陇县店子上片麻状地质体本来面目的恢复及地质矿产意义

在一比五万区调中依据岩貌、接触关系、产状、包体、组构、岩石化学和地球化学诸方面的资料，恢复并论述了店子上一带片麻状地质体的本来面目，证明其为片麻状闪长岩，并非变质表壳岩，确定了其在测区岩浆演化序列中的位置；并对岩浆侵位与成矿作用之间的关系进行了探讨。     

造山带高压、超高压变质岩形成和折返的地球动力学研究─—以中国中部为例

秦岭、大别、苏鲁地区是横亘中国中部的复合型大陆造山带，已成为世界高压、超高压变质岩研究的典型地区，在大陆动力学研究中具重要意义。本文综述了该带高压、超高压变质岩的多样性、多期性、区域分带性和形成折返的四种模式，即碰撞外来岩块模式、俯冲－碰撞－逆冲模式、碰撞－走滑转换－逆冲推覆模式和多期多成因复合模式。并指出高压、超高压变质岩的原岩属性、形成时代、ｐＴｔ轨迹、形成深度和岩浆作用等是深入研究形成和折返机制的关键问题。强调以构造为主的多学科综合研究是解决其地球动力作用过程的有效途径。     

滇西澜沧变质带中白云母b_0值特征及其多期变质作用意义

滇西澜沧变质带中199件白云母b_0值分析结果表明,b_0值均在0.9020nm以上。与澜沧变质带遭受蓝片岩相高压变质作用的事实相吻合。此外,白云母b_0值的统计规律显示,澜沧变质带经历了多期变质作用,一期为高压变质作用,另一期为中压变质作用,这也与已知的地质现象相符。由此可见,白云母b_0值可以很好地反映多期变质作用。     

Fluid infiltration and regional metamorphism of the Waits River Formation, north-east Vermont, USA

Abstract The Siluro-Devonian Waits River Formation of north-east Vermont was deformed, intruded by plutons and regionally metamorphosed during the Devonian Acadian Orogeny. Five metamorphic zones were mapped based on the mineralogy of carbonate rocks. From low to high grade, these are: (1) ankerite-albite, (2) ankerite-oligoclase, (3) biotite, (4) amphibole and (5) diopside zones. Pressure was near 4.5kbar and temperature varied from c. 450° C in the ankerite-albite zone to c. 525° C in the diopside zone. Fluid composition for all metamorphic zones was estimated from mineral equilibria. Average calculated χ_co2[= CO₂/(CO₂+ H₂O)] of fluid in equilibrium with the marls increases with increasing grade from 0.05 in the ankerite-oligoclase zone, to 0.25 in the biotite zone and to 0.44 in the amphibole zone. In the diopside zone, χ_CO2 decreases to 0.06. Model prograde metamorphic reactions were derived from measured modes, mineral chemistry, and whole-rock chemistry. Prograde reactions involved decarbonation with an evolved volatile mixture of χ_CO2 > 0.50. The χ_CO2 of fluid in equilibrium with rocks from all zones, however, was generally <0.40. This difference attests to the infiltration of a reactive H₂O-rich fluid during metamorphism. Metamorphosed carbonate rocks from the formation suggests that both heat flow and pervasive infiltration of a reactive H₂O-rich fluid drove mineral reactions during metamorphism. Average time-integrated volume fluxes (cm³ fluid/cm² rock), calculated from the standard equation for coupled fluid flow and reaction in porous media, are (1) ankerite-oligoclase zone: c. 1 × 10⁴; (2) biotite zone: c. 3 × 10⁴; (3) amphibole zone: c. 10 × 10⁴; and diopside zone: c. 60 × 10⁴. The increase in calculated flux with increasing grade is at least in part the result of internal production of volatiles from prograde reactions in pelitic schists and metacarbonate rocks within the Waits River Formation. The mapped pattern of time-integrated fluxes indicates that the Strafford-Willoughby Arch and the numerous igneous intrusions in the field area focused fluid flow during metamorphism. Many rock specimens in the diopside zone experienced extreme alkali depletion and also record low χ_CO2. Metamorphic fluids in equilibrium with diopside zone rocks may therefore represent a mixture of acid, H₂O-rich fluids given off by the crystallizing magmas, and CO₂-H₂O fluids produced by devolatilization reactions in the host marls. Higher fluxes and different fluid compositions recorded near the plutons suggest that pluton-driven hydrothermal cells were local highs in the larger regional metamorphic hydrothermal system.     

