T230 Proterozoic Accretion of the North American Continent – United Plates of America Revisited II

Tuesday, 27 September 2016
1:30 PM - 5:30 PM
Mile High Ballroom 3B

GROWTH AND EVOLUTION OF SOUTHERN LAURENTIA IN THE CONTEXT OF THE NUNA SUPERCONTINENT: PALEOPROTEROZOIC CONNECTIONS BETWEEN AUSTRALIA/ANTARCTICA (MAWSON) AND LAURENTIA

Paper number: T230-13
Program: Technical Sessions
Time: 4:30 PM – 4:45 PM

Authors

Abstract

The growth and evolution of Laurentia from 1.85 to 1.0 Ga coincides with the assembly of the supercontinents Nuna and Rodinia. In the Paleoproterozoic, south Australian cratons and Laurentia are thought to form a continuous orogenic system that both faced an open ocean across a long-lived convergent margin. We present a regional zircon U-Pb and Lu-Hf geochronologic dataset of paired igneous and detrital zircon grains to provide geochronologic and isotopic fingerprint for crustal provinces in Laurentia and compare these to Australian blocks to understand the interaction between the two continental blocks from 1.85 to 1.6 Ga. Mojave province has voluminous 1.78-1.75 Ga paragneisses interpreted to have been immature sandstones (metaturbidites); they have detrital zircon age spectrum with 1.85 and 2.5 Ga peaks and yield εHf(t) values that range from +10 to -10 and +5 to -5 respectively. Based on this signature, we correlate Mojave province metasedimentary rocks with 1.75 Ga Vishnu Schist of Grand Canyon and with crust of the Mawson Continent. The best correlation between what we propose as a greater “Vishnu Basin” in Laurentia is the Wallaroo Group in the eastern Gawler craton. However, some paleogeographic constraints place Australian components of the Mawson continent adjacent to western Canada. Granitoids that intrude these metasedimentary successions in Mojave also yield evolved εHf(t) values of +5 to -5 for the 1.79-1.68 Ga plutons and >2.0 Ga inherited zircon cores and xenocrysts, which is similar to western Grand Canyon and to Australia. Suturing of Mojave and Yavapai crust in Laurentia took place during 1.75 Ga subduction such that imbricated trench fill turbidities of Vishnu, and possible Australian correlates, overlap crustal province boundaries. Yavapai and Mazatzal metasedimentary rocks are dominated by Laurentian detritus with unimodal 1.73-1.6 Ga detrital zircon age peaks and juvenile εHf(t) values ranging from +12 to 0. Granitoids that intrude the Yavapai and Mazatzal province are also juvenile and share the same Hf isotopic compositions as the metasedimentary rocks they intrude. These data strengthen correlations within the Nuna supercontinent and favor models which posit amalgamation of Australia and Laurientia within Nuna by 1.75 Ga.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-282384

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