Publication: Fast sediment underplating and essentially coeval juvenile magmatism in the
Ordovician margin of Gondwana, Western Sierras Pampeanas, Argentina
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2012
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Elsevier Science B. V., Amsterdam
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Abstract
Metasedimentary high-pressure upper amphibolite facies gneisses (1.2±0.1 GPa and 780±45 °C) at Las
Chacras, Sierra de Valle Fértil, are tectonically juxtaposed to thewesternmost parts (outboard) of the Famatinian
(Early Ordovician) magmatic arc, which underwent syn-plutonic middle crust high-grade metamorphism at
lower pressure. U–Pb SHRIMP zircon data suggest that the gneisses contain Famatinian igneous detritus, so
that their sedimentary protoliths were probably deposited in a forearc basin and then rapidly underthrust and
accreted to the lower crust of the arc, essentially coevallywith arc magmatismat 468±4 Ma. Chemically and isotopically
juvenile garnetiferous amphibolites within the gneisses are recognised as representing themost primitive
magmas so far observed in this belt, which has often been considered to be a continental arc derived from
isotopically mature sources. This is consistent with the idea that at least part of the dominant Famatinian
magmatism originated in depleted mantle but was heavily contaminated by crustal components.