冀东地区英云闪长质片麻岩的变质结构、P-T-t和水活度

通过英云闪长质片麻岩变质结构的研究,把变质作用分为四个演化阶段,用三组分五个矿物相ACF体系P-T成因格子表示了这个演化过程。四个变质阶段矿物地质温度和压力计算结果构成了逆时针P-T-t轨迹。角闪石生成二辉石的平衡反应计算表明,主期变质水活度明显高于峰期变质水活度。水活度越高角闪石向二辉石转化温度越高,因此水活度是麻粒岩相变质作用的独立因素之一。     

Growth and deformation of porphyroblasts in the Foothills terrane, central Sierra Nevada, California: negotiating a microstructural minefield

Abstract The main porphyroblastic minerals in schists and phyllites of the Foothills terrane, Western Metamorphic Belt, central Sierra Nevada, California, are cordierite and andalusite (mostly chiastolite). Less commonly, biotite, muscovite, chlorite, garnet or staurolite are also present as porphyroblasts. The variety of porphyroblast and matrix microstructures in these rocks makes them suitable for testing three modern hypotheses on growth and deformation of porphyroblasts: (1) porphyroblast growth is always syndeformational; (2) porphyroblasts nucleate only in low-strain, largely coaxially deformed, quartz-rich (Q) domains of a crenulation foliation and are dissolved in active high-strain, non-coaxially deformed, mica-rich (M) domains, the spacing between which limits the size of the porphyroblasts; and (3) porphyroblasts generally do not rotate, with respect to geographical coordinates, during deformation, provided they do not deform internally, so that they may be used as reliable indicators of the orientation of former regional structural surfaces, even on the scale of orogenic belts. Some porphyroblast–matrix relationships in the Foothills terrane are inconsistent with hypotheses 1 and 2, and others are equivocal. For example, in many rocks it cannot be determined whether the porphyroblasts grew where the strain had already been partitioned into M and Q domains, whether the porphyroblasts caused this partitioning, or both. Although most porphyroblasts appear to be syndeformational, as predicted by hypothesis 1, observations that do not support the general application of hypotheses 1 and 2 to rocks of the Foothills terrane include: (a) lack of residual crenulations in many strain-shadows and alternative explanations where they are present; (b) absence of porphyroblasts smaller than the distance between nearest mica-rich domains; (c) nucleation of crenulations on existing porphyroblasts, rather than nucleation of porphyroblasts between existing crenulations; (d) presence of micaceous ‘arcs’in an undifferentiated matrix against some porphyroblasts, suggesting static growth; (e) absence of crenulations in porphyroblastic rocks showing sedimentary bedding; and (f) porphyroblasts with very small, random inclusions, which are probably pre-deformational. Similarly, porphyroblasts that have overgrown sets of crenulations and porphyroblasts with micaceous ‘arcs’are probably post-deformational, at least on the scale of a large thin section and probably over much larger areas, judging from mesoscopic structural evidence. Some porphyroblasts in rocks of the Foothills terrane do not appear to have rotated, with respect to geographical coordinates, during matrix deformation, in accordance with hypothesis 3, at least on the scale of a large thin section. However, other porphyroblasts evidently have rotated. In some instances, this appears to be due to mutual interference, but many apparently rotational porphyroblasts are too far apart to have interfered with each other, which indicates that the rotation was associated with deformation of the matrix. The occurrence of planar bedding surfaces adjacent to porphyroblasts about which bedding and/or foliation surfaces are folded suggests rotation of the porphyroblasts during non-coaxial flow parallel to bedding, rather than crenulation of the matrix foliation around static porphyroblasts. It appears that porphyroblasts may rotate during deformation if the matrix is relatively homogeneous, so that the strain is effectively non-coaxial. This may occur after homogenization of a matrix in response to the strongest degree of crenulation folding, whereas the same porphyroblasts may have been inhibited from rotating previously, when strain accumulation was partitioned in the matrix.     

Refining the P–T records of UHT crustal metamorphism

Ultra‐high‐temperature (UHT) metamorphism occurs when the continental crust is subjected to temperatures of greater than 900 °C at depths of 20–40 km. UHT metamorphism provides evidence that major tectonic processes may operate under thermal conditions more extreme than those generally produced in numerical models of orogenesis. Evidence for UHT metamorphism is recorded in mineral assemblages formed in magnesian pelites, supported by high‐temperature indicators including mesoperthitic feldspar, aluminous orthopyroxene and high Zr contents in rutile. Recent theoretical, experimental and thermodynamic data set constraints on metamorphic phase equilibria in FMAS, KFMASH and more complex chemical systems have greatly improved quantification of the P–T conditions and paths of UHT metamorphic belts. However, despite these advances key issues that remain to be addressed include improving experimental constraints on the thermodynamic properties of sapphirine, quantifying the effects of oxidation state on sapphirine, orthopyroxene and spinel stabilities and quantifying the effects of H₂O–CO₂ in cordierite on phase equilibria and reaction texture analysis. These areas of uncertainty mean that UHT mineral assemblages must still be examined using theoretical and semi‐quantitative approaches, such as P(–T)–μ sections, and conventional thermobarometry in concert with calculated phase equilibrium methods. In the cases of UHT terranes that preserve microtextural and mineral assemblage evidence for steep or ‘near‐isothermal’ decompression P–T paths, the presence of H₂O and CO₂ in cordierite is critical to estimates of the P–T path slopes, the pressures at which reaction textures have formed and the impact of fluid infiltration. Many UHT terranes have evolved from peak P–T conditions of 8–11 kbar and 900–1030 °C to lower pressure conditions of 8 to 6 kbar whilst still at temperature in the range of 950 to 800 °C. These decompressional P–T paths, with characteristic dP/dT gradients of ～25 ± 10 bar °C^?1, are similar in broad shape to those generated in deep‐crustal channel flow models for the later stages of orogenic collapse, but lie at significantly higher temperatures for any specified pressure. This thermal gap presents a key challenge in the tectonic modelling of UHT metamorphism, with implications for the evolution of the crust, sub‐crustal lithosphere and asthenospheric mantle during the development of hot orogens.     

