New Zealand Journal of Geology and Geophysics abstracts

---

Penetration of deformation-driven meteoric water into ductile rocks: isotopic and model observations from the Southern Alps, New Zealand

PHÆDRA UPTON
PETER O. KOONS

Department of Geology
University of Otago
P.O. Box 56
Dunedin, New Zealand

C. PAGE CHAMBERLAIN

Department of Earth Science
Dartmouth College
Hanover
New Hampshire, 03755, U.S.A.

Abstract  A stable isotope laser fluorination probe was used to examine oxygen isotope zoning within foliation-parallel quartz veins of two Alpine Fault mylonite samples and two Alpine Schist samples, all of amphibolite facies. The technique used has a spatial resolution of c. 1 mm, and we found variation of d¹⁸O values within individual samples and between schist and mylonites. d¹⁸O values from individual mylonite quartz veins showed a slight variation of up to 1[[perthousand]]. By contrast, there was up to 2.4[[perthousand]] variation within veins from outside the fault zone.

Equilibrium fluid d¹⁸O values were calculated for aqueous fluids from which the quartz precipitated. The calculated values range from 5 to 13[[perthousand]]. They suggest the involvement of a near-surface fluid just beneath the brittle-ductile transition which is depleted in ¹⁸O relative to the fluid calculated to be in equilibrium with the local metamorphic assemblage.

The geochemical evidence of penetration of fluids depleted in ¹⁸O into ductile rocks constrains models of the mechanics of fluid flow. Ductile rocks are impermeable to fluids driven solely by thermal and topographic gradients. Simple numerical experiments illustrate the need for coupling of deformation and fluid flow to allow access of meteoric water into ductile material.

Keywords  stable isotopes; fluid flow; meteoric fluids; Alpine Fault mylonites; Alpine Fault; Alpine Schist; Southern Alps; deformation coupled flow; collisional orogen

New Zealand Journal of Geology and Geophysics, 1995, Vol. 38: 535-543

0028-8306/95/3804-0535 $2.50/0 (c) The Royal Society of New Zealand 1995

PDF file of entire paper: medium quality (1396K); (scanned from paper original: notes about this process)

---

This year's abstracts | Journal home page | All abstracts | Publishing home page