Geologia e petrologia das rochas riolíticas do Cerro Ana Dias, região de Quitéria, sudeste do RS.

Content Provider	Semantic Scholar
Author	Oliveira, Diego Skieresz De
Copyright Year	2012
Abstract	Ana Dias Rhyolite is situated in the region of Quitéria, located nearly 25 miles South of Butiá, Rio Grande do Sul, Brazil. It is inserted in the context of Pelotas batholite, defined as a petrotectonic association characterized by granite suits with subordinate occurrence of mafic rocks and xenoliths of metamorphic rocks, generated since the ending of Neoproterozoic until the beginning of Paleozoic. Granite suites are affected by zones of NE-SW ductile shear direction, representing the main conducts for the ascension of batholite’s magmatism. The acid magmatism responsible for Ana Dias Rhyolite’s generation is commonly related to the most differentiated phases of Dom Feliciano suite (550-570 Ma), entailed to the final stages of Pelotas batholite, East of Sul-Rio-Grandense Shield. Ana Dias Rhyolite is characterized as an intrusive body, lengthened on NE direction, dimensions 11 x 3 miles, intrusive on gneisses of Arroio dos Ratos Complex, Quitéria granite, Passo da Divisa granitites, and Serra do Erval granite. Rhyolites also occur in the form of metric dykes as late manifestations, intruding the main body and the fitting rocks on NE-SW direction. Generally, rhyolite rocks present porphyritic to serialized texture and gradational variation to fineequigranular rocks. The phenocrysts are suberic to euhedral of faceted quartz, K-feldspar and subordinately plagioclase and/or hornblend and constitute about 20% to 40% of the volume of the rock. Its matrix is aphanite to very fine-equigranular, with quartz-feldspar composition, along with subordinate presence of biotite. The rhyolites that occur as dykes invariably present a porphyritic texture, with euhedral phenocrysts (40-50%) of Kfeldspar (1-1,5cm) and quartz (0,3cm), wrapped by a microcrystalline, feldspar-quartz matrix. On TAS diagram, the studied rocks occupy the rhyolite field, next to the limit between alkaline and subalkaline series. They present a metaluminous to peraluminous character and elevated content of SiO2, alkali, FeOt/FeOt+MgO and agpaitic index and low contents of Al2O3, CaO, and MgO. The values of Zr, Rb, Y, Nb, and Ga are moderate in comparison to the relatively low contents of Ba and Sr. These geochemistry characteristics of larger elements and traces are common in acid magmas of alkaline affinity. The behavior of some trace elements and REE, when normalized according ORG values, shows an enrichment in more incompatible elements, which along the negative anomaly in Ba, the slight enrichment in Ce related to adjacent elements, and the enrichment of K2O and Rb related to Nb, are characteristics of magmas derivate of mantelic sources, enriched in incompatible elements with some degree of crustal participation. The REE pattern shows a moderate enrichment of light REE and a strong anomaly in Eu. On decriminalizing diagrams of tectonic environments, the samples occupy the granite field type A and post-collision environment. The litochemical data obtained preliminarily indicate a genetic entailment with the most different granite rocks of Dom Feliciano suite of Pelotas batholite, associated to neoproterozoic post-collision magmatism of Sul-Rio-Grandense Shield.
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Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article