东川、滇中地区中元古代地层格架

STRATIGRAPHIC FRAMEWORK OF THE MESOPROTEROZOIC IN DONGCHUAN AND CENTRAL YUNNAN REGION

东川、滇中地区是上扬子陆块出露元古代地层最广泛的地区,但露头又断续分布在不同的地点。由于缺乏古生物及年龄资料,在不同地区多以岩性进行地层划分与对比,而出现了"正层"与"倒层"观点之分歧。通过对东川及滇中地区地层中所夹的火山岩年龄测试及重要界面的观察与研究,发现东川地区黑山组凝灰岩中锆石U-PbSHRIMP年龄为1503±17 Ma,滇中地区黑山头组凝灰岩中锆石U-Pb SHRIMP年龄为1047±15 Ma,它们不是同一时段的沉积产物,不能进行简单地对比,并证实两个地区都为"正层序"。因而,建议各自保持自已的地层分区,独立建立自已的地层序列。

The Proterozoic strata outcrop widely in Dongchuan and Central Yunnan but the outcrops are discontinuously distributed in these areas. Due to the lack of paleontological and age data, there have been conficting views on the stratigraphic sequence and correlation of these strata. We here report a SHRIMP zircon age of 1503±17 Ma from a volcanic tuff in the Heishan Formation of the Dongchuan region, and a 1047±15 Ma SHRIMP zircon age from the Heishantou Formation in Central Yunnan. Thus, the two Formations are of different depostional ages and ther cannot be correlated. We also confirm that the stratigraphic sequences in both regions are of ＂nomal stratigraphic sequence＂. Therefore, it is recommended that the Mesoproterozoic stratigraphic units be maintained separately in these two regions because they are of different ages.