Elsevier Encyclopedia of Geology

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highly metamorphosed sedimentary and igneous

rocks. From about 1650 Ma, the EEC was subject to

repeated episodes of rifting, with the development of

intracratonic basins (aulacogens). This rifting also

controlled the structure of the eastern margin of the

craton, with general subsidence leading to widespread

deposition. The latter continued until the onset of

Timanian Orogeny in the Vendian. Thereafter, uplift

and deep erosion reduced most of the orogen to a

peneplain which, early in the Palaeozoic, developed

as a rifted margin to the craton-cored continent; the

latter is generally referred to by palaeogeographers as

Baltica. Deposition along the eastern edge of Baltica

continued, mostly in passive margin shelf facies, until

the beginning of the Uralian Orogeny in the Late

Palaeozoic.

The name Baltica is applied to both a palaeocon-

tinent (with a core of the EEC) and a plate (i.e. the

continent with surrounding oceanic crust, reaching out

to the plate boundaries) which existed in the Late

Precambrian and Early Palaeozoic. Characteristic

endemic faunas defined its independence from other

major continents in the Early Cambrian. Baltica

became a part of Laurussia during the mid-Palaeozoic

Caledonian Orogeny. Baltica came into existence as

an independent plate as the result of Neoproterozoic

rifting and fragmentation of the supercontinent Rodi-

nia; exactly when is not well defined. However, the

eastern (Timanian) oceanic margin of Baltica was

clearly established earlier in the Neoproterozoic than

the north-western Baltoscandian margin.

The foreland folding and thrusting of the Timanide

Orogen (Figure 2) extends for a length of at least

3000 km from the southern Urals (where it disap-

pears beneath younger successions), northwards

along the Uralian deformation front and then

northwestwards via the Timan Range and northern

edge of the Kola Peninsula to the Varanger Peninsula

of northernmost Norway. Here, the Timanide Oro-

gen is truncated by the mid-Palaeozoic, Scandian

thrust front of the Scandinavian Caledonides and

the latter is inferred to continue northwards through

the Barents Sea to the northern edge of the Eurasian

Shelf (Figure 1).

How far east the Timanides extended is not known.

Timanian deformed and metamorphosed rocks occur

throughout the western flank of Ural Mountains and

into southern and central Novaya Zemlya. They do-

minate the Baltica margin complexes which underlie

the main Palaeozoic allochthons of ocean-derived

Figure 1 North-western Russia: tectonic relationships. M:

Mitushev Bay, S: Sulmenev Bay, V: Vaigach Island.

Figure 2 Timanide Complexes of the Urals and Timan Range.

50 EUROPE/Timanides of Northern Russia

ophiolites and island-arc volcano-sedimentary assem-

blages, and the latter, towards the east, are covered by

Mesozoic successions of the West Siberian Basin.

The timing of the Timanian Orogeny is constrained

by the ages of the youngest sedimentary successions

involved in the Precambrian deformation and the

oldest unconformably overlying sediments. The latter

are generally Ordovician, but locally (beneath

Kolguev Island and the Pechora Basin and on Novaya

Zemlya) reach back into the Cambrian, the oldest

strata (late Early Cambrian) occurring in central

Novaya Zemlya. The youngest strata involved in the

Timanian deformation include tillites in southern

areas and contains Vendian acritarchs. Late Vendian

successions in some Timanian foreland areas are de-

veloped in molasse facies. Thus, it can be inferred that

the Timanian Orogeny occurred in the Vendian (Late

Vendian in the front of the orogen; perhaps earlier in

the hinterland) and lasted at least until the end of the

Vendian, during uplift and erosion of the orogen, prior

to Early Cambrian peneplanation and then the start

of Palaeozoic platform deposition along the Baltica

margin.

The different parts of the Timanide Orogen are

summarized below, starting in the foreland fold-and-

thrust belt and then continuing eastwards beneath the

Pechora Basin to the metamorphic complexes of the

Subarctic and Polar Urals and Novaya Zemlya.

