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GSA Annual Meeting in Seattle, Washington, USA - 2017

Paper No. 69-1
Presentation Time: 9:00 AM-5:30 PM

GIGAYEAR REPETITION OF MANTLE CONVECTION MODES AND ITS RELATION TO SUPERCONTINENT CYCLES


COLLINS, William J.1, MARTIN, Erin1, MURPHY, J. Brendan2, MITCHELL, Ross N.3 and SPENCER, Christopher J.1, (1)Department of Applied Geology, Curtin University, Kent Street, Bentley, 6102, Australia, (2)Department of Earth Sciences, St. Francis Xavier University, Antigonish, NS B2G 2W5, Canada, (3)Department of Geology and Geophysics, Yale University, New Haven, CT 06520-8109; Department of Applied Geology, Curtin University, Kent Street, Bentley, 6102, Australia, william.collins@curtin.edu.au

The giga-annum periodicity in global radiogenic Hf and Sr isotopic trends is investigated by integrating data from tectonics, geodynamics, and palaeomagnetism, in order to build a holistic geodynamic model linking modes of mantle convection to plate tectonic motions over the last 2,500 Myr. The gigacycle reflects an alternating dominance between degree-2 and degree-1 mantle convective flow, manifest as the presence and absence of a hemispheric subduction girdle, respectively. The girdle is currently represented by the circum-Pacific subduction system and is geologically recorded by Phanerozoic circum-Pacific accretionary orogens. Degree-1 convection resulted in the amalgamation of Columbia ca. 2,000 Myr ago and Gondwana ca. 550 Myr ago accompanied by peaks in crustal reworking (-εHf), whereas degree-2 convection produced Nuna ca. 1,600 Myr ago and Pangaea 200 Myr ago accompanied by peaks in mantle input (+εHf). The change from degree-2 to degree-1 coincided with Rodinia amalgamation ca. 1,100 Myr ago, when the circum-Nuna subduction girdle collapsed. The gigacycles are rhymthic oscillations of mantle circulation patterns that control plate motion trajectories and contrasting styles of supercontinent amalgamation.

Session No. 69--Booth# 100

D32. Geochemistry (Posters)
Sunday, 22 October 2017: 9:00 AM-5:30 PM
Halls 4EF (Washington State Convention Center)
Geological Society of America Abstracts with Programs. Vol. 49, No. 6
doi: 10.1130/abs/2017AM-305135
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