The distribution and evolution of fluid pressure and its influence on natural gas accumulation in the Upper Paleozoic of Shenmu-Yulin area,Ordos Basin

On the basis of measuring the pressure distribution and analyzing its origin in the Carboniferous and Permian of Shenmu-Yulin area, the evolution history of ancient pressure is restored mainly by means of the basin numerical simulation technique, in which the paleo-pressure has been constrained by the compaction restoration and the examination of fluid inclusion temperature and pressure. Then the development and evolution history of abnormal pressure and its effect on gas migration and accumulation are investigated. Studies show that the pressure in southeastern and northwestern parts of studied area is near to hydrostatic pressure, whereas in the remainder vast area the pressure is lower than the hydrostatic pressure, which is caused by difficulty to measure pressure accurately in tight reservoir bed, the calculating error caused by in-coordinate between topography relief and surface of water potential, pressure lessening due to formation arising and erosion. There are geological factors beneficial to forming abnormal high pressure in the Upper Palaeozoic. On the distraction of measured pressure, paleo-pressure data from compaction restoration and fluid inclusion temperature and pressure examining, the evolution history of ancient pressure is restored by the basin numerical simulation technique. It is pointed out that there are at least two high peaks of overpressure in which the highest value of excess pressure could be 5 to 25 MPa. Major gas accumulated in main producing bed of Shanxi Fm (P₁s) and lower Shihezi Fm (P₂x), because of two-fold control from capillary barrier and overpressure seal in upper Shihezi Fm (P₂s). In the middle and southern districts, the two periods of Later Jurassic to the middle of Early Cretaceous, and middle of Later Cretaceous to Palaeocene are main periods of gas migration and accumulation, while they belong to readjustment period of gas reservoirs after middle of Neocene.

     

The distribution and evolution of fluid pressure and its influence on natural gas accumulation in the Upper Paleozoic of Shenmu-Yulin area, Ordos Basin

On the basis of measuring the pressure distribution and analyzing its origin in the Carboniferous and Permian of Shenmu-Yulin area, the evolution history of ancient pressure is restored mainly by means of the basin numerical simulation technique, in which the paleo-pressure has been constrained by the compaction restoration and the examination of fluid inclusion temperature and pressure. Then the development and evolution history of abnormal pressure and its effect on gas migration and accumulation are investigated. Studies show that the pressure in southeastern and northwestern parts of studied area is near to hydrostatic pressure, whereas in the remainder vast area the pressure is lower than the hydrostatic pressure, which is caused by difficulty to measure pressure accurately in tight reservoir bed, the calculating error caused by in-coordinate between topography relief and surface of water potential, pressure lessening due to formation arising and erosion. There are geological factors beneficial to forming abnormal high pressure in the Upper Palaeozoic. On the distraction of measured pressure, paleo-pressure data from compaction restoration and fluid inclusion temperature and pressure exa- mining, the evolution history of ancient pressure is restored by the basin numerical simulation technique. It is pointed out that there are at least two high peaks of overpressure in which the highest value of excess pressure could be 5 to 25 MPa. Major gas accumulated in main producing bed of Shanxi Fm (P1s) and lower Shihezi Fm (P2x), because of two-fold control from capillary barrier and overpressure seal in upper Shihezi Fm (P2s). In the middle and southern districts, the two periods of Later Jurassic to the middle of Early Cretaceous, and middle of Later Cretaceous to Palaeocene are main periods of gas migration and accumulation, while they belong to readjustment period of gas reservoirs after middle of Neocene.     

