Homogeneous temperature of plagioclase melt inclusions in volcanic rocks from the Mariana Trough and its implication to magma evolution

The crystallization temperatures of plagioclase melt inclusions in volcanic rocks from the Mariana Trough was studied. Results show that those in andesite (H5-T3-2) from the southern Mariana Trough are mainly in 1 050~1 150 ℃ and did not affected by later magmatic evolution; those in basaltic andesite (H5-T1-3) from the central Mariana Trough are mainly 900~1 050 ℃; and those in dacite (H5-T1-1) are mainly 1 050~1 150 ℃. The homogenization temperatures of melt inclusions in basalt (H5-T2-2, H5-T2-3) plagioclase near 18°N in the Mariana Trough are mainly 1 050~1 150 ℃, showing a continuous cooling trend, and only a small part crystallizes at a lower temperature of 1 000~1 050 ℃, and the sudden drop in the An value at the edge of plagioclase phenocryst reflects a rapid cooling of the magma ejection. In addition, the homogenization temperature of the melt inclusions in basalt andesite (H5-T2-1) plagioclase showed the characteristics of "bimodal" pattern of 850~950 ℃ and 1 050~1 150 ℃. The banding characteristics and the An value variation of plagioclase indicate that the plagioclase experienced two distinct crystallization stages and magma mixing, and there might be a magma chamber in the shallow part of the Mariana Trough, where the magma chamber temperature is about 850~950 ℃. The magmatic evolution process near 18°N in the Mariana Trough is complex, and different periods of magmatic evolution may occur.