Timanian Foreland Fold and

Thrust Belt

Two very different Neoproterozoic sedimentary suc-

cessions are preserved along the western front of the

Timanide Orogen, the one in the Southern and

Middle Urals and the other further to the north-west.

In the Timan Range and north-westwards to the

Varanger Peninsula, thick turbidite-dominated suc-

cessions occur in thrust sheets emplaced south-

westwards onto platform facies, shallow marine

carbonate (often stromatolite-bearing) and silici-

clastic formations. These turbidites were apparently

deposited along the margin of the East European

Craton in continental slope and rise environments.

These sedimentary rocks occur in upright to SW-

vergent folds and are generally well preserved, with

excellent characteristic sedimentary structures

(graded bedding and Bouma sequences) and low

grade of metamorphism (low greenschist facies).

Only locally in the exposed thrust belt, on the Kanin

Peninsula and northernmost Timan, are more

deformed and metamorphosed sedimentary rocks pre-

sent in the Timanide thrust sheets, providing evidence

of the influence of regional high amphibolite facies

metamorphism at depth within this part of the orogen.

Blueschists have also been reported in the north-

easternmost parts of the Kanin Peninsula. The turbi-

dite-dominated successions are extensively intruded

by pre-tectonic dolerite dykes and, in northern

Timan, by an alkaline suite of gabbros, granites, and

syenites, often nepheline-bearing, yielding zircon

U/Pb ages of ca. 615 Ma.

To the south-west of the main Timanide de-

formation front, Late Vendian generally non-marine

siliciclastic successions in the Varanger Peninsula,

the Mezen Basin, and further south-east in the orogen

were derived from the Timanide hinterland to the

north-east, and are inferred to be molasse.

In the southern Urals (see Europe: The Urals), the

Neoproterozoic turbidite facies is not exposed, and

thick (up to 15 km) intracratonic successions were

deposited from the beginning of the Mesoproterozoic

to the Late Neoproterozoic, dominated by shallow-

water siliciclastic and carbonate formations with

some rift volcanics and sub-volcanic intrusions.

These successions are called Riphean and are overlain

by Early Vendian tillites and Late Vendian molasse, the

latter a response to Timanian Orogeny further east.

The type area for Riphean stratigraphy is located in

the core of a major Late Palaeozoic fold, the Bashkir-

ian Anticlinorium, in the foreland fold-belt of the

Urals (Figure 2). Beneath a major Ordovician uncon-

formity, the folded and faulted Riphean and Vendian

sedimentary rocks are overlain by a more deformed

and, in part, more metamorphosed (amphibolite

facies, locally with eclogites) allochthon, the Beloretsk

Terrane. Neoproterozoic turbidites, similar to those

in the Timan Range, may have been deposited in the

areas at present occupied by the hinterland of the

Southern Urals; if this was the case, they are now in

the unexposed footwall beneath the Beloretsk Terrane.

Further north, in the middle Urals (Figure 2), another

major Uralian fold, the Kvarkush-Kamennogorsk Anti-

clinorium, like the Bashkirian Anticlinorium (above),

also contains Proterozoic successions below a post-

Timanian, Ordovician unconformity. The siliciclastic

and carbonate formations of this region are thought

to be Neoproterozoic in age, reaching up into Early

Vendian tillites and, probably, Late Vendian molasse.

Of particular interest is the occurrence in the Kvarkush

area of blue schists of Late Vendian (or possibly earliest

Cambrian) age, thrust on to the other less metamorph-

osed, low greenschist facies sedimentary rocks. Ordovi-

cian quartzites overlie these Precambrian rocks and

structures with major unconformity.

