排序方式： 共有25条查询结果，搜索用时 31 毫秒
1.
Fernando Nieto Nicolás Velilla Donald R. Peacor Miguel Ortega Huertas 《Contributions to Mineralogy and Petrology》1994,115(3):243-252
Dioctahedral smectite is present as a retrograde alteration product of chlorite in Permian-Triassic red slates of the Malaguide Complex in Sierra de Espuña (Betic Cordillera). Mineral assemblages and textures, illite crystallinity indices, and fluid inclusion data indicate sub-greenschist facies conditions that reached at least 180°C in the higher-grade tectonic unit of the Malaguide Complex, preceding formation of smectite. Smectite, having K as the dominant interlayer cation, occurs ubiquitously intercalated with trioctahedral chlorite as thin packets of layers and as individual layers that commonly change to chlorite along layers. Although some chlorite is typically homogeneous and trioctahedral, much chlorite shows signs of alteration and has compositions corresponding to different degrees of smectite contaimination. The incompatibility of metamorphic grade with the occurrence of smectite, the general association of chlorite and smectite, and the textural relations collectively show that dioctahedral smectite is derived through replacement of trioctahedral chlorite. Such replacement occurs on a regional basis and demonstrates that caution must be used in interpreting the occurrence of smectite in pelites as being due to prograde processes. Alteration of trioctahedral chlorite under oxidizing conditions due to introduction of phreatic water after uplift of the Betic Cordillera is proposed as the cause of formation of smectite. 相似文献
2.
Yen-Hong Shau Melanie E. Feather Eric J. Essene Donald R. Peacor 《Contributions to Mineralogy and Petrology》1991,106(3):367-378
Electron microbeam techniques have been used to examine submicroscopically intergrown paragonite, phengite and chlorite from
the South Fork Mountain Schist of the Franciscan Terrane of northern California, which was subjected to blueschist facies
metamorphism. The sample also contains quartz, albite, lawsonite, and rutile. The subassemblage albite-lawsonite-rutile requires
metamorphic conditions on the low-temperature side of the equilibrium albite+lawsonite+rutile=paragonite+sphene+quartz+H2O (T<200° C and P<7.4 kbars based on thermodynamic data of Holland and Powell 1990). The white micas appear to be optically
homogeneous, but back-scattered electron images can distinguish two different micas by their slight difference in contrast.
Electron microprobe analyses (EMPA) of micas show Na/(Na+K) ranging from 0.2 to 0.8. The two micas are resolved by transmission
electron microscopy (TEM) as packets of phengite and paragonite that range from 20 to several hundred nm in thickness. The
compositions, determined by analytical electron microscopy (AEM), constrain the limbs of the phengite-paragonite solvus to
values of Na/(Na+K)=<0.02 and 0.97, representing less mutual solid solution than ever reported by EMPA. The textural relations
imply that the sheet silicates were derived from reactions between fluids and detrital clays and that they are in an intermediate
stage of textural development. We caution that microprobe analyses of apparently homogeneous sheet silicates may yield erroneous
data and lead to faulty conclusions using phengite barometry and paragonite-muscovite thermometry, especially in fine-grained
rocks that formed at relatively low temperatures.
Contribution no. 473 from the Mineralogical Laboratory, Department of Geological Sciences, The University of Michigan, Ann
Arbor, Michigan, USA 相似文献
3.
Eocene shales metamorphosed by a naturally ignited coal seam in the Powder River Basin, Wyoming record a continuum of mineralogic and textural changes from relatively unaltered shale to melt developed during pyrometamorphism. Samples collected along a section 2 m in length, corresponding to a temperature range of approximately 1300°C, were examined optically and by XRD, SEM, and STEM. The low temperature samples are comprised primarily of silt-sized quartz, K-feldspar, and minor amounts of other detrital minerals in a continuous matrix of illite/smectite (I/S). Delamination of phyllosilicates due to dehydroxylation occurs early in the sequence with curling of individual layers from rim to core. Within one-half meter of melted areas, phyllosilicates have undergone an essentially isochemical reconstitution with nucleation and growth of mullite crystals with maximum diameters of 50 nm, randomly distributed within a non-crystalline phase that replaces I/S. Large detrital grains remain for the most part unaffected except for the inversion of quartz to tridymite/cristobalite. Within 1 mm of the solid/melt interface, the mullitebearing clay mineral matrix is essentially homogeneous in composition with obscure grain boundaries, caused by apparent homogenization of poorly crystalline material. This material is similar in composition to parent clays and acts as a matrix to angular, remnant tridymite/cristobalite grains. Rounded, smaller silica grains have reaction rims with the non-crystalline matrix; K-feldspar is no longer present (apparently reacted with the matrix) and the matrix contains abundant pore space due to shrinkage upon dehydroxylation. As isolated pods of paralava (glass) or fractures are approached, Fe–Ti–Al oxides become abundant. Vesicular glass is separated from clinker by a well-defined interface and contains numerous phenocrysts. XRF analyses and reduced area rastering using EDS imply enrichment of the melt phase in Fe, Ca, Mg and Mn, apparently due to vapor transport from other layers lower in the sedimentary sequence.Contribution No. 490, the Mineralogical Laboratory, Department of Geological Sciences, The University of Michigan 相似文献
4.
Philip Brown Eric J. Essene Donald R. Peacor 《Contributions to Mineralogy and Petrology》1978,67(3):227-232
Manganese-rich metamorphic rocks containing violan from St. Marcel, Piedmont, Italy formed under blueschist facies conditions,
yielding an unusual suite of minerals including omphacite-albite-quartz, braunite, microcline, hollandite, piedmontite, and
strontian calcite. Violan, a violet-colored pyroxene, is shown to be a manganoan omphacite having a primitive unit cell, and
is found in the same sample as diopside, possibly indicating a solvus relation. A manganoan phlogopite and a celadonitic muscovite
coexist in one sample with microcline. The occurrence of celadonite and phlogopite is the first from the blueschist facies
and the celadonite component in the dioctahedral mica is buffered at a maximum by coexistence with phlogopite, microcline,
and quartz. Various phase relations are used to establish the P and T of equilibration at 8±1 kbar and 300±50 °C, respectively, while the oxygen fugacity is shown to have been very high, for
these temperatures, as consistent with braunite+quartz and the presence of piedmontite.
Contribution No. 343, from the Mineralogical Laboratory, Department of Geology and Mineralogy, The University of Michigan,
Ann Arbor, MI 48109, USA 相似文献
5.
Yu -Chyi Yau Donald R. Peacor Eric J. Essene 《Contributions to Mineralogy and Petrology》1986,94(1):127-134
Amphiboles and pyroxenes occurring in the Salton Sea Geothermal Field were found to contain coherent intergrowths of chain silicates with other than double and single chain widths by using transmission and analytical electron microscopy. Both occur in the biotite zone at the temperature (depth) interval of 310° C (1,060 m) to 330° C (1,547m) which approximately corresponds to temperatures of the greenschist facies. The amphiboles occur as euhedral fibrous crystals occupying void space and are composed primarily of irregularly alternating (010) slabs of double or triple chains, with rare quadruple and quintuple chains. Primary crystallization from solution results in euhedral crystals. Clinopyroxenes formed mainly as a porefilling cement and subordinately as prismatic crystals coexisting with fibrous amphiboles. Fine lamellae of double and triple chains are irregularly intercalated with pyroxene. AEM analyses yield formulae (Ca1.8Mg2.9Fe1.9Mn0.1) Si8O21.8(OH)1.8 (310° C) and (Ca2.0Fe2.5Mg2.3) Si8O21.8 (OH)2.0 (330° C) for amphiboles and (Ca1.1Fe0.6Mg0.3) Si2O6 for clinopyroxene. Thermodynamic calculations at Pfluid=100 bar of equilibrium reactions of (1) 3 chlorite +10 calcite + 21 quartz = 3 actinolite + 2 clinozoisite + 8 H2O + 10 CO2 and (2) actinolite+ 3 calcite+ 2 quartz = 5 clinopyroxene + H2O + 3 CO2 using Mg-end member phases indicate that formation of amphibole and pyroxene require very water-rich conditions
at temperatures below 330° C.Contribution No. 420 from the Mineralogical Laboratory, Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 相似文献
6.
Lung -Chuan Kuo Jung H. Lee Eric J. Essene Donald R. Peacor 《Contributions to Mineralogy and Petrology》1986,94(1):90-98
The occurrence and chemistry of immiscible silicate glasses in a tholeiite mesostasis from the Umtanum formation, Washington, were investigated with transmission electron microscopy and analytical electron microscopy (TEM/AEM). TEM observation reveals isolated, dark globules (2.1 micron or less in diameter) randomly distributed in a transparent matrix glass interstitial to plagioclase laths. The globules less than 0.3 micron and larger than 0.8 micron fall beyond the linear relationship defined by the 0.3–0.8 micron globules in a plot of the logarithm of number versus size. Large globules (0.7 micron or larger in diameter) range from homogeneous to heterogeneous in optical properties and chemistry. Homogeneous globules are completely glassy, whereas heterogeneous globules contain crystalline domains. AEM analyses show that the globules have high Si, Fe, Ca, and Ti with subordinate Mg, Al, P, S, Cl, K, and Mn, which gives high normative fa, px, il, and ap. The matrix glass consists dominantly of Si with low Al and minor Na and K, yielding a high normative qz, or, ab, and an.It is proposed that the silicate liquid immiscibility occurs by reaction of network-modifying cations (NMCs) with dominantly chain-like anionic units in the parental melt to form less polymerized, NMC-bearing units and highly polymerized, Si-rich units. The globules nucleated metastably under supercooled conditions, and medium-size globules become either larger or smaller at lower temperatures. Internal nucleation of NMC-rich phases occurred in some larger globules upon cooling. 相似文献
7.
Semi‐pelitic rocks ranging in grade from the prehnite–pumpellyite to the greenschist facies from south‐eastern Otago, New Zealand, have been investigated in order to evaluate the reactions leading to formation and breakdown of stilpnomelane. Detrital grains of mica and chlorite along with fine‐grained authigenic illite and chlorite occur in lower‐grade rocks with compactional fabric parallel to bedding. At higher grades, detrital grains have undergone dissolution, and metamorphic phyllosilicates have crystallized with preferred orientation (sub)parallel to bedding, leading to slaty cleavage. Stilpnomelane is found in metapelites of the pumpellyite–actinolite facies and the chlorite zone of the greenschist facies, but only rarely in the biotite zone of the greenschist facies. Illite or phengite is ubiquitous, whereas chlorite occurs only rarely with stilpnomelane upgrade of the pumpellyite‐out isograd. Chemical and textural relationships suggest that stilpnomelane formed from chlorite, phengite, quartz, K‐feldspar and iron oxides. Stilpnomelane was produced by grain‐boundary replacement of chlorite and by precipitation from solution, overprinting earlier textures. Some relict 14 Å chlorite layers are observed by TEM to be in the process of transforming to 12 Å stilpnomelane layers. The AEM analyses show that Fe is strongly partitioned over Mg into stilpnomelane relative to chlorite (KD≈2.5) and into chlorite relative to phengite (KD≈1.9). Modified A′FM diagrams, projected from the measured phengite composition rather than from ideal KAl3Si3O10(OH)2, are used to elucidate reactions among chlorite, stilpnomelane, phengite and biotite. In addition to pressure, temperature and bulk rock composition, the stilpnomelane‐in isograd is controlled by variations in K, Fe3+/Fe2+, O/OH and H2O contents, and the locus of the isograd is expected to vary in rocks of different oxidation states and permeabilities. Biotite, quartz and less phengitic muscovite form from stilpnomelane, chlorite and phengite in the biotite zone. Projection of bulk rock compositions from phengite, NaAlO2, SiO2 and H2O reveals that they lie close to the polyhedra defined by the A′FM minerals and albite. Other extended A′FM diagrams, such as one projected from phengite, NaAlO2, CaAl2O4, SiO2 and H2O, may prove useful in the evaluation of other low‐grade assemblages. 相似文献
8.
Philip E. Brown Eric J. Essene Donald R. Peacor 《Contributions to Mineralogy and Petrology》1980,74(4):417-425
Electron microprobe analysis of manganese silicates from Balmat, N.Y., has helped elucidate phase relations for Mn-bearing pyroxenes and pyroxenoids. A compilation of these data along with published and unpublished analyses for phases plotting on the CaSiO3-MgSiO3-MnSiO3 and CaSiO3-FeSiO3-MnSiO3 faces of the RSiO3 tetrahedron has constrained the subsolidus phase relations. For the system CaSiO3-FeSiO3-MnSiO3, the compositional gaps between bustamite/hedenbergite, bustamite/ rhodonite and rhodonite/pyroxmangite are constrained for middle-upper amphibolite facies conditions and extensive solid solutions limit possible three phase fields. For the CaSiO3-MgSiO3-MnSiO3 system much less data are available but it is clear that the solid solutions are much more limited for the pyroxenoid structures and a continuum of compositions is inferred for clinopyroxenes from diopside to kanoite (MnMgSi2O6) for amphibolite facies conditions (T=650° C). At lower temperatures, Balmat kanoites are unstable and exsolve into C2/c calciumrich (Ca0.68Mn0.44Mg0.88Si2O6) and C2/c calciumpoor (Ca0.12Mn1.02Mg0.86Si2O6) phases. At temperatures of 300–400° C the calcium-poor phase subsequently has undergone a transformation to a P21/c structure; this exsolution-inversion relationship is analogous to that relating augites and pigeonites in the traditional pyroxene quadrilateral. Rhodonite coexisting with Mn-clinopyroxenes is compositionally restricted to Mn0.75–0.95Mg0.0–0.15Ca0.05–0.13SiO3. For the original pyroxene+rhodonite assemblage, the Mg and Ca contents of the rhodonite are fixed for a specific P (6kbars)-T (650° C)-X(H2O)-X(CO2) by the coexistence of talc+quartz and calcite+quartz respectively.Contribution No. 363, from the Mineralogical Laboratory, Department of Geological Sciences, The University of Michigan, Ann Arbor MI 48109, USA 相似文献
9.
Andrew M. Isaacs Philip E. Brown John W. Valley Eric J. Essene Donald R. Peacor 《Contributions to Mineralogy and Petrology》1981,77(2):115-120
Samples of a garnet granulite from the mafic border units of the Lake Chatuge, Georgia alpine peridotite body were found to contain lamellar intergrowths of a pargastic amphibole in augite having the typical appearance of an exsolution feature. Single crystal X-ray diffraction, optical, electron microprobe and conventional and analytical electron microscopic studies have provided data limiting the compositions and structures of the coexisting phases. Individual lamellae of both materials are from 0.5 to 2.0 m in width with the lamellar interface parallel to {0 1 0}. The formulae of the minerals, as determined by a combination of electron microprobe and analytical electron microscopy, are (Na0.1Ca1.0Mg0.6Fe3+
0.3)(Si1.8Al0.2)O6 for the pyroxene and Na0.7Ca1.9(Mg2.1Fe2+
1.4Fe3+
0.5Ti0.1Cr0.1Al0.8)(Si5.9Al2.1) O22(OH)2 for the amphibole. Several other studies have described intergrowths similar to those observed in this work, in general favoring exsolution as the formation mechanism for the intergrowths. In the Lake Chatuge samples however, replacement of pyroxene by amphibole is in part indicated by continuous gradation of amphibole lamellae into amphiboles rimming the clinopyroxenes.Contribution No. 368 from the Mineralogical Laboratory, Department of Geological Sciences, The University of Michigan, Ann Arbor, Michigan 相似文献
10.
Jung Hoo Lee Donald R. Peacor Daniel D. Lewis Robert P. Wintsch 《Contributions to Mineralogy and Petrology》1984,88(4):372-385
Phyllosilicates in rocks which are transitional from mudstone to slate from Lehigh Gap, Pa., have been studied by a variety of techniques, including high resolution Transmission Electron Microscopy and Analytical Electron Microscopy. The principal minerals are white mica which is transitional from illite in mudstone to ordered twolayer mica in slate, and chlorite. 7Å berthierine occurs more rarely. Dioctahedral and trioctahedral layers are shown to be interleaved in individual crystals at all scales between the following two end members: (1) both random and regular 11 interlayering at the scale of individual layers, as shown, in part, by lattice fringe images. (2) packets of trioctahedral and dioctahedral layers up to a few thousand Ångstroms or microns in thickness, detectable with ordinary optical techniques. The complete range of intermediate structures is represented in samples which are in transition to slate. Bulk analytical (EMPA), X-ray diffraction or other measurements are shown to result in averages over both kinds of layers when TEM techniques are not used.Contribution No. 400 from the Mineralogical Laboratory, Department of Geological Sciences, The University of Michigan 相似文献