Skip Navigation



Journal of Petrology Advance Access published online on April 19, 2008
Journal of Petrology, doi:10.1093/petrology/egn018
This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Supplementary Data
Right arrow All Versions of this Article:
49/6/1069    most recent
egn018v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrowRequest Permissions
Google Scholar
Right arrow Articles by Mahoney, J. J.
Right arrow Articles by Randriamanantenasoa, A.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

© The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Geochemistry of the Volcan de l’ Androy Basalt–Rhyolite Complex, Madagascar Cretaceous Igneous Province

J. J. Mahoney1,*, A. D. Saunders2, M. Storey3 and A. Randriamanantenasoa4

1School Of Ocean And Earth Science And Technology, University Of Hawaii, Honolulu, Hi 96822, USA
2Geology Department, University Of Leicester, Leicester Le1 7Rh, Uk
3Department Of Environment, Technology And Social Studies, Roskilde University, Dk-4000, Roskilde, Denmark
4Laboratoire De GéOlogie Appliquée, Université D’ Antananarivo, Antananarivo, Madagascar

Received June 7, 2007; Revised typescript accepted March 13, 2008


  Abstract

The 4000 km2 Androy massif in southeastern Madagascar is a >2000 m thick sequence of interbedded basalt and rhyolite erupted during a widespread Cretaceous episode of predominantly basaltic volcanism. Two geochemically different groups of basalt, tholeiitic group B1 and mildly alkalic B2, are present, as are two different groups of rhyolite, R1 and R2. Both the basalts and rhyolites appear to have issued from relatively nearby feeders, as compositionally equivalent intrusions are exposed in the vicinity. The R2 rhyolites define a whole-rock Rb–Sr isochron of 84·0 ± 2·4 Ma (2{sigma}), the same, within error, as an 40Ar–39Ar sanidine age reported by earlier workers. Plate reconstructions suggest that the area was near the Marion hotspot at this time. Some involvement of hotspot mantle is allowed, but not required, by Nd–Pb–Sr isotope data for the basalts. The two types of basalt may have formed by different amounts of melting of the same mantle source, which remains rather poorly specified, but group B1 was affected much more than B2 by contamination with continental material, probably Archean crust. The R1 rhyolites are petrogenetically related to the B1 basalts, with which they are interbedded. The R2 rhyolites may be derived from melts of frozen high-{varepsilon}Nd B1 basalt coupled with fractionation and assimilation of relatively small amounts of crust. Alternatively, although these rhyolites were erupted significantly later than the B2 basalts, they may have formed through advanced crystal fractionation of B2-type magma and relatively small amounts of crustal assimilation. Separate magmatic plumbing systems appear to have existed more or less contemporaneously in the Androy area.

KEY WORDS: large igneous province; rhyolite; mantle plume; basalt; Madagascar

*Corresponding author. Telephone: 1-808-956-8705. E-mail: jmahoney{at}hawaii.edu


Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?




Disclaimer:
Please note that abstracts for content published before 1996 were created through digital scanning and may therefore not exactly replicate the text of the original print issues. All efforts have been made to ensure accuracy, but the Publisher will not be held responsible for any remaining inaccuracies. If you require any further clarification, please contact our Customer Services Department.