Tectonic evolution of Paleozoic orogenic events

Abstract

The Paleozoic Era included multiple Wilson cycles between ca. 540 Ma and ca. 250 Ma. Today, the remnants of these cycles (as fragments ranging from rift basalts to calc-alkaline granitoids) are spread along continents as pieces of a jigsaw puzzle that challenge geologists. Three major Paleozoic orogenic events (i.e., Appalachian, Variscan and Ross) are examined in this dissertation that have recorded and preserved the remnants of different stages of a Wilson cycle. The study of these three mountain building events simultaneously, although they occurred thousands of kilometers away from each other, provides insight into deciphering each other. This was made possible through the fundamental laws of geology and the principles of tectonics that hold true for events independent of their position in space and time.

As James Hutton stated in 1700’s, “The present is the key to the past.” This is the fundamental philosophy behind reconstructive tectonics research, where investigations on fragments that are exposed at or near Earth’s surface today enable us to revert the time and understand the spatial and temporal evolution of Earth. This fundamental understanding brings us, as a whole geoscience community, the opportunity to estimate long term evolution of the environments we currently occupy. In other words, with tectonics research, we are creating a key for the future, from the past.

Tectonic events record their signatures in rock and mineral chemistry, through elemental behavior and the occurrence of different chronometers. Where chemical information provides the type and character of a given event, chronometers allow us to put that information in a temporal context. In this dissertation, through application of integrated geochronological and geochemical methods, several long-lasting debates/problems were addressed. The results of each project, with newly acquired high precision data from various lithologies, have contributed to the advancement of the completion of each orogenies jigsaw puzzle. Furthermore, the combined application of geochronological and geochemical methods displayed their harmony and strength for the investigation of tectonic events.

Through these applications, (1) middle-Silurian ocean-island-basalt magmatism and Devonian-Carboniferous polymetamorphism recorded within the Western Blue Ridge of the Southern Appalachians, (2) the multi-stage tectonic events ranging from the Middle-Ordovician birth of Rheic Ocean to its late-Carboniferous Variscan termination recorded in the Central Sakarya Terrane, and (3) the petrogenesis and early-Paleozoic thermal evolution of the extensive Granite Harbor Intrusive suite within the Central Transantarctic Mountains were studied as chapters of this dissertation. The diverse range of lithologies examined and the analytical capabilities utilized provided new constraints and fresh perspectives to the understanding and modeling of each orogenic event.