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Accretion of juvenile crust at the Early Palaeozoic Antarctic margin of Gondwana: geochemical and geochronological evidence from granulite xenoliths
Authors:M Gemelli  S Rocchi  G Di Vincenzo  M Petrelli
Institution:Dipartimento di Scienze della Terra, Universitàdi Pisa, Via S.Maria 53, 56126 Pisa, Italy;;Istituto di Geoscienze e Georisorse, CNR, Via Moruzzi 1, 56127 Pisa, Italy;;Dipartimento di Scienze della Terra, Universitàdi Perugia, P.zza Università, 06123 Perugia, Italy
Abstract:Geodynamic models for the Antarctic sector of the active Early Palaeozoic Palaeo-Pacific margin of Gondwana are based on the nature and age of the deep crust of the Robertson Bay terrane, the outermost lithotectonic unit of the margin. As this crustal block is covered with thick turbidite deposits, the only way to probe the deep crust is through the analysis of granulite xenoliths from Cenozoic scoria cones. Low-K felsic xenoliths yield the oldest (Middle Cambrian) laser-probe U–Pb ages on zircon areas with igneous growth zoning. This finding, along with the positive whole-rock εNd(500Ma), suggests that these felsic rocks derived from a juvenile magma formed during the Early Palaeozoic Ross orogenic cycle. Mafic xenoliths have geochemical-isotopic compositions similar to those of modern primitive island arcs, suggesting the involvement of subducted oceanic crust in their magma genesis and accretion of juvenile crust at the Antarctic margin of Gondwana.
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