Timing and Style of Subduction-Related Deformation, Central Great Valley, California

Douglas P. Imperato

The geometry and kinematic history of the major structures of the central Great Valley of California were evaluated in an attempt to determine the regional history of deformation during subduction tectonics. A series of maps and cross sections were constructed integrating stratigraphic correlation of more than 300 well logs, seismic-reflection data, and published outcrop maps. Piercing points were used to establish kinematic histories.

Results indicate that the eastern margin of the central Great Valley was dominated by extension and basement-involved normal faults, from Santonian (Late Cretaceous) time (possibly earlier) through middle Eocene time (possibly later). This area was dominated by shortening and reactivation of normal faults as reverse faults, from middle Eocene time (and possibly later) through early Miocene time (and possibly later). Dextral strike-slip may have occurred on basin-parallel faults, beginning after early Eocene time (probably during Neogene time). These phases-of deformation were concurrent with intermittent periods of shortening and thrust faulting along the Coast Range and related faults on the western basin margin, beginning in Late Cretaceous time (and possibly earlier).

Throughout much of Late Cretaceous and early Tertiary time, the central Great Valley was thus dominated by extension and normal faults on the eastern basin margin, and shortening and thrust faults on the western basin margin. Such contrasting styles of deformation are observed in modern forearc basins. Tectonic implications of a shift to shortening and reverse faults on the eastern basin margin in Eocene to early Miocene time, however, remains enigmatic.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California