云南澜沧老厂花岗斑岩形成年龄及地质意义

应用锆石SHRIMPU-Pb法和辉钼矿Re-Os同位素测年法对斑岩的形成时代进行精确定年。结果表明:成矿花岗斑岩体的形成年龄为44.6±1.1Ma;辉钼矿Re-Os等时线年龄为43.78±0.78Ma;成岩成矿期与滇西新生代岩浆-成矿作用高峰期吻合。结合区域地质条件和岩浆的可能源岩年龄(126.7±3.5Ma～529.3±13Ma)等资料分析,提出花岗斑岩在成因上与印支地块与滇缅泰地块陆内俯冲碰撞引发的地幔上涌及地壳重熔作用有关,岩浆来源具壳-幔混合特征。研究还证实滇西地区喜山期存在与隐伏花岗斑岩有关的大规模成矿作用。

Rock-forming Ages of the Laochang Granite-Porphyry, Lancang, Yunnan and Their Geological Significance

The Laochang polymetallic deposit, situated in the south part of the late Palaeozoic Changning-Menglian continental rift belt in western Yunnan, is one of the areas with significant breakthrough for a new discovery of great thick porphyry molybdenum ore bodies in the depths since 2008. This paper provides precise rock-forming ages of the granite-porphyry by the SHRIMP zircon U-Pb and molybdenite Re-Os dating methods. The results show that the forming age of the granite-porphyry is 44.6±1.1Ma, and the Re-Os isochron age of molybdenites 43.78±0.78Ma. The rock- and ore-forming ages are in consistent with the peak phase of Cenozoic magmatism-mineralization of western Yunnan. For this reason, combining dating with regional geological conditions and the ages (126.7±3.5Ma～529.3±13Ma) of possible source rocks of the magma, it is suggested that the genesis of the concealed granite-porphyry may be related to mantle upwelling and crustal anatexis, and its origin exhibits the mixing features coming from crust-derived and mantle-derived magmas caused by intracontinental collision and subduction between the Indo-Chinese block and Yunnan-Burma block. It has also demonstrated that a large-scale Mo(Cu)-mineralization related to Himalayan concealed granite-porphyries exists in western Yunnan.