Presentation on theme: "Contrasting Geodynamics of Small Cold and Giant Hot Orogens C. Beaumont R. Jamieson P. Fullsack Dalhousie University, Canada B.Lee M. Nguyen Susan Ellis."— Presentation transcript:
Contrasting Geodynamics of Small Cold and Giant Hot Orogens C. Beaumont R. Jamieson P. Fullsack Dalhousie University, Canada B.Lee M. Nguyen Susan Ellis New Zealand Adrian Pfiffner University of Bern, Switzerland Institute of GEOLOGICAL & NUCLEAR SCIENCES limited
Orogen wavelength vs. convergence HT VA NZ, EA Modified from Ellis (1995)
Eastern Swiss Alps NARROW -- < 250 km moderate crustal temperatures (< 700 C) little crustal melting most intense crustal deformation intense mantle lithosphere deformation three-dimensionality generally not a first-order control on wavelength “Small Cold (SC) Orogens” New Zealand Southern Alps Wellman, 1979
high crustal temperatures and extreme crustal thickening crustal melting most intense crustal deformation most intense mantle lithosphere deformation three-dimensionality may be a first-order control on wavelength “Giant Hot (GH) Orogens” WIDE -- > 1000 km X
Extrusion of mid-lower crust (Grapes, 1995; Walcott, 1998) Batt and Braun, 1999 Felsic crust Total erosion Convergence 10mm/a 6 Ma Retro shear zone Secondary pro-shear Primary pro- shear 0 C 600 C 30 km
shortening = 40 km Vertical velocity 20 C/km geotherm 1 cm/yr Gerbault and Ellis, submitted 10 21 10 24 x
Structural Geology Transect Little et al. in press
Arthur’s Pass: Campaign data sets Beavan and Ellis, in prep.
Post-seismic signal VISCOELASTIC MODEL: Lower crustal channel =10 18 Pa s OBSERVATIONS
“Small Cold (SC) Orogens”“Giant Hot (GH) Orogens” High non-linear viscosities make extrusion less likely Inherited material heterogeneities can influence dynamics Low linear viscosities (partial melt)+erosion can cause extrusion
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