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青藏高原碰撞造山带:Ⅱ.晚碰撞转换成矿作用   总被引:75,自引:31,他引:75  
许多古老造山带的碰撞造山过程,因从晚碰撞向后碰撞的转换,既不清楚,又难以界定,常被分为碰撞和后碰撞2个阶段。文章对青藏高原碰撞造山过程进行了分析,发现其具有明显的3段性,由此将碰撞造山过程分为主碰撞(65~41Ma)、晚碰撞(40~26Ma)和后碰撞(25~0Ma)3个阶段。其中,晚碰撞造山作用发生于印度与亚洲大陆的持续汇聚和SN向挤压背景之下,以陆内俯冲、大规模逆冲推覆、走滑断裂系统的发育为特征,导致了区域尺度的地壳缩短及藏东富碱斑岩和碳酸岩_正长岩、藏北钾质_超钾质火山岩的大规模产出。晚碰撞期成矿作用强烈发育,主要集中于高原东缘的构造转换带,成矿高峰期集中于(35±5)Ma。现已识别出4个重要的成矿事件:①与大规模走滑断裂系统有关的斑岩型Cu_Mo(Au)成矿事件,形成著名的玉龙斑岩铜矿带(40~36Ma);②与碳酸岩_正长岩杂岩有关的REE成矿事件,在二叠纪攀西古裂谷带内发育勉宁—德昌喜马拉雅期REE成矿带(41~27Ma);③与逆冲推覆构造系统有关的热卤水型Pb_Zn_Ag_Cu成矿事件,集中产出于兰坪盆地,形成大型Pb_Zn_Ag矿集区(40~30Ma);④与大规模剪切系统有关的剪切带型Au成矿事件,形成著名的哀牢山大型Au矿带(63~28Ma)。晚碰撞成矿作用主要发育于陆内转换造山环境,受大规模走滑_推覆_剪切作用控制,受控于统一的深部作用过程,与软流圈上涌导致的幔源或壳/幔混源岩浆活动密切相关。在综合研究基础上,初步建立了晚碰撞转换成矿模型。  相似文献   
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Plio-Pleistocene acidic volcanism of the northeastern part of the Armenian highland is related to a continental collision zone as a result of convergence between Eurasia and Arabia lithosphere plates. The development of volcanism is divided into three stages of 10–17, 4.5–7.5 and 0.1–2.8 Ma. A crustal origin model is proposed to explain the geochemical and petrogenetic aspects of the acidic volcanism formation. Spatially separated Ba-rich and Rb-rich geochemical types of rhyolites were revealed, indicating more evolved and primitive rhyolitic magma types, respectively. The variation interval of the primary 87Sr/86Sr ratio was found to be from 0.70438 to 0.70636. Age and lateral variation of geochemical and isotopic parameters were determined by differences of initial substrates and degrees of their partial melting. The mechanisms of rhyolitic magma evolution were the remelting of heterogeneous sialitic materials and low-pressure fractional crystallization in isolated magmatic chambers. These facts confirm the model of crustal anatexis origin of the eutectic melts. The eutectic rhyolitic magma was generated by an open-system melting in the presence of deep-horizon mobile K–Rb fluids, initiated by mantle resources.  相似文献   
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