Skip Navigation

This Article
Right arrow Full Text Freely available
Right arrow FREE Full Text (PDF) Freely available
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 Dall'agnol, R.
Right arrow Articles by Pichavant, M.
Right arrow Search for Related Content
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

Journal of Petrology | Volume 40 | Number 11 | Pages 1673-1698 | 1999
© Oxford University Press 1999

An Experimental Study of a Lower Proterozoic A-type Granite from theEastern Amazonian Craton, Brazil

R. Dall'agnol1, B. Scaillet2 and M. Pichavant2

1 Centro De Geociências, Universidade Federal Do Pará CP 1611, 66075–900, BELÉM, PA, BRAZIL
2 Institut Des Sciences De La Terre D'Orléans, Crscm-Cnrs 1A RUE DE LA Férollerie,45071 Orléans CEDEX 2, France

Received July 31, 1998; Revised typescript accepted May 4, 1999


  Abstract

The Jamon granite is representative of the Lower Proterozoic (1.88 Ga) oxidized A-type granites of the eastern part of the Amazonian craton. The dominant facies is a metaluminous to slightly peraluminous hornblende biotite monzogranite with K2O/Na2O between 0.8 and 1.5 and FeOt/(FeOt + MgO) between 0.8 and 0.9. In contrast to many other A-type granites, the Jamon granite is characterized by early hornblende crystallization and the presence of magnetite. Crystallization experiments were performed on glass at 300 MPa between 700 and 900°C for various melt H2O contents and for both oxidizing and reducing fO2 [NNO (nickel-nickel oxide) + 2.5 and NNO - 1.5 on average]. For NNO + 2.5 and under H2O-rich conditions, ilmenite, clinopyroxene, magnetite and hornblende are near-liquidus phases, followed by plagioclase. The orthopyroxene stability field is restricted to high temperatures and H2O contents in the melt <5 wt %. In contrast, for NNO - 1.5, magnetite and titanite are absent and orthopyroxene (never observed in the granite), clinopyroxene and ilmenite are the liquidus phases. Conditions of crystallization of amphibole, magnetite and plagioclase constrain the initial melt H2O content to between 4.5 and 6.5 wt %. Plagioclase cores crystallized from 870 to 720°C. Clinopyroxene, amphibole and biotite Fe/(Fe + Mg) values suggest fO2 around NNO + 0.5 during crystallization of the granite. The demonstration of relatively hydrous conditions and oxidizing fO2 for the Jamon granite stresses the diversity of A-type magmas in terms of H2O contents and redox states. The Jamon granite was most probably generated from oxidized Archaean igneous rocks of mafic-intermediate composition.

KEY WORDS: A-type granite; experiments; Lower Proterozoic; oxygen fugacity; water content

* Corresponding author:email:rodal{at}ufpa.br


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


This article has been cited by other articles:


Home page
 J PetrologyHome page
G. Girard and J. Stix
Magma Recharge and Crystal Mush Rejuvenation Associated with Early Post-collapse Upper Basin Member Rhyolites, Yellowstone Caldera, Wyoming
J. Petrology, November 3, 2009; (2009) egp070v1.
[Abstract] [Full Text] [PDF]


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.