Accretion of juvenile crust at the Early Palaeozoic Antarctic margin of Gondwana: geochemical and geochronological evidence from granulite xenoliths

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 eNd(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

Long‐lived orogenic construction along the paleo‐Pacific margin of Gondwana (Deep Freeze Range, North Victoria Land, Antarctica)

“…Subduction zone metamorphism along the Wilson Terrane–Bowers Terrane junction was associated with ongoing back‐arc extension inboard the Wilson Terrane as documented by a widespread postorogenic magmatism at circa 490–495 Ma [ Rocchi et al , 2009, 2011]. This renewed stage of convergence culminated with the pervasive, NE directed overthrusting in the Wilson Terrane at about 470–480 Ma, likely in connection with the arrival of the thick continental crust of the Robertson Bay Terrane [ Gemelli et al , 2009] at the subduction front. This event might have interrupted the subduction of the Admiralty Block at the trench [e.g., Cloos , 1993] and can be thus considered to mark the final juxtaposition of the Wilson Terrane to the Admiralty Block (collisional stage) and the ending stage of the Ross‐Delamerian orogen in Antarctica (Figure 12b).…”

Time–space focused intrusion of genetically unrelated arc magmas in the early Paleozoic Ross–Delamerian Orogen (Morozumi Range, Antarctica)

“…Recent works (Bracciali et al, 2009;Federico et al, 2006;Ferraccioli et al, 2002Ferraccioli et al, , 2009Gemelli et al, 2009;Rocchi et al, 2003;Roland et al, 2004;Tessensohn and Henjes-Kunst, 2005) led to an updated model of the Ross Orogeny in Victoria Land (Rocchi et al, 2011). In this new Cambrian scenario, the convergent paleo-Pacific margin of Gondwana consisted of a main continuous subduction zone coupled with local, transient subduction zones related to a more or less continuous ribbon of outboard pieces of stretched forearc regions.…”

Identification and isotopic studies of early Cambrian magmatism (El Carancho Igneous Complex) at the boundary between Pampia terrane and the Río de la Plata craton, La Pampa province, Argentina

“…Elsewhere, evidence of juvenile Cambrian magmatism has been found e.g. in a segment of the Ross orogen (Robertson Bay terrane, Victoria Land), inferred to be underlain by a thinned crust of Tonian age (Nd model ages averaging 980 Ma, and positive epsilon Nd values; Gemelli et al, 2009;Rocchi et al, 2010). Similarly, the inferred presence of juvenile Tonian magmatic rocks in the (otherwise, mostly Paleo-Mesoproterozoic) substratum of southern Pampia could indicate a zone of thinned basement, possibly associated with the early stage of Rodinia's breakup.…”