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      Deformación, vetas, inclusiones fluidas y la evolución tectónica de las rocas cretácicas de Valle de Bravo, Estado de México, México Translated title: Deformation, veins, fluid inclusions and the tectonic evolution of the Valle de Bravo Cretaceous rocks, Estado de Mexico, Mexico

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          Abstract

          En el área de Valle de Bravo, Estado de México, afloran dos ensambles de rocas cretácicas con metamorfismo de muy bajo grado: (1) rocas metasedimentarias (EMS), y (2) rocas metavolcánicas (EMV). Estas unidades forman parte de la secuencia mesozoica volcanosedimentaria metamorfizada de Ixtapan de la Sal - Teloloapan. La historia de deformación en la zona está definida por tres eventos de acortamiento subhorizontales (D1, D2 y D3), que coinciden en rumbo NE-SW, pero con direcciones alternadas de transporte tectónico. D1 tiene una vergencia general hacia 043°, D2 hacia 218° y D3 hacia 045°. Estos tres eventos han sido identificados en diversas localidades de los estados de Guerrero y Michoacán, representando importantes fenómenos de deformación a escala regional. D1 muestra deformación dúctil a escala de grano, mientras que D2 es dúctil-quebradizo y D3es netamente quebradizo. Mediante el análisis de microestructuras en lámina delgada, a escala de afloramiento y con la determinación cuantitativo-comparativa de vetas mediante análisis de imágenes, se propone que D1 representa el pico metamórfico y deformacional y que D2 y D3 ocurrieron durante la exhumación de las rocas. Asociadas a los eventos D1 y D2, se desarrollaron dos generaciones de vetas, V1 y V2, cuya abundancia depende del grado de penetratividad de la deformación; es decir, de los fenómenos de deformación a escala microscópica (principalmente disolución por presión/reprecipitación) que movilizan material soluble que se deposita en forma de vetas en etapas tardías de la deformación. Adicionalmente a las vetas V1 y V2, se identificó también un sistema de vetas tardías (V3) asociadas a fallas normales que cortan estructuras D3. Análisis petrográfico y microtermométrico de inclusiones fluidas en cristales de cuarzo y calcita se realizaron en las tres generaciones de vetas en un área de 15 km² en el EMS. Las temperaturas de homogeneización obtenidas fueron, en promedio, de 250 °C para V], entre 167 y 202 °C para V2, y 220 °C para V3. Las correspondientes salinidades aparentes obtenidas fueron, en promedio, de entre 6.1 y 7.4 (V1), 5.2 (V2),y 2.6y 4.6 (V3) % en peso de NaCl equivalente. Los datos obtenidos en las vetas están de acuerdo con una exhumación progresiva de las rocas del área de estudio, ya que tanto las temperaturas de homogeneización como las salinidades asociadas a deformación son menores en V2 que en V1 . Mientras que las temperaturas de V3 indican que fluidos relativamente más calientes circularon a lo largo de fallas normales posteriormente a D1, D2yD3.

          Translated abstract

          In the Valle de Bravo area, central Mexico, two assemblages of cretaceous rocks are exposed. Both units present very low grade metamorphism: (1) a meta-sedimentary rock assemblage (EMS), and (2) a meta-volcanic rock assemblage (EMV). These rocks are part of the Ixtapan de la Sal - Teloloapan volcano-sedimentary metamorphosed Mesozoic sequence. The history of deformation of the two assemblages is represented by three sub-horizontal shortening events (D1, D2yD3), that display similar NE-SW orientation, but alternating tectonic transport direction. D1 has a general vergence toward 043 °, whereas D2 toward 218°, and D3 toward 045°. The three events have been recognized in different localities in Guerrero andMichoacan states, and they represent important shortening episodes at regional scale. Event D1 exhibits ductile deformation at grain scale, while D2 is brittle-ductile, and D3 presents strictly brittle characteristics. We propose that D1 is the peak metamorphic/deformational event and that D2 and D3 occurred during exhumation of the rocks. During D1and D2, two generations of veins (V1 and V2, respectively) were developed. Abundance of the veins has been related directly to the penetrativity of deformation; which suggests that the mobilization of soluble material (mainly by pressure-solution/re-precipitation) was the effective mechanism of deformation at the microscopic scale. This soluble material was deposited in veins in later stages of the deformation event and was more intense during D1. This is demonstrated by the analysis ofmicrostructures in thin section, by outcrop observations and by the comparative-quantitative determination of density of veins through image analysis. In addition to the earlier V1 and V2 veins, late veins (V3) were also identified, and are associated dominantly to normal faults that cut D3 structures. Petrography and microthermometric analyses on fluid inclusions were done on quartz and calcite crystals of the three generations of veins in a 15 km² area in the EMS. The average homogenization temperatures were: 250 °Cfor V1, between 167 and 202 °Cfor V2 and 220 °Cfor V3. Corresponding salinities obtained were: between 6.1 y 7.4 (V1), 5.2 (V1), and between 2.6 and 4.6 (V3) (weight % ofNaCl equivalent). The data obtained in V1 and V2 are in agreement with a progressive exhumation of the rocks in the studied area, while the temperatures measured in V3 indicate that hotter fluids circulated along normal faults and associated vertical fractures after D3.

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          • Abstract: not found
          • Article: not found

          The crack–seal mechanism of rock deformation

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            • Record: found
            • Abstract: not found
            • Article: not found

            Tectono-stratigraphic terranes and mineral resource distributions in Mexico

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              • Record: found
              • Abstract: not found
              • Article: not found

              ROLE OF FLUID PRESSURE IN MECHANICS OF OVERTHRUST FAULTING

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                Author and article information

                Journal
                rmcg
                Revista mexicana de ciencias geológicas
                Rev. mex. cienc. geol
                Instituto de Geología, UNAM (México, DF, Mexico )
                1026-8774
                2007-2902
                2008
                : 25
                : 1
                : 59-81
                Affiliations
                [03] D. F. orgnameUniversidad Nacional Autónoma de México (UNAM) orgdiv1Instituto de Geología México
                [04] D. F. orgnameUniversidad Nacional Autónoma de México (UNAM) orgdiv1Instituto de Geofísica orgdiv2Departamento de Recursos Naturales México
                [01] D. F. orgnameUniversidad Nacional Autónoma de México (UNAM) orgdiv1Instituto de Geología orgdiv2Posgrado en Ciencias de la Tierra México
                [02] D. F. orgnameUniversidad Nacional Autónoma de México (UNAM) orgdiv1Instituto de Geología orgdiv2Departamento de Geología Regional México tolson@ 123456servidor.unam.mx
                Article
                S1026-87742008000100004 S1026-8774(08)02500100004
                59f9c82f-45e6-4cdd-8763-7bf8e7b8f3a8

                This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

                History
                : 24 January 2007
                : 15 October 2007
                : 15 October 2007
                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 55, Pages: 23
                Product

                SciELO Mexico


                deformación,exhumation,exhumación,Cretácico,pliegues,microtermometría,México,microthermometry,Valle de Bravo,Mexico,folds,veins,deformation,vetas,Cretaceous

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