Basement of the Pechora Basin

From the Timan Range, the Timanide Orogen ex-

tends eastwards beneath the Palaeozoic and younger

EUROPE/Timanides of Northern Russia 51

strata of the Pechora Basin (Figure 2) to the foreland

fold and thrust belt of the Polar Urals. The Phaner-

ozoic cover thickens eastwards into the Uralian fore-

deep, where the unconformably overlying successions

are 10–15 km thick and the character of the under-

lying basement is unknown. However, in some central

parts of the Pechora Basin, along NW-trending axes of

uplift, the basement reaches to within a few kilometres

ofthe surface anddeepdrilling (about seventy holes) has

succeeded in penetrating the entire cover succession

to sample the basement. On the basis of this drilling,

and also regional potential field (gravity and magnetic)

anomaly maps, it has been possible to reconstruct

a simple geological map of the pre-Palaeozoic rocks

(Figure 3) beneath the Pechora Basin.

To the east of the Timan Range, three main tecto-

nostratigraphic zones have been recognised. The

western is referred to as the Izhma Zone and is a

direct easterly extension of the Timan Range turbidite

assemblages. Towards its eastern contact to the adja-

cent Pechora Zone, it is intruded by granites, mainly

of calc-alkaline composition. The Pechora Zone is

well seen on the potential field maps, it being well

defined by a broad belt of NW-trending magnetic

anomalies. Drillcores show that the Pechora Zone is

dominated by volcanic and volcaniclastic rocks, ex-

tensively intruded by plutons, mainly of mafic and

intermediate composition. Calc-alkaline granites also

occur in this zone; together with those in the Izhma

Zone, they yield ages of 550–560 Ma and apparently

date the end of Timanian deformation and meta-

morphism in this part of the hinterland (Figure 4).

Further east, the Bolshezemelskaya Zone also is pre-

served locally in structural highs, accessible to the

drilling-rig. Acid volcanic rocks and granites have

been sampled here from below the Ordovician uncon-

formity, and somewhat older zircon ages of ca 570

and 620 Ma have been obtained from the latter, along

with Grenville-age xenocrysts.

Previous literature, especially in Russia, contains

several different names for the Bol’shezemel’skaya

Terrane (e.g., Khoreyer and Novozemel’skaya) of

continental blocks inferred (mostly on geophysical

evidence) to exist at depth below the Pechora Basin

and southern Barents Sea.

Pre-Ordovician Complexes of the

Subarctic Urals

The Neoproterozoic complexes of the Pechora and

Bol’shezemel’skaya zones, identified at depths of sev-

eral kilometres beneath the Pechora Basin, strike

south-eastwards into the mountain front of the Sub-

arctic Urals. Within the Uralian frontal folds and

lower thrust sheets, pre-Ordovician formations

are exposed. Andesitic volcanic rocks dominate

these Precambrian rocks in the northern Urals,

along strike to the south from the Pechora Zone.

Further to the north, in the subarctic Urals, a variety

of granitic gneisses, granites, and metasediments

occur, apparently as a southern continuation of the

Bol’shezemel’skaya Zone. Isotopic ages are less

reliable in these associations, but the presence of

Mesoproterozoic metasediments and granites, and

unconformably overlying Neoproterozoic siliciclastic

(mainly quartzites) and carbonate formations, and

acid volcanic rocks, are well documented. Early

Ordovician conglomerates and quartzites overlie the

Neoproterozoic successions with marked unconform-

ity. Thus, it can be inferred that a Precambrian com-

plex, differing in age and character from the

Palaeoproterozoic and Archaean rocks of the EEC,

occurs within the Timanide hinterland, outboard of

the Pechora Zone calc-alkaline volcanic suites.

Polar Urals

North of the Arctic Circle in the Uralide Orogen,

Neoproterozoic complexes comprise major compon-

ents in the footwall to the Palaeozoic ocean-derived

allochthons. In the core of foreland folds, beneath

Ordovician quartzites, a fragmented ophiolite

(Enganepe Terrane) has been dated by the U/Pb zircon

method to 670 Ma, and is associated with arc

Figure 3 Pre-Palaeozoic basement of theTiman-Pechora region.

