甘肃永登碱性熔岩中残留单斜辉石特征

The Characteristics of Residual Clinopyoxene of Alkali-lava in Yongdeng County,Gansu Province

对甘肃永登石灰沟一带分布的变白榴石响岩,辉石白榴岩,暗色粗面岩中的残留单斜辉石的产出条件,光学性质,化学成分进行了研究,确定上述各类岩石中残留的单斜辉石属于含钛普通辉石.化学成分主要是由 CaMgSi_2O_6约为80.00%,CaFeSi_2O_4约为13.96%,NaFeSi_2O_6约为3%,CaTiAl_2O_6约为3%,同时还含有少量的 CaAlSiAlO_6分子及 Mn 等组分.TiO_2的含量在0.65%～1.33%之间,平均为0.95%。因此认为该碱性熔岩应是由碱度较高的碱性玄武岩岩浆演化而来,属岛孤火山作用产物.

This paper studieds the growing conditions,optical properties and chemicalcompositions of residual clinopyoxene in epileucite phonolite,augite leucitite,andmelano-trachyte in alkali-lava distributing around Shihuaigou Channel in Yongdengcounty.It has been determined that the residual clinopyoxene in these rocks belongs totitanaugite.The chemical compositions of residual clinopyoxene are approximately 80.00% CaMgSiO_6,13.96%CaAlSi_2O_6,3.00%,NaTial_2O_6,3.00%NaFeSi_2O_6,and traces ofCaAlSi_2O_6 and MnO;The content of TiO_2 is between 0.65% and 1.33%,its average val-ue is 0.95%.As a trsult,this paper holds that the alkali-lava evolves from the alkali-balaltic magma with higher alkalinity,is the productions of island volcanism.