Dynamic metamorphism within the Rakeahua batholith, Mason and Doughboy Bay region, Stewart Island
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Abstract:
A reconnaissance geological map at 1:25 000 is presented for a previously unmapped Mason-Doughboy Bay area on the west coast of Stewart Island. Five granitoid plutons with faulted and intrusive contacts within the Rakeahua Batholith have been identified.
The Walkers Hill Fault (new name) separates the Hellfire granitoid complex (Allibone, 1986) to the north from the Mason-Doughqoy suite (this study) to the south.
The Mason-Doughboy suite consists of four plutons and the Gutter High Strain Zone (new name). The youngest pluton is the Adams Hill Leucogranite (new name) which intrudes the other three, Doughboy Bay Granodiorite (new name), Ernest Island Diorite (new name) and the oldest, Walkers Hill Diorite (new name).
The Mason Bay Granodiorite (Allibone, 1987 and this study) to the north of the Walkers Hill Fault is younger than the post-emplacement tectonism, overprinted in the Mason-Doughboy suite.
The Mason Bay Granodiorite is in faulted contact with the Walkers Hill Diorite. The Adams Hill Leucogranite forms an intrusion breccia with both the Walkers Hill Diorite and Doughboy Bay Granodiorite. Adams Hill Leucogranite dykes, also intrude the Doughboy Bay Granodiorite. Intrusive contacts between the Ernest Island Diorite and the Adams Hill Leucogranite are complex, and concurrently folded within the Gutter High Strain Zone. Major and trace element chemistry of the five plutons indicates I-type affinities, but suggests S-type character for granite tectonites from the Gutter High Strain Zone.
The Gutter High Strain Zone is a localised narrow zone of predominantly ductile deformation, 1-2km wide. Development of the zone was accompanied by dynamic metamorphism, associated with movement, to greenschist facies conditions.
A progressive sequence of granite - granite tectonites - mylonites, and calc-silicate metasediment, garnet quartzites and amphibolites are found within the Gutter High Strain Zone. The zone has regionally inferred significance.
Syn-posttectonic deformation of the Gutter High Strain Zone is synchronous with post-emplacement tectonism of the Mason-Doughboy suite, these events are older than the Walkers Hill Fault. It is unclear if the intrusion of the Adams Hill Leucogranite is cause or symptomatic of the Gutter High Strain Zone, but is syn-posttectonic.
Magmatic Cu-sulphide textures in globules from host Adams Hill Leucogranite dykes indicate immiscibile melts.
Possible meteorite impact crater features proposed by Bishop et al. (1987 an unpublished preliminary report) are equally explained by natural geological and geomorphological phenomena. There were no 'potential' economic resources discovered in the field.
The Walkers Hill Fault (new name) separates the Hellfire granitoid complex (Allibone, 1986) to the north from the Mason-Doughqoy suite (this study) to the south.
The Mason-Doughboy suite consists of four plutons and the Gutter High Strain Zone (new name). The youngest pluton is the Adams Hill Leucogranite (new name) which intrudes the other three, Doughboy Bay Granodiorite (new name), Ernest Island Diorite (new name) and the oldest, Walkers Hill Diorite (new name).
The Mason Bay Granodiorite (Allibone, 1987 and this study) to the north of the Walkers Hill Fault is younger than the post-emplacement tectonism, overprinted in the Mason-Doughboy suite.
The Mason Bay Granodiorite is in faulted contact with the Walkers Hill Diorite. The Adams Hill Leucogranite forms an intrusion breccia with both the Walkers Hill Diorite and Doughboy Bay Granodiorite. Adams Hill Leucogranite dykes, also intrude the Doughboy Bay Granodiorite. Intrusive contacts between the Ernest Island Diorite and the Adams Hill Leucogranite are complex, and concurrently folded within the Gutter High Strain Zone. Major and trace element chemistry of the five plutons indicates I-type affinities, but suggests S-type character for granite tectonites from the Gutter High Strain Zone.
The Gutter High Strain Zone is a localised narrow zone of predominantly ductile deformation, 1-2km wide. Development of the zone was accompanied by dynamic metamorphism, associated with movement, to greenschist facies conditions.
A progressive sequence of granite - granite tectonites - mylonites, and calc-silicate metasediment, garnet quartzites and amphibolites are found within the Gutter High Strain Zone. The zone has regionally inferred significance.
Syn-posttectonic deformation of the Gutter High Strain Zone is synchronous with post-emplacement tectonism of the Mason-Doughboy suite, these events are older than the Walkers Hill Fault. It is unclear if the intrusion of the Adams Hill Leucogranite is cause or symptomatic of the Gutter High Strain Zone, but is syn-posttectonic.
Magmatic Cu-sulphide textures in globules from host Adams Hill Leucogranite dykes indicate immiscibile melts.
Possible meteorite impact crater features proposed by Bishop et al. (1987 an unpublished preliminary report) are equally explained by natural geological and geomorphological phenomena. There were no 'potential' economic resources discovered in the field.
Thesis description:
86 leaves : ill. (some col.), maps (some col.) ; 31 cm.
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1988Peden
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POLYGON ((167.801917249000098 -46.933524157999955,167.800935740000114 -46.944838614999981,167.800200876000076 -46.953635467999959,167.757773444000122 -46.97920875799997,167.74404663100006 -46.987474919999954,167.737165038000057 -47.059346132999963,167.684472425000081 -47.056991516999972,167.68622090000008 -47.039149046999967,167.654595123000036 -47.037868405999973,167.659993271000076 -46.980791361999934,167.66394725400005 -46.938901808999958,167.664261219000082 -46.935886950999986,167.716260213000055 -46.938373871999943,167.735494164000102 -46.939287499999978,167.737441125000032 -46.91970459099997,167.753742014000068 -46.920364261999964,167.802886674000092 -46.92233534099995,167.802061597000034 -46.931862915999943,167.801917249000098 -46.933524157999955))
Collection
Citation
Peden, Ross, 1961-, “Dynamic metamorphism within the Rakeahua batholith, Mason and Doughboy Bay region, Stewart Island ,” Otago Geology Theses, accessed February 13, 2025, https://theses.otagogeology.org.nz/items/show/223.