Paleozoic tectonism on the East Gondwana margin: Evidence from SHRIMP U-Pb zircon geochronology of a migmatite-granite complex in West Antarctica

• Published in: Tectonophysics
• Main Authors: Siddoway, Christine Smith, Fanning, Christopher
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier
• Subjects: Keywords: Accretionary orogen; East Gondwana; Migmatite-granite complex; SHRIMP U-Pb zircon geochronology; West Antarctica; Granite; Landforms; Silicate minerals; Tectonics; Zircon; Geochronology; accretionary prism; continental margin; extensional tectonics; geoch Accretionary orogen; New Zealand; Fosdick Mountains; Antarc*; Antarctica; Antarctica New Zealand
• Online Access: http://hdl.handle.net/1885/39888; https://doi.org/10.1016/j.tecto.2009.04.021; https://openresearch-repository.anu.edu.au/bitstream/1885/39888/5/u4027924xPUB185_2009.pdf.jpg; https://openresearch-repository.anu.edu.au/bitstream/1885/39888/7/01_Siddoway_Paleozoic_tectonism_on_the_2009.pdf.jpg

The Fosdick Mountains migmatite-granite complex in West Antarctica records episodes of crustal melting and plutonism in Devonian-Carboniferous time that acted to transform transitional crust, dominated by immature oceanic turbidites of the accretionary margin of East Gondwana, into stable continental crust. West Antarctica, New Zealand and Australia originated as contiguous parts of this margin, according to plate reconstructions, however, detailed correlations are uncertain due to a lack of isotopic and geochronological data. Our study of the mid-crustal exposures of the Fosdick range uses U-Pb SHRIMP zircon geochronology to examine the tectonic environment and timing for Paleozoic magmatism in West Antarctica, and to assess a correlation with the better known Lachlan Orogen of eastern Australia and Western Province of New Zealand. NNE-SSW to NE-SW contraction occurred in West Antarctica in early Paleozoic time, and is expressed by km-scale folds developed both in lower crustal metasedimentary migmatite gneisses of the Fosdick Mountains and in low greenschist-grade turbidite successions of the upper crust, present in neighboring ranges. The metasedimentary rocks and structures were intruded by calc-alkaline, I-type plutons attributed to arc magmatism along the convergent East Gondwana margin. Within the Fosdick Mountains, the intrusions form a layered plutonic complex at lower structural levels and discrete plutons at upper levels. Dilational structures that host anatectic granite overprint plutonic layering and migmatitic foliation. They exhibit systematic geometries indicative of NNE-SSW stretching, parallel to a first-generation mineral lineation. New U-Pb SHRIMP zircon ages for granodiorite and porphyritic monzogranite plutons, and for leucogranites that occupy shear bands and other mesoscopic-scale structural sites, define an interval of 370 to 355 Ma for plutonism and migmatization. Paleozoic plutonism in West Antarctica postdates magmatism in the western Lachlan Orogen of Australia, but it coincides with ...