印度-欧亚侧向碰撞带构造-岩浆演化的动力学背景与过程——以藏东三江地区构造演化为例

The dynamic setting and processes of tectonic and magmatic evolution of the oblique collision zone between Indian and Eurasian plates:Exemplified by the tectonic evolution of the Three River region,eastern Tibet.

对于印度与欧亚板块的侧向碰撞带,即藏东三江地区的新生代构造分析揭示出三种不同性质的构造样式,它们形成于不同的地质时期,发育于不同的地壳层次:(1)区域规模至露头尺度上发育的具有薄皮属性的逆冲断层与推覆构造,它们广泛分布于三江地区,尤其是兰坪-思茅盆地内;(2)以红河-哀牢山断裂、澜沧江和怒江-高黎贡山断裂等为代表的区域高温型走滑韧性剪切带构造和局部发育的脆性走滑断裂构造,后者在中新生代盆地内部断裂更为发育;(3)遍布全区发育的变质核杂岩构造与地堑-半地堑盆地。区域岩浆活动性与区域构造事件的发生具有密切的时空联系。区域性递进收缩事件与走滑事件发生于碰撞过程的早期阶段,并随后伴随着早期具有岩石圈板块俯冲性质的碰撞弧高钾岩浆活动,而后期的递进伸展事件诱发了板内伸展环境中的晚期高钾岩浆活动。二者之间的碱性岩浆活动间歇期,对应着区域构造体制的转变与区域伸展作用的发生,变质核杂岩的发育与微弱的钙碱性岩浆活动是其最直接的表现。区域古地磁资料分析表明,印度-欧亚板块之间的板块相互作用、区域板块与地块的旋转以及由此所致的不同构造环境制约着各种地质事件的发生与发展。北向运动的印度板块的旋转致使三江地块在新生代演化中发生了两次规模与特点不一的地块旋转过程,即早期的大角度快速旋转和晚期的小角度慢速旋转事件。它们分别对应于早期的递进收缩变形、走滑事件和具有碰撞弧属性的碱性岩浆活动与中期的区域伸展、变质核杂岩的发育与微弱的钙碱性岩浆活动性,以及后期的递进伸展作用和晚期陆内碱性岩浆活动性。

Through detailed structural analysis of Cenozoic deformation in the oblique collision zone between Indian and Eurasian plates, i.e. in the Three River region in eastern Tibet, three different structural styles are recognized. They are formed at different crustal levels in Cenozoic： 1 ） thin-skinned thrust faults and nappe structures developed from outcrop to regional scales. They are widely distributed in the Three River region, especially in Lanping-Simao basin; 2） regional high-temperature strike-slip ductile shear zones, exemplified by Red River-Ailao Shan, Lancang River and Nujiang River-Gaoligong Shan shear zones, and local brittle strikeslip faults. The latter are common in the Mesozoic and Cenozoic in Lamping-Simao basin. 3） Metamorphic core complexes and graben or half-subgraben basins are distributed all around in a fan-shaped area between the Red River-Ailao Shan and Sagaing shear zones. Regional magmatic activities are closely related to tectonic activities both temporally and spatially. Regional progressive shortening and strike-slip faulting occurred in the early stage of the collision process. They may have triggered the high potassium magmatism with subduction-related characteristics. Late stage progressive extension resulted in high-potassium magmatism of intraplate characteristics. A magmatic gap between the two periods of alkaline magmatic activities is in coincidence with the changing in regional tectonic systems and the occurrence of regional extension, which is shown directly by the exhumation of metamorphic core complexes and weak calcalkaline magmatic activities. In combination with regional paleo-magnetic data, it is shown that the interaction between Indian and Eurasian plates, the rotation of regional plates and crustal blocks, and hence induced tectonic processes may provide constraints on the occurrence of different geological events. It is suggested that the clockwise and anticlockwise rotation of the northerly moving Indian plate gave rise to two stages of rotation of crustal blocks in the Three River region, an early large angle and high speed rotation and a late small angle and slow rotation. Such rotation of crustal blocks are the major cause of the early stage of progressive shortening, strike-slip faulting, and magmatic arc type alkaline magmatic activities, an intermediate stage of exhumation of metamorphic core complexes and calc-alkaline magmatic activities, and a late stage of progressive extension and intraplate alkaline activities.