Journal of Petrology Advance Access originally published online on August 27, 2004
Journal of Petrology 2004 45(11):2287-2302; doi:10.1093/petrology/egh056
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Journal of Petrology 45(11) © Oxford University Press 2004; all rights reserved
Crustal Growth by Magmatic Accretion Constrained by Metamorphic P–T Paths and Thermal Models of the Kohistan Arc, NW Himalayas
1 INSTITUTE FOR STUDY OF THE EARTH'S INTERIOR, OKAYAMA UNIVERSITY, YAMADA 827, MISASA, TOTTORI 682-0193, JAPAN
2 DEPARTMENT OF GEOSCIENCES, GRADUATE SCHOOL OF SCIENCE, OSAKA CITY UNIVERSITY, 3-3-138 SUGIMOTO, OSAKA 558-8585, JAPAN
Magmatic accretion is potentially an important mechanism in the growth of the continental crust and the formation of granulites. In this study, the thermal evolution of a magmatic arc in response to magmatic accretion is modeled using numerical solutions of the one-dimensional heat conduction equation. The initial and boundary conditions used in the model are constrained by geological observations made in the Kohistan area, NW Himalayas. Taking consideration of the preferred intrusion locations for basaltic magmas, we consider two plausible modes of magmatic accretion: the first involves the repeated intrusion of basalt at mid-crustal depths (‘intraplate model’), and the second evaluates the simultaneous intrusion of basalt and picrite at mid-crustal depths and the base of the crust respectively (‘double-plate model’). The results of the double-plate model account for both the inferred metamorphic P–T paths of the Kohistan mafic granulites and the continental geotherm determined from peak P–T conditions observed for granulite terranes. The double-plate model may be applicable as a key growth process for the production of thick mafic lower crust in magmatic arcs.
KEY WORDS: thermal model; magmatic underplating; P–T path; granulite; lower crust
* Corresponding author. Present address: Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180, USA. Telephone: +1-518-276-8827. Fax: +1-518-276-2012. E-mail: yoshta{at}rpi.edu
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