Abstract:
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.