HR: 15:30h
AN: V53D-08    [Abstracts]
TI: Magmatic Processes and Emplacement Dynamics in Layered Mafic Intrusions: Insights From Magnetic Fabric Studies
AU: * Maes, S M
EM: maess@strose.edu
AF: Department of Physical and Biological Sciences, The College of Saint Rose, 432 Western Avenue, Albany, NY 12203, United States
AU: Ferré, E C
EM: eferre@geo.siu.edu
AF: Department of Geology, Southern Illinois University-Carbondale, Carbondale, IL 62901, United States
AU: Tikoff, B
EM: basil@geology.wisc.edu
AF: Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706, United States
AB: This study focuses on documentation of magmatic structures and constraining emplacement dynamics, using new developments in rock magnetism, in two layered mafic intrusions: Insizwa sill (South Africa) and the Sonju Lake intrusion (Minnesota). Magnetic susceptibility tracks subtle variations in magnetic mineral content and is used to distinguish between open and closed magmatic systems, which are expected to yield distinct magnetic patterns. AMS measurements provide petrofabric data, used to constrain the dynamics of magma emplacement and to distinguish between flow and static layering processes. The mafic systems examined include an open system in which multiple pulses of magma most certainly occurred and an almost completely closed system. The Insizwa sill, an open magmatic system, is part of the Mesozoic Karoo Igneous Province in South Africa. Continuous borehole core logging of magnetic susceptibility and the anisotropy of magnetic susceptibility (AMS) confirms that variation in the prominent vertical zonation of magnetic properties generally correspond to petrologically and geochemically determined layers. Magnetic properties also document the lateral continuity of recognizable petrologic layers, and corroborate earlier suggestions that the sill formed by multiple pulses of magma. The Sonju Lake intrusion, an almost completely closed system, is part of the Proterozoic Midcontinent Rift System, NE Minnesota. The observed upward increasing magnetic susceptibility trend suggests construction of a simple sill by a single magma pulse. A petrofabric study investigated the emplacement and flow patterns within the Sonju Lake intrusion. The magnetic fabrics documented in the layered series of the intrusion are consistent with sub-horizontal to inclined emplacement and show evidence that the cumulate layers were deposited in a dynamic environment. By integrating aspects of petrology, geochemistry, and rock magnetism, a better understanding of layered mafic intrusions is achieved. Magnetic properties provide additional insight into magmatic processes and magma transfer, and may be used to distinguish between open and closed system magmatic systems.
DE: 1518 Magnetic fabrics and anisotropy
DE: 1519 Magnetic mineralogy and petrology
DE: 3618 Magma chamber processes (1036)
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting