HOLOCENE PALEOINTENSITIES - THELLIER EXPERIMENTS ON SUBMARINE BASALTIC GLASS FROM THE EAST PACIFIC RISE

A complete description of the geomagnetic field requires both paleodir ectional and paleointensity data. Although the paleointensity data bas e has grown steadily over the last three decades, it remains limited i n time and space (the majority of data are of Holocene age and come fr om Europe). Furthermore, it has been difficult to assess the reliabili ty of the paleointensity determinations. Here we present, paleointensi ty determinations on precisely dated Holocene (0 to 3500 years old) su bmarine basaltic glass from the East Pacific Rise (15-degrees-S to 22- degrees-S). Although hysteresis measurements and low-temperature isoth ermal remanent magnetization (IRM) acquisition experiments document a significant contribution of superparamagnetic grains, high blocking te mperatures (above 400-degrees-C) and Curie temperatures between 490-de grees-C and 550-degrees-C indicate a single-domain low-Ti magnetite as the carrier of the remanent magnetization. This notion is further sup ported by the fact that saturation of remanence is achieved in moderat e fields of about 200-300 mT. Submarine basaltic glass proves to be ne arly ideal for paleointensity determinations in that it produces a hig h success rate for Thellier experiments. Twenty-six out of 30 samples resulted in acceptable paleointensity determinations. Multiple experim ents on splits from the same sample show good reproducibility. The pal eointensities for zero age glasses correspond precisely with the prese nt field intensity at the site of recovery. The results of the remaini ng samples range from 16.7 to 53.9 muT with corresponding virtual axia l dipole moments (VADM) of 3.61 X 10(22) to 11.9 X 10(22) A m2. The in tensities vary rapidly with time excluding a westward drifting nondipo le component as the source for these fluctuations. Basaltic glass is f requently recovered in both dredged and drilled material froin the oce an floor. The availability of submarine basaltic glass throughout the world oceans therefore holds great potential for a better distribution of paleointensity data through time and space.