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basin is over 5–6 km thick and opens towards the east.

The Colorado Basin, another aulacogenic basin, de-

veloped along the suture between Patagonia and the

south-western Gondwana continent. The timing and

geometry of this basin are similar to those of the

Salado Basin. Towards the west, the Colorado Basin

is linked with the retroarc basin of the Neuque

embayment.

San Jorge Basin The intracratonic San Jorge Basin

developed with an east–west trend during Middle

Jurassic to Early Cretaceous times, during the open-

ing of the Weddell Sea and the South Atlantic Ocean.

During the Late Cretaceous, thick sequences of molasse

deposits unconformably overlaid the previous rocks.

Thick sequences of clastic deposits and tuff layers

record the volcanic activity in the Andes during Cret-

aceous and Palaeogene times. Most of the basin was

filled by continental deposits, with the first Atlantic

marine transgression in Maastrichtian–Paleocene

times.

Mesozoic Provinces

Important rift deposits that accumulated in north-

western-trending depocentres are recorded in most

of central and southern Argentina. The synrift de-

posits are of Late Triassic–Early Jurassic age, and

consist of redbeds and alkaline basalts. A younger

reactivation of these rift systems occurred in the

Early Cretaceous, the time at which (125 Ma) the

first oceanic crust formed in the South Atlantic Ocean

at these latitudes. The Cretaceous rifts are subpar-

allel to the continental margin (Figure 7) and were

controlled by the sutures of the Palaeozoic accreted

terranes.

Two important rhyolitic geological provinces, the

Choiyoi and the Chon Aike, were developed in the

Andean and extra-Andean regions in Mesozoic times.

Together these provinces constitute one of the largest

rhyolitic provinces in the world, with an extension

exceeding 1 000 000 km

The Choiyoi Province

The Choiyoi province is characterized by an extensive

rhyolitic plateau that developed between northern

Chile, at 24



S latitude, and the northern part of

Patagonia, at 40



S latitude. The region consists of

thick piles of rhyolitic lavas, ignimbrites, and volca-

niclastic deposits, occasionally interbedded with la-

custrine limestones. These rocks were deposited in

half-graben systems, with frequent thickness changes

that indicate a synextensional deposition. The age of

formation varies from 280 Ma in the north to 226 Ma

in the southern sector. Volcanic activity had a climax

265 Ma, when ash-flow tuffs fell over most of the

extra-Andean part of Argentina and southern Brazil,

even reaching South Africa. This generalized exten-

sion followed terrane accretion and deformation in

Late Palaeozoic times, which was associated with the

cessation of subduction along the Pacific margin.

The Chon Aike Province

The rhyolitic Chon Aike Province covers most of

Patagonia south of 40



S and also extends into the

Antarctic Peninsula and further south. It is composed

of abundant rhyolitic lavas, ignimbrites, and tuffs,

with minor amounts of alkaline basalts interbedded

in the lower part of the succession. Seismic lines

through the Austral Basin show the half-graben geom-

etry of these deposits. The volcanic sequences exposed

in the Somuncura

Massif are between 185 and

170 My old, whereas the rhyolites exposed in the

Deseado Massif are younger, between 165 and

155 My old. The equivalent rocks in the Tierra del

Fuego Island are about 140 My old. All together,

these rocks again show a decrease in age to south of

the acidic volcanism, and are associated with the

early rifting that led to the opening of the Weddell

Sea and the South Atlantic Ocean.

Palaeozoic Terranes

Most of the basement of Argentina was the result of

collision and amalgamation of continental fragments

formed during Palaeozoic times. Ophiolitic assembl-

ages, magmatic arcs, and older orogens cover most of

the present stable extra-Andean platform. Among the

main continental fragments are the Cuyania, Pampia,

Chilenia, and Patagonia terranes (Figure 6).

Cuyania

Previously known as the Precordillera Terrane, Cuya-

nia is one of the best known allochthonous pieces

that docked against the western Gondwana margin

during Middle Ordovician times. It consists of a

middle Proterozoic metamorphic basement, with am-

phibolites, marbles, and granitoids with a typical

Grenvillian signature. Cambrian limestones bearing

Olenellus trilobites denote a Laurentian provenance;

this has been confirmed by palaeomagnetic studies.

The Early Ordovician carbonate rocks are followed

by black shales that are unconformably overlaid by

conglomerates and sandstones, interbedded with typ-

ical Gondwanian glacial deposits of latest Ordovician

age. The arrival of this terrane is documented by an

active calc-alkaline series of granitoids that developed

along the continental margin of Gondwana from Late

Cambrian to Early Ordovician times. These rocks,

ARGENTINA 161

Figure 7 Mesozoic rift systems associated with the opening of the Atlantic margin. The intracratonic rifts were partially controlled by

the sutures of the Palaeozoic accreted terranes. Along the main Andes, extensional basins were controlled by negative trench

roll-back velocity in the retroarc basins.

162 ARGENTINA

together with subsequent peraluminous granites,

show a magmatic arc and postcollisional plutons

along 1000 km of central Argentina. The Cuyania

Terrane is bounded by two series of ophiolites, one

in the western margin of the present Precordillera,

and the other along the western margin of the Pampia

Terrane.

Pampia

The Pampia cratonic block hosted an Early Palaeo-

zoic magmatic arc, which consists of metamorphic

and igneous rocks penetratively deformed during

Late Proterozoic–Early Cambrian times, at the time

of the Pampean Orogeny. A Late Proterozoic ophiolite

bounds the eastern margin of the terrane. The proto-

margin of western Gondwana is exposed along the

eastern Sierras Pampeanas, where relics of Late Pro-

terozoic–Early Cambrian tonalites, granodiorites,

and granites constituted the magmatic arc. The colli-

sion between the Pampia Terrane and the Gondwana

protomargin is constrained by a series of rhyolites and

other volcanic rocks of Early to Middle Cambrian age

that unconformably overlie the deformed basement

rocks. Low-grade metamorphic rocks, up to 5 km

thick, constituted the synorogenic sequence preserved

in the Cambrian foreland basin.

Chilenia

The amphibolites and schists with Grenvillian-age

zircons, poorly exposed along the main Andes be-

tween Chile and Argentina, formed the basement of

the Chilenia Terrane. Although the basement is

well preserved along the Cordones del Plata and El

Portillo, most of the metamorphic rocks are covered

by several kilometres of sedimentary and volcanic

rocks on the Principal and Frontal Cordilleras. An

ophiolitic belt of Ordovician to Devonian age separ-

ates this basement from the Cuyania Terrane. The

docking of the rocks is constrained by the Early

Carboniferous marine deposits that finally amalgam-

ated the allochthonous terranes of central Argentina.

Patagonia

The Patagonian basement records a Precambrian

history that started in the Middle Proterozoic, as

detected in detrital zircon fractions from the Deseado

Massif and from the western part of the Somun-

cura

Massif. The northern sector of the Somuncura

Massif has evidence of a superimposed Brasiliano

deformation.

Crustal growth of Patagonia began in the Early

Palaeozoic, when a magmatic arc was developed in

the northern margin of the Somuncura

Massif. Age

constraints for this magmatic belt indicate Middle to

Late Ordovician to Late Carboniferous and Early Per-

mian ages, showing that an active margin lasted until

Early Permian times. The Deseado Massif was also

the locus of Early Palaeozoic magmatism. Granitoids

of Ordovician to Silurian age show a north-western-

trending arc, parallel to penetrative deformation pre-

served in slates and schists of Late Precambrian age. It

has been proposed that both basement blocks were

independent terranes that amalgamated during the

Early Palaeozoic to form a microcontinent that col-

lided with Gondwana in Permian times, to form the

Ventania fold-and-thrust belt.

