扬子地块西南部地球化学异常层与地壳演化和成矿作用

本文通过对扬子地块西南部自上元古界板溪群到三叠系发育在盆地和下斜坡背景中泥质岩的系统元素地球化学研究，首次发现了下寒武统、上泥盆统和上二叠统这三个在元素地球化学性质上明显不同于其它层位的地球化学异常层。通过元素地球化学异常层与本区地壳演化和成矿作用关系的研究，使我们认识到，后太古代沉积地层中的元素地球化学特征与地壳演化之间存在着密切的内在联系，可通过这些地层的元素地球化学体系来恢复地壳发育和演化历史；同时，在正常沉积地层中，元素的富集和亏损程度是有限的，只有在那些与地壳发展演化的特定阶段相对应的层段中，某些元素才有可能高度富集而成为重要的矿源层。这对应用元素地球化学体系正确认识地壳演化和成矿作用的时控性具有重要的指导意义。

GEOCHEMICALLY ABNORMAL HORIZONS AND THEIR RELATIONS TO CRUSTAL EVOLUTION AND MINERALIZATION IN SOUTHWEST YANGTZE MASSIF

Systematic studies of trace elements and REE geochemistry of mudstones deposited in the basin and lower slope environments from Upper Proterozoic to Triassic in the Southwest Yangtze Massif have led to a discovery of three geochemically abnormal horizons:Lower Cambrian,Upper Devonian and Upper Permian. The enriched elements in this area are mainly concentrat ed in these geochemically abnormal horizons, and the degree of enrichment and deficiency of trace elements in other horizons is very limited. These geochemically abnormal horizons are corre sponding to the periods of pulling apart of geotectonic cycles,which illustrates that the uncommon depositional sources pouring into the basin from the interior of the earth may be one of the most important causes for the production of geochemical anomalies in these horizons. A series of research on mineralization indicates that the main low-temperature strata-bound ore deposits discovered in the SOuthwest Yangtze Massif occur in the Cambrian,Devonian,and' Permian-Triassic strata. The results of isotope tracer research indicate that most of the metallogenic elements in these ore deposits come from the host strata, illustrating that the geochemically abnormal horizons may have made great contributions to these ore-forming processes.