Analytical and numerical models of hydrothermal fluid flow at fault intersections

Fault intersections are the locus of hot spring activity and Carlin‐type gold mineralization within the Basin and Range, USA. Analytical and numerical solutions to Stokes equation suggest that peak fluid velocities at fault intersections increase between 20% and 47% when fracture apertures have identical widths but increase by only about 1% and 8% when aperture widths vary by a factor of 2. This suggests that fault zone intersections must have enlarged apertures. Three‐dimensional finite element models that consider intersecting 10‐ to 20‐m wide fault planes resulted in hot spring activity being preferentially located at fault zone intersections when fault zones were assigned identical permeabilities. We found that the onset of convection at the intersections of the fault zones occurred in our hydrothermal model over a narrow permeability range between 5 × 10^?13 and 7 × 10^?13 m². Relatively high vertical fluid velocities (0.3–3 m year^?1) extended away from the fault intersections for about 0.5–1.5 km. For the boundary conditions and fault plane dimensions used, peak discharge temperatures of 112°C at the water table occurred with an intermediate fault zone permeability of 5 × 10^?13 m². When fault plane permeability differed by a factor of 2 or more, the locus of hot spring activity shifted away from the intersections. However, increasing the permeability at the core of the fault plane intersection by 40% shifted the discharge back to the intersections. When aquifer units were assigned a permeability value equal to those of the fault planes, convective rolls developed that extend about 3 km laterally along the fault plane and into the adjacent aquifer.     

Hydrothermal convection in and around mineralized fault zones: insights from two- and three-dimensional numerical modeling applied to the Ashanti belt, Ghana

Among hydrogeological processes, free convection in faults has been cited as a possible cause of gold mineralization along major fault zones. Here, we investigate the effects of free convection to determine whether it can cause giant orogenic gold deposits and their regular spatial distribution along major fault/shear zones. The approach comprises: (i) coupled two- and three-dimensional numerical heat- and fluid-flow simulations of simplified geological models; and (ii) calculation of the rock alteration index (RAI) to delineate regions where precipitation/dissolution can occur. Then, comparing the deduced alteration patterns with temperature distribution, potential areas of gold mineralization, defined by T  > 200°C and RAI < 0, are predicted. The models are based on the orogenic Paleoproterozoic ore deposits of the Ashanti belt in western Africa. These deposits occur in the most permeable parts of the fault zone, where the lateral permeability contrast is the highest. For a simple geometry, with a fault zone adjacent to a sedimentary basin half as permeable, we note a transition from three-dimensional circulation within the fault to a two-dimensional convective pattern in the basin far from the fault. Moreover, whereas two-dimensional undulated isotherms dominate in the basin, three-dimensional corrugated isotherms result from the preferred convective pattern within the fault, thus enhancing a periodic distribution of thermal highs and lows. In our most elaborate three-dimensional model with an imposed lateral permeability gradient, the RAI distribution indicates that fluid circulation in fault zones gives rise to a spatial periodicity of alteration patterns consistent with field data.     

3D numerical modeling of hydrothermal processes during the lifetime of a deep geothermal reservoir

Understanding hydrothermal processes during production is critical to optimal geothermal reservoir management and sustainable utilization. This study addresses the hydrothermal (HT) processes in a geothermal research doublet consisting of the injection well E GrSk3/90 and production well Gt GrSk4/05 at the deep geothermal reservoir of Groß Schönebeck (north of Berlin, Germany) during geothermal power production. The reservoir is located between ?4050 to ?4250 m depth in the Lower Permian of the Northeast German Basin. Operational activities such as hydraulic stimulation, production (T = 150°C; Q = ?75 m³ h^?1; C = 265 g l^?1) and injection (T = 70°C; Q = 75 m³ h^?1; C = 265 g l^?1) change the HT conditions of the geothermal reservoir. The most significant changes affect temperature, mass concentration and pore pressure. These changes influence fluid density and viscosity as well as rock properties such as porosity, permeability, thermal conductivity and heat capacity. In addition, the geometry and hydraulic properties of hydraulically induced fractures vary during the lifetime of the reservoir. A three‐dimensional reservoir model was developed based on a structural geological model to simulate and understand the complex interaction of such processes. This model includes a full HT coupling of various petrophysical parameters. Specifically, temperature‐dependent thermal conductivity and heat capacity as well as the pressure‐, temperature‐ and mass concentration‐dependent fluid density and viscosity are considered. These parameters were determined by laboratory and field experiments. The effective pressure dependence of matrix permeability is less than 2.3% at our reservoir conditions and therefore can be neglected. The results of a three‐dimensional thermohaline finite‐element simulation of the life cycle performance of this geothermal well doublet indicate the beginning of thermal breakthrough after 3.6 years of utilization. This result is crucial for optimizing reservoir management. Geofluids (2010) 10 , 406–421     

Downward hydrocarbon migration predicted from numerical modeling of fluid overpressure in the Paleozoic Anticosti Basin,eastern Canada

The Anticosti Basin is a large Paleozoic basin in eastern Canada where potential source and reservoir rocks have been identified but no economic hydrocarbon reservoirs have been found. Potential source rocks of the Upper Ordovician Macasty Formation overlie carbonates of the Middle Ordovician Mingan Formation, which are underlain by dolostones of the Lower Ordovician Romaine Formation. These carbonates have been subjected to dissolution and dolomitization and are potential hydrocarbon reservoirs. Numerical simulations of fluid‐overpressure development related to sediment compaction and hydrocarbon generation were carried out to investigate whether hydrocarbons generated in the Macasty Formation could migrate downward into the underlying Mingan and Romaine formations. The modeling results indicate that, in the central part of the basin, maximum fluid overpressures developed above the Macasty Formation due to rapid sedimentation. This overpressured core dissipated gradually with time, but the overpressure pattern (i.e. maximum overpressure above source rock) was maintained during the generation of oil and gas. The downward impelling force associated with fluid‐overpressure gradients in the central part of the basin was stronger than the buoyancy force for oil, whereas the buoyancy force for gas and for oil generated in the later stage of the basin is stronger than the overpressure‐related force. Based on these results, it is proposed that oil generated from the Macasty Formation in the central part of the basin first moved downward into the Mingan and Romaine formations, and then migrated laterally up‐dip toward the basin margin, whereas gas throughout the basin and oil generated in the northern part of the basin generally moved upward. Consequently, gas reservoirs are predicted to occur in the upper part of the basin, whereas oil reservoirs are more likely to be found in the strata below the source rocks. Geofluids (2010) 10 , 334–350     

论华中抗日根据地的优抚工作

华中抗日根据地十分注重对退伍、伤残军人和抗属的优抚工作:制定优抚法律、政策,设立社会保障机构,开展优抚政策的宣传教育,组织拜年和节日慰问活动,帮助抗属解决生产生活问题,减轻各种税费,抚恤烈士,安置伤残、退伍军人。优抚经费既包括政府拨款,也包括民间筹集。华中抗日根据地优抚工作的特点是:物质与精神保障相结合;适度保障,维持基本生活;对国民党军队一视同仁;把保障与鼓励自力更生相结合。优抚工作对于动员民众参军参战,密切党政军民关系,配合统一战线的开展等方面都具有重要的意义。     

Topography‐driven flow versus buoyancy‐driven flow in the U.S. midcontinent: implications for the residence time of brines

Topography‐driven flow is normally considered to be the dominant groundwater flow system in uplifted sedimentary basins. In the U.S. midcontinent region east of the Rocky Mountains, the presence of brines derived from dissolution of halite suggests that significant topography‐driven flushing has occurred to remove older brines that presumably formed concurrently with Permian evaporites in the basin. However, the presence of evaporites and brines in the modern basin suggests that buoyancy‐driven flow could limit topography‐driven flushing significantly. Here we used numerical models of variable‐density fluid flow, halite dissolution, solute transport, and heat transport to quantify flow patterns and brine migration. Results indicate the coexistence of large‐scale topography‐ and buoyancy‐driven flow. Buoyancy‐driven flow and low permeability evaporites act to isolate brines, and the residence time of the brines was found to be quite long, at least 50 Myr. The modern distribution of salinity appears to reflect near‐steady‐state conditions. Results suggest that flushing of original evaporatively‐concentrated brines occurred tens of millions of years ago, possibly concurrent with maximum uplift ca. 60 Ma. Simulations also suggest that buoyancy‐driven convection could drive chemical exchange with crystalline basement rocks, which could supply significant Ca²⁺, Sr²⁺, and metals to brines.     

从国际法论中日钓鱼岛争端及其解决前景

章认为从国际法方面看钓鱼岛的主权属于中国,日本所主张的“无主地先占”原则根本不能成立。根据联合国新海洋法和国际司法判例,钓鱼岛不应享有大陆架和专属经济区,亦不具有划界效力。中日东海大陆架的划分应遵循公平和自然延伸的原则。在和平解决争端的前景下,钓鱼岛问题面临三种可能的选择。     

Mobilization of ore fluids during Alpine metamorphism: evidence from hydrothermal veins in the Variscan basement of Western Carpathians,Slovakia

Hydrothermal polymetallic veins of the Gemeric unit of the Western Carpathians are oriented coherently with the foliation of their low‐grade Variscan basement host. Early siderite precipitated from homogeneous NaCl‐KCl‐CaCl₂‐H₂O brines with minor CO₂, while immiscible gas–brine mixtures are indicative of the superimposed barite, quartz–tourmaline and quartz–sulphide stages. The high‐salinity aqueous fluid (18–35 wt%) found in all mineralization stages corresponds to formation water modified by interaction with crystalline basement rocks at temperatures between 140 and 300°C. High brominity (around 1000 ppm in average) resulted from evaporation and anhydrite precipitation in a Permo‐Triassic marine basin, and from secondary enrichment by dissolution of organic matter in the marine sediments at diagenetic temperatures. Sulphate depletion reflects thermogenic reduction during infiltration of the formation waters into the Variscan crystalline basement. Crystallization temperatures of the siderite fill (140–300°C) and oxygen isotope ratios of the parental fluids (4–10‰) increase towards the centre of the Gemeric cleavage fan, probably as a consequence of decreasing water/rock ratios in rock‐buffered hydrothermal systems operating during the initial stages of vein evolution. In contrast, buoyant gas–water mixtures, variable salinities and strongly fluctuating P–T parameters in the successive mineralization stages reflect transition from a closed to an open hydrothermal system and mixing of fluids from various sources. Depths of burial were 6–14 km (1.7–4.4 kbar, in a predominantly lithostatic fluid regime) during the siderite and barite sub‐stages of the north‐Gemeric veins, and up to 16 km (1.6–4.5 kbar, in a hydrostatic to lithostatic fluid regime) in the quartz–tourmaline stage of the south‐Gemeric veins. The fluid pressure decreased down to approximately 0.6 kbar during crystallization of sulphides. U‐Pb‐Th, ⁴⁰Ar/³⁹Ar and K/Ar geochronology applied to hydrothermal muscovite–phengite and monazite, as well as cleavage phyllosilicates in the adjacent basement rocks and deformed Permian conglomerates corroborated the opening of hydrothermal veins during Lower Cretaceous thrusting and their rejuvenation during Late Cretaceous sinistral transpressive shearing and extension.     

城市历史文化研究中几个理论性问题的刍荛之见

城市之历史文化,是城市发展之重要资源。本文就当前城市历史文化研究中几个重要但研究又较为薄弱的理论问题,即研究城市历史文化的意义与作用、关于历史城市之界定,城市历史文化研究的主要内容进行了阐述,提出了具体见解;以期深入推进城市历史文化之理论性与实证性研究工作。     

对区域社会和谐发展问题的思考

实现区域社会和谐发展是构建社会主义和谐社会的基础。我国地域宽广,不同区域在经济社会发展程度、自然资源、生态环境、历史文化传统及其所面临的问题等方面,都有自身的特点。从民主法治、公平正义、诚信友爱、安定有序、充满活力、人与自然和谐相处等六个方面入手,结合区域自身特点,切实解决区域社会和谐发展中面临的现实问题,不断推进区域社会和谐,进而由每一个区域的社会和谐,走向全社会的和谐,这可能是构建社会主义和谐社会合理的路径选择。     

