The Depositional Response Of Hefei Basin To The Activities Of Tan-Lu Fault Zone

Hefei basin that is located on the southern fringe of the North China plate and by the side of Tan-Lu fault zone is a Mesozoic Cenozoic continental basin. The formation and evolution scenario of the basin are interrelated directly with the activities of Tan-Lu fault zone. The deposition shows a good response relationship to the structures of the fault. The fault zone has been controlling the deposition of Hefei basin all the time.The pre-Jurassic basement of Hefei basin was composed of thrusts. Indosinian foreland thrusts in pre- Jurassic bedrocks of the basin increase towards the Tan-Lu fault zone, indicating Indosinian activity of the fault zone. Appearance of marginal faces, parallel depositional center near the Tan-Lu fault zone, the obvious faulted down boundary in the eastern part and the overlapping boundary from east to west inside the basin indicated that the fault zone occurred as the eastern boundary of the basin in Jurassic and acted as provenance of the basin in east due to strike-slip uplifting of the Zhangbaling belt. Fiv40Ar/39Ar plateau ages of muscovite from the Tan-Lu strike-slip mylonite on the eastern margin of the Dabie orogenic belt are 192.5 ± 1.7Ma,196.6±3.9Ma, 189.7 ±0.6Ma,197.8 ±1.3Ma and 190.4± 1.1Ma which represent cooling ages of syn-orogenic strike-slip faulting. These phenomena suggest that Tan-Lu fault zone originated from Inosinian continent-continent collision between the North and South China plates. The Tan-Lu fault zone started as a transform fault during the collision. The basin was controlled by both Dabie orognic belt and Tan-Lu fault zone. The model of the basin is a complex type that was composed of foreland and strike-slipping flexure in this period.The depositional character of Zhuxiang formation in the basin reads as follows: A series of NNE alluvial fan were formed along the fault. The half-deep lake to deep lake faces appeared by west side of the fault, towards the west the saucer lake faces, shore deposit and flood plain face appeared in proper order. The depositional center of lower Cretaceous was formed in eastern part of the basin, and the depositional depth was pinch-out and thinning out from the east to the west. The tectonic framework of eastern faulting and west overlapping were formed. According to the characters of the compositional heavy mineral, diameter and composition of gravel, primary sedimentary structure, the sediments came from east part of the basin. They had distinguishing feature of near provenance and quickly deposit. These phenomena show that the fault has strongly activities at the same time. At that time Tan-Lu fault zone occurred a large-scale left-lateral displacement. The strike-slip movement on the Tan-Lu fault zone caused the Zhangbaling uplifting which became source region and the Hefei basin appeared strike-slip flexure at the west side of the fault. In this time the strike-slipping mylonite, ultramylonite as well as associated igneous and magmatic intrusion and eruptive activity of volcano were formed along the fault. The 40Ar/39Ar values of the mylonite is 120Ma, The 40Ar/39Ar values of muscovite from magmatic body that formed along the fault are 127.87 ±0.46Ma, 120.00 ± 0.5Ma,the K-Ar data from volcanic rock is 119.2 ±2.3Ma.These dating demonstrate that the faultbelt has experienced sinistral strike-slip movement in the Early Cretaceous. The strike-slip event in early Cretaceous made the largest contribution to the basin was that It broke the basin pattern of foreland and strike-slipping flexure in Indosinian and went into a newly NNE structure pattern. This indicated that the tectonic scenario of the basin had been changed from Teties structure to the Pacific tectonics.The extensional activities of Hefei basin occurred in the period between Late Cretaceous and Paleogene. As a result, the extensional normal faults were took place along the pre-existing nearly EW faults and the Tan-Lu fault zone. The deposition of half-graben was formed. But it appeared east faulting and west overlapping along the Tan-Lu...