Evidence for mid to lower crustal electrical anisotropy at the South Chilean active continental margin
Abstract
In late 2000, long period electromagnetic variation measurements have been carried out in the Chilean Southern Andes around 39°S, where the oceanic Nazca plate converges with the South American continent at a rate of approx.~6.5 mm/a. Most field stations are aligned along two profiles running from the coast to the Chilean border with Argentina, both traversing the Recent and Mio-Pliocene volcanic arc, which comprises the more than 950 km long intra-arc resp.~trench-parallel Liquiñe-Ofqui-Fault, dividing an obviously due to the subduction obliqueness (~25°) and, especially to the south, to the indentation of the Chile Ridge at lat.~46° northward moving fore-arc sliver from the continent. Below and east of the volcanic chain, isotropic 2-D modelling of magnetic and magnetotelluric transfer functions revealed conductivity anomalies of ~10 Ω m in mid to lower crustal depths, which is comparably moderate when compared with anomalies found in the Central Andes. As induction vectors are very uniformly deviated from the perpendicular to the structural axis, magnetic data seem to have clear signature of continental mid to lower crustal horizontal electrical anisotropy. The anisotropy strike is not well constrained, but clockwise oblique to the structural resp.~morphological strike, coinciding with the direction of maximum horizontal stress as deduced from the distribution of volcanic flank eruptions at nearby stratovolcanoes. One possible explanation for the proposed anisotropy are conductive magmatic dykes, oriented parallel to the direction of maximum horizontal stress and not just confined to a narrow band below the volcanic arc.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFMGP51A0986S
- Keywords:
-
- 1515 Geomagnetic induction;
- 8010 Fractures and faults;
- 8045 Role of fluids;
- 8105 Continental margins and sedimentary basins;
- 9360 South America