Geology of the Lake Roe area, Southern Fiordland New Zealand
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Abstract:
An area of approximately 14 sq. km of geology was mapped in the Lake Roe area of central Southern Fiordland.
The area of regional basement studied involved a complex association of high grade metamorphic and igneous rocks of inferred Paleozoic age.
Metasediments include quartzofeldspathic schists (frequently very rich·in quartz and pyrite.) pelitic schists and gneisses, and amphibolites. The highest grade mineral assemblages indicate the sillimanite - orthoclase isograde was reached during regional metamorphism of the Barrovian type. The schists and gneisses are invaded by concorndant lenses and apophyses of granodiorite and lesser granites. The development of migmatite i.e. lit-par-lit injection gniesses, is related to granitic intrusion during metamorphism. These lithologies in turn are cut by slightly discordant, essentially linear masses of metagabbro. Some gabbronorites retain relict olivine, spinel, and corona textures. Most have been altered to hornblende and plagioclase minerals, by the permeation of hydrous fluids during crystallisation and subsequent cooling. The eastern metagabbros display relict igneous layering. The entire sequence has been intruded by a second phase of granodiorite and granite. These rocks are observed invading the western metagabbro, and as NW-SE trending acid pegmatite dyke swarms.
The overall structure is apparently simple, with the sequence of schists, gneisses and concordant sheets of granitic rocks striking between NNW and NNE dipping moderately steeply to the west. Later gabbroic and granitic intrusion (with the exception of the acid pegmatites) follow this regional structural trend.
Petrographic description of the representative rocks types is included. An attempt was made to analyse the alkali feldspars for composition and structural state, from a variety of rock types bearing this phase. Only limited success was achieved.
Broad geologic trends in the Lake Roe area show similarities to those of the Western Manapouri - WQmot Pass area mapped by Turner in 1938.
The area of regional basement studied involved a complex association of high grade metamorphic and igneous rocks of inferred Paleozoic age.
Metasediments include quartzofeldspathic schists (frequently very rich·in quartz and pyrite.) pelitic schists and gneisses, and amphibolites. The highest grade mineral assemblages indicate the sillimanite - orthoclase isograde was reached during regional metamorphism of the Barrovian type. The schists and gneisses are invaded by concorndant lenses and apophyses of granodiorite and lesser granites. The development of migmatite i.e. lit-par-lit injection gniesses, is related to granitic intrusion during metamorphism. These lithologies in turn are cut by slightly discordant, essentially linear masses of metagabbro. Some gabbronorites retain relict olivine, spinel, and corona textures. Most have been altered to hornblende and plagioclase minerals, by the permeation of hydrous fluids during crystallisation and subsequent cooling. The eastern metagabbros display relict igneous layering. The entire sequence has been intruded by a second phase of granodiorite and granite. These rocks are observed invading the western metagabbro, and as NW-SE trending acid pegmatite dyke swarms.
The overall structure is apparently simple, with the sequence of schists, gneisses and concordant sheets of granitic rocks striking between NNW and NNE dipping moderately steeply to the west. Later gabbroic and granitic intrusion (with the exception of the acid pegmatites) follow this regional structural trend.
Petrographic description of the representative rocks types is included. An attempt was made to analyse the alkali feldspars for composition and structural state, from a variety of rock types bearing this phase. Only limited success was achieved.
Broad geologic trends in the Lake Roe area show similarities to those of the Western Manapouri - WQmot Pass area mapped by Turner in 1938.
Thesis description:
77 leaves : illus., maps (2 fold. in pocket) ; 31 cm.
Department:
OU geology Identifier:
1974Bowman
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Abstract Only
Location (WKT, WGS84):
POLYGON ((167.19177220500012 -45.685241785999949,167.190941216000056 -45.725837427999977,167.1287469560001 -45.723603975999936,167.104014948000099 -45.704087165999965,167.100240627000062 -45.683864626999934,167.145483453000111 -45.674615484999947,167.19177220500012 -45.685241785999949))
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Citation
Bowman, R. G., “Geology of the Lake Roe area, Southern Fiordland New Zealand,” Otago Geology Theses, accessed June 12, 2025, https://theses.otagogeology.org.nz/items/show/76.