青海沱沱河多才玛特大型Pb-Zn矿床——定位预测方法与找矿突破过程

青海南部沱沱河地区的多才玛矿床是最近找矿突破发现的一个特大型铅锌矿床.由于赋矿规律不清,找矿方向不明,勘查曾一度陷入困境.针对制约找矿突破的关键地质问题,笔者开展了成矿潜力、矿床赋存规律、矿体定位预测研究,经钻探验证,实现了找矿突破.通过区域对比,认为沱沱河地区与“三江”带内兰坪等其他地区的地质背景相似,具有发育大型沉积岩容矿贱金属矿床的潜力;发现区域发育大型逆冲构造和含膏盐红层沉积、具有碳酸盐岩和暗色泥岩组合等,显示有利的成矿地质环境;区域和矿床内发育大规模高强度的铅锌化探异常,具有形成大型铅锌矿床的潜力.通过填图等研究,指出多才玛矿床为密西西比河谷型(MVT)矿床,产于逆冲推覆构造系统前锋带,矿体赋存于逆冲断裂上盘,受那益雄组碎屑岩和九十道班组灰岩岩相过渡部位及可能的逆冲推覆构造系统派生的反冲构造的控制,矿石主体为热液溶蚀角砾岩型.通过音频大地电磁测深测量,揭示了矿床深部物性特征和构造岩相特点,确定了孔莫陇矿段南侧深部铅锌矿化体的空间位置,并制定了钻探验证方案.经后期勘查,在预测区内探获了品位高、厚度大的铅锌矿体,使该矿段铅锌资源量由原来的76.2万吨增至259万吨,找矿取得重大突破.由此,通过综合分析,提出了一套综合地质、化探异常付化显示、地球物理、遥感等手段的多才玛式矿床定位预测方法组合.     

中扬子中侏罗统陆相高分辨率层序 地层格架及构造控制

[摘 要] 中扬子中侏罗统主要散布于中扬子前陆盆地各次级盆地中,应用现代沉积学、高分辨率层序地层学理论,结合露头岩性、古生物、沉积相分析等手段,发现中侏罗统主要为辫状河、辫状河三角洲或扇三角洲以及滨浅湖沉积体系,在不同区域,分别以花家湖组、沙溪庙组和千佛崖组地层命名。不同区域层序特征既有差异,又存在相似性。根据高分辨率层序地层学理论,将花家湖组、沙溪庙组和千佛崖组分别划分为4 个、4个和2个三级层序,局部地区还可细划四级层序,整个中侏罗统大致相当于1个二级层序。此层序地层格架的形成主要是受构造因素控制,即印支期以来中扬子地区发生强烈的构造变形和运动而形成复杂的盆山耦合体系,层序横向展布和纵向叠加于前陆盆地中。     

平庄盆地充填沉积特征和聚煤规律

根据地层和构造形迹发育特点，简述了平庄盆地诞生、成长及消亡的演化历史。从岩性、粒度分析、垂向层序、沉积断面结构、砂砾岩体几何形态等方面论述了盆地晚中生代充填沉积相的５种类型、各沉积相的空间配置关系；并进一步论述了盆地含煤地层——下白里统古园组、元宝山组的沉积环境。指出了聚煤构造、沉积环境拉煤的规律及找煤远景区段。     

The inter‐relationships between long‐lived metamorphism,pluton emplacement and changes in the direction of bulk shortening during orogenesis

Foliation intersection/inflexion axes combined with pseudosections and garnet‐core isopleths reveal only 1.5 kbar variation in P–T conditions while plutons were emplaced regionally and deformation and metamorphism continued during orogenesis lasting 70 Myr. Tectonism ended with slight decompression into the cordierite stability field. Garnet growth was always overstepped by up to 100 °C occurring at conditions that staurolite growth was also possible. Episodic start, stop, start growth behaviour of both of these phases throughout this period did not result from the effects of bulk composition on their stability fields. Different porphyroblast growth patterns in same bulk composition and outcrop samples reveals reaction start/stop behaviour was controlled by the manner in which deformation partitioned through an outcrop. The regional isograds were established during the first period of bulk shortening near orthogonal to the orogen trend. They did not migrate across lower grade rocks during each of the subsequent periods of metamorphism in spite of dramatic changes in the direction of bulk shortening; rather they contracted slightly. During the youngest periods of orogenesis directed at a high angle to the current orogen trend the isograds were folded about axial planes parallel to the fold belt. The regional distribution of these isograds directly reflects the oldest period of pluton emplacement, with both controlled by orogen‐scale partitioning of bulk shortening at a high angle to the current orogen trend relative to intervening zones of transform‐like shear.     

The multivariate controls of hydraulic geometry: A causal investigation in terms of boundary shear distribution

Most downstream hydraulic geometry exponents have been found to be very close to the classic values reported by Leopold and Maddock (1953). These have been viewed as the simplified cases to general trends because the hydraulic geometry of alluvial channels is actually the product of ‘multivariate controls’ (Richards, 1982). This paper is an attempt to develop a soundly based foundation for the explanation of the physical mechanisms of these controls. A quantitative relationship between channel shape and boundary shear distribution developed from experimental flume results is found to be applicable in some instances to alluvial channels, particularly to stable canals. On the basis of this relationship, it is shown that downstream hydraulic geometry is determined not only by flow discharge, but also by channel slope, channel average roughness and sediment composition of the channel boundary. This is strongly supported by our analysis of 529 observations from both stable canals and natural rivers in the U.S.A. and the U.K. The difference between regime relations in canals and the hydraulic geometry of rivers appears to be caused mainly by channel slope and average roughness, which can be regarded as constants only in stable canals. The close relationship between discharge and channel average roughness observed in canals is not repeated in natural channels, partly because of the variety of flow values used to define the channel-forming discharge. Furthermore, it is indicated that the effects of the sediment composition of the channel boundary on hydraulic geometry are significant and need further investigation.     

LICHEN GROWTH RATES ON GLACIER FORELANDS IN SOUTHERN NORWAY: PRELIMINARY RESULTS FROM A 25-YEAR MONITORING PROGRAMME

A unique 25-year lichen growth monitoring programme involving 2,795 individuals of the Rhizocarpon subgenus at 47 sites on 18 glacier forelands in the Jotunheimen–Jostedalsbreen regions of southern Norway is reported. The data are used to address fundamental questions relating to direct lichenometry: spatial and temporal variability in lichen growth rates, climatic effects on lichen growth rates, lichen growth models, and implications for lichenometric dating. Mean annual (diametral) growth rate ranged from 0.43 to 0.87 mm yr⁻¹ between sites, which is attributed primarily to local habitat differences. Interannual variability in annual mean growth rate exceeded 1.0 mm yr⁻¹ at some sites. Annual mean growth rates for all sites combined varied from 0.52 to 0.81 mm yr⁻¹ and was positively correlated with annual mean temperature and winter mean temperature (both r = 0.64, p <0.005) but not with summer seasonal temperature: positive correlations with annual and winter precipitation were less strong and the correlation with summer precipitation was marginally significant (r = 0.41 p <0.10). Growth-rate models characterized by annual growth rates that remain approximately constant or increase with lichen size up to at least 120 mm tended to fit the data more closely than a parabolic model. This is tentatively attributed to a long 'linear/mature' phase in the growth cycle. Comparison with growth rates inferred from indirect lichenometry suggest that such high measured growth rates could not have been maintained over the last few centuries by the largest lichens used in southern Norway for lichenometric dating. Several hypotheses, such as the effects of competition and climate change, which might explain this paradox, are discussed.     

基于时态的地理信息系统控件的开发与应用

介绍了时态地理信息的由来及发展现状,分析了时态GIS的概念、功能和各种模型.介绍了如何实现普通GIS向时态GIS的转化,并通过实例展示了时态GIS的应用.     

The partial equilibration of garnet porphyroblasts in pelitic schists and its control on prograde metamorphism,Glen Roy,Scotland

Garnet porphyroblasts in sillimanite‐bearing pelitic schists contain complex textural and compositional zoning, with considerable variation both within and between adjacent samples. The sillimanite‐bearing schists locally occur in regional Barrovian garnet zone assemblages and are indicative of a persistent lack of equilibrium during prograde metamorphism. Garnet in these Dalradian rocks from the Scottish Highlands preserves evidence of a range of metamorphic responses including initial growth and patchy coupled dissolution–reprecipitation followed by partial dissolution. Individual porphyroblasts each have a unique and variable response to prograde metamorphism and garnet with mainly flat compositional profiles co‐exists with those containing largely unmodified characteristic bell‐shaped Mn profiles. This highlights the need for caution in applying traditional interpretations of effective volume diffusion eliminating compositional variation. Cloudy garnet with abundant fluid inclusions is produced during incomplete modification of the initial porphyroblasts and these porous garnet are then particularly prone to partial replacement in sillimanite‐producing reactions. The modification of garnet via a dissolution–reprecipitation process releases Ca into the effective whole‐rock composition, displacing the pressure–temperature positions of subsequent isograd reactions. This represents the first report of internal metasomatism controlling reaction pathways. The behaviour of garnet highlights the importance of kinetic factors, especially deformation and fluids, in controlling reaction progress and how the resulting variability influences subsequent prograde history. The lack of a consistent metamorphic response, within and between adjacent schists, suggests that on both local and regional scales these rocks have largely not equilibrated at peak metamorphic conditions.     

Compositional controls on coexisting prehnite-actinolite and prehnite-pumpellyite facies assemblages in the Tal y Fan metabasite intrusion, North Wales: implications for Caledonian metamorphic field gradients

Abstract The Tal y Fan Intrusion is a 110 m thick sub-concordant metabasite sheet intruded into volcaniclastic and pyroclastic rocks of Ordovician age in North Wales. Despite low grade metamorphism, primary textural zones resulting from initial cooling of the sheet are preserved and retain primary mineralogical and chemical variations which influenced the nature and extent of metamorphic recrystallization. This has resulted in a vertical sequence of secondary mineral assemblages through the intrusion. During early hydrothermal alteration K-feldspar replaced plagioclase micropheno-crysts in the marginal and contact zones, and olivine in the central zone was replaced by saponite. Subsequent regional metamorphism resulted in the development of (metastable) prehnite-pumpellyite-epidote assemblages in two sub-zones characterized by high Fe₂O₃. Elsewhere the assemblage prehnite-actinolite-epidote developed except in the contact and marginal zones where activity of CO₂ suppressed both prehnite and pumpellyite. Both assemblages contain excess albite, quartz and chlorite and, on the basis of uniform mineral compositions over the area of an individual thin section, are considered to represent buffered equilibrium assemblages indicative of prehnite-pumpellyite and prehnite-actinolite facies conditions. A metamorphic temperature of 310° C at 1.85 kbar is obtained using the P-T-X grid of Liou, Maruyama & Cho (1985), which implies a field gradient of ～ 44° C km^-1. Assuming that metamorphism relates to burial, an overburden thickness of ～ 7 km is indicated. Total maximum thicknesses, however, of Ordovician, Silurian and Lower Devonian strata, in the area, do not exceed 6 km indicating a field gradient of 52° C km^-1. These relatively high gradients may possibly be related to concealed late Caledonian intrusions, or alternatively may result from high heat flow as a consequence of crustal thinning, rapid sedimentation and intense magmatic activity in a marginal basin setting.     

Spatial transformations in a “loosening state”: South Africa in a comparative perspective

This study explores the spatial transformation of urban South Africa since the ending of Apartheid rule two decades ago. It places this experience within the context of countries which have also gone through a “loosening” of political control and of related controls over spatial arrangements. The paper provides a discussion of South Africa’s spatial trends between 1996 and 2011, focusing on urbanisation; urban form; and socio-spatial segregation, and exploring the extent to which changes identified are shaped by the state, private sector investment, and the everyday actions of households and individuals. It shows that South Africa’s urban spatial transformation, post-Apartheid, is both idiosyncratic and comparable. The consequences of spatial controls, and of their loosening, have been diverse across countries, but also within countries. Loosening has led to differing relationships between state, citizenry and private enterprise, and to complex new crossing points between these groupings, affecting spatial change. In South Africa, significant trends have been: movement to the major cities where employment growth is stronger; levels of racial desegregation; and densification of parts of cities and towns, along with peripheral growth and employment decentralisation. Many of the changes however are differentiated across space and between settlements. While proactive state policies have had some impact (not necessarily in the direction of desired spatial transformation), and there are complex interrelationships, our empirical studies suggest that the major weight of evidence is towards the roles of private enterprise and people in shaping spatial change, enabled in part by forms of state loosening.