HR: 09:00h
AN: T31E-05    [Abstracts]
TI: The Possible Role of Mantle Instabilities in Initiating Back-Arc Spreading
AU: Stern, T
EM: tim.stern@vuw.ac.nz
AF: Institute of Geophysics, Victoria University of Wellington, P.O. Box 600, Wellington, 6012, New Zealand
AU: Salmon, M
EM: michelle.salmon@vuw.ac.nz
AF: Institute of Geophysics, Victoria University of Wellington, P.O. Box 600, Wellington, 6012, New Zealand
AU: Salmon, M
EM: michelle.salmon@vuw.ac.nz
AF: RSES, ANU, Canberra, 0200, Australia
AU: Stratford, W
EM: ws@geol.ku.dk
AF: Dept of Geology, University of Copenhagen, Copenhagen, 1350, Denmark
AU: Seward, A
EM: anya.seward@vuw.ac.nz
AF: Institute of Geophysics, Victoria University of Wellington, P.O. Box 600, Wellington, 6012, New Zealand
AU: * Smith, E
EM: euan.smith@vuw.ac.nz
AF: Institute of Geophysics, Victoria University of Wellington, P.O. Box 600, Wellington, 6012, New Zealand
AU: Henderson, M
EM: mark.henderson@vuw.ac.nz
AF: Institute of Geophysics, Victoria University of Wellington, P.O. Box 600, Wellington, 6012, New Zealand
AU: Ewig, E
EM: erik.ewig@vuw.ac.nz
AF: Institute of Geophysics, Victoria University of Wellington, P.O. Box 600, Wellington, 6012, New Zealand
AU: Savage, M
EM: martha.savage@vuw.ac.nz
AF: Institute of Geophysics, Victoria University of Wellington, P.O. Box 600, Wellington, 6012, New Zealand
AU: Greve, S
EM: sonja.greve@vuw.ac.nz
AF: Institute of Geophysics, Victoria University of Wellington, P.O. Box 600, Wellington, 6012, New Zealand
AB: Back-arc extension and spreading has been splitting apart the central North Island of New Zealand since the Pliocene. But the impressive volcanism and geothermal activity linked to this extension belies the extensive period of compression, and thrusting that dominated the pre-Pliocene tectonics of the central North Island. Up to 100 km of Oligocene-Miocene shortening is estimated from both deep seismic lines and plate reconstructions beneath the western North Island. Crustal uplift, erosion and sedimentary deposition easily account for the removal of the shortened crust during this time. Yet, the consequences of shortening ~ 100 km of mantle lithosphere are not so obvious. We present a series of seemingly disparate geophysical and geological observations that appear to be most easily explained by thickening of the mantle lithosphere and its ultimate disposal by viscous flow and detachment. These observations include: 1. Parallel zones of late Miocene extension and volcanism that developed each side of the central region of compression; 2. A rapid, domal, surface-uplift of ~1 km for western and central North Island that is dated at ~ 5 Ma and is over a region 200 by 200 km in extent; 3. Low Pn and Sn wave-speeds indicating the mantle lithosphere is missing; 4. Lack of Pn and SKS anisotropy in the western North Island despite anisotropy being pervasive elsewhere in New Zealand; 5. Unusually thin crust (~ 25 km) over much of the western North Island; 6. High-K volcanism over the western North Island during the Pliocene. 7. 600 km deep earthquakes beneath the western North Island. Any one of these 7 observations could be explained by the plate tectonic paradigm. It is, however, the explanation of all 7 observations by a single process that makes the concept of convective removal of thickened mantle lithosphere so compelling. If correct, the late-Miocene removal of the thickened mantle lithosphere was a possible kick-start mechanism for consequent Pliocene back-arc extension and spreading within the central North Island.
DE: 8104 Continental margins: convergent
DE: 8108 Continental tectonics: compressional
DE: 8109 Continental tectonics: extensional (0905)
DE: 8110 Continental tectonics: general (0905)
DE: 8162 Rheology: mantle (8033)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting