摘要:
通过1∶5万马兰幅区域地质调查,首次在东泉戈壁地区发现了环斑花岗岩。东泉戈壁环斑花岗岩分布于南天山碰撞带中部,岩体以富含暗色细粒闪长质包体和具有特殊的环斑结构为特征。该花岗岩呈岩株状产出,岩石化学以较高的Al2O3(14.47%～15.44%)、K2O(3.93%～4.7%)和Na2O(3.4%～3.7%),富集轻稀土和大离子亲石元素,具有弱的δEu(平均为0.79)负异常等为特征,表现出与典型的板内奥长环斑花岗岩明显不同的地球化学特征。其形成时代为晚石炭世 (305±1 Ma),恰好是南天山洋盆向北俯冲碰撞造山末期阶段,据此认为东泉戈壁环斑花岗岩可能是一种造山带型环斑花岗岩,形成于板块碰撞后的抬升环境下的I型花岗岩。
Abstract:
Through 1∶50000 geological mapping of Malan,the authors discovered rapakivi granitein Dongquangobi area for the first time. Dongquangobi rapakivi granite is distributed in the middle section of South Tianshan collision belt,the rock is characterized by rich dark fine-grained dioritic inclusions and special rapakivi texture. This granite appears stock-like,its petrochemistry is characterized by higher Al2O3(14.47%～15.44%)、K2O(3.93%～4.7%)和Na2O(3.4%～3.7%), rich in LREE and LILE and with weak δEu (an average of 0.79) negative anomaly,showing that it has obviously different geochemical characteristics compared with typical wiborgite in the plate. Its formation age is the Late Carboniferous(305±1Ma),which exactly is the end stage ofSouth Tianshan ocean basin subducted northward collisional orogenesis,so it can be concluded that the Dongquangobi rapakivi granite may be a type of orogenic belt rapakivi granite,which is I-type granite formed in the uplifting environment after plate collision.
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