内蒙古索伦地区晚古生代沉积构造背景——来自上二叠统哲斯组碎屑锆石年代学的制约

LATE PALEOZOIC SEDIMENTARY TECTONIC SETTING IN SUOLUN AREA OF INNER MONGOLIA:Evidence from the Detrital Zircon Chronology of Upper Permian Zhesi Formation

上二叠统哲斯组广泛出露于东北地区南部,主要由砂岩、泥岩、灰岩、页岩组成,含腕足、苔藓虫和腹足化石.对内蒙古索伦地区的哲斯组中粗粒长石岩屑砂岩和中细粒长石砂岩样品进行了LA-ICP-MS锆石U-Pb测年,数据记录了4个年龄区间:(265±2)~(348±8)Ma,峰值年龄为(272±2)Ma;(358±3)~(453±4)Ma,峰值年龄(403±3)Ma;(470±6)~(555±4)Ma,峰值年龄为(511±3)Ma;剩余的前寒武纪锆石(693±7)Ma,(834±9)Ma,(854±6)Ma,(886±5)Ma,(1175±7)Ma,(1440±8)Ma,(1748±17)Ma和(2150±13)Ma.其中峰值年龄为272 Ma的锆石年龄占绝对优势(达到51%),并与大石寨组火山岩和北侧的岛弧岩浆岩一致,403 Ma和511 Ma峰值年龄为东北地区泛非期变质杂岩的年龄范围,其余古老年龄也均为大兴安岭变质基底的年龄范围.上述年龄特征显示,哲斯组物源主要来自相邻地区分布的早古生代岛弧火山岩,少量来自东北相邻地块的变质基底.鉴于东北地区哲斯组分布范围广,岩性多为碳酸岩和碎屑岩,古生物化石保存完整,沉积环境稳定,证明哲斯组应为大陆边缘沉积.

The Upper Permian Zhesi Formation widely distributed in the southern Northeast China is mainly composed of sandstone,mudstone,limestone and shale,and contains brachiopod,bryozoan and gastropod fossils.The LA-ICP-MS zircon U-Pb dating data of medium-coarse feldspar lithic sandstone and fine-medium feldspar sandstone samples from Zhesi Formation in Suolun area of Inner Mongolia records four groups of age range,among which the zircons with the peak age of 272 Ma are predominant(51%)and consistent with the volcanic rocks of Dashizhai Formation and the island-arc magmatic rocks on the north,the peak ages of 403 Ma and 511 Ma are in the age range of Pan-African metamorphic complex in Northeast China and the other ancient ages are also covered by the age range of Daxinganling metamorphic basement.The above age characteristics indicate that the sources of Zhesi Formation are mainly the Early Paleozoic island-arc volcanic rocks distributed in adjacent areas,with a few from the metamorphic basement of northeast adjacent blocks.Considering the wide distribution of Zhesi Formation in Northeast China with mostly carbonate and clastic rocks,the well-preserved paleontological fossils and stable sedimentary environment,it is proved that Zhesi Formation should be continental margin deposits.