HR: 0800h
AN: T41A-1166    [Abstracts]
TI: Did the Cocos-Nazca Spreading Center Form at a Transform Fault During Farallon Plate Break-Up?
AU: * Barckhausen, U
EM: udo.barckhausen@bgr.de
AF: BGR Federal Institute for Geosciences and Natural Resources, Stilleweg 2, Hannover, 30655 Germany
AU: Ranero, C R
EM: cranero@ifm-geomar.de
AF: IfM-Geomar and SFB 574, Wischhofstrasse 1-3, Kiel, 24148 Germany
AU: Weinrebe, W
EM: wweinrebe@ifm-geomar.de
AF: IfM-Geomar and SFB 574, Wischhofstrasse 1-3, Kiel, 24148 Germany
AB: The break-up of the Farallon plate was the most important event during the Early Miocene plate tectonic reorganization of the East Pacific. The opening of a new oceanic spreading center perpendicular to the existing Pacific spreading is unique and probably had far-reaching consequences for the active continental margins of Central- and South America. Most of the original fissure where the Farallon plate split into the Cocos plate and the Nazca plate has already been subducted beneath Central- and South America together with much of the oceanic crust that was formed during the early phase of Cocos-Nazca spreading. This makes a full reconstruction of plate kinematics in the area back to the time of the opening poorly constrained and leaves many questions open about the mechanisms involved and the subduction zones affected by this event. The remains of the fissure in the Cocos- and Nazca plates have been identified offshore Costa Rica and Peru, resp., where they have been investigated with geophysical methods in recent years. The 600 km long still existing segment of the fissure in the Nazca plate has recently been almost completely mapped with swath bathymetry. If the origin of the Farallon break-up was a transform fault then this structure must also be present on the Pacific plate in the area conjugate to the Farallon remains offshore Costa Rica and Ecuador. However, very few ship data were available from this area in the Central Pacific so far and at the scale of satellite altimetry no such structures were detectable. During a R/V Sonne cruise the area in question was investigated with magnetics, gravity, and swath bathymetry to fill a major gap in the framework of East Pacific plate tectonic development and to test the transform fault hypothesis. The magnetic measurements were carried out with a gradiometer and a three-component vectormagnetometer to identify the almost north-south striking seafloor spreading anomalies at low geomagnetic latitude.
DE: 8155 Plate motions--general
DE: 8164 Stresses--crust and lithosphere
DE: 3005 Geomagnetism (1550)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology and bottom photography
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting