Comparison of rhyolites from continental rift, continental arc and oceanic island arc: Implication for the mechanism of silicic magma generation
Article first published online: 2 DEC 2010
© 2010 Blackwell Publishing Asia Pty Ltd
Volume 20, Issue 1, pages 78–93, March 2011
How to Cite
Ayalew, D. and Ishiwatari, A. (2011), Comparison of rhyolites from continental rift, continental arc and oceanic island arc: Implication for the mechanism of silicic magma generation. Island Arc, 20: 78–93. doi: 10.1111/j.1440-1738.2010.00746.x
- Issue published online: 24 FEB 2011
- Article first published online: 2 DEC 2010
- Received 09 March 2010; accepted for publication 09 September 2010.
- continental arc;
- continental rift;
- fractionation of mantle-derived magma;
- oceanic island arc;
- partial melting of mafic crust;
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, Al2O3, and Sr, and extremely low abundance of trace elements including K2O. In contrast, the Ethiopian continental rift rhyolites are characterized by low contents of CaO, Al2O3, and Sr, and high contents of K2O, 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.