Crustal Block Rotation in a Migrating Transform Zone: Oriented Piston Cores Study

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Much of Dr. Kleinrock's research has focused on mechanics ofthe now-classic propagating spreading center at 95.9'W on the East Pacific Rise. An oddity of this and all propagators is the ocean crust gets transferred from one lithospheric plate to another as the "active" spreading axis advances into and splits the "old" crust. Complex deformation patterns are known to develop between the active and inactive spreading centers. Two theories exist to explain this deformation: 1) the "deck of cards model" that predicts displacement is accomodated along pervasive ridge-normal faults: and 2) the "bookshelf tectonics" model that predicts deformation is taken up by crustal block rotation about vertical axes. Dr. Kleinrock will test the latter by examining piston cores for down-core rotation relative to the earth's magnetic field. During a recent cruise, he supervised the acquisition of 6 piston cores within the regions of suspected deformation at the 95.5'W system. Each was equipped with a corehead camera to record obsolute orientation, rotation, and departures from vertical that occured during the coring process. Dr. Lisa Tauxe at Scripps will conduct full-core, pass-thorough cryogenic magnetometer measurements on these cores. When split, subsamples will be analyzed for remnant magnetization, Inclination and declination values derived from these analyses will be provided to Dr. Kleinrock who will then incorporate the corehead information to remove corring artifacts to construct a down-core history of absolute rotation for each core. He estimates that at least 45' of block rotation has occurred in the region, and the technique proposed here will be able to resolve rotations of roughly 10'.