Abstract: Formation and Deformation of Neogene Basins Around the Pacific Rim

James C. Ingle Jr.

Episodes of rapid crustal spreading along the East Pacific Rise between 25 and 15 Ma correlate with a period of widespread formation of Neogene marginal seas, borderlands, and basins along the convergent margins of the Farallon, Pacific, Philippine, and Nasca plates. Plate-edge responses to fast spreading included increased rates of convergence, subduction, and accelerated motion along basin-bounding transform and strike-slip faults. These later processes led to a major period of back-arc spreading, formation of pull-apart basins, and a general tectonic reorganization of the Pacific rim in late Oligocene-early Miocene time ca. 23 Ma. Most basins formed during the early Miocene experienced further tectonic subsidence through the early late Miocene. Subsequently, an equally widespread episode of compressive margin deformation and uplift commenced during the late Pliocene and accelerated daring the Pleistocene as an apparent consequence of a vector change in the Pacific plate--once again resulting in a major tectonic and paleogeographic reorganization of the Pacific rim. Typically, a complete cycle of basin formation and destruction encompassed only 20 m.y. Moreover, each tectonic phase had profound consequences for the evolution of local, regional, and global paleoceanography and climate due to rapid changes in (1) continental margin and basin configuration, (2) depth of basin sills, and (3) the closing of major Pacific inter-ocean gateways which collectively affected the character and distribution of water masses, upwelling, and the production and storage f carbon in basin depocenters. The relatively high rates of sediment accumulation characterizing most Neogene basins resulted in expanded records of the tectonic, depositional, and oceanographic events characterizing each stage in basin evolution. This report focuses on rates and styles of basin subsidence and uplift as revealed through quantitative back-stripping analysis of basin stratigraphies in three contrasting crustal, tectonic, depositional, and oceanographic settings including the Japan Sea, East China Sea, and the Gulf of California. The results allow detailed evaluation of variations in rates of total versus tectonic (residual) subsidence, identification of thermal and mechanically driven phases of subsidence, the effects of variations in sediment loading, and the correlation f distinctive phases in basin history with plate and microplate dynamics.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California