新疆达拉布特蛇绿混杂岩中辉长岩岩石学、微量元素地球化学和锆石U-Pb年代学研究

Petrology,geochemistry and zircon U-Pb chronology of gabbro in Darbut ophiolitic mélange,Xinjiang

新疆西准噶尔地区达拉布特蛇绿混杂岩带中的辉长岩、辉长玢岩、角闪辉长岩呈不规则块体分布于蛇纹石化的地幔岩(尖晶石蛇纹岩)中。锆石SHRIMP定年显示角闪辉长岩形成于426±6Ma(MSWD=0.87),表明达拉布特所代表的古洋盆在中志留世就已存在。岩相学和微量元素地球化学研究表明,辉长岩、辉长玢岩、角闪辉长岩均来源于富Cr的地幔源区,确认3类岩石为同源岩浆演化的产物。选取达拉布特尖晶石二辉橄榄岩为源区所做的模拟显示:尖晶石二辉橄榄岩发生15%的部分熔融后的残余体形成了方辉橄榄岩,熔体通过分离结晶形成辉长岩,剩余熔体结晶形成辉长玢岩和角闪辉长岩。

Gabbro,gabbroporphyrite and hornblende gabbro,occurring in spinel serpentinite as irregular blocks in the Darbut ophiolitic mélange,West Junngar （North Xinjiang,NW China）,are studied in this paper.The hornblende gabbro was dated to be 426±6Ma （MSWD=0.87） by zircon SHRIMP.This indicates the Darbut Paleo-Ocean existed at Middle Silurian.Petrography and trace element geochemistry of the whole rocks and minerals suggest that gabbro,gabbroporphyrite and hornblende gabbro were derived from Cr-enriched mantle source,and these rocks were formed in different stages of magma evolution.Based on the calculation using Darbut spinel-lherzolite as mantle source,gabbro was formed by the melt fractional crystallization,while gabbroporphyrite and hornblende gabbro were formed via crystallization of the remnant melts.