安徽巢湖北部地区早石炭世碎屑锆石年代及其沉积意义分析

The Early Carboniferous zircon U-Pb chronology and its sedimentary significance in the northern Chaohu area,Anhui, East China

安徽巢湖北部地区石炭系出露完整,层序清楚,沉积类型多样,是下扬子地区研究石炭系的重要地区之一。本研究在分析石炭系剖面的基础上,结合U-Pb碎屑锆石年代学分析,探讨了巢湖北部地区早石炭世物源特征。本研究共对两组岩石样品进行了LA-ICP-MS U-Pb锆石年代学分析,第一组样品为采集于高骊山组中段的砂岩,第二组样品为采集于和州组顶部的砂屑生屑灰岩。高骊山组样品锆石最晚年龄为404.4±10.2Ma,最早年龄为3194.1±40.7Ma,获得了两个峰值年龄435±6Ma与846±14Ma。和州组样品锆石最晚年龄为410±10.8Ma,最早年龄为2780±46.0Ma,获得了两个峰值年龄448±20Ma与849±12Ma。早石炭世沉积特征及年龄数据表明,巢湖北部地区早石炭世的陆源碎屑沉积主要来源于扬子海周围晋宁期及加里东期形成的古陆,部分沉积物可能来自其他古陆。

The Carboniferous system is well developed in the northern Chaohu area, the sequence and boundaries of different formations are clear, sedimentary types are very abundant. This area is one of the key places for the Carboniferous researches in China. Based on sedimentary characteristics, and detrital zircon U-Pb chronology characteristics, provenance of the Lower Carboniferous debris in this area are discussed. Samples for LA-ICP-MS zircon U-Pb dating were taken from the sandstones in the middle part of the Gaolishan Formation and biocalcarenites in the top of the Hezhou Formation respectively. Zircon concordant ages of the Gaolishan Formation are in the range of 404.4 ± 10. 2Ma to 3194. 1±40. 7Ma, peak ages are 435±6Ma and 846 ± 14Ma; zircon concordant ages of the Hezhou Formation are in the range of 410. 0 ± 10. 8Ma to 2779. 9±46.0Ma, peak ages are 849 ± 12Ma and 448 ±20Ma. Such sedimentary characteristics and zircon ages indicate that, the provenance region were closely related to the old lands around the Lower Yangtze ocean which were Formed in Jinning Period and Caledonian Period, part of the sediment may come from other ancient land.