摘要
金沙江韧性剪切带为一条宽60-80km的大型平移剪切带，在金沙江向两侧，变形强度逐渐变弱，金沙江北起玉树、经江达、巴塘、德钦后折入青藏高原，构造位置处于义敦岛弧带与羌塘地块之间。由于其独特的构造位置，金沙江地区变形和变质较复杂。通过野外和室内的研究得出以下结论：
(1)金沙江韧性剪切带经历了三期主要变形和变质期次，D1期变形以透入性劈理的发育为特征，M1期变质形成十字石-蓝晶石带、铁铝榴石带，指示了华力西期金沙江俯冲碰撞地壳增厚的过程；D2期变形为褶劈理和鞘褶皱，M2期变质形成矽线石带，指示了印支期地壳增厚的快速减薄的过程；D3期变形为脆性断层，对应的M3期变质为区域性退变质，指示了喜马拉雅期印度板块与欧亚板块碰撞形成的。
(2)P-T图显示十字石蓝晶石带到夕线石带呈降温降压的趋势，为顺时针的P-T轨迹。代表俯冲碰撞地壳增厚产生的中温高压变质作用和碰撞后地壳迅速减薄产生的中温低压变质作用的过程，中温低压变质事件叠加在早期的高压变质作用之上，这被看成是造山带增厚的伸展垮塌的结果。
(3)运动学涡度为0.78-0.97，指示金沙江韧性剪切带的剪切类型为一般剪切，以简单剪切为主。
(4)石英的运动学涡度指示本区岩石经历了从中温-中低温-低温的一系列韧性变形过程。所有样品均经历低温变形，与显微镜下矿物的普遍退变质一致。石英C轴结晶优选以中温和中低温最为明显。后期的低温变质变形叠加在早期的中温韧性变形之上。
The Jinshajiang ductile shear zone with width of60-80km has the component ofstrike-slip, located between the Yidun Arc and Qiangtang Block, at the northwestern Yunnanand western Sichuan provinces, SW China. This ductile shear zone along the SN-strikingJingshajiang Suture was produced by the closing of the Paleotethys Ocean in Late Permianto Triassic. Based on field investigation and indoor analysis, the conclusions are as follows:
(1) The Jinshajiang ductile shear zone experienced3major deformational andmetamorphic events: D1and M1are penetrative foliation and bearing of staurolite-kyanite-almandine, which indicate the crustal thickening of subduction and collision duringthe Variscan; D2are crenulation cleavage and sheath fold, M2are sillimanite, whichindicates the crustal thinning during the Indosinian; D3and M3are brittle fault and regionalretrograde metamorphism, which were produced by the collision of the Indian and Tibetplateau.
(2) P-T clockwise path show trend of cooling from staurolite and kyanite to almandine.The path represent process of the medium temperature and high pressure metamorphismproduced by the crustal thickening to the medium temperature and low pressuremetamorphism due to the crustal thinning, which is attributed to the collapse of the orogen.
(3) The kinematics vorticity (Wk) is0.78to0.97, which shows Jinshajiang ductileshear zone are general shear with major component of simple shear.
(4) The kinematics vorticity (Wk) based on the EBSD of quartz indicates theJinshajiang ductile shear experienced the shearing process of median to low temperature. Allsamples experiende the low temperature process is consistent with the retrogrademetamorphism observed in the microscope. The preferred orientation of the quartz C-axisare have the characteristics of median temperature obviously, which was overprinted by thelow temperature metamorphism.
引文
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