美国迫使台湾当局从华南边境和沿海岛屿撤兵问题研究

肯尼迪政府时期的美国对华政策已经开始孕育着一些变革。其政府内部先后讨论过一些调整方案,但在国际国内各种复杂因素的制约下没有取得重大突破,其中台湾当局不断施加的干扰和阻碍是一个重要原因。在此时期,美国曾迫使台湾当局从缅泰老“金三角”地区撤军,并试图透迫蒋介石从金门、马祖等沿海岛屿撤防,双方施压与抗压、牵制与反牵制的互动关系十分明显。尽管美国政策设计者们已经认识到美国对华政策必须服务于美国和整个“自由世界”的广泛利益而非台北政权一家的利益,但实际上还是难以摆脱台湾当局的牵制。另外,更重要的阻力来自于美国国内政治的掣肘,而其政策调整的幅度局限于“两个中国”之类的方案,也是根本行不通的。     

A simulation of the hydrothermal response to the Chesapeake Bay bolide impact

Groundwater more saline than seawater has been discovered in the tsunami breccia of the Chesapeake Bay Impact Crater. One hypothesis for the origin of this brine is that it may be a liquid residual following steam separation in a hydrothermal system that evolved following the impact. Initial scoping calculations have demonstrated that it is feasible such a residual brine could have remained in the crater for the 35 million years since impact. Numerical simulations have been conducted using the code HYDROTHERM to test whether or not conditions were suitable in the millennia following the impact for the development of a steam phase in the hydrothermal system. Hydraulic and thermal parameters were estimated for the bedrock underlying the crater and the tsunami breccia that fills the crater. Simulations at three different breccia permeabilities suggest that the type of hydrothermal system that might have developed would have been very sensitive to the permeability. A relatively low breccia permeability (1 × 10^?16 m²) results in a system partitioned into a shallow water phase and a deeper superheated steam phase. A moderate breccia permeability (1 × 10^?15 m²) results in a system with regionally extensive multiphase conditions. A relatively high breccia permeability (1 × 10^?14 m²) results in a system dominated by warm‐water convection cells. The permeability of the crater breccia could have had any of these values at given depths and times during the hydrothermal system evolution as the sediments compacted. The simulations were not able to take into account transient permeability conditions, or equations of state that account for the salt content of seawater. Results suggest, however, that it is likely that steam conditions existed at some time in the system following impact, providing additional evidence that is consistent with a hydrothermal origin for the crater brine.     

New insights from reactive transport modelling: the formation of the sericitic vein envelopes during early hydrothermal alteration at Butte, Montana

A reactive transport computer code has been employed to model hydrothermal alteration of a granitoid rock bordering a discrete vein channel. The model suggests that the grey sericitic and sericitic with remnant biotite alteration envelopes at the porphyry copper deposit at Butte, Montana, can be formed by a reducing, low pH, and low salinity fluid under constant temperature and pressure conditions of approximately 400 °C and less than 100 MPa during a time span of approximately 100 years or less. Hydrothermal alteration has little effect on the porosity of the host rock (Butte Quartz Monzonite), and the diffusivity of the aqueous species also changes little. A sequence of mineral reaction fronts characterizes the alteration envelopes. The biotite dissolution front occurs closest to the vein channel and marks the transition from the grey sericitic to sericitic with remnant biotite envelope. The plagioclase dissolution front occurs farthest into the matrix and marks the edge of relatively fresh Butte Quartz Monzonite. From the properties of the quasi‐stationary state approximation ( Lichtner 1988 ; Lichtner 1991 ), it follows that once the sequence of reaction fronts is fully established, their relative locations remain constant and the widths of the reaction zones increase with the square root of time.     

