New Zealand Journal of Geology and Geophysics abstracts
Provenance history of a Late Triassic–Jurassic Gondwana margin
forearc basin, Murihiku Terrane, North Island, New Zealand:
petrographic and geochemical constraints
Roger M. Briggs
Matthew P. Middleton
Campbell S. Nelson
Department of Earth Sciences
University of Waikato
Private Bag 3105
Hamilton, New Zealand
Abstract The Murihiku Terrane in the North Island
was a forearc basin adjacent to a volcanic arc along the eastern margin
of Gondwana during the Mesozoic. The rocks that infill the basin are
mainly volcaniclastic sandstones and mudstones, often turbiditic, with
sparse shellbeds, rhyolitic tuffs, carbonaceous sandstones, plant beds,
concretionary horizons, and rare thick granitoid-rich conglomerates.
Petrographic studies of the rock fragments in the sandstones show that
andesites are the dominant lithic type, but there is a wide range of
other lithologies, including dacites, rhyolites, ignimbrites,
granitoids, quartzofeldspathic mica schists, rare amphibolites, and
reworked mudstones and sandstones. The sandstones are texturally and
mineralogically immature and suggest deposition relatively close to a
source of high relief, undergoing physical rather than chemical
weathering in cool- to cold-temperate conditions. Geochemical analyses
of 67 whole-rock volcaniclastic sandstones and siltstones indicate that
they were derived from an active and dissected volcanic arc in a
convergent margin setting built upon relatively thin continental crust.
Modal petrographic data and whole-rock geochemistry both confirm that
there were systematic variations with time in the composition of
clastic material being supplied to the basin. From the Late Triassic to
Middle Jurassic, there was a decrease in silicic volcanic material,
plutonics, and metamorphics, and an increase in the supply of andesitic
detritus. This was followed in the Late Jurassic by a broader range of
volcanic detritus, varying from basaltic andesite to rhyolite, which
may have been caused by progressive extension of the volcanic arc and
thinning of the crust, a precursor to the breakup of Gondwana in the
Early–Middle Cretaceous. Comparison with the Southland segment of the
Murihiku Terrane in the South Island suggests that there were
significant along-arc source variations, with relatively less silicic
but greater andesitic and continental crust contributions in the North
Island than in Southland. This may be analogous to the modern
Taupo-Kermadec arc where there is a south–north along-arc transition
from a continental to an oceanic arc.
Keywords Murihiku Terrane; western North Island;
Triassic; Jurassic; petrography; geochemistry; provenance
G03063; Received 17 October 2003; accepted 21 November 2003; Online
publication date 1 December 2004
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47:
589–602
0028–8306/04/4704–0589© The Royal Society of New Zealand 2004
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