Paleosecular Variation Recorded in Pleistocene Volcanic Rocks of Ascension Island, South Atlantic Ocean (abs)

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American Geophysical Union




In recent years, numerous mathematical models for generation of the geomagnetic field have been developed. Surface observations of the Earth's field are needed to develop, refine, and test these geodynamo models. Paleomagnetic studies can extend such observations into the past, and a substantial paleosecular variation (PSV) database has been compiled for the past 5 Ma. A global distribution of PSV data is needed, but the distribution of paleomagnetic data is very uneven, concentrated mainly in the northern hemisphere. The middle of the south Atlantic Ocean is one place where PSV data is lacking. This study gathered paleomagnetic data from lava flows of Ascension Island in the south-central Atlantic where rock units were previously dated to be between 0.12 and 1.5 Ma. Paleomagnetic samples from 68 sites were collected between May 14 and June 18, 2001. Preliminary paleomagnetic analyses of 24 sites were performed at the University of Puget Sound paleomagnetic laboratory. Fifteen sites yield normal directions, 6 sites give reversed directions, and 3 sites exhibit intermediate directions (VGP latitude less than 60o). Ar/Ar dating will be performed at the University of Wisconsin, Madison, and paleointensity studies will be done at Scripps Institute in San Diego. The resulting data will fill a large gap in the PSV database for the past 5 Ma.