Low-grade metamorphism in granitoids and volcanic rocks, Cordillera Neuquina, Argentina
Granitoid and volcanic rocks of the Cordillera Neuquina between 38°45′ and 39°30′ south latitude have been metamorphosed under zeolite, prehnite-pumpellyite, and transitional greenschist facies conditions. This low-grade metamorphism is related to the circulation of hydrothermal solutions associated...
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| Autores principales: | , |
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| Formato: | JOUR |
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| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_08959811_v3_n4_p247_VattuonedePonti |
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| Sumario: | Granitoid and volcanic rocks of the Cordillera Neuquina between 38°45′ and 39°30′ south latitude have been metamorphosed under zeolite, prehnite-pumpellyite, and transitional greenschist facies conditions. This low-grade metamorphism is related to the circulation of hydrothermal solutions associated with Tertiary(?) subvolcanic bodies and/or shallow intrusives through a pre-existing fracture system. Three progressive metamorphic zones have been established, with temperatures ranging from 100° to 300°C and pressures less than 4 kb. The pressures are similar to those estimated for metamorphic rocks at Taringatura, New Zealand, and in the Tanzawa Mountains of Japan. The mineral assemblages are influenced by host-rock composition. In the granitoids, the sequence is: Zone I - heulandite, stilbite, K-feldspar, albite, quartz, calcite; Zone II - chlorite, prehnite, pumpellyite, albite, K-feldspar, titanite, quartz; and Zone III - chlorite, pistacite, piedmontite, titanite, actinolite, K-feldspar, albite, quartz, calcite. In the basalts, the sequence is: Zone I - heulandite, stilbite, calcite; Zone II - analcime, thomsonite, laumontite, natrolite, celadonite, albite; and Zone III - chlorite, pistacite, actinolite, pumpellyite, laumontite, albite, quartz. In the andesites, the sequence is: Zone I - stilbite, calcite, quartz; Zone II - pumpellyite, chlorite, titanite, celadonite, albite, quartz, calcite; and in Zone III - pistacite, quartz, chlorite, albite. Pyrite, chalcopyrite, arsenopyrite, and copper are always found in association with quartz and epidote in Zone III. © 1991. |
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