HR: 0800h
AN: GP11A-0012    [Abstracts]
TI: Reorganization Of Magnetic Carriers Due To Pressure-Solution, A New Remagnetization Mechanism From The Southwestern Pyrenees
AU: * Oliva-Urcia, B
EM: boliva@umich.edu
AF: Universidad de Zaragoza, Pedro Cerbuna s/n, Zaragoza, 50009 Spain
AU: * Oliva-Urcia, B
EM: boliva@umich.edu
AF: University of Michigan, 1100 N. University Ave., Ann Arbor, MI 48109 United States
AU: Pueyo, E L
EM: unaim@unizar.es
AF: Universidad de Zaragoza, Pedro Cerbuna s/n, Zaragoza, 50009 Spain
AU: Pueyo, E L
EM: unaim@unizar.es
AF: Unidad de GeologĦa y GeofĦsica. IGME, Fernando el Cat˘lico 47, 4C, Zaragoza, 50009 Spain
AU: Larrasoa¤a, J C
EM: jclarra@unizar.es
AF: Universidad de Zaragoza, Pedro Cerbuna s/n, Zaragoza, 50009 Spain
AB: The ultimate cause of widespread remagnetizations remains elusive. Mechanisms such as orogenic fluids, burial diagenesis dolomitization, dedolomitization, maturation of organic matter, migration of hydrocarbons and thermal metamorphism can also account for widespread remagnetizations, but only under specific geochemical scenarios that do not apply to many widespread remagnetizations. Paleomagnetic analyses in the South Pyrenean Zone in Spain, show the presence of a widespread remagnetization in the Internal Sierras, the southern border of the Axial Zone and the northern part of the Jaca-Pamplona basin. This remagnetization component has always a reverse polarity, was acquired after folding and affects Triassic red beds, Upper Cretaceous carbonatic rocks and Tertiary turbidites. The areal distribution of the remagnetization coincides with a domain of pressure-solution cleavage, outside of the cleavage domain there is not such a secondary component. This circumstance together with the apparent correlation between the intensity of the remagnetization and the density of cleavage planes lead us to propose a new, and alternative remagnetization mechanism that can explain widespread remagnetizations in orogens. The mechanism that produces the new orientation of magnetic minerals is related to the evolution of the orogenic wedge when the highest tectonic load produces an extensive cleavage domain in the core of the Western Pyrenees. Formation of pressure-solution cleavage planes drives the partial dissolution of the matrix allowing the ferromagnetic minerals (less soluble and heavier) to reorient freely in the presence of the ambient magnetic field. We are aware of other studies reporting remagnetizations in relation of cleavage formation. The appeal of our new mechanism is that it does not necessarily involve the dissolution or neoformation of magnetic minerals, as typically assumed regardless of clear evidence, but rather reorganization of preexisting magnetic grains, although chemical rearrangements can also occur . Further analysis aiming at quantitative estimation of cleavage development and remagnetization intensity together with SEM observations, are necessary to confirm this new mechanism.
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1533 Remagnetization
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005