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ABSTRACT: ODP Leg 129 Results: Studies of Old Pacific History

Roger L. Larson, Yves Lancelot

At this writing, ODP Leg 129 is scheduled to drill in the Pigafetta and possibly East Mariana basins of the western Pacific in December 1989-January 1990 to investigate "Old Pacific History." This leg is dedicated to recovering sedimentary and igneous material from the oldest portion of the Pacific plate, estimated to be of Jurassic age.

Despite these estimates by geophysical inference that an area of the Pacific plate approximately equal to the continental U.S. is Jurassic in age, no Jurassic material has ever been recovered from the deep Pacific. This current attempt is targeted by recent magnetic lineation and multichannel seismic surveys indicating that sedimentary sequences up to 600 m thick with basal ages of mid- to Late Jurassic lie below a water depth of 5700 m. We hope to sample these sequences and the Jurassic ocean crust beneath them for the following purposes: (l) dating the world's oldest magnetic lineation patterns, (2) studying the paleoclimate history of the world's Jurassic superocean, (3) determining the geochemistry of sediment and igneous ocean crust near a subduction zone for comparison with the eochemistry of the neighboring arc volcanism, (4) determining the crustal magnetization, paleolatitude, and petrology of the oldest Pacific ocean crust, and (5) determining the northern limit of the mid-Cretaceous volcanic complex commonly known as the Darwin Rise.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990