安徽庐枞火山-构造洼地的形成、演化及成矿

FORMATION AND DEVELOPMENT OF THE MESOZOIC LUJIANG-ZONGYANG VOLCANIC-STRUCTURAL DEPRESSION IN ANHUI PROVINCE AND THEIR RELATION TO MINERALIZATION

庐枞火山-构造洼地是在构造和火山岩浆活动共同作用下产生的。从190Ma至105Ma其演化过程可分为五个阶段,共出现了9种金属和硫铁矿矿床类型,这些矿床在时-空分布上具有明显的规律性,在成因上具有一定的内在联系,构成了在长期沉降基底士的火山-构造洼地内、外与橄榄安粗岩系有关的成矿系列。本文提供了一个在剪切-挤压与剪切-拉张交替作用,而以剪切-拉张为主的构造背景下,在活动大陆边缘与板内过渡地带,一个火山-构造洼地及其成矿作用演化的四维模型。

The formation of the Lujiang-Zongyang volcanic-structural depression resulted from the com- ??bined actions of tectonism and volcanism. The extensional structure after collition-amalgamation-inland orogeny between the North China and Yangtze plate formed the fault trough in the Early to Middle Jurassic; then, due to the 'Ancient Pacific'-Eurasian plate convergence and left-slip shear of the Tanchen-Lujiang deep fault, under the NW-SE corupressional stress, there occurred NE-, NW-, SN- and EW- trending faults in the sedimentary rocks of basement. The tensile action after partial relaxation of accumulated stress caused the uplift of upper mantle materials and the emerging of shoshonite magma, as well as the appearance of the magma chamber with a area of 800 km^2 at shallow levels. The contraction of magma volume brought about by the volcanic explosion and the action of regional tensile stress resulted in the formation of the Lujiang-Zongyang volcanic-structural depression.The evolution of the Lujiang-Zongyang volcanic-structural depression underwent five stages from 190 to 105Ma, i. e. the fluviatile-lacustrine facies-sediment stage in the fault trough, the early explosive eruption-depression stage, the revived upheaval-overall uplift stage, the late explosive eruption-local depression stage, and the late uplift stage. Due to the distinction of oreforming conditions among various stages, there were 9 types of metallic and sulphur ore deposits: formed in the five stages. These deposits show obvious regularities in the tempo-spatial distribution and certain relationship in origin, and constitute a metallogenetic series related to shoshonite volcanic activities within or around the Mesozoic volcanic-structural depression on. the basement.This study suggests a four-dimensional model of the evolution and forming process of a typical volcanic-structural depression and their relation to mineralization in the transition belt from active margin to inner plate under the alternate stress fields of compression-shear and shear-tension, but dominated by the latter.