52 EUROPE/Timanides of Northern Russia

volcanites and a variety of volcaniclastic sedimentary

rocks. Further east, in the Uralian thrust sheets,

where the Palaeozoic metamorphic grade is higher,

mafic island-arc related igneous complexes contain

580 Ma old gabbros, and, within the overlying

Palaeozoic eclogite-bearing associations, similar ages

characterise the igneous protoliths. Thus, in the most

easterly exposed hinterland of the Timanide Orogen,

the main Neoproterozoic component is derived from

oceanic domains.

Novaya Zemlya

Northwards and north-eastwards from the Polar

Urals, the Uralide Orogen continues via the Pai Khoi

Peninsula, Vaigach Island, and the Kara Strait into

Novaya Zemlya (Figure 1). Only the foreland folds

and thrusts of the Uralide Orogen are preserved on

land in Novaya Zemlya, the hinterland of the orogen

being buried beneath the Mesozoic successions of the

Kara Shelf.

As in the Polar Urals, major foreland anticlines

and thrusts expose Neoproterozoic complexes

beneath Lower Palaeozoic unconformities. On south-

ern Novaya Zemlya and Vaigach Island, Lower and

Middle Ordovician quartzites and limestones overlie

greenschist facies metaturbidites. Further north, in the

central parts of the archipelago (Figure 1), in the vicin-

ity of the Mitushev Bay and Sulmenev Bay, Vendian

(ca 600 Ma old) granites have been found, in the latter

case intruded into schists, marbles, quartzites, and am-

phibolites. Whereas in the Mitushev Bay area, Silurian

conglomerates rest unconformably on the granites,

further north at Sulmenev Bay, both Ordovician and

Cambrian strata overlie the unconformity, the oldest

strata reaching back into the late Early Cambrian.

Thus, in these northernmost hinterland areas, the

unconformity may have been established in the Ven-

dian. The amphibolite facies complex near Sulmenev

Bay contains Mesoproterozoic detrital zircons; some

authors infer that Precambrian orogeny there may

have been older than Timanian (e.g., Grenville-age)

and subsequently influenced by Timanian magmatism.

Barents Shelf

The Timanian rock units in the basement below the

Pechora Basin strike north-westwards into the south-

ern Barents Shelf and their associated geophysical

(potential field) signatures can be followed towards

the central parts of the Barents Sea, where they fade

beneath the thickening Palaeozoic and Mesozoic

successions of the Barents Shelf basins. Seismic studies,

both near-vertical reflection and wide-angle refrac-

tion, have identified a thick wedge of Timanian meta-

sediments along the southern margin of the Barents

Sea towards the Kola Peninsula. Further out into the

Barents Shelf, the identification of Timanian rocks is

controversial and mainly based on the interpretation

of seismic velocity data. Only on Franz Josef Land

(Figure 1), is there clear evidence of a Timanide bedrock

and even this is limited to a single deep drillhole located

on the westernmost island, which penetrated a Lower

Carboniferous unconformity to reach low greenschist

facies, small folded Vendian meta-turbidites at 2–3km

depth.

Timanide Tectonic Evolution

Evidence of the Timanian Orogeny occurs over a

wide area of north-eastern Europe. It provides a

basis for reconstructing the Neoproterozoic to Early

Figure 4 Diagramatic profile (SW–NE) through the Timan-Pechora region in the Devonian, prior to the Uralian Orogeny.

EUROPE/Timanides of Northern Russia 53

Palaeozoic tectonic evolution of this part of Baltica;

however, its fragmentary character and the extensive

Phanerozoic cover of the Pechora and Barents Shelf

basins, imply that these reconstructions are, at best,

rudimentary. A major dilemma is the lack of evidence

of the character of the Timanide hinterland to the

east of the Urals – from the Palaeozoic ocean-derived

allochthons and eastwards beneath the Mesozoic

cover of the West Siberian Basin. In addition, it is

probable that the Timanide Orogen extended both

further south-eastwards, prior to the Uralian Or-

ogeny, and north-westwards prior to the Caledonian

Orogeny, but evidence is lacking.

There follows here a tectonic synthesis (Figure 5),

based on the evidence presented above.

