冀东太平寨地区斜方辉石的地质特征和成因研究

冀东太平寨地区太古宙麻粒岩相变质杂岩中,含有岩浆成因和变质成因的两类斜方辉石,后者又可分为早、晚两期。在地质产状研究的基础上,据岩相学、矿物化学成分和温度、压力条件,阐明了斜方辉石的成因。研究结果为该区划分地质事件和探索早期地壳演化历史提供了重要的依据。     

北京密云麻粒岩相区变质作用演化及PTt轨迹的研究

北京密云麻粒岩相区在早前寒武纪时期主要经历了两期变质作用。每期变质作用又可划分为三个连续的变质阶段，峰期阶段的Ｐ－Ｔ条件均达到了麻粒岩相．第一期变质作用约结束于２５００Ｍａ，具有与造山带相似的顺时针ＰＴｔ轨迹，峰期阶段Ｔ为８００～９００℃，Ｐ＝０．９８～１．０２ＧＰａ，这种轨迹主要与早期平卧褶皱和推覆构造使地壳大幅度增厚有密切关系。第二期变质作用约发生在１８００Ｍａ，ＰＴｔ轨迹为具近等压加热（ＩＢＨ）特点的顺时针轨迹，峰期阶段Ｔ为７６０～８１０℃，Ｐ为０．９６～１．０４ＧＰａ，这种轨迹与大陆地壳的拉伸作用有密切关系。     

Fluid inclusions in rocks from the amphibolite-facies gneiss to charnockite progression in southern Karnataka, India: direct evidence concerning the fluids of granulite metamorphism

Abstract Fluid inclusion studies of rocks from the late Archaean amphibolite-facies to granulite-facies transition zone of southern India provide support for the hypothesis that CO₂,-rich H₂O-poor fluids were a major factor in the origin of the high-grade terrain. Charnockites, closely associated leucogranites and quartzo-feldspathic veins contain vast numbers of large CO₂-rich inclusions in planar arrays in quartz and feldspar, whereas amphibole-bearing gray gneisses of essentially the same compositions as adjacent charnockites in mixed-facies quarries contain no large fluid inclusions. Inclusions in the northernmost incipient charnockites, as at Kabbal, Karnataka, occasionally contain about 25 mol. % of immiscible H₂O lining cavity walls, whereas inclusions from the charnockite massif terrane farther south do not have visibile H₂O Microthermometry of CO₂ inclusions shows that miscible CH₄ and N₂ must be small, probably less than 10mol.%combined. Densities of CO₂ increase steadily from north to south across the transitional terrane. Entrapment pressures calculated from the CO₂ equation of state range from 5 kbar in the north to 7.5 kbar in the south at the mineralogically inferred average metamorphic temperature of 750°C, in quantitative agreement with mineralogic geobarometry. This agreement leads to the inference that the fluid inclusions were trapped at or near peak metamorphic conditions. Calculations on the stability of the charnockite assemblage biotite-orthopyroxene-K-feldspar-quartz show that an associated fluid phase must have less than 0.35 H₂O activity at the inferred P and T conditions, which agrees with the petrographic observations. High TiO₂ content of biotite stabilizes it to lower H₂O activities, and the steady increase of biotite TiO₂ southward in the area suggests progressive decrease of aH₂O with increasing grade. Oxygen fugacities calculated from orthopyroxene-magnetite-quartz are considerably higher than the graphite CO₂-O₂ buffer, which explains the absence of graphite in the charnockites. The present study quantifies the nature of the vapours in the southern India granulite metamorphism. It remains to be determined whether CO₂-flushing of the crust can, by itself, create large terranes of largeion lithophile-depleted granulites, or whether removal of H₂O-bearing anatectic melts is essential.     

中国东北及邻区大陆边缘构造

中国东北及邻区大陆边缘包括两个构造带。内带由裂解的古陆碎块组成，其北部与古亚洲洋的演化有关，南部与古太平洋演化有关。外带由中生代地体组成。它们是晚古生代到早中生代的洋壳碎块与晚中生代的深海沟堆积组成的混杂体带。古亚洲洋封闭后到现代太平洋板块活动前，即由泥盆纪到侏罗纪曾存在过另一个大洋－古太平洋，其洋底扩张活动形成了上述的构造带。晚侏罗世后本区发育左旋平移断裂系，晚白垩世一早第三纪形成了大陆缘火山－     

Garnet-bearing Granulite Facies Rock Xenoliths from Late Mesozoic Volcaniclastic Breccia, Xinyang, Henan Province

This paper presents the primary results of petrologic, mineralogical and petrochemical studies of garnet-bearing granulite facies rock xenoliths from Xinyang, Henan Province. These xenoliths, which are found in a pipe of late Mesozoic volcaniclastic breccia, are of high density (3.13-3.30 g/cm3) and high seismic velocity (Vp = 7.04-7.31 km/s), being products of underplating of basaltic magmas and had experienced granulite facies metamorphism. The underplating and metamorphism took place before the eruption of the host rock. Petrographical studies and equilibrium T-P calculations show that these xenoliths were captured at a 49 km depth and experienced at least a 16 km uplift before they were captured. The dynamics of the uplift could be related to the continent-continent collision between the North China plate and the Yangtze plate during the Triassic.     

