Article Volume 13, Number 1 28 January 2012 Q01018, doi:10.1029/2011GC003872 ISSN: 1525-2027 Physical properties of surface outcrop cataclastic fault rocks, Alpine Fault, New Zealand C. Boulton Department of Geological Sciences, University of Canterbury, PB 4800, Christchurch 8042, New Zealand (
[email protected]) B. M. Carpenter Department of Geosciences, Pennsylvania State University, 522 Deike Building, University Park, Pennsylvania 16802, USA V. Toy Department of Geology, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand C. Marone Department of Geosciences, Pennsylvania State University, 522 Deike Building, University Park, Pennsylvania 16802, USA [1] We present a unified analysis of physical properties of cataclastic fault rocks collected from surface exposures of the central Alpine Fault at Gaunt Creek and Waikukupa River, New Zealand. Friction experi- ments on fault gouge and intact samples of cataclasite were conducted at 30–33 MPa effective normal stress (sn′) using a double-direct shear configuration and controlled pore fluid pressure in a true triaxial pressure vessel. Samples from a scarp outcrop on the southwest bank of Gaunt Creek display (1) an increase in fault normal permeability (k=7.45 Â 10À20 m2 to k = 1.15 Â 10À16 m2), (2) a transition from frictionally weak (m = 0.44) fault gouge to frictionally strong (m = 0.50–0.55) cataclasite, (3) a change in friction rate depen- dence (a-b) from solely velocity strengthening, to velocity strengthening and weakening, and (4) an increase in the rate of frictional healing with increasing distance from the footwall fluvioglacial gravels contact. At Gaunt Creek, alteration of the primary clay minerals chlorite and illite/muscovite to smectite, kaolinite, and goethite accompanies an increase in friction coefficient (m = 0.31 to m = 0.44) and fault- perpendicular permeability (k=3.10 Â 10À20 m2 to k = 7.45 Â 10À20 m2).