马里亚纳海槽火山岩中斜长石熔体包裹体的均一温度及其对岩浆演化的指示意义

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

    • 摘要: 马里亚纳海槽南部安山岩(H5-T3-2)中斜长石结晶温度主要集中在1 050~1 150 ℃,未受到后期岩浆演化的影响。马里亚纳海槽中部玄武质安山岩(H5-T1-3)中斜长石结晶温度主要集中在900~1 050 ℃;英安岩(H5-T1-1)中斜长石结晶温度主要集中在1 050~1 150 ℃。马里亚纳海槽18°N附近玄武岩(H5-T2-2、H5-T2-3)斜长石中熔体包裹体的均一温度主要集中在1 050~1 150 ℃,并呈连续降温趋势,只有少部分在1 000~1 050 ℃的较低温度结晶,边缘部An值骤降则反映岩浆喷出快速冷却的过程;玄武质安山岩(H5-T2-1)斜长石中熔体包裹体的均一温度具有“双峰”式特征,主要分布在850~950 ℃和1 050~1 150 ℃ 2个温度范围。结合斜长石的环带特征及其An值变化特征,分析结果表明,该斜长石有2个明显不同的结晶阶段,发生了岩浆混合作用,且在马里亚纳海槽浅部可能存在温度约为850~950 ℃的岩浆房,岩浆到达浅部岩浆房后发生岩浆混合,最终喷出洋底。马里亚纳海槽18°N附近的岩浆演化过程较为复杂,发生了不同周期的岩浆演化过程。

       

      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.

       

    /

    返回文章
    返回