Abstract
Quartz phenocrysts of rhyolitic welded tuff from Mt. Jang, Pusan, preserve not only clear and homogeneous glass inclusions but also partially devitrified inclusions. The glass inclusion that contains a trapped liquidus phase comprises a vapor bubble, whereas the devitrified inclusions are commonly associated with micro-cracks. These glass inclusions are composed of highly evolved peraluminous potassic rhyolites, and are more differentiated than those of the bulk rocks. Hornblende and plagioclase phenocrysts began to crystallize earlier than potassium feldspar and quartz phenocrysts. Melt temperatures prior to the eruption and quenching were probably 740–765°C, estimated from the homogenization temperature of glass inclusions. Distinctive long prismatic crystal form of glass inclusions suggests that part of the phenocrysts grew in the stability field of α-quartz and thus the tuff unitprobably solidified at least below the β-α inversion temperature. Total volatile contents in melts (obrained by summing H2O, F, and CI) vary from 1.8 to 4.0 wt%. Textural and mineralogical characteristics suggest that magma was water-saturated shortly before or during the eruption. H2O content of the glass (ca. 1.0–3.0 wt%) suggests a water saturation pressure\((P_{H_2 O} )\) of about 200–600 bars. This pressure implies a minimum depth of 0.5–1.6 km for the magma chamber.
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Yang, K. Glass inclusions in quartz phenocrysts of rhyolites, Mt. Jang, Pusan, Korea. Geosci J 1, 50–56 (1997). https://doi.org/10.1007/BF02910450
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DOI: https://doi.org/10.1007/BF02910450