Age and geochemistry of an 'anorogenic' crustal melt and implications for I-type granite petrogenesis

J. Encarnación, S.B. Mukasa

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30 Scopus citations

Abstract

The Capoas intrusion is a metaluminous, high-K calc-alkaline, I-type biotite granite emplaced within Permian-Jurassic sedimentary rocks of the North Palawan Continental Terrane (NPCT) in the western Philippines. The NPCT is a fragment of the Mesozoic Andean-type margin of southeast China that was separated from the mainland during the late Oligocene-early Miocene opening of the South China Sea. Zircons from the granite have xenocrystic cores, and form a discordant array with a lower intercept age of 15 (+3/-4) Ma. Monazites have concordant 207Pb/235U ages with a mean age of 13.4 (±0.4) Ma. The late middle Miocene age and the location of the pluton in the NPCT uniquely constrain the formation of the Capoas granite in a post-rifting, non-collisional tectonic setting unrelated to any subduction zone. The major and trace element geochemistry of the granite and the presence of apparently Proterozoic xenocrystic zircon indicate that the pluton is composed largely, if not entirely, of older continental crust. The only viable heat source for crustal melting and/or assimilation was widespread basaltic magmatism that occurred in the area following cessation of seafloor spreading in the South China Sea in early Miocene time. The geochemical affinity of the Capoas granite with calc-alkaline magmatic arc and collisional granites is therefore a function of the source rocks that were melted to produce the granite rather than the specific tectonic setting in which the granite was generated. The calc-alkaline source rocks most likely formed in the Mesozoic Andean-type margin of south China and subsequently underwent partial melting in late middle Miocene time in an 'anorogenic' setting. © 1997 Elsevier Science B.V.
Original languageEnglish (US)
Pages (from-to)1-13
Number of pages13
JournalLithos
Volume42
Issue number1-2
StatePublished - 1997

Bibliographical note

Cited By :22

Export Date: 3 November 2016

Keywords

  • Geochemistry
  • Geochronology
  • Granite
  • Igneous petrology
  • Philippines
  • Southeast Asia

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