南盘江地区浅层地壳结构与金矿分布模式

Texture of the Upper Crust and Pattern of the Disseminated Gold Deposits Distributed in Nanpanjiang Area

南盘江地区位于大陆板块内部．受控于特提斯和濒太平洋构造两大地球动力学背景。浅层地壳主要由沉积岩构成．是与伸展构造和碰撞构造作用有关沉积盆地的产物。该区地壳属大陆地壳范畴．可分为上中下三层。上地壳结构具有“层、块、带”的规律组合和有序排布；中下地壳是“分块分带”的．并在平面上呈“币”字型。该区产有卡林型和红土型两种金矿。前者可进一步分为以沉积岩（石灰岩、砂屑岩）和火山碎屑岩为容矿岩石的两种类型．属浅成低温热液矿床；后者则分为喀斯特崩塌红土型和原地残积红土型两种，它们是特殊喀斯特环境的产物。南盘江地区的地壳结构、盆地性质和变形图象控制着该区卡林型金矿的分布．是同一碰撞造山进程中统一成矿作用的产物，具有“多层沙的构形；红土型金矿的分布则主要受气候、地形、地貌和地文期的控制，特别与地壳表面形态密切相关。

Abstract:The Nanpanjiang area referred in this monograph covers the neighbouring area,with atotal of approximately 4, 500 km2,between the Southwest Guizhou,the Southeast Yunnan,and the Northwest Guangxi,where there is a widespread distribution of terrigenous elastic flysch sediments of the middle to late Triassic age.During the'late Mesozoic period,the NanpanjianS area was tectonically located in theintraplate under the geodynamic setting controlled primarily by the T.ethyan plate,and secondly by the Pacific plate. After the late Triassic time, it formed a part of the continentalorogenic belt attributed to collision of the indian plate with the Asian plate.The integrated geophysical data indiC.ste this study area is situated within the 'easternside of the trend of Longmenshan gravity gradient and closely adjacent to the Dian-Qianmantle depression in eastern Yunnan and western Guizhou. Some thermal anomalies withlow temperature exist in the upper crust of this area.The geochemical anomalies are strongly characterized by high An in values in thisarea' Depending on An background,they can be identified as two geochemical provinces ofYangtze and Youjiang.The views above comprise the premiss for studies on relations of gold ore-formingprocess to the crustal texture in Nanpanjiang area.The upper crust in this area,especially at its shallow level,consists predominantly ofsedimentary rocks that can be distinctively divided into two major classes of carbonaterocks and terrigenous siliciclastics, minor igneous rocks and pyroclastics. The carbonaterocks and terigenous siliceous elastics,respectively representing shallow-sea and relativelydeep-water sedimentary environments,are the emphasis on descriptions of lithology in thispaper'From the present understanding of geodynamic setting in the study ares,sedimentarybasins developed since the late Palaeozoic age are classified as two types of basins with foursubdivisions, originally related senarately to extention and collision,of which the peripheralforeland basins and the passive continental margin baisns are particularly discussed here indetail.' The deformation image of the upper crust in the 'area. has been outlined,Ba'ed on thesix structural sequences determined previously,the author focus his attention on two majorstructural belts,i. e.,northwest- and northeast-trendinS belt,stressing the importance ofthe former's strike-slip faulting and recognizing its a squeeze-up during the process of collision-orogency,and pointing out the latter is a result of the crust extension during postcollision-orogency. In the same time,a further recognition on implication of the superimposed folds well developed widely for control of the disseminated-gold mineralization in theNanpanjiang area is proposed.With help of the principles of sequence stratigraphy, the marine sedimentary stratafrom Devonian to Triassic in the Nanpanjiang area have been investigated in outcrops anddivided into 18 order-ill sequences corresponded to 2 order-I and 6 order-II sedimentarycycles. The stratigraphic framework of two major sequences during the period. of the Devonian through early --late Permiian to Triassic and their lithologic units have been establis bed.The geological and geophysical data available reveal that the crust in the Nanpanjiangarea occurres vertically as three spheres of the upper, the middle and the lower unit. At.shallow level,the upper crust is predom manily made up of bed imentary rocks and displaysa ordered texture of 'ktratiform-block-belts. Noted worthy,neverthelcss,the upper crust isnonhomscneous in vertical and horizontal destribution of this \trail form(block-belt' structures. Downward,the mid-lower crust is composed of metamorphosed rocks in mid to highgrade cut laterially and longititudiually by a series of different strike deep crustal faultswith a pattern of blocked-belted structures which is premise for development of the structural styles within the upper crust' In general,the'crust in this study area with thickness of39-- 45 km is thinned from southeast to north'west,contrasting with t