Evaluation of P-T and fO(2) Conditions of Crystallization of Monzonitic Rocks of the Velitkenay Granite-Migmatite Massif (Arctic Chukotka) Based on Mineral Thermobaro- and Oxybarometry

摘要

The physico-chemical parameters of crystallization of the Early Cretaceous Velitkenay granite-migmatite pluton (Arctic coast of Chukotka, near Cape Billings) are reconstructed using mineral thermobarometry and oxybarometry. The magmatic rocks are dominated by monzonitic rocks (quartz monzodiorites and monzodiorites), with less common granodiorites and leucogranites. The limitations on and critical parameters of the amphibole composition are considered for correct application of thermobarometry. The most reliable pressure estimations for the early-phase monzonitic rocks are calculated using an amphibole geobarometer range from 2.2 to 4.2 kbar. The calculated crystallization temperature varies from 684 to 823 degrees C (plagioclase-amphibole geothermometer) at oxygen fugacity from +0.2 to +0.7 relative to NNO buffer. The obtained P-T data on the Velitkenay monzonitic rocks are consistent with the conditions of amphibolite facies metamorphism typical of the Chukotka granite-metamorphic domes, the formation of which is related to post-collisional extension.