摘要
运用LA-ICP-MS锆石U-Pb年代学方法,分析探讨了鄂尔多斯盆地南缘南曹德组和庄河沟组的沉积时代、物源特征及其所处的华北(鄂尔多斯地块)与北秦岭地体之间的构造演化关系。结果表明:两件砂岩样品的碎屑锆石年龄谱基本一致,测年数据集中分布在820~995 Ma(n=13)、1041~1203 Ma(n=23)、1223~1451 Ma(n=36)、1458~1650 Ma(n=24)、1659~1935 Ma(n=39)、2017~2445 Ma(n=7)6个区间,对应的峰值年龄分别接近832Ma、1120 Ma、1330 Ma、1590 Ma、1856 Ma和2090 Ma。这与邻区经典的震旦系正目观组和罗圈组具有相似的碎屑锆石年龄谱特征,年轻主峰年龄832Ma,包含有4个820~834Ma的年轻单颗粒锆石年龄,显著有别于以往认为与之可比的研究区近邻剖面锆石U-Pb高频主峰年龄主要集中在454Ma的奥陶系平凉组,由此认为南曹德组和庄河沟组应属于新元古代晚期832Ma之后或震旦纪的沉积岩石单元。锆石U-Pb年龄谱的区域对比进一步揭示,南曹德组和庄河沟组的滨浅海沉积碎屑物源明显具有来自华北(鄂尔多斯)陆块与北秦岭(杂岩)地体的双向混合物源特征,表明华北陆块与北秦岭地体至少在832Ma之前的格林威尔晚期已经碰撞拼合为一体,随后在新元古代晚期拼合大陆边缘接受了大致与Rodinia超大陆裂解事件相当的陆缘海相碎屑岩沉积。
The south Ordos basin（S-OB）is located at the west part of the South-sector of North China Block（SNCB）,involved in the multiple orogeny of the North Qinling Belt（NQB）that is composed of the S-NCB to the north and the north Qinling terrain（NQT）to the south.The pre-Ordovician tectonic correlation between the NQT and NCB,as well as the tectonic affinity of the NQT,is still controversial.Here,detrital zircon U-Pb dating analysis of 2-sample sandstones from the neritic-littoral deposits of Nancaode and Zhuanghegou Formations,outcropped in the S-OB,are carried out at the State Key Lab.of Continental Dynamics,China.All the concordant zircons（n=155）from sampled sandstones show broadly similar age patterns with a wide range of 825～2445 Ma.The largest population of zircons exhibits ages of 1659～1935 Ma（n=39）with a peak age at ca.1.86 Ga;and the subordinate populations display ages of2017～2445 Ma（n=7）,1458～1650 Ma（n=24）,1223～1451 Ma（n=36）,1041～1203 Ma（n=23）and825～995 Ma（n=13）with the peak ages of ca.2.09 Ga,1.59 Ga,1.33 Ga,1.12 Ga and 0.83 Ga,respectively.It indicates that the detritus of the the 2-formation deposites were mainly sourced from the metamorphic basement rocks of the NCB and subordinately from the complex and igneous rocks of the NQT.Also,the spectrum of the 2-sample zircon ages,with youngest peak age of 832 Ma,is quite similar to that of interlayered sandstones of the late Neoproterozoic（Sinian）tillites exposed in the neighbor study areas of the southwest Ordos basin,but very different from that of sandstones of the Ordovician Pingliang formation outcropped in the S-OB,suggesting the deposit time of the analyzed sample host rocks to be late Neoproterozoic（Sinian）with no more than ca.0.83 Ga.All of the above reveal that the sedimentary sources of late Neoproterozoic Nancaode and Zhuanghegou Formations are bidirectionally from the NCB and NQT,indicating the NQT was amalgamated to the NCB during the Grenvillian collision to late uplift process.So,it
作者
康昱
陈刚
夏晓雨
任帅锋
张卫刚
师平平
KANG Yu;CHEN Gang;XIA Xiaoyu;REN Shuaifeng;ZHANG Weigang;SHI Pingping(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi＇ an,710069;Changqing Oil field Company,PetroChina Company Limited,CNPC,Xi＇ an,710021)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2018年第9期1829-1842,共14页
Acta Geologica Sinica
基金
国家自然科学基金重点项目(编号41630312)
大陆动力学国家重点实验室科技部重点专项(编号BJ14252)
国家基础科学人才培养基金(编号XDCX2016-16)
中国地质调查局海相油气资源调查项目(编号1212011220761)联合资助成果
