摘要
“后碰撞”作为大陆碰撞造山作用的特定过程,以其重要的构造演化标示性特征和强烈的爆发式金属成矿作用,受到人们的高度重视。但涉及后碰撞的一系列重要地质问题,如后碰撞期的构造特征与演化历程、岩浆发育序列和岩石构造组合、伸展成矿作用与矿床系列组合等,尚未得到清楚完好的识别、理解和阐示。文章系统研究和总结了青藏高原后碰撞造山与成矿作用特征,提出了后碰撞伸展成矿作用的构造控制模型。研究表明,现今处于后碰撞阶段的青藏高原,中新世以来主要经历了两阶段发育历史。后碰撞早期阶段主要发生下地壳流动与上地壳缩短(>18Ma):下地壳塑性流动并向南挤出,在藏南地区形成EW向延伸的藏南拆离系(STD)和高喜马拉雅,上地壳强烈逆冲推覆,在拉萨地体发育EW向展布的逆冲断裂系;晚期阶段主要发生地壳伸展与裂陷(<18Ma):垂直碰撞带的EW向伸展,形成一系列横切青藏高原的NS向正断层系统(≤13·5Ma)及其围陷的裂谷系和裂陷盆地。后碰撞岩浆作用以形成钾质_超钾质火山岩、钾质埃达克岩、钾质钙碱性花岗岩与淡色花岗岩为特征,集中发育于冈底斯构造_岩浆带和藏南特提斯喜马拉雅。淡色花岗岩与藏南拆离构造有关,其他钾质_超钾质岩浆活动则与EW向地壳伸展有关。青藏高原后碰撞成矿作用强烈而复杂,主要形成斑岩型Cu矿、热液脉型Sb_Au矿、矽卡岩型和热液脉型Ag_Pb_Zn矿以及现代热泉型Cs_Au矿等重要矿床类型。斑岩型Cu矿及矽卡岩型多金属矿床形成于后碰撞伸展环境,岩浆起源于加厚的镁铁质新生下地壳;热液脉型Sb_Au矿发育于藏南拆离带及变质核杂岩周围,系中新世地热田浅成低温热液活动产物。热液脉型Ag_Pb_Zn矿主要产于拉萨地体内部的逆冲构造带内,与地壳流体的迁移汇聚过程有关。青藏高原后碰撞成矿作用在上地壳层次受3大构
As a significant and late stage process in the coUisional orogeny characterized by a variety of geological features indicating tectonic evolution and large-scale, high-intense mineralization, post-coUision has aroused much interest among geologists. However, numerous geological issues, such as post-collisional structural features and tectonic evolution, magmatic sequences and tectonic-magmatic associations, and metallogensis and mineralization systems in the post-collisional settings, have not yet been fully understood. This paper studied and summarized the major features of post-coUisional orogeny and related metallogensis, and proposed a tectonic model for metallogensis in the post-collisional setting in Tibet. The available data indicate that there have been at least two stages of tectonic evolution since Miocene in the Tibetan plateau, which is now tectonically in a post-collisional stage. The low-crustal flow and upper-crustal shortening took place in an early post-collisional stage （ 〉 18 Ma）, which led to the southward extrusion of the low-crustal materials, producing the EW-tending south Tibetan detachment system （STD） and the High Himalayan block to the south, and the EW-striking thrust faulting systems and the thrust nappe structures along the Gangdese range in the Lhasa terrane, respectively. The crust extension and rifting occurring in the late post-collisional stage （ 〉 18 Ma） formed a series of NS-striking normal faults and associated rifting basins （≤13.5 Ma） across the Tibetan plateau. The post-collsional magmatism in Tibet is characterized by the mid-Miocene ultra-potassic and potassic volcanic rocks, adakitic intrusives, and calc-alkaline granites developed along the Gangdese batholiths, and the south Tibetan lecuogranites related to STD. Mineralization during the post-coUisional periods produced a variety of significant mid-Miocene deposits, including the porphyry Cu deposits and the associated skarn Ag-Pb-Zn deposits along the Gangdese batholiths, the epithermal Sb-Au dep
出处
《矿床地质》
CAS
CSCD
北大核心
2006年第6期629-651,共23页
Mineral Deposits
基金
国家基础研究计划"印度-亚洲大陆主碰撞带成矿作用"973项目(2002CB4126)
杰出青年项目的联合资助
关键词
地质学
后碰撞
钾质岩浆岩
成矿作用
深部过程
青藏高原
geology, post-coUision, potassic magmatic rocks, metallogeny, deep lithospheric process, Tibetan plateau
