STRATIGRAPHY AND STRUCTURE OF THE MENDENHALL GNEISS

ABSTRACT

An undergraduate thesis presented on the Stratigraphy and Structure of the Mendenhall Gneiss including structural and lithologic data colleted in remote regions of the Angeles National Forest, southern California. Geologic field mapping of basement rocks in the south central San Gabriel Mountains has yielded data enabling correlation of the largest continuous section of metamorphic rock with displaced rock bodies located on opposing sides of strike-slip fault zones. Palinspastic reconstructions provide insights that can be used for correlation with mountain ranges such as the Chocolate and Orocopia Mountains located more than 200 km south, and on the north side of the San Andreas Fault. New data supports tighter constraints on piercing points along the San Gabriel Fault with 218 ± 3 Ma Triassic Mt. Lowe intrusive rocks in contact with 1700 Ma Paleoproterozoic Mendenhall Gneiss. Large and small scale structural features provide information which can be used to aid in reconstruction of late Cenozoic brittle deformation events, as well as help in the determination of which land mass (Antarctica, Australia, Siberia or China) rifted from the western Laurentian margin during the 750 Ma break up of Rodinia.