Petrogénesis de gneisses de alto grado y leucogranitos de granate del complejo ígneo metamórfico Puerto Edén, Magallanes, Chile
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2018
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es
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Universidad Andrés Bello
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Rocas metamórficas, migmatitas y leucogranitos del Complejo Ígneo Metamórfico Puerto Edén se encuentran intruidas por el Plutón Monte Albion, un cuerpo consituido principalmente por monzogranitos porfídicos con fenocristales de feldespato potásico y schlieren de biotita, de forma elipsodal y orientación norte-sur. Gneisses y leucogranitos ubicados en el contacto con el Plutón Monte Albión, son estudiados para establecer el nivel de emplazamiento del plutón que tiene una edad de cristalización de c. 142 Ma. Se seleccionaron un gneiss de sillimanita-biotita y un leucogranito de granate, de un mismo afloramiento, para realizar el modelamiento termodinámico con el software Perple_X en el sistema MnNCKFMASHTO. Considerando la intersección de isópletas de la fracción molar de granate (XFe, XMn, XMg y XCa) en el leucogranito se estimaron las condiciones de máxima presión y temperatura son de 4,0 ± 1,0 kbar y 690 ± 30ºC. En el gneiss de sillimanita la intersección de isópletas #Fe [Fe+2/(Fe+2/Mg)] en biotita y de la moda de sillimanita permiten establecer que el peak metamórfico ocurrió a presiones de 4,1 ± 1,0 kbar y temperaturas de 690 ± 30°C; en el campo de estabilidad de la asociación mineralógica biotita + cordierita + feldespato potásico + plagioclasa + sillimanita + cuarzo + ilmenita + magnetita. Los resultados son consistentes y evidencian un origen común para ambas muestras. El peak metamórfico en el gneiss de sillimanita está en el campo de facies anfibolita de alta temperatura y baja presión. El modelo predice que la génesis del gneiss habría involucrado procesos de fusión parcial, por deshidratación de muscovita y/o biotita, con una generación de 40-45 % vol. de fundidos que se segregaron y formaron leucogranitos en el mismo afloramiento. La intersección de isópletas de Si en muscovita y #Fe en biotita en el gneiss de sillimanita indican presiones de 2,4 ± 1,0 kbar y temperaturas de 600 ± 30 ºC. Considerando el carácter tardío de la muscovita, texturalmente ubicada entre sillimanita y biotita, se asocian a una trayectoria retrógrada de metamorfismo. La trayectoria presión-temperatura-tiempo es en sentido horario. Se establece que el Plutón Monte Albión se emplazó a profundidades de 10-15 km en una zona de cizalle de escala cortical activa durante el desarrollo temprano, etapa de “rifting”, de la Cuenca Rocas Verdes. La generación de migmatitas y granitos peraluminosos podría estar asociada al “input” calórico asociado al ascenso astenosférico en un régimen tectónico extensional o transtensional.
Metamorphic rocks, migmatites and leucogranites of the Puerto Edén Igneous and Metamorphic Complex are intruded by the Monte Albion Pluton, a body consisting mainly of porphyritic monzogranites with phenocrysts of potassium feldspar and schlieren of biotite, ellipsodal in shape and with north-south orientation. Gneisses and leucogranites located in the contact with Monte Albion Pluton, are studied to establish the emplacement level of pluton that has a crystallization age of c. 142 Ma. A sillimanite-biotite gneiss and a garnet leucogranite, from the same outcrop, were selected to perform the thermodynamic modeling with the Perple_X software in the MnNCKFMASHTO system. Considering the intersection of isolates of the molar fraction of garnet (XFe, XMn, XMg and XCa) in the leucogranite, the maximum pressure and temperature conditions were estimated at 4.0 ± 1.0 kbar and 690 ± 30ºC. In the sillimanite gneiss, the intersection of isolplths of #Fe [Fe+2 / (Fe+2 / Mg)] in biotite and the mode of sillimanite, allow establishing that peak metamorphicsm occurred at pressures of 4.1 ± 1.0 kbar and temperatures of 690 ± 30 ° C; in the stability field of biotite + cordierite + potassium feldspar + plagioclase + sillimanite + quartz + ilmenite + magnetite. The results are consistent and show a common origin for both samples. The metamorphic peak in the sillimanite gneiss is in the field of amphibolite facies of high temperature and low pressure. The model predicts that the genesis of the gneiss would have involved partial melting processes, by dehydration of muscovite and / or biotite, with a generation of 40-45% vol. of melts that segregated and formed leucogranites in the same outcrop. The intersection of isopleths of Si in muscovite and #Fe in biotite in the sillimanite gneiss indicate pressures of 2.4 ± 1.0 kbar and temperatures of 600 ± 30 ° C. Considering the late nature of muscovite, texturally located between sillimanite and biotite, these results would be associated with the retrograde trajectory of metamorphism. The pressure-temperature-time trajectory is clockwise. It is established that the Monte Albión Pluto was emplaced at depths of 10-15 km within a crustal scale shear zone during the early development, rifting stage, of the Rocas Verdes Basin. The generation of migmatites and peraluminous granites could be associated to the caloric "input" associated with astenospheric ascent in an extensional or transtensional tectonic regime.
Metamorphic rocks, migmatites and leucogranites of the Puerto Edén Igneous and Metamorphic Complex are intruded by the Monte Albion Pluton, a body consisting mainly of porphyritic monzogranites with phenocrysts of potassium feldspar and schlieren of biotite, ellipsodal in shape and with north-south orientation. Gneisses and leucogranites located in the contact with Monte Albion Pluton, are studied to establish the emplacement level of pluton that has a crystallization age of c. 142 Ma. A sillimanite-biotite gneiss and a garnet leucogranite, from the same outcrop, were selected to perform the thermodynamic modeling with the Perple_X software in the MnNCKFMASHTO system. Considering the intersection of isolates of the molar fraction of garnet (XFe, XMn, XMg and XCa) in the leucogranite, the maximum pressure and temperature conditions were estimated at 4.0 ± 1.0 kbar and 690 ± 30ºC. In the sillimanite gneiss, the intersection of isolplths of #Fe [Fe+2 / (Fe+2 / Mg)] in biotite and the mode of sillimanite, allow establishing that peak metamorphicsm occurred at pressures of 4.1 ± 1.0 kbar and temperatures of 690 ± 30 ° C; in the stability field of biotite + cordierite + potassium feldspar + plagioclase + sillimanite + quartz + ilmenite + magnetite. The results are consistent and show a common origin for both samples. The metamorphic peak in the sillimanite gneiss is in the field of amphibolite facies of high temperature and low pressure. The model predicts that the genesis of the gneiss would have involved partial melting processes, by dehydration of muscovite and / or biotite, with a generation of 40-45% vol. of melts that segregated and formed leucogranites in the same outcrop. The intersection of isopleths of Si in muscovite and #Fe in biotite in the sillimanite gneiss indicate pressures of 2.4 ± 1.0 kbar and temperatures of 600 ± 30 ° C. Considering the late nature of muscovite, texturally located between sillimanite and biotite, these results would be associated with the retrograde trajectory of metamorphism. The pressure-temperature-time trajectory is clockwise. It is established that the Monte Albión Pluto was emplaced at depths of 10-15 km within a crustal scale shear zone during the early development, rifting stage, of the Rocas Verdes Basin. The generation of migmatites and peraluminous granites could be associated to the caloric "input" associated with astenospheric ascent in an extensional or transtensional tectonic regime.
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Petrogénesis, Leucogranitos, Chile, Puerto Edén