CAJ | 학술논문

沉积盆地地层序列中的凝灰岩是源区造山活动的直接产物，与造山带的活动性密切相关。鄂尔多斯及周缘盆地下侏罗统凝灰岩的相继发现，对于探讨早侏罗世构造演化的关键时限和大地构造背景提供了证据。以凝灰岩的锆石U-Pb年代学为线索，厘定了早侏罗世凝灰岩喷发的期次及关键时限，同时辅助以重点区域凝灰岩的地球化学特征，探讨了凝灰岩喷发的大地构造背景。研究认为：①下侏罗统凝灰岩分布具有明显的区域性，集中分布在鄂尔多斯盆地西南缘平凉、安口一带，鄂尔多斯盆地东北缘的宁武-静乐盆地及广灵盆地内，与北秦岭造山带和燕山造山带的演化密切相关；②不同地区凝灰岩的喷发时限并不完全具有等时性，鄂尔多斯西南缘平凉策底、安口地区凝灰岩的时代分别为175.2 Ma ±2.4 Ma和168.4 Ma ±1.3 Ma，宁武-静乐盆地陈家半沟剖面火山碎屑岩的时代为179.2 Ma ±0.79 Ma，浑源-广灵盆地板塔寺剖面凝灰岩的年龄为171 Ma ±1.0 Ma，总体上处于早侏罗世晚期至中侏罗世早期；③在凝灰岩微量元素Th/Hf-Ta/Hf构造环境判别图解中，所有投点全部落入了大陆裂谷带或者初始裂谷玄武岩区，反映了早侏罗世至中侏罗世早期鄂尔多斯及周缘地区整体上处于陆内拉张的构造背景。凝灰岩喷发时限的确定，也为鄂尔多斯盆地中生代热演化年代学的研究提供了直接的证据。
침적분지지층서렬중적응회암시원구조산활동적직접산물，여조산대적활동성밀절상관。악이다사급주연분지하주라통응회암적상계발현，대우탐토조주라세구조연화적관건시한화대지구조배경제공료증거。이응회암적고석U-Pb년대학위선색，전정료조주라세응회암분발적기차급관건시한，동시보조이중점구역응회암적지구화학특정，탐토료응회암분발적대지구조배경。연구인위：①하주라통응회암분포구유명현적구역성，집중분포재악이다사분지서남연평량、안구일대，악이다사분지동북연적저무-정악분지급엄령분지내，여북진령조산대화연산조산대적연화밀절상관；②불동지구응회암적분발시한병불완전구유등시성，악이다사서남연평량책저、안구지구응회암적시대분별위175.2 Ma ±2.4 Ma화168.4 Ma ±1.3 Ma，저무-정악분지진가반구부면화산쇄설암적시대위179.2 Ma ±0.79 Ma，혼원-엄령분지판탑사부면응회암적년령위171 Ma ±1.0 Ma，총체상처우조주라세만기지중주라세조기；③재응회암미량원소Th/Hf-Ta/Hf구조배경판별도해중，소유투점전부락입료대륙렬곡대혹자초시렬곡현무암구，반영료조주라세지중주라세조기악이다사급주연지구정체상처우륙내랍장적구조배경。응회암분발시한적학정，야위악이다사분지중생대열연화년대학적연구제공료직접적증거。
Tuff in stratigraphic sequences of sedimentary basins is a direct product of the orogenic activity of the source region,and is closely related to orogenic activity .The successive discovery of the Lower Jurassic tuff in Ordos Basin and its periphery is very important for constraining the key timing of tectonic evolution and tectonic background .In this pa-per,we determined the critical time of tuff eruption for the Lower Jurassic using zircon U-Pb geochronology .In conjunc-tion with the tuff geochemistry in the key areas ,we discussed the tectonic background for tuff eruption .The following re-sults were obtained .The distribution of the Lower Jurassic tuff show obvious regional differences .They mainly occur in the Pingliang and Ankou counties in the southwestern Ordos Basin and in the Ningwu-Jingle Basin and Guangling Basin of the northeastern Ordos Basin ,and are closely related to the evolution of the North Qinling Orogenic belt and the Yanshan Orogenic belt .The eruption of tuff is not completely synchronous in different regions .The tuff on Cedi section and Ankou section of the southwestern Ordos Basin are dated at 175.2 Ma ±2.4 Ma and 168.4 Ma ±1.3 Ma respectively ,the volca-niclastic rocks on the Chenjiabangou section of Ningwu-Jingle Basin at 179.2 Ma ±0.79 Ma,and the tuff on the Bantasi section of Hunyuan-Guangling Basin at 171.0 Ma ±1.0 Ma.Overall,the eruption of tuff is date at the late Early Jurassic to early Middle Jurassic .On the Th/Hf-Ta/Hf diagrams ,all the points fall into the continental rift zones or the initial rift zones,which indicates the extensional tectonic setting from the Early Jurassic to early Middle Jurassic in Ordos Basin and its periphery .The timing of tuff eruption may provide a direct chronological evidence for study of the Mesozoic thermal e-volution of the Ordos Basin .