皖南前南华纪浅变质岩系的沉积地质特征及其构造古地理意义

皖南地区前南华纪浅变质岩系是江南造山带东段的重要组成部分。根据对本区前南华纪浅变质地层——环沙组和牛屋组所进行的沉积地质学研究,可识别出浊积岩相和深海—半深海相沉积,两者均属活动类型沉积建造。进一步的沉积相序研究表明,环沙组沉积环境总体反映出浅—深—浅—深的沉积变化,牛屋组沉积环境总体反映出由深变浅的沉积变化。对发育于环沙组和牛屋组上段的小型斜层理进行测量,经水平校正后两者古流向都指向北,证明其物源都来自南方。沉积岩骨架颗粒统计结果表明,环沙组物源构造属性为岩浆弧,牛屋组上段物源构造属性为再旋回造山带。结合侵入牛屋组下段的花岗岩地球化学特征研究,推测环沙组沉积于弧后盆地,牛屋组下段沉积于边缘海盆地,牛屋组上段沉积于周缘前陆盆地。在总结前人研究成果的基础上,探讨了江南造山带东段本区相应时段的大地构造演化格局。

Sedimentary characteristics of the pre-Nanhua epi-metamorphic rock series in southern Anhui Province and the tectono-paleogeographic implications

The pre-Nanhua epi-metamorphic stratum in southern Anhui Province is an important part of the Jiangnan oregenic belt. Based on the sedimentary study of the Huansha and Niuwu formations, we can identify turbidite and deep sea-bathyal facies that both belong to the active type of sedimentary formation. Our research revealed that the sedimentary environment of the Huansha Formation reflects a shallow-deep sequence, while the Niuwu Formation features an upward-shallowing sequence. The sedimentary diffusion of the Huansha and upper Niuwu formations is northward directed, suggesting the provenances for the two formations must be from the south. Ternary plots of the sandstone point-count data showed that the Huansha and upper Niuwu formations were plotted in the magmatic-arc and recycled orogen fields, respectively. Combined with the geochemical research on granite intrusion in the Niuwu Formation, we conclude that the proto-basin of the Huansha Formation is back-arc basin, whereas the lower and upper Niuwu formations are marginal sea and peripheral foreland basins, respectively.