摘要
西藏东部嘉玉桥拆离系核部杂岩构造特征及其大地构造意义周详１王根厚２普布次仁１曾庆高１嘉玉桥拆离系是笔者等（１９９２）在藏东地区新发现的一种伸展构造类型。它发育在班公湖－怒江缝合带的嘉玉桥地段。拆离系核部杂岩即李璞（１９５９）最早命名的“嘉玉桥岩系”，...
The Jiayuqiao detachment system developed in eastern Xizang(Tibet)may be interpreted as a new type of extensional structures.Its main features are generalized as follows. (1)The core complexes in the detachment system with a broader span of metamorphic facies(low greenschist facies to amphibolite facies)and ages(Late Palaeozoic to Proterozoic)were mostly created in the late Variscan to Indosinian and finalized in the early Yanshanian.At least three structural stratigraphic systems have been identified in ascending order for the core complexes as a kind of “chaotic ordering”,structurally integrated systems.They are the Tongka lamellatized rock group(pre Sinian),the Jiayuqiao schistositized rock group(pre Carboniferous),and the Bangda folded rock group(Late Palaeozoic),all of which are superimposed in proper order upon two main detachment surfaces,thus constituting the relatively complete“three layer structure”of the crustal configuration in the detachment system. (2)The main deformational stage of the core complexes is characterized by SE(140°)—NW(320°) orientated,regionally extensional faulting.The 40 Ar 39 Ar dating of the metamorphic minerals formed during this stage range between 164 and 166 Ma,nearer to those of the early sedimentary cover(Early to Middle Jurassic)of the complex system.The occurrence of the detachment processes is generally related to the transtention of the Bangong Nujiang oceanic crust during the Early and Middle Jurassic.The extensional structures have unique “nonorogenic”features and are parallel to orogenic strike slip and pull apart structural regimes. (3)The earlier deformation and metamorphism in the complex system,on one hand,are a reflection of the late Variscan and Indosinian convergent and accretionary processes.The corresponding structural parts appear to have the features of the foreland accretionary wedge in the subduction zone,probably relevant to the closure of the Palaeo Tethyan tectonic domain in eastern Xizang.On the other hand,the later supergene structural deformation mirrors the intensive reworking of the detachment system by the closure and collision of the Neo Tethyan(northern)domain.Therefore,the core complexes in the detachment system became a “regenerated”orogenic unit in the Bangong Nujiang suture zone. Unlike the metamorphic core complexes in the Basin Range system in western America and the “South Xizang detachment system” in the Himalayan mountain chain,the Jiayuqiao detachment system may be of prime importance for the study of the orogenic zones in the Tethyan tectonic domain.
出处
《沉积与特提斯地质》
CAS
CSCD
1997年第21期58-63,共6页
Sedimentary Geology and Tethyan Geology
