| 晋东北侏罗纪盆地早中侏罗世沉积充填记录及其构造意义 |
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| 关键词:Jurassic basin Early-middle Jurassic sedimentary cycle heavy minerals zircon U-Pb geochronology |
| 基金项目:中国地质科学院地质力学研究所基本科研业务费项目(编号: DZLXJK201208);国家专项“深部探测技术与实验研究”(编号: SinoProbe-08-01);国家自然科学基金项目(编号: 41372122);中国地质调查局地质调查项目(编号: 1212011121095) |
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| Early-Middle Jurassic Basin-fill Record of the Basin Groups in Northeastern Shanxi and Its Tectonic Implications |
| A series of significant geological processes termed as the “Yanshanian movement”, comprising such activities as tectonic deformation, magmatic-metallogenic systems, abrupt changes of climate and environment, occurred in the central and eastern parts of China as well as eastern Asia in the transition period of Jurassic and Cretaceous, but the initiation timing as well as the development process of the “Yanshanisn movement” has not been well established, and some controversies still exist. In this study, the timing of Yanshanisn movement initiation was revealed by investigating the Jurassic basin of northeastern Shanxi, and the initiation timing of the Yanshanian movement was analyzed in detail by determining the boundaries of sedimentary cycles, identifying the heavy minerals assemblage type in clastic rocks and conducting zircon U-Pb isotope dating. The results indicate that the Jurassic orogeny was probably initiated during the sedimentation period of basal conglomerate of the middle Jurassic Yungang Formation (J2yg). The switch from transgressive lacustrine deposition to regressive lacustrine deposition in the sedimentary successions of the Middle Jurassic Yungang Formation (J2yg) indicates that the regional stress field might have changed from early expansion to late compression. In addition, the change in primary constituents from early quartz-feldspar to late feldspar-detritus was observed in clastic rocks. Meanwhile, the heavy mineral assemblage was predominated by stable zircon at the early stage and by relatively stable garnet at the late stage. The timing of the conglomerate development at the bottom of the Middle Jurassic Yungang Formation (J2yg) is probably ~168.0 Ma, as inferred from the age of zircons in tuffaceous micrite ((160.6±0.55) Ma) on the top of the Middle Jurassic Yungang Formation (J2yg) and the age of zircons in pyroclastic rock((179.2±0.79) Ma)in the middle of lower Jurassic Yongdingzhuang Formation (J1y). The age of 168.0 Ma is believed to be the timing of Yanshanian movement initiation. The results presented in this study provide a new sedimentary constraint on the timing of Yanshanian movement initiation. |
| LI Zhen-hong,DONG Shu-wen,QU Hong-jie.2014.Early-Middle Jurassic Basin-fill Record of the Basin Groups in Northeastern Shanxi and Its Tectonic Implications[J].Acta Geoscientica Sinica,35(3):285-294. |
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