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Plagiogranites and gabbroic rocks from the Mingora ophiolitic mélange, Swat Valley, NW Frontier Province, Pakistan

Published online by Cambridge University Press:  05 July 2018

M. Barbieri ,
A. Caggianelli ,
M. R. Di Florio  and
S. Lorenzoni
M. Barbieri
Affiliation:
Dipartimento di Scienze delia Terra, piazzale A. Moro, I-00185 Roma, Italy
A. Caggianelli
Affiliation:
DiTEc Univ. Basilicata, via N. Sauro 85, I-85100 Potenza, Italy
M. R. Di Florio
Affiliation:
Dipartimento Geomineralogico, via E. Orabona 4, I-70124 Bail, Italy
S. Lorenzoni
Affiliation:
Dipartimento Geomineralogico, via E. Orabona 4, I-70124 Bail, Italy
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Abstract

Major, trace element composition and Sr isotopic data were collected for gabbroic rocks, plagiogranites and albitites in the ophiolite assemblage from Swat Valley (NW Frontier Province, Pakistan). Petrographic study revealed that these rocks were subjected to important structural and mineralogical modifications due to greenschist-epidote-amphibolite facies sub-sea-floor metamorphism and to brecciation. On the other hand, the examination of whole rock chemical composition and of chemical trends showed that these rocks were affected by some chemical modifications, concerning especially Na2O, K2O and Rb. The very low contents of HFS (high field strength) and RE elements found in gabbroic rocks and plagiogranites were considered to be a primary magmatic feature pointing in part to their cumulitic nature and in part to an origin from a refractory parental magma. The Sr isotopic data indicate that gabbroic rocks and plagiogranites were subjected to exchange with sea water. The particular chemical features shared by gabbroic rocks and plagiogranites suggested that fractional crystallization was a possible evolution process. In contrast, albitites are characterized by anomalously high contents in HFSE and LREE and by values of the 87Sr/86Sr ratio very close to sea water. These features suggest a more complex origin with respect to gabbroic rocks and plagiogranites.

Keywords

plagiogranitesgabbroic rocksalbititesophiolitesPakistan
Type
Petrology and Geochemistry
Information
Mineralogical Magazine , Volume 58 , Issue 393 , December 1994 , pp. 553 - 566
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1994

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