Elsevier Encyclopedia of Geology

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Figure 25 Tectonic map of the continental lithosphere of Australia-New Guinea (yellow) and Sundaland (part of the Eurasian Plate;

yellow) and the surrounding oceanic lithosphere (blue), including the Pacific Plate and the Solomon sub-Plate to the north-east. The

ocean is marked by Deep Sea Drilling Project and Ocean Drilling Program sites (bullseyes) and selected seafloor-spreading magnetic

anomalies. The age of the continent–ocean boundary is given in Ma. The oblique blue band across northern Australia signifies

Miocene or younger sediment. Also shown are the orientation of maximum horizontal stress and the plate vector. AP, Abyssal Plain;

Continued

AUSTRALIA/Phanerozoic 231

and Hervey Basins behind the Baldwin arc. The

fore-arc basin and accretionary prism (Figure 2viii)

extended north as the Connors–Auburn arc.

In central Australia, the uplifted Arunta Block shed

alluvial fans to the south, which were themselves

folded and eroded. Fans in the Munyarai Trough

were likewise shed from the overthrusting Musgrave

Block. The eastward flow from central Australia

through the Adavale Basin swung northwards (parallel

to the Connors–Auburn arc) in the Drummond Basin

and debouched in the Broken River Embayment,

which was deformed in the latest Devonian.

Figure 26 Morphology of Australia and the neighbouring land, sea, and ocean. Shown in eastern Australia are the Great

Escarpment (green dots) and the drainage divide (red line). Reproduced with permission from Veevers JJ (ed.) (2000) Billion-Year

Earth History of Australia and Neighbours in Gondwanaland

. Sydney: GEMOC Press.

BR, Bismarck Rift; C, Cuvier; G, Gascoyne; J, Jerboa-1; NP, Naturaliste Plateau; SA, South Australia; TL, Tasman Line; TFS, Tamar

Fracture System; WP, Wallaby Plateau; WR, Woodlark Rift. Reproduced with permission from Veevers JJ (ed.) (2000)

Billion-Year Earth

History of Australia and Neighbours in Gondwanaland

. Sydney: GEMOC Press.

232 AUSTRALIA/Phanerozoic

Figure 27 Velocities of sites on the Australian Plate and adjacent Pacific and Eurasian plates. Red arrows indicate velocities

measured by GPS; double-shafted green arrows indicate velocities calculated from NUVEL-1A at selected 10



crosses. For each

arrow, the fine line is the north azimuth, the three-digit numeral the bearing, and the italicized numeral the velocity in mm year

1

. The

thrust line of Timor passes through DSDP (Deep Sea Drilling Project) site 262. Reproduced with permission from Veevers JJ (ed.)

(2000)

Billion-Year Earth History of Australia and Neighbours in Gondwanaland. Sydney: GEMOC Press.

Table 1 The three stratitectonic regimes in the development of Phanerozoic Australia

Regime Age (Ma) Platform stratigraphy Tectonics Latitude

Potoroo 99–0 Quartz, carbonate, and evaporite Post-Pangaean High to tropical

Innamincka 320–99 Glacigenic and coal measures Pangaean Polar

Uluru 544–320 Quartz and carbonate Gondwanaland Tropical

AUSTRALIA/Phanerozoic 233

The North China terrane broke off the Palaeo-

Tethyan margin. In the north, the Goulburn Graben

was initiated; the Bonaparte Basin was rejuvenated

and Frasnian alluvial fans were deposited at the

foot of a fault and succeeded by a Famennian reef

complex. In the Ord Basin, sand was deposited south-

wards from the same fault block. In the northern

Canning Basin, gravel fans from the Kimberley Block

mingled with a reef complex on a platform in

front of a deep axis; to the south, the paralic Tan-

dalgoo Formation was deposited in an arm of the

sea. In the Carnarvon Basin, shelf limestone and in-

shore quartz sand give way in Pendock-1 to reef

carbonate. Reworked Late Devonian conodonts in

the Perth Basin suggest that the shoreline extended

southwards.

