Tectonic Thermal Evolution Research Articles

Discussion on Deep Geothermal Characteristics and Exploration Prospects in the Northern Jiangsu Basin

The Northern Jiangsu Basin (NJB), located at the northeast edge of the Yangtze block, is not only rich in oil and gas resources but also contains abundant geothermal resources. Nevertheless, the distribution of geothermal resources at medium depth in the NJB is still unclear due to its complex geological structure and tectonic–thermal evolution process, which restricts its exploitation and utilization. The characteristics of the geothermal field and distribution of geothermal reservoirs within the NJB are preliminarily analyzed based on available temperature measurements and geothermal exploration data. The prospective areas for the exploration of deep geothermal resources are discussed. The analysis results show that (1) Mesozoic–Paleozoic marine carbonate rocks are appropriate for use as principal geothermal reservoirs for the deep geothermal exploration and development within the NJB; (2) the geothermal field is evidently affected by the base fluctuation, and the high-temperature area is mainly concentrated at the junction of the Jianhu uplift and Dongtai depression; (3) the southeast margin of Jinhu sag, Lianbei sag, the east and west slope zone of Gaoyou sag, the low subuplifts within the depression such as Lingtangqiao–Liubao–Zheduo subuplifts, Xiaohai–Yuhua subuplifts and the west of Wubao low subuplift, have good prospects for deep geothermal exploration.

Constraints on a long-lived Paleoproterozoic metamorphic process in a middle- to lower-grade metamorphic complex, Songshan area, southern North China craton: Evidence from minor- and trace-element thermometry and geochronology

Abstract The Dengfeng Complex and Songshan Group comprise a middle- to lower-grade metamorphic complex with abundant lithological associations in the Songshan area (central Henan, China), representing an excellent opportunity to investigate the thermal history of the North China craton. The polymetamorphic Dengfeng Complex is a typical granite-greenstone belt that records a late Paleoproterozoic metamorphic event (ca. 1.95–1.80 Ga) overprinting on a late Neoarchean metamorphic event (ca. 2.51–2.41 Ga). In contrast, the Songshan Group preserves well-developed stratigraphic sequences and sedimentary structures with greenschist-facies metamorphism. Numerous studies have focused on the late Neoarchean metamorphic event from the Dengfeng Complex, whereas the thermal evolution of ca. 1.95–1.80 Ga units from the Dengfeng Complex and Songshan Group has been largely overlooked. Quartzite of the Songshan Group unconformably overlies schists of the Dengfeng Group, and they show coherent NNE-SSW–striking schistosity structures with dip angles of ~50°–65°. Here, the metamorphic temperatures from the Dengfeng Group were constrained to be ~510–550 °C by the Ti-in-biotite geothermometer. The Ti-in-quartz and Zr-in-rutile geothermometers record metamorphic temperatures of ~480–550 °C or 520–555 °C for the Songshan Group, respectively. Laser ablation–inductively coupled plasma–mass spectrometry U-Pb dating of monazite and rutile constrains the timing of metamorphism of the Songshan Group to be ca. 1.94–1.83 Ga, while zircon constrains the timing of metamorphism of the Dengfeng Complex to be ca. 2.53 Ga and ca. 1.95–1.87 Ga. By integrating geochronologic data from the Dengfeng Complex and Songshan Group, the ca. 2.53 Ga metamorphic age of amphibolite may be connected with Neoarchean subduction-accretion processes, whereas the consistent temperature obtained in this study ca. 1.95–1.83 Ga indicates that the Songshan area may have experienced a long-lived metamorphic event, which could have resulted from the final collision between the Western and Eastern blocks of the North China craton in the late Paleoproterozoic. The persistence of a Paleoproterozoic hot orogen for millions of years was probably the norm in the North China craton, which provides new insights into the tectonic-thermal evolution in the southern North China craton.

