川西地区甲基卡穹隆的构造变形特征

Structural deformation of the Jiajika dome in western Sichuan

甲基卡穹隆因其丰富的锂辉石资源而闻名,在华北、扬子和羌塘3个板块之间的南北向和东西向双向收缩背景下,形成了其复杂的变形特征。穹隆顶部地层平缓,向外逐渐变陡,总体为同心圆状向外倾的复式背斜。顶部发育有A型等斜平卧褶皱、肠状石英脉及对称型压力影;翼部变质矿物多被拉伸旋转而呈不对称状,表现出向穹隆周围的正向剪切运动;穹隆外围地层产状较陡,多发育直立紧闭褶皱及倒转褶皱。总体来说,甲基卡穹隆岩浆底辟作用前,先后经历了南北向及东西向的挤压,成穹后再一次经历南北和东西向挤压的两期构造运动,属于构造变形与岩浆作用的共同产物。

The Jiajika dome in western Sichuan is famous for its abundant spodumene resources. Both the NS-and EW-trending convergence of the North China,Yangtze and Qiangtang blocks resulted in the complex structural deformation of the Jiajika dome. Generally,the Jiajika dome appears as a concentric anticlinorium where the coral strata are gentle,and become gradually steeper outwards. There are A-type isoclinal recumbent folds,ptygmatic quartz veins and symmetrical pressure shadows on the top of the dome. The metamorphic minerals on the limbs are almost strenched and rotated into asymmetrical formes,displaying the nature of a positive shear movement from the limbs outwards. The vertical tight folds and overturned folds occur in the steeper strata around the dome. On the whole,the Jiajika dome is interpreted as the products of joint tectonism and magmatism,and has successively experienced two phases of tectonic movements,i. e.,two phases of NS-and EW-trending tectonic compression.