琼中高级变质杂岩中单颗粒锆石Pb-Pb年龄及其地质意义

琼中地区存在由片麻岩、混合岩、麻粒岩和紫苏花岗岩组成的高级变质杂岩。对其中片麻岩和麻粒岩开展了单颗粒锆石Pb-Pb年代学研究,分别获得1483±13Ma和499±24Ma的年龄数据。结合现有地质资料, 认为琼中地区先后经历了新太古代表壳岩系形成、中元古代变质—岩浆再造和加里期构造热事件改造等3个主要演化阶段。     

Supported TiO2 on Kaolin,Cordierite, and Calcite for Photocatalytic Removal of Dyes from Wastewater

Kaolin, cordierite, and calcite are investigated as supports for TiO₂. The prepared TiO₂/support samples are examined for the removal of organic dyes from wastewater. The samples are preliminarily investigated to identify the optimal loaded system using synthetic wastewater containing methylene blue (MB). Data indicate that the investigated support significantly affects the photocatalytic activity of the supported TiO₂. Low photocatalytic activity toward MB degradation is observed upon using TiO₂/calcite when compared to the unsupported TiO₂. Interaction between calcite and titania species probably occurrs to produce the less photoactive CaTiO₃ amorphous species. Anatase TiO₂ is obtained upon using kaolin and cordierite as supports. The low photocatalytic performance of the TiO₂/kaolin sample is also observed. A high concentration of MB on TiO₂/kaolin surfaces blocks the photoactive sites. TiO₂/cordierite shows the highest photocatalytic activity compared to the unsupported TiO₂ as well as the other TiO₂/support samples. Rigid cordierite particles suppress the agglomeration of TiO₂ particles during the preparation, leading to a high exposed surface of TiO₂ towards light illumination. TiO₂/cordierite is investigated for the removal of organic dye from real wastewater collected from a textile dyeing factory. Color removal of up to 46% is achieved upon UV irradiation.     

Variations in fluid activity across the Etive thermal aureole, Scotland: evidence from cordierite volatile contents

The H₂O and CO₂ content of cordierite was analysed in 34 samples from successive contact metamorphic zones of the Etive thermal aureole, Scotland, using Fourier‐transform infrared spectroscopy (FTIR). The measured volatile contents were used to calculate peak metamorphic H₂O and CO₂ activities. Total volatile contents are compared with recently modelled cordierite volatile saturation surfaces in order to assess the extent of fluid‐present v. fluid‐absent conditions across the thermal aureole. In the middle aureole, prior to the onset of partial melting, calculated aH₂O values are high, close to unity, and measured volatile contents intersect modelled H₂O–CO₂ saturation curves at the temperature of interest, suggesting that fluid‐present conditions prevailed. Total volatile contents and aH₂O steadily decrease beyond the onset of partial melting, consistent with the notion of aH₂O being buffered to lower values as melting progresses once free hydrous fluid is exhausted. All sillimanite zone samples record total volatile contents that are significantly lower than modelled H₂O–CO₂ saturation surfaces, implying that fluid‐absent conditions prevailed. The lowest recorded aH₂O values lie entirely within part of the section where fluid‐absent melting reactions are thought to have dominated. Samples within 30 m of the igneous contact appear to be re‐saturated, possibly via a magmatically derived fluid. In fluid‐absent parts of the aureole, cordierite H₂O contents yield melt–H₂O contents that are compatible with independently determined melt–H₂O contents. The internally consistent cordierite volatile data and melt–H₂O data support the conclusion that the independent P–T estimates applied to the Etive rocks were valid and that measured cordierite volatile contents are representative of peak metamorphic values. The Etive thermal aureole provides the most compelling evidence, suggesting that the cordierite fluid monitor can be used to accurately assess the fluid conditions during metamorphism and partial melting in a thermal aureole.     

Granulites and garnet–cordierite gneisses from Dronning Maud Land, Antarctica

Abstract The central sector of Mühlig-Hofmannfjellet (3°E/71°S) in western Dronning Maud Land (East Antarctic shield) is dominated by large intrusive bodies of predominantly orthopyroxene-bearing quartz syenites (charnockites). Metasedimentary rocks are rare; however, two distinct areas with banded gneiss–marble–quartzite sequences of sedimentary origin were found during the Norwegian Antarctic Research Expedition NARE 1989/90. Cordierite-bearing metapelitic gneisses from two different localities contain the characteristic mineral assemblage: cordierite + garnet + biotite + K-feldspar + plagioclase + quartz ± sillimanite ± spinel. Thermobarometry indicates equilibration conditions of about 650°C and 4 kbar. Associated orthopyroxene–garnet granulites, on the other hand, revealed pressures of about 8 kbar and temperatures of 750°C. The earlier granulite facies metamorphism is not well preserved in the cordierite gneisses as a result of excess K-feldspar combined with interaction with an H₂O-rich fluid phase, probably released by the cooling intrusives. These two features allowed the original high-grade K-feldspar + garnet assemblages to recrystallize as cordierite–biotite–sillimanite gneisses, completely re-equilibrating them. Phase relationships indicate that the younger metamorphic event occurred in the presence of a fluid phase that varied in composition between the lithologies.     

Orthopyroxene–sillimanite–quartz assemblages: distribution, petrology, quantitative P–T–X constraints and P–T paths

Granulite facies magnesian metapelites commonly preserve a wide array of mineral assemblages and reaction textures that are useful for deciphering the metamorphic evolution of a terrane. Quantitative pressure, temperature and bulk composition constraints on the development and preservation of characteristic peak granulite facies mineral assemblages such as orthopyroxene + sillimanite + quartz are assessed with reference to calculated phase diagrams. In NCKFMASH and its chemical subsystems, peak assemblages form mainly in high‐variance fields, and most mineral assemblage changes reflect multivariant equilibria. The rarity of orthopyroxene–sillimanite–quartz‐bearing assemblages in granulite facies rocks reflects the need for bulk rock X_Mg of greater than approximately 0.60–0.65, with pressures and temperatures exceeding c. 8 kbar and 850 °C, respectively. Cordierite coronas mantling peak minerals such as orthopyroxene, sillimanite and quartz have historically been used to infer isothermal decompression P–T paths in ultrahigh‐temperature granulite facies terranes. However, a potentially wide range of P–T paths from a given peak metamorphic condition facilitate retrograde cordierite growth after orthopyroxene + sillimanite + quartz, indicating that an individual mineral reaction texture is unable to uniquely define a P–T vector. Therefore, the interpretation of P–T paths in high‐grade rocks as isothermal decompression or isobaric cooling may be overly simplistic. Integration of quantitative data from different mineral reaction textures in rocks with varying bulk composition will provide the strongest constraints on a P–T path, and in turn on tectonic models derived from these paths.     

High-temperature cordierite migmatites in the north-eastern Grenville Province

Abstract In the northeastern part of the Grenville Province, along the gulf of St Lawrence, cordierite is widespread in the migmatites of Baie Jacques Cartier (BJC) and Baie des Ha! Ha! (BHH). In the BJC area, rafts of mesosome occur in a pervasive network of leucosome consisting of cordierite-bearing pegmatite. In BHH, however, the mesosome and leucosome are well segregated and locally separated by thin biotite –hornblende melanosomes. Leucosomes in the BJC area record the highest temperatures (oxide thermometry = 900°C), whereas leucosomes of BHH and mesosomes of both areas indicate peak temperatures around 800°C (oxide thermometry; biotite–garnet thermometry with fluorine-rich biotite). Peak pressures were constrained at 720 MPa using the Ilm-Sil–Qtz–Grt–Rt (GRAIL) equilibrium. The area is thought to have undergone extensive melting under relatively modest pressures. The highest temperatures recorded in the BJC area are probably related to a pervasive impregnation of this terrane by aluminous granitic melts. Most post-peak P–T estimates for the mesosomes fall on a nearly isobaric, clockwise, P–T path (0.6 MPa/°C) with the exception of the high-temperature leucosomes of BJC, which fall about 100°C away from this path; this is additional evidence for the external origin of these leucosomes. The ultimate source of heat that generated the migmatites is thus though to be an underlying plutonic complex (anorthosite?).     

吉林省晚古生代造山带二叠纪移置地体及古地理原型

吉林省晚古生代造山带是西伯利亚板块与中朝板块离散、聚敛后褶皱造山带的一部分，又处于与滨太平洋构造域的复合部位，地质构造极为复杂。现存的岩石—地层体乃是经历多次构造运动移置、改造的结果。以生物地层学、沉积地质学为基础，综合应用构造学及地球化学理论和方法，详细地研究此造山带的生物地理区、岩相古地理、岩石化学和古地磁学等内容，首先发现在二叠纪时有四个移置地体组成，即延边、吉中、松辽和白城。根据生物古地理特征、物质成分判别及其沉积序列，确定各地体的古纬度和古构造环境，结合地球动力学分析，再造构造古地理原型，乃是一个活动大陆边缘的复合边缘海盆。