Carboniferous (350–300 Ma)

South-eastern Australia was subjected to an Early

Carboniferous (350–330 Ma) east–west contraction,

followed by Mid-Carboniferous emplacement of

granites (Figure 2x) and finally north–south contrac-

tion in megakinks. Similar events took place in North

Queensland. In between, nonmarine deposition in the

Drummond Basin ended at 330 Ma when gentle

folding began. Central Australia was terminally

folded and thrusted in the Mid-Carboniferous

(320 Ma) Alice Springs Orogeny, which was echoed

by transpression in the Canning Basin, by folding and

faulting in the Carnarvon Basin, and by overthrusting

in the Officer Basin. These movements, represented

by the Mid-Carboniferous lacuna, mark the termin-

ation of the Uluru regime (when the Uluru Arkose

was upended) and the inception of the Innamincka

regime.

This rapid uplift and concomitant downwearing

must have produced copious amounts of sediment,

yet the depositional record over the Australian plat-

form, except the eastern and north-western margins,

is blank. Where could the sediment have gone? The

paradox is resolved by postulating that uplift

combined with rapid polar movement triggered not

only an alpine glaciation in the east but also a contin-

ent-wide dry-based ice-sheet (Figure 10), which

carried away sediment shed from the nunataks of

the central uplifts and from the eastern cordillera and

deposited nonmarine glacial sediment in the Werrie

Trough. Only during its retreat in the earliest Permian

did the ice release its load of sediment.

The Mid-Carboniferous marked a turning point

in Australia, from the Uluru regime, with warm-

water low-latitude carbonate facies, to the Inna-

mincka regime, with cold-water high-latitude detrital

facies.

Latest Carboniferous–Earliest

Permian (302–280 Ma)

The Mid-Carboniferous lacuna ended with the latest

Carboniferous (306 Ma) onset of Pangaean Extension

I, which was accompanied by the eruption of S-type

granites and felsic volcanics in north-eastern Australia

and followed at 302 Ma by deposition of glaci-

genic sediment in the space provided by the extension

(Figure 11). Eastern Australia was subjected to con-

tinuing dextral transtension, which produced an

orocline, related pull-apart basins, and widespread

magmatism (Figure 2xii). At polar latitudes ice flowed

into depressions between uplands, and on the periphery

into marine basins.

The west was extended into grabens and synclines.

Ice flowed northwards over and around the ancestral

Great Western Plateau and across the Canning Basin.

Farther north, the ice possibly flowed through the

Bonaparte Basin and through the restored position

of the Tangchong–Malay–Sumatra Block in Sibu-

masu to the shore of Palaeo-Tethys. In central and

eastern Australia, ice flowed from the central and

central-eastern uplands into the Pedirka and Arckar-

inga basins, and from the central-eastern upland east-

wards into the Cooper Basin, which also received ice

from the ancestral eastern Australian foreswell to the

east. From the Ross upland in Antarctica, ice flowed

northwards into areas that were later, at 288 Ma,

covered by an ephemeral shallow sea that followed

the melting of the ice.

Early Permian (280–258 Ma)

By 265 Ma, the magmatic arc, marked by granite and

tuff, had migrated northwards opposite central

Queensland (Figure 12), and the following tracts,

from craton to margin, can be identified: first, an

epicontinental basin with nonmarine sediment;

second, foreswell I (vertical bands), which shed quart-

zose sediment into, third, the initial foreland basin

of the Bowen–Gunnedah–Sydney Basin, which is

marked by coal alternating with shallow-marine de-

posits; and, fourth, an orogen and magmatic arc

that were intensely deformed in the Gogango Over-

folded Zone, which shed sediment back into the

foreland basin. In adjoining Antarctica, foreswell

I separated coal measures on the craton from the

foreland basin.

In the west, marine sediment alternated with

nonmarine sediment including coal.

Late Permian (258–250 Ma)

The magmatic arc propagated north-east to a position

opposite 250 Ma tuff (Figure 13). Coal measures

234 AUSTRALIA/Phanerozoic

reached a climax. The New England Fold Belt and

adjacent basins were deformed (Figure 2xiii), and

copious sediment flowed into the foreland basin and

the distal Galilee Basin. The last ice melted. The Kin

Kin terrane approached the trench.

