Supercontinent integrity between 0.8 and 0.6 Ga: the nemesis of Rodinia?
Published:January 01, 2015
J. D. A. Piper, 2015. "Supercontinent integrity between 0.8 and 0.6 Ga: the nemesis of Rodinia?", Continent Formation Through Time, N. M. W. Roberts, M. Van Kranendonk, S. Parman, S. Shirey, P. D. Clift
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The view that the pre-Phanerozoic continental crust records transient supercontinent cycles separated by intervals of diverse shield motion has dominated interpretation of the Precambrian aeon. Of two separated supercontinent intervals, the latter, ‘Rodinia’, is considered to result from Meso-Neoproterozoic accretion and progressive dismemberment by fragmentation after c. 0.9 Ga. Although the present palaeomagnetic database does not permit this premise to be reliably tested by diverse relative movements, the alternative proposition that the crust comprised a quasi-integral lid during pre-Phanerozoic history is eminently testable because it demands conformity of poles to a single position or otherwise to a single apparent polar wander path (APWP). In the event, palaeomagnetic poles assigned to 0.8–0.6 Ga conform to a single (‘Franklin–Adelaide’) APW Track merging into a long interval (c. 0.75–0.6 Ga) of near-static polar behaviour employing reconstruction parameters derived from pre-0.8 Ga data. This is supported by a robust independent indicator, namely the history of rifting to drifting at c. 0.6 Ga as predicted from the subsidence histories of early Palaeozoic passive margins. Multiple environmental changes near the Precambrian–Cambrian boundary correlate with this transition. Evidence demonstrating that continental crust comprised a quasi-integral lid at 0.8–0.6 Ga with break-up confined to the Ediacaran Period is summarized. The Rodinia hypothesis postulating prolonged break-up from a contrasting reconstruction is shown to be fundamentally flawed and should now be discarded.
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Continent Formation Through Time
The continental crust is our archive of Earth history, and the store of many natural resources; however, many key questions about its formation and evolution remain debated and unresolved:
What processes are involved in the formation, differentiation and evolution of continental crust, and how have these changed throughout Earth history?
How are plate tectonics, the supercontinent cycle and mantle cooling linked with crustal evolution?
What are the rates of generation and destruction of the continental crust through time?
How representative is the preserved geological record?
A range of approaches are used to address these questions, including field-based studies, petrology and geochemistry, geophysical methods, palaeomagnetism, whole-rock and accessory-phase isotope chemistry and geochronology. Case studies range from the Eoarchaean to Phanerozoic, and cover many different cratons and orogenic belts from across the continents.