Tectono-Geomorphological Evolution of an Extensional Back-Arc Province, Baja California: Object-Oriented Classification and Slope-Area Analysis

Hesham F. El-Sobky and Steven L. Dorobek
Texas A&M University, College Station, TX

The Neogene tectonic history of eastern Baja California (includes most of the land area eastward of the main, north-south oriented, drainage divide that extends along the length of the peninsula) has been controlled by oblique rifting. Rifting began at ~5 Ma and has separated the peninsula of Baja California from mainland Mexico.

In this study we attempt to quantify the main forcing factors that controlled the tectono-geomorphological evolution of the eastern part of the peninsula since 5 Ma. Extensional deformation, bedrock lithology, long-term climatic changes, and evolving surface processes are the main factors that controlled the tectono-geomorphological evolution of the eastern Baja. Thirty-four drainage basins were extracted from a 15-m absolute digital elevation model for the peninsula. Lithological variations within these basins were identified using an object-oriented supervised classification for stacked-vectors, which incorporates many different terrain attributes (e.g., DEM, hillshaded relief, aspect, slope, etc). Stream length gradient indices also were extracted for the thirty-four basins. Steepness index and concavity index values were extracted for bedrock channels and were used along with slope-area analyses to investigate the response of streams to differential rock uplift in each basin. Channels in nine basins have steepness index values greater than 0.07, which reveals their immature nature, and in turn, might reflect either higher rock uplift rates or more recent uplift in these basins.