In the west, Sibumasu broke off, the shoreline re-

gressed, and rhyolitic to undersaturated volcanics

were erupted.

Early Triassic (250–242 Ma)

The arc advanced to New Guinea, and plutons satur-

ated the suture zone of the amalgamated Kin Kin

terrane (Figure 14). In the foreland basin, cratonic

and orogenic drainage joined in axial flow from a

saddle just north of 30



S (present coordinates), and

volcanolithic sediment poured westwards into the

Galilee Basin. Tectonics was as before, but the surface

environment was radically different. Coal measures

and tuff were replaced by measures with redbeds

devoid of both coal and tuff. The coal gap reflects

the global extinction of peat-forming plants at the

Permian–Triassic boundary, and tuff was eliminated

by weathering in the warmer climate, even at polar

latitudes.

In the west, shale was deposited behind a transgres-

sive shoreline.

Early–Middle Triassic (242–234 Ma)

Volcanolithic sandstone was deposited in the foreland

basin (Figure 15). Sediment flow in the Bowen Basin

was now wholly southerly, and this was joined later

in the stage by cratonic (quartzose) sediment flowing

in an easterly direction from the Cooper–Galilee

Basin. In the Sydney Basin the Hawkesbury Sandstone

was derived from the Ross craton to the south-west,

which also fed a quartz sandstone in Tasmania. The

pole was nearby but ice is not indicated.

Mid-Triassic (234–227 Ma)

The complex of events called Gondwanides II in-

cluded thrusting of the fold belt over the final deposits

of the foreland basin and the spread of volcanolithic

sediment to the west (Figure 16). The fold belt itself

was intruded by granite along a transcurrent fault. At

the same time, the northern Canning Basin was

broadly folded during wrenching.

Late Triassic (227–200 Ma)

The Late Triassic saw the onset of Pangaean Exten-

sion II. In the east the change from contraction to

extension reflected a change from shallowly to steeply

dipping subduction (Figure 17). Maar diatremes were

erupted in the Sydney Basin, and a 212 Ma syenite

complex was emplaced in Victoria.

Deposition of coal resumed after a gap of 23 Ma.

New intramontane basins included the Ipswich and

Tarong coal basins; the Eromanga Basin with car-

bonaceous sediment subsided in the sump between

the fold belt and the craton; the Leigh Creek and

associated coal basins subsided on Proterozoic

crust; and deposition of coal resumed in Tasmania

and Antarctica.

In the west, the margins were rejuvenated by

wrenching, downfaulting, and folding. Uplands in the

Pilbara Block and Yilgarn Craton shed coarse detritus

into the rifted Perth and Carnarvon Basins. Volcanics

accompanied rifting in the Exmouth Plateau.

Early and Middle Jurassic

(200–160 Ma)

The Permian–Triassic sedimentary successions were

capped and intruded by a flood of 184–179 Ma tho-

leiitic basalts in southern Africa, Antarctica, and Tas-

mania, and by scattered volcanics in south-eastern

Australia (Figure 18). The Eromanga Basin expanded

across central-eastern Australia, with quartzose sedi-

ment derived from the craton and volcanolithic

sediment from a presumed arc. In Tasmania, the doler-

ite rose into the Permo-Triassic sedimentary rocks of

the Tasmania Basin as sills up to 400 m thick and

dykes up to 1 km wide. Extrusive tholeiite is known

near the southern tip only. In south-eastern Australia,

the magma forms flows and shallow intrusions.

Thick sands accumulated in the western rifts, and

sand sheets lay behind transgressive shorelines in the

Canning and Bonaparte Basins.

Late Jurassic (160–144 Ma)

Argo Land split off north-western Australia at

156 Ma as a result of seafloor spreading in the Argo

Abyssal Plain (Figure 19). The rifts along the western

and southern margins continued to fill with sand and

silt. The Eromanga Basin expanded northwards to

New Guinea.

Neocomian to Aptian (140.5–115 Ma)

In a radical change, the shoreline advanced into the

interior of Australia (Figure 20). The epeiric sea isol-

ated large islands in the north-west and north and was

confined by the rising rifted arch to the south and by

the magmatic arc of the Pacific margin to the north-

east. Volcanolithic sediment from the arc overran

sediment from the craton.

AUSTRALIA/Phanerozoic 235

The Southeast Indian Ocean opened at 132 Ma

between India and Australia–Antarctica.

Cenomanian (99–93 Ma)

The change from the Innamincka regime to the

Potoroo regime was marked by breakup along the

southern margin, cessation of subduction in the east,

and intense uplift of the eastern Highlands and epeiro-

genic uplift elsewhere, all occasioned by the 99 Ma

change in the azimuth of subduction of the Pacific

Plate from head-on (red arrows in Figure 21)toside-

swipe (black arrows). A detachment fault along the

continent–ocean boundary separated passive-margin

mountains on the upper-plate margin, buoyed by thick

underplating of mantle-derived melts, from the conju-

gate extremely attenuated lower-plate margin of the

Lord Howe Rise. Drainage was divided near the pre-

sent coast into a long south-western slope feeding the

Ceduna depocentre, which accumulated 8 km of Late

Cretaceous sediment, and a short eastern slope feeding

the low-lying eastern borderland.

The emergence of the land, in particular the rising

(and eroding) of the eastern highlands, forced a major

Cenomanian (99 Ma) regression at a time of marine

flooding elsewhere. The inception of south-western

drainage into the Australian–Antarctic depression

coincided with the inception of the juvenile ocean

that grew out of the rifted arch and was preceded by

130–105 Ma deposition of volcanogenic sediment in

the Otway, Bass, and Gippsland basins. In the east,

the 120–105 Ma Whitsunday Volcanic Province was

succeeded by ca. 99 Ma alkaline volcanics, and the

previous volcanogenic sediment from the arc and in

the south-eastern rift basins was succeeded by quart-

zose sediment. In the north and west, the shoreline

regressed to and beyond its present position, and

carbonate replaced detrital sediment on the margin

of the widening Indian Ocean.

Eocene (35 Ma)

Following the opening of the Tasman Sea and Coral

Sea, the Potoroo regime can be shown on a modern

geographical base except for the higher palaeolati-

tudes (Figure 22). The sea transgressed the western

half of the southern margin, and an ancestral Arafura

Sea lay between northern Australia and New Guinea.

Relaxation of the platform saw sediment accumu-

late in the central-eastern lowlands and in grabens

in central Australia and south-eastern Queensland,

including deposits of oil shale and, in isolated

pockets, fluviolacustrine gravel, sand, silt, clay, and

lignite, which were overlain by basalt in the eastern

Highlands, too small to show in Figure 22. In the

west, the uplift was etched by rivers except in an

area of lakes in the south-west.

Miocene (24–5 Ma)

At 20 Ma, another transgression in the south crossed

the Nullarbor Plain, the Adelaide region, the Murray

Basin, and Bass Strait, and thick lignite accumulated

in the onshore Gippsland Basin (Figure 23). Sheets of

sand accumulated in the Lake Eyre drainage system

and in the Murray Basin.

In New Guinea, the Sepik terrane had docked by

25 Ma and thrusted south-westwards to form a fore-

land basin; it was joined at 15 Ma by a composite

terrane in the south-east, and at 10 Ma by terranes in

the north and north-west. Miocene and younger

marine to nonmarine sediment was deposited behind

a foreswell across northern Australia. By the end of

the Miocene the geography of the region was as it is

today except that the palaeolatitude (at 16 Ma) was



farther south than today.

Pleistocene (1.8 Ma to 10 ka)

By the end of the Pleistocene, at 10 ka, sea-level was

halfway between the level at the Last Glacial Maxi-

mum and its present level (Figure 24). Lakes occupied

the Gulf of Carpentaria and the Bass Strait, and, as

today, dry lakes covered much of interior Australia.

The central-eastern lowlands in New South Wales

were covered by sheets of fluvial sediment. Glacial

deposits were confined to Tasmania and the Mount

Kosciusko area. Aeolian dunes covered much of

the arid interior, including the relict drainage of the

south-west.

Present Tectonics and Morphology

The continental lithosphere of Australia–New Guinea

is surrounded by the oceanic lithosphere of divergent

oceans on its western, southern, and eastern margins

and of convergent oceans on its northern margin from

Timor to the Papuan Peninsula (Figure 25). The con-

vergent boundary is marked by high relief, 3 km above

sea-level in Timor and 5 km in New Guinea (Figure

26), intense Earth movement and seismicity, and scat-

tered volcanicity. South of this boundary, as befits its

intraplate position, Australia is low-lying, with a relief

of 2.2 km in the south-east and little more than 1 km

elsewhere, relatively quiescent, except for diffuse

seismicity in the north-west sector, in zones about

Meckering in the south-west, in South Australia,

and in the south-east, and has only two areas of

volcanicity, one in north-east Queensland, the other

on the southern margin at 141



236 AUSTRALIA/Phanerozoic

The submarine features of the divergent margins

have a certain bilateral symmetry about the meridian

halfway across Australia: complexes of marginal plat-

eaus and abyssal plains are backed by a broad shelf in

the north, and narrow margins expand into long ap-

pendages (Naturaliste Plateau and Tasmania–South

Tasman Rise) in the south. This pattern extends to

the arrangement of seafloor-spreading magnetic

anomalies in that the azimuth of the anomalies off

the west coast is reflected in that off the east coast,

while the set to the south is crossed by the line of

symmetry. The age of onset of spreading follows an-

other pattern, with anticlockwise propagation from

156 Ma in the north-west through 132 Ma in the

west, and 99 Ma in the south, and as back-arc spread-

ing at 83.5 Ma, 68 Ma, and 64 Ma in the south-east,

62 Ma in the north-east, and 5 Ma off eastern New

Guinea.

Present Motion

Figure 27 shows the velocities (azimuth and magni-

tude) from a few years of Global Positioning System

(GPS) measurements and from the NUVEL-1A

global-plate-motion model averaged over several mil-

lion years. For example, the GPS estimate in western

Victoria of 58.3 mm year

1

at 022



approximates the

NUVEL-1A estimate of 61 mm year

1

at 019



, and

that near Darwin of 67.2 mm year

1

at 034.9



matches the NUVEL-1A estimate of 71 mm year

1

at 033



. Most of this motion comes from seafloor

spreading in the Southeast Indian Ocean at a full

rate of 60 mm year

1

from an almost stationary

Antarctica.

The stations on mainland New Guinea, including

one near the plate boundary, record an azimuth of

ca. 050



, which locates them on the south-western

(Australian) side of the plate boundary. On the other

side, the Pacific Plate is moving at a velocity of 66 mm

year

1

at 289



, almost at a right angle to Australia’s

motion, confirming the idea expressed by Alfred

Wegener that the Pacific’s westerly motion has planed

off the obtruding anvil of New Guinea.

According to NUVEL-1A, the Eurasian Plate is

moving slowly south-eastwards. GPS measurements

on either side of the Flores and Wetar thrusts show

that the southern Banda arc is virtually accreted to the

Australian plate margin and that most of the conver-

gence seems to be accommodated by left-lateral slip

at the plate boundary, suggesting that the Timor

Trough is now inactive as a thrust.

Further Reading

BMR Palaeogeographic Group (1990) Evolution of a Con-

tinent. Canberra: Bureau of Mineral Resources, Geology

and Geophysics.

Veevers JJ (ed.) (1984) Phanerozoic Earth History of

Australia. Oxford: Clarendon Press.

Veevers JJ (ed.) (2000) Billion-Year Earth History of Aus-

tralia and Neighbours in Gondwanaland. Sydney:

GEMOC Press.

Veevers JJ (2001) Atlas of Billion-Year Earth History of

Australia and Neighbours in Gondwanaland. Sydney:

GEMOC Press.

