中国东部黄山的成山过程及其构造意义

黄山是否存在过冰川是长期争议的科学问题,反对者的证据之一是黄山的海拔高度不能满足终年积雪的要求。这种认识源于地理学家对黄山成山过程的推测,没有考虑黄山岩体和区域地质演化所反映的成因信息。黄山岩体为一个主要由4个岩性单元组成的早白垩世复式小岩基,从早到晚、由边缘到中心依次为温泉细粒黑云母二长花岗岩、云谷寺连续不等粒粗粒黑云母正长花岗岩、狮子岭斑状黑云母正长花岗岩和贡阳山细粒黑云母碱长花岗岩组成。这种结构变化表明黄山地区发生过同侵位剥蚀作用,暗示岩浆侵位深度越来越小,受挤压构造力的驱动。与此相应,狮子岭单元的钾长石斑晶定向排列和云谷寺单元中的原生节理垂直于相邻两单元的接触界面,暗示黄山花岗岩具有强力侵位的特点。因此,黄山岩体形成于挤压构造环境,而不是前人推测的伸展环境。这种认识与区域构造变形和盆地分析的证据一致,暗示黄山地区曾经处于挤压造山环境,具有造山带型厚陆壳。对比岩浆起源深度和现今地壳厚度,可以合理地推测,晚白垩世以来黄山地区地壳减薄了约14～29 km,其地貌响应约为194～418 km。据此,黄山在早白垩世的海拔高度可能达到2 693～4 776 m。因此,黄山形成于地壳沉陷过程中的差异侵蚀,而不是地壳的阶段式隆升。     

区域变质作用对北京房山侵入体 冷却影响的数值模拟

摘 要 通过传热数值模拟分析了区域变质作用对北京西山房山侵入体冷却的影响。结果表 明‚房山侵入体必须处在周围长期高温下才能维持其中央从角闪石 K-Ar 封闭温度到榍石有效 径迹保留温度长达15∙1 Ma 的缓慢冷却。侵入体冷却自早到晚分为以侵入体高温为主导的、 以区域变质衰减为主导的和抬升剥蚀3个冷却阶段。区域变质发生在中、晚侏罗世‚持续到 早白垩世晚期。     

Water-Tank Studies of Separating Flow Over Rough Hills

The present work investigates the lower boundary condition for flows over a steep, rough hill. Simple asymptotic arguments together with the mixing-length hypothesis are used to derive a local analytical solution that is tested against three different flow conditions. In all, 36 velocity profiles are compared with the proposed expression. The experiments were carried out in a water channel and velocity measurements were made through laser Doppler anemometry. The extent of separated flow was made to vary as a function of the roughness and the Reynolds number. The analysis includes regions of attached as well as separated flow. In particular, the solution of Stratford is studied at the points of separation and re-attachment and found to apply equally well in rough walls.     

Constraints on the early metamorphic evolution of Broken Hill, Australia, from in situ U-Pb dating and REE geochemistry of monazite

The Broken Hill Pb-Zn deposit, New South Wales Australia, is hosted in granulite facies gneisses of the Southern Curnamona Province (SCP) that have long been known to record a polydeformational and polymetamorphic history. The details of this potentially prolonged tectonothermal history have remained poorly understood because of a historical emphasis on conventional (i.e. grain mount) U-Pb zircon geochronology to reveal details of the sedimentary, magmatic and metamorphic history of the rock that crops out in the vicinity of the city of Broken Hill. An alternative approach to unravelling the metamorphic history of the granulite facies gneisses in and around Broken Hill is to date accessory minerals, such as monazite, that participate in sub-solidus metamorphic reactions. We have taken advantage of the high spatial resolution and high sensitivity afforded by SHRIMP monazite geochronology to reconstruct the early history of the metamorphic rocks at Broken Hill. In contrast to previous studies, in situ analysis of monazite grains preserved in their original textural context in polished thin sections is used. Guided by electron microprobe X-ray maps, SHRIMP U-Pb dates for three distinct monazite compositional domains record pulses of monazite growth at c. 1657 Ma, c. 1630 Ma and c. 1602 Ma. It is demonstrated that these ages correspond to monazite growth during lower amphibolite facies, upper amphibolite facies and granulite facies metamorphism, respectively. It is speculated that this progressive heating of the SCP crust may have been driven by inversion of the upper crust during the Olarian Orogeny that was pre-heated by magmatic underplating at c. 1657 Ma.     

On the periodically evolving orbits in the singly averaged Hill problem

We continue to analyze the periodic solutions of the singly averaged Hill problem. We have numerically constructed the families of solutions that correspond to periodically evolving satellite orbits for arbitrary initial values of their eccentricities and inclinations to the plane of motion of the perturbing body. The solutions obtained are compared with the numerical solutions of the rigorous (nonaveraged) equations of the restricted circular three-body problem. In particular, we have constructed a periodically evolving orbit for which the well-known Lidov-Kozai mechanism manifests itself, just as in the doubly averaged problem.     

A comparison of wind-tunnel experiments and numerical simulations of neutral and stratified flow over a hill

A comparison is made of numerical and experimental results for flow over two-dimensional hills in both neutral and stably stratified flow. The numerical simulations are carried out using a range of one-and-a-half order and second-order closure schemes. The performance of the various turbulence schemes in predicting both the mean and turbulent quantities over the hill is assessed by comparing the results with new wind-tunnel measurements. The wind-tunnel experiments include both neutral and stably stratified flow over two different hills with different slopes, one of which is steep enough to induce flow separation. The dataset includes measurements of the mean and turbulent parts of the flow using laser Doppler anemometry. Pressure measurements are also made across the surface of the hill. These features make the dataset an excellent test of the model performance. In general second-order turbulence schemes provide the best agreement with the experimental data, however, they can be numerically unstable for steep hills. Some modifications can be made to the standard one-and-a-half order closure scheme, which results in improved performance at a fraction of the computation cost of the second-order schemes.     

Variations of stable isotopes with depth in regolith calcite cements in the Broken Hill region, Australia: Palaeoclimate evolution signal?

Twenty two samples of calcretes from seven depth-profiles in the Menindee catchment, Broken Hill region, Australia were analysed for their inorganic and organic carbon contents and inorganic carbon and oxygen isotopes. The organic carbon content is very low (from 0.06 to 0.31 wt.%) while inorganic carbon (carbonate) is up to 3.9 wt.%. Both δ¹³C and δ¹⁸O become more positive closer to the surface. Carbon isotopes vary from − 8.5‰ to −5.5‰ PDB. Oxygen isotopes vary from − 6‰ to − 1.8‰ V-PDB. Depth-related δ¹³C and δ¹⁸O variations correlate over at least 15 km and show no significant variation along the flow path. δ¹³C values increase by 3‰ and δ¹⁸O values increase by 4‰ with decreasing depth in a 1.40 m thick soil profile. The variation is interpreted to indicate an increasingly elevated air temperature, greater water stress and subsequently an aridification of the area through time. The Broken Hill calcrete data confirm that climatic evolution can be deduced from isotopic series and be applied successfully to the Broken Hill region.     

干热岩（HDR）资源研究与开发技术综述

干热岩（HDR－hot dry rock)是应用前景很好的清洁，可再生能源，其研究与开发仅有20余年历史，但已经表现出巨大的利用价值和发展潜力，美国芬顿山和日本肘折地区是干热岩研究开发的成功范例，干热岩技术的原理是：通过钻井向地下深处的高温岩体中注入低温水，这些水在地下成为高温高压超临界流体，并使岩体产生具有一定方位的裂隙系统，形成热储构造；然后在适当位置钻－眼或几眼生产井贯穿热储构造，用于提取热能，根据热量提取分析可在干热岩在相当长的时间内保持稳定的热量提取速率，个有很高的实用经济价值，此外，干热岩在水岩相互作用，深部精细地球物理方法和裂隙系统三维模拟等方面具有极高的科学研究价值。     

Mineral distribution and provenance of heavy mineral sands (zircon,ilmenite, rutile) deposits from the NW Murray Basin,far western NSW,Australia

Abstract

There is significant economic interest in the Murray Basin of southeastern Australia as it is proving to be a major heavy mineral sands (HMS) province that will be one of Australia’s major source for production of rutile, zircon and ilmenite. The distribution and provenance of HMS resources in the Murray Basin is poorly understood because of its huge size, limited exploration and the complex depositional, structural and weathering mechanisms in their development. In this paper, we focus on the Copi North and Magic deposits some 130–180?km south of Broken Hill, NSW. The heavy mineral assemblages of the Copi North and Magic deposits are very similar, with the main economic minerals being ilmenite, leucoxene, pseudorutile, rutile and zircon. Intensive fracturing and brecciation are identified in many samples and are inferred to have been initially caused by multi-stage deformational processes associated with metamorphism and then further developed through alluvial and eolian transportation. Both deposits are classified as ‘medium sands, symmetrical, mesokurtic and moderately well-sorted’. The majority of economic minerals are of low to medium sphericity and subrounded, along with abundant polished eolian quartz grains. The Copi North deposit has coarser and more poorly sorted sediments with higher HMS grades and magnetics content than the Magic deposit, reflecting a higher energy depositional environment. The main source for the HMS for the Copi North and Magic deposits is largely ascribed to the Broken Hill Block. Previous studies have shown that the Broken Hill orebody underwent substantial sub-aerial weathering over hundreds of millions of years. In addition, the complex metamorphic events experienced by the Broken Hill Block were capable of forming the broad series of minerals identified within the Copi North and Magic deposits. The HMS were believed to have been transported through paleovalleys near the Mulculca Fault in a southeast direction representing a feeder system into the NW Murray Basin. Both deposits feature a relatively linear geometry (roughly parallel to the strike of the paleoshoreline), with high HMS grades, modest tonnages, and coarser sediments when compared to WIM-style offshore deposits. Compared to other strandline HMS deposits of the Murray Basin, they are smaller in size although have similar high grades of 3.7–6.9% THM and similar proportions of the HMS assemblage of ilmenite, leucoxene, rutile and zircon. Deposits of similar size and grade are likely to occur throughout the northern part of the Murray Basin.

1. KEY POINTS

2. Both the Copi North and Magic deposits contain similar mineral assemblages with the provenance of the heavy minerals ascribed to the Broken Hill Block.

3. A relatively high energy inshore environment is inferred for the Copi North deposit while a lower energy environment associated with either a foreshore or backshore environment is inferred for the Magic deposit.

4. Deposits of similar mineralogy, grades and size are likely to occur elsewhere throughout the northern Murray Basin.

     

Active fault traces along Bhuj Fault and Katrol Hill Fault, and trenching survey at Wandhay, Kachchh, Gujarat, India

Several new active fault traces were identified along Katrol Hill Fault (KHF). A new fault (named as Bhuj Fault, BF) that extends into the Bhuj Plain was also identified. These fault traces were identified based on satellite photo interpretation and field survey. Trenches were excavated to identify the paleoseismic events, pattern of faulting and the nature of deformation. New active fault traces were recognized about 1km north of the topographic boundary between the Katrol Hill and the plain area. The fault exposure along the left bank of Khari River with 10m wide shear zone in the Mesozoic rocks and showing displacement of the overlying Quaternary deposits is indicative of continued tectonic activity along the ancient fault. The E-W trending active fault traces along the KHF in the western part changes to NE-SW or ENE-WSW near Wandhay village. Trenching survey across a low scarp near Wandhay village reveals three major fault strands F1, F2, and F3. These fault strands displaced the older terrace deposits comprising Sand, Silt and Gravel units along with overlying younger deposits from units 1 to 5 made of gravel, sand and silt. Stratigraphic relationship indicates at least three large magnitude earthquakes along KHF during Late Holocene or recent historic past.