摘要
长乐 -南澳断裂带是东南沿海地区陆内强烈变质 -变形带。带内沉积岩、火山岩和早白垩世的钙碱性角闪石黑云花岗岩和花岗闪长岩都已发生可达角闪岩相的变质和石英 -长石相韧性剪切变形。鉴于高温矿物和强烈韧性变形多出现在深成岩附近 ;远离深成岩 ,变质和变形就逐渐减弱 ,故本文认为 ,至少有一部分变质变形的热源是由岩浆提供的。韧剪组构和糜棱质花岗岩是在岩浆侵位的晚期或长乐 -南澳断裂带左旋走滑时 ,在中地壳部位同时形成的 ,长乐断裂带中花岗岩的组构记录了一期同走滑变形的岩浆作用 ,“软变形”作用。据此 ,长乐 -南澳带内花岗岩的形成是受走滑剪切应力和岩浆热双重制约的 ,是在走滑过程中实现的。其动力来源可能与晚中生代的太平洋板块沿日本中央构造线—台湾纵谷带朝东亚陆缘的斜向俯冲有关。
The Changle-Nan'ao fault is anant tectonic zone with strongly Late Mesozoic granitic magmatism and metamorphism-ductile shear deformation in the coastal region of Southeastern China. All Pre-Late Cretaceous sedimentary rocks, volcanic and volcanoclastic rocks and Late Cretaceous CA?type hornblende biotite granite and granodiorite were matamorphosed and deformed to form various amphibolite?facies metamorphic rocks and quartz?feldspar?facies ductile sheared rocks characterized by penetrative fabrics that are developed well in the wallrocks and granitc rocks. In this zone, a NE striking sheared foliations are subvertical, streching lineations are subhorizontal, and non?coaxial ductile deformed fabrics occur widespreadly. Kinematic study suggests that this is a sinistral strike?slip ductile shear zone with slip?down component partly; Late motion sense of dextral strike?slip ductile shear exists locally. Granitic bodies are distributed in the central part of the fault zone. From the center of shear zone to the outer part, metamorphic grade decreases from amphibolite facies gneiss to greenschist facies phyllite and slate; metamorphic minerals change from sillimanite to garnet, mica and sericite. Mylonization and ductile shear fabrics are also weakened from the center of ductile shear zone or of granitic body to the outer parts. Many small?scale ductile deformed zones were found in the Changle-Nan'ao zone. Single deformed zones have a width from several meters to dozens meters. Asymmetric ductile shear criteria that can be used to distinguish a sense of shear include σ? type asymmetric porphyroclastic system, feldspar or quartz augen structure, fish?tails of mica, S? C composite foliation, dynamical recrystallized quartz aggregates in an oblique direction and fibrous chlorite pressure shadows around a large pyrite, and so on. This paper proposes that this zone was a high temperature domain provided by shear heating, and ductile deformed fabrics were formed syntectonically during emplacement of granitic magma, which provided the heat for metamorphism. This is confirmed by occurrence of most high temperature minerals near granitoids, and the metamorphism and deformation in wall rocks away from granitic bodies becomes weaker gradually. Ductile deformation took place in the interval of 100～120 Ma and at the depth of middle crust. Metamorphism, mylonitization and granitic magmatism resulted from a Late Mesozoic collision of Pacific oceanic plate that subducted toward the continental margins of Eastern Asia along the Japanese Central Tectonic Line to the longitudinal valley zone in Taiwan. Three phases of granitic magmatism can be recognized in the zone: the subduction?type or CA?type granitoids with low?K 2O content about 160～180 Ma, the strike?slip?type foliated and mylonitized granitoids about 100～120 Ma, and the A?type or extensional type granite accompanied by magma mixing or basaltic magma underplating.
出处
《高校地质学报》
CAS
CSCD
2000年第3期368-378,共11页
Geological Journal of China Universities
基金
国家自然科学基金重点资助项目!(496 32 0 80 )
关键词
花岗岩类
变质-变形
断裂
岩浆活动
晚中生代
granitoids
metamorphism-deformation
structural constraints
Late Mesozoic
Changle-Nan'ao fault zone
