Generation and preservation of continental crust in collisional orogenic systems

Abstract

The continental crust is the archive of Earth history. Much of what we know about the development of Earth is learned from the continental crust, and it is within the crust that many natural resources are found. Hence, understanding its formation and evolution is a key aspect to a deeper knowledge of the Earth system. This thesis is a study of the processes that have formed and shaped the distribution of continental crust, with specific focus on crustal development associated with the Rodinian supercontinent and the Grenville Orogeny spanning ca. 1200 to 900 Ma. Specifically it addresses an aspect of the incompleteness of the record of continental crust formation. The preserved continental crust is punctuated with periods of lesser and greater frequency of geologic features, e.g., the temporal distribution of the ages of mineral deposits, juvenile granitoids, eclogites, granulites, and the U-Pb crystallization ages of zircons now preserved in modern and ancient sediments (see Gastil, 1960; Barley and Groves, 1992; Condie, 1998; Campbell and Allen, 2008; Brown, 2007; Bradley, 2011). In addition, interpretive features in the geologic record also have an apparent episodic distribution such as passive margins (Bradley, 2011) and supercontinents (Condie, 1998). The episodic nature of these geologic phenomena implies either an episodic formation or preferential preservation of continental crust. These two end member models have been explained through a number of geologic processes such as eruption of superplumes, global disruption of thermal structure of the mantle, assembly of supercontinents, collisional orogenesis. Through the chapters outlined below, this thesis explores the connection of these episodic geologic events with key isotopic signals, principally U-Pb, Hf, and O isotopes in zircon supplemented by sedimentology, structural geology, and igneous geochemistry. It comprises a series of chapters developed around manuscripts prepared for publication.