HR: 0800h
AN: T41E-1267    [Abstracts]
TI: Focused Deformation in the Lower Crust During Continental Extension: Fiordland, New Zealand
AU: * King, D S
EM: dsking@uvm.edu
AF: University of Vermont, Department of Geology Delehanty Hall, Burlington, VT 05405-1758 United States
AU: Klepeis, K A
EM: keith.klepeis@uvm.edu
AF: University of Vermont, Department of Geology Delehanty Hall, Burlington, VT 05405-1758 United States
AU: Goldstein, A
EM: agoldstein@mail.colgate.edu
AF: Colgate University, Department of Geology, Hamilton, NY 13346 United States
AU: Gehrels, G
EM: ggehrels@geo.arizona.edu
AF: University of Arizona, Department of Geosciences, Tucson, AZ 85721 United States
AU: Clarke, G L
EM: geoffc@mail.usyd.edu.au
AF: University of Sydney, School of Geosciences Division of Geology and Geophysics, Sydney, NSW 2006 Australia
AB: Lower crustal flow plays an important role in the large-scale rifting of continents, however the lack of preserved structures associated with lower crustal flow have made field studies difficult. Exposures located in Fiordland, New Zealand provide a unique opportunity to observe a portion of the lower crust that has been brought from depths of more than 40 km. These exposures contain extensional structures which formed 108 Ma during the initiation of continental rifting that led to the opening of the Tasman Sea (84 Ma). Field observations show that the upper-amphibolite facies Doubtful Sound Shear Zone (DSSZ) is a lower crustal extensional detachment that separates garnet granulites deformed at 14 kbar from calc-silicate and pelitic schists deformed at 7-9 kbar in a zone of deformation <1 km wide. Within the DSSZ strain was concentrated along an anastomosing network of shear bands. The DSSZ also appears to be part of a similar larger-scale network of shear zones which continue to higher structural levels. The DSSZ formed along the margin of a dioritic batholith which was emplaced 119-126 Ma during convergence and uplift that preceded the initiation of continental rifting. Deformation in the DSSZ is solid-state and appears to have occurred in the absence of large amounts of melt. There is no evidence for major magmatism in the region during extension. The network of shear zones is a possible mechanism for the transfer of strain to higher structural levels where core-complex-style extension was occurring simultaneously to movement on the DSSZ. These results provide information useful in creating a geometric model for behavior of the lower crust below active core complexes and in reconstructing a sequence of events that took place in the early stages of non-volcanic continental rifting.
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 8109 Continental tectonics--extensional (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 5104 Fracture and flow
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting