递增变质作用若干问题评述

递增变质作用以沿造山带中区域热动力异常中心发育递增变质带和热为特征，变质作作用时间上的演经与其在空间上的变化之间的关系，变质作用的温度，压力在时间的变化规律，这些规律所反映的变质作用热动力时空演化过程和机制以及变质作用的根本原因等，是变质地质学的基本问题，递增变质作用在时间上的演化与其空间上的变化是有机统一地过程。建立变质作用时空框架，客观地揭示变质作用时空溶化规律造山过程，是递增变质作用研究的必     

韧性剪切带型金矿成矿特征研究现状

综述了近几年韧性剪切带型金矿研究成果,包括韧性剪切带与金矿化在时间、空间和成因的关系及剪切带的历史演化性质对成矿类型与地球化学特点的控制。在此基础上,预测了近期可能的几个发展方向。     

地质流体力学研究的进展

归纳了地质流体力学研究中目前常用的三个基础理论,即双扩散对流理论,边界层理论和相似理论,重点总结了其在岩浆岩石学、成矿学、地球物理学及沉积岩石学等研究领域内的进展。     

Investigation for geothermal energy in Sweden

Preliminary investigations of the geothermal energy potential in Sweden are being carried out in crystalline rocks of Precambrian age, as well as in the Triassic Buntsandstone. The geothermal potential of fracture zones is also being investigated. Different methods for prospecting have been tried and compared.     

Melt Inclusions in Primitive Olivine Phenocrysts: the Role of Localized Reaction Processes in the Origin of Anomalous Compositions

Melt inclusions are small portions of liquid trapped by growingcrystals during magma evolution. Recent studies of melt inclusionshave revealed a large range of unusual major and trace elementcompositions in phenocrysts from primitive mantle-derived magmaticrocks [e.g. in high-Fo olivine (Fo > 85 mol %), spinel, high-Anplagioclase]. Inclusions in phenocrysts crystallized from moreevolved magmas (e.g. olivine Fo < 85 mol %), are usuallycompositionally similar to the host lavas. This paper reviewsthe chemistry of melt inclusions in high-Fo olivine phenocrystsfocusing on those with anomalous major and trace element contentsfrom mid-ocean ridge and subduction-related basalts. We suggestthat a significant portion of the anomalous inclusion compositionsreflects localized, grain-scale dissolution–reaction–mixing(DRM) processes within the magmatic plumbing system. The DRMprocesses occur at the margins of primitive magma bodies, wheremagma is in contact with cooler wall rocks and/or pre-existingsemi-solidified crystal mush zones (depending on the specificenvironment). Injection of hotter, more primitive magma causespartial dissolution (incongruent melting) of the mush-zone phases,which are not in equilibrium with the primitive melt, and mixingof the reaction products with the primitive magma. Localizedrapid crystallization of high-Fo olivines from the primitivemagma may lead to entrapment of numerous large melt inclusions,which record the DRM processes in progress. In some magmaticsuites melt inclusions in primitive phenocrysts may be naturallybiased towards the anomalous compositions. The occurrence ofmelt inclusions with unusual compositions does not necessarilyimply the existence of new geologically significant magma typesand/or melt-generation processes, and caution should be exercisedin their interpretation. KEY WORDS: melt inclusions; olivine; geochemistry; mush zones; MORB; subduction-related magmas     

Surface stresses associated with arrested dykes in rift zones

Many theoretical models predict that arrested dykes may generate major grabens at rift-zone surfaces. Arrested dyke tips in eroded rift zones, however, are normally not associated with major grabens or normal faults that could be generated by dyke-induced stresses ahead of the tips, and normal faults and grabens tend to be less common in those parts of eroded rift zones where dykes are comparatively abundant. Similarly, there are feeder dykes, as well as dykes arrested a few metres below the surface, that do not generate faults or grabens at the surface. Here I propose that this discrepancy between theoretical models and field observations may be explained by the mechanical layering of the crust. Numerical models presented here show that abrupt changes in Young's moduli, layers with high dyke-normal compressive stresses (stress barriers), and weak, horizontal contacts have large effects on the dyke-induced stress fields. For the models considered, the surface tensile stresses induced by arrested dykes are normally too small to lead to significant fault or graben formation at the rift-zone surface. The only significant dyke-induced surface tensile stresses (2 MPa) in these models are for a dyke tip arrested at 1 km depth below the surface of a rift zone with a weak contact at 400 m depth and subject to extension. That tensile stress, however, peaks above the ends of the weak horizontal contact, which, in the model considered, occur at distances of 4 km to either side of the dyke, and shows no simple relation to the depth to the dyke tip. Thus, for a layered crust with weak contacts, straightforward inversion of surface geodetic data to infer dyke geometries may result in unreliable results.Editorial responsibility: A. Woods     

陕京输气管道断裂带形变监测GPS网的数据处理及形变分析

介绍了2000年陕京输气管道断裂带形变监测GPS网的数据处理过程,并对1999年和2000年两期成果进行了形变分析,其结果将为跨越断裂带的输气管道的形变监测提供借鉴.     

Spinel–cordierite symplectites replacing andalusite: evidence for melt-assisted diapirism in the Bushveld Complex, South Africa

Spinel–cordierite symplectites partially replacing andalusite occur in metapelitic rocks within the cores of several country rock diapirs that have ascended into the upper levels of layered mafic/ultramafic rocks in the Bushveld Complex. We investigate the petrogenesis of these symplectites in one of these diapirs, the Phepane dome. Petrographic evidence indicates that at conditions immediately below the solidus the rocks were characterized by a cordierite‐, biotite‐ and K‐feldspar‐rich matrix and 5–10 mm long andalusite porphyroblasts surrounded by biotite‐rich fringes. Phase relations in the MnNCKFMASHT model system constrain the near‐solidus prograde path to around 3 kbar and imply that andalusite persisted metastably into the sillimanite + melt field, where the fringing relationship between biotite and andalusite provided spatially restricted equilibrium domains with silica‐deficient effective bulk compositions that focused suprasolidus reaction. MnNCKFMASHT pseudosections that model these compositional domains suggest that volatile phase‐absent melting reactions consuming andalusite and biotite initially produced a moat of cordierite surrounding andalusite; reaction progressed until all quartz was consumed. Spinel is predicted to grow with cordierite at around 720 °C. Formation of the aluminous solid products was strongly controlled by the receding edge of andalusite grains, with symplectites forming at the andalusite‐cordierite moat interface. Decompression due to melt‐assisted diapiric rise of the floor rocks into the overlying mafic/ultramafic rocks occurred close to the thermal peak. Re‐crossing of the solidus at P = 1.5–2 kbar, T > 700 °C resulted in preservation of the symplectites. Two features of the silica‐deficient domains inhibited resorption of spinel. First, the cordierite moat armoured the symplectites from reaction with crystallizing melt in the outer part of the pseudomorphs. Second, an up‐T step in the solidus at low‐P, which may be in excess of 100 °C higher than the quartz‐saturated solidus, resulted in high‐T crystallization of melt on decompression. Even in metapelitic rocks where melt is retained, preservation of spinel is favoured by decompression.