摘要
本文首次报导苏鲁造山带西缘新发现的北东向郯庐高压左旋走滑韧性剪切带。剪切带糜棱岩中长石与石英皆广泛发生了动态重结晶,其重结晶型式指示变形温度高达600～700℃。糜棱岩基质中新结晶的白云母,经电子探针分析指示为多硅白云母,所计算的形成压力为1.03～1.45 GPa,表明形成于地壳底部的高压榴辉岩相环境。工作中对剪切带糜棱岩中6个多硅白云母样品进行了^(40)Ar/^(39)Ar测年,其中2个超糜棱岩基质中新结晶多硅白云母分别给出了209.9±1.5Ma 和214.3±1.4Ma(皆晚三叠世)的^(40)Ar/^(39)Ar 坪年龄,指示了左旋走滑的冷却年龄。这些年龄值与苏鲁超高压变质带内已有的多硅白云母^(40)Ar/^(39)Ar 年龄基本一致,表明郯庐断裂带形成于华北与华南板块的碰撞造山期。结合其它地质现象,笔者认为在这两个板块碰撞中郯庐断裂带是以陆内左旋变换断层的型式出现的,从而将大别与苏鲁造山带大规模左行错开。
High-pressure sinistral strike-slip shear belts in the NE-trending Tan-Lu fault zone along the western margin of the Sulu orogenic belt are first reported in this paper. Feldspar and quartz grains show widespread dynamical recrystallization in the mylonites of the shear belts. Their recrystallization patterns indicate deformation temperatures as high as 600 -700℃. According to electron microprobe analysis, syn-mylonization white mica in matrixes of the mylonites is phengite, and pressure of 1.03 - 1.45 GPa were calculated for the mylonization. This demonstrates that the shear belts were developed under conditions of high-pressure eclogite facies at base levels of crust. 6 phengite samples from mylonites in the shear belts were dated by the ^40Ar/^39Ar technique. 2 syn-mylonization phengite samples from ultramylonite yield ^40Ar/^39Ar plateau ages of 209.9 ± 1.5 Ma and 214.3 ± 1.4 Ma （late Triassic） respectively. They are interpreted as representing cooling ages of the sinistral faulting. These ages are basically consistent with phengite ^40Ar/^39Ar ages obtained from inner parts of the Sulu orogenic belt, indicating that the Tan-Lu fault zone was developed during the period of collision between the North and South China plates. Considering other geological phenomena, it is proposed that the Tan-Lu fault occurred as an intra-continental sinistral transfer fault zone during collision of the North and South China plates, and sinistrally offset the Dabie and Sulu orogenic belts on a large scale.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2005年第6期1687-1702,共16页
Acta Petrologica Sinica
基金
国家自然科学基金(编号:40272094)
