Studies of the proterozoic tectonic evolution of the southwestern United States

John Martin Seeley, University of Texas at El Paso


This dissertation is comprised of an introductory chapter (1) and four subsequent chapters (2, 3, 4, and 5) which concentrate on the evolution of Proterozoic rocks of the southwestern United States. ^ Chapter 2 utilizes gravity and magnetic geophysical techniques to delineate subsurface occurrences of Mesoproterozoic Unkar and Neoproterozoic Chuar Group rocks in northern Arizona and southern Utah. These rocks were delineated using gravity and aeromagnetic data, in combination with gravity profile modeling, seismic velocity analysis, geologic cross-sections, analysis of surface geologic structures, and analysis of drilling data. Delineation of Proterozoic extensional trends within this region provides insights in to Proterozoic paleogeography along the southwestern margin of Laurentia. ^ Chapter 3 focuses on the geologic mapping and areal distribution of the Mesoproterozoic Apache Group, Troy Quartzite and diabase in central Arizona. Landsat TM imagery was used in combination with existing geologic maps of the region to define the areal distribution of these units. Results were used to construct a regional-scale photo-geologic map of exposed Middle Proterozoic rocks. ^ Chapter 4 introduces a sequence stratigraphic model for siliciclastic rocks of the Mesoproterozoic Lanoria Formation of the Franklin Mountains, Texas, comprised of 700+ m of marine shelf and marginal marine sandstone, siltstone and mudstone. It is divided into six members (L1 through L6). Four facies associations are identified: proximal, distal shelf; tidal flat; incised valley; and, estuarine/deltaic. Six stratigraphic sequences have been interpreted. Sequences LS1, LS2, LS4 and LS6 represent marine shelf deposits. Sequence LS3 comprises incised valley fill and overlying tidal flat deposits. Sequence LS5 comprises incised valley fill overlain by estuarine/deltaic sediments. Sequences, facies, and paleocurrents suggest a northward sloping platform, indicating a southern source. Tidal processes dominated on proximal portions, while storm processes dominated on distal portions. ^ Chapter 5 of this manuscript presents a hypothesis for the Proterozoic tectonic evolution of southwestern Laurentia during the Mesoproterozoic and Neoproterozoic. Recent tectonic models of Grenville-age rocks along this margin document arc-continent and continent-continent collision ca. 1150–1120 Ma. Current interpretations, however, do not take into account the prior, and coeval tectonic history of Proterozoic rocks of southwestern regions of Laurentia that currently comprise the southwestern United States. ^

Subject Area


Recommended Citation

Seeley, John Martin, "Studies of the proterozoic tectonic evolution of the southwestern United States" (1999). ETD Collection for University of Texas, El Paso. AAI9947585.