Tectonic–thermal evolution since the Mesozoic in the Suhongtu Depression, Yingen–Ejina Basin: Constraints from Apatite fission track and vitrinite reflectance

The Yingen–Ejina Basin (YEB) located in the western part of the North China Plate is a significant area for petroleum exploration. During the Early Cretaceous, the YEB witnessed the extensive development of source rocks. However, the subsequent tectonic evolution and multi‐stage thermal history of these source rocks have posed challenges to oil and gas exploration in the basin. This study focuses on the Mesozoic and Cenozoic tectonic evolution of the YEB, utilizing Apatite fission track (AFT) and vitrinite reflectance (Ro) data of samples from Well BC‐1 in the Suhongtu Depression, northern YEB. The central ages of six AFT samples ranged from 28 ± 2 to 49 ± 3 Ma with corresponding track lengths between 10.8 ± 1.9 and 12.3 ± 1.5 μm. Combining with the study of Ro and thermal history simulation, the thermal history of the YEB is summarized as follows: In the late Early Cretaceous, the study area experienced tectonic elevation, as evidenced by the discontinuous change in Ro values along the vertical column. Towards the end of the Late Cretaceous, there was a subsidence in the study area. The Ro data indicate that the Early Cretaceous source rocks, although experiencing several tectonic uplifts, had remained within the hydrocarbon generation temperature range, and reached the maximum thermal uplifts before the end of the Late Cretaceous. Therefore, hydrocarbon generation from early Cretaceous source rocks is an important exploration target in the study area and will be the focus of oil and gas exploration in the future.

Triassic Paleo-Tethyan slab break-off constrained by a newly discovered 211 Ma dacite–rhyolite suite in the Qiangtang terrane, central Tibet

• A newly discovered Late Triassic volcanic suite in the eastern Qiangtang subterrane includes dacites and A-type rhyolite. • This suite was emplaced at 211 Ma and was generated via partial melting of the Qiangtang continental crust. • The formation of this volcanic suite reflects the slab break-off of the Paleo-Tethyan in the Late Triassic. Triassic igneous rocks are widely exposed in the central Qiangtang terrane, Tibet. However, Triassic tectonic–thermal evolution in the central Qiangtang terrane and the evolution of the Paleo-Tethyan Ocean are still unclear. In this study, we report zircon U–Pb ages, and whole-rock major- and trace- element compositions, and Sr–Nd isotope data for the newly discovered Late Triassic Tumen volcanic rocks. The volcanic rocks consist of interlayered dacite and rhyolite (SiO 2 = 63.8–69.7 wt%) with a thickness of approximately 150 m. New zircon U–Pb dating reveals the eruption of this volcanic suite at 211 Ma. Geochemical data show that the volcanic suite has a wide range of K 2 O (1.36–5.46) values and high-molar Al 2 O 3 /(CaO+K 2 O+Na 2 O) values (0.97–1.36). All samples clearly show the enrichment of light rare earth element, with (La/Yb) N = 6.79–11.03 and (La/Sm) N = 3.23–4.44, and distinct negative Eu anomalies (Eu/Eu* = 0.44–0.70). All samples exhibit the depletion of high field strength elements (e.g., Ti, Nb, and Ta), and enrichment in large-ion lithophile elements (e.g., Rb and K). The dacite–rhyolite suite has a narrow range of ( 87 Sr/ 86 Sr) i ratios (0.7102–0.7132) and ε Nd (t) values (−10.2 to −10.0), with Nd isotope model ages of 1.76–1.82 Ga. Zircon saturation temperatures (860℃–921℃) and geochemical characteristics show that the samples are A-type granitoids and were likely generated by partial melting of the Qiangtang continental crust. The rise of the asthenospheric mantle caused by the slab break-off provides a large amount of heat and materials for the igneous rocks in the Shuanghu–Longmucuo suture zone during the Late Triassic.

Discussion on Mesozoic Geochemical Characteristics and Genesis of Nadanhada Terrane

Through field geological survey and drilling exploration in Sanjiang Basin, combined with geochemical analysis, the tectonic thermal evolution history of intrusive rocks is studied. The results show that the Early Mesozoic siliceous rocks in Qianjin Depression of Sanjiang Basin are widely distributed. The siliceous rocks are of post diagenetic hydrothermal metasomatic origin, and the hydrocarbon source rock indicators are good, which is expected to be a new formation for oil and gas exploration in Sanjiang area. The time temperature thermal history simulation of fission track shows that there have been two rapid cooling events (late Early Cretaceous Late Cretaceous and Paleocene Eocene) in the Nadanhadaling area since the Mesozoic era, with cooling rates of 3.42~4.81 ℃/Ma and 1.43~1.83 ℃/Ma, respectively. The two rapid cooling processes were caused by the subduction of the Pacific plate. The rapid cooling during the Early Cretaceous to the Late Cretaceous was caused by the change of the subduction direction of the Pacific plate and the collision and superposition of the Okot Motsk block and the East Asian continental margin; The rapid cooling from Paleocene to Eocene was mainly caused by the subduction and retreat of the Pacific plate, which made the East Asian continental margin in an extensional environment and caused denudation and cooling in most parts of Northeast China.

