I. Neoproterozoic-paleozoic supercontinental tectonics and true polar wander. II. Temporal and spatial distributions of proterozoic glaciations

Citation

Evans, David Aspinwall (1998) I. Neoproterozoic-paleozoic supercontinental tectonics and true polar wander. II. Temporal and spatial distributions of proterozoic glaciations. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/grbc-aa41. https://resolver.caltech.edu/CaltechTHESIS:11152012-083234968

Abstract

The Proterozoic Eon, occupying nearly half of Earth history from 2.5 to 0.5 billion years ago, is marked at its beginning and end by dramatic events in the tectonic, paleoclimatic, chemical, and biological evolution of the planet. The onset of the Proterozoic Eon witnessed the emergence of continents and perhaps the introduction of plate tectonics, Earth's first extensive ice ages, oxygenation of the hydro-atmosphere, and development of eukaryotes. The end of the Proterozoic Eon is characterized by supercontinental turnover and very rapid continental drift rates, a series of glaciations which left their marks on every continent, the rise of atmospheric oxygen to sustain multicelled organisms, and an evolutionary "explosion" of animal life.

Establishment of coherent paleogeographies of these important intervals is a crucial prerequisite for describing the events and understanding the underlying processes. Paleomagnetism is the most direct quantitative method for charting continental drift through time. The purpose of this dissertation is to use paleomagnetism to constrain tectonic and paleoclimatic processes at the beginning and end of the Proterozoic Eon.

A paleomagnetic study of Early Cambrian rocks in western Mongolia finds somewhat ambiguous results and addresses tectonic models of the Paleo-Asian Ocean. Review of the most reliable studies among the Proterozoic-Cambrian global paleomagnetic database permits the hypothesis that an episode of inertial interchange true polar wander (TPW) occurred in Early Cambrian time. The Cambrian TPW event and a previously hypothesized Ordovician-Devonian TPW migration share a common axis and suggest the existence of long-lived mantle mass anomalies inherited from the previous supercontinent, Rodinia. The breakup of Rodinia and subsequent amalgamation of Gondwanaland appear analogous in several ways to the Gondwanaland-Super-Asia supercontinental transition, suggesting a 500-600-Myr cyclicity.

An exhaustive review of paleomagnetic and geochronological constraints upon Neoproterozoic glaciogenic deposits fails to find a convincing high-paleolatitude occurrence. Detailed study of one of these deposits in South China reveals a reliable paleomagnetic pole implying a paleolatitude of 34±2°, with both paleoclimatic and paleogeographic implications. A reliable estimation of 11±5° depositional paleolatitude for 2.2-billion-year-old lavas directly overlying a glaciogenic formation in South Africa, extends the occurrence of low-latitude continental ice sheets further back into the Precambrian.

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