Paleozoic evolution of western Marie Byrd Land, Antarctica

Abstract

We report geochemical data from (meta-) sedimentary and igneous rocks that crop out in the Ford Ranges of western Marie Byrd Land and discuss the evolution and reworking of the crust in this region during Paleozoic subduction along the former Gondwanan convergent plate margin. Detrital zircon age spectra from the Swanson Formation, a widespread low-grade metaturbidite sequence, defi ne distinct populations in the late Paleoproterozoic, late Mesoproterozoic, and Neoproterozoic-Cambrian. The late Paleoproterozoic group records magmatism derived from a mixed juvenile and crustal source. By contrast, the late Mesoproterozoic group yields Hf isotope values consistent with derivation from a juvenile Meso proterozoic source inferred to be an unexposed Grenville-age orogenic belt beneath the East Antarctic ice sheet. For the Neoproterozoic-Cambrian population, Hf isotope values indicate reworking of these older materials during Ross-Delamerian orogenesis. New U-Pb ages from the Devonian-Carboniferous Ford Granodiorite suite across the Ford Ranges reveal an extended period of arc magmatism from 375 to 345 Ma. For four younger samples of Ford Granodiorite, Hf and O isotope values in zircon suggest involvement of a larger (meta-)sedimentary component in the petrogenesis than for two older samples. This contrasts with the secular trend toward more juvenile values documented from Silurian toPermian granite suites in the Tasmanides of eastern Australia and Famennian to Tournasian granite suites in New Zealand, pieces of continental crust that were once contigu-ous with western Marie Byrd Land along the Gondwana margin. The differences may relate to an along-arc change from the typical extensional accretionary mode in eastern Australia to a neutral or an advancing mode in West Antarctica, and to an across-arc difference in distance from the trench between the New Zealand fragments of Zealandia and western Marie Byrd Land. Upper Devonian anatectic granites in the Ford Ranges most likely record reworking of early Ford Granodiorite suite members during arc magmatism. † Current address:

Multianalytical provenance analysis of Eastern Ross Sea LGM till sediments (Antarctica): Petrography, geochronology, and thermochronology detrital data

“…The petrographic features of the two groups of granitoids identified in detrital clasts are similar to those of the two granitic suites cropping out in Marie Byrd Land, the Devonian Ford Granodiorite, and the Cretaceous Byrd Coast Granite. The black and white granodioritic to tonalitic biotite‐hornblende variety (i.e., Thin section 15 in Figure ) is similar in texture, grain size and modal mineralogy to those exhibited by granodioritic to tonalitic Ford Granodiorite [ Weaver et al ., , Yakymchuk et al ., ]. Chemical analysis of clinoamphiboles revealed similarities between Mg‐hornblendes found in a biotite‐hornblende tonalite from marine record and those of a Ford Granodiorite sample from the Phillips Mountains (Figure a).…”

“…The most consistent Zrn‐UPb Precambrian age is 987–1039 Ma; this age population appears to be quite common from both sides of the Ross Embayment, being present in detrital zircons from offshore samples located in the Central and Western Ross Sea [ Licht et al ., ; Licht and Palmer , ], and from Beacon Supergroup rocks in the central Transantarctic Mountains [ Elliot and Fanning , ]. However, since this age population is present also from Swanson Formation rocks [ Pankhurst et al ., ; Yakymchuk et al ., ] and from BIS and KIS subglacial till samples [ Licht et al ., ] (Figure ), direct attribution to a West Antarctic source for this age population appears to be likely for trough 5 and 6 samples.…”

“…Two hypotheses have been proposed for this event: subduction [ Weaver et al ., ] or back‐arc extension [ Tulloch et al ., ]. It is unclear if plutons of Ford Granodiorite were emplaced in Ford Ranges during short‐lived pulses or prolonged magmatism during the Devonian‐Carboniferous [ Pankhurst et al ., ; Siddoway and Fanning , ; Yakymchuk et al ., ].…”

“…Yakymchuk et al . [] uncover detrital UPb ages of the sedimentary Swanson Fm., in the Ford Ranges, with a major Neoproterozoic‐Cambrian (500–750 Ma) and minor Mesoproterozioc (930–1180 Ma), Paleoproterozoic (1560–1930 Ma), and Paleozoic (387 ± 22 Ma) age populations.…”

“…Crustal extension in Cretaceous produced also the emplacement of mafic dykes throughout the Ford Ranges [Siddoway et al, 2005;Saito et al, 2013]. Within the Ford Ranges, a migmatitegranite complex is exposed in the Fosdick Mountains [Siddoway et al, 2004a], with orthogneisses and paragneisses which underwent at least two high-grade metamorphic events, in Devonian-Carboniferous and Cretaceous time, respectively [Korhonen et al, 2010a[Korhonen et al, , 2010b[Korhonen et al, , 2012Yakymchuk et al, 2015]. The granulite facies gneisses consist of migmatitic paragneisses with discrete domains of melanosome which typically contains cordierite, sillimanite, biotite, quartz, plagioclase, and k-feldspars, with or without garnet, and coarser grained leucosome containing quartz, k-feldspar, anti-perthite, and biotite, with or without garnet [Korhonen et al, 2010a[Korhonen et al, , 2010b.…”