The Early Paleozoic intrusive magmatism and tectonic thermal evolution in the Hala Lake area, southern Qilian, NW China

南祁连增生杂岩带作为祁连造山带的构造单元之一，是研究祁连造山带与柴达木地块构造演化及二者耦合关系的关键地区，得到了国内外学者的广泛关注。前人对南祁连增生杂岩早古生代以来的构造热演化历史研究相对较少，且缺少相对准确的年代学数据约束。本文通过对南祁连增生杂岩带哈拉湖地区阿腊郭勒岩体二长花岗岩开展LA-ICP-MS锆石U-Pb定年、岩石地球化学特征、锆石和磷灰石裂变径迹年龄测试及热历史模拟，并结合野外地质调查和构造演化特征，揭示南祁连增生杂岩带哈拉湖地区的构造热演化历史和山脉隆升过程。结果显示：（1）南祁连哈拉湖地区在中志留世发生一期岩浆侵入事件（425~429Ma），其形成的岩体具有壳源花岗岩特征，产出于同碰撞的构造环境，说明该期岩浆事件是与祁连洋洋壳俯冲结束后的柴北缘地区大陆碰撞过程中的岩浆活动有关；（2）该岩体经历了中志留世至晚泥盆世的岩浆侵位与快速冷却阶段以及晚泥盆世-侏罗纪的构造平稳与缓慢冷却阶段；（3）早白垩世以来的中低温冷却和快速隆升的构造热演化历史。此外，祁连山地区自始新世以来经历了多期与印度欧亚-板块碰撞有关的构造变形。;As an important tectonic unit of the Qilian orogenic belt, the southern Qilian accretionary belt plays a significant role in studying the tectonic evolution and their coupling relationship between the Qilian orogenic belt and the Qaidam block. Although wide attention has been paid to this belt by geologists all over the world, the tectono-thermal evolution of the southern Qilian accretionary belt since Early Paleozoic is still unclear due to the lack of relatively precise geochronological data constraints. In this paper, we integrated field obervations, LA-ICP-MS zircon U-Pb age, geochemical characteristics, low-temperature themochronometry (apatite- and zircon-fission track ages) and thermal history modeling to provide constraints on the tectono-thermal history and range growth of the Hala Lake area in the southern Qilian accretionary belt. The results suggest that the southern Qilian accretionary belt experienced a multi-phase tectono-thermal evolution history, including:(1) Early Paleozoic intrusive magmatism and rapid cooling due to the Qilian orogeny from Middle Silurian (425~429Ma) to Late Devonian, with continental crust resource characters and generating from syn-collisional tectonic setting of the monzonitic granites, which indicates that this period of magmatism was related to the continental's collision of southern Qilian accretionary belt and the Qaidam block after the ocean crust subduction of Qilian Ocean; (2) tectonic quiescence and slow cooling during Late Devonian to Jurassic; (3) mid-low temperature cooling and rapid uplift since Early Cretaceous. Furthermore, the Cenozoic Qilian Shan thrust belt also experienced multi-phase structural deformations since Eocene as a result of the India-Asia collision.

Hydrocarbon Accumulation Process and Mechanism in the Lower Jurassic Reservoir in the Eastern Kuqa Depression, Tarim Basin, Northwest China: A Case Study of Well Tudong 2 in the Tugerming Area.

