Cretaceous metamorphic core complexes in the Otago Schist, New Zealand
The median antiformal axis of the Otago Schist, New Zealand, is marked by a zone of relatively high-grade (up to garnet-blotite-albite) greenschist facies rocks. 40Ar/39Ar geochronology has been carried out in conjunction with structural analysis in regions distant from the effects of the Alpine Fau...
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2015
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ftanucanberra:oai:digitalcollections.anu.edu.au:1885/34765 2023-05-15T13:57:36+02:00 Cretaceous metamorphic core complexes in the Otago Schist, New Zealand Forster, Margaret Lister, Gordon 2015-12-08T22:33:38Z http://hdl.handle.net/1885/34765 unknown Blackwell Publishing Ltd 0812-0099 http://hdl.handle.net/1885/34765 Australian Journal of Earth Sciences Keywords: argon-argon dating continental breakup Cretaceous Gondwana greenschist facies metamorphism structural geology New Zealand Argon-argon dating Continent breakup Geochronology Metamorphic core complexes New Zealand Otago Schist Journal article 2015 ftanucanberra 2015-12-28T23:24:41Z The median antiformal axis of the Otago Schist, New Zealand, is marked by a zone of relatively high-grade (up to garnet-blotite-albite) greenschist facies rocks. 40Ar/39Ar geochronology has been carried out in conjunction with structural analysis in regions distant from the effects of the Alpine Fault to determine the origin of this metamorphic welt. We have determined that the metamorphic welt is bounded on its northern and southern sides by multistage ductile shear zone(s) marked by intensely developed fabrics, and/or low-angle normal faults. These structures extend over a strike length of >∼200 km and on the southern side of the metamorphic welt they mark the boundary between the Caples and the Torlesse terranes. The oldest such shear zone formed between 122 and 118 Ma. The metamorphic welt was exhumed beneath low-angle normal faults and ductile shear zones that formed from 112 to 109 Ma. The shear zones form the carapace to elongate domal culminations in the central Otago Schist. These geomorphological features are Cretaceous metamorphic core complexes dissected by younger Quaternary faults. Exhumation of the shear zones occurred shortly before volcanogenic sediments began to deposit on a Cretaceous unconformity. We propose that both the Cretaceous unconformity and the underlying ductile shear zones and low-angle faults are a direct result of extensional tectonism. The ductile shear zones display both 'cross-belt' and 'belt-parallel' stretching lineations. Cross-belt stretching may have been caused by rollback of the subducting Pacific slab. Belt parallel extension is interpreted to have taken place during extension associated with rifting between Australia and Antarctica, prior to breakup. Article in Journal/Newspaper Antarc* Antarctica Australian National University: ANU Digital Collections New Zealand Pacific |
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Open Polar |
collection |
Australian National University: ANU Digital Collections |
op_collection_id |
ftanucanberra |
language |
unknown |
topic |
Keywords: argon-argon dating continental breakup Cretaceous Gondwana greenschist facies metamorphism structural geology New Zealand Argon-argon dating Continent breakup Geochronology Metamorphic core complexes New Zealand Otago Schist |
spellingShingle |
Keywords: argon-argon dating continental breakup Cretaceous Gondwana greenschist facies metamorphism structural geology New Zealand Argon-argon dating Continent breakup Geochronology Metamorphic core complexes New Zealand Otago Schist Forster, Margaret Lister, Gordon Cretaceous metamorphic core complexes in the Otago Schist, New Zealand |
topic_facet |
Keywords: argon-argon dating continental breakup Cretaceous Gondwana greenschist facies metamorphism structural geology New Zealand Argon-argon dating Continent breakup Geochronology Metamorphic core complexes New Zealand Otago Schist |
description |
The median antiformal axis of the Otago Schist, New Zealand, is marked by a zone of relatively high-grade (up to garnet-blotite-albite) greenschist facies rocks. 40Ar/39Ar geochronology has been carried out in conjunction with structural analysis in regions distant from the effects of the Alpine Fault to determine the origin of this metamorphic welt. We have determined that the metamorphic welt is bounded on its northern and southern sides by multistage ductile shear zone(s) marked by intensely developed fabrics, and/or low-angle normal faults. These structures extend over a strike length of >∼200 km and on the southern side of the metamorphic welt they mark the boundary between the Caples and the Torlesse terranes. The oldest such shear zone formed between 122 and 118 Ma. The metamorphic welt was exhumed beneath low-angle normal faults and ductile shear zones that formed from 112 to 109 Ma. The shear zones form the carapace to elongate domal culminations in the central Otago Schist. These geomorphological features are Cretaceous metamorphic core complexes dissected by younger Quaternary faults. Exhumation of the shear zones occurred shortly before volcanogenic sediments began to deposit on a Cretaceous unconformity. We propose that both the Cretaceous unconformity and the underlying ductile shear zones and low-angle faults are a direct result of extensional tectonism. The ductile shear zones display both 'cross-belt' and 'belt-parallel' stretching lineations. Cross-belt stretching may have been caused by rollback of the subducting Pacific slab. Belt parallel extension is interpreted to have taken place during extension associated with rifting between Australia and Antarctica, prior to breakup. |
format |
Article in Journal/Newspaper |
author |
Forster, Margaret Lister, Gordon |
author_facet |
Forster, Margaret Lister, Gordon |
author_sort |
Forster, Margaret |
title |
Cretaceous metamorphic core complexes in the Otago Schist, New Zealand |
title_short |
Cretaceous metamorphic core complexes in the Otago Schist, New Zealand |
title_full |
Cretaceous metamorphic core complexes in the Otago Schist, New Zealand |
title_fullStr |
Cretaceous metamorphic core complexes in the Otago Schist, New Zealand |
title_full_unstemmed |
Cretaceous metamorphic core complexes in the Otago Schist, New Zealand |
title_sort |
cretaceous metamorphic core complexes in the otago schist, new zealand |
publisher |
Blackwell Publishing Ltd |
publishDate |
2015 |
url |
http://hdl.handle.net/1885/34765 |
geographic |
New Zealand Pacific |
geographic_facet |
New Zealand Pacific |
genre |
Antarc* Antarctica |
genre_facet |
Antarc* Antarctica |
op_source |
Australian Journal of Earth Sciences |
op_relation |
0812-0099 http://hdl.handle.net/1885/34765 |
_version_ |
1766265306884341760 |