The origin of formation of the amphibolite-granulite transition facies

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The Ohio State University

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The origin of formation of the amphibolitegranulite transition facies may be from deep burial in the earth's crust or it may come from the tectonic process of an orogenic event related to continental collision zones. Temperatures needed to form this transition facies are on the order of 600°c to 800°c, with the accompanying pressures of 5 to almost 8 kbar. These conditions of temperature and pressure can be met by each above hypothesis for the transition facies. In the deep crustal model, it is known that upon reaching the depths of 10-35 km the temperatures and pressures at this depth are suitable to form this facies. Similarly, in the hypothesis of the orogenic event, these temperature and pressure conditions can be created by a descending slab of continental material into the earth's interior. In order to come to a conclusive opinion on which hypotheses formed the transition facies, a study of the facies involved must be completed. This includes: defining the facies involved by their mineral compositions, evaluating the temperature and pressure conditions which affect the formation of the facies involved, and taking into account the content and composition of H20 and C02 activities in fluid inclusions found in these facies. Finally, a description and study of the two previous mentioned hypotheses has been carried out and a conclusion as to which process formed the amphibolite-granulite transition facies is stated.