东昆仑五龙沟金矿田控矿构造带的变形条件——来自EBSD组构的启示

摘要

五龙沟金矿田是东昆仑地区最重要的金矿集中区之一, 金矿田主要控矿构造为偏脆性断裂破碎带,在三条控矿构造带中仅在萤石沟—红旗沟构造带邻近北侧的局部出露韧性变形带.本文作者运用电子背散射衍射技术(EBSD)技术方法, 对东昆仑五龙沟金矿田萤石沟—红旗沟构造带变形岩石的组构分析显示, 花岗质糜棱岩韧性变形强烈, 大部分样品石英变形机制是以中温I级柱面(1010)<1120>滑移为主, 变形式样比较单一;少量样品为中高温 II 级柱面(1010)<0001>滑移和中低温底面(0001)<1120>滑移.从岩石组构特点结合宏观构造分析, 五龙沟金矿田萤石沟—红旗沟构造带及其邻近北侧经历了中-中深层次、中-中高温条件(15~25 km, t=350~550°C, P=0.40~0.60 Gpa)的韧性变形,局部叠加中浅层次、中低温条件(10~15 km, t=250~350°C, P=0.25~0.40 Gpa)的韧脆性变形;而岩金沟和三道梁—苦水泉构造带为低温低压条件的脆性破碎带.结合变形花岗闪长岩年代学资料, 确定构造变形时代为早中生代.%The Wulonggou gold orefield is one of the most important gold ore concentration areas in Eastern Kunlun Mountains, and three brittle ore-controlling fault fracture zones are developed in the orefield. i.e., Yanjingou zone, Yinshigou–Hongqigou zone and Sandaoliang–Kushuiquan zone. The ductile deformation is only outcropped in some areas near the northern side of the Yinshigou–Hongqigou structural zone. Based on the EBSD petro-fabrics analysis of deformed rocks from Yinshigou–Hongqigou structural zone of the Wulonggou gold orefield, the authors have drawn the conclusions as follows. (1) There happened a strong deformation of the rocks in some area near the northern side of the Yinshigou–Hongqigou structural zone in the orefield. (2) Quartz in most granitic mylotite samples was mainly deformed along its prismatic I glide system with a single deformation type, while quartz in partial samples was deformed along its prismatic II and basal or basal-near glide system. (3) The deformation of the mylotite occurred mostly at a medium and medium-great depth of 15~25 km, at a middle and med-high temperature of 350~550°C and under a middle pressure of 0.40~0.60 GPa, with only part of them being superimposed deformation late at a low-medium depth of 10~15 km and a low-middle of 250~350°C and under a low-middle pressure of 0.25~0.40 GPa. (4) There developed brittle fracture zone in Yanjingou zone and Sandaoliang–Kushuiquan zone. (5) Combined with the age of deformed granodiorite, the authors consider that the ductile deformation in the orefield occurred in early Mesozoic.