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3D geodynamic framework of the Southern Alps

This project involved Phaedra Upton, Dave Craw, Peter Koons (University of Maine) and a number of collaborators both nationally and internationally.

The tectonically active Southern Alps of New Zealand are an ideal setting in which to study the geodynamic response of a collisional orogen to far-field tectonic boundary conditions and the extent to which rheological parameters can influence that response. A wealth of geological and geophysical data exists for the Southern Alps, enhanced by the recent SIGHT transect across the Southern Alps, which provides valuable constraints for mechanical analysis. Using three-dimensional mechanical models we have an ongoing project aimed at investigating the geodynamics of the Southern Alps orogen. In particular, we am interested in the three-dimensional nature of the orogen, which results from the obliquely convergent relative plate motion vector and from variations in the nature of the two colliding plates along strike of the plate boundary.

In conjunction with mechanical modelling, we have mapped active faults in the central eastern Southern Alps, concentrating on the Mackenzie and Rangitata/Lake Heron Basins. NE- and N-striking, oppositely dipping thrust fault pairs dominate active faulting in the region. We am interested in the style of faulting and what it can tell us about the nature of pre-existing structures, the response of the crust to the current tectonic regime and if pre-existing structure is exerting any control on the modern tectonics.

Fluids can play a significant role in how the crust responses to tectonic driving forces. Our work in the central eastern Southern Alps has shown that near-surface fluids, with a small but measurable component of deeply sourced fluid, dominate upper crustal fluid flow in this region. These fluids have been imaged by magnetotellurics by the SIGHT research group. We use this information as input into mechanical models, which investigate the influence of fluids on the geodynamics of the orogen.

Presentations

AGU 2005 – Upton and Koons Three-dimensional geodynamic modeling of the Southern Alps of New Zealand: Integrating models and observations to understand crustal rheology

AGU 2002 – Upton, Koons and Craw. Orogenic fluid flow: Coupling of deformation and fluid transport within the Central Southern Alps, New Zealand

Publications

Upton, P., Koons, P.O., Craw, D., Henderson, M., and Enlow, R. Along strike differences in the Southern Alps of New Zealand: Consequences of inherited variation in rheology. /Submitted to Tectonics/

Upton, P. and Koons, P.O. (2007) Three-dimensional geodynamic framework for the Central Southern Alps, New Zealand: Integrating geology, geophysics and mechanical observations. In: D Okaya, Stern T, Davey F
(eds) AGU volume, Geotectonic Investigation of a Modern Continent-Continent Collisional Orogen: Southern Alps, NZ

Upton, P., Craw, D., James, Z., and Koons, P.O. (2004) Structure and late Cenozoic tectonics of the Southern Two Thumb Range, mid-Canterbury, New Zealand. New Zealand Journal of Geology and Geophysics.47 , 141-153.

Upton, P., Craw, D., Caldwell, T.G., Koons, P.O. James, Z., Wannamaker, P.E., Jiracek, G.J., and Chamberlain, C.P. (2003) Upper crustal fluid flow in the outboard region of the Southern Alps, New Zealand.Geofluids,3, 1-12.

Koons, P.O., Craw, D., Cox, S., Upton, P., Templeton, A. and Chamberlain, C.P. (1998) Fluid flow during active convergence: A Southern Alps model from mechanical and geochemical observations.Geology. 26,159-162.

Upton, P. (1998) Modelling localization of deformation and fluid flow in a compressional orogen: Implications for the Southern Alps of New Zealand.American Journal of Science. 289,296-323.

Upton, P., Koons, P.O. and Chamberlain, C.P. (1995) Penetration of deformation-driven meteoric water into ductile rocks; isotopic and model observations from the Southern Alps, New Zealand.New Zealand Journal of Geology and Geophysics. 38, 535-544.