岩石矿物学杂志2012，Vol.31Issue(5)：681-690,10.
西藏措勤尼雄矿田滚纠铁矿金云母矿物学特征及40Ar-39Ar年代学
Mineralogical characteristics and 40Ar-39Ar dating of phlogopite from the Gunjiu iron deposit in the Nixiong Ore Field, Coqen, Tibet
摘要
Abstract
The Nixiong ore field, located in the Longgeer-Gongbujiangda fault uplift zone, is an important part of Coqen-Shenzha iron and copper metallogenic belt. The Gunjiu iron deposit lies in the northwest of the Nixiong ore field. The ore bodies mainly occur in the contact zone, which lie between the intrusive granodiorite and mon-zogranite and the Permian Dibucuo Formation, with some also located in the interlayer fracture zone of Dibucuo Formation. The main metallic minerals include magnetite, hematite and maghemite, with small amounts of limonite and goethite, whereas the skarn minerals such as grossular, andratite, diopside, sahlite, ferrosalite, serpentine, phlogopite, actinolite, epidote and chlorite are developed in the Gunjiu iron deposit. Among these minerals the phlogopite is closely associated with magnetite. Electron microprobe analysis and 40Ar-39Ar dating of phlogopite were conducted in this paper. Electron microprobe analyses show that the phlogopite from the Gunjiu iron deposit is rich in magnesium but low in iron, with Mg/(Fe + Mg + Mn+ Ti) value being 0.90~ 0.94. The 40Ar-39Ar dating of phlogopite does not yield a plateau age or isochron age but a total age of 112.3 Ma. The value represents the time that magnetite started to precipitate and is well consistent with the published LA-ICP-MS zircon U-Pb age of 113.6 ±1.6 Ma and 112.6 ±1.6 Ma from granodiorite and monzogranite. The result suggests that the iron mineralization took place in late Early Cretaceous at about 113 Ma. Different from iron mineralization, the copper mineralization mainly occurred in early Late Cretaceous at about 87 Ma. Combined with regional geology and the published data, the authors hold that the Gunjiu iron deposit is related to the southward subduction of Bangong Co-Nujiang Ocean crust. In late Early Cretaceous (113 Ma), the Gangdise and the Qiangtang continental crust started to collide. The subducted oceanic crust of Bangong Co-Nujiang began to rotate under the diving inertia and/or gravity drag. Because of the rotation of the oceanic crust, the astheno-spheric fluids were upwelling and caused partial melting of the lithospheric mantle and the overlying crust due to the tremendous heat. At last there formed the mixed magma, which intruded upward under the back-arc exten-sional condition, forming intrusive rocks and fractionated a large number of ore-forming fluids. Meanwhile, the ore-forming fluids met the stratigraphic formation. There occurred contact metasomatism and eventual formation of the magnetite deposit.关键词
40Ar-39Ar测年/矿物学/金云母/滚纠铁矿/尼雄矿田/措勤/西藏Key words
40Ar-39Ar dating/ mineralogy/ Gunjiu iron deposit/ Nixiong ore field/ Coqen/ Tibet分类
天文与地球科学引用本文复制引用
于玉帅,杨竹森,刘英超,田世洪,纪现华,高原,赵灿,赵武强,刘阿睢..西藏措勤尼雄矿田滚纠铁矿金云母矿物学特征及40Ar-39Ar年代学[J].岩石矿物学杂志,2012,31(5):681-690,10.基金项目
"十一五"国家科技支撑计划项目(2006BAB01A04) （2006BAB01A04）
国家重点基础研究发展计划973项目(2011CB403100,2009CB421007) （2011CB403100,2009CB421007）
地质调查计划项目(1212010918014) （1212010918014）