Quantitative reconstruction of formation paleo-pressure in sedimentary basins and case studies

Paleo-pressure reconstruction in sedimentary basins is one of the most important aspects of hydrocarbon accumulation research. In view of the advantages and disadvantages of the current methods for paleo-pressure research, a new method to reconstruct the paleo-pressure is presented in this paper. According to the geological background, quantitative analyses of the factors that might control overpressure were first conducted to clarify the contributions of each mechanism during different geological periods. Pressure evolution was reconstructed by fluid-compaction modelling with constraints imposed by the paleo-pressures obtained from fluid inclusions or differential stress methods. Determining the mechanisms responsible for overpressures during geological history is the basic prerequisite for paleo-pressure research. Thus, quantitative studies were conducted of the contributions of disequilibrium compaction, gas charging, oil cracking, temperature reduction, and tectonic uplift and subsidence to overpressures. Three case studies of paleo-pressure reconstruction were performed for the Sinian strata in the Sichuan Basin, Ordovician strata in the north uplift in the Tarim Basin and the Permian strata in the Sulige Gas Field in the Ordos Basin, where these three study sites are normally pressured, weakly over-pressured and abnormally low pressured at present, respectively. The new method developed in this paper is very important for the practical reconstruction of the paleopressure in marine strata and ancient strata in deep basins.     

川中古隆起超压分布与形成的地温场因素

温度和压力是沉积盆地两个重要的物理场,温度影响着超压的形成和分布.本文根据钻孔实测温度和压力数据分析了川中古隆起现今压力与温度的关系;在实验室对封闭流体进行了多组温-压关系实验;利用等效镜质体反射率和包裹体测温数据恢复了川中古隆起不同井区在白垩纪抬升之前的最大古地温,并在此基础上分析了温度降低对研究区超压的影响;最后探讨了生烃增压和欠压实超压形成过程中温度的作用.研究结果表明,川中古隆起现今超压层的压力系数与温度呈正相关关系;在绝对密封的条件下,当压力大于15 MPa时,温度每变化1℃,压力变化1.076 MPa.川中地区不同井区自晚白垩世以来的差异性降温是现今同一超压层系超压强度不同的主要因素,此外超压层还应发生了流体的横向压力传递和泄漏.下古生界原油裂解形成超压的时间是180~110 Ma;气态烃伴生的盐水包裹体均一温度暗示了在90 Ma超压发生调整.盆地模拟结果显示温度对上三叠统须家河组的欠压实增压影响微弱.     

Total Dissolved Gas Pressure Measurements for Assessing Contaminant Degradation Processes in Groundwater

The total dissolved gas pressure (P_TDG ) probe has been used in groundwater studies for over a decade, but rarely in assessing contaminant degradation, despite the many degradation reactions that produce or consume dissolved gases. Here we present three studies to demonstrate the application of P_TDG measurements to groundwater experiencing contaminant degradation, with discussion of its benefits and limitations. The first study is a pilot‐scale laboratory experiment simulating dissolved ethanol contamination of an anaerobic sand aquifer. Continuous monitoring of P_TDG showed the rapid onset of microbial hydrocarbon degradation via denitrification and fermentation. The subsequent formation of a gas phase was revealed when P_TDG began mimicking the bubbling pressure (P_G *; sum of hydrostatic and atmospheric pressure), fluctuating with atmospheric pressure. Some deviations of P_TDG above P_G * occurred also, which may hold promise for signalling substantial changes in the rate or type of degradation process (here, the onset of methanogenesis). In the second study, synoptic field measurements at a petroleum plume site demonstrated how elevated P_TDG could identify wells with evidence of hydrocarbon degradation (denitrification and/or methanogenesis). And finally, combined field measurements of dissolved oxygen (DO) and P_TDG in monitoring wells of a nitrate‐contaminated aquifer (Abbottsford‐Sumas) revealed areas where denitrification was likely occurring. Limitations to P_TDG use identified in these studies included the masking of degradation processes by the presence of a gas phase, as when trapped following water table fluctuations or formed from rigorous degradation reactions, and confounded assessment of P_TDG patterns from other natural or anthropogenic processes that can also influence groundwater P_TDG .     

