新疆洪古勒楞蛇绿岩中含长二辉橄榄岩的成因探讨

Origin of PI-Lherzolite in the Hongguleleng Ophiolite, Xinjiang

洪古勒楞蛇绿岩中的含长二辉橄榄岩产于斜辉辉橄岩和堆晶岩之间,并与斜辉辉橄岩顶部的糜稜岩化带平行分布。含长二辉橄榄岩以其具有地幔橄榄岩特有的变晶结构和Ng(100)高温变形组构,以及含斜方辉石等特点而区别于堆晶岩。在矿物成分、化学成分及锶同位素等力面,含长二辉橄榄岩具有介于地幔橄榄岩和堆晶岩之间的某些过渡特征。含长二辉橄榄岩中新生矿物的出现,提供了基性熔体渗入的证据。斜辉辉橄岩顶部的糜稜岩化带可能是岩浆房底部基性熔体下渗的通道。笔者认为,含长二辉橄榄岩为基性熔体渗入到先前已亏损的斜辉辉橄岩中,并与之重新平衡的产物。

The Pl-lherzolite is located between the harzburgite and cumulates in the Hongguleleng ophiolite and parallel to the mylonitized zone at the top of the harzburgite.The Pl-lherzolite differs from the cumulates in having blastic texture and high-temperature deformed fabric of Ng[100] characteristic of the mantle peridotite and yielding orthopyroxene. In respect of mineralogy and petrology as well as strontium isotope, the Pl-lherzolite exhibits some features of transition from the cumulates to the mantle peridotite.The appearance of new-born minerals(clinopyroxene and plagioclase) in the Pl-lherzolite provides an evidence for the penetration of basic melt. The mylonitized zone may be a passage for the basic melt derived from the bottom of the magma chamber, which has penetrated into the harzburgite.From the above, the authors conclude that the Pl-lherzolite is the product of the reequilibrium between the depleted harzburgite and the basic melt.