HR: 1340h
AN: GP33A-0089    [Abstracts]
TI: Reversal Asymmetry in the Paleomagnetic Data at 1.1 GA -- New Results From SW Arizona Sills
AU: * Pesonen, L J
EM: lauri.pesonen@helsinki.fi
AF: Division of Geophysics, University of Helsinki, Gustav Hällströmin katu 2, P.O. Box 64, Helsinki, 00014 Finland
AU: Donadini, F
EM: fabio.donadini@helsinki.fi
AF: Division of Geophysics, University of Helsinki, Gustav Hällströmin katu 2, P.O. Box 64, Helsinki, 00014 Finland
AU: Korhonen, K
EM: kimmo.korhonen@hut.fi
AF: Laboratory of Geoenvironmental Technology, Helsinki University of Technology, Otakaari 1, P.O. Box 1000, Espoo, 02015 Finland
AU: Deutsch, A
EM: deutsca@uni-muenster.de
AF: Institute of Planetology, University of Münster, Wilhelm-Klemm-Str. 10, Münster, 48149 Germany
AU: Harlan, S
EM: sharlan@gmu.edu
AF: Department of Environmental Science and Policy, George Mason University, 4400 University Drive, MSN 5F2, Fairfax, VA 22030-4444 United States
AU: Nevanlinna, H
EM: heikki.nevanlinna@fimr.fi
AF: Finnish Meteorological Institute, Space Research, Vuorikatu 24, P.O. Box 503, Helsinki, 00101 Finland
AB: Large Igneous Provinces (LIPs) represent times when huge volumes of mafic magma were emplaced in a relatively short period of time. One of the most dramatic LIP is the 1.11 - 1.08 Ga Keweenawan rift-related magmatism in the Lake Superior area of North America. This event can be correlated with the diabase province of the SW USA and with coeval Umkondo magmatic activity in southern Africa. These magmatic activities coincide with the Grenvillian (NAM) and Natal-Namagua (Africa) collisional events related to the assembly of Rodinia supercontinent. However, the docking history of Laurentia with other Rodinia continents is poorly defined due to significant inclination asymmetry between the normal and reversed polarities. The reversal asymmetry, so far identified with certainty only in Lake Superior region, are explained by four models: (i) fast continental drift during the reversal crossing ( R to N), (ii) unremoved secondary components, (iii) non-averaging secular variation in (particularly R) paleomagnetic data and (iv) significant contribution of the non-dipole field at 1.11-1.08 Ga. In order to shed further light to the problem we initiated a project which includes global analysis of 1.1 Ga paleomagnetic, paleointensity and paleosecular variation data. For this reason we carried out new samplings of the 1.1 Ga sills and dykes of the Gila County and Sierra Ancha Mountains of SW Arizona. The new samples are petrographically studied and the least altered-ones will be dated by isotopic techniques. Preliminary paleomagnetic results of the Arizona samples will be presented and compared with those from the Lake Superior province of North America, from the Umkondo Province of Africa and from the probably coeval sediments of Siberia. The possible non-dipole field will be identified with novel spherical harmonic analysis applied to the 1.1 Ga paleomagnetic data.
DE: 1535 Reversals: process, timescale, magnetostratigraphy
DE: 1599 General or miscellaneous
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005