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Combination of quantitative textural analyses and in situ chemical-isotopic techniques in the study of felsic microgranular enclaves: implications to the evolution of magmatic chambers

Grant number: 11/07074-4
Support type:Regular Research Grants
Duration: June 01, 2012 - February 28, 2015
Field of knowledge:Physical Sciences and Mathematics - Geosciences - Geology
Principal researcher:Adriana Alves
Grantee:Adriana Alves
Home Institution: Instituto de Geociências (IGC). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Recent studies in granite petrogenesis are strongly influenced by the finding that mafic microgranular enclaves (mme) witness frequent and volumetrically significant contribution of mantle-derived magmas to the origin and evolution of granitic melts, be it as a heat source or as a source compositional diversity. On the other hand, the origin of felsic microgranular enclaves (fme) is still a matter of debate; current hypotheses consider them as fragments of chilled margins, products of protracted hybridization between invading basic magmas and resident granite mushes, or as products of interaction between fairly similar melts. Felsic microgranular enclaves are widespread in many granite plutons from SE Brazil, in many cases surpassing mme in size and volume. Two groups of occurrences will be studied in more detail in order to investgate the different scenarios: with and without clear connections with mafic magmas. In the Mauá, Mogi das Cruzes and Itapeti plutons - mainly composed by (muscovite)-biotite monzogranite - only fme occur, and the participation of more mafic melts is not evident from field structures or from whole rock and mineral chemical/isotope data. Our preferred model relates the fme to self-mixing events, suggesting mingling/mixing between highly viscous and chemically similar felsic endmembers. However no satisfactory model regarding the bearing of enclave formation on the evolutionary processes of magmatic chambers was proposed.In the rapakivi Salto Pluton, fme are large (dm to meter-sized) and widespread, except in a central body of porphyry granite. Scattered cm-sized mme of variable composition, some clearly brought as inclusions in the fme, are thought to represent different stages of hybridization, as indicated by disequilibrium features observed in the host syenogranites surrounding mme (rapakivi texture; mafic-rimmed quartz). However, there is no clear evidence that significant volumes of mafic magmas reached the granitic chamber, as the mme are much less frequent and occur in smaller size compared to fme.The different occurrences of fme highlight the various mechanisms of self-mixing in granitic magma chambers, involving replenishment by less evolved granitic magma or invasion of basic magmas provoking reheating of a granitic mush with remobilization of less dense, but hotter, interstitial melt. In this scenario, this project was designed to evaluate the potential of the combined use of quantitative textural studies and in situ chemical and isotopic analyses for the determination of the role played by different magma batches on enclave formation and the consequences of such process on the evolution of magmatic chambers. (AU)

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Scientific publications (4)
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
ALVES, ADRIANA; JANASI, VALDECIR DE ASSIS; PEREIRA, GIOVANNA DE SOUZA; PRADO, FERNANDO ARAUJO; MUNOZ, PATRICIO R. M.. Unravelling the hidden evidences of magma mixing processes via combination of in situ Sr isotopes and trace elements analyses on plagioclase crystals. LITHOS, v. 404-405, . (11/07074-4, 07/08683-9, 19/17550-0)
ALVES, ADRIANA; JANASI, VALDECIR DE ASSIS. Tracking the oxygen fugacity of enclave-forming granitic melts through plagioclase trace element signatures. CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, v. 175, n. 7, . (11/07074-4)
ALVES, ADRIANA; PEREIRA, GIOVANNA DE SOUZA; JANASI, VALDECIR DE ASSIS; HIGGINS, MICHAEL; POLO, LIZA ANGELICA; JURIAANS, ORLANDO STANLEY; RIBEIRO, BRUNO VIEIRA. The origin of felsic microgranitoid enclaves: Insights from plagioclase crystal size distributions and thermodynamic models. LITHOS, v. 239, p. 33-44, . (07/08683-9, 11/07074-4)
PATRICIO MONTECINOS MUNOZ; ADRIANA ALVES; ROGÉRIO GUITARRARI AZZONE; PABLO CORDENONS; SANDRA MORANO; WALTER SPROESSER; SOLANGE DE SOUZA. Microanálises isotópicas de Sr de plagioclásio e apatita magmáticos via LA-MC-ICP-MS no CPGeo-USP. BRAZILIAN JOURNAL OF GEOLOGY, v. 46, p. 227-243, . (10/20425-8, 10/20380-4, 11/07074-4)

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