Crustal structure of Fiordland, New Zealand |
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| Authors: | GJH Oliver JH Coggon |
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| Abstract: | A generalised crustal structure of Fiordland is proposed.Detailed mapping in part of Western Fiordland has led to the recognition of a basement granulite facies lower crustal material, probably Precambrian in age) separated by a regional thrust zone from a cover sequence (amphibolite facies gneisses, of Lower Paleozoic age). With the recognition of the basement—cover relationship and the aid of aeromagnetic anomalies Fiordland has been divided into four, generally north-northeast trending, regions. The Western Fiordland region is composed chiefly of basement rocks. The Central Fiordland and Southwestern Fiordland regions are made up predominantly of amphibolite and greenschist-facies metasediments and gneissic granodiorites of the cover sequence, which in Central Fiordland have a regional dip to the east, off the basement. The Eastern Fiordland region is characterised by a series of basic, intermediate and acid intrusive rocks. The more prominent magnetic anomalies in Eastern Fiordland, Southwestern Fiordland, and a large anomaly off the coast of Western Fiordland, are all considered to be caused by intrusive bodies. The presence of a positive gravity anomaly over Western Fiordland, coupled with a gravity low offshore, is consistent with the lower crust being uplifted and exposed in this area. Continuing shallow and intermediate-depth seismic activity beneath Fiordland, as well as the large size of the gravity anomaly, suggest that tectonic forces are currently acting to maintain Western Fiordland at its unusually high level.Fiordland thus displays a cross-section of continental crust: Precambrian(?) metaigneous granulites in the lower crust; Lower Paleozoic metasedimentary amphibolitefacies gneisses and melted equivalents in the middle crust; Mesozoic intrusives, and overlying Cretaceous and Tertiary sediments in the upper crust. |
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