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A variety of tectonic models for the Lower Paleozoic evolution of the Rowe-Hawley Zone (RHZ) in western New England describe the formation suprasubduction zone arc complexes and collision with Laurentia to produce the Taconic orogeny. Models developed for parts of the RHZ (e.g., western Massachusetts and Connecticut (Karabinos et al., 1998) and Newfoundland (van Staal et al., 2001)) have been translated along-strike. To test translation of various models along-strike across New England, geochemical data from major RHZ units in Vermont, Massachusetts, and Connecticut were compared for potential correlation. Element abundance data from previously analyzed meta-igneous rocks from the Mount Norris Intrusive Suite, North River Igneous Suite, and Barnard Gneiss from Vermont; Hawley Formation and Charlemont Mafic Intrusive Suite from Massachusetts; and Collinsville Formation of Connecticut were compiled; a set of meta-basalts from the Barnard Gneiss of Vermont were analyzed for their major and trace elements; and a set of 21 selected samples from these units were analyzed for Nd isotopes. These data were also compared to published data from units of the Bronson Hill Arc in central New England.

This thesis focuses on the effects of volcanism, river incision, epeirogenic uplift, and faulting on the landscape evolution of the Grand Canyon region. In the first chapter the migration of increasingly asthenospheric basaltic volcanism is used to constrain lithospheric modification of the Colorado Plateau margins. Buoyancy modification of the upper mantle, driven by the upwelling, is a likely driver for recent uplift of the area. In the second chapter, correlation between oversteepened rivers and areas of high-velocity upper mantle is used to show that recent and ongoing mantle-driven uplift is modulating the surface along the western margin of the Colorado Plateau. Differential oversteepening of rivers in the Zion National Park area can't be explained by climatic or bedrock-hardness differences and are best explained by localized uplift of the area, which explains the area's high relief and dramatic slot canyons. In the third chapter, new geochronology and geochemistry are used to reconstruct the timing, sequence, and structure of Grand Canyon's lava dams. Associated gravel deposits, internal cooling structures, and a general lack of lacustrine deposits suggests that the dams were removed in multiple stages and probably did not last for more than a few hundred to thousand years. Perched gravels under lava dams show steady incision rates indicating that the blockages were ephemeral and did not significantly affect long-term bedrock incision. In the final chapter, new Grand Canyon incision rates are used to quantify the spatial and temporal variations in incision. Results show temporally steady incision at any one location and a spatial pattern of increasing incision towards the east. This spatial pattern is most consistent with differential uplift of the area. Temporally steady incision suggests a lack of transient incision most consistent with sustained uplift. These studies suggest at the landscape of the region is young and actively being modified by deep forcing. Recent mantle-driven uplift associated with the convective modification of the lithosphere has steepened rivers and driven incision of deep canyons. Repeated lava damming of the Colorado River by comparison had a much smaller effect on the geomorphology or incision history of Grand Canyon.