攀西会理群的碳酸盐滑积岩等深积岩及其构造条件浅析

THE CARBONATE OLISTASTROME AND THE CONTOURITE IN THE HUILI GROUP, PANX1 AREA, AND THEIR STRUCTURAL CONTROL

本文通过对岩石的原生沉积构造和结构成分的研究,确定了浅变质岩系中碳酸盐复理石——野复理石建造的主要岩石成囡类型,有滑积岩、崩塌跌积岩和等深积岩所组成,由重力崩落、碎屑流、液化沉积物流和浊流所形成。它们的岩相特征表明当时沉积盆地中存在水下缓坡和陡崖以及与之并存的深水槽盆,是同沉积构造活动的产物。 上列岩石的物质组成特点是内外源混积,构成砂质(或含砂)碳酸盐浊积岩系列。将统计之石英、长石(少量),砾屑含量投影于Schwab的三端元图上,表明是台地断陷或断块复活的产物。因此滑积岩、崩塌跌积岩等可作为指示盆地同沉积断裂活动历史的地质参数。

The carbonate olistostrome and thecontourite of the Proterozoic Huili Group in Panxi area were found in the Kengshanying Formation. They constitute with other carbonates a suile of flysch formation of cpimetamorphic carbonate. The total thickness is of about 1700m.The rocks were formed form the gravity collapse,the liquified sediment flow, the debris flow and the turbidity current. The characteristic of the major genetic types are as follows:(1) Olistostrome, the contorted bedding,the rip-up and the truncation structures indicate that submarine slope was dipping toward north.(2) Collapse breccia, composed of gravels with various sizes, which are non- sorted and formed by rolling and collapsing of semiconsolidated rocks. It is a proximal deposit with synsedimentary fault activity indicating the existance of submarine cliff.(3) Contourite, its a rewinnowed turbidite and shows the tectonic activity of the basin floor approaching stable.In addition, the accompanied carbonate turbidite, demonstrates from the ternary plot that they were formed through faulting and subsiding of a platform or through reactivity of a fault block.The cyclic evolution of the beds suggests there had been periodic synsedimentary tectonic activities. Each period starts from an initial slow subsidence then followed by a sudden intensive faulting subsidence. The framework of lithofacies and palaeogeography shows the development of platform (west-south west) -slope-trough had been controlled by a fault running east-west which also caused the northern part subsiding and southern part uplifting.To sum up, the characteristics in mineral composition, texture and structure of the rocks, the sedimentary sequence and the lithofacies and palaeogeographic framework altogether demonstrate the existence of synsedimentary fault activity. Especially, the olistostrome and the collapse breccia arc indices to the depositional and tectogentic history.