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.     

Development of fluid conduits in the auriferous shear zones of the Hutti Gold Mine, India: evidence for spatially and temporally heterogeneous fluid flow

The gold mineralization of the Hutti Mine is hosted by nine parallel, N–S trending, steeply dipping, 2–10 m wide shear zones, that transect Archaean amphibolites. The shear zones were formed after peak metamorphism during retrograde ductile D₂ shearing in the lower amphibolite facies. They were reactivated in the lower to mid greenschist facies by brittle–ductile D₃ shearing and intense quartz veining. The development of a S₂–S₃ crenulation cleavage facilitates the discrimination between the two deformation events and contemporaneous alteration and gold mineralization. Ductile D₂ shearing is associated with a pervasively developed distal chlorite–sericite alteration assemblage in the outer parts of the shear zones and the proximal biotite–plagioclase alteration in the center of the shear zones. D₃ is characterized by development of the inner chlorite-K-feldspar alteration, which forms a centimeter-scale alteration halo surrounding the laminated quartz veins and replaces earlier biotite along S₃. The average size of the laminated vein systems is 30–50 m along strike as well as down-dip and 2–6 m in width.Mass balance calculations suggest strong metasomatic changes for the proximal biotite–plagioclase alteration yielding mass and volume increase of ca. 16% and 12%, respectively. The calculated mass and volume changes of the distal chlorite–sericite alteration (ca. 11%, ca. 8%) are lower. The decrease in δ¹⁸O values of the whole rock from around 7.5‰ for the host rocks to 6–7‰ for the distal chlorite–sericite and the proximal biotite–plagioclase alteration and around 5‰ for the inner chlorite-K-feldspar alteration suggests hydrothermal alteration during two-stage deformation and fluid flow.The ductile D₂ deformation in the lower amphibolite facies has provided grain scale porosities by microfracturing. The pervasive, steady-state fluid flow resulted in a disseminated style of gold–sulfide mineralization and a penetrative alteration of the host rocks. Alternating ductile and brittle D₃ deformation during lower to mid greenschist facies conditions followed the fault-valve process. Ductile creep in the shear zones resulted in a low permeability environment leading to fluid pressure build-up. Strongly episodic fluid advection and mass transfer was controlled by repeated seismic fracturing during the formation of laminated quartz(-gold) veins. The limitation of quartz veins to the extent of earlier shear zones indicate the importance of pre-existing anisotropies for fault-valve action and economic gold mineralization.     

Deformation mechanism maps for feldspar rocks

Deformation mechanism maps for feldspar rocks were constructed based on recently published constitutive laws for dislocation and grain boundary diffusion creep of wet and dry plagioclase aggregates. The maps display constant temperature contours in stress-grain size space for strain rates ranging from 10⁻¹⁶ to 10⁻¹² s⁻¹.Two fields of dominance of grain boundary diffusion-controlled creep and dislocation creep are separated by a strongly grain size-sensitive transition zone. For wet rocks, diffusion-controlled creep dominates below a grain size of about 0.1–1 mm, depending on temperature, stress, strain rate and feldspar composition. Plagioclase aggregates containing up to 0.3 wt.% water as often found in natural feldspars are more than 2 orders of magnitude weaker than dry rocks. The strength of water-bearing feldspar rocks is moderately dependent on composition and water fugacity.For a grain size range of about 10–50 μm commonly observed in natural ultramylonites, the deformation maps predict that diffusion-controlled creep is dominant at greenschist to granulite facies conditions. Low viscosity estimates of 10¹⁸–10¹⁹ Pa·s from modeling postseismic stress relaxation and channel flow of the continental lower crust can only be reconciled with laboratory experiments assuming dislocation creep at high temperatures >900 °C or, at lower temperatures, diffusion creep of fine-grained rocks possibly localized in abundant high strain shear zones. For similar thermodynamic conditions and grain size, lower crustal rocks are predicted to be less than order of magnitude weaker than upper mantle rocks.     

Inhabiting the Imaginary: Factory Women at Home on Batam Island, Indonesia

Batam Island, Indonesia, located a short ferry ride away from Singapore, is a place where tourism and industry have been developed simultaneously and a border area where “developed” and “developing” nations meet. Government officials, investing international corporations and the “factory women” who work in the island's industrial estates arrive in Batam ‐ native to none of them ‐ with their own preconceptions and goals. When challenges not foreseen through master planning arise, the authorities cling ever more tightly to their physical and structural development model: the nearby city‐state of Singapore. Conversely, the factory workers who travel intranationally to work in this export processing zone (EPZ) find their objectives contested in the face of the Master Plan, corporate agendas and ethnic fusions characterising this transnational capitalist space. Entering into the homes of three groups of women migrants living and working in Batam, the relationship between the private realm that they inhabit and the social contexts in which they participate publicly is investigated. Some of the choices that women make at and about home are identified, and their ability to “micro‐resist” these external structures is explored. At home, the dynamic relationship between the Batam development project and the women's own hopes and visions of the place ‐ sometimes parallel and sometimes incongruous ‐ are revealed. As they experience life on Batam, their “social imaginaries” of it are shaped into various new realities, and their homes, removed from the confines of the factory floor, thus become spaces of release from these tensions.