HR: 10:20h
AN: V41D-01 INVITED     [PDF]
TI: Thermal Evolution of the Deep Roots of a Magmatic Arc, Fiordland, New Zealand
AU: * Flowers, R M
EM: rflowers@mit.edu
AF: Massachusetts Institute of Technology, Dept of Earth, Atmospheric and Planetary Sciences, 77 Massachusetts Ave., Cambridge, MA 02139 United States
AU: Bowring, S A
EM: sbowring@mit.edu
AF: Massachusetts Institute of Technology, Dept of Earth, Atmospheric and Planetary Sciences, 77 Massachusetts Ave., Cambridge, MA 02139 United States
AU: Tulloch, A J
EM: andy.tulloch@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, Private Bag 1930, Dunedin, NZL New Zealand
AU: Klepeis, K A
EM: kklepeis@zoo.uvm.edu
AF: University of Vermont, Dept of Geology, Burlington, VT 05405 United States
AB: Reconstruction of detailed thermal profiles and histories in magmatic arcs is crucial for understanding arc development and evolution, because deformation, metamorphism, crustal melting, and a wide range of physical properties are temperature dependent. Fiordland, New Zealand contains a rare exposure of the deep roots of a Mesozoic magmatic arc, and provides an exceptional opportunity to develop high-resolution cooling histories through its middle and lower crust. The ca. 120 Ma granulite-facies Western Fiordland Orthogneiss is a $>$ 10 km thick batholith dominated by dioritic rocks. New U-Pb thermochronologic data in rocks within the upper part of the Western Fiordland Orthogneiss exposed in Doubtful Sound record post-magmatic cooling through the 650-600$\deg$C closure temperature of titanite at ca. 113 Ma. Subsequent slower cooling below 400$\deg$C is recorded by rutile from the Western Fiordland Orthogneiss at ca. 74 Ma. The upper contact of the Western Fiordland Orthogneiss is defined by the Doubtful Sound extensional shear zone, with mid-Paleozoic metasedimentary cover of the Deep Cove Gneiss of the Tuhua Sequence in the hanging wall. A calcsilicate within the Deep Cove Gneiss immediately above the shear zone yields metamorphic titanite with a U-Pb date of ca. 113 Ma. This suggests new metamorphic titanite growth during heating of the cover sequence associated with emplacement of the Western Fiordland Orthogneiss. Additional U-Pb thermochronologic data from the base of the Western Fiordland Orthogneiss will allow us to better evaluate the cooling history across the entire thickness of the batholith. The integration of these thermal histories with structural and metamorphic data through this middle and lower crustal profile will provide a unique multi-dimensional view of the evolution of this magmatic arc.
DE: 1035 Geochronology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting