Metamorphism and granite genesis in the Hidaka Metamorphic Belt, Hokkaido, Japan   总被引：3，自引：0，他引：3  

Y. OSANAI  M. KOMATSU  M. OWADA 《Journal of Metamorphic Geology》1991,9(2):111-124

The Main Zone of the Hidaka Metamorphic Belt is an uplifted crustal section of island-arc type. The crust was formed during early Tertiary time, as a result of collision between two arc–trench systems of Cretaceous age. The crustal metamorphic sequence is divided into four metamorphic zones (I–IV), in which zone IV is in the granulite facies. A detailed study of the evolution of the Hidaka Belt, based on a revised P–T–t analysis of the metamorphic rocks, notably a newly found staurolite-bearing granulite, confirms a prograde isobaric heating path, after a supposed event of tectonic thickening of accretionary sedimentary and oceanic crustal rocks. During the peak metamorphic event (c. 53 Ma), the regional geothermal gradient attained 33–40° C km^?1, and the highest P–T condition obtained from the lowest part of the granulite unit is 830° C, 7 kbar. In this part, X_H2O of Gt–Opx–Cd gneiss is about 0.15 and that of Gt–Cd–Bt gneiss is 0.4. The P–T–X_H2O condition of the granulite unit is well within a field where fluid-present partial melting of pelitic and greywacke metamorphic rocks takes place. This is in harmony with the restitic nature of the Gt–Opx–Cd gneiss in the lowest part of the granulite unit. The possibility that partial melting took place in the Main Zone is significant for the genesis of the peraluminous (S-type) granitic rocks within it. The S-type granitic rocks in this zone are Opx–Gt–Bt tonalite in the granulite zone, Gt–Cd–Bt tonalite in the amphibolite zone, and Cd–Bt–Mus tonalite in the Bt–Mus gneiss zone. The mineralogical and chemical nature of these strongly peraluminous tonalitic rocks permit them to be regarded as having been derived from S-type granitic magma generated by crustal anatexis of pelitic metamorphic rocks in deeper crust.  相似文献   

The nature and distribution of fluids during amphibolite facies metamorphism, Naxos (Greece)   总被引：1，自引：0，他引：1  

I. S. BUICK  T. J. B. HOLLAND 《Journal of Metamorphic Geology》1991,9(3):301-314

On the basis of fluid inclusion evidence, pervasive influx of deep-seated CO₂-rich fluids has been invoked to account for mid- to upper amphibolite facies (M2_B) metamorphism on the island of Naxos (Cyclades, Greece). In this paper, mineral devolatilization and melt equilibria are used to constrain the composition of both syn- and post-peak-M2_B fluids in the deepest exposed levels of the metamorphic complex. The results indicate that peak-M2_B fluids were spatially and compositionally heterogeneous throughout the high-grade core of the complex, whereas post-peak-M2_B fluids were generally water-rich. The observed heterogeneities in syn-M2_B fluid composition are inconsistent with pervasive CO₂-flushing models invoked by previous workers on the basis of fluid inclusion evidence. It is likely that few CO₂-rich fluid inclusions on Naxos preserve fluids trapped under peak metamorphic conditions. It is suggested that many of these inclusions have behaved as chemically open systems during the intense deformation that accompanied the uplift of the metamorphic complex. A similar process may explain the occurrence of some CO₂-rich fluid inclusions in granulite facies rocks.  相似文献   

Decompressional coronas and symplectites in granulites of the Musgrave Complex, central Australia   总被引：2，自引：0，他引：2  

G. L. CLARKE  R. POWELL 《Journal of Metamorphic Geology》1991,9(4):441-450

Abstract In granulite facies metapelitic rocks in the Musgrave Complex, central Australia, reaction between S1 garnet and sillimanite involves the development in S2 of both garnet + cordierite + hercynitic spinel + biotite and hercynitic spinel + cordierite + sillimanite + biotite. The S2 assemblages occur either in coronas and symplectites, mainly around garnet, or, in rocks in which S2 is more strongly developed, as recrystallized assemblages. Ignoring the presence of biotite and ilmenite, the mineral textures can be accounted for qualitatively by a consideration of the model system FeO-MgO-Al₂O₃-SiO₂ (FMAS); the textural relationships accord with decompression accompanying the change from S1 to S2. However, since biotite and ilmenite are involved in the assemblages, the parageneses are better accounted for in terms of equilibria in the expanded model system K₂O-FeO-MgO-Al₂O₃-SiO₂-H₂-TiO₂-Fe₂O₃ (KFMASHTO), i.e. AFM + TiO₂+ Fe₂O₃. The coronas reflect the tectonic unroofing of at least part of the Musgrave Complex from peak S1 conditions of about 8 kbar to S2 conditions of about 4 kbar.  相似文献   

吉林省南部下元古界集安群地质特征与沉积期古环境分析   总被引：5，自引：0，他引：5  

王福润 《吉林地质》1991,10(2):31-41

根据集安群地质特征,岩石化学,稳定同位素特征分析认为:蚂蚁河组沉积期古环境为强氧化泻湖相;荒岔沟组沉积期为强还原的泻湖相、大东岔组沉积期为开阔正常浅海潮坪相。集安群从发生发展到结束古环境演化规律是:构造上,由优地槽向冒地槽演化,气候上由炎热向温湿演化;古地理环境从有障壁的局限海变为无障壁的开阔海;从咸化海向正常海,从泻湖相向潮坪相转化。  相似文献   

黔南桂北下三叠统碳酸盐海岸—陆架沉积总体的沉积构成及沉积过程分析     

周杰  夏文臣  张国平 《地球科学》1991,(6)

在黔南桂北下三叠统进行沉积过程和沉积构成分析的基础上,识别出了构成碳酸盐海岸—陆架沉积总体的4种成因单位和7种沉积相。同时本文还对碳酸盐海岸—陆架沉积总体的演化过程及其与其它沉积总体的空间组合关系进行了讨论。  相似文献   

冀东陆壳结构的岩石学模型   总被引：7，自引：4，他引：7       下载免费PDF全文

吴宗絮  郭才华 《地震地质》1991,13(4):369-376

冀东地区的古老变质岩系是一个出露的大陆地壳断面。根据变质岩系的变质相、亚相的研究和地质温压计计算的结果推定的深度,并结合地球物理测深资料,以及笔者测定和前人的岩石高压下波速实验资料提出了本区大陆地壳结构的岩石学模型。下地壳由麻粒岩相岩石组成,上部为角闪石麻粒岩亚相的中性成分的麻粒岩,下部为辉石麻粒岩亚相的基性成分的麻粒岩构成,底部夹有透镜状蛇纹石化橄榄岩以及紫苏花岗岩。中地壳主要由高角闪岩相的中性-中酸性成分的片麻岩、片岩构成,顶部为低角闪岩相的片麻岩、片岩,广泛发育英云闪长岩和花岗闪长岩岩体,含隙间高温流体相(fluid phase),形成高导-低速层。上地壳主要为绿片岩相(部分低角闪岩相)的板岩、千枚岩、片岩、变粒岩以及花岗岩组成,顶部为沉积盖层  相似文献   

垭头铀矿床控矿沉积相及成因     

张宝成 《铀矿地质》1991,(4)

垭头铀矿是湘西沅麻盆地白垩系红层中较为典型的沉积矿床,位于盆地东北缘,靠雪峰隆起,置于Z_b,(?)_(1x),地层之上。本文是在综合野外实践的基础上,研究矿床的沉积特点、控矿沉积相以及矿床成因。  相似文献   

顺便伽玛测量在水化普查中的找铀效果     

胡正安 《铀矿地质》1991,7(6):360-366

在铀矿普查中,伽玛测量具有经济、快速、轻便、连续测量的特点。在水化普查中作顺便伽玛测量,投资少、收效快,并可直接发现供详查揭露的矿化点。在生产布置上与水化测量相互适应。通过一遍工作之后,可取得2套各具特点的资料。在资料解释及运用上,二者可互为补充。对无水地段,水化测量为空白区,可用伽玛测量补其不足。伽玛测量可为水化异常解释提供资料,水化异常的规模及浓度的高低又是推测深部矿化情况的依据。从统计结果证实,比例尺为上1:2.5万的顺便伽玛测量与1:1万的正规伽玛测量比较,发现异常机率可达60％。可见将顺便伽玛测量资料在测量精度上降一级使用,是可以满足精度要求的。  相似文献   

706矿点钻孔放射性水异常的揭露评价     

廖瑞福 《铀矿地质》1985,(4)

本文总结了706矿点水中放射性元素的富集、迁移、分布特点及其与水的化学成分的关系,作者评价了该区放射性水异常的铀成矿远景,并进一步指导了水化学找矿工作。另外,根据该矿点的水文地质条件和氡的迁移规律,定量预测了盲矿体赋存的空间位置。  相似文献   

Can injection tests reveal the potential for fault movements?     

J. Noorishad  P. A. Witherspoon 《Pure and Applied Geophysics》1984,122(2-4):608-618

The role of fluids in faulting mechanism and triggering earthquakes is widely accepted. The effective-stress law is the basis for the postulated theories. Using a generalized version of this law, applicable to both continuum and discontinuities, hydromechanical behaviour of a horizontal fracture in a hypothetical fluid-injection problem is investigated. In this problem the increasing intake flow rates, unpredictable by the traditional fluid-flow solutions, brings out another significant aspect of the role of the fluid pressure in rocks. By reducing the magnitude of the compressive effective stresses the fluid pressure causes elastic recovery in fractures. Simple rheologic models are used to demonstrate this fact. Such effects may lead to permeability increases in the rock mass, depending on the magnitude of the fluid pressure. Such variations in permeability, however, are governed by the path dependency of the fracture-deformation response. Therefore, a significant increase in permeability is an indication of comparability of the state of stress and the applied fluid pressure.This index may reveal the potential of hydroactivation of faults, as may arise in the regions of dam reservoirs, underground waste injections, and known faults, for certain ranges of working pressures relevant to each of the above-cited situations. Fluid-injection tests under constant working pressures are suggested as a means revealing the likelihood of movement on the faults.  相似文献