Cooling and exhumation of the oldest Sanqiliu uranium ore system in Motianling district,South China Block

The Sanqiliu uranium deposit belongs to a uranium ore system in Motianling district. It is the oldest uranium deposit in South China. Primary uranium mineralization occurred almost simultaneously with the emplacement of the host granites and subsequent dykes, and it has a relatively high grade of uranium (0.421%). We clarify the age of mineralization and investigate the cooling history through new pitchblende U–Pb and apatite fission‐track thermochronology. The pitchblende U–Pb results indicate that uranium mineralization occurred at ~801–759 Ma. Fractionation of uranium and lead at ~374–295 Ma is interpreted as remobilization and resetting of the original uranium. The Motianling area has apatite fission‐track ages of 57 to 18 Ma. By combining our results with previous work, we conclude that the deposit cooled slowly and was exposed at the surface during the Cenozoic. The timing and depth of exhumation helped to preserve and avoid erosion of the uranium deposit, and highlight the potential for regional uranium exploration.     

Hydrogeochemical Processes and Quality Assessment of Groundwater in Sulin Mining Area,Northern Anhui Province,China

Water Resources - In mining areas, coal production, agriculture, and drinking use had increased the demand for fresh groundwater. It was essential to obtain a deeper understanding of the...     

Geochronology and geochemistry of Cenozoic basalts from eastern Guangdong, SE China: constraints on the lithosphere evolution beneath the northern margin of the South China Sea

The ⁴⁰Ar–³⁹Ar dating reveals three episodes of basaltic volcanism in eastern Guangdong of SE China since the late Eocene (i.e., 35.5, ~20 and 6.6 Ma). The Miocene alkali olivine basalts (~20 and 6.6 Ma) have OIB-like trace element characteristics, which is coupled with low (⁸⁷Sr/⁸⁶Sr)_i, high ε_Nd(t), and high ε_Hf(t). In contrast, the late Eocene basalts (35.5 Ma) have overall characteristics of “Island Arc” basalts with strong negative Ta–Nb–Ti anomalies in the primitive mantle-normalized multi-element diagram with high (⁸⁷Sr/⁸⁶Sr)_i, negative ε_Nd(t), and relatively low ε_Hf(t). All basalts have unexpectedly high ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb, delineating a DUPAL signature in the sources. The late Eocene Arc-like basalts may reflect contributions of relict ancient metasomatized mantle lithosphere that melted as the result of extension-induced asthenospheric upwelling and heating, whereas the Miocene OIB-like basalts may represent partial melting of the asthenospheric mantle beneath the thickened lithosphere. We propose that the Cenozoic basaltic volcanism in eastern Guangdong records an overall lithospheric thickening process beneath SE China, that is, a continental rift system from its maximum extension in the late Eocene to its waning in the Miocene. This interpretation is consistent with the evolution of the South China Sea, whose origin is most consistent with the development of a passive continental margin. The seafloor spreading of the South China Sea during ~ 32–16 Ma may not result from the effect of the “Hainan” mantle plume, but rather played a positive role in allowing the mantle plume to express on the surface.     

Simulation of advective methane flux and AOM in Shenhu area, the northern South China Sea

Anaerobic oxidation of methane (AOM) occurring in the marine sediment is an important process for methane cycle and methane sequestration. In this work, a one-dimensional numerical model was developed to study the distribution of advective methane flux with the AOM process. The model has been applied to investigate the gas hydrates bearing sediments of Shenhu areas located in the northern South China Sea, where advective methane transport was detected. The modeling results suggest that methane flux will be consumed in the sediment column via dissolution, sorption, and AOM reaction. Only when the methane flux was one order of magnitude higher than current level, then a portion of methane will enter water column and possibly escape to the atmosphere. The numerical simulation also revealed that, due to the lower permeability of the silt–clay sediments, a much thicker sulfate-methane transition zone exists in the Shenhu area, where AOM is able to consume more.     

Assessment of groundwater resources based on AutoCAD technique

The catchment areas with the hydrological data in the southern region of the Cretaceous system are divided into seven categories according to the distribution characteristics of physical geographic conditions, watershed, lithology and geological structure. River baseflow of the Cretaceous system in the Ordos Basin is 1.143 billion m³/a. Baseflow of the Jing River drainage area is 538 million m³/a, which accounts for 47.0 % of the total, and baseflow of the Wuding River drainage area is 352 million m³/a, which accounts for 30.8 %. The AutoCAD technique of baseflow separation is chosen for two reasons. Firstly, the automated technique neither has the true physical basis, nor the relation to groundwater movement. Selection of $ \alpha $ value must refer to manual method for baseflow separation. Each pass will result in less baseflow as a percentage of total flow. Secondly, it is always thought that the manual method for baseflow separation is based on physical reasoning. The AutoCAD technique is essentially manual baseflow separation using the drafting tools available in AutoCAD. During the manual baseflow separation process, it makes the calculation workload substantial. The greatest benefits of using AutoCAD for calculation are to reduce the workload, enhance the efficiency, and provide more precise results. Hence, the AutoCAD technique provides a new way for baseflow separation.     