Tasman Orogenic Belt

D R Gray, University of Melbourne, Melbourne, VIC,

Australia

D A Foster, University of Florida, Gainesville, FL, USA

Introduction

The eastern part of Australia formed along the

margin of Gondwana during the Palaeozoic due to

the accretion of oceanic platform and basinal

sequences (Figure 1). A region of eastern Australia

over 1000 km wide now consists of three distinct

orogenic belts (the Delamerian, Lachlan–Thomson,

and New England orogens), which are collectively

referred to as the Tasman Orogenic Belt (Figures 1

and 2). This deformed and metamorphosed tract of

rocks was once part of a major orogenic system that

extended some 20 000 km along the Gondwanan

margin, incorporating parts of the Andes in South

America (see Andes), the Cape Fold Belt in southern

Africa, and the Ross Orogen in Antarctica (see Ant-

arctic)(Figure 1). In eastern Australia accretion oc-

curred in a stepwise fashion, with an eastward

younging from the Cambrian to the Triassic, reflected

AUSTRALIA/Tasman Orogenic Belt 237

by peaks of deformation in the Early to Middle Cam-

brian, Late Ordovician–Silurian, and Permian–Trias-

sic in the respective orogenic belts (Table 1).

Crustal growth occurred largely by the addition of

turbidites (ocean-floor submarine-fan deposits),

cherts (ocean-basin deposits), mid-ocean ridge basalts

(oceanic crust), andesites (island arc), and granites.

These younger, largely Palaeozoic, rocks occur to

the east of the exposed Precambrian cratonic crystal-

line basement; the boundary between the two is

known as the Tasman Line (Figure 2). They represent

a significant addition (approximately 30% by surface

area) to the Australian continent whilst it was part of

Gondwana. Younger basinal sedimentary sequences

Figure 1 Simplified geological map of Gondwana with modern-day continental outlines, showing regions of Precambrian shield and

the younger orogenic belts. IGCP, Gondwana map base.

238 AUSTRALIA/Tasman Orogenic Belt

(e.g. Great Artesian, Murray, and Sydney–Bowen

Basins) now cover much of belt (Figure 3).

Accretion was accompanied by marked structural

thickening and shortening (by about 75%) of Neo-

proterozoic platform and rift basinal sequences (Dela-

merian part), a Cambrian–Orodovician composite

turbidite submarine fan overlying Cambrian oceanic

crust (Lachlan part), and Carboniferous–Permian arc,

fore-arc, and trench (subduction complex) and Per-

mian foreland basin sequences (New England part)

(Figure 3). For a large part of the history (Silurian–

Early Carboniferous), deformation occurred by mas-

sive telescoping, with thrusting largely directed away

from the cratonic core, together with components of

strike-slip translation within a progressively deform-

ing and prograding sediment fan along the Gondwa-

nan margin. The margin was intruded by voluminous

granitic plutons (accounting for up to 35% of the

area), derived from subduction-generated mantle

magmas and lower- to middle-crustal melting, be-

tween the Late Ordovician and the Triassic (Figure 3).

The spatial and temporal variations in deformation,

metamorphism, and magmatism across the Tasman

Orogenic Zone show how subduction–accretion

complexes are monotonous turbidite sequences

evolve through time and eventually form crust of

continental thickness and character.

Tasman Orogen Make-up

The Delamerian, Lachlan–Thomson, and New Eng-

land Orogens, which form the composite Palaeozoic

and Mesozoic Tasman Orogen (Figure 2), are distin-

guished by their lithofacies (Figure 3), differing tec-

tonic settings, and timing of orogenesis and eventual

consolidation with the Australian craton (Table 1).

The Delamerian Orogen involved an inverted intra-

cratonic rift, the Lachlan Orogen involved closure of

a south-west-Pacific style marginal basin incorpor-

ating Bengal Fan-sized turbidite fans, and the New

England Orogen involved a deformed arc–subduction

complex belt.

Figure 2 The major geological elements of Australia, showing the Tasman Orogen along the eastern margin. Location of the more

detailed map area of Figure 3 is shown.