Ar-Ar geochronology of Late Mesozoic volcanic rocks from the Yanji area, NE China and tectonic implications

Ar-Ar dating results of late Mesozoic-Cenozoic volcanic rocks from the Yanji area, NE China provide a new volcano-sedimentary stratigraphic framework. The previously defined “Triassic-Jurassic” volcanic rocks (including those from Sanxianling, Tuntianying, Tianqiaoling and Jingouling Fms.) were erupted during 118―106 Ma, corresponding to Early Cretaceous. The new eruption age span is slightly younger than the main stage (130―120 Ma) of the extensive magmatism in the eastern Central Asian Orogenic Belt and its adjacent regions. Subduction-related adakites occurring in the previously defined Quanshuicun Fm. were extruded at ca. 55 Ma. Based on these new Ar-Ar ages, the late Mesozoic to Palaeocene volcano-sedimentary sequences is rebuilt as: Tuopangou Fm., Sanxianling/Tuntianying Fm. (118―115 Ma), Malugou/Tianqiaoling Fm. (K1), Huoshanyan/Jingouling Fm. (108―106 Ma), Changcai Fm. (K2), Quanshuicun Fm. (~55 Ma) and Dalazi Fm. Our results suggest that subduction of the Pa- laeo-Pacific Ocean beneath the East Asian continental margin occurred during 106 to 55 Ma, consistent with the paleomagnetic observations and magmatic records which indicated that the Izanagi-Farallon ridge subduction beneath the southwestern Japan took place during 95―65 Ma.     

Pore pressure in deep bore-holes: Its measurement and relation with seismic activities

The method of measuring the pore pressure of stratum fluid in deep bore-holes is presented. Taking the sedimentary basins in North China as an example, the variation law of pore pressure measured in strata within the depth range of 0 to 4 km is analyzed. Furthermore, the relation between the regional distribution of abnormal pore pressures in 3 000 m depth and seismic activities is discussed in connection with the earthquakes of M _S5.0 that occurred after 1 900 in the studied region. The study result indicates that the strata pore pressure P ₀ measured in deep bore-holes is not exactly the same as the hydrostatic pressure PH. Ultra pore pressure does exist, though not commonly. The relation that the pore pressures (P ₀₁, P ₀₂ and P ₀₃) measured in exploration, evaluation and exploitation wells in Oil-fields and the hydrostatic pressuree (P _H) of the above wells is as follows: 1 P ₀₁>P ₀₂>P _H>P ₀₃ in areas with ultra pore pressures; 2 P _H>P ₀₁>P ₀₂>P ₀₃ in areas where the pore pressures are normal or on the lower side. The relation between the regional distribution of ultra pore pressures and the activity of earthquakes of M _S5.0 has been analyzed. The result shows that, with latitudes 36.0°–36.5°N as a demarcation, pore pressures are ultra-high in the south and are normal or lower in the north. In the south, the measured pore pressure is obviously higher than the hydrostatic pressure below the depth of about 2 000 m and it increases as a power function with increasing depth; meanwhile, the earthquake activity there is weaker. In the north, however, the measured pore pressure increases as a linear function with increasing depth; meanwhile, the earthquake activity there is stronger. This project sponsored by the Chinese Joint Seismological Science Foundation.     

Measurement and research method of metallogenic depths of Jiaojia orefield and Linglong orefield Shandong Province, China

Taking the contribution of the tectonic force to the total hydrostatic pressure into account, the author puts forward a new method on the calculation of the depth of petrogenesis and metallogenesis which is summarized as follows: first the tectonic added hydrostatic pressured P_s is subtracted from the total hydrostatic pressure P, then using their difference P_r, according to the general method the depth of petrogenesis and metallogenesis can be determined in consideration of lateral constraint. By the new method the following data on the depths of the metallogenesis are obtained: 2 243.6 m (No. I and No. II veins with metallogenic epoch of 105 Ma) and 1 632. 38 m (No. III vein with 105 Ma) for Jiaojia orefield, and 3 454.97 m (NE-trending zone with 213.2 Ma), 1 902.79 III (ENE-trending zone with 100.28 Ma), 1 090.97 m (NE-trending zone with 80.67 Ma) and 720.55 m (NNE-trending zone with 71.86 Ma) for Linglong orefield. Project supported by the Foundation of the State Planning Commission, China and the Foundation of the State Science and Technology Commission, China.     

