Magnetotelluric Evidence for Mid-Crustal Fluids in an Active Transpressive Continental Orogen, South Island, New Zealand
Abstract
Forty-two magnetotelluric (MT) soundings acquired across the tectonically active South Island, New Zealand revealed a distinct, mid-crustal conductivity anomaly beneath the Southern Alps. Conductive pathways link the mid-crustal conductor to the surface near prominent faults, such as the Alpine Fault, where large-scale exhumation occurs. Aqueous fluids released during prograde metamorphism in the thickening crustal root of the transpressive continental orogen are believed to be the source of the mid-crustal conductor. Interconnected fluids, which may be less than 1 percent saline, augmented by shear deformation, would result in high conductivities. Hence, high conductivities along tectonic strike (anisotropy), as observed in the Alpine Fault zone, imply greater fluid interconnectivity due to increased deformation rates along strike. Fluids ascending across the brittle-ductile transition during exhumation would migrate through hydrofractures producing shallow, hydrothermal veining and gold mineralization. Two-dimensional inversion and sensitivity testing of the MT data validated the mid-crustal conductor and conductive pathways confirming the legitimacy of fluid interconnection, ascension, and subsequent gold mineralization. Therefore, MT successfully imaged the source and migration pathways of gold-bearing fluids from as deep as 20 km in the crust.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFMGP12B..05G
- Keywords:
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- 0910 Data processing;
- 1744 Tectonophysics;
- 8102 Continental contractional orogenic belts