Petrología del cuerpo serpentinítico traiguanca, XI Región de Aysén, Chile
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2018
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es
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Universidad Andrés Bello
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Licencia CC
Resumen
El presente trabajo contribuye con nuevos antecedentes para elucidar el significado geológico de los cuerpos serpentiníticos aflorantes en la zona septentrional del Complejo Metamórfico Andino Oriental. Se lleva a cabo una investigación petrológica, desde un enfoque basado en observaciones de campo, estudios petrográficos, análisis mediante microscopía electrónica de barrido, microsonda electrónica, difracción de rayos X, espectroscopía micro-Raman y características geoquímicas, en el cuerpo serpentinítico Traiguanca, ubicado en las cercanías de Bahía Murta, XI región de Aysén de Chile. El cuerpo ultramáfico expone un plano de brecha de falla que separa serpentinitas macizas en su zona topográfica inferior de serpentinitas foliadas en su dominio topográfico superior. Se halla cortado por numerosas venas de serpentina, carbonato y talco. El cuerpo revela una diversidad de arreglos texturales, siendo el más conspicuo la textura interpenetrativa, atinente a una interconexión caótica de dagas de antigorita y granos de magnetita. De igual modo se reconocen pseudomorfos de serpentina (bastitas), agregados microcristalinos, arreglos masivos, texturas interligadas, veteadas y fibrosas radiales. El reconocimiento de antigorita, lizardita y crisotilo a través de métodos analíticos de difracción de rayos X y espectroscopía micro-Raman, en conjunto con la ausencia de olivino metamórfico, indicarían que las rocas ultramáficas experimentaron rangos variables de presión y temperatura, aunque sin sobrepasar los 600-700°C. Estas observaciones permiten sugerir que el protolito originario de las rocas ultramáficas hidratadas correspondería a una dunita de espinela crómica altamente refractaria, la cual habría alcanzado un grado de serpentinización total en un margen activo. Asimismo, se sugieren al menos tres eventos de serpentinización, y al menos un evento de deformación, que habría dado lugar a una foliación localizada y venas de serpentina paralelamente distribuidas. En etapas ulteriores, proporciones óptimas de CO2 se habrían incorporado a los fluidos mineralizantes, responsabilizándose de la cristalización de carbonato y talco, a expensas de la desestabilización previa de serpentinas.
The present investigation contributes with new records to elucidate the geological significance of serpentinites outcropping in the septentrional zone of the Eastern Andean Metamorphic Complex. A petrological research is carried out, on the basis of field observations, petrographic studies, electron microprobe analysis, scanning electron microscope, X-ray diffraction, micro-Raman spectroscopy and geochemical characteristics of the Traiguanca serpentinite body, located near Bahía Murta, Aysén, Chile. The ultramafic body exposes a fault breccia plane which splits massive serpentinite in their inferior topographic zone from foliated serpentinite in their superior topographic domain. The ultramafic body is crosscutted by numerous serpentine, carbonate and talc veins. These serpentinites reveal a diversity of textural arrangements, being the most conspicuous the interpenetrative texture, pertinent to a chaotic interconnection of antigorite blades and magnetite grains. In the same way, the serpentinites show pseudomorphic serpentine textures (bastites), microcrystalline aggregates, massive arrangements, interlocking, veined and fibrous radial textures. The recognition of antigorite, lizardite, and chrysotile by means of X-ray diffraction and micro-Raman spectroscopy, in conjunction with the absence of metamorphic olivine, would suggest that these serpentinites underwent variable ranges of pressure and temperature, without exceeding 600-700°C. These observations suggest that the protolith of the hydrated ultramafic rocks would correspond to a highly refractory chromian spinel-bearing dunite, which would have reached a maximum serpentinization degree in an active margin. Likewise, three stages of serpentinization are recognized, and at least one deformation event would have originated a localized foliation and parallel serpentine veinlets. In later stages, optimal proportions of CO2 would have incorporated into the mineralizing fluids, giving rise to the crystallization of carbonates and concomitant talc at the expense of the serpentine breakdown.
The present investigation contributes with new records to elucidate the geological significance of serpentinites outcropping in the septentrional zone of the Eastern Andean Metamorphic Complex. A petrological research is carried out, on the basis of field observations, petrographic studies, electron microprobe analysis, scanning electron microscope, X-ray diffraction, micro-Raman spectroscopy and geochemical characteristics of the Traiguanca serpentinite body, located near Bahía Murta, Aysén, Chile. The ultramafic body exposes a fault breccia plane which splits massive serpentinite in their inferior topographic zone from foliated serpentinite in their superior topographic domain. The ultramafic body is crosscutted by numerous serpentine, carbonate and talc veins. These serpentinites reveal a diversity of textural arrangements, being the most conspicuous the interpenetrative texture, pertinent to a chaotic interconnection of antigorite blades and magnetite grains. In the same way, the serpentinites show pseudomorphic serpentine textures (bastites), microcrystalline aggregates, massive arrangements, interlocking, veined and fibrous radial textures. The recognition of antigorite, lizardite, and chrysotile by means of X-ray diffraction and micro-Raman spectroscopy, in conjunction with the absence of metamorphic olivine, would suggest that these serpentinites underwent variable ranges of pressure and temperature, without exceeding 600-700°C. These observations suggest that the protolith of the hydrated ultramafic rocks would correspond to a highly refractory chromian spinel-bearing dunite, which would have reached a maximum serpentinization degree in an active margin. Likewise, three stages of serpentinization are recognized, and at least one deformation event would have originated a localized foliation and parallel serpentine veinlets. In later stages, optimal proportions of CO2 would have incorporated into the mineralizing fluids, giving rise to the crystallization of carbonates and concomitant talc at the expense of the serpentine breakdown.
Notas
Tesis (Geólogo)
Este trabajo ha sido financiado por el Proyecto FONDECYT 1130227.
Este trabajo ha sido financiado por el Proyecto FONDECYT 1130227.
Palabras clave
Petrología, Chile, Aysén, Serpentinita