The Ilha Anchieta Quartz Monzonite: the southernmost expression of ca. 500 Ma post-collisional magmatism in the Ribeira Belt

Autor(es)

Azevedo Sobrinho, Jose M. ^[1] ; Janasi, Valdecir A. ^[2] ; Simonetti, Antonio ^[3] ; Heaman, Larry M. ^[3] ; Santoro, Jair ^[1] ; Diniz, Helio N. ^[1]

Afiliação do(s) autor(es)

^[1] Secretaria Meio Ambiente Estado Sao Paulo, Inst Geol, BR-04301903 Sao Paulo - Brazil

^[2] Univ Sao Paulo USP, Inst Geociencias, Dept Mineral & Geotecton, BR-05508080 Sao Paulo - Brazil

^[3] Univ Alberta, Dept Earth & Atmospher Sci, Edmonton, AB T6G 2E3 - Canada

• Tipo de documento: Artigo Científico
• Fonte: Anais da Academia Brasileira de Ciências; v. 83, n. 3, p. 891-906, SEP 2011.
• Citações Web of Science: 8

Resumo

The Ilha Anchieta Quartz Monzonite (IAQM) occupies most of the homonymous island in the coast of the state of São Paulo, and is intrusive into foliated rocks of the ~565 Ma Ubatuba Charnockite. The main petrographic variety is a porphyritic biotite-hornblende quartz monzonite with 2-4 cm tabular microcline megacrysts set in a medium-grained groundmass and magmatic foliation. Outcrop-scale structures indicate cumulative processes (modal and grain-size magmatic banding) and interaction with basic magmas (mafic microgranular enclaves). Lithogeochemical data indicates that the main variety is intermediate to acid (S1O2 = 63-67%), alkali-calcic, metaluminous and magnesian (mg# ~30), showing moderate Sr (300-400 ppm) and Ba (~1500 ppm) contents and relatively high HFSE (Nb = 40 ppm; Zr = 550-700 ppm). The older charnockites are more silicic (S1O2 = 71-78%), ferroan(mg# = 12-16), and have very low Sr (13-80 ppm) contents, resulting in Ba/Sr ratios remarkably higher than the IAQM (10 versus 4). LA-MC-ICPMS U-Pb zircon dating of the IAQM yielded 499.7 ± 5.9 Ma. This is the youngest magmatic age identified so far in the crystalline basement of the state of São Paulo, and indicates that the pluton is the southernmost expression of the post-collisional "G5" magmatism in the Ribeira Belt. (AU)

• 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