苏鲁造山带东部荣成榴辉岩中蓝晶石及绿辉石的分解——一种可能的新成因解释

在麻粒岩相条件下，荣成含蓝晶石榴辉岩发生退变质，其中的绿辉石退变质成透辉石＋中长石组成的后成合晶，蓝晶石大部分被冠状体取代，基于详细探针分析结果的成分迁移估算显示，冠状体的形成需要从绿辉石的分解中获取CaO,MgO,FeO，绿辉石的分解包含两个反应：一个为绿辉石中的硬玉分子与石英结合形成钠长石；另一个发生在绿辉石内部各端员组分之间，后者不但形成后成合晶，而且为蓝晶石周围冠状体的形成提供CaO,MgO,FeO，蓝晶石的分解未能给后成合晶的形成提供SiO2，绿辉石与蓝晶石在分解时并冰形成一个封闭体系，它们均从周围环境中获取SiO2。

Decomposition of Kyaniteand Omphacite in the Rongcheng Kyanite Eclogite, Eastern Sulu UHPM Terrane

Decomposition of kyanite and omphacite occurred during thedecompression of kyanite_bearing eclogite at Rongcheng County, forming coronas around kyanite and symplectite after omphacite. The coronas are composed of intergrowth of anorthite and radial vermicular Fe_Mg spinel in the inner part (inner corona) and anorthite along the rim (outer corona). The symplectite is made up of intergrowth of myrmekitic diopside and plagioclase (An30). Textural criteria suggest that the corona and the symplectite are coupled. The quantification of material transfer indicates that the formation of the corona gained Ca, Mg and Fe from the breakdown of the omphacite but provided no silica for the symplectization of the omphacite. The formation of the corona included two reactions, which took place simultaneously at different sites: reaction 1: 1Kyanite + 0.096Mg + 0.128Fe + 0.275Ca= 0.275An + 0.224Sp + 0.395Si + 0.979Al + 1.778O; reaction 2: 0.451Si + 0.434Al + 0.212Ca + 0.013Na + 1.778O = 0.225An. The silica, Al and O in reaction 2 were part of the products of the reaction 1. Two reactions between end_members of the omphacite are assumed, which provided Ca, Fe and Mg for the coronazition of the kyanite, and produced symplectite after omphacite:These two coupled_decomposed minerals do not constitute a closed system. The decomposition of both omphacite and kyanite obtained silica from their surroundings.