The Cenozoic Tectono‐Thermal Evolution of Depressions Along Both Sides of Mid‐Segment of Tancheng‐Lujiang Fault Zone, East China

AbstractThere are many depressions along both sides of the Tancheng‐Lujiang (Tanlu) Fault zone, and their tectono‐thermal evolution histories played an important role in the hydrocarbon generation and accumulation within the depressions. The Cenozoic thermal gradient evolution histories of 120 wells in six depressions along the middle part of Tancheng‐Lujiang Fault Zone were modeled by using the vitrinite reflectance and apatite fission track data in this paper. Based on these modeling results, the characteristics of thermal evolution of the Jiyang, Changwei, Linqing, Jizhong, Bozhong, and Huanghua depression were analyzed. Generally, the thermal gradients of the depressions decreased during the Cenozoic time. The thermal gradients were relatively high in the Paleogene, but in the Neogene they were only a little higher than that of present‐day. The modeling results of thermal history and the tectonic subsidence history reconstruction fit well with the evolution stages of riftsubsidence basin to down‐warped basin. The thermal gradients are different in six depressions and decrease with the increasing distance to the Tanlu fault zone. The thermal gradients were higher in the depressions within the Tanlu Fault zone, such as Liaohe basin, Bozhong and Changwei depression, with the gradient up to 57~59°C/km in the early Paleogene, and they maintained the high level during the whole Cenozoic time in Changwei depression and Liaohe basin. The relatively lower gradient in the Bozhong depression was resulted from large amount of tectonic subsidence during the Neogene. However, the thermal gradients and their evolution in the Jizhong and Linqing depressions far away from Tanlu Fault zone were lower with 53°C/km and 50°C/km respectively in the early Paleogene. The above results show that the activity of Tanlu Fault zone in Cenozoic played an important role in the thermal fields of these depressions. The different thermal fields of the depressions along the both sides of mid‐segment of the Tanlu Fault zone were macro‐controlled by the evolution of Tanlu Fault and partly controlled by the depression‐controlling faults at the same time.