Minerals In Metamorphic Rocks Research Articles

変成鉱物の粒径分布と空間分布

This paper reviews recent progress in analysis of crystal size distributions (CSD) and spatial dispositions of minerals in metamorphic rocks. Mineral growth in metamorphic rocks consists of two stages: the recrytallization stage in which nucleation and growth makes in progress by net transfer reactions and the annealing stage in which Ostwald ripening is operative. Minerals from contact aureoles will preserve the original CSD produced by nucleation and growth because it may suffer little annealing effects. Two distinct CSD patterns, however, has been reported from contact aureoles. One is that by Kretz, which shows nearly log-normal distribution, indicating time-dependent nucleation rate under the assumption of constant growth rate. The other is that by Cashman and Ferry, which shows CSD pattern caused by constant rates of nucleation and growth. Normal or log-normal size distributions of minerals from regional metamorphic terrain has been also an enigma, because such CSD can be produced either by Ostwald ripening, or by diffusion-controlled nucleation and growth. This paper will give an overview for the resolution of these problems.

Oxygen diffusion rates in quartz exchanged with CO 2

Oxygen self diffusion rates were determined in quartz samples exchanged with 18O-enriched CO 2 between 745 and 900°C and various pressures, and the diffusion profiles were measured using an ion microprobe. The activation energy ( Q) and preexponential factor ( D 0 ) at P(CO 2) = P(tot) = 100 bar, for diffusion parallel to the c-axis are 159 ( ± 13) kJ/g atom and 2.10 (+0.75/ −0.55) × 10 −8 cm 2/s. This rate is approximately 100 times slower than that obtained from hydrothermal experiments and 100 times faster than a previous 1-bar quartz-O 2 exchange experiment. The oxygen diffusion rate measured at 0.6 bar, 888°C, and at 900°C in vacuum is in agreement with the previous 1-bar exchange experiments with 18O 2. The effect of higher CO 2 pressures is small. At 900°C, the diffusion rate exchanged with CO 2 is = 2.35 × 10 −15 cm 2/s at 100 bar, 2.24 × 10 −15 cm 2/s at 3.45 kbar and 8.13 × 10 −15 cm 2/s at 7.2 kbar. There is probably a diffusing species, other than oxygen, that enhances the oxygen diffusion rate in these quartz-CO 2 systems, relative to that occurring at very low pressures or in a vacuum. The effect of this diffusing species, however, is not as strong as that associated with H 2O. Preserved oxygen isotope fractionations between coexisting minerals in a slowly cooled, high-grade metamorphic terrane will vary depending upon whether a water-rich phase was present or not. Closure temperatures will be approximately 100°C higher in rocks where no water-rich phase was present during cooling. The measured fractionations between coexisting minerals in metamorphic rocks may potentially be used as a sensor of water presence during retrogression.

Silicate versus trace mineral susceptibility in metamorphic rocks

Rates of change of magnetic susceptibility during leaching can characterize the presence of certain common types of magnetic minerals in metamorphic rocks. In this study the results of leaching are confirmed by mineral separation, optical microscopy, scanning electron microscopy (SEM) and microchemical analysis under SEM. Leaching curves provide a simple, rapid way of determining the relative roles of oxides, sulfides, and silicates in carrying the susceptibility in metamorphic rocks.

変成鉱物の化学組成の累進的変化

The chemical compositions of solid-solution minerals in metamorphic rocks are controlled by equilibria not only of exchange reactions but also of net-transfer reactions among coexisting minerals. In rocks with a variance of 2, the compositions of solid-solution minerals are functions of temperature and pressure alone as is illustrated in Figs. 2 and 3, and so can be used as a measure of the P-T condition under which the rocks were recrystallized. In rocks with a variance of 3 or greater, on the other hand, the compositions of solid-solution minerals vary not only with temperature and pressure but also with the bulk-rock composition (Fig. 4). The growth of zoned crystals causes fractional crystallization, resulting in a change of composition of the reacting system. If the variance of the system is 3 or greater, the change of the composition of the reacting system causes a change in the composition of the crystallizing mineral.Pelitic metamorphic rocks are commonly simplified as belonging to the 6-component system : Al2O3-FeO-MgO-K2O-SiO2-H2O. In this case the mineral assemblages may be shown on the THOMPSON AFM diagram. Any 3-AFM phase assemblage in the diagram has a variance of 2, whereas any 2-AFM phase assemblage has a variance of 3.In the paragenetic relations of garnet, MnO commonly plays an essential role, and so garnet-bearing metapelites are commonly treated as belonging to the 7-component system : Al2O3-FeO-MgO-MnO-K2O-SiO2-H2O. Most metapelites with MnO-rich garnet have a variance of 3 or greater. Garnets in low- and middle-grade metamorphic rocks are usually strongly zoned. Hence, the composition (or the MnO content) of garnet is strongly influenced by the initial bulk-rock composition and fractional crystallization. SPEAR (1988) has calculated the progressive compositional change of garnet that grows not only under complete equilibrium condition but also with fractional crystallization for garnet-bearing 3-AFM phase assemblages that are observed in the Barrovian sequence.In the Sanbagawa high P/T ratio metamorphic belt, progressive metamorphism is represented by a sequence of the chlorite zone, garnet zone (with no biotite), and biotite zone (with garnet) for metapelites. In other words, garnet begins to occur at a considerably lower temperature than biotite. In the garnet zone, garnet probably forms by reaction involving Tschermak exchange component like (4), whereas in the biotite zone, garnet forms by the same reactions as in the garnet zone of the Barrovian sequence. Such a change in the garnet-producing reactions between the two zones may cause a break in the MnO and FeO curves in the composition profile of zoned garnets. Some of the observed features of the compositional trends of garnets could be ascribed to the effect of a variation in bulk-rock composition.The average composition of zoned garnets in metapelite shows a progressive decrease of the MnO content with increasing metamorphic grade. This is probably related mainly to a progressive increase of the amount of garnet. Higher pressure tends to increase the amount of garnet, and to decrease its MnO content.

