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ABSTRACT: Paleomagnetic Analysis of Tectonic History of the Izu-Bonin Arc Based on ODP Leg 126 Deep-sea Cores

Masato Koyama, Stanley Cisowski, Philippe Pezard

A paleomagnetic study was made on the deep-marine sediments and volcanic rocks drilled by Ocean Drilling Program (ODP) Leg 126 from the Izu-Bonin forearc region. This study evaluates the sense and amount of the tectonic drift and/or rotation associated with the evolution of the Philippine Sea plate. The ages of the measured samples range from the Oligocene to Pleistocene. The samples were measured using cryogenic and spinner magnetometers. Alternating field and thermal demagnetization experiments show that many of the samples have stable remanence and are suitable for paleomagnetic studies. Paleomagnetic polarity reversal sequence between Chron C10 and Brunhes was identified with the help of biostratigraphic studies. Oligocene to early Miocene samples show significantly s allower inclinations than that of the present and suggest the northward drift of the Izu-Bonin forearc region. We also discuss the period and exact amount of the drift as well as the problem of the tectonic rotation of the arc.

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