Further Reading

Mpodozis C and Ramos VA (1990) The Andes of Chile

and Argentina. In: Ericksen GE, Can

as, Pinochet MT,

and Reinemud JA (eds.) Geology of the Andes and

Its Relation to Hydrocarbon and Mineral Resources,

Earth Sciences Series, vol. 11, pp. 59–90. Menlo Park,

CA: Circum-Pacific Council for Energy and Mineral

Resources.

Ramos VA (1994) Geology of South America. Encyclopae-

dia Britannica 27: 580–583.

Ramos VA and Alema

n A (2000) Tectonic evolution of

the Andes. In: Cordani UJ, Milani EJ, Thomaz Filho A,

and Campos DA (eds.) Tectonic Evolution of South

America, pp. 635–685. Rı

´o

de Janeiro: 31st International

Geological Congress.

Ramos VA and Keppie D (eds.) (1999) Laurentia–

Gondwana Connections before Pangea. Special Paper

336. Boulder, CO: Geological Society of America.

Ramos VA and McNulty B (eds.) (2002) Flat-slab sub-

duction in the Andes. Journal of South American Earth

Sciences 15(1): Special Issue.

Tankard AJ, Sua

rez SR, and Welsink HJ (eds.) (1995) Pet-

roleum Basins of South America. American Association of

Petroleum Geologists Memoir 62. Tulsa, OK: American

Association of Petroleum Geologists.

ARGENTINA 163

ASIA

Contents

Central

South-East

Central

S G Lucas, New Mexico Museum of Natural History,

Albuquerque, NM, USA

Introduction

Central Asia encompasses a land area of 5.9 million km

and includes the countries of Kazakstan, Turkmenistan,

Uzbekistan, Kyrgyzstan, and Tajikistan (Figure 1),

which became independent of the Soviet Union in

1991. Some geographers also include portions of

neighbouring Afghanistan, Pakistan, western China,

and Mongolia in Central Asia, but this review focuses

on the regional geology of the five former Soviet

republics. Most of Central Asia is steppe (arid grass-

land) and desert, which contrasts sharply with its

mountain ranges, which are some of the world’s

longest (the Tien Shan is 2500 km long) and tallest

(more than 7000 m).

Kazakstan

The largest state in Central Asia, Kazakstan, is half the

size of the USA and has a land area of 2 717 300 km

It thus occupies about half the total area of Central

Asia. Kazakstan is mostly steppe and desert, but in the

south and southeast the Tien Shan, Zailiski Alatau,

and Dzhungarian mountain ranges have peaks that

exceed 7000 m in altitude (Figure 2). In contrast, the

Karagie Depression in western Kazakstan in the Cas-

pian Sea basin is 132 m below sea level, the lowest

point on land after the Dead Sea. Large Kazak lakes

include one of the largest in the world, Lake Balkash,

with a surface area in excess of 17 000 km

Physiographically, Kazakstan is a vast country

south of the western Siberian lowlands, north of the

Tien Shan Mountains, east of the Caspian Sea and

west of the Altai ranges that run along its eastern

borders with China and Mongolia. Kazakstan

includes part of the South Caspian Basin (Depres-

sion), with a sedimentary fill of Jurassic–Neogene

age as much as 20 km thick, one of the most import-

ant oil-producing regions in the world. It also encom-

passes the southern tip of the Ural Mountains, most

of which are in Russia. The extensive Kazak deserts

and uplands cover most of the country. Internally-

drained basins with saline lakes extend across the

northern part of Kazakstan–the Tengiz, Balkash and

Alakol basins. A chain of deserts (including the Bet-

pak Dala) north of the Tien Shan Mountains and

south of Lake Balkash grade northward into steppes

and forested uplands.

Precambrian and Palaeozoic rocks are exposed in all

of the major mountain ranges of Kazakstan, as well as

in the Mangyshlak Peninsula (which juts into the Cas-

pian Sea) and in the North Caspian basin. Mesozoic

and Cenozoic rocks are the widespread fill of various

sedimentary basins, including the South Caspian,

North Caspian, Turan, Turgay, Balkash, Alakol, Ily

(Chu), and Zaysan basins.

The Precambrian rocks exposed in the Kazak moun-

tain ranges consist of mostly schists, gneisses, marbles,

and igneous rocks. Palaeozoic rocks are mostly of

sedimentary origin, being Cambrian–Ordovician

marine strata and volcanic rocks, Silurian–Early Car-

boniferous clastic sediments, volcanic rocks, cherts

and ophiolites and Late Pennsylvanian–Permian non-

marine and marine sedimentary rocks. Notably, in the

North Caspian Basin, salt domes have formed in a

thick (4–5 km) succession of Permian salt. From the

Tien Shan to north of Lake Balkash, the Kazak moun-

tain ranges also expose remnants of a huge magmatic

belt of mid-Carboniferous to Permian age, composed

of lavas, tuffs, and ignimbrites, with an aggregate

thickness of 5 to 6 km.

In Kazakstan, Early Triassic rocks are mostly tuffs

and basalts, but, younger Mesozoic rocks are mostly

nonmarine sedimentary rocks, though some marine

strata of Mesozoic age are present.

The large lakes of Kazakstan have long geological

histories. A good example is Lake Zaysan in north-

eastern Kazakstan. Today, Lake Zaysan is located

164 ASIA/Central

between the Altai and Targabatay ranges, is fed by the

Cherny Itrysh River to the east and historically was

about 100 km long, 32 km wide and 8 m deep. Begin-

ning in the Late Cretaceous, a lake basin formed in the

Zaysan basin and still exists today. The contracting

and expanding lake basin thus has endured for more

than 65 million years, and it has left nearly a kilometer

of sedimentary basin fill, which is well exposed along

the uplifted basin flanks (Figure 3A). These sediment-

ary rocks contain one of the most remarkable and

continuous Cenozoic fossil records in Asia, including

fossils of charophytes, land plants, ostracods, mol-

luscs, fishes, turtles, crocodiles, birds, and mammals.

Other Cenozoic lake basins in eastern Kazakstan also

contain thick and fossiliferous sedimentary basin fills

(Figure 3B).

Kazakstan is a country rich in oil, gas, and mineral

resources. Oil and gas in Mesozoic and Palaeogene

strata in the South Caspian basin are one of the

world’s great oil reserves. More than 300 coal de-

posits have been identified in Kazakstan, constituting

proven reserves in excess of 170 billion tons. These

coal deposits are mostly in Carboniferous rocks in the

Kazak mountain ranges.

Kazakstan has a diverse and extensive mineral

wealth, including important deposits of lead, zinc,

iron, manganese, nickel, copper, tin, molybdenum,

aluminum, and gold. Palaeozoic rocks are generally

host to these metals.

Figure 2 The Zaily Alatau in eastern Kazakstan is typical of the

high mountain ranges of the Tien Shan Mountains that character-

ise much of Central Asia.

Figure 1 Map of Central Asia (modern topography) showing the boundaries of the Palaeozoic terranes. (With permission from

Fortey and Cocks (2003).)

ASIA/Central 165

Turkmenistan

Turkmenistan encompasses an area of 448 100 km

most of which (about 80%) is the vast Kara Kum

(Black Sand) Desert. Elevations across this desert drop

from 100–200 m in the east, to 28 m below sea level at

the coastline of the Caspian Sea. Along the south-

western frontier of Turkmenistan, the Kopetdag and

Balkhan Mountains reach elevations of up to 2912 m,

and the western edge of the Tien Shan Mountains just

reaches the eastern border of Turkmenistan. The vast

Kara Kum is mostly blanketed by Quaternary deposits,

and the mountain ranges in the southwestern part

of Turkmenistan mostly expose Mesozoic (especially

Triassic) rocks, as is true of the mountainous south-

eastern part of the country. The only significant

outcrops of Palaeozoic strata, and of metamorphic

and igneous rocks, are in the western Tien Shan

Mountains.

Turkmenistan can thus be divided into two geo-

logic regions, the Kara Kum platform and the south-

ern mountainous (orogenic) belt. In the subsurface

of the Kara Kum, extensive drilling has revealed

Precambrian metamorphic rocks overlain by a thick,

much deformed succession of Palaeozoic strata

(mostly of Silurian, Devonian, and Carboniferous

age), Palaeozoic granites and less deformed, mostly

nonmarine, strata of Late Carboniferous, Permian,

and Triassic age, with an aggregate thickness of 5 to

6 km. These strata are overlain by essentially flat-

lying Jurassic, Cretaceous, and Cenozoic sedimentary

rocks, that typically have an aggregate thickness of 1

to 2 km, though they reach thicknesses of 8 to 10 km

in local sedimentary basins.

The mountainous belt of Turkmenistan is mostly

made up of strongly deformed Mesozoic and Paleo-

gene rocks that represent a wide array of environ-

ments, from nonmarine Triassic red beds, to Jurassic

marine limestones, to Cretaceous shallow marine

glauconitic claystones. The Tien Shan Mountains in

Turkmenistan are a continuation of the same rocks

better exposed in Uzbekistan.

Most of the topography in Turkmenistan is the

result of Late Cenozoic tectonism. This tectonic ac-

tivity continues today and is most evident in numer-

ous earthquakes, some with Richter values greater

than 7, especially in the southwestern part of the

country. Pliocene–Pleistocene oscillations of the water

level in the Caspian Sea drove water all the way out to

the main part of the Turkmenistan plains. During the

Soviet era, between the 1950s and 1980s, the Great

Kara Kum Canal was built across southern Turk-

menistan, from its eastern border to the Caspian

Sea, a distance of some 1400 km. This canal, major

irrigation projects along the Amu-Darya and Syr-

Darya rivers, and the damming of other rivers helped

aridify the Aral Sea region, turning it into a rapidly

shrinking waterbody (Figure 4).

Turkmenistan is a major oil and gas producer,

particularly in the area that adjoins the Caspian Sea.

Deposits of potassium salt, halite, and sulphate in

the Kara Kum platform have yielded important

deposits of iodine and bromine. All economic pro-

duction of these chemical elements is from rocks of

Jurassic–Eocene age.

Figure 4 This 10-metre-long fishing boat was abandoned along

the arid and receding shoreline of the Aral Sea.

Figure 3 (A) Uplifted Palaeogene strata along the Kalmakpay

River at the foot of the Targabatay Range in the Zaysan basin.

(B) Miocene lake sediments near Aktau Mountain on the northern

flank of the Ily basin in eastern Kazakstan.

166 ASIA/Central

Uzbekistan

Uzbekistan encompasses an area of 447 400 km

and

has a varied landscape from the western portion of

the Tien Shan Mountains in the east and the Pamir-

Altai ranges to the south-east, to the Kyzyl Kum (‘Red

Sand’) Desert and shores of the Aral Sea to the north-

west. The country is located between two of the great

rivers of Central Asia, the Amu-Darya and the Syr-

Darya, both of which have headwaters in the Tien

Shan Mountains and flow to the Aral Sea.

The Tien Shan Mountains in Uzbekistan, as else-

where, have a core of Palaeozoic (especially Silurian,

Devonian, and Carboniferous age) sedimentary rocks

and Precambrian–Early Palaeozoic metamorphic

rocks that are intensely deformed. The metamorphic

rocks include ophiolites, which are evidence of the

ancient collapse of ocean basins as island arcs and

other microcontinents were amalgamated to form

what is now Central Asia. Granitic intrusions, that

range in age from Cambrian to Triassic, are also pre-

sent in the Uzbek portion of the Tien Shan. North of

the Tien Shan, the bedrock of Uzbekistan is primarily

Mesozoic and Cenozoic sedimentary rocks.