By the Early Neoproterozoic, after a long period

(Mesoproterozoic) of intracontinental rifting, a pas-

sive margin had been established along the eastern

edge of the EEC, at least from northern Norway to

the Middle Urals. The change from an extensional to

a compressional regime in the Vendian, with the onset

of the Timanian Orogeny, is well defined in the fore-

land fold-and-thrust belt along this part of the EEC

margin and extending southwards into the southern

Urals. Deposition of a Late Vendian molasse facies in

foreland basins along the length of the orogen pro-

vides evidence of the timing of hinterland uplift and

foreland deformation.

The Timanian Ocean existing along the eastern

margin (present-day coordinates) of the EEC in the

Figure 5 Timanian tectonic evolution, from the Early Neoproterozoic to the Late Vendian.

54 EUROPE/Timanides of Northern Russia

Neoproterozic, during deposition of the Timanian con-

tinental margin turbidites, development of the Pechora

magmatic arc and Engane-Pe ophiolites, has been re-

ferred to in previous literature by several names, e.g.,

Palaeo-Asian, Turkistan, and Aegir, based on different

interpretations of continent–ocean relationships. The

latter are not well constrained and the informal term

Timanian Ocean is preferred here.

Towards the hinterland, the dominance in the

Pechora zone of mafic to intermediate calc-alkaline

igneous suites and volcanogenic sedimentary rocks

has been interpreted to imply thrusting of oceanic

domains onto the thick passive margin turbidites of

the EEC margin (Izhma Zone). The western contact

of the Pechora Zone is not well defined, but the

presence of Timanian blue schists along strike, both

to the southeast, in the northern Urals (Kvarkush)

and to the northwest, in the easternmost Kanin

Peninsula, suggests that subduction-related arc mag-

matism culminated in thrust emplacement onto the

EEC margin.

The existence of microcontinental terranes (blocks)

in the Timanian Ocean has been widely inferred

(indeed, some authors regard the Timanides as a

number of NW-trending aulacogens with oceanic

crust separating continental blocks). The micro-

continental terranes differ from the EEC by having

Grenville-age signatures with a Mesoproterozoic

metasedimentary succession intruded by ca.

1000 Ma granites. The oceanic character of the adja-

cent Pechora Zone favours the interpretation that

these outboard terranes (e.g., the Bol’shezemel’skaya

Zone, and perhaps the Novaya Zemlya metamorphic

rocks at Sulmenev Bay) were not accreted to the EEC

until the Vendian.

To the east of the Bol’shezemel’skaya Zone, Late

Neoproterozoic ophiolites in the front of the Polar

Urals (Engane-Pe) and calc-alkaline intrusions in

some of the Uralian allochthons further east, provide

the only evidence of the oceanic character of the most

internal parts of the Timanide hinterland. Taken to-

gether with the lack of evidence of the character of the

Timanides east of the Urals, this has allowed the

widely accepted hypothesis that Timanian Orogeny

resulted from the subduction and accretion of Neo-

proterozoic ocean floor and island-arc assemblages,

along with some fragments of continents (micro-

continents), but without the involvement of a major

Asian continent (e.g., Siberia). Continent–continent

collision has not been favoured and the Neoprotero-

zoic Timanian Ocean has been regarded as a forerun-

ner of the Palaeozoic Uralian Ocean. This attractive

hypothesis remains largely unconstrained.

Timanian orogenesis was contemporaneous with

the passive margin evolution of north-western

Baltica’s Baltoscandian margin. It was also approxi-

mately contemporaneous with orogeny in many other

parts of the world; for example, the Baikalian along

the margin of the Siberian Craton, the Cadomian of

western Europe and the Pan-African of many parts of

Africa and the Middle East. Palaeomagnetic evidence

has indicated that Baltica rotated about 120



counter-

clockwise between the Vendian and the Mid-Ordovi-

cian, prior to Caledonian collisional orogeny in the

Silurian. This evidence has prompted a variety of

palaeogeographic reconstructions relating the Tima-

nides to these other orogens. It also implies that the

rotation of Baltica may have accompanied the Tima-

nian Orogeny, implying a significant component of

dextral transpression during terrane accretion.

Further Reading

Belyakova LT and Stepanenko Vya (1991) Magmatism and

geodynamics of the Baikalide Basement of the Pechora

Syneclise. Doklady Akademii nauk SSSR, (geologiya)

106–117 (in Russian).

Bogatsky VI, Bogdanov NA, Kostyuchenko SL, Senin BV,

Sobolev SF, and Khain VE (1996) Tectonic map of the

Barents Sea and the northern part of European Russia:

explanatory notes. Moscow: Institute of the Lithosphere,

Russian Academy of Sciences Moscow.

Cocks LRM and Fortey RA (1998) The Lower Palaeozoic

margins of Baltica. Geologiska Foreningens Forhandlin-

ger 120: 173–179.

Cocks LRM and Torsvik TH (2002) Earth geography from

500 to 400 million years ago: a faunal and palaeomag-

netic review. Journal of the Geological Society, London

159: 631–644.

Dushin VA (1997) Magmatism and geodynamics of

the palaeocontinental sector of the northern part of the

Urals. Moscow Nedra. pp. 211 (in Russian).

Gee DG and Pease VL (2005) The Neoproterozoic Tima-

nide Orogen of Eastern Baltica. Geological Society of

London, Memoir.

Gee DG, Belyakova LT, Pease V, Larionov AN, and

Dovzhikova E (2000). New, single zircon (Pb-evapo-

ration) ages from Vendian intrusions in the basement

beneath the Pechora Basin, northeastern Baltica. Polar-

forschung 68: 161–170.

Korago EA, Kovaleva GN, Ilin VF, and Pavlov LG (1992)

Tectonics and metallogeny of the early Kimmeridgian

of Novaya Zemlya, pp. 1–196. St Petersburg: Nedra

(in Russian).

Lopatin BG, Pavlov LG, Orgo VV, and Shkarubo SI (2001)

Tectonic structure of Novaya Zemlya. Polarforschung

69: 131–135.

EUROPE/Timanides of Northern Russia 55

Olovyanishnikov VG, Roberts D, and Siedlecka A (2000)

Tectonics and sedimentation of the Meso- to Neoproter-

ozoic Timan Varanger Belt along the northeastern margin

of Baltica. Polarforschung 68: 269–276.

Puchkov VN (1997) Structure and geodynamics of the

Uralian orogen. Geological Society of London Special

Publications 121: 201–236.

Roberts D and Siedlecka A (2002) Timanian orogenic

deformation along the northeastern margin of Baltic,

Northwest Russia and Northeast Norway, and Avalonian-

Cadomian connections. Tectonophysics 352: 169–184.

Siedlecka A (1975) Late Precambrian stratigraphy and

structure of the northeastern margin of the Fennos-

candian Shield (East Finnmark Timan region). Norges

geologiske undersokelse 316: 313–348.

Torsvik TH and Rehnstro

m EF (2001) Cambrian palaeo-

magnetic data from Baltica: implications for true polar

wander and Cambrian palaeogeography. Journal of the

Geological Society, London 158: 321–329.

Willner AP, Ermolaeva T, and Stroink L (2001) Contrasting

provenence signals in Riphean and Vendian sandstones

in the SW Urals (Russia): constraints for a change

from passive to active continental margin conditions

in the Neoproterozoic. Precambrian Research 110:

215–239.

Caledonides of Britain and Ireland

J F Dewey, University of California Davis, Davis,

CA, USA, and University of Oxford, Oxford, UK

R A Strachan, University of Portsmouth,

Portsmouth, UK

Introduction

The term ‘Caledonian’ is derived from the Latin word

for Scotland and has been used widely with reference

to the Early to Mid-Palaeozoic orogenic belt that is

exposed in the British Isles, eastern Greenland, and

Scandinavia (Figure 1). When these areas are restored

to their relative positions prior to the Cretaceous–

Tertiary opening of the North Atlantic (Figure 1), it

can be seen that they were formerly continuous,

comprising the northern part of the Mesozoic super-

continent Pangaea. The Caledonian Orogeny is the

oldest of three main Palaeozoic collisional events that

formed Pangaea, the other two being the Variscan

and Uralian orogenies.