欠压实超压层自然电位测井响应机理研究

以欠压实超压层为研究对象,利用双水模型和热动力学理论,推导了欠压实超压泥质砂岩、泥岩的薄膜电位方程,分析了压实作用对薄膜电位造成的影响以及欠压实超压泥质砂岩储层自然电位的响应特征.理论研究表明:压实作用对泥岩薄膜电位影响显著,对于盐水泥浆,泥岩薄膜电位随压实系数的变大而增加,淡水泥浆条件下,泥岩薄膜电位随压实系数的变大...     

Mechanism of diapirism and episodic fluid injections in the Yinggehai Basin

The diapirism in the Yinggehai Basin is a combined result of strong overpressure caused by rapid sedimentation of fine-grain sediments and the tensile stress field resulting from right-lateral slip of the boundary-fault. The diapirism showed multiple-stage, episodic nature, and caused intermittent counter-direction onlaps and changes in the thickness of strata. The shallow gas reservoirs in the diapir structural zone displayed obvious inter-reservoir compositional heterogeneities, and their filling history could be divided into 4 stages, with gases injected during different stages having different hydrocarbon gas, CO₂ and N₂ contents and different stable isotope compositions. The multiple-episode, intermittent activities of the diapirs, multiple-stage, non-continuous injections of fluids, and the transient thermal effect of fluid flow as well as the strong migration fractionation reflected episodic fluid injection and natural gas accumulation.     

水合物层下伏游离气渗漏过程的数值模拟及实例分析

海洋环境中天然气水合物层是理想的毛细管封闭层,游离气被抑制在水合物层下,游离气层的气体压力随气体聚集和气层厚度的增加而升高,当气压超过封闭层的毛细管力时,游离气会克服毛细管进入压力、刺入上伏封闭层孔隙空间,毛细管封闭作用随之消失,从而形成水合物下伏游离气向海底的渗漏.通过对该过程进行的数值模拟计算表明：渗漏气体是以活塞式驱动上伏沉积层中的孔隙水向海底排出,水合物稳定带内流体渗漏速度随水流柱高度的减小而增加,当水流阻抗大于相应沉积层段的静岩压力时,沉积层将转变为流沙,流沙沉积被海流移除后便在海底留下凹陷麻坑.麻坑形成后流体运移通道演化为气体通道,气体快速排放.麻坑深度主要取决于游离气层的厚度和水合物封闭层（底界）的深度,而与沉积层的渗透率无关.麻坑深度一定程度上指示了渗漏前水合物层下伏游离气层的资源量.对布莱克海台海底麻坑深度的数值模拟计算表明,形成4 m深的海底麻坑需要至少22 m厚的游离气层.     

Tectonic thermal history and its significance on the formation of oil and gas accumulation and mineral deposit in Ordos Basin

The analyzing data on stratigraphic temperature measurement, thermal conductivity of the strata and radioactive heat production rate show that the present average geothermal gradient in the Ordos Basin is 2.93 °C/100 m, and the average heat flow value is 61.78 mW/m², which belongs to the mesothermal basin, and the value of the present geothermal gradient and heat flow in the east is higher than that in the west. The sandstone radioactive heat production rate of Zhiluo Group in Dongsheng Uranium deposits of Yimeng uplift is obviously higher in the mudstone, indicating that there exists a uranium anomaly. Based on studies of the present thermal field of the basin, the late-Mesozoic paleotemperature and paleogeothermal gradient are determined by using different kinds of paleotemperature methods. According to the anomaly of the late-Mesozoic paleotemperature gradient and magmatic event age, there was a tectonic thermal event in the early Cretaceous epoch of late-Mesozoic. This article rebuilds tectonic thermal history of different tectonic units by thermal history simulation using basin simulating software. The evolution of oil-gas and coal, and accumulation (mineralization) of mineral uranium are all controlled by the tectonic thermal history in the Ordos basin, especially by the tectonic thermal event that happened in the late Mesozoic. For both the gas source rocks of upper Paleozoic group and lower paleozoic group, the gas was largely generated in the early Cretaceous epoch of the late Mesozoic. The main petroleum generation period for Yanchang Group in Triassic system is the early Cretaceous epoch too, and the highest thermal maturity of the coal of Permo-Carboniferous, Triassic, and Jurassic reaches is the early Cretaceous epoch also. Early Cretaceous epoch is still one of the most important mineralizing periods of uranium.     

Depositional processes and gas pore pressure in pyroclastic flows: an experimental perspective

The depositional processes and gas pore pressure in pyroclastic flows are investigated through scaled experiments on transient, initially fluidized granular flows. The flow structure consists of a sliding head whose basal velocity decreases backwards from the front velocity (U _f) until onset of deposition occurs, which marks transition to the flow body where the basal deposit grows continuously. The flows propagate in a fluid-inertial regime despite formation of the deposit. Their head generates underpressure proportional to U _f ² whereas their body generates overpressure whose values suggest that pore pressure diffuses during emplacement. Complementary experiments on defluidizing static columns prove that the concept of pore pressure diffusion is relevant for gas-particle mixtures and allow characterization of the diffusion timescale (t _d) as a function of the material properties. Initial material expansion increases the diffusion time compared with the nonexpanded state, suggesting that pore pressure is self-generated during compaction. Application to pyroclastic flows gives minimum diffusion timescales of seconds to tens of minutes, depending principally on the flow height and permeability. This study also helps to reconcile the concepts of en masse and progressive deposition of pyroclastic flow units or discrete pulses. Onset of deposition, whose causes deserve further investigation, is the most critical parameter for determining the structure of the deposits. Even if sedimentation is fundamentally continuous, it is proposed that late onset of deposition and rapid aggradation in relatively thin flows can generate deposits that are almost snapshots of the flow structure. In this context, deposition can be considered as occurring en masse, though not strictly instantaneously.     

Linking uplift,erosion, and sedimentation using landscape evolution models: Madagascar since the Late Cretaceous

We present a study to estimate the large-scale landscape history of a continental margin, by establishing a source-to-sink volume balance between the eroding onshore areas and the offshore basins. Assuming erosion as the primary process for sediment production, we strive to constrain a numerical model of landscape evolution that balances the volumes of eroded materials from the continent and that deposited in the corresponding basins, with a ratio imposed for loss of erosion products. We use this approach to investigate the landscape history of Madagascar since the Late Cretaceous. The uplift history prescribed in the model is inferred from elevations of planation surfaces formed at various ages. By fitting the volumes of terrigenous sediments in the Morondava Basin along the west coast and the current elevation of the island, the landscape evolution model is optimized by constraining the erosion law parameters and ratios of sediment loss. The results include a best-fit landscape evolution model, which features two major periods of uplift and erosion during the Late Cretaceous and the middle to late Cenozoic. The model supports suggestions from previous studies that most of the high topography of the island was constructed since the middle to late Miocene, and on the central plateau the erosion has not reached an equilibrium with the high uplift rates in the late Cenozoic. Our models also indicate that over the geological time scale a significant portion of materials eroded from Madagascar was not archived in the offshore basin, possibly consumed by chemical weathering, the intensity of which might have varied with climate.     

Hydrocarbon source systems and formation of gas fields in Sichuan Basin

The formation of large and middle gas fields in Sichuan Basin is investigated based on source wntrolling theory and hydrocarbon source systems. It is indicated that Є₁, S_l, P₁, P₂ and T₃ are the main source beds and Є₁/Z₂ d, C₂ h/S₁, P₁/P₂, P₂ ch/P₂, T_1,2/P,T3 x /T3 x are important hydrocarbon source systems in the basin. All these source systems are the prospective formations and exploration spaces of large and middle gas fields. It is also emphasized that hydrocarbon generation intensity is the most important geochemical factor to estimate large and middle gas fields. Project supported by the “85–102” Chinese National Key Science and Technology Project.     

