HR: 1340h
AN: V23A-0680    [Abstracts]
TI: 3D Visualization of "Frozen" Dynamic Magma Chambers in the Duluth Complex, Northeastern Minnesota
AU: * Peterson, D M
EM: dpeters1@nrri.umn.edu
AF: Natural Resources Research Institute, University of Minnesota, Duluth 5013 Miller Trunk Highway, Duluth, MN 55811-1442 United States
AU: Hauck, S A
EM: shauck@nrri.umn.edu
AF: Natural Resources Research Institute, University of Minnesota, Duluth 5013 Miller Trunk Highway, Duluth, MN 55811-1442 United States
AB: The Mesoproterozoic Duluth Complex and associated intrusions of the Midcontinent Rift in northeastern Minnesota constitute one of the largest, semi-continuous, mafic intrusive complexes in the world, second only to the Bushveld Complex of South Africa. These rocks cover an arcuate area of over 5,000 square kilometers and give rise to two strong gravity anomalies (+50 & +70 mgal) that imply intrusive roots to more than 13 km depth. The geometry of three large mafic intrusions within the Duluth Complex have been modeled by the integration of field mapping and drill hole data with maps of gravity and magnetic anomalies. The igneous bodies include the South Kawishiwi, Partridge River, and Bald Eagle intrusions that collectively outcrop over an area of > 800 square kilometers. The South Kawishiwi and Partridge River intrusions host several billion tons of low-grade Cu-Ni-PGE mineralization near their base, while the geophysical expressions of the Bald Eagle intrusion have the same shape and dimensions as the "bulls eye" pattern of low velocity seismic reflection anomalies along the East Pacific Rise. These anomalies are interpreted to define regions of melt concentrations, i.e., active magma chambers. This suggests that the funnel-shaped Bald Eagle intrusion could be an example of a "frozen" dynamic magma chamber. In support of this analogy we note that the magmatic systems of intracontinental rifts, mid-ocean ridges, extensional regimes in back-arc environments, and ophiolites have a common characteristic: the emplacement of magma in extensional environments, and the common products in all four are varieties of layered intrusions, dikes and sills, and overlying volcanic rocks. 3D visualization of these intrusions is integral to the understanding of the Duluth Complex magmatic system and associated mineralization, and can be used as a proxy for study of similar systems, such as the Antarctic Ferrar dolerites, worldwide.
DE: 3618 Magma chamber processes (1036)
DE: 3642 Intrusive structures and rocks
DE: 3665 Mineral occurrences and deposits
DE: 8109 Continental tectonics: extensional (0905)
DE: 8434 Magma migration and fragmentation
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005