上扬子地块北缘灯影组硅质岩系硅、氧同位素特征及其成因!

The Isotopic Characteristics of Silicon and Oxygen and the Genesis of the Dengying Siliceous Rock Series in the North Verge of the Upper Yangtze Block

通过对上扬子地块北缘大巴山构造带与碑坝穹窿构造带中震旦系灯影组硅质岩的硅、氧同位素进行研究以探究其成因.结果显示,研究区硅质岩及石英脉中δ30Si值为0.6‰～1.6‰,全为正高值,与沉积成因硅质岩的δ30Si值十分接近,并且该地区当时处于浅海陆棚环境,沉积物受陆源碎屑影响较大,也说明其为沉积成因;另外,硅质岩及石英脉中δ18 O值为20.3‰～21.6‰,与沉积成岩石英的δ18O一致,通过硅质岩氧同位素地质温度计计算得出,该地区硅质岩形成温度明显的高于古海水温度,表明研究区有海底热水的参与.最后推断研究区硅质岩系是沉积成因的,且在沉积过程中有海底热水的参与.

The genesis of the Sinian Dengying siliceous rocks in the Dabashan and the Beiba dome tectonic belts, north Verge of the Upper Yangtze block, was investigated by studying their silicon and oxygen isotopes. The δ30 Si values of the siliceous rocks and the quartz veins in the study area were in the range of 0.6‰-1.6‰. These values are all positive high values and are very close to those of sedimentary originated siliceous rocks, other studies had showed that the study region was in a neritic platform environment with great effect from terrigenous clastics, all of these suggested that the siliceous rocks are sedimentary originated. The δ18O of siliceous rocks and quartz veins in the study area are in the range of 20.3‰-21.6‰, consisting with the δ18O values of sedimentary rocks. The geological thermometer calculation of the siliceous rocks using oxygen isotope showed that the formation temperature of silicalites in this area was significantly higher than that of the ancient sea, indicating effects of submarine hot water. In summary, we concluded that the siliceous rock series in the study area were sedimentary originated and were affected by submarine hot water during deposition.