Shannon Molloy's Honours Thesis Abstract

Thesis Title: 
Remote Sensing Techniques for the Mapping of Arc to Rift Transitional Rocks in Central Baja California

The central Gulf of California coast region of the Baja Peninsula records the transition from arc to rift tectonics.  As a consequence of the changing tectonic regime, magmatic activity in the area changed from arc-related andesites to rift-related basalt-andesite-rhyolite pyroclastics.  Associated with rifting was the development of the Santa Rosalia basin, one of several proto-Gulf basins to develop, and the Boléo Cu-Co-Zn-Mn district.  The aim of this study was to utilize remote sensing techniques in order to see if it is possible to map the arc and rift lithologies of the Santa Rosalia basin and its border lands.  A key goal was to assess if remote sensing techniques could be used to differentiate between arc- and rift-related igneous units, that make up the central peninsular arch (Sierra Santa Lucia) and form the western boundary of the Santa Rosalia basin; as various studies over the past decade have shown that Sierra Santa Lucia is not comprised entirely of arc-related andesite.  An additional objective of the work is to assess the plausibility for the existence of a collapse caldera that lies along the west-south western margin of the Santa Rosalia basin.  Confirmation of a rift-related caldera would establish a key genetic link between early Gulf magmatism, incipient basin sedimentation and hydrothermal activity of the Boleo district.

To answer these questions, remote sensing techniques were utilized to analyze a 30m resolution Landsat 8 satellite imagery.  Based on the spectral bands of the Landsat 8 imagery and remote sensing techniques, such as band ratios and combinations, principal components analysis, and classification, some of the rock types present were separated based on their differing mineralogy and a geological map was created.  By taking advantage of specific spectral bands such as 2/4:6/7:4/6, 4/2, and 7/6, arc to rift volcanic rocks could be differentiated from unlithified alluvium and carbonates and sulphates.  However, it was not possible to separate arc volcanic rocks from rift volcanic rocks because their mineralogical differences were too subtle to produce different spectral responses.