川西新元古界开建桥组底部沉凝灰岩锆石SHRIMP U-Pb年龄及其地质意义

ZIRCON SHRIMP U-Pb AGE OF SEDIMENTARY TUFF AT THE BOTTOM OF NEOPROTEROZOIC KAIJIANQIAO FORMATION IN WESTERN SICHUAN,AND ITS GEOLOGICAL IMPLICATION

从凉红-苏雄剖面开建桥组底部沉凝灰岩中获得了801.3 Ma±7.2 Ma锆石SHRIMP U-Pb年龄,与前人获得的苏雄组803 Ma±12 Ma年龄高度一致,不仅有效地约束了开建桥组的沉积时代,还从地质年代学上进一步证实了两者之间的同时异相关系,为华南新元古界地层格架的建立提供了新的年龄证据。结合前人研究成果,本文认为开建桥组的沉积时限为800 Ma^725 Ma,与康滇地区澄江组、扬子东南缘莲沱组和上墅组可以对比。同位素年代学、岩石地球化学及沉积学等研究表明,800 Ma左右是整个华南地区裂谷盆地沉积充填序列第二个旋回的开启时间。

It was generally considered that Suxiong Formation and Kaijianqiao Formation were the contemporaneous deposits with different facies,however,it was absence of high-quality chronological data constraint.This paper reported firstly the zircon SHRIMP U-Pb age of 801.3 Ma±7.2 Ma from the sedimentary tuff in the bottom of Kaijianqiao Formation at the Lianghong-Suxiong section.The age was highly consistent with the existed data（803 Ma±12 Ma）of Suxiong Formation,which restricted effectively not only the depositional time of Kaijianqiao Formation,but also confirmed further those were contemporaneous deposits with different facies,geochronologically,providing a new evidence to establish the Neoproterozoic stratigraphic framework in South China.This paper regarded the depositional timing of Kaijianqiao Formation was 800Ma-725Ma,correlated with Chengjiang Formation in the Kangdian rift basin,Liantuo Formation and Shangshu Formation in the southeastern margin of Yangtze Block.These researches of the isotopic chronology,petrogeochemistry and sedimentology etc suggested that ca.800 Ma was the opening time of the second sedimentary sequence cycle of rift basins in South China.