The Lower Jurassic reservoir has recently made a significant breakthrough in petroleum exploration in the Tugerming area of the eastern Kuqa depression, Tarim Basin, northwest China. Therefore, it is significantly essential to simulate the hydrocarbon charging process and analyze the accumulation mechanism in the study area. In our study, we mainly combine three geochemical techniques to identify the origin of crude oils and fluid inclusion characteristics in the target well (Tudong 2), including gas chromatography–mass spectrometry (GC–MS), comprehensive two-dimensional GC-time-of-flight MS (GC × GC–TOFMS), fluid inclusion analysis, and quantitative fluorescence technique. Combined comprehensive experiments with a set of burial history and tectonic thermal evolution history realize the reconstruction of the hydrocarbon charging process in the Yangxia formation. The results show that Jurassic coal-bearing source rocks are primary hydrocarbon sources, and there are three hydrocarbon charging events in the Lower Jurassic reservoir. First, the mature oils have expelled into the reservoir during the early-middle period (15–10 Ma) of the Miocene Kangcun Formation, forming yellow fluorescent oil inclusions and most of the quantitative grain fluorescence (QGF) indexes exceed 4. Second, numerous condensate oils have charged into the reservoir in the period of late Miocene Kangcun Formation-early Kuqa Formation (9–6 Ma), accompanied by blue-white oil inclusions and QGF on extract intensity greater than 4. Finally, vast natural gas has accumulated in the reservoir since Kuqa Formation (5–0 Ma), resulting in the adjustment of ancient reservoir and residual bitumen. Interestingly, we find that the hydrocarbon accumulation mechanism is characterized by self-generation and self-storage in the Jurassic Yangxia Formation, and the study area has prominent characteristics of late accumulation. Thus, the evidence obtained from our analysis suggests favorable geological conditions for the formation of a large oil and gas reservoir in the eastern Kuqa Depression.

Modeling of tectono-thermal evolution of Permo-Carboniferous source rocks in the southern Qinshui Basin, China: Consequences for hydrocarbon generation

As a main coalbed methane-producing area in China, Qinshui Basin has undergone typical tectonic thermal evolution as a result of the destruction of the North China Craton since the Late Paleozoic. This work describes the construction of a comprehensive tectono-thermal model for the southern Qinshui Basin (SQB) with which to reveal the maturation and hydrocarbon generation of the coal-bearing source rocks. The organic geochemical results show that in the present day, the source rocks comprise Type III kerogen containing more than 2.0 wt % TOC and that the Ro ranges from 2.05% to 3.24%, suggesting appropriate thermal maturity and excellent gas generation potential. Modeling results indicate that from the Late Carboniferous to the Late Triassic, the coal-bearing strata entered the first rapid subsidence stage and reached a burial depth of about 5000 m in the Late Triassic, with a geothermal gradient of 42 °C/km and maximum temperature of 118 °C. Consequently, the maturity of source rocks increased to the first peak and entered the late oil stage. Due to the destruction of the North China Craton, lithospheric thinning, and associated magmatic activity during the Late Jurassic to Early Cretaceous, the study area experienced an abnormal thermal event, with an average geothermal gradient of 58 °C/km and a maximum heat flow of 124 mW/m2, and the source rocks reached the dry gas stage rapidly, so that secondary large-scale hydrocarbon generation occurred in the Early Cretaceous. Overall, the coal-bearing source rocks of the SQB underwent deep burial thermal metamorphism in the Late Triassic and intense magmatic thermal metamorphism in the Early Cretaceous, and the latter was completely controlled by magmatic events caused by the Craton destruction.

