贺兰山构造带构造—地层层序及构造演化

Tectono‑stratigraphic sequence and tectonic evolution in the Helanshan Mountains tectonic belt

贺兰山构造带及邻区形成演化经历有多期叠加改造和多个伸展—聚敛旋回构造运动,形成了区域内多套构造—地层层序,因此,开展贺兰山构造带构造—地层层序及构造演化研究对深入理解其地质结构和油气勘探有着重要的意义。本文旨在综合利用野外调查、地震数据和1:50000区域地质资料,采用野外实地调查和地震剖面精细解析相结合的方法对研究区区域不整合面的分布特征和规律进行详尽分析研究,根据区域不整合面的发育特征,建立区域地层年代格架,划分构造—地层层序,进而对盆地演化阶段进行探讨。研究表明,研究区自下至上发育Pt2Ch‑Jx/Pt1、Є1/AnЄ、C2/O、T/P、J1‑2/An J、K1/An K1、E3q—N/AnE,据此将研究区垂向上划为7个构造—地层层序:基底构造层、中元古界构造层、震旦系—奥陶系构造层、石炭系—三叠系构造层、侏罗系构造层、下白垩统构造层、新生界构造层。贺兰山构造带构造演化经历中新元古代—早古生代陆缘盆地坳陷—裂谷演化阶段;晚古生代—中三叠世陆相盆地坳陷沉积阶段;晚三叠世局部伸展;中侏罗世—早白垩世大规模逆冲推覆阶段,普遍发育多条大型北东向逆冲断裂;始新世开始进入盆—岭构造形成阶段。

The tectonic evolution of the Helanshan Mountain tectonic belt(the following refers to as“HTB”)have undergone multiple periods superimposed transformation and multiple extension‑convergent cycles of tectonic movement,forming multiple sets of structure stratigraphic sequences.Therefore,it is of great significance and practical value to study the tectono‑stratigraphic sequence and tectonic evolution of the HMTB,which can deepen the understanding of the geological structure and the petroleum exploration.In order to carry out the stratigraphic sequence,the regional unconformity distribution characteristics are studied and chronostratigraphic framework section are established by the field investigation,the seismic data and the 1∶50000 regional geological survey data.then the division of tectonic‑stratigraphic sequence and evolution stage are discussed.The results show that,7 different types of unconformities are identified from the bottom to the top,namely:Pt2Ch‑Jx/Pt1,Є1/AnЄ,C2/O,T/P,J1‑2/An J,K1/An K1,E3q—N/AnE,which represent the regional reflection of crustal movement.According to the development characteristics of the unconformable surface,the study area is vertically divided into 7 structure‑stratigraphic sequences,which are from bottom to top:basement tectonic layer,Middle Proterozoic tectonic layer,Sinian‑Ordovician structural layer,Carboniferous‑Triassic structural layer,Jurassic structural layer,Lower Cretaceous structural layer and Neozoic structural layer.The results show that the HTB underwent the Middle Neoproterozoic‑Early Paleozoic continental margin basin depression‑rift evolution stage;Late Paleozoic‑Middle Triassic continental basin depression sedimentary stage;local extension of Late Triassic;in the Middle Jurassic‑Early Cretaceous stage of massive thrust;the Eocene began to enter the basin‑ridge tectonic formation stage.