合肥盆地中生代地层锆石年代学分析及其大地构造意义

发布时间：2018-06-16 15:19

本文选题：合肥盆地 + 沉积时代　；参考：《合肥工业大学》2017年硕士论文

【摘要】：合肥盆地位于大别造山带北侧、郯庐断裂带西侧,其发育过程与这两大构造带演化密切相关。本次工作对合肥盆地南部与东部出露的中生代砂岩与火山岩进行了锆石年代学研究,从而限定了各组地层的沉积时代,确定了火山岩喷发时间,指示了沉积物的源区。这些年代学数据表明,合肥盆地南部的中生代碎屑岩自下而上分别为下侏罗统防虎山组、中侏罗统圆筒山组或三尖铺组、下白垩统凤凰台组与周公山组(或黑石渡组)与上白垩统戚家桥组,其间缺失上侏罗统。盆地东部白垩系自下而上为下白垩统朱巷组与响导铺组和上白垩统张桥组。该盆地出露的毛坦厂组或白大畈组火山岩喷发时代皆为早白垩世(130-120 Ma)。盆地南部的下—中侏罗统及白垩系源区皆为大别造山带,分别对应该造山带的后造山隆升与造山后伸展隆升。而盆地东部白垩系的源区一直为东侧的张八岭隆起带,后者属于郯庐断裂带伸展活动中的上升盘。华北板块和华南板块在中三叠世沿着秦岭-桐柏-红安-大别造山带发生陆-陆碰撞,造山带北部秦岭-桐柏造山带微陆块以具有古生代弧岩浆活动为显著特征。然而,人们尚不确定它是否能向东延伸到大别造山带形成一条条带状微大陆。为了解决这个问题,我们又对合肥盆地南部北淮阳构造带佛子岭群变质砂岩进行了LA-ICP-MS U-Pb锆石年代学分析。这些锆石年代学信息与前人地球物理学数据显示,大别造山带北部也存在一微陆块—北淮阳微陆块,介于肥中缝合线(古生代)和晓天-磨子潭缝合线(三叠纪)之间。北淮阳微陆块北部被合肥盆地沉积物覆盖,仅南部出露地表。由于二郎坪洋向南俯冲,北淮阳微陆块于早古生代出现弧岩浆活动。晚古生代期间,北淮阳微陆块南侧的古特提斯洋向北俯冲,该微陆块也相应出现了弧岩浆活动。早泥盆世末期,通过弧—陆碰撞,北淮阳微陆块成为华北板块南缘的增生体。由此表明,与秦岭-桐柏造山带相似,大别造山带也由北部古生代增生体系和南部三叠纪碰撞体系组成。在华北与南华板块三叠纪最终碰撞之前,整个秦岭-桐柏-红安-大别造山带中存在一条长度超过900 km,宽度约为50-100 km的条带状微陆块,可能起源于中新元古代沿扬子板块边缘的大陆裂解。
[Abstract]:The Hefei basin is located in the north of the Dabie orogenic belt and in the west of the Tanlu fault zone. The development process of the basin is closely related to the evolution of the two tectonic belts. The zircon chronology of Mesozoic sandstone and volcanic rocks exposed in the southern and eastern part of Hefei basin has been carried out in this work, thus limiting the sedimentary age of each group of strata, determining the eruption time of volcanic rocks and indicating the source region of the sediments. These geochronological data indicate that the Mesozoic clastic rocks in the southern part of Hefei Basin are the Lower Jurassic Fanghushan formation, the Middle Jurassic Cylindrical formation or the Sanjianpu formation from the bottom to the top, respectively. The lower Cretaceous Fenghuangtai formation, Zhougongshan formation (or Heshidu formation) and Upper Cretaceous Qijiaqiao formation are missing from the upper Jurassic. The Cretaceous system in the eastern part of the basin is composed of the lower Cretaceous Zhuxiang formation, the Xiangdaopu formation and the Upper Cretaceous Zhangqiao formation from the bottom to the top. The volcanic rocks of Maotanchang formation or Baidafan formation exposed in this basin are of early Cretaceous age of 130-120 Ma. The lower-middle Jurassic and Cretaceous source areas in the southern part of the basin are Dabie orogenic belts, respectively, for the post-orogenic uplift and post-orogenic extension uplift of the ought orogenic belt. The source region of the Cretaceous in the eastern part of the basin is the Zhangbaling uplift belt in the east, which belongs to the uplift in the extension of the Tanlu fault zone. In the Middle Triassic, the North China plate and the South China plate collided with each other along the Qinling-Tongbai-Hongan-Dabie orogenic belt. The microcontinental blocks of the Qinling-Tongbai orogenic belt in the northern part of the orogenic belt are characterized by Paleozoic arc magmatic activity. However, it is not certain whether it can extend eastward to the Dabie orogenic belt to form a strip of microcontinents. In order to solve this problem, LA-ICP-MS U-Pb zircon chronology analysis has been carried out for the metamorphic sandstone of the Foziling Group in the northern Huaiyang structural belt in the southern part of Hefei Basin. These zircon chronological information and previous geophysical data show that there is also a microcontinental block in the northern part of the Dabie orogenic belt, which lies between the suture line in Fizhong (Paleozoic) and the suture line of Xiaotian-Mozitan (Triassic) in the northern part of the Dabie orogenic belt. The north Huaiyang microcontinental block is covered by the sediments of Hefei basin, only the southern part is exposed to the surface. Due to the subduction of Erlangping Ocean to the south, arc magma occurred in the early Paleozoic in the North Huaiyang microcontinental block. During the late Paleozoic, the PaleoTethys ocean on the southern side of the North Huaiyang microcontinental block subducted northward, and the arc magma occurred accordingly. At the end of the early Devonian, the North Huaiyang microcontinental block became an accretionary body in the southern margin of the North China plate by arc-continent collision. It is shown that the Dabie orogenic belt, similar to the Qinling-Tongbai orogenic belt, is also composed of the northern Paleozoic accretive system and the southern Triassic collision system. Before the Triassic Triassic collision between North China and South China, there was a strip of microcontinental block in the Qinling Tongbai Hongan-Dabie orogenic belt with a length of more than 900 km and a width of about 50-100 km. It may originate from the continental fragmentation along the margin of the Yangtze plate in the MesoNeoproterozoic.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P597.3;P542

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