西藏驱龙斑岩铜钼矿床中UST石英的发现：初始岩浆流体的直接记录  

Direct record of primary fluid exsolved from magma:Evidence from unidirectional solidification texture(UST) in quartz found in Qulong porphyry copper deposit,Tibet

作　　者：杨志明[1] 侯增谦[1] 李振清[2] 宋玉财[1] 谢玉玲[3] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质科学院矿产资源研究所,北京100037 [3]北京科技大学土木与环境工程学院,北京100083

出　　处：《矿床地质》2008年第2期188-199,共12页Mineral Deposits

基　　金：国家自然科学重点基金(编号:40730419);国家基础研究规划973项目(批准号:2002CB412600)资助

摘　　要：单向固结结构（UST）是浅成侵位的岩浆出溶过程中形成的一种特殊结构，一般由梳状石英与细晶（斑岩）岩交互生长而成，少数产于斑岩与围岩接触部位，其内的原生包裹体被认为是初始流体出溶的可靠记录。作者在西藏驱龙铜矿床中首次发现了具有单向固结结构的石英。研究表明，驱龙UST石英存在于后期侵位的二长花岗斑岩与花岗闪长岩的接触部位，部分为高温β石英；UST石英中原生包裹体的成分主要为高盐度液相，除石盐子矿物外，还含有硬石膏等其他子矿物。阴极发光及显微测温结果表明，初始流体的出溶发生在高温（t≥573℃）、高压（声≥150-200MPa）条件下，出溶的流体为高温、高盐度[w（Nacleq）为44．5％～58％]流体，同时还具有较高的氧逸度。因形成压力较高，判断UST石英不可能由较浅侵位的二长花岗斑岩岩枝冷凝出溶而形成，从而推测驱龙铜矿床深部存在着孕育成矿斑岩的大型岩基。The unidirectional solidification texture （UST） is usually an anisotropic texture defined by thin （2 mm to 50 mm） and alternate bands of crenulate and coarse-grained prismatic quartz （comb quartz） and microcrystalline aplite porphyry. Such a texture has also been found developed along contacts of porphyritic intrusions. The UST, found in the Qulong deposit, is characterized by continuous veins of comb quartz at the porphyry contact. Apical terminations of quartz crystals are pointed to the porphyry intrusion. Despite the fact that quartz in UST is optically continuous, the cathodoluminescence （CL） image reveals concentric growth zones in coarse-grained prismatic quartz. Some quartz in the unidirectional solidification textures shows equant bipyramidal and hexagonal growth forms, indicating characteristics of high-temperature β-quartz. Re-entrants and in some cases embay-ments, along with irregular overgrowths, imply resorption, Primary inclusions in the UST quartz are dominated by hypersaline liquid inclusions. Microthermometric experiments reveal that the inclusions exhibit homogenization by halite （or anhydrite） dissolution between 400℃ and 〉590℃, whereas the vapor disappearance ranges from 200℃ to 333℃. The true trapping temperature must have been much higher （≥573℃）, given that these inclusions were trapped during the growth of equant bipyramids of β-quartz. Reconstruction of the pressure-tem-perature trapping conditions confirms that these inclusion fluids were probably trapped at an unbelievably high pressures （≥150-200 MPa）, which accounts for the existence of a relatively large magma chamber below the deposit.

关 键 词：地质学 单向固结结构(UST) 流体出溶 斑岩铜矿 驱龙 西藏 

分 类 号：P618.41[天文地球—矿床学] P618.65[天文地球—地质学]