福建龙岩万安稀土矿床地质特征及成因探讨

万安稀土矿产于华力西-印支期似斑状中粗粒黑云母二长花岗岩和燕山早期第三次侵入细粒花岗岩风化壳中,矿体形态、产状受风化壳和地形控制,呈面型分布。主矿体规模大,成矿物质来源与花岗岩有关,属风化壳离子吸附型稀土矿床。     

Advances in Re-Os Isotopic Dating in Geochronology of Hydrocarbon Accumulation

Rhenium-Osmium (Re-Os) isotopic dating applied to the geochronology of hydrocarbon accumulation has been the forefront of international research in the last 10 years and has achieved significant achievements. However, our current researches are lacking in Re-Os isotopic chronology on the geochronology of hydrocarbon accumulation. The successful application of the Re-Os geochronology has enabled the determination of accurate and precise depositional ages for Organic-Rich Sedimentary rocks (ORS), the establishment of timing constraints of oil generation or migration, and the fingerprinting of the source of oil. On the basis of literatures study both at home and abroad, this article mainly dealt with the principle of Re-Os isotopic dating and analyzed the accumulation processes of Re and Os in a seawater-sediment system. Meanwhile, the test samples, sample preparation and analytical methodology of Re-Os isotopic dating were summarized. The results revealed that the initial ¹⁸⁷Os/¹⁸⁸Os ratio could constrain the age of oil generation or migration, and effectively evaluated the relationship between source rock and oil. The radiogenic ¹⁸⁷Os/¹⁸⁸Os ratio showed a positively correlated relationship with source rock age. This article proposed that hydrocarbon mature, biodegradation and water washing had minimal or no effect on data scatter about Re-Os isochron. However, the effects of postdepositional mobility of Re and Os, variations in the initial ¹⁸⁷Os/¹⁸⁸Os ratio, and thermochemical sulfate reduction could result in data scatter. The reproducibility and accuracy of Re-Os age was also closely related to the sample particle size and sample amount. Compared with other isotopic dating, the biggest advantage of Re-Os isotopic dating is to study geological body related to accumulation process, and to obtain direct evidence of hydrocarbon accumulation period. From what was discussed above, the article discussed the existing problems and put forward the future hot research and development direction of Re-Os isotope system, so as to promote the deep development of relative theory and technology of Re-Os isotopic dating.     

火山岩储层质量预测方法探讨——以松辽盆地徐家围子断陷为例

松辽盆地徐家围子断陷深层火山岩储层具有埋藏深、 温度高、 压力大、 物性差、 非均质性强的特征。为了预测火山岩储层类型和质量在平面上的变化规律,本文讨论了影响火山岩储层物性的主要地质因素。结果表明,火山岩的物性主要受火山岩相（组）和所处对应碎屑岩成岩阶段的影响。距火山口越远的火山岩相组的火山岩储层,其孔隙度和渗透率越低。火山岩工业气层主要分布在晚成岩阶段A期以前的火山岩储层中。在晚成岩阶段B期,只有少量低产气层。本文充分考虑徐家围子断陷火山岩相和成岩作用对火山岩储层物性的影响与控制,应用成岩模拟软件,预测了成岩阶段的横向展布,通过叠合营三段火山岩相图和成岩阶段预测图,预测了火山岩储层的类型和质量,目前已发现工业气流的井主要分布在断陷中部的Ⅱ、 Ⅲ类火山岩储层中。     

热与克拉通破坏

大陆克拉通是地球表面上相对稳定的构造单元。从地热学的角度考虑,克拉通岩石圈的稳定意味着地表热流等于对流地幔岩石圈底部提供的热流加上岩石圈内部由放射性衰变产生的热量。太古代稳定克拉通一般具有冷的地热特征,且处于热平衡状态。打破克拉通热平衡的因素有多种,如岩石圈地幔的放射性生热、来自深部的地幔柱、板块俯冲等。华北是全球古老克拉通遭受破坏最明显和最典型的地区,其破坏与中生代太平洋板块向东亚的深俯冲密切相关。古太平洋板块快速俯冲并停滞在地幔转换带脱水、形成宽约1 000 km的低粘大地幔楔,导致地幔对流增强。在活跃地幔对流的热侵蚀与橄榄岩-熔体相互作用共同作用下,华北克拉通在中生代期间迅速减薄。经过中生代加热减薄的华北克拉通岩石圈强度显著变弱,在俯冲板块后撤作用下,岩石圈拉张并进一步减薄,地表热流升高。华北克拉通破坏是一个漫长的历程,期间大地热流的演化特征呈现出由中生代以前的低值演化至新生代的高值再过渡到现今的中等状态（接近全球大陆平均值）。     

Synthetic seismic intensity for historic earthquakes in the North China Plain: implications for the regional seismic hazard

Multiple approaches are used to study the potential seismic hazard in the North China Craton (NCC, or North China Plain), where approximately 15 % of the Chinese population resides and under which active faults are located. In this study, we develop a new modified Mercalli intensity (MMI) attenuation relationship for the NCC using intensity data from 10 instrumentally recorded events. We then utilize this relationship to infer the magnitude and epicentral location of historic events based on the method proposed by Bakun and Wentworth (Bull Seismol Soc Am 87(6):1502–1521, 1997). In addition, a modified stochastic finite fault model is employed to simulate the strong ground motions caused by these historic events. The simulated peak ground accelerations and velocities are then converted into regional MMI distributions through empirical relationships, and these synthetic MMI maps are compared to field observations. The resultant MMI attenuation versus distance models of the 1976 M _w 7.6 Tangshan event and the 1679 M 8.0 Sanhe-Pinggu event are consistent with the empirical attenuation relationships, and the location and size of the meizoseismal area (>VIII) are consistent with observations. The successful modeling of these historic events indicates that a stochastic finite fault model constrained by the regional MMI attenuation relationship can be used to evaluate a wide range of scenarios based on modern computational simulations. These findings may also provide useful information for the estimation and mitigation of potential seismic hazards in this region.