Metamorphic Core Complexes and Its Significance in the Continental Crustal Evolution

Metamorphic core complexes are a basic structural pattern related toextensional tectonics.Several characteristics of different scales of metamorphiccore complexes in the Fangshan and Yunmengshan(Beijing),Zhongtiaoshan(Shanxi),and Dengfong(Henan)are examined.A three-layer model formetamorphic core complexes is suggested.The conclusion is that metamorphiccore complexes are the result of multiphase intracontinental crustal extensionsand are an important tectonic pattern.which exposes the basementmetamorphic rocks to the ground surface in the intracontinental cover.     

Pseudotachylite from the Main Zone of the Hidaka metamorphic belt, Hokkaido, northern Japan

Pseudotachylite veins have been found in the mylonite zone of the Hidaka metamorphic belt, Hokkaido, northern Japan. They are associated with faults with WNW-ESE to ENE-WSW or NE-SW trends which make a conjugate set, cutting foliations of the host mylonitic rocks with high obliquity. The mylonitic rocks comprise greenschist facies to prehnite-pumpellyite facies mineral assemblages. The mode of occurrence of the pseudotachylite veins indicates that they were generated on surfaces of the faults and were intruded as injection veins along microfractures in the host rocks during brittle deformation in near-surface environments. An analysis of the deformational and metamorphic history of the Hidaka Main Zone suggests that the ambient rock temperature was 200–300° C immediately before the formation of the Hidaka pseudotachylite. Three textural types of veins are distinguished: cryptocrystalline, microcrystalline and glassy. The cryptocrystalline or glassy type often occupies the marginal zones of the microcrystalline-type veins. The microcrystalline type is largely made up of quench microlites of orthopyroxene, clinopyroxene, biotite, plagioclase and opaque minerals with small amounts of amphibole microlites. The interstices of these microlites are occupied by glassy and/or cryptocrystalline materials. The presence of microlites and glasses in the pseudotachylite veins suggests that the pseudotachylites are the products of rapid cooling of silicate melts at depths of less than 5 km. The bulk chemical composition of the pseudotachylite veins is characterized by low SiO₂ and a high water content and is very close to that of the host mylonitic rocks. This indicates that the pseudotachylite was formed by virtual total melting of the host rocks with sufficient hydrous mineral phases. Local chemical variation in the glassy parts of the pseudotachylite veins may be due to either crystallization of quench microlites or the disequilibrium nature of melting of mineral fragments and incomplete mixing of the melts. Pyroxene microlites show a crystallization trend from hypersthene through pigeonite to subcalcic augite with unusually high Al contents. The presence of pigeonite and high-Al pyroxene microlites, of hornblende and biotite microlites and rare plagioclase microlites may indicate the high temperature and high water content of the melt which formed the pseudotachylite veins. The melt temperatures were estimated to be up to 1100° C using a two-pyroxene geothermometer. Using published data relating water solubilities in high-temperature andesitic magmas to pressure, a depth estimate of about 4 km is inferred for the Hidaka pseudotachylites. Evidence derived from pseudotachylites in the Hidaka metamorphic belt supports the conclusion that pseudotachylite is formed by frictional melting along fault surfaces at shallow depths from rocks containing hydrous minerals.     

