HR: 09:45h
AN: V41A-08    [PDF]
TI: Transient Dilatancy in the Transport of Magma and Flareup Magmatic Events
AU: * Johnson, S E
EM: johnsons@maine.edu
AF: University of Maine, Department of Earth Sciences, Orono, ME 04469 United States
AU: Koons, P O
EM: peter.koons@maine.edu
AF: University of Maine, Department of Earth Sciences, Orono, ME 04469 United States
AU: Upton, P
EM: phaedra.upton@maine.edu
AF: University of Maine, Department of Earth Sciences, Orono, ME 04469 United States
AB: Migmatite belts around the world show features that have led workers to conclude that melts move into strain heterogeneities such as boudin necks and shear zones. The inference generally made is that these are transient sites of relatively low pressure. In the Main Martir Thrust zone of the Peninsular Ranges batholith, synkinematic migmatites formed in a kinematically well-constrained setting. Melt layers on the thrust zone occupy shear bands and are connected across short jogs at a high angle to the thrust-zone boundaries. This geometry is analogous to dilatant jogs that form between interacting brittle cracks. The formation of these features at elevated T suggests that elevated strain rates, elevated magma pressures, or both played an important role in embrittlement. Magmatic arcs are commonly long-lived, but their construction is apparently dominated by a limited number of transient magmatic events. In the Peninsular Ranges batholith, approximately 50% of the exposed arc was emplaced between 99 and 92 Ma, leading to production rates on the order of 75-100 km*3/km/m.y. Several different explanations have been proposed for such transient flareup events, and here we explore, in 3-D, the implications of crustal-scale dilatancy to magma formation and transport processes during lithospheric subduction, using the North Island of New Zealand as a modern analog.
DE: 1206 Crustal movements--interplate (8155)
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 1744 Tectonophysics
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting