Example of three pyroxenes coexisting in magnetite gabbro of the western Panskye Tundras, Kola peninsula

摘要

The rare paragenesis of three pyroxenes: augite, pigeonite and hypersten, has been discovered in magnetite gabbro of the western Panskye Tundras layered intrusion. Co-existence of this triplet become possible due to replacement of orthopyroxene by pigeonite during some period of time, with simultaneous crystallization of both these pyroxenes. This period was characterized by rather narrow interval of P-T condition variations within the field of intersection between the magma liquidus temperature line and the line of pigeonite-orthopyroxene inversion. According to the calculated data. crystallization of the magnetite gabbro took place under pressure not higher than 1-2 kbar and 797-844 deg C temperatures.