The origin of olivine-plagioclase coronas in metagabbros from the Adirondack Mountains, New York

Olivine-plagioclase coronas in metagabbros from the Adirondack Mountains, New York (USA) are spatially well-organized reaction textures consisting most commonly of sequential layers of orthopyroxene, clinopyroxene, plagioclase, and garnet; the textures are characteristic of diffusion-controlled reaction kinetics. Although similar coronas have been interpreted by previous workers in terms of an isochemical steady-state diffusion model, petrographical relations and material-balance calculations establish that coronas in the Adirondack metagabbros cannot be treated as isochemical and do not form in a single-stage steady-state process; instead they evolve through time in a complex open-system reaction. In this study, the isochemical diffusion model is modified to account for elemental fluxes across the outer boundaries of the coronal reaction band, thereby approximating the open-system behaviour of the coronas. The sequence and relative proportions of product minerals calculated by the open-system steady-state model correspond closely to those observed in coronas of the Adirondacks, over a wide range of values for the relative diffusivities of chemical components involved in the reaction, regardless of the particular method used to determine material balance in the reaction texture. Despite this correspondence, petrographical evidence for successive replacement of coronal product layers reveals that the Adirondack coronas evolved through one or more transient states, rather than forming in a single-stage steady-state process. There is no evidence that the successive replacement of coronal product layers resulted from changes in pressure or temperature, but there is petrographical evidence that these changes resulted from modification of the composition of reactant plagioclase as the corona-forming reaction proceeded. This is confirmed by the fact that the evolution of the coronas over time can be replicated with the open-system diffusion model by simulating the effect of the gradual exhaustion of plagioclase as a source of the Ca and Si components required for reaction. These simulations suggest that successive stages in the evolution of the coronas are characterized by these product sequences: (i) orthopyroxene-clinopyroxene-plagioclase-garnet; (ii) orthopyroxene-clinopyroxene-garnet; and (iii) orthopyroxene-garnet. All of these stages, and the transitions between them, are observed petrographically. Coronas in Adirondack metagabbros appear, therefore, to have originated in a complex, open-system, diffusion-controlled reaction in which the product assemblages changed as the reaction progressed.     

黑龙江依兰、牡丹江变质带蓝闪片岩特征

通过对黑龙江省依兰、牡丹江等地的蓝闪片岩产出的地质环境、岩石类型、原岩类型的研究和对蓝闪石类及与其共生的多硅白云母、黑硬绿泥石、红帘石的测试鉴定,证明依兰、牡丹江两地的蓝闪片岩为高压地质环境的产物,属于蓝闪绿片岩相。     

Petrology of amphibolite-facies mafic and ultramafic rocks from the Catalina Schist, southern California: metasomatism and migmatization in a subduction zone metamorphic setting

Abstract The Catalina Schist of southern California is a subduction zone metamorphic terrane. It consists of three tectonic units of amphibolite-, high- P greenschist- and blueschist-facies rocks that are structurally juxtaposed across faults, forming an apparent inverted metamorphic gradient. Migmatitic and non-migmatitic metabasite blocks surrounded by a meta-ultramafic matrix comprise the upper part of the Catalina amphibolite unit. Fluid-rock interaction at high- P , high- T conditions caused partial melting of migmatitic blocks, metasomatic exchange between metabasite blocks and ultramafic rocks, infiltration of silica into ultramafic rocks, and loss of an albitic component from nonmigmatitic, clinopyroxene-bearing metabasite blocks.
Partial melting took place at an estimated P =˜8–11 kbar and T =˜640–750°C at high H₂O activity. The melting reaction probably involved plagioclase + quartz. Trondhjemitic melts were produced and are preserved as leucocratic regions in migmatitic blocks and as pegmatitic dikes that cut ultramafic rocks.
The metasomatic and melting processes reflected in these rocks could be analogous to those proposed for fluid and melt transfer of components from a subducting slab to the mantle wedge. Aqueous fluids rather than melts seem to have accomplished the bulk of mass transfer within the mafic and ultramafic complex.