Structure, Evolution and Tectonic Significance of the Eastern Boundary of the Outer Continental Borderland

Abstract

The Continental Borderland adjacent to southern California and northern Baja California is an exceptionally wide (240 km) region of ridges, islands, and bathymetric basins as deep as 2 km. This continental margin area consists of a relatively intact outer ‘terrane’ to the west that includes Cretaceous and Paleogene forearc sedimentary rocks, and a highly extended inner ‘terrane’ to the east characterized by metamorphic basement rocks exhumed during early-Miocene oblique rifting. To better understand this continental rifting process, we use regional grids of multichannel seismic reflection data, and stratigraphic information from industry wells and sea floor samples to investigate the nature and tectonic development of the boundary between the outer forearc Nicolas terrane and the inner denuded, exhumed Catalina terrane. The data show that this terrane boundary is largely defined by an angular unconformity that overlies and helps form an eastward pinch-out of Outer Borderland forearc strata of earliest Miocene through Cretaceous age. These forearc sedimentary rocks were removed along the boundary as a result of early-to-middle Miocene uplift and erosion associated with exhumation of the Catalina basement farther east. The boundary is not, as previously postulated, predominantly fault controlled, as Nicolas forearc sedimentary rocks are present on both sides of a fault system near the northern part of the terrane boundary. This East Santa Cruz Basin fault system is a predominantly east-dipping, Miocene oblique-normal fault system that has been reactivated with blind to partly blind oblique-reverse displacement. In addition, there is no simple through-going fault system farther south along the southern part of the terrane boundary.

AAPG Datapages/Search and Discovery Article #90266 © 2016 AAPG Pacific Section and Rocky Mountain Section Joint Meeting, Las Vegas, Nevada, October 2-5, 2016