北山红石山地区晚古生代火山岩LA-ICP-MS锆石U-Pb年龄及其构造意义

北山地区古亚洲洋的闭合时间和晚古生代构造演化倍受关注且久有争议.晚古生代地层及其接触关系对探讨以上问题具有重要意义,但该区地层学研究薄弱,很大程度上制约了对构造演化的深入讨论.本文获得的北山红石山地区上古生界“下石炭统绿条山组、白山组”和“下二叠统双堡塘组”火山岩的LA-ICP-MS锆石U-Pb年龄,分别为296.8±3.5Ma、314.9±3.3Ma和299.4±5.9Ma,时代为晚石炭世-早二叠世,相当于北山地区干泉组层位.原“白山组”与“双堡塘组”之间的平行不整合不成立,表明石炭纪-二叠纪为同期裂谷盆地.原“绿条山组”与中泥盆统的角度不整合实为干泉组与中泥盆统的角度不整合,代表了古亚洲洋的闭合与增生造山时间发生在中泥盆世与早石炭世之间.

LA-ICP-MS zircon U-Pb dating of the Late Paleozoic volcanic rocks from the Hongshishan area of the Beishan orogenic belt and its tectonic significances

Much remains to be discovered concerning the time of collision of the Paleoasian Ocean and the Late Paleozoic evolution in the Beishan orogenic belt. The insufficient research on the Late Paleozoic strata of the Beishan orogenic belt, to a great extent, limits the further discussion of the tectonic evolution. This paper shows that the LA-ICP-MS zircon U-Pb ages of the "Early Carboniferous Lvtiaoshan and Baishan formations" and the "Early Permian Shuangbaotang Formation" volcanics from the Hongshishan area are 296.8±3.5Ma, 314.9±3.3Ma, and 299.4±5.9Ma respectively, which belong to the Late Carboniferous-Early Permian Ganquan Formation of the Beishan orogenic belt. The relationship between the "Shuangbaotang Formation" and "Baishan Formation" should not be disconformable as thought before, which suggests an entire Carboniferous-Permian rift basin. And the unconformity between the "Lvtiaoshan Formation" and the Middle Devonian could be the one between the Ganquan Formation and the Middle Devonian, which implies the closure of the Paleoasian Ocean between the Middle Devonian and Early Carboniferous.