的温度条件为 :6 0 8～ 76 6℃。角闪岩相退变质的温度、压力条件分别为 :5 2 3～ 80 0℃ ,0 .5 0～ 0 .98GPa。由此可以判定本区中生代侵入杂岩母岩浆的起源深度应在 2 0～ 34km之间 ,即岩浆起源于深部地壳。

The Mesozoic intrusive complex in the Xuzhou—Suzhou area is compos ed mainly of monzodioritic porphyry-diorite-monzonite, which belong to the calc-alkalin e rock series. Petrology and geochemistry of the Mesozoic intrusive complex are similar to those of typical adakites. Therefore, the Mesozoic intrusive complex might be called adakitic rock. Eclogite, garnet gneiss xenoliths and relic garne ts often occur in the Mesozoic intrusive complex. Petrography of the deep-seate d xenoliths indicates that the eclogite xenoliths were trapped in the host magma after they were subjected to eclogite facies metamorphism and amphibolite facie s retrogressive metamorphism. The results of mineral balance p-T estimation show that thep-T conditions of eclogite facies metamorphism and amphibolit e facies retrogressive metamorphism are 608~766℃ and 523~800℃,0 50~0 98 GPa, r espectively. It can be concluded that the parental magma of the Mesozoic intrusi ve complex could be as deep as 20~34 km in the crust, that is, the magma was der ived from the deep crust.