The Monte Santo Alkaline Intrusive Suite (MSAIS) is an association syenite foid, nepheline syenite and syenite, which are intruded in metapelites of the Rio do Coco meta-volcanic-sedimentary Sequence, presenting abund...The Monte Santo Alkaline Intrusive Suite (MSAIS) is an association syenite foid, nepheline syenite and syenite, which are intruded in metapelites of the Rio do Coco meta-volcanic-sedimentary Sequence, presenting abundant pegmathoid veins cutting all of them. The ages obtained by Shrimp (1051 ± 22 Ma, 1048 ± 11 Ma) are very close those younger age obtained by U-Pb laser ablation (1056 ± 21), beeing interpreted as crystallization age. These dating reveal also that MSAIS rocks were affected by common succession of younger events below 550 Ma ago, responsible by the later rocky bodies of varying composition occurring in the region, including the alkaline pegmatites hosted in the nepheline syenite of the MSAIS.展开更多
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-sedi- mentary Sequence and a...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-sedi- mentary 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 suggests 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.展开更多
文摘The Monte Santo Alkaline Intrusive Suite (MSAIS) is an association syenite foid, nepheline syenite and syenite, which are intruded in metapelites of the Rio do Coco meta-volcanic-sedimentary Sequence, presenting abundant pegmathoid veins cutting all of them. The ages obtained by Shrimp (1051 ± 22 Ma, 1048 ± 11 Ma) are very close those younger age obtained by U-Pb laser ablation (1056 ± 21), beeing interpreted as crystallization age. These dating reveal also that MSAIS rocks were affected by common succession of younger events below 550 Ma ago, responsible by the later rocky bodies of varying composition occurring in the region, including the alkaline pegmatites hosted in the nepheline syenite of the MSAIS.
文摘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-sedi- mentary 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 suggests 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.