The Caledonian orogenic belt has three main arms

(Figure 1): the North Atlantic Caledonian Belt and its

southern extension, the Appalachian Belt, which were

both formed by the closure of the Iapetus Ocean, and

the Tornquist Belt, which resulted from the closure

of the Tornquist Sea. These belts separate areas of

Archaean and Proterozoic crust, which formed the

palaeocontinents of Laurentia (North America,

Greenland, and the northern British Isles), Baltica

(Scandinavia and the Baltic), and Eastern Avalonia

(the southern British Isles, Belgium, and the adjacent

crust). Eastern Avalonia is the northernmost of a

group of continental fragments that were originally

derived from Gondwana and include Western Avalo-

nia, Iberia, and Armorica. The collision of these frag-

ments through the Mid- to Late Palaeozoic resulted in

the Variscan orogenic belt (see Europe: Variscan Or-

ogeny), which just impinges on the south of the

British Isles.

Palaeogeographical and Tectonic

Framework

The Caledonian plate-tectonic cycle began in the Mid-

to Late Neoproterozoic with the rifting and break-up

of the supercontinent Rodinia and the subsequent

dispersion of continental blocks to form the Iapetus

Ocean. Palaeomagnetic studies indicate that, in the

Late Cambrian to Early Ordovician, Laurentia occu-

pied an equatorial position to the north of Baltica and

Avalonia (the latter was still attached to Gondwana at

this stage). The distance across the Iapetus Ocean

between the locations of present-day Scotland and

England was probably about 5000 km, and the

width of the Tornquist Sea, which separated Gon-

dwana from Baltica, was probably about 1300 km.

Each continent was characterized by a distinctive

trilobite fauna. The initial closure of Iapetus was

associated with the development of a southwards-

dipping intraoceanic subduction zone and volcanic

arc off the eastern Laurentian margin. The collision

during the Early to Mid-Ordovician between the

Laurentian margin and the volcanic arc resulted in

the Grampian orogenic event (Figure 2). Subduction

polarity then reversed to dip northwards beneath

the Laurentian margin.

Eastern Avalonia rifted from Gondwana in

the Arenig and drifted rapidly northwards between

480 Ma and 460 Ma to reach a similar latitude to

Baltica during the Caradoc. A southwards-dipping

subduction zone was located along the northern

Iapetan margin of Eastern Avalonia. As on the Laur-

entian margin, a suprasubduction zone ophiolite–arc

56 EUROPE/Caledonides of Britain and Ireland

Figure 1 Simplified Caledonian tectonic map of the British Isles with their Appalachian continuation shown in the inset. Bl,

Ballantrae Ophiolite; BO, Borrowdale Volcanics; CB, Central Belts; CBC, Clew Bay Complex; GGF, Great Glen Fault; GR, Grangegeeth

Terrane; HBC, Highland Border Complex; HBF, Highland Boundary Fault; LL, Leadhills Line; M, Moine; Ma, Manx Group; MSF, Menai

Straits Fault; MSG, Monian Supergroup; MT, Moine Thrust; MVT, Midland Valley Terrane; OBF, Orlock Bridge Fault; RIL, Red Indian

Line; SC, South Connemara Terrane; SCG, South Connemara Group; Sk, Skiddaw Group; SL, Slane Fault; SMT, South Mayo Trough;

SUF, Southern Uplands Fault; TL, Tornquist Line; Ty, Tyrone Ophiolite; WFZ, Wicklow Fault Zone.

