摘要
对浮岩中斜长石斑晶中的包裹体及玻璃基质中的包裹体首先进行双面光薄片的镜下观察，然后进行了系统的均化法与爆裂法测温试验。观察与试验结果表明：(1)斜长石中的包裹体均为玻璃质+气泡的两相包裹体，未发现气—液包裹体。固化包裹体为玻璃质，非晶质的固化包裹体外即是大量的气泡，特别是基质当中气泡更为发育，说明熔浆中含有丰富的挥发性组分，同时也说明包裹体形成于较浅的地质条件下。(2)长石中包裹体的均化温度不受包裹体特征不同的影响，均化温度分布范围从910—1250℃，峰值明显，计算的均化温度为Tz=(1081.4±177.9)℃，但还存在有高于1250℃的均化温度峰。包裹体均化法测试结果说明浮岩中斜长石的形成过程至少有两个阶段：第一阶段的岩浆温度在1200—1300℃左右，在此温度下形成的是An值较高的基性斜长石，同时结晶的还有辉石等矿物，斜长石结晶第二个阶段时的熔浆温度在1100℃以下，这一阶段持续的时间长，跨越的温度范围大，应是岩浆在近地表和岩浆喷出过程中的岩浆快速冷却期，同时伴随有矿物大规模晶出。(3)包裹体中的气相部分均聚合成圆形或近圆形，说明温度下降速度较快。斑晶斜长石中部分包裹体与基质玻璃中包裹体的形成温度是连续变化的。
A lot of researches involving both mineralogy and geochem istry have been carried out on rhydacitic pumice which are most widely distribut ed in the Okinawa Trough. But, no research of inclusions in phenocrysts has been reported up to now. In this experiment, inclusions in plagioclase and glassy ma trix are first examined with polished thin sections under microscope, and then t ested for the measurements of homogenization temperature and decrepitation metho d temperature. The test results and conclusions are as follows. (1) There are only solid phase and gas inclusions in the plagioclase phenocryst s, no liquid inclusion and the matrix is especially rich in gas inclusions, sugg esting that the magmatic melt contained a large amount of volatile components. (2) Inclusions with different characters have similar homogenization temperature of (1081.4±177.9)℃. The temperature measuring test yielded two peak t emperatures of about 1081 and over 1250℃ implying two crystallization stage of plagioclase phenocrysts. (3) There is continuous temperature change from inclusions in the plagioclase to those in the matrix. This approved a rapid cooling course of magmatic melt whic h met seawater before erupting.
出处
《海洋与湖沼》
CAS
CSCD
北大核心
2001年第1期67-73,共7页
Oceanologia Et Limnologia Sinica
基金
国家自然科学基金重点资助项目!49625609
49421007号。
