Publication Date:
2022-05-25
Description:
Author Posting. © American Geophysical Union, 2000. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 105 (2000): 5835-5857, doi:10.1029/1999JB900318.
Description:
We use new seismic and gravity data collected during the 1994 Los Angeles
Region Seismic Experiment (LARSE) to discuss the origin of the California Inner
Continental Borderland (ICB) as an extended terrain possibly in a metamorphic core
complex mode. The data provide detailed crustal structure of the Borderland and its
transition to mainland southern California. Using tomographic inversion as well as
traditional forward ray tracing to model the wide-angle seismic data, we find little or no
sediments, low (#6.6 km/s) P wave velocity extending down to the crust-mantle boundary,
and a thin crust (19 to 23 km thick). Coincident multichannel seismic reflection data show
a reflective lower crust under Catalina Ridge. Contrary to other parts of coastal
California, we do not find evidence for an underplated fossil oceanic layer at the base of
the crust. Coincident gravity data suggest an abrupt increase in crustal thickness under the
shelf edge, which represents the transition to the western Transverse Ranges. On the shelf
the Palos Verdes Fault merges downward into a landward dipping surface which separates
“basement” from low-velocity sediments, but interpretation of this surface as a detachment
fault is inconclusive. The seismic velocity structure is interpreted to represent Catalina
Schist rocks extending from top to bottom of the crust. This interpretation is compatible
with a model for the origin of the ICB as an autochthonous formerly hot highly extended
region that was filled with the exhumed metamorphic rocks. The basin and ridge
topography and the protracted volcanism probably represent continued extension as a
wide rift until ;13 m.y. ago. Subduction of the young and hot Monterey and Arguello
microplates under the Continental Borderland, followed by rotation and translation of the
western Transverse Ranges, may have provided the necessary thermomechanical
conditions for this extension and crustal inflow.
Description:
The LARSE experiment
was funded by NSF EAR-9416774, the U.S. Geological Survey’s Earthquake
Hazards and Coastal and Marine Programs, and by the Southern
California Earthquake Center (SCEC).
Repository Name:
Woods Hole Open Access Server
Type:
Article
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