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121.
Danba (丹巴) domal metamorphic terrain belongs to Songpan (松潘)-Ganze (甘孜) orogenic belt, where typical Barrovian and Buchan metamorphic zones are preserved. The former included chlorite, biotite, garnet, staurolite, kyanite and sillimanite zones, while the latter only developed silimanite+muscovite and sillimanite+K-feldspar zones. Integrated study has been carried on metamorphic reactions of garnet production and consumption, P-T paths and P-T-X-M phase relation and thermal tectonic model for Danba metamorphic zones. Petrological textures in thin sections show that garnet production and consumption in kyanite-sillimanite zone is mainly attributed to ChI+Ms+PI+Q=Grt+Bt+H2O and kyanite=sillimanite respectively. Based on mineral compositions, the geothermobarometry gives an average P, T condition of (4.9±0.3)×108 Pa, 543±30℃ for the first growth stage of the garnet and (5.8±0.3)±108 Pa, 534±29 ℃ for the second stage of garnet growth respectively. Anti-counter clockwise P-T paths were drawn using Gibbs method by NCMnKFMASH system for sample G98686 in the kyanite zone. The P-T-X-M modeling for the first mineral assemblages shows that the prediction is similar to the measured values in gossular, almandine and spessartine but mole fraction of pyrope and Fe/(Fe+Mg) deviated far from the contours; while that for the second mineral assemblages exhibits that the prediction is consistent with the measured value of pyrope, grossular content and Fe/(Fe+Mg) of garnet. A thermal tectonic model that there are at least three structure levels across the thrnst-decollement zones is presented according to the P-T paths, metamorphic grades and deformation styles for the staurolite-kyanite zone of the Barroviau type metamorphism, which will provide some constraints for the evolution of the nappe complex. 相似文献
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湖北铜绿山铜铁矿床中煌斑岩的矿物学特征及岩石成因初探 总被引:1,自引:1,他引:1
湖北铜绿山矽卡岩型铜铁矿床处于长江中下游铁铜成矿带西部的鄂东南矿集区。最近我们在该矿区工作中采集到两条侵入于含矿石英二长闪长玢岩中的煌斑岩脉。本文对这些煌斑岩脉进行了详细的镜下岩相学观察,并对其中造岩矿物黑云母、辉石和长石进行了电子探针成分分析。根据这些数据本文论述了煌斑岩的物源、形成环境以及岩浆体系的物理化学条件。研究表明,煌斑岩中云母为富镁黑云母,其形成的岩浆体系处于中低氧逸度(近Ni-Ni O);黑云母与全岩都具有高钛特征,表明煌斑岩的物源深度可能来自较深部地幔(如软流圈)。煌斑岩中辉石为单斜辉石,环带较为发育,有韵律环带和正环带,其韵律环带的形成可能是由于岩浆温压环境存在振荡性变化而形成的。铜绿山矿床中煌斑岩属于云煌岩;其岩浆来源具幔源性,受到地壳的混染作用不强。 相似文献
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湖南宝山铜钼铅锌银多金属矿田围岩蚀变与矿化分带特征 总被引:7,自引:2,他引:7
宝山铜钼铅锌银矿田主要由中部、东部、西部和北部4个矿床组成,属岩浆期后高中温含矿热液接触交代矽卡岩型铜钼金属铋矿床、中低温热液充填交代铅锌银矿床。矿田围岩蚀变强烈,并与矿化关系密切,具有以岩体为中心向外呈现明显的围岩蚀变和矿化分带特征,可作为找矿的重要标志。 相似文献
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Controls on metamorphic equilibration: the importance of intergranular solubilities mediated by fluid composition 下载免费PDF全文
W. D. Carlson J. D. Hixon J. M. Garber R. J. Bodnar 《Journal of Metamorphic Geology》2015,33(2):123-146
A dramatic demonstration of the role of intergranular solubility in promoting chemical equilibration during metamorphism is found in the unusual zoning of garnet in pelitic schist exposed at Harpswell Neck, Maine, USA. Many garnet crystals have irregular, patchy distributions of Mn, Cr, Fe and Mg in their inclusion‐rich interiors, transitioning to smooth, concentric zoning in their inclusion‐poor outer rims; in contrast, zoning of Ca and Y is comparatively smooth and concentric throughout. We re‐assess the disputed origin of these zoning features by examining garnet growth in the context of the thermal and structural history of the rocks, and by evaluating the record of fluid–rock interaction revealed in outcrop‐scale veining and fluid‐inclusion assemblages. The transition in the character of garnet zoning correlates with the onset of a synkinematic, simple‐shear‐dominated phase of garnet growth and with a shift in the composition of the intergranular fluid from CO2‐rich to H2O‐rich. Compositional variations in garnet are therefore best explained by a two‐stage growth history in which intergranular diffusive fluxes reflect differences in the concentration of dissolved species in these two contrasting fluids. Interiors of garnet crystals grew in the presence of a CO2‐rich fluid, in which limited solubility for Mn and Cr (and perhaps Fe and Mg) produced patchy disequilibrium overprint zoning, while appreciable solubility for Ca and Y permitted their rock‐wide equilibration. Rims grew in the presence of an H2O‐rich fluid, in which high intergranular concentrations for all elements except Cr enabled diffusion over length scales sufficient for rock‐wide equilibration. This striking example of partial chemical equilibrium during reaction and porphyroblast growth implies that thermal effects may commonly be subsidiary in importance to solubilities in the intergranular medium as determinants of length scales for metamorphic equilibration. 相似文献
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Mario Benhumea Leon 《Geotechnical and Geological Engineering》1989,7(1):59-68
Summary The seismic events occurring on 19 and 20 September 1985, whose epicentre was located in the coastal region of Michoacan, Mexico, produced tremendous damage in Mexico City. As a result of these losses the civil authorities of the city decided to study and evaluate the mechanical characteristics of the subsoil. To achieve this, it was necessary to drill several boreholes to obtain needed geophysical and geotechnical information. The geophysical method of electrical resistivity was the most appropriate to the research. This method enabled us to understand the structure and soil characteristics of the Mexican Valley. 相似文献
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本文对西藏厅宫大型铜矿进行了详细研究,矿床详细的地质岩相学-蚀变以及典型剖面填图表明,矿区存在2个岩浆事件高峰,即始新世的钾长花岗岩(~50 Ma)和中新世的斑状二长花岗岩、英云闪长斑岩及闪长玢岩(约13~17 Ma)。野外和室内研究发现,厅宫矿区存在2期重要的矿化事件,即始新世(~50 Ma)铜矿化及中新世(~15Ma)的铜钼矿化。始新世含矿岩体为钾长花岗岩,其最主要的特点是其成矿岩体结构的特殊性,表现在该矿床的成矿岩体没有典型的斑状结构,而是独特的细晶-似伟晶结构,说明含矿岩浆发生过骤冷,可能是流体突然逃逸,矿物结晶的固相点发生漂移所致。同时,该岩体还发育大量显微文象结构、显微晶洞构造等,均说明岩浆曾经富水,并且曾经流体饱和;中新世含矿岩体为具有埃达克岩特征的斑状二长花岗岩,主要以脉状的铜、钼矿化为主。该矿床蚀变分带类似于冈底斯带其他斑岩矿床。时间上,分别为早期的钾硅酸盐化、转换阶段的青磐岩化、随后的绢英岩化及最晚期的泥化蚀变;空间上,以含矿岩体为中心向外依次为钾硅酸盐化、绢英岩化、青磐岩化,最晚期的泥化呈补丁状或条带状叠加早期各类蚀变。铜矿化主要发生在始新世的黑云母化阶段和中新世的绢英岩化阶段,而钼矿化主要发生在中新世的钾硅酸盐化和绢英岩化的转换阶段。 相似文献