FURTHER SIGNS OF AN ENRICHED MANTLE SOURCE UNDER THE NEOPROTEROZOIC ARAÇUAÍ-RIBEIRA MOBILE BELT
作者： Isabel Pereira Ludka , Cristina Maria Wiedemann-Leonardos
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摘要: Isolated small bodies of Neoproterozoic coronitic gabbros crop out in the states Espirito Santo (Jacutinga and Itaoca) Rio de Janeiro (Amparo), central portion Aracuai-Ribeira Mobile Belt. The rocks from Jacutinga Itaoca are mainly gabbronorites show a wide range modal/textural varieties recording crystal-setting processes normally found layered intrusions. Amparo intrusion is formed by rock, also present as layers Itaoca. primary mineral assemblage consists olivine, opx, cpx, plagioclase, ilmenite, Ti-magnetite sulphides. Coronitic overgrowths related to olivine-plagioclase reaction form concentric rims amphibole simplectitic amphibole-spinel around olivine cores. They all very similar shape composition pointing towards physical-chemical crystallization conditions. Different gepthermometric measurements yielded temperatures 800°C, which close those calculated for opx-cpx pairs (800/940°C). absence regional deformational metamorphic paragenesis compatible with their into middle/ lower crust during late collisional phase. A long lasting cooling environment at magmatic stage induced sub-solidus reactions. Low K sub-alkaline signatures clear enrichment some incompatible elements such Ba, Sr LREE associated high 87 Sr/ 86 initial ratios (around 0.706-0.708) anomalous-chemical characteristics these gabbros. Enriched mantle types (EM1, EM2 HIMU) Sr-initial frequently Southern Hemisphere. chemical anomalies obtained this study could be largescale phenomena, Dupal anomaly.
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