Reversal Asymmetry in the Paleomagnetic Data at 1.1 GA -- New Results From SW Arizona Sills

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.