Origin of natural sulphur-bearing immiscible inclusions and H2S in oolite gas reservoir, Eastern Sichuan

Based on results of microscopic observation and laser Raman analysis about fluid inclusions, multiple special forms of immiscible inclusions that contain sulphur, liquid hydrocarbon, bitumen, etc. were discovered in samples collected from the H₂S gas reservoir-containing carbonates in the Lower Triassic Feixianguan Formation in the Jinzhu-Luojia area, Kai County, Sichuan Province. Based on the lithology and burial history of the strata involved as well as measurement results of homogenization temperature of fluid inclusions, bitumen reflectivity, etc., it is concluded that the H₂S in the gas reservoir resulted from the thermal reaction between hydrocarbons in reservoir and CaSO₄ in the gypsum-bearing dolostone section at the high temperature (140°C–17°C) oil-cracked gas formation stage in Late Cretaceous. Thereafter, research on a great number of immiscible inclusions in the reservoir reveals that elemental sulphur resulted from oxidation of part of the earlier-formed H₂S and further reaction between sulphates, hydrocarbons and H₂S in geological fluids in H₂S-bearing gas reservoir at a temperature of 86°C–89°C and a pressure of 340×10⁵Pa and during the regional uplift stage as characterized by temperature decrease and pressure decrease in Tertiary. Meanwhile, gypsum, anhydrite and calcite formed at this stage would trap particles like elemental sulphur and result in a variety of special forms of immiscible inclusions, and these inclusions would contain information concerning the complexity of the fluids in the reservoir and the origin of H₂S and natural sulphur in the gas reservoir.     

构造应力超压机制的定量分析

构造应力一直被认为是超压形成的重要机制,但对其研究还处于定性的分析阶段．本文利用以有限元方法为基础的盆地数值模型,在一维的剖面上考虑构造应力强度、构造作用时间及方式、地层的物理成岩特征及其岩石渗透率等因素的变化,对构造应力在地层压力演化中的作用进行了模拟分析．获得了一些构造应力作为超压形成机制的新认识：（1）构造应力在水平方向上增加了地层的压实作用;（2）在极端条件下,构造应力所引起的超压增量可达构造应力的一半;（3）上覆地层因构造应力的作用而发生的更为强烈的压实结果对其下伏地层内压力的演化也很重要,其增加的超压增量可达构造应力的15%～20％．     

Ultrasonic velocities of North Sea chalk samples: influence of porosity, fluid content and texture

We have studied 56 unfractured chalk samples of the Upper Cretaceous Tor Formation of the Dan, South Arne and Gorm Fields, Danish North Sea. The samples have porosities of between 14% and 45% and calcite content of over 95%. The ultrasonic compressional‐ and shear‐wave velocities (V_P and V_S) for dry and water‐saturated samples were measured at up to 75 bar confining hydrostatic pressure corresponding to effective stress in the reservoir. The porosity is the main control of the ultrasonic velocities and therefore of the elastic moduli. The elastic moduli are slightly higher for samples from the South Arne Field than from the Dan Field for identical porosities. This difference may be due to textural differences between the chalk at the two locations because we observe that large grains (i.e. filled microfossils and fossil fragments) that occur more frequently in samples from the Dan Field have a porosity‐reducing effect and that samples rich in large grains have a relatively low porosity for a given P‐wave modulus. The clay content in the samples is low and is mainly represented by either kaolinite or smectite; samples with smectite have a lower P‐wave modulus than samples with kaolinite at equal porosity. We find that ultrasonic V_P and V_S of dry chalk samples can be satisfactorily estimated with Gassmann's relationships from data for water‐saturated samples. A pronounced difference between the V_P/V_S ratios for dry and water‐saturated chalk samples indicates promising results for seismic amplitude‐versus‐offset analyses.     

