Nature of metamorphism of low-temperature metamorphic rocks in the continent-ocean transition zone (by the example of Pensantain Sequence of Western Kamchatka)

Abstract

The nature of low-temperature metamorphic rocks in the continent-ocean transition zone has been studied on the example of metamorphosed Late Cretaceous volcanic-sedimentary deposits of Western Kamchatka (Pensantain Sequence).The Pensantain Sequence consists of prevailing albite-actinolite-epidote-muscovite-chlorite schists. Albit-lavsonite-muscovite-chlorite and кiebeckit-epidote-albite-chlorite schists also participate in Pensantain stratum. The temperature and pressure of the metamorphism of the Pensantain metamorphic rocks were determined by computer modeling using the «Selector C» program. P-T conditions of metamorphism (T = 360± 50°С; P = 3800 ± 500 bar) correspond to facies transition from the greenschist to the blueschist facies. Computer modeling was performed for two samples. This is the first application of the «Selector C» program to determine the P-T conditions of low-temperature metamorphism. The geodynamic conditions and the time of metamorphism were reconstructed. It has been established that rocks of the Pensantain Sequence were formed in the Early Paleogene during collisional metamorphism.

Keywords

• kamchatka
• collisional metamorphism
• thermobarometry
• lawsonite
• green schist