徐州-宿州地区榴辉岩类捕虏体中角闪石的结构、矿物化学及成因意义

AMPHIBOLES IN ECLOGITE XENOLITHS FROM XUZHOU-SUZHOU AREA,CENTRAL CHINA——TEXTURE,MINERAL CHEMISTRY AND THEIR TECTONIC IMPLICATIONS

徐州-宿州地区中生代闪长质岩石中存在丰富的榴辉岩类捕虏体。对该类捕虏体的岩相学和矿物化学研究表明,其中的角闪石具有4种产状:1)位于石榴石中的早期角闪石包裹体,为镁质普通角闪石;2)与榴辉岩中矿物平衡存在的原生角闪石,为韭闪石或韭闪石质普通角闪石;3)位于石榴石和单斜辉石周边的退变角闪石,主要为浅闪石质和阳起石质普通角闪石;4)沿单斜辉石解理分布的出溶角闪石,主要为浅闪石、浅闪石质角闪石和含亚铁韭闪石质普通角闪石。不同产状角闪石矿物化学成分的差异和温压估算结果显示,榴辉岩类捕虏体经历了一个顺时针的P-T演化轨迹,进而反映了中生代早期华北克拉通东部造山作用的存在。

Abundant eclogite xenoliths are found in Mesozoic dioritic rocks from Xuzhou-Suzhou area,central China. On the basis of petrography and mineral chemistry of the xenoliths,the amphiboles in them can be subdivided into four kinds of occurrences ,i. e. ,1） the early amphibole inclusions within garnet,being maganesio-hornblende; 2） the primary amphiboles equilibrated with omphacite and garnet in eclogite,belonging to pargasite and pargasitic hornblende; 3） the retrograde amphiboles around garnet and clinopyroxene, mainly being edenitic and actinolitic hornblendes; and 4） the exsolving amphiboles within clinopyroxenes, mainly being edenite, edenitic hornblende and/or ferroan pargasitic hornblende. Mineral chemistry and P-T estimation results of the amphiboles of different occurrences indicate that the eclogite xenoliths were subjected to a clockwise P-T evolutional path, implying that an orogenic event happened in the eastern part of the North China Craton in the early Mesozoic.