The Mesozoic rocks were mostly deposited in

small, tectonically active basins in the southern and

western parts of Uzbekistan. On the Ustyurt Plateau

(the portion of Uzbekistan southwest of the Aral Sea)

and in southern Uzbekistan, the Triassic rocks are

mostly nonmarine sediments. Jurassic rocks, how-

ever, are much more widespread and are a mixture

of marine and nonmarine sediments. The Cretaceous

rocks are similarly widespread. The Lower Cret-

aceous strata are mostly of nonmarine origin, but

some marine strata are present and are the host

rocks for petroleum. The Upper Cretaceous rocks

are mostly marine strata of limestone and gypsum;

they contain important uranium deposits.

Palaeogene rocks in Uzbekistan are of both marine

and nonmarine origin and contain reserves of oil and

gas. The thickest cover of the low-lying regions of the

country, however, is the Neogene strata, which are up

to 6 km thick. Much of this thickness is alluvial sedi-

ments that were shed from the rising Tien Shan.

Quaternary sediments are also products of the Tien

Shan uplift and provide evidence of four pulses of

uplift in the form of four prominent river terrace

levels. To the north of the mountains, they are

covered by a veneer of reddish orange sand dunes, 5

to 60 m thick, that make up the Kyzyl Kum Desert of

northern Uzbekistan.

Oil, gas, and uranium deposits of Uzbekistan have

just been mentioned. Mineral deposits are diverse and

include copper, zinc, gold, and mercury, mostly in

hydrothermal concentrations. Some Uzbek basaltic

diatremes of Triassic age even yield diamonds.

Kyrgyzstan

A relatively small country, with an area of

198 500 km

, Kyrgyztan is a mountainous land dom-

inated by the Tien Shan Mountains, with peaks as

high as 7439 m. Exposed rocks range in age from

Archaean to Cenozoic. Much of the older bedrock

of Kyrgyzstan (the bedrock core of the Tien Shan) is

constructed primarily from a few Palaeozoic (primar-

ily of Late Ordovician and Carboniferous age) island

arcs that collided during the Late Palaeozoic–Early

Mesozoic.

In Kyrgyzstan, Precambrian rocks have small out-

crop areas in the mountains, which mostly expose

Palaeozoic sedimentary rocks (especially of Ordovi-

cian, Silurian, Carboniferous, and Permian ages) as

well as many Palaeozoic granitic intrusive rocks.

Basin floors are covered with Cenozoic rocks, and

Mesozoic strata are primarily exposed along uplifted

basin margins.

The principal and largest basin in Kyrgyzstan is

the Fergana Basin, which occupies much of the west-

ern part of the country and extends into eastern

Uzbekistan. In the various Kyrgyz basins, Triassic

and Jurassic strata are intensely folded, coal-bearing

rocks that reach an impressive 5 km thick in the

Fergana Basin. These rocks yield an extensive record

of fossil plants (Figure 5). Overlying Cretaceous and

Paleocene–Eocene rocks are a mixture of shallow

marine, shoreline, and terrestrial sediments that are

more than 2 km thick in the Fergana basin. Subse-

quent Cenozoic sediments are wholly nonmarine in

origin, and are more than 4 km thick in the Fergana

Basin. At various times, the Fergana Basin was filled

with a lake surrounded by mountains several hundred

meters high. Today, however, the largest lake basin in

Kyrgyzstan is Issyk-Kul in the Tien Shan along the

northern frontier with Kazakstan.

Tectonic activity in Kyrgyzstan during the Plio-

Pleistocene produced the final uplift of the mountains

and the deposition of thick continental sediments in

the intermontane basins under cold and arid Pleisto-

cene glacial conditions. This is when the current Tien

Shan Mountains developed, and there was intense

folding of the basinal Mesozoic and Cenozoic rocks.

Kyrgyzstan is a highly seismic country where numer-

ous large earthquakes occur, especially in the eastern

Fergana Basin and in the Kyrgyz and Kungey mountain

ranges along the northern frontier.