Alpine tectonic evolution of a Jurassic subduction-accretionary complex: Deformation,kinematics and Ar/Ar age constraints on the Mesozoic low-grade schists of the Circum-Rhodope Belt in the eastern Rhodope-Thrace region,Bulgaria-Greece

Deformation of the Circum-Rhodope Belt Mesozoic (Middle Triassic to earliest Lower Cretaceous) low-grade schists underneath an arc-related ophiolitic magmatic suite and associated sedimentary successions in the eastern Rhodope-Thrace region occurred as a two-episode tectonic process: (i) Late Jurassic deformation of arc to margin units resulting from the eastern Rhodope-Evros arc–Rhodope terrane continental margin collision and accretion to that margin, and (ii) Middle Eocene deformation related to the Tertiary crustal extension and final collision resulting in the closure of the Vardar ocean south of the Rhodope terrane. The first deformational event D₁ is expressed by Late Jurassic NW-N vergent fold generations and the main and subsidiary planar-linear structures. Although overprinting, these structural elements depict uniform bulk north-directed thrust kinematics and are geometrically compatible with the increments of progressive deformation that develops in same greenschist-facies metamorphic grade. It followed the Early-Middle Jurassic magmatic evolution of the eastern Rhodope-Evros arc established on the upper plate of the southward subducting Maliac-Meliata oceanic lithosphere that established the Vardar Ocean in a supra-subduction back-arc setting. This first event resulted in the thrust-related tectonic emplacement of the Mesozoic schists in a supra-crustal level onto the Rhodope continental margin. This Late Jurassic-Early Cretaceous tectonic event related to N-vergent Balkan orogeny is well-constrained by geochronological data and traced at a regional-scale within distinct units of the Carpatho-Balkan Belt. Following subduction reversal towards the north whereby the Vardar Ocean was subducted beneath the Rhodope margin by latest Cretaceous times, the low-grade schists aquired a new position in the upper plate, and hence, the Mesozoic schists are lacking the Cretaceous S-directed tectono-metamorphic episode whose effects are widespread in the underlying high-grade basement. The subduction of the remnant Vardar Ocean located behind the colliding arc since the middle Cretaceous was responsible for its ultimate closure, Early Tertiary collision with the Pelagonian block and extension in the region caused the extensional collapse related to the second deformational event D₂. This extensional episode was experienced passively by the Mesozoic schists located in the hanging wall of the extensional detachments in Eocene times. It resulted in NE-SW oriented open folds representing corrugation antiforms of the extensional detachment surfaces, brittle faulting and burial history beneath thick Eocene sediments as indicated by 42.1–39.7 Ma ⁴⁰Ar/³⁹Ar mica plateau ages obtained in the study. The results provide structural constraints for the involvement components of Jurassic paleo-subduction zone in a Late Jurassic arc-continental margin collisional history that contributed to accretion-related crustal growth of the Rhodope terrane.     

基于磷灰石裂变径迹约束的北黄海盆地热演化研究

热演化历史的研究对于盆地分析和油气勘探具有重要意义.北黄海盆地是中国近海海域油气勘探程度较低的盆地之一,迄今未见专门的热演化研究报道.笔者利用北黄海盆地中生代砂岩的磷灰石裂变径迹分析结果,结合地质条件约束,模拟获得了中生代以来盆地的热演化史.结果表明,北黄海盆地经历了两次增温和两次冷却的热演化过程,并在100-80 Ma时盆地的热历史出现明显变化,表明在晚白垩世北黄海盆地发生过一次较大的构造-热事件.磷灰石裂变径迹分析所表明的北黄海盆地的热历史与盆地原型演化阶段相对应,而这种热历史和盆地的演化过程与区域构造背景相关.磷灰石裂变径迹所揭示的热演化史对于深化认识北黄海盆地的地质演化过程和油气勘探潜力具有重要意义.