Metastability of granulites and processes of eclogitisation in the UHP region of western Norway

The Flatraket Complex, a granulite facies low strain enclave within the Western Gneiss Region, provides an excellent example of metastability of plagioclase‐bearing assemblages under eclogite facies conditions. Coesite eclogites are found <200 m structurally above and <1 km below the Flatraket Complex, and are separated from it by amphibolite facies gneisses related to pervasive late‐orogenic deformation and overprinting. Granulites within the Flatraket Complex equilibrated at 9–11 kbar, 700–800°C. These predate eclogite facies metamorphism and were preserved metastably in dry undeformed zones under eclogite facies conditions. Approximately 5% of the complex was transformed to eclogite in zones of fluid infiltration and deformation, which were focused along lithological contacts in the margin of the complex. Eclogitisation proceeded by domainal re‐equilibration and disequilibrium breakdown of plagioclase by predominantly hydration reactions. Both hydration and anhydrous plagioclase breakdown reactions were kinetically linked to input of fluid. More pervasive hydration of the complex occurred during exhumation, with fluid infiltration linked to dehydration of external gneisses. Eclogite facies shear zones within the complex equilibrated at 20–23 kbar, 650–800°C, consistent with the lack of coesite and with the equilibration conditions of external HP eclogites. If the complex experienced pressures equivalent to those of nearby coesite eclogites (> 28 kbar), unprecedented metastability of plagioclase and quartz is implied. Alternatively, a tectonic break exists between the Flatraket Complex and UHP eclogites, supporting the concept of a tectonic boundary to the UHP zone of the Western Gneiss Region. The distribution of eclogite and amphibolite facies metamorphic overprints demonstrates that the reactivity of the crust during deep burial and exhumation is strongly controlled by fluid availability, and is a function of the protolith.     

New data on the geology and age of the Koreyskaya River area (south Sikhote-Alin)

Abstract The geological structure of the Koreyskaya River area exhibits a complex combination of turbidite—olistostrome deposits making up a matrix and synsedimentary tectonic enclosures represented by allochthons of formations different in age and genesis. Three tectono-stratigraphic units can be distinguished, that have been combined into a single section by accretion. New data on radiolarians have been used to date the tectonic enclosures and matrix. Abundant Mesozoic radiolarians (from Triassic to Late Jurassic) and also Late Permian radiolarians were found in cherty and siliceous mudstone olistoliths and cherty allochthons.     

徐武家麻粒岩相糜棱岩

内蒙中部土贵乌拉南徐武家早前寒武纪麻粒岩地体中发育北东向韧性剪切带,其中发现有宽达5km 的麻粒岩相糜棱岩剖面,成分相当于紫苏辉长岩、钠质花岗岩和泥质岩的麻粒岩相糜棱岩出露齐全,保存完整。二辉斜长麻粒岩中紫苏辉石、斜长石、钾长石和透辉石斑晶普遍发育强烈的塑性形变;细粒重结晶相矿物组合 Hy+Di+Pl+Kf+Hb+Bi+Scap+Q 显示糜棱岩形成于麻粒岩相变质条件,二辉石矿物对给出温度 T=710℃。该糜棱岩带与麻粒岩相变辉长岩和地壳熔融型石榴子石花岗岩密切共生,这一事实既确证了韧性剪切带在麻粒岩变质过程中发育,为研究该区麻粒岩相岩带构造演化找到了一个构造标志,同时,也为深入探讨下地壳的实际构造过程,包括麻粒岩相条件下剪切形变发生的饥理以及克拉通化提供了地质实例。     

贺兰山群变质杂岩主期变质作用的温压环境研究

分布于贺兰山脉北部的贺兰山群变质杂岩的主期变质作用达角闪麻粒岩相,其矿物组合特征与低压相系麻粒岩相似、利用共生矿物组合和矿物对的温度计、压力计估算主期变质温度740—764(?),压力460—501MPa。温度压力条件与低压相系的地热梯度线较接近,变质作用强度具面型分布的特征,与东部密云、冀东等地的麻粒岩相区相似,但变质压力明显低,压力类型也不同,应属不同构造背景下的变质产物。     

Silica-undersaturated sapphirine, spinel and kornerupine granulite facies rocks, NE Strangways Range, Central Australia

Small pods of silica-undersaturated Al-rich and Mg-rich granulite facies rocks containing sapphirine, pleonastic spinel, kornerupine, cordierite, orthopyroxene, corundum, sillimanite and gedrite are scattered throughout the NE Strangways Range, Central Australia. These are divided into four distinct rock types, namely orthopyroxene-rich aluminous granofels and metapelitic gneisses containing sapphirine, spinel or kornerupine. Two granulite facies metamorphic events are recognized, of which only the first (M1) is considered in this paper. Peak metamorphic mineral parageneses indicate that the M1 thermal maximum occurred at approximately 900–950 °C and 8–9 kbar. All samples are characterized by profuse and diverse coronitic and symplectic reaction textures. These are interpreted as evidence for the sequential crossing of the following reactions in the system FMAS: cordierite + spinel + corundum = sapphirine + sillimanite, cordierite + spinel = orthopyroxene + sapphirine + sillimanite, sapphirine + spinel + sillimanite = orthopyroxene + corundum, sapphirine + sillimanite = cordierite + orthopyroxene + corundum. Phase stability relationships in FMAS and MASH indicate an anticlockwise P–T path terminated by isobaric cooling. Such a path is exemplified by early low-P mineral parageneses containing spinel, corundum and gedrite and the occurrence of both prograde and retrograde corundum. Reaction textures preserve evidence for an increase in aH₂O and aB₂O₃ with progressive isobaric cooling. This hydrous retrogression resulted from crystallization of intimately associated M1 partial melt segregations. There is no evidence for voluminous magmatic accretion giving rise to the high M1 thermal gradient. The M1 P–T path may be the result of either lithospheric thinning after both crustal thickening and burial of the supracrustal terrane, or concomitant crustal thickening and mantle lithosphere thinning.