西秦岭海西—印支期裂陷活动及其与古特提斯的关系

Rift-Faultings of Hercynian-Indosinian Epoch of Western Qingling Orogenic Belt and Its Relationship with Palaeotethys

海西—印支期，西秦岭地区受古特提斯洋的影响在前海西期变质基底之上发育三期裂陷活动（１．泥盆纪；２．石炭纪；３．二叠至三叠纪），造成该区地层展布呈条带状．深水沉积与浅水沉积相间，以及活动型海槽沉积与稳定型浅海沉积相间的格局．是加里东期之后秦岭构造带东西分异的主要原因。

uring Hercynian-Indosinian Epoch, Western Quiling Mt. was located on the margin of Palaeotethys where developed three time rift-faultings developed(1. Devonian, 2. Carboniferous,3. Permian-Triassic)that caused the strata distributed in the form of belts and Shallow-water and deep-water sediments appeared at intervals on the plane.Every rift-faulting can be divided into three stages: rift-faulting stage, calm stage and compressional stage. During rift-faulting stage carbonate plateform rifted and depressed, deepwater trough basins were formed. Depositional sequence from shallow to deep water contains several layers of olistro-gravity current sediments which consist chiefly of olistromes, debris flow deposits and turbidites. Its compositions are not complex, mainly coming from adjacent plateform and their provenances are linear not point. It is spectacular that giant carbonate oliatoliths were formed that are several tens of meters to one thousand meters in diameter. During calm stage the basin was gradually filled to form up-shallowing sequence. During compressional stage the sediments of thousands of meter in basins were compressed and folded to desposite piedmont molase facies and continental-oceanic alternative facies. The alteration of rift-faulting and compressive stages made rift-faulting happened periodicalvy.Synsedimentary faults are the main structure which controlled olistro-gravity current complex sediments.