Year of Publication

2009

Degree Name

Doctor of Philosophy (PhD)

Document Type

Dissertation

College

Arts and Sciences

Department

Geology

First Advisor

Dr. William A. Thomas

Abstract

Neoproterozoic-Early Cambrian continental rifting related to the breakup of the supercontinent Rodinia framed the continental margin of eastern Laurentia and the departing cratons around the opening Iapetus Ocean. The result of continental extension was the production of a zig-zag set of promontories and embayments on the eastern Laurentian margin defined by northeast-trending rift segments offset by northwesttrending transform faults.

The St. Lawrence promontory defines the Laurentian margin in western Newfoundland. There, Neoproterozoic-Carboniferous clastic, volcanic, and carbonate successions record protracted continental rifting and passive-margin thermal subsidence followed by destruction of the margin during the early, middle, and late Paleozoic Appalachian orogenic cycles. Palinspastic restoration of deformed Paleozoic strata by a set of balanced cross sections resolves the structure, stratigraphy, and timing of Paleozoic tectonic events on the St. Lawrence promontory. Synrift and post-rift subsidence profiles, as well as abrupt along-strike variations in the age, thickness, facies, and the palinspastically restored extent of synrift and post-rift stratigraphy, indicate the St. Lawrence promontory was founded upon a low-angle detachment rift system. Upperplate margins, lower-plate margins, and transform faults that bound zones of oppositely dipping low-angle detachments are recognized along specific segments of the promontory.

A detailed U-Pb and Lu-Hf isotopic detrital zircon study elucidates the identity of specific cratons conjugate to the St. Lawrence promontory in the pre-rift configuration of Rodinia. Approximately 510 zircons from 9 samples collected from basement and overlying Early Cambrian synrift rocks in Newfoundland were analyzed by LA-ICP-MS for U-Pb ages and Hf isotopic ratios. Synrift samples yielded ages ranging from 3605 Ma to 544 Ma with maximum age frequencies of 1000-1200 Ma (Grenville), 1350-1450 Ma (Pinware), and 2650-2800 Ma (Superior), while two basement samples yielded U-Pb ages of 1044 Ma and 1495 Ma. 177Hf/176Hf isotopic ratios of ca.1000 Ma, 1200 Ma, and 1400- 1600 Ma zircons from Newfoundland basement and synrift rocks are a close match to reported 177Hf/176Hf ratios for Baltican zircons of the same vintage, suggesting that Baltica was conjugate to the St. Lawrence promontory.

Included in

Geology Commons

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