Geological Society of America

69 D32. Geochemistry (Posters)

Sunday, 22 October 2017
9:00 AM - 5:30 PM
Halls 4EF

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

Paper number: 69-1
Program: Technical Sessions
Time: 9:00 AM – 5:30 PM

Authors

William J. Collins Presenting Author
Curtin University, Bentley
Erin Martin
Richmond, VIC
Brendan Murphy
St. Francis Xavier University, Antigonish, NS
Ross N. Mitchell
Yale University, New Haven, CT
Ross N. Mitchell
Curtin University, Bentley
Christopher J. Spencer
Curtin University, Perth

Abstract

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.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-305135

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