Geochemistry and Petrography of Alkaline rocks from Monte Santo Alkaline Intrusive Suite, Westhern Araguaia Belt, Tocantins State, Brazil

The 6th ENGII Conference(Workshop6 2014)——The Monte Santo Alkaline Intrusive Suite (MSAIS) is an association syenite foid, nepheline syenite and syenite. The MSAIS rocks are intruded in metapelites of the Rio do Coco meta-volcanic-sedimentary Sequence and are abundant pegmathoid veins cutting all of them. The mineral paragenesis is represented by aegirina, arfvedsonite, albite and nepheline, crystallized during the initial phase of crystallization. A late magmatic phase show nepheline, perthite, calcite and biotite, and a hydrothermal phase allowed for the formation of cancrinite, sodalite, analcime and natrolita associated with altered nepheline. The geochemical analyses showed metaluminous and medium to high potassium characteristics, being classified as miaskitic rocks, according to agpaicity and the Na+K>1/6Si indexes. However, the mineralogical assemblage suggest a low to medium agpaitic composition, which can be related to a transition from miaskitic to agpaitic crystallization regime. The rare earth elements showed depletion in heavy rare earth and a strong negative Eu anomaly and enrichments in the some lithophile elements, suggesting a differentiated pattern later, which can be associated to metasomatic alterations.

关键词： 碱性侵入岩 地球化学 岩石学 矿物学 稀土元素 The 6th ENGII Conference(Workshop6 2014)

主讲人：A.P. Rubia Ribeiro Viana 机构：Federal University of Mato Grosso

时长：0:13:52 年代：2014年