EUROPE/Caledonides of Britain and Ireland 57

complex was obducted onto the Eastern Avalonian

margin during that margin’s collision with a north-

wards-dipping subduction zone, followed by polarity

flip to southwards-directed subduction. The oceanic

tract that opened between Eastern Avalonia and

Gondwana is known as the Rheic Ocean. At

460 Ma, Eastern Avalonia was probably about

1000 km west of Baltica, and the width of the Iapetus

Ocean was reduced to approximately 2000 km across

the British sector. The intermediate position of Ava-

lonia during its transit across the closing Iapetus

Ocean is reflected in the changing affinities of its

brachiopods, from Gondwanan to a mixture of

genera with ancestors from Baltica and Laurentia,

through the Ordovician. By Late Ordovician–Early

Silurian times (440 Ma), the Iapetus Ocean and the

Tornquist Sea had narrowed sufficiently to allow

the interchange of the larvae of most benthic animals.

Eastern Avalonia collided with Baltica during

the Ashgill. By this time, the width of the Iapetus

Ocean across the British sector had been reduced to

around 1300 km.

Sinistrally oblique collision between the combined

Avalonia–Baltica landmass and Laurentia occurred

between 435 Ma and 425 Ma to form the continent

Laurussia. The ‘hard’ collision of Baltica with the

eastern Greenland–northern Scotland segment of

Laurentia resulted in the Scandian orogenic event. In

contrast, the ‘soft’ collision of Eastern Avalonia

with Laurentia was not associated with regionally

Figure 2 Schematic sections illustrating the Ordovician tectonic evolution of the Grampian Zone.

58 EUROPE/Caledonides of Britain and Ireland

significant shortening, suggesting that Eastern

Avalonia and Baltica may have been only loosely

coupled during the final collision. The Iapetus Suture

is referred to as the Solway Line, because it is appar-

ently located in the Solway Firth, albeit obscured

entirely by unconformably overlying Carboniferous

strata.

Between 425 Ma and 410 Ma, sinistral relative

motion between Laurentia and Baltica–Avalonia

became orogen-parallel and was associated mainly

with displacement along the Great Glen, Highland

Boundary, and Southern Uplands faults. From about

410 Ma, the Caledonides went into regional sinistral

transtension, resulting in the formation of a series of

transtensional Old Red Sandstone basins. These

events were contemporaneous with the rapid contrac-

tion of the Rheic Ocean as Gondwana approached

Laurussia. During the Early to Mid-Devonian, East-

ern Avalonia was affected by widespread Acadian

deformation. Although this has traditionally been

assigned to the Caledonian orogenic cycle and the

closure of Iapetus, it postdates the latter by ca.

20 Ma. Alternatively, the Acadian event could be the

result of the collision of Armorica with the southern

margin of Avalonia. The collision of Armorica with

Avalonia and the collision of Iberia with the southern

margin of Armorica during the Mid-Devonian

could be viewed as the early stages of the protracted

Variscan Orogeny, which ultimately resulted in the

assembly of Pangaea.

The along-strike continuation of the Caledonides

in Newfoundland provides, arguably, the best-

exposed section across the orogen, which can be

used as a template to aid the understanding of other

sectors such as the British Isles. The Caledonides of

the British Isles are subdivided by major faults into a

series of terranes, each with a coherent internal his-

tory. The correlation of geological units and events

across terrane-bounding faults is commonly problem-

atic. These structures display evidence of long and

complex reactivation histories, although the last

major displacement for most faults north of the Iap-

etus Suture was during Silurian to Devonian time.

Although the detail of the tectonic template is

extremely complex, there are three main groups of

terranes: those north of the Fair Head–Clew Bay Line

and Highland Boundary Fault, which have Lauren-

tian affinities; those south of the Solway Line, which

have Gondwanan affinities; and the intermediate

terranes, which represent fragments of continental

margin, island arc, and oceanic lithosphere within a

composite complex suture zone. Seismic imaging

indicates that the Iapetus Suture dips moderately to

the north, separating reflective Avalonian crust from

overthrust non-reflective Laurentian crust.

Terranes and their Geotectonic

Affinities