HR: 14:40h
AN: GP23B-05 INVITED     [Abstracts]
TI: AMS of an Analogue Non-Scale Model Simulating Diapiric Pluton Emplacement
AU: * Hrouda, F
EM: fhrouda@agico.cz
AF: AGICO Inc., Jecna 29a, Brno, 621 00 Czech Republic
AU: * Hrouda, F
EM: fhrouda@agico.cz
AF: Institute of Petrology and Structural Geology, Albertov 6, Prague, 128 43 Czech Republic
AU: Kratinova, Z
EM: zkrat@natur.cuni,cz
AF: Institute of Petrology and Structural Geology, Albertov 6, Prague, 128 43 Czech Republic
AU: Zavada, P
EM: prokox@seznam.cz
AF: Institute of Petrology and Structural Geology, Albertov 6, Prague, 128 43 Czech Republic
AU: Schulmann, K
EM: schulman@illite.u-strasbg.fr
AF: Universite Louis Pasteur Strasbourg I., 5, rue Descartes, Strasbourg, 67084 France
AB: Development of magnetic fabric within a pluton during its diapiric ascent was investigated using an analogue non-scale model of plaster of Paris containing small amount of fine-grained (less than 0.09 mm) homogeneously mixed magnetite, with resulting bulk susceptibility being in the order of 10-3 [SI]. The apparatus for this modelling consists of a manual squeezer with calibrated spring and a perspex container. Stratified coloured to visualize internal flow geometries, weak plaster layer at the bottom of the container was forced to intrude overlying fine-grained (>0.017mm) sand through a hole in a board attached to the squeezer. A retarding compound was admixed into the plaster to postpone the solidification of plaster. After solidifying the model, small oriented cylindrical specimens (7 mm in diameter and 6 mm in height) were drilled and their anisotropy of magnetic susceptibility (AMS) was measured with the KLY-4S Kappabridge. The magnetic fabric in the margins of the vertical column of the diapir is characterized by high degree of AMS (P'=1.26-1.30), neutral to oblate AMS ellipsoid (T=0.2-0.6) and vertical magnetic lineations and foliations. In the vent area, the degree of AMS is also high, but the AMS ellipsoid being strongly prolate (T= -1 to -0.8) with vertical magnetic lineations. In the interior of the plug above the vent zone, abrupt transition into horizontal lineations and foliations take place and the low degree of AMS (P'=1.05-1.10) marks the area where strongly prolate magnetic fabric is being gradually changed into the magnetic fabric characterized by neutral to oblate AMS ellipsoid. This type of magnetic fabric extends to the apical part of the body. In the extrusive portions of the diapir, oblate magnetic fabric increases in anisotropy (T=0.8-1, P'=1.26-1.29), while the front of the radial extrusion shows horizontal lineations parallel to the margin and neutral AMS ellipsoids (T=0.2-0.6,P'=1.23-1.26). This changeover of fabric thus indicates divergent flow in the radial extrusion. The development of AMS fabric is correlated with complex flow pattern indicated by coloured and originally horizontal plaster layers. Narrow shear zones in the margins of the plug indicate non-linear behavior of plaster during experiments.
DE: 1518 Magnetic fabrics and anisotropy
DE: 1519 Magnetic mineralogy and petrology
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting