Microgranitic Enclaves as Products of Self-mixing Events: a Study of Open-system Processes in the Maua Granite, Sao Paulo, Brazil, Based on in situ Isotopic and Trace Elements in Plagioclase

Autor(es)

Alves, Adriana ^[1] ; Janasi, Valdecir de Assis ^[1] ; Simonetti, Antonio ^[2] ; Heaman, Larry ^[2]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Geociencias, BR-05508080 Sao Paulo - Brazil

^[2] Univ Alberta, Dept Earth & Atmospher Sci, Edmonton, AB T6G 2E3 - Canada

• Tipo de documento: Artigo Científico
• Fonte: JOURNAL OF PETROLOGY; v. 50, n. 12, p. 2221-2247, DEC 2009.
• Citações Web of Science: 15

Resumo

Felsic microgranular enclaves with structures indicating that they interacted in a plastic state with their chemically similar host granite are abundant in the Maua Pluton, SE Brazil. Larger plagioclase xenocrysts are in textural disequilibrium with the enclave groundmass and show complex zoning patterns with partially resorbed An-rich cores (locally with patchy textures) surrounded by more sodic rims. In situ laser ablation-(multi-collector) inductively coupled plasma mass spectrometry trace element and Sr isotopic analyses performed on the plagioclase xenocrysts indicate open-system crystallization; however, no evidence of derivation from more primitive basic melts is observed. The An-rich cores have more radiogenic initial Sr isotopic ratios that decrease towards the outermost part of the rims, which are in isotopic equilibrium with the matrix plagioclase. These profiles may have been produced by either (1) diffusional re-equilibration after rim crystallization from the enclave-forming magma, as indicated by relatively short calculated residence times, or (2) episodic contamination with a decrease of the contaminant ratio proportional to the extent to which the country rocks were isolated by the crystallization front. Profiles of trace elements with high diffusion coefficients would require unrealistically long residence times, and can be modeled in terms of fractional crystallization. A combination of trace element and Sr isotope data suggests that the felsic microgranular enclaves from the Maua Pluton are the products of interaction between end-member magmas that had similar compositions, thus recording `self-mixing' events. (AU)

• Processo FAPESP: 04/09942-0 - Petrogênese de plútons graníticos da região de Mogi das Cruzes, SP: interação de magmas e gênese de enclaves micrograníticos
• Beneficiário: Adriana Alves
• Modalidade de apoio: Bolsas no Brasil - Doutorado Direto
• Processo FAPESP: 07/00635-5 - Contribuições do manto e diferentes reservatórios crustais no magmatismo granítico neoproterozóico no Sudeste brasileiro
• Beneficiário: Valdecir de Assis Janasi
• Modalidade de apoio: Auxílio à Pesquisa - Regular