New Zealand Journal of Geology and Geophysics abstracts
Contrasting structural styles during polyphase granitoid intrusion,
South Victoria Land, Antarctica
SARAH JONES
Geology Department
University of Otago
P.O. Box 56
Dunedin, New Zealand
Abstract Four granitoid plutons intruded in the Walcott Bay
area, South Victoria Land, during the Paleozoic Ross Orogeny, display markedly
different structural styles. Bonney Pluton is a variably megacrystic
hornblende-biotite granite batholith which outcrops over an area of
1000 km2. The southern end of the body is located in the
Walcott Bay area, and it is the oldest of the four granitoid bodies
(530-520 Ma). The pluton synkinematically intruded Koettlitz Group
metasediments under mid-upper amphibolite facies conditions (700deg.C,
5 +/- 1 bars). Bonney Pluton fabrics are highly variable, with
weak magmatic fabrics in the pluton centre grading to well-developed,
solid-state deformation fabrics in high strain zones at the southwestern
margins. Armitage Pluton is a non-megacrystic hornblende-biotite body, which
intruded central parts of Bonney Pluton while it was incompletely crystallised.
The body forms randomly oriented dikes and stocks and is chemically distinct
from Bonney Pluton. A weak magmatic fabric is developed through the body,
subparallel to magmatic lineations in central parts of Bonney Pluton.
Chancellor Orthogneiss is a strongly deformed biotite granite, which
discordantly intrudes metasediments as randomly oriented dikes and stocks.
Solid-state deformation fabrics overprint magmatic fabrics throughout the body,
indicating post-emplacement ductile deformation. This body was emplaced into
host rock close to or at the brittle-ductile transition, at least biotite zone
conditions. Hidden Granite is an undeformed biotite granite which discordantly
intrudes metasediments and older granitoid bodies as randomly oriented dikes
and stocks. Mafic dikes coevally intrude the granite, infilling fractures with
consistent northeast-southwest orientations, at a late stage of granite
crystallisation. Hidden Granite was emplaced into a brittle host rock, above
the brittle-ductile transition.
The changing structural styles of the four plutons reflect intrusion during
progressive uplift. The nearly parallel nature of the elongation direction of
post-emplacement ductile fabrics in Chancellor Orthogneiss, and the extension
direction indicated by brittle structures in Hidden Granite, suggests a
geometric relationship exists between these fabrics and structures. The
northwest-southeast elongation direction also remains relatively constant
during post-emplacement deformation of the plutons.
Keywords South Victoria Land; granite plutons; emplacement;
deformation
New Zealand Journal of Geology and Geophysics, 1997, Vol. 40: 237-251
0028-8306/97/4002-0237 $7.00/0 (c) The Royal Society of New Zealand
1997
PDF file of entire paper: medium quality (2116K); (scanned from paper original: notes about this process)
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