西藏东部嘉玉桥变质杂岩内中侏罗世高压剪切作用：来自多硅白云母的证据  

Middle Jurassic high-pressure shearing reveled by phengite in Jiayuqiao metamorphic complex,eastern Tibet.

作　　者：王根厚[1,2] 张维杰[1] 周详 贾建称[4] 于海亮[1] 

机构地区：[1]中国地质大学北京地球科学与资源学院,100083 [2]中国地震局地球物理所,100081 [3]西藏自治区地质调查院,拉萨850000 [4]中国煤炭科学研究总院西安分院,陕西西安710054

出　　处：《岩石学报》2008年第2期395-400,共6页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(49802019);中国地质调查局资助项目“1：25万仓来拉幅区域地质调查(200313000001)”

摘　　要：藏东嘉玉桥变质杂岩分布于班公错-怒江缝合带南西,出露宽度约15～20km,延伸长度约120km。藏东嘉玉桥变质杂岩与上覆中侏罗统呈滑脱断层接触,滑脱带内发育各种韧性剪切组构。滑脱带内钠长石英构造片岩中石英呈矩形条带,多硅白云母与石英矩形条带构成S-C组构,石英颗粒应变测量表明Flinn图解K=∞,代表近水平伸展滑脱。获得多硅白云母变质条件相当于蓝片岩相,压力属于高压变质相,多硅白云母测年结果为167.27±0.99 Ma,为中侏罗世高压剪切作用,暗示班公-怒江缝合带中侏罗世伸展与高压剪切作用密切相关。Jiayuqiao metamorphic complex is located at the southwestern of Bangong-Nujian suture with a width of 15 -20km and a length of more than 120km. A detachment fault, which includes variable of ductile shearing fabrics, separated the Jiayuqiao metamorphic complex in the core from the middle Jurassic in the cover. Phengite was first identified in this detachment fault. Within the detachment fault, the rectangle quartz ribbons form the S-foliation and Phengites form the C-foliation, and both combining produce typical S-C fabric. Strain measurements for the quartz grain give K = ∞ when plotting in Flinn diagram, which indicates a strongly sub-horizontal detachment deformation. The rectangle quartz ribbons indicate a metamorphic grade of high-greenschist to low amphibolite facies, while EMP analyzed results of the phengite plot in the metamorphic grade of blueschist with a high pressure. The separated phengite was dated at 167.27 ±0. 99 Ma using the^40 Ar/^39 Ar method, and thus revels a middle Jurassic high-pressure shearing tectonic event occurred in eastern Tibetan, and might implicate that the Banggong-Nujiang suture first formed at middle Jurassic.

关 键 词：西藏东部 嘉玉桥变质杂岩 多硅白云母 班公错-怒江缝合带 

分 类 号：P542.3[天文地球—构造地质学] P551[天文地球—地质学]