AUSTRALIA/Tasman Orogenic Belt 239

Delamerian Orogen

The Delamerian Orogen is the oldest and innermost

part, immediately adjacent to the Precambrian cra-

tonic core. The Delamerian Orogen was tectonically

active from the Late Precambrian (ca. 650–600 Ma) to

the Late Cambrian (ca. 500 Ma). It is now an arcuate

craton-verging thrust belt with foreland-style folds

and detachment-style thrusts. Duplexes in deformed

Cambrian deep-water sandstones and mudstones

(Kanmantoo Group) overlie less deformed and meta-

morphosed Neoproterozoic shelf sequences (Adelai-

dean). Metamorphic grade increases to the east, where

polyphase deformation and amphibolite-grade meta-

morphism with local development of kyanite–

sillimanite assemblages are spatially and temporally

confined to the aureoles of synkinematic granites that

are conformably aligned with the structural grain.

Lachlan Orogen

The Lachlan Orogen is the largest and the cen-

trally located orogenic belt (Figure 2) with a marked

similarity of sedimentary facies and structural style.

It was active from the Ordovician and has a com-

plex amalgamational and deformational history. The

western and central parts of the Lachlan Orogen are

dominated by a turbidite succession consisting of

quartz-rich sandstones and black shales. These are

laterally extensive over a present width of 800 km

and have a current thickness exceeding 10 km. The

eastern Lachlan Orogen consists of shoshonitic vol-

canics, volcaniclastic rocks, and limestone, as well as

quartz-rich turbidites and extensive black shales in

the easternmost part (Figure 3).

ThewesternLachlanOrogenconsistsofaneast-

wards-vergent thrust system with alternating zones

of north-westwards- and northwards-trending struc-

tures. The central Lachlan Orogen is dominated

by north-westwards-trending structures and consists

of a south-westwards-vergent thrust belt linked to a

fault-bounded metamorphic complex (Wagga-Omeo

Metamorphic Belt). The eastern Lachlan Orogen is

dominated by a northwards-trending structural grain

and eastwards-directed thrusting, which caused inver-

sion of extensional basins in the west. Tight-to-open

chevron folds (accommodating between 50% and 70%

shortening) cut by predominantly westwards-dipping

high-angle reverse faults are part of different thrust

systems within the Lachlan Orogen. The chevron

folds are upright and gently plunging, but become

Table 1 Orogens and subprovinces of the Tasman Orogenic Belt

Orogen Delamerian (West) Western Lachlan Central Eastern

New England

(East)

Main lithofacies Platform to deep-

water clastic

margin sequence

Quartz-rich turbidite

sequence on

oceanic crust

Quartz-rich turbidite

sequence on

oceanic crust

Platform carbonates

and clastics with

rhyolites and

dacitic tuffs

Volcanogenic

clastic

Initial setting Late Proterozoic

rifted margin

Cambro-Ordovician

submarine fan in

back-arc basin

Ordovician

submarine fan in

back-arc basin

Ordovician rifted

arc

Late

Palaeozoic

fore-arc–

arc–trench

Oldest lithology Basic volcanics Cambrian basic

volcanics

(

ca. 505 Ma)

Tremadocian chert Ordovician

andesitic

volcanics

(

ca. 485 Ma)

Ordovician

basic

volcanics

Main deformation Early to Middle

Cambrian

(

ca. 520–500 Ma)

Late Ordovician–

Silurian

(ca. 450–420 Ma)

Late Ordovician–

Early Devonian

(ca. 450–410 Ma)

Silurian–Early

Carboniferous

(ca. 430–360 Ma)

Late

Permian–

Triassic

(

ca. 265–

230 Ma)

Tectonic vergence Westwards-directed

thrusting

Eastwards-directed

thrusting

Overall strike-slip

(

ca. 410–400 Ma)

with south-

westwards-

directed thrusting

(

ca. 440–420 Ma)

Eastwards-directed

thrusting

Westwards-

directed

thrusting

Main plutonism Cambrian

(520–490 Ma)

Late Devonian

(380–360 Ma)

Late Silurian (ca.

430–400 Ma)

Late Silurian–

Devonian

(

ca. 430–380 Ma)

Late

Permian–

Triassic

(

ca. 270–

210 Ma)

240 AUSTRALIA/Tasman Orogenic Belt

Elsevier Encyclopedia of Geology - vol I A-E

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