In Kyrgyzstan, oil and gas is produced in the Fer-

gana Basin from Jurassic, Cretaceous, and Cenozoic

ASIA/Central 167

strata, and coal is also mined there. The Jurassic coal-

bearing rocks in the Uzgen basin of western

Kyrgyzstan are up to 5 km thick, and they are the

most extensive exposures of Jurassic rocks in Central

Asia. Minerals of economic importance are mercury,

antimony, gold, and tin, mostly found in hydrothermal

or skarn deposits.

Tajikistan

The smallest Central Asian country, with a land area of

143 100 km

, more than 90% of Tajikistan is covered

by mountains. The southern edge of the Tien Shan

Mountains (also called the Trans-Altai Mountains) is

along the northern edge of Tajikistan. Most notable

are the Pamir Mountains, with glaciated peaks as high

as 7495 m. The Pamirs (the name is from a Farsi word

meaning ‘high level valleys’) are actually a high

plateau with an average elevation of about 6000 m.

The eastern two-thirds of Tajikistan is the Trans-

Altai and Pamir Mountains. The Pamirs are faulted

belts of rocks that range from Late Palaeozoic in the

north to Early Cenozoic in the south. In the western

part of Tajikistan, where its capital city of Dushanbe

is located, the Tajik depression is a basin with a

sedimentary basin fill 6 km thick that consists of Jur-

assic salt deposits, Cretaceous–Oligocene marine

strata, and younger Cenozoic nonmarine strata.

These rocks are intensely folded, and the Jurassic

salt includes a detachment surface that is being under-

thrust. Indeed, Tadjikistan (particularly under the

Pamirs) is a place where the subduction of continental

lithosphere is taking place. Because of this, it is a

region of high seismicity, with earthquakes concen-

trated along the Pamirs and the southern margin of

the Trans-Altai Mountains.

Geologic History

Central Asia is composed of a mosaic of ancient

continental blocks which were microplates or

independent terranes at various times in the Palaeo-

zoic. Figure 1 shows a number of these terranes which

are positioned between the old cratons of Baltica

(most of northern and eastern Europe), Siberia (only

part of modern Siberia) and the southern peri-Gond-

wanan terranes which include Mangyshlak, the South

Caspian Terrane, and the various terranes which

make up Arabia today. The many central Asian

terranes shown together make up the tectonically

complex ‘Altaids’: some have some Precambrian

slivers in their cores, but most originated within

island arc settings at various times in the Palaeozoic.

The Lower Palaeozoic faunas contained within

many of them are abundant and often distinctive,

indicating liaisons and/or oceanic separations be-

tween their Lower Palaeozoic positions. These rela-

tively small terranes progressively collided and

amalgamated with each other, mostly during the

Upper Palaeozoic during the formation of Pangaea.

The results of the collisions are most evident in the

bedrock cores.

In Central Asia, Late Palaeozoic compression, col-

lision, and subduction was followed by Mesozoic

extension, with widespread emplacement of granite

batholiths and diabase dike intrusions, as well as the

development of large sedimentary basins. During

the Late Palaeozoic–Mesozoic, Central Asia was

part of the Pangaean supercontinent, and as Pangaea

split apart it remained part of southern Eurasia.

The Cenozoic geological history of Central Asia has

been dominated by the collision of India with Eurasia

during the Paleogene. This collision reactivated old

structures along the Pangaean collisional zones. The

Figure 5 Triassic fern-like plants from the Fergana Basin in

Kyrgyzstan.

168 ASIA/Central

northward propagation of deformation from the col-

lision saw India thrust under Tibet, subsidence of

many of the Cenozoic sedimentary basins of Central

Asia, rise of the southern and then the northern Tien

Shan, and also the deformation of more northerly

uplifts. This deformation thus produced the dramatic

basins and ranges that characterize the Central Asian

landscape today.

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