新疆西准噶尔包古图组凝灰岩锆石SHRIMP年龄及其地质意义

SHRIMP U-Pb zircon ages of tuff in Baogutu Formation and their geological significances

西准噶尔地区出露巨厚层的下石炭统火山-沉积岩,包括太勒古拉组、包古图组和希贝库拉斯组,前人主要通过生物化石来确定各组之间的层位关系,并存在争论。本文对包古图金矿区包古图组中3个蚀变凝灰岩样品开展的锆石SHRIMF年代学研究表明,凝灰岩的年龄分别为328.4Ma(MSWD=0.72)、342.6Ma(MSWD=0.76)和336.5Ma(MSWD=1.6)。结合太勒古拉组年代学数据和下石炭统火山-沉积地层的分布关系,确定西准噶尔下石炭统火山-沉积地层从下到上依次为:希贝库拉斯组、包古图组和太勒古拉组。

Lower Carboniferous volcanic - sedimentary rocks including Tailegula, Baogutu and Xibeikulasi formations are widely distributed in western Junggar. The ages of the three formations were defined by fossils before. Three altered tuff samples are dated to be 328. 4Ma (MSWD = 0. 72), 342. 6Ma (MSWD = 0. 76) and 336. 5Ma (MSWD = 1. 6) by zircon SHRIMP, respectively, which helps constraining the age of the Baogutu Formation. A combination of the zircon SHRIMP ages, and the distribution relationship between the three formations suggest that the Tailegula Formation is the youngest, and the Xibeikulasi Formation is the oldest in the Lower Carboniferous.