The Time Averaged Field at the Equator: Ecuador

University Of Florida, Gainesville FL

Investigators

Abstract

Opdyke EAR-0229130 This study will undertake a time averaged field (TAF) study of late Pliocene - Pleistocene lava flows in the equatorial volcanic province of Ecuador, where abundant volcanism offers excellent possibilities of sampling. More than 54 stratovolcanoes in Ecuador form part of the northern segment of the Andean volcanic belt, called the Northern Volcanic Zone (NVZ), which extends from 5o N to 2o S latitude (covering parts of Colombia and Ecuador). Paleomagnetic sampling and rock sampling for 40Ar/39Ar dating is planned on at least 40 sites. Fieldwork will be carried out with the collaboration of Dr. Minard Hall, professor of the Department of Geophysics (Escuela Politecnica Nacional, Quito), who is the person with the most knowledge and experience of the volcanology of Ecuador. His knowledge of the volcanic stratigraphy of the area will expedite and optimize fieldwork. Paleomagnetic and Ar/Ar laboratory analysis will be made at the University of Florida. Paleointensity studies will be carried out on as many sites as possible. This study will help to fill an existing gap in the paleomagnetic database of suitable secular variation studies at equatorial latitudes. State of the art measurements during fieldwork, laboratory and data analysis will be applied in this study in order to obtain results sensitive to non-dipole contributions of the magnetic field (about 5% of the total magnetic field). This study will comply with present day selection criteria of paleomagnetic databases According to model G of secular variation, angular dispersion at the equator can be attributed solely to the quadrupole family of harmonics and not to the main dipole, thus making Ecuador a strategic point of observation of the paleomagnetic field. The agreement observed in many studies between latitudinal variations of the angular dispersion (relative to the Earth's axis of rotation) of the present field and the paleomagnetic field will be tested. This study will contribute to enhance the paleomagnetic database of lava flows which at the present moment seem to indicate, although not conclusively due to deficiencies of the database, the coincidence between longitudinal structures in the TAF of the last 5 Ma and the present field. On the other hand changes of the present field in the last two decades have lead some to suggest an on-going reversal scenario (Hulot et al., 2002) which could be hardly considered a normal state of the magnetic field. This study will undertake a much-needed secular variation study in Ecuador, following rigorous paleomagnetic techniques with excellent age control.