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Comparison of rhyolites from continental rift, continental arc and oceanic island arc: Implication for the mechanism of silicic magma generation
Author(s) -
Ayalew Dereje,
Ishiwatari Akira
Publication year - 2011
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/j.1440-1738.2010.00746.x
Subject(s) - geology , rift , continental crust , continental arc , continental margin , silicic , island arc , geochemistry , partial melting , oceanic crust , continental shelf , subduction , crust , tectonics , earth science , paleontology , basalt , oceanography
We discuss the chemical compositions of rhyolites from three distinct tectonic settings: (i) the continental rift from Ethiopia (both Oligocene–Miocene and Quaternary rhyolites); (ii) the early Miocene continental arc of Japan (the Mt Wasso rhyolites related to the rifting of the Japan Sea); and (iii) the oceanic Izu–Bonin Island Arc. The comparison reveals that the oceanic island arc rhyolites have high contents of CaO, Al 2 O 3 , and Sr, and extremely low abundance of trace elements including K 2 O. In contrast, the Ethiopian continental rift rhyolites are characterized by low contents of CaO, Al 2 O 3 , and Sr, and high contents of K 2 O, and are enriched in the whole range of trace elements. The continental arc Mt Wasso rhyolites are apparently low in Nb content, although they display similar chemical trends to those of the Ethiopian rhyolites. This obvious difference in the chemical signatures of the rhyolites from the three tectonic settings is the consequence of their derivation from different sources. The implication of this result is that fractional crystallization processes were dominant in the rift‐related rhyolites both from continental rift and continental arc regardless of the prevailing tectonic setting and the nature of the crust (age, thickness, composition), whereas the oceanic island arc rhyolites may form through partial melting of young, mafic crust.