云南香格里拉县洛吉蛇绿混杂岩中单斜辉石的矿物学特征
Compositional characteristics of clinopyroxenes from the Luoji ophiolitic mélange in Shangri-La County, Yunnan Province
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摘要: 提要：洛吉蛇绿混杂岩分布于云南香格里拉县，由镁铁质—超镁铁质堆晶岩块、辉长-辉绿岩墙群、玄武岩及条带状硅质岩等以构造混杂方式产出。岩相学研究发现其中堆晶岩块与玄武岩中单斜辉石具有相似性，矿物化学成分研究表明洛吉蛇绿混杂岩单斜辉石种属为富镁贫铁和高钙的普通辉石，其母岩浆属亚碱性系列的拉斑玄武岩浆，辉石晶体中阳离子取代特征显示其形成于高温低压的条件，辉石形成温度为986~1118 ℃，压力为0.18~0.22 GPa，结合矿物成分和演化特征，认为该套混杂岩为甘孜—理塘蛇绿岩带残余产物。Abstract: Abstract: In Shangri-La County of Yunnan Province, the authors documented an ophiolitic mélange which is composed of mafic-ultramafic cumulate rocks, diabase-gabbro dykes, basalts and banded cherts. On the basis of petrological observations and mineral compositions of clinopyroxenes from the mafic-ultramafic cumulate rocks and basalts, the clinopyrixenes were divided into two groups, one group is rich in magnesium and depleted in iron while the other group is rich in calc. Both of the two groups of clinopyroxenes belong to augites, whose parental magma was sub-alkaline tholeitic basalt. Cation substitution features indicate that the augites were formed under the condition of high temperature and low pressure. T-P calculations show that the augites were formed at 986 to 1118 °C and 0.18 GP to 0.22 GP. It is suggested that the Luoji mélange is probably a part of the Garzê-Litang ophiolite.
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