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ABSTRACT

The central Los Angeles basin represents the deepest part of a basin that apparently resulted from rapid and prolonged lithospheric thinning owing to extension between rotating blocks. Subsidence in this tectonic setting began about 18 Ma and presumably reflects isostatic adjustment to the thinning of the buoyant crust. Sediment starving in the period immediately following the initiation of rapid subsidence resulted in a deep water-filled basin that reached water depths in excess of 2 km during Pliocene time. Sedimentation accelerated immediately following the widespread extrusion of andesitic and basaltic volcanics about 16 Ma. Maximum tectonic subsidence, which may require 50% to 75% of lithospheric thinning under the central deep, is about 3 km depending on assumptions. This amount of thinning can be used to estimate the maximum time-temperature history of basin sediments. The pattem of subsidence is best explained by a model of crustal rotation between right-slip faults that results in both extension in the early development of the basin and compression in the later phase of basin development.

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