新疆中天山北缘韧性剪切带研究

THE DUCTILE SHEAR ZONE ON THE NORTHERN MARGIN OF THE CENTRAL TIANSHAN MOUNTAINS ,XINJIANG

在新疆中天山北缘发现有一条巨大的韧性剪切带，延伸５００ｋｍ以上，宽３ｋｍ。剪切带内发育着各种变形构造和显微构造。磁组构研究表明剪切带变形强烈，属韧性剪切变形，磁面理和磁线理同等发育。有限应变测量结果表明剪切带为不均匀简单剪切加围岩的均匀应变。应变强度１．０９，压缩量达５９％，富林参数为０．９。变形路径斜率接近４５°。剪切带的总位移量平均值为４４８２ｍ，水平位移量为２８４９ｍ，垂直俯冲位移量为３４５５ｍ。该韧性剪切带形成于晚志留世—泥盆纪末，前后共延续了大约６０Ｍａ。变形时的温压为３１２℃和４３３巴。应力场为σ１＝３５１°∠１１°，σ３＝９３°∠２９°。应变速率为２．４×１０－１５／秒，平均剪应变为４．５。

A gigantic ductile shear zone has been found on the northern margin of the Central Tianshan Mountains,Xinjiang.It generally extends in a WNW direction as long as more than 500 km with a width of about 3 km.Studies of various kinds of deformation structures ,microstructures and magnetic fabrics indicate that it has undergone strong ductile shear .Finite strain measurements show that the shear was an inhomogeneous simple one with a strain strength of 1.09,a Flinn factor of 0.9,a deformation slope close to 45° and a compression volume up to 59%.The horizontal(strike-slip)displacement of the shear zone is 2849 m and the vertical subduction (dip-slip) displacement of 3455 m with a total displacement of 4482 m.The ductile shear zone was formed in the Late Silurian-terminal Devonian and the shear persisted about 60 Ma.The deformation occurred at 312℃ and 433 bars,in a stress field with σ 1=351°∠11°and σ 3=93°∠29°,at a strain rate of 2.4×10 -5 /sec and with an average strain of 4.5.The origin of this ductile shear zone is related to the collision of the Junggar Paleo-ocean and the Central Tianshan massif.