Phase relations of pyroxene and amphibole in greenstone, blueschist and eclogite of the Franciscan Complex, California

The phase relations of pyroxenes, amphiboles and associated minerals in metamorphic rocks of the Franciscan Complex can be graphically depicted on a ternary diagram which has at its apices the metamorphic clinopyroxene end members, viz NaAl-NaFe3+-Ca(Fe2+, Mg). Phases are plotted by projection from a constant subassemblage of minerals. This analysis allows interpretation of the effects of pressure, temperature, bulk rock composition and fluid composition on stability of minerals within the Franciscan.

The Principle of Constituent Analysis, with Special Reference to the Calculation of Weight Percentages of Minerals in Metamorphic Rocks

The principle of constituent analysis is introduced. Assuming that a component (end member) consists of n variables in percentage form and that m different components (m ≤ n) constitute each of N samples, the samples can be treated as N points in m-dimensional space. Points represented by m end members are characterized by being non-coplanar and non-collinear in m-dimensional space. The amount of the mth end member contained in a sample is calculated as Xm−1i/Xm−1 m, where Xm−1 is the length of (m−1)th orthogonal axis; i and m in subscript Xm−1 are for the sample and mth end member, respectively; and the end members are successively put on the origin of the coordinate, X1, X1−X2, X1−X2−X3,…, and X1−X2 …−Xm−1 axes.In a metamorphic rock, m points are equivalent to constituent minerals. If the chemical compositions of constituent minerals and the bulk chemical composition of the rock are known, the method outlined in this paper provides information on equilibrium assemblages and allows computation of the amounts of constituent minerals.

La cause de l'orientation des mineraux dans les roches metamorphiques

Abstract The orientation of minerals in metamorphic rocks is postulated as resulting from selective pressure solution, not from rotation, during deformation. The calculations upon which the hypothesis is based are given. If the pressure-solution hypothesis is correct, statistical studies of the distribution of crystal orientations can indicate not only the direction of principal stress but also the relative pressures in different directions.

Notes on Rock-forming Minerals (33) Additional Data on the Opaque Minerals in Metamorphic Rocks of Japan: Finding of Linnaeite and Cobaltite.,

Notes on Rock-forming Minerals (33) Additional Data on the Opaque Minerals in Metamorphic Rocks of Japan: Finding of Linnaeite and Cobaltite.,

Relationship Between O18/O16 Ratios in Coexisting Minerals of Igneous and Metamorphic Rocks

Research Article| June 01, 1962 Relationship Between O18/O16 Ratios in Coexisting Minerals of Igneous and Metamorphic Rocks: Part 2. Application to Petrologic Problems HUGH P TAYLOR, JR.; HUGH P TAYLOR, JR. The Pennsylvania State University, University Park, Pa Search for other works by this author on: GSW Google Scholar SAMUEL EPSTEIN SAMUEL EPSTEIN California Institute of Technology, Pasadena, Calif Search for other works by this author on: GSW Google Scholar Author and Article Information HUGH P TAYLOR, JR. The Pennsylvania State University, University Park, Pa SAMUEL EPSTEIN California Institute of Technology, Pasadena, Calif Publisher: Geological Society of America Received: 20 Jun 1960 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1962, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1962) 73 (6): 675–693. https://doi.org/10.1130/0016-7606(1962)73[675:RBORIC]2.0.CO;2 Article history Received: 20 Jun 1960 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation HUGH P TAYLOR, SAMUEL EPSTEIN; Relationship Between O18/O16 Ratios in Coexisting Minerals of Igneous and Metamorphic Rocks: Part 2. Application to Petrologic Problems. GSA Bulletin 1962;; 73 (6): 675–693. doi: https://doi.org/10.1130/0016-7606(1962)73[675:RBORIC]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Oxygen isotopic analyses of coexisting minerals in igneous rocks indicate the crystallization history and mineral paragenesis of these rocks. Detailed variations in the O18/O16 fractionations among minerals can be readily explained on the basis of equilibrium crystallization of magma with incomplete reaction. In every instance in which conclusive information exists, the isotopic results are in excellent agreement with the crystallization sequence determined by conventional geologic criteria. Most rocks analyzed fall into a consistent pattern with respect to petrologic type.As is to be expected on the basis of their lower-temperature origin, O18/O16 fractionations among coexisting minerals in metamorphic rocks are in general somewhat larger than in igneous rocks. These data also suggest, however, that oxygen isotopic equilibrium is not always established during metamorphism. The higher the grade the greater is the apparent tendency for a metamorphic rock to approach the igneous-rock range of oxygen isotopic composition. This is most probably a result of exchange with a reservoir of relatively constant oxygen isotopic composition during metamorphism. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The section CaSiO3-MgSiO3-Al2O3

SummaryPhase relationships in the section CaSiO3-MgSiO3-Al2O3 through the quaternary system CaO-MgO-Al2O3-SiO2 have been determined. The bearing of the results on the genesis of aluminous pyroxenes and associated minerals in metamorphic rocks is discussed.

On Some Minerals in Metamorphic Rocks from the Vicinity of Bessi, Sikoku(Part 1 Amphibole Group)

On Some Minerals in Metamorphic Rocks from the Vicinity of Bessi, Sikoku(Part 1 Amphibole Group)

On Some Minerals in Metamorphic Rocks from the Vicinity of Bessi, Si-koku(Part 2 Epidote Group)

On Some Minerals in Metamorphic Rocks from the Vicinity of Bessi, Si-koku(Part 2 Epidote Group)