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Monzonite suites: the innermost Cordilleran plutonism of Patagonia

Rapela, C. W.; Pankhurst, R. J.. 1996 Monzonite suites: the innermost Cordilleran plutonism of Patagonia. Transactions of the Royal Society of Edinburgh: Earth Sciences, 87 (1-2). 193-203. 10.1017/S026359330000660X

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Abstract/Summary

In Patagonia a Triassic-Early Jurassic Cordilleran interior magmatic belt preceded the widespread eruption of Middle Jurassic syn-extensional rhyolites. Two plutons (La Calandria and La Leona) represent the easternmost plutonic rocks of this belt, > 750 km east of the present oceanic trench. They define a high-K calc-alkaline monzonite series in contrast with the main Andinotype arc magmatism of the Pacific margin: they are enriched in large ion lithophile elements (K, Rb, Ba, Sr and Th), LREE and P2O5 and depleted in HREE and Y, with low FeO*/MgO ratio. The range of observed compositions (56-76% SiO2) resulted from high-level fractionation of plagioclase, hornbleńde, biotite, K-feldspar and accessories (sphene, apatite and zircon). Initial 87Sr/86Sr ratios, average εNdt and mean depleted-mantle Nd model ages of the two plutons are 0·70487, -0·5 and 1050 Ma for La Calandria and 0·70509, -1·4 and 1125 Ma for La Leona, respectively. They are thus isotopically more primitive than the Middle Jurassic rhyolites, previously attributed to partial melting of Mesoproterozoic mafic lower crust. The preferred model for the origin of the monzonites is remelting of an amphibole- + garnet-bearing, plagioclase-poor, high-K mafic source (?underplating). This occurred in a distal sector of a dying oblique subduction regime, immediately preceding the extensional silicic volcanism.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1017/S026359330000660X
Programmes: BAS Programmes > Pre 2000 programme
ISSN: 0263-5933
Additional Keywords: granites, Jurassic, geochemistry, isotopes, petrogenesis, modelling, subduction, South America, Andes, Deseado Massif
Date made live: 28 Nov 2016 14:49 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/515260

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