Modelamiento termodinámico y petrogenético de metapelita del complejo metamórfico Diego de Almagro, en la región de Magallanes, Chile (51°30`S)
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2023
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es
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Universidad Andrés Bello
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Licencia CC
Resumen
El Complejo Metamórfico Diego de Almagro (CMDA) (51°30´S) representa un ejemplo
del paleoprisma de acreción Cretácico preservado en el margen convergente en la Patagonia
Chilena insular. Compuesto por rocas que incluyen material volcánico y sedimentario que fueron
expuestas a procesos tectonometamórficos. Se divide en dos unidades metamórficas, Complejo
Almagro (CA) y Unidad Lazaro (UL) y se encuentran separados tectónicamente por la Zona de
Cizalle Puerto (ZCP). La UL se encuentra formada por rocas máficas de tipo N-MORB entre ellas
anfibolitas, anfibolitas migmatiticas y esquistos de mica blanca y granate. El CA está formado por
anfibolitas de granates, esquistos azules, eclogitas y micaesquistos formados en condiciones
transicionales de P/T que varían entre facies de esquistos azul y eclogita, la cual registra una
variación térmica. Este complejo fue formado por subducción y acreción de fragmentos oceánicos
derivados del fondo marino con edades y trayectorias presión-temperatura-tiempo (P-T-t) muy
heterogéneos. La muestra estudiada perteneciente al CA se encuentra asociada a la acreción frontal
pero aun así por su variabilidad en los rangos de P-T consiguió estar expuesta a la acreción basal.
El propósito de este trabajo es determinar las condiciones de P/T a las que estuvo sometido
el metamorfismo de la roca perteneciente al CA, donde mediante análisis petrográficos, químicos
mineralógicos y geotermobarométricos se lleva a cabo un modelamiento termodinámico realizado
con el software Perple_X para determinar las fases minerales. Las condiciones máximas de
metamorfismo varían desde los 9,5 y 11,7 Kbar con temperaturas de 477°C a 507°C,
correspondientes a un gradiente geotérmico de ~16°C/Km en su “peak” metamórfico con
trayectorias P-T-t en sentido horario. Desde los resultados obtenido se asocian facies de anfibolita
de epidota y se propone una modelo a partir de las fases de granate y fengita+clorita. Estos
resultados exponen la dinámica del paleoprisma de acreción, además de revelar que la roca estuvo
expuesta a dos procesos de exhumación y con un gradiente geotérmico que fluctuó en los ~16-
18°C/Km durante el Cretácico.
The Diego de Almagro Metamorphic Complex (DAMC) (51°30’S) is an example of a Cretaceous accretionary paleoprism preserved at the convergent margin in insular Chilean Patagonia. It is composed of rocks, including volcanic and sedimentary material, that were exposed to tectonometamorphic processes. The complex is divided into two metamorphic units, the Almagro Complex (AC) and the Lazaro Unit (UL), which are tectonically separated by the Port Shear Zone (PCZ). The UL is formed by mafic rocks of N-MORB type, including amphibolites, migmatitic amphibolites, white mica, and garnet schists. The CA is formed by garnet amphibolites, blue schists, eclogites, and mica schists formed under transitional P/T conditions varying between blue schist and eclogite facies, which record a thermal variation. This complex was formed by the subduction and accretion of oceanic fragments derived from the seafloor with very heterogeneous ages and pressure-temperature-time (P-T-t) trajectories. The studied sample belonging to the AC is associated with frontal accretion, but due to its variability in P-T ranges, it was also exposed to basal accretion. The purpose of this work is to determine the P/T conditions to which the metamorphism of the rock belonging to the CA was subjected. Petrographic, chemical mineralogical, and geothermobarometric analyses were conducted to carry out thermodynamic modeling with the Perple_X software to determine the mineral phases. The maximum metamorphism conditions vary from 9.5 to 11.7 Kbar with temperatures ranging from 477°C to 507°C, corresponding to a geothermal gradient of approximately 16°C/Km at its metamorphic peak with clockwise P-T-t trajectories. Based on the results obtained, amphibolite-epidotic facies are associated, and a model based on garnet and phengite+chlorite phases is proposed. These results expose the dynamics of the accretionary paleoprism and reveal that the rock was exposed to two exhumation processes and a geothermal gradient that fluctuated at approximately 16-18°C/Km during the Cretaceous period.
The Diego de Almagro Metamorphic Complex (DAMC) (51°30’S) is an example of a Cretaceous accretionary paleoprism preserved at the convergent margin in insular Chilean Patagonia. It is composed of rocks, including volcanic and sedimentary material, that were exposed to tectonometamorphic processes. The complex is divided into two metamorphic units, the Almagro Complex (AC) and the Lazaro Unit (UL), which are tectonically separated by the Port Shear Zone (PCZ). The UL is formed by mafic rocks of N-MORB type, including amphibolites, migmatitic amphibolites, white mica, and garnet schists. The CA is formed by garnet amphibolites, blue schists, eclogites, and mica schists formed under transitional P/T conditions varying between blue schist and eclogite facies, which record a thermal variation. This complex was formed by the subduction and accretion of oceanic fragments derived from the seafloor with very heterogeneous ages and pressure-temperature-time (P-T-t) trajectories. The studied sample belonging to the AC is associated with frontal accretion, but due to its variability in P-T ranges, it was also exposed to basal accretion. The purpose of this work is to determine the P/T conditions to which the metamorphism of the rock belonging to the CA was subjected. Petrographic, chemical mineralogical, and geothermobarometric analyses were conducted to carry out thermodynamic modeling with the Perple_X software to determine the mineral phases. The maximum metamorphism conditions vary from 9.5 to 11.7 Kbar with temperatures ranging from 477°C to 507°C, corresponding to a geothermal gradient of approximately 16°C/Km at its metamorphic peak with clockwise P-T-t trajectories. Based on the results obtained, amphibolite-epidotic facies are associated, and a model based on garnet and phengite+chlorite phases is proposed. These results expose the dynamics of the accretionary paleoprism and reveal that the rock was exposed to two exhumation processes and a geothermal gradient that fluctuated at approximately 16-18°C/Km during the Cretaceous period.
Notas
Memoria (Geólogo)
Palabras clave
Geología, Modelamiento Geológico, Chile, Región de Magallanes