Temple Basin, near Arthurs Pass, South Island, New Zealand
| mackinnon_1983.pdf |
Origin of the Torlesse terrane and coeval rocks,
South Island, New Zealand
THOMAS C. MACKINNON* University of Otago, Box 56, Dunedin, New Zealand
A B S T R A C T
The Carboniferous to Lower Cretaceous
Torlesse terrane and Haast Schist derivatives
constitute the major part of the complexly
deformed facies of the Eastern Province
of New Zealand. Strata consist mainly
of quartzofeldspathic graywacke and mudstone,
intercalated with minor but widely
distributed conglomerate, and volcanics
with associated chert and limestone. Clastic
rocks were deposited largely by sediment
gravity-flow mechanisms in a deep-marine
environment. Also present are a few highly
fossiliferous shallow-marine and terrestrial
deposits of limited areal extent, which rest
unconformably on or in fault contact with
Torlesse flysch. Several periods of deformation
are recognized and mélange is present
on both local and regional scales. Metamorphism
ranges from zeolite to greenschist
facies. The bulk of the rocks fall into five
areally extensive and mutually exclusive
fossil zones of the following ages: Permian
(Atomodesmd), Middle Triassic, early Late
Triassic (?) ( Torlessia), Late Triassic ( Mono-
tis), and Late Jurassic-Early Cretaceous.
Contacts between major fossil zones are
mainly tectonic. Petrographic analysis permits
subdivision of Torlesse sandstones into
five major petrofacies that correspond in
age to the five major fossil zones. The sandstone
petrofacies (mainly arkosic), together
with the composition of conglomerate clasts
(mainly indurated Torlesse rocks), indicate
that the source terrane was a continental
volcano-plutonic arc, probably part of
Gondwanaland, coupled with autocannibalistic
reworking of older uplifted Torlesse
rocks.
In contrast to the quartzofeldspathic
nature of the Torlesse, coeval sedimentary
rocks of the Eastern Province are volcanogenic.
They are thought to represent related
forearc-basin (Maitai-Murihiku terranes)
and trench-complex (Caples terrane) deposits
derived from a volcanic island arc
(Brook Street terrane). Three petrofacies
are established for Maitai-Murihiku and
Caples sandstones. The petrofacies indicate
a common, evolving, immature to submature
volcanic island arc source for these
terranes.
A reconstruction of New Zealand's Eastern
and Western Provinces is proposed. In
Permian and Triassic times, the Torlesse
was deposited in trench, slope, or borderland
basins along a trench-transform margin
fronting a continental volcano-plutonic arc
source (Western Province-Gondwanaland).
Deposition was spasmodic but voluminous
and was accompanied by concurrent deformation
and accretion resulting in parallel
belts of Torlesse rock younging outward
from the Gondwanaland margin. At the
same time, the Brook Street terrane volcanic
arc and associated terranes were forming
to the west of the Torlesse site, separated
from Gondwanaland by a marginal
sea. In latest Triassic or Early Jurassic
times, the Torlesse was rafted into the volcanic
arc system via transform faulting
approximately parallel to the Gondwana
margin. The collision event resulted in tectonic
thickening of Torlesse and Caples
rocks at the plate interface and metamorphism
to Haast Schist. The source was then
dominated by older, partly metamorphosed
Torlesse terrane, newly uplifted along the
collision front. Closing of the marginal sea
behind the Brook Street terrane in Late
Jurassic-Early Cretaceous times resulted in
juxtapositioning with the Western Province
(Gondwanaland) along the Median Tectonic
Line.
South Island, New Zealand
THOMAS C. MACKINNON* University of Otago, Box 56, Dunedin, New Zealand
A B S T R A C T
The Carboniferous to Lower Cretaceous
Torlesse terrane and Haast Schist derivatives
constitute the major part of the complexly
deformed facies of the Eastern Province
of New Zealand. Strata consist mainly
of quartzofeldspathic graywacke and mudstone,
intercalated with minor but widely
distributed conglomerate, and volcanics
with associated chert and limestone. Clastic
rocks were deposited largely by sediment
gravity-flow mechanisms in a deep-marine
environment. Also present are a few highly
fossiliferous shallow-marine and terrestrial
deposits of limited areal extent, which rest
unconformably on or in fault contact with
Torlesse flysch. Several periods of deformation
are recognized and mélange is present
on both local and regional scales. Metamorphism
ranges from zeolite to greenschist
facies. The bulk of the rocks fall into five
areally extensive and mutually exclusive
fossil zones of the following ages: Permian
(Atomodesmd), Middle Triassic, early Late
Triassic (?) ( Torlessia), Late Triassic ( Mono-
tis), and Late Jurassic-Early Cretaceous.
Contacts between major fossil zones are
mainly tectonic. Petrographic analysis permits
subdivision of Torlesse sandstones into
five major petrofacies that correspond in
age to the five major fossil zones. The sandstone
petrofacies (mainly arkosic), together
with the composition of conglomerate clasts
(mainly indurated Torlesse rocks), indicate
that the source terrane was a continental
volcano-plutonic arc, probably part of
Gondwanaland, coupled with autocannibalistic
reworking of older uplifted Torlesse
rocks.
In contrast to the quartzofeldspathic
nature of the Torlesse, coeval sedimentary
rocks of the Eastern Province are volcanogenic.
They are thought to represent related
forearc-basin (Maitai-Murihiku terranes)
and trench-complex (Caples terrane) deposits
derived from a volcanic island arc
(Brook Street terrane). Three petrofacies
are established for Maitai-Murihiku and
Caples sandstones. The petrofacies indicate
a common, evolving, immature to submature
volcanic island arc source for these
terranes.
A reconstruction of New Zealand's Eastern
and Western Provinces is proposed. In
Permian and Triassic times, the Torlesse
was deposited in trench, slope, or borderland
basins along a trench-transform margin
fronting a continental volcano-plutonic arc
source (Western Province-Gondwanaland).
Deposition was spasmodic but voluminous
and was accompanied by concurrent deformation
and accretion resulting in parallel
belts of Torlesse rock younging outward
from the Gondwanaland margin. At the
same time, the Brook Street terrane volcanic
arc and associated terranes were forming
to the west of the Torlesse site, separated
from Gondwanaland by a marginal
sea. In latest Triassic or Early Jurassic
times, the Torlesse was rafted into the volcanic
arc system via transform faulting
approximately parallel to the Gondwana
margin. The collision event resulted in tectonic
thickening of Torlesse and Caples
rocks at the plate interface and metamorphism
to Haast Schist. The source was then
dominated by older, partly metamorphosed
Torlesse terrane, newly uplifted along the
collision front. Closing of the marginal sea
behind the Brook Street terrane in Late
Jurassic-Early Cretaceous times resulted in
juxtapositioning with the Western Province
(Gondwanaland) along the Median Tectonic
Line.
