New Zealand Journal of Geology & Geophysics abstracts
Early Cretaceous dextral transpressional deformation within the
Median Batholith, Stewart Island, New Zealand
A. H. Allibone
Rodinian Pty Ltd
PO Box 1970
Queanbeyan, NSW 2620, Australia
rodinian@msn.com
A. J. Tulloch
GNS Science
Private Bag 1930
Dunedin 9054, New Zealand
a.tulloch@gns.cri.nz
Abstract The character, timing, and
significance of
deformation within the Median Batholith has been debated since at least
1967, with allochthonous and autochthonous models proposed to account
for internal variations in the character of the batholith. Stewart
Island provides excellent exposures of intrabatholithic structures,
allowing many aspects of the deformation history within the batholith
to be analysed, far removed from the effects of later deformation
related to the current plate boundary.
Median Batholith rocks in northern and
central Stewart Island are deformed by three major structures: the
Freshwater Fault System, Escarpment Fault, and Gutter Shear Zone.
Lineation orientations, Al in hornblende geobarometry, and Ar-Ar
thermochronology indicate up to c. 7 km of NNE-directed uplift of
the hanging wall of the Escarpment Fault between c. 110 and 105
Ma. Unlike the Escarpment Fault, a wide range of mineral elongation
lineation orientations, including many oblique to the strike and dip of
related foliations, characterise both the Gutter Shear Zone and
Freshwater Fault System. Lineation and limited sense of shear data
indicate dextral-reverse movement on both structures during development
of their dominant ductile fabrics. Crosscutting and intrusive
relationships indicate movement on the Freshwater Fault System after
c. 130 Ma and on the Gutter Shear Zone between 120 and 112 Ma. The
amount of movement on the Freshwater Fault System and Gutter Shear Zone
remains largely unconstrained. However, the 342 ± 24 Ma age of a
granite clast in a Paterson Group lithic tuff horizon at Abrahams Bay
overlaps that of Carboniferous plutons in the block immediately south
of the Freshwater Fault System, implying that the Paterson Group is
little displaced from the basement rocks through which it was erupted.
The three structures mapped on Stewart
Island form part of a narrow transpressional mobile belt active within
the Jurassic–Cretaceous arc on the outboard margin of the Western
Province during the later stages of arc development between c. 125
and 105 Ma. Deformation is largely confined to the area outboard of the
Paleozoic metasedimentary basement in southern Stewart Island. In
central Stewart Island, transpressional deformation began on the broad
amphibolite facies Gutter Shear Zone. Subsequent deformation was
focused along the narrower Escarpment Fault, which offset the
c. 300°C isotherm in the upper crust. All three structures on
Stewart Island likely form part of a regional-scale network of
transpressional shear zones and faults that includes the Indecision
Creek and Grebe Shear Zones in eastern Fiordland. Transpressional
deformation along these structures broadly coincided with loading of
the Western Fiordland Orthogneiss in northern Fiordland by c. 6
kbar, indicating that contractional deformation affected all levels of
the crust at this time.
Keywords Stewart Island; Gutter Shear Zone;
Escarpment Fault;
Freshwater Fault System; Median Batholith; Median Tectonic Zone;
Western Province; transpression; lineation
G07028; Online publication date 8 May 2008; Received 26 November
2007; accepted 31 March 2008
New Zealand Journal of Geology & Geophysics, 2008, Vol. 51:
115–134
0028–8306/08/5102–0115 © The Royal Society of New Zealand 2008
PDF file of entire paper: Print-quality
(5853K) | screen-quality (4093K)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
