|关键词||南黄海盆地 中部隆起 埋藏史 古地温 磷灰石裂变径迹 构造热演化史|
基于改进的McKenzie拉张模型理论，将地球动力学模拟技术与传统古温标法相结合，对南黄海北部坳陷进行构造热演化史研究，表明中部隆起和北部坳陷作为同属南黄海盆地的二级构造单元，其白垩纪以来的热史演化趋势具有一致性，整体表现为伸展断陷盆地的热史演化趋势特征，即裂陷期古热流逐渐增高，进入裂后期古热流开始降低，差异在于中部隆起古热流整体较北部坳陷低，前者晚白垩世末期最高约为70 mW/m2，而北部坳陷古新世早期可达71.7~75.5 mW/m2，最高可达80mW/m2。
|其他摘要||The central uplift is the largest tectonic unit of the South Yellow Sea Basin (SYSB), which is not only the key study area of regional tectonic evolution, but also the potential area of current resource exploration. Based on the comprehensive description of drilling cores, experimental analysis, interpretation of logging and seismic data of the first deep whole-core drilling CSDP-2 well in central uplift of SYSB, the burial history and tectonic thermal evolution history have been studied by a serious of research methods and simulation techniques.|
The first-stage drilling results of the CSDP-2 well have revealed the Neogene, Triassic, Permian, Carboniferous and Devonian. The burial history of central uplift has been studied based on the establishment of stratigraphic framework, seisimic interpretation and estimation of eroded thickness. Dominated by regional transgression during Carboniferous, the central uplift gradually turned into the stage of marine deposition after the late Devonian continental deposition, but the deposition rate was relatively lower. The deposition rate is significantly accelerated during the early Permian, then the alternative marine and continental deposition has formed because of regional uplift and regression at the end of early Permian. The study area suffered intense tectonic compression influenced by the Indosinia tectonic movement during Triassic. The detachment surface interlaid in the Permian argillaceous strata interval drilled by CSDP-2 may be the result of tectonic thrust during this period. The central uplift experienced strong denudation from the middle-late Cretaceous, and the eroded thickness is 1220m calculated by sonic-logging data and 1400m calculated by vitrinite reflectance. The general subsidence happened in Neogene and the unconsolidated sedimentary strata formed.
CSDP-2 well revealed the constant temperature zone at a depth of about 80m, of which the temperature is 15.8℃. The neutral point depth range is roughly in the vicinity of 1100m, and the average geothermal gradient is about 24.11~24.28℃/km. The thermal evolution history of the central uplift was studied by means of paleo-geothermal gradient method, fluid inclusion temperature measurement and apatite fission track (AFT) stochastic inversion. Results show that the paleotemperature of Paleozoic is about 40℃ at the end of Carboniferous and there is a significant temperature-rise process during the early Peimian and then tends to be steady. There is another short-term temperature-rise process at the end of Permian. The paleotemperature generally keep stable during Triassic and then rapidly rise from the late Triassic to early-middle Jurassic when the central uplift has not yet suffered large-scale uplift and denudation, and modeling results from vitrinite reflectance show that the highest paletemperature of Carboniferous and Permian can respectively reach 190℃ and 170℃ and the heat flow can reach 126 mW/m2. The maximum paleogeothermal gradient is about 59℃/km during this time, which is much higher than the present geothermal gradient. The paleotemperature and heat flow both began to decline from the late Jurassic followed by a slight rise, which is resulted from the rift development and rapid continental deposition during the early Cretaceous. During the mid-late Cretaceous, the denudation rate accelerated and resulted in the paleotemperature continuously decreased, and the paleo-heat flow began to decline until the end of Cretaceous when the rift development of the SYSB roughly finished. The AFT thermal history inversion results from the Permian samples show that it has not yet entered the annealing zone during the early Cretaceous, and the paleotemperature is about 100~140℃, corresponding to the results of fluid inclusion temperature measurement. The AFT inversion results reveal two distinct cooling events, the first happened from the late Cretaceous to the early Paleocene when the paleotemperature declined to about 80℃, and then followed by a slow cooling process until the late Oligocene when the other rapid cooling event happened and continued to the early Miocene. Since the Neogene, the paleotemperature slowly rised to the current level.
Based on the theory of advanced McKenzie extension model, the geodynamic modeling and traditional geothermometer simulation are integrated and applied to reconstruct the tectono-thermal evolution history of the northern depression of the South Yellow Sea Basin during Mesozoic-Cenozoic. Modeling results show that the central uplift and northern depression, which are both the secondary tectonic units of SYSB, experienced similar thermal evolution history since Cretaceous and characterized by the heat flow trend of rift basin, showing a distinct increase process during the rifting stage and a continus decrease process during the post-rifting stage. By contrast, the paleo-heat flow of the central uplift is generally lower than the north depression, the maximum value of the former can reach 70 mW/m2 at the end of the Late Cretaceous while the paleo-heat flow of north depression is about 71.7~75.5 mW/m2 during the early Paleocene and the highest is about 80mW/m2.
|庞玉茂. 基于CSDP-2井的南黄海中部隆起构造热演化史研究[D]. 北京. 中国科学院大学,2017.|