俄罗斯远东“中国移民问题”论析

在俄罗斯远东乃至全俄罗斯,“中国移民问题”是一个被有关势力上升到政治层面加以夸大、炒作的敏感问题。其主要肇因既有历史基因的复萌,也有现实利益的驱动。在其影响下,中俄两国开展劳务合作的潜力远未得到应有的发挥。近年来,俄虽有部分学者和政界人士能较为客观地分析中国移民问题,阐述利用中国劳务的必要性,且积极探讨利用中国劳务的有效途径,但俄罗斯社会对中国人持有的戒备和排斥心理仍相当浓厚。对此,我们应多从自身方面找原因,改进做法,积极应对,促使俄罗斯社会改变对中国人的偏见,从而将远东变成中俄合作真正的窗口和桥梁。     

Numerical modeling of the origin of calcite mineralization in the Refugio‐Carneros fault,Santa Barbara Basin,California

Many faults in active and exhumed hydrocarbon‐generating basins are characterized by thick deposits of carbonate fault cement of limited vertical and horizontal extent. Based on fluid inclusion and stable isotope characteristics, these deposits have been attributed to upward flow of formation water and hydrocarbons. The present study sought to test this hypothesis by using numerical reactive transport modeling to investigate the origin of calcite cements in the Refugio‐Carneros fault located on the northern flank of the Santa Barbara Basin of southern California. Previous research has shown this calcite to have low δ¹³C values of about ?40 to ?30‰PDB, suggesting that methane‐rich fluids ascended the fault and contributed carbon for the mineralization. Fluid inclusion homogenization temperatures of 80–125°C in the calcite indicate that the fluids also transported significant quantities of heat. Fluid inclusion salinities ranging from fresh water to seawater values and the proximity of the Refugio‐Carneros fault to a zone of groundwater recharge in the Santa Ynez Mountains suggest that calcite precipitation in the fault may have been induced by the oxidation of methane‐rich basinal fluids by infiltrating meteoric fluids descending steeply dipping sedimentary layers on the northern basin flank. This oxidation could have occurred via at least two different mixing scenarios. In the first, overpressures in the central part of the basin may have driven methane‐rich formation waters derived from the Monterey Formation northward toward the basin flanks where they mixed with meteoric water descending from the Santa Ynez Mountains and diverted upward through the Refugio‐Carneros fault. In the second scenario, methane‐rich fluids sourced from deeper Paleogene sediments would have been driven upward by overpressures generated in the fault zones because of deformation, pressure solution, and flow, and released during fault rupture, ultimately mixing with meteoric water at shallow depth. The models in the present study were designed to test this second scenario, and show that in order for the observed fluid inclusion temperatures to be reached within 200 m of the surface, moderate overpressures and high permeabilities were required in the fault zone. Sudden release of overpressure may have been triggered by earthquakes and led to transient pulses of accelerated fluid flow and heat transport along faults, most likely on the order of tens to hundreds of years in duration. While the models also showed that methane‐rich fluids ascending the Refugio‐Carneros fault could be oxidized by meteoric water traversing the Vaqueros Sandstone to form calcite, they raised doubts about whether the length of time and the number of fault pulses needed for mineralization by the fault overpressuring mechanism were too high given existing geologic constraints.     

关于抗美援朝战争史研究的几个焦点问题

抗美援朝战争是新中国成立初期美国侵略当局强加给中国人民的一场战争,也是新中国历史上第一场战争。这场战争为新中国的巩固、建设和发展奠定了基础,是新中国的立国之战。自20世纪90年代以来,随着中国、俄罗斯陆续公布和解密了一批有关抗美援朝战争(朝鲜战争)的历史档案,翻译出版美国、韩国、日本等学者研究著作的增多,研究中出现了许多不同认识。中国人民为进行这场战争付出了重大代价和牺牲,应对这场战争的必要性、正义性和积极意义应给予正确评价。     

钩沉索隐探微发新——桑吉仁谦土族史专著研讨会发言摘要

冬季的青海高原朔风扑面,寒意袭人,2010年12月17日,西宁龙电宾馆会议室内却暖意融融,气氛热烈,由青海土族研究会和青海省文联文学创作研究室联合举办的桑吉仁谦作品研讨会在