鄂尔多斯盆地中东部奥陶系马家沟组凝灰岩锆石SHRIMP U-Pb年龄、Hf同位素特征及地质意义  

Zircon SHRIMP U-Pb ages and Hf isotope characterestics of the zircons from tuff in Ordovician Majiagou Formation in the central—eastern Ordos Basin and their geological significance

作　　者：吴浩文 苏中堂[1,2,3] 裴文超 魏柳斌[1,4,5] 任静 张成弓[1,2] 付斯一 WU Haowen;SU Zhongtang;PEI Wenchao;WEI Liubin;REN Jing;ZHANG Chenggong;FU Shiyi(Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu,610059;State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Chengdu University of Technology),Chengdu,610059;Key Laboratory of Deep-time Geography and Environment Reconstruction and Applications of Ministry of Natural Resource,Chengdu University of Technology,Chengdu,610059;Research Institute of Exploration and Development,PetroChina Changqing Oilfield Company,Xi’an,710018;National Engineering Laboratory for Exploration and Development of Low-Permeability Oil and Gas Fields,Xi’an,710018)

机构地区：[1]成都理工大学沉积地质研究院,成都610059 [2]油气藏地质及开发工程国家重点实验室(成都理工大学),成都610059 [3]成都理工大学深时地理环境重建与应用自然资源部重点实验室,成都610059 [4]中国石油长庆油田公司勘探开发研究院,西安710018 [5]低渗透油气田勘探开发国家工程实验室,西安710018

出　　处：《地质论评》2024年第5期1767-1787,共21页Geological Review

基　　金：中国石油长庆油田重大科技专项(编号:CQZDZX2021)的成果。

摘　　要：鄂尔多斯盆地奥陶系马家沟组五段(以下简称马五段)上部发育两层凝灰岩,通常作为地层划分的区域标志层,研究凝灰岩锆石年龄能厘定马家沟组年代地层格架并确定其沉积期的构造背景。对盆地S148井和T56井马五段凝灰岩进行锆石SHRIMP U-Pb定年及Hf同位素特征分析,得到两组锆石年龄458.4±2.4 Ma和460.9±2.9 Ma,将马家沟组沉积期厘定为中奥陶统达瑞威尔阶—上奥陶统桑比阶。锆石微区原位Hf同位素测试点n(176Hf)/n(177Hf)值变化范围为0.282687~0.280820,εHf(t)值在6.67~11.32之间,二阶段模式年龄变化范围为720~1024 Ma。对比盆地周缘凝灰岩锆石U-Pb年龄及Hf同位素特征,认为马家沟组凝灰岩可能来自于盆地西南方向的北秦岭和/或北祁连造山带,凝灰岩就位前北秦岭洋和/或北祁连洋开始向北俯冲消减进入洋陆转换阶段,中奥陶世晚期盆地西南缘开始转化为活动大陆边缘。Objectives:The Ordovician Majiagou Formation has become the most popular carbonate formation in the Ordos Basin due to its potential for oil and gas exploration,but its age attribution remains controversial.In the Ordos Basin,two layers of tuff develop in the upper part of the 5th Member of the Ordovician Majiagou Formation(hereinafter referred to as the“Ma-5”Member),which are commonly used as regional marker beds for stratigraphic division.Studying the zircon ages of these tuffs can establish the chronological stratigraphic framework of the Majiagou Formation and determine the tectonic setting during its depositional period.Methods:We conducted zircon SHRIMP U-Pb dating and in-situ Hf isotopic characteristic analyses on the tuffs of the Ma-5 Member from the Well S148 and the Well T56 in the Ordos Basin.Results:The zircon SHRIMP U-Pb dating result of the tuff shows that the 206 Pb/238U ages of the tuff sample from the Well T56 ranges from 442.3 Ma to 474.3 Ma,with a weighted average age of 460.9±2.9 Ma,and those of the tuff sample from the Well S148 ranges from 442.0 to 471.6 Ma,with a weighted average age of 458.4±2.4 Ma.The measured n(176Hf)/n(177Hf)ratios of in-situ zircon Hf isotopes range from 0.282687 to 0.280820,andεHf(t)values vary from 6.67 to 11.32,with two-stage model ages ranging from 720 to 1024 Ma.Conclusions:Based on the zircon age results from the tuff of the Ma-5 Member,the depositional period of the Ma-5 Member has been constrained to the Middle Ordovician Darriwilian Stage to the Upper Ordovician Sandbian Stage.A comparison of the U-Pb ages and Hf isotope characteristics of zircons from the tuffs at the periphery of the Ordos Basin suggests that the volcanic tuffs of the Ma-5 Member may have originated from the North Qinling and/or North Qilian orogenic belts in the southwestern part of the basin.Furthermore,it is inferred that prior to the emplacement of the tuffs,the North Qinling and/or North Qilian Ocean initiated a northward subduction and entered a stage of ocean—land transition,

关 键 词：锆石U-Pb年龄 Hf同位素 凝灰岩 达瑞威尔阶 马家沟组 

分 类 号：P618.13[天文地球—矿床学]