新疆北山地区漩涡岭镁铁质-超镁铁质层状岩体岩石学与矿物学研究

Petrography and Mineralogy of the Xuanwoling Mafic-Ultramafic Layered Intrusion in the Beishan Region, Xinjiang

位于新疆北山地区的漩涡岭岩体是一堆晶层理发育的镁铁质—超镁铁质层状岩体。岩石类型主要有纯橄岩、橄长岩、橄榄辉长岩和辉长岩等。主要的造岩矿物有橄榄石、辉石、斜长石、铬尖晶石,岩相学特征表明岩浆在演化过程中经历了橄榄石、尖晶石、斜长石、斜方辉石和单斜辉石的分离结晶,结晶次序依次为橄榄石+尖晶石→斜长石→辉石,表明结晶时压力较低。漩涡岭岩体的纯橄岩中橄榄石的Fo高达90.1%,这不同于新疆北部黄山岩带、喀拉通克岩体群以及甘肃金川岩体的橄榄石Fo组成,利用橄榄石最高Fo值估算得到漩涡岭岩体的母岩浆的Mg#为0.73～0.75,岩浆的液相线温度高达1330～1350℃,其岩浆为高温高Mg的苦橄质岩浆,这为塔里木东北部二叠纪地幔柱活动提供了新的证据。

The Xuanwoling intrusion, located in the Beishan region in the northeastern Tarim Block, NW China, is one of the mafic-ultramafic intrusions with cumulate texture and rhythmic layering.The rocks in this area contain dunite, troctolite, olivine gabbros and gabbros. Major minerals are olivine,pyroxene, plagioclase, and picotite. Petrographical characters indicate that the Xuanwoling intrusion had undergone fractional crystallization, with crystallization sequence of olivine+spinel, plagioclase and pyroxene, indicating the crystallization pressure was lower than 0.5~0.8GPa.Olivines from this intrusion have high Fo values (up to 90.1%),and this differs from that of ith Kalatongke,Huangshan and Jinchuan intrusions. The Fo molecular of olivine was used to estimates the Mg# values of prarental magma of Xuanwoling intrusion. Th result shows Mg# of the parental magma is 0.73~0.75,and the crystallization temperature of the Xuanwoling intrusion is 1330~1350℃ higher than basalt liquidus temperature about 130℃.Therefore, the magma is picritic magma with high temperature and high MgO, providing new evidence for Permian mantle plume activity in northeastern Tarim.