云南香格里拉洛吉乡基性-超基性岩中单斜辉石矿物成分特征及其地质意义

云南香格里拉洛吉乡出露一套基性-超基性岩块,前人对其属性的认识有分歧.岩相学研究发现该岩块具有正堆积结晶和补堆积结晶的特点,岩石化学特征具有贫碱、高钙和低氧逸度的特征,其母岩浆为亚碱性系列,并且显示出堆晶层状岩系演化特征.对其中的单斜辉石进行了矿物成分及化学成分研究,结果表明辉石种属为透辉石,晶体中类质同像替代现象普遍,阳离子取代特征显示出形成于高温低压的条件.温压计算结果表明透辉石形成平均温度为1 084℃,平均压力为0.15 GPa,结合岩石的成分和演化特征,认为该岩石形成于洋中脊,属洋壳组成的基性-超基性堆晶岩系,为甘孜-理塘延伸带的残余产物.

Mineralogical composition characteristics and geological significance of the clinopyroxene from ultrabasic-basic rocks at Luoji Village, Shangri-La County, Yunnan Province

There exists a suite of ultrabasic-basic rock blocks in Luoji Village of Shangri-La County,whose nature is in debate.Petrologic studies show that this suite of rock blocks can be divided into two categories,one is of orthocumulate texture,and the other is of adcumulate texture.Petrologic geochemistry suggests that the rock blocks are low in alkali and oxygen fugacity,but high in calcium content.The original magma is proved to be of the sub-alkaline series with layer cumulate rock characteristics.Mineral composition and chemical composition of the clinopyroxene from ultrabasic-basic rocks suggest that the clinopyroxene is diopside and cation isomorphism is common.Temperature-pressure calculation implies that crystallization occurred under the condition of high temperature(1 084℃) and low pressure(0.15 GPa).The ultrabasic-basic rock blocks in the study area are products of mid-ocean ridge with the composition of oceanic curst,probably being the relics of Garze-Litang suture belt.