New Zealand Journal of Geology & Geophysics abstracts
Petrology and geochronology of the volcaniclastic and volcanogenic
Mesozoic Loch Burn Formation in eastern Fiordland, New Zealand
J. M. Scott1,*
I. M. Turnbull2
T. A. Ewing3
A. H. Allibone4
J. M. Palin1
A. F. Cooper1
1Geology Department
University of Otago
PO Box 56
Dunedin 9054, New Zealand
2GNS Science
PO Box 1930
Dunedin 9054, New Zealand
3Research School of Earth Sciences
The Australian National University
Canberra, ACT 0200, Australia
4Rodinian Pty Ltd
PO Box 1804
Fyshwick, ACT 2609, Australia
*Corresponding author: scoja310@student.otago.ac.nz
Abstract The Loch Burn Formation in
eastern Fiordland is the
metamorphosed and eroded effusive product of a long-lived Jurassic to
Early Cretaceous volcanic arc. Relict sedimentary features within
meta-volcaniclastic components indicate sedimentation in a mostly
terrestrial or shallow-water environment that was fed by debris flows
from proximal granitic and volcanic high points. In the Murchison
Mountains, deposition is constrained by a c. 342 Ma granite, which
is unconformably overlain by the Loch Burn Formation, and a c. 158
Ma quartz diorite that intrudes the Loch Burn Formation. This latter
age is 8–9 m.y. older than a volcanic clast from Loch Burn Formation
and a sandstone horizon previously dated from the Stuart Mountains, and
therefore supports previous suggestions that the Loch Burn Formation is
a long-lived and time-transgressive unit. The Carboniferous basement
provides a potential source for detrital zircon in metasediment,
inherited zircon in the intrusive quartz diorite, and some granitoid
clasts within the formation. Geochemical similarities between the
quartz diorite, volcanic clasts within the Loch Burn Formation, and
nearby Jurassic to Early Cretaceous Darran Suite plutons imply that the
Loch Burn Formation is the volcanic equivalent of the Darran Suite. The
distinctive lithological, geochemical, age, and internal relationships
of the Loch Burn Formation are also seen in the volcano-sedimentary
Largs Group of northern Fiordland and Paterson Group of Stewart Island,
suggesting that these three units are lithological and chronological
equivalents to one another.
The Loch Burn Formation provides a
comprehensive record of the tectonic evolution of eastern Fiordland,
with several episodes of uplift and burial. These are: uplift and
erosion of a Carboniferous plutonic basement by c. 195 Ma;
deposition of the older part of the Loch Burn Formation sequence in the
Jurassic before burial and intrusion by Darran Suite plutons at 158 Ma;
deposition continuing until at least 148 Ma; metamorphism of the entire
Loch Burn Formation at greenschist and amphibolite facies conditions;
uplift, erosion, and then deposition of the overlying Eocene sediments;
reburial to zeolite facies depths beneath the Tertiary Te Anau and
Waiau Basins; final uplift in the Pliocene.
Keywords Loch Burn Formation; Darran
Suite; Largs Group;
Paterson Group; Fiordland; petrology; U-Pb zircon ages; tectonics
G07025; Online publication date 29 April 2008; Received 8 October
2007; accepted 10 March 2008
New Zealand Journal of Geology & Geophysics, 2008, Vol. 51:
89–103
0028–8306/08/5102–0089 © The Royal Society of New Zealand 2008
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