Hydrocarbon accumulation period and process in Baobab area of Bongor Basin

The hydrocarbon reservoirs of Baobab area in the Northern Slope of the Bongor Basin in Chad, are very important petroleum exploration region in the basin. Baobab area could be divided into BS zone, BC zone and BN zone according to the tectonic distribution characteristics. All the three zones develop sandstone reservoirs, and the BC zone is mainly buried-hills reservoirs. Based on the analysis of the oil-source relationship of BS, BN and BC zone, the hydrocarbon accumulation period and adjustment process was investigated using a suite of hydrocarbon generation and expulsion history, tectonic thermal evolution history, GOI characteristics of fluid inclusions, microfluorescence determination and temperature measurement technology. The results show that crude oils of BS zone were sourced from BS zone source rock, oils of BN zone from BN zone source rock, and oil of BC zones from both of BS and BN source rocks. The history of hydrocarbon generation and expulsion history of source rock shows that the source rocks in BS zone matured earlier than the source rocks of BN. The hydrocarbon accumulation occurred in the early Late Cretaceous in BS zone, and in the middle Late Cretaceous in BN zone. The hydrocarbon accumulation period in the BC reservoirs was controlled by the hydrocarbon generation and expulsion history of source rock in BS and BN zones, which was a continuous process with different accumulation intensities during the Late Cretaceous. Due to the effects of tectonic events during Late Cretaceous, buried hill reservoirs of BC zone experienced the primary hydrocarbon accumulation of about 80-55 Ma and the secondary hydrocarbon accumulation at about 25 Ma. The reconstruction of buried-hill reservoirs in BC zone is obvious. The migration of crude oils from the ancient reservoir to the higher part of the Baobab structure along the faults and fractures due to tectonic inversion formed a new reservoir, and the oil-water contact became shallower about 357 m.

Burial and thermal evolution of coal-bearing strata and its mechanisms in the southern North China Basin since the late Paleozoic

During the interaction between the South China plate and the North China plate, the southern North China Basin (SNCB) underwent a strong tectonic thermal evolution in the early Mesozoic. Recently, burial history reconstruction and thermal maturity simulation of coal-bearing strata from the Late Carboniferous to the present were carried out in the SNCB. Rock-Eval pyrolysis (12 samples), vitrinite reflectance (60 samples), apatite fission track (AFT) analysis (17 samples), and PetroMod 1D were performed on wells located in the SNCB. Geothermal gradients were found to range between 30.3 and 36.4 °C/km, averaging 31.0 °C/km, and present heat flow was found to vary between 51 and 58, averaging 55 mW/m2. The paleo heat flow model with higher heat flow peaks of 86 mW/m2 during the first rifting phase resulted in the best fit between the calculated and the observed vitrinite reflectance and bottom hole temperatures in the modeling. Using this model of thermal maturity history combined with AFT analysis, we analyze the main hydrocarbon generation stages and discuss the coupling relationship of thermal maturity history with tectonic evolution. The results indicate that tectonic activities restrict the thermal maturity evolution of source rocks to a large extent by controlling the geotemperature. The thermal history demonstrates that two phases of heating (315–163 Ma, 83–38 Ma, depositing) happened to the source rocks, separated by two cooling (163–83 Ma, 38–23 Ma, uplifting) events. The maturity history indicates that the process of hydrocarbon generation can be divided into three stages in the SNCB (315–163 Ma, thermal genesis gas generation stage; 163–83 Ma, gas reservoir destruction stage; 83–0 Ma, secondary biogas generation stage). Hydrocarbon generation started as early as 198 Ma with a peak at 162 Ma, and expulsion started at around 195 Ma. The Taiyuan and Shanxi formations' source rocks reached a high maturity (1.0% < Ro < 1.3%) with a greater potential for hydrocarbon generation, and the Xiashihezi formation is mid-mature (0.7% < Ro < 1.0%) with limited hydrocarbon generation potential at the present day.

鄂尔多斯盆地南部富县地区三叠系延长组长8油层组油气成藏期次与时限

多旋回叠合盆地的油气成藏期次与时限研究是成藏地质学研究热点及前缘领域。鄂尔多斯盆地延长组长8油层组作为深层油气勘探的重点层位，其成藏期次与时限鲜有报道。根据含油气砂岩样品的包裹体薄片岩相学与荧光分析分析，研究区存在两期不同产状的烃类流体包裹体(FI)，第一期烃类FI呈带状分布在石英加大边、石英矿物早期裂缝中，显示褐色或浅绿色荧光；第二期烃类FI分布在切穿石英及其加大边裂缝，或晚期方解石胶结物，显示浅黄色或黄绿色荧光。根据与烃类FI同期的盐水FI均一温度的测试分析，早期FI均一温度分布在85℃~135℃，峰值接近105℃；晚期分布在135℃~155℃，峰值接近145℃。结合构造热演化史，该区存在两期幕式充注成藏过程，主要成藏时限为164 Ma和 127 Ma。为盆地延长组油气成藏机理及过程研究提供了新认识。 Timing and stages of oil-gas accumulation (OGA) are hot spots and key frontier for petroleum accumulation geology in multi-cycle superimposed basin. As the important deep oil-gas reservoir of exploration, timing and stages of OGA of Chang 8 member of Yanchang formation in Ordos Basin are rarely reported. According to the lithofacies and fluorescence analysis of hydrocarbon fluid inclusions (FI) from sandstone samples, there are two different occurrence fluid inclusions for Chang 8 member of Yanchang formation in the study area. The first occurrence of hydrocarbon FI is banded in the quartz plus side, quartz mineral early cracks, showing brown or light green fluorescence. The second occurrence of the hydrocarbon FI is distributed in the cut-off quartz and its increased fissures, or late calcite cements, showing light yellow or yellowish green fluorescence. According to the test analysis of the homogeneous temperature of the salt water FI with the hydrocarbon FI, the early FI homogeneous temperature distribution is in a range of (85˚C - 135˚C) with the peak of 105˚C; the late distribution is in a range of (135˚C - 155˚C) with the peak of 145˚C. Combined with the history of tectonic thermal evolution, it reveals that the Chang 8 reservoirs went through 2-stage OGA of 164Ma and 127 Ma, which provides a new understanding for the mechanism and process of hydrocarbon accumulation in the Yanchang Formation.

Analyses on the tectonic thermal evolution and influence factors in the deep-water Qiongdongnan Basin

To reveal the tectonic thermal evolution and influence factors on the present heat flow distribution, based on 154 heat flow data, the present heat flow distribution features of the main tectonic units are first analyzed in detail, then the tectonic thermal evolution histories of 20 profiles are reestablished crossing the main deep-water sags with a structural, thermal and sedimentary coupled numerical model. On the basis of the present geothermal features, the Qiongdongnan Basin could be divided into three regions: the northern shelf and upper slope region with a heat flow of 50–70 mW/m2, most of the central depression zone of 70–85 mW/m2, and a NE trending high heat flow zone of 85–105 mW/m2 lying in the eastern basin. Numerical modeling shows that during the syn-rift phase, the heat flow increases generally with time, and is higher in basement high area than in its adjacent sags. At the end of the syn-rift phase, the heat flow in the deepwater sags was in a range of 60–85 mW/m2, while in the basement high area, it was in a range of 75–100 mW/m2. During the post-rift phase, the heat flow decreased gradually, and tended to be more uniform in the basement highs and sags. However, an extensive magmatism, which equivalently happened at around 5 Ma, has greatly increased the heat flow values, and the relict heat still contributes about 10–25 mW/m2 to the present surface heat flow in the central depression zone and the southern uplift zone. Further analyses suggested that the present high heat flow in the deep-water Qiongdongnan Basin is a combined result of the thermal anomaly in the upper mantle, highly thinning of the lithosphere, and the recent extensive magmatism. Other secondary factors might have affected the heat flow distribution features in some local regions. These factors include basement and seafloor topography, sediment heat generation, thermal blanketing, local magmatic injecting and hydrothermal activities related to faulting and overpressure.

Lithospheric thermal isostasy of north continental margin of the South China Sea

Accompanied with rifting and detaching of the north continental margin of the South China Sea, the crust and the lithosphere become thinner away from the continental margin resulting from the tectonic activities, such as tensile deformation, thermal uplift, and cooling subsidence, etc.. Integrated with thermal, gravimetric, and isostatic analysis techniques, based on the seismic interpretation of the deep penetration seismic soundings across the northern margin of the South China Sea, we reconstructed the lithospheric thermal structure and derived the variation of the crust boundary in the east and west parts of the seismic profile by using gravity anomaly data. We mainly studied the thermal isostasy problems using the bathymetry of the profiles and calculated the crust thinning effect due to the thermal variety in the rifting process. The results indicate that the thermal isostasy may reach 2.5 km, and the compositional variations in the lithospheric density and thickness may produce a variation of 4.0 km. Therefore, the compositional isostatic correction is very important to recover the relationship between surface heat flow and topography. Moreover, because of the high heat flow characteristic of the continental margin, building the model of lithospheric geotherm in this region is of great importan for studying the Cenozoic tectonic thermal evolution of the north passive continental margin of the South China Sea.