368 research outputs found

    Formation of corrensite, chlorite and chlorite-mica stacks by replacement of detrital biotite in low-grade pelitic rocks

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    Transmission and scanning electron microscopy were utilized to investigate the nature and mechanisms of alteration of abundant detrital biotite of volcanic origin and progressive modification of phyllosilicate aggregates in a prograde sequence of pelitic rocks (illite crystallinity index = 0.19–0.58dΛ2θ) from the GaspÉ Peninsula in Quebec. Detrital biotite has been diagenetically altered to form corrensite and chlorite through two mechanisms; (1) layer-by-layer replacement gave rise to interstratification of packets of layers and complex mixed layering via several kinds of layer transitions between biotite and chlorite, corrensite or smectite; (2) dissolution-transport-precipitation resulted in the formation of relatively coarse-grained aggregates of randomly orientated, corrensite-rich flakes and fine-grained corrensite intergrown with chlorite and illite in the matrix. The data show that stacks consisting of alternating packets of trioctahedral and dioctahedral phyllosilicates originated during early diagenesis when lenticular fissures in strained altering biotite were filled by dioctahedral clays. Subsequent prograde evolution of dioctahedral clays occurred through deformation, dissolution and crystallization, and overgrowth. Illite evolved to muscovite, with K in part provided through biotite alteration, and corrensite/chlorite to homogeneous chlorite. The alteration of detrital biotite is closely related to the formation of titanite and magnetite in diagenetic rocks, and pyrite, calcite and anatase or rutile in the higher grade rocks. The observations demonstrate that detrital biotite of volcanic origin may be the principal precursor of chlorite in chlorite-rich metapelites originating in marginal basins. The mineral parageneses suggest that the transitions from corrensite to chlorite and illite to muscovite may be a function of local chemistry and time.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75643/1/j.1525-1314.1994.tb00065.x.pd

    Mineralogy op yoredale series rocks in Upper Teesdale with special reference to clay minerals

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    A description of the stratigraphy of the area studied is given in which the variations in lithology and sequence are illustrated. The methods of clay mineral analysis are discussed and it is concluded that X-ray analysis is most useful for the present work. The argillaceous rocks are classified into types on characteristics recognisable in the field and the results of petrographic and X-ray analyses are tabulated. Apart from kaolinite, which is post-depositional in origin, only three different clay minerals occur: illite, chlorite and mixed- layer. Different types of argillaceous rock have different clay mineral assemblages. Associated arenaceous and calcareous rocks are similarly classified on field characters and are analysed petrographically. A system of sandstone classification is proposed. The relationship between the clay mineralogy of a sedimentary rock and the origin, transport, deposition and post-depositional history of the minerals is discussed. Recent shallow water marine and deltaic sedimentation are reviewed and the various facies recognised in the Gulf of Mexico and the Mississippi Delta are enumerated. It is postulated that the Yoredale sediments were deposited in a shallow water marine environment from a series of small shoal-water deltas. The different sediment types and their mineralogies are related to different conditions in the various facies of the environment. Repetition of the sedimentation in the form of cycles is discussed briefly. An additional chapter deals with the igneous rocks intruding the sediments and the metamorphic effects of the Whin Sill upon the country rocks

    Direct dating of mid-crustal shear zones with synkinematic allanite:new in situ U-Th-Pb geochronological approaches applied to the Mont Blanc massif

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    International audienceDating the timing of motion on crustal shear zones is of tremendous importance for understanding the assembly of orogenic terranes. This objective is achieved in this paper by combining petrological and structural observations with novel developments in in situ U-Th-Pb geochronology of allanite. A greenschist facies shear zone within the Mont Blanc Massif is documented. Allanite is synkinematic and belongs to the mylonitic assemblage. LA-ICP-MS U-Th-Pb isotope analyses of allanite reveal high contents and highly radiogenic isotopic compositions of the common-Pb component. The use of measured Pb-isotope compositions of associated minerals (feldspars and chlorite) is critical for accurate common-Pb correction, and provides a powerful mechanism for linking allanite growth to the metamorphic assemblage. A mean 208Pb/232Th age of 29.44 ± 0.95 Ma is accordingly taken for synkinematic allanite crystallisation under greenschist facies conditions. This age reflects the timing of the Mont Blanc underthrusting below the Penninic Front and highlights the potential of directly dating deformation with allanite

    Approaches to the low grade metamorphic history of the karakaya complex by chlorite mineralogy and geochemistry

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    In this study, chlorite is used to investigate the diagenetic-metamorphic evolution and accurate geological history of the different units belonging to the Karakaya complex, Turkey. Primary and secondary chlorite minerals in the very low-grade metamorphic rocks display interference colors of blue and brown and an appearance of optical isotropy. Chlorites are present in the matrix, pores, and/or rocks units as platy/flaky and partly radial forms. X-ray diffraction (XRD) data indicate that Mg-Fe chlorites with entirely IIb polytype (trioctahedral) exhibit a variety of compositions, such as brunsvigite-diabantite-chamosite. The major element contents and structural formulas of chlorite also suggest these were derived from both felsic and metabasic source rocks. Trace and rare earth element (REE) concentrations of chlorites increase with increasing grade of metamorphism, and these geochemical changes can be related to the tectonic structures, formational mechanics, and environments present during their generation. © 2015 by the authors; licensee MDPI, Basel, Switzerland

    Cap rock efficiency of geothermal systems in fold-and-thrust belts: Evidence from paleo-thermal and structural analyses in Rosario de La Frontera geothermal area (NW Argentina)

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    Cap rock characterization of geothermal systems is often neglected despite fracturing may reduce its efficiency and favours fluid migration. We investigated the siliciclastic cap rock of Rosario de La Frontera geothermal system (NW Argentina) in order to assess its quality as a function of fracture patterns and related thermal alteration. Paleothermal investigations (XRD on fine-grained fraction of sediments, organic matter optical analysis and fluid inclusions on veins) and 1D thermal modelling allowed us to distinguish the thermal fingerprint associated to sedimentary burial from that related to fluid migration. The geothermal system is hosted in a Neogene N-S anticline dissected by high angle NNW- and ENE-striking faults. Its cap rock can be grouped into two quality categories: • rocks acting as good insulators, deformed by NNW–SSE and E–W shear fractures, NNE-SSW gypsum- and N-S-striking calcite-filled veins that developed during the initial stage of anticline growth. Maximum paleo-temperatures (< 60 °C) were experienced during deposition to folding phases.• rocks acting as bad insulators, deformed by NNW-SSE fault planes and NNW- and WNW-striking sets of fractures associated to late transpressive kinematics. Maximum paleo-temperatures higher than about 115 °C are linked to fluid migration from the reservoir to surface (with a reservoir top at maximum depths of 2.5 km) along fault damage zones.This multi-method approach turned out to be particularly useful to trace the main pathways of hot fluids and can be applied in blind geothermal systems where either subsurface data are scarce or surface thermal anomalies are lacking.Fil: Maffucci, R.. Universita Degli Studi Della Tuscia; Italia. Universita Degli Studi Roma Tre; ItaliaFil: Corrado, Sveva. Universita Degli Studi Roma Tre; ItaliaFil: Aldega, L.. Instituto de Investigaciones Universitarias Roma la Sapienza; ItaliaFil: Bigi, S.. Instituto de Investigaciones Universitarias Roma la Sapienza; ItaliaFil: Chiodi, Agostina Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones en Energía no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de Física. Instituto de Investigaciones en Energía no Convencional; ArgentinaFil: Di Paolo, L.. Eni E&P Division; ItaliaFil: Giordano, G.. Universita Degli Studi Roma Tre; ItaliaFil: Invernizzi, C.. Universita Degli Di Camerino; Itali

    Mineralogical aspects of interstratified chlorite-smectite associated with epithermal ore veins: A case study of the Todoroki Au-Ag ore deposit, Japan

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    Chlorite (C)-corrensite (Co)-smectite (S) seriesminerals occur as vein constituents in the two epithermal ore veins, the Chuetsu and Shuetsu veins of the Todoroki Au-Ag deposit. The characteristics of the C-Co-S seriesminerals indicate that the clays may be products of direct precipitation from hydrothermal fluids and subsequent mineralogical transformations during and/or after vein formation. The minerals from the Chuetsu vein are characterized by 'monomineralic' corrensite showing an extensive distribution throughout the vein, and trioctahedral smectite occurring locally. The Shuetsu vein minerals are characterized by C-Co series minerals which can be divided into three different types: a I type including discrete chlorite with minor amounts of S layers, a II type comprising interstratified C/Co and discrete chlorite, and a III type characterized by segregation structures of C and Co layers. The C-Co series minerals show slightly different spatial distributions in the Shuetsu vein. Different epithermal environments during the vein formations and possible kinetic effects may have played a role in the formation and conversion of Co-C series at the Shuetsu vein and S-Co series at the Chuetsu vein

    Aspects of pressure solution as a deformation mechanism

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    Optimization Of Power From Food Waste Using Membrane-less Microbial Fuel Cell

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    Fossil fuels have supported the industrialization and economic growth of countries during the past centuries and it is clear that they cannot indefinitely sustain in a longer time. In this study, Microbial Fuel cell (MFC) had potential solution to generate electricity power and at the same time could reduce the abundant of food waste (1.64 kg/daily, around 8 tonnes/year) which dumped in the landfill. The MFC operated electrochemically incorporate electrogenic bacteria (EB) acted as a biocatalyst in order to produce electricity. The performance of the MFC using food waste is evaluated using one-factor-at-a-time (OFAT) method. the optimization performance of the MFC using food waste was evaluated using method of one factor at one time (OFAT) and it was focused to pH for power generation. To determine the generated electricity the polarization curve was used to evaluate the performance of MFC. The chemical oxygen demand (COD) of food waste is studied. Optimization of pH condition in MFC under certain pH ranging from 5 to 9, with other condition. Results shows that pH 8 is the most suitable pH for Bacillus strain that was chosen for this experiment. With voltage generated resulted 807 mV, highest biomass produced 35.46 mg/L, and power density produced 373.3 mW/m2. In conclusion, pH environment condition in MFC will affect the efficiency of performance for energy production. The increase in EB biomass also increased the voltage in the ML-MFC, proving that EB biomass and voltage were associated with growth
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