New Zealand Journal of Geology and Geophysics abstracts

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Oxygen, carbon, and strontium isotopic constraints on timing and sources of crustal fluids in an active orogen: South Island, New Zealand

T. W. Horton¹
J. D. Blum²
D. Craw³
P. O. Koons⁴
C. P. Chamberlain¹*

¹Geological and Environmental Sciences Department
Stanford University
Stanford, CA, 94305, USA
email: chamb@pangea.stanford.edu

²Department of Geological Sciences
University of Michigan
425 East University Avenue
Ann Arbor, MI 48109, USA
email: jdblum@umich.edu

³Geology Department
University of Otago
P.O. Box 56, Dunedin, New Zealand
email: dave.craw@stonebow.otago.ac.nz

⁴Department of Geological Science
Bryand Global Sciences Center
University of Maine, Orono, ME 04469-5790, USA
email: Peter.Koons@maine.edu

*Corresponding author.

Abstract   Active deformation on New Zealand’s South Island can be divided into four tectonic zones: Inboard, Main Divide, Outboard, and Marlborough strike-slip. On the basis of stable isotope data (δ¹³C and δ¹⁸O) we suggest that calcite veins are formed from a mixed meteoric and metamorphic water in the Inboard and Main Divide tectonic zones, as well as the Alpine-Wairau Fault of the Marlborough strike-slip zone. We suggest that the metamorphic waters are derived from the breakdown of biotite at c. 25 km, a depth which corresponds to a conductive zone identified by a recent magnetotelluric study across central South Island. These metamorphic fluids exit the orogen along the steep faults that border the Southern Alps. ⁸⁷Sr/⁸⁶Sr ratios of vein and fault-zone calcite suggest that calcite formation is associated with young tectonically driven hydrothermal fluid flow in the Inboard, Main Divide, and Wairau Fault zones. The age of calcite formation in the Outboard, Awatere, and Hope Fault zones could not be explicitly determined.

Keywords   calcite; stable isotopes; strontium isotopes; fluid flow; New Zealand

G02026; Received 17 May 2002; accepted 19 March 2003; online publication date 10 September 2003
New Zealand Journal of Geology & Geophysics, 2003, Vol. 46: 457-471
0028-8306/03/4603-0457 $7.00/0 © The Royal Society of New Zealand 2003

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