The Characteristics Of Tectonics And Paleogeothermal Field About Hefei Basin

Hefei basin, located at the South-east margin of the North-China continental block, is closely adjacent to Qinling-Dabie orogen and Tanlu fault zone. It is a multi-cycle reformed basin during the Mesozoic and the Cenozoic. According to the principles of systematic, dynamic and comprehensive, the characteristics of tectonics and paleogeothermal field of Hefei basin are studied, by means of the combinative methods of geology, geophysics and multi-testing about vitrinite reflectance and apatile fission track.At present, the main tectonic features of Hefei basin could be concluded as follows: Firstly, with the primary fault planes sloped to south, the early thrust faults are reversed to the normal lastly and have multi-period movements. Secondly, The basin has the double basements of the deformational-metamorphic crystalline basement (Archean-Paleoproterozoic) and the deformational-sedimentary basement(Mesoproterozoic-Paleozoic). Thirdly, The stucture of the basin has the feature showing belt from south to north and block from east to west. Also, The basin could be divided into three tectonic elements from south to north, such as: Shucheng depression zone in south , Hefei-Liuan taphrogen zone in central part , and Huoqiu-Zuxiang clinoform zone in north.The reconstruction of origional basin shows that Hefei basin has experiencedthree evolutionary stages during Mesozoic and Cenozoic. There are different paleotectonic elements of the basin during different periods. The paleotectonic elements of compressive-depressional basin in Jurassic could be divided into three tectonic elements such as: Shucheng depression in south, clinoform in central part, and Huoqiu uplift in north. The paleotectonic elements of shear compressive-depressional basin in early Cretaceous could be divided into four tectonic elements such as: Shucheng thrust-swell zone in south, Daqiao depression in the northeast, Shouxian-Feixi swell in central part, and Yingshang-Dingji depression in west. Thepaleotectonic elements of the extensional faulted basin in late Cretaceous-Paleogene could be divided into five tectonic elements such as: Shucheng downchasm zone, Liuan-Fanghushan fault-salient, Dingji-Feidong downchasm zone, Huoqiu-Zuxiang salient, Yingshang-Dingyuan downchasm.The reconstruction of paleogeothermal field shows that the paleogeothermal field of Hefei basin has undergone four evolutionary periods at least, such as: Pre-Jurassic middle-high paleogeothermal period, Jurassic-early Cretaceous high paleogeothermal period, late Cretaceous-Paleogene middle-low paleogeothermal period, and Neogene-Quaternary low paleogeothermal period. So, late Jurassic-early Cretaceous is the highest paleogeothermal period of Hefei basin. Furthermore, the primary generative period of the Upper Paleozoic, the Jurassic, and the Lower Cretaceous source rock is all about the late Jurassic-early Cretaceous, and the primary generative period of the Upper Cretaceous and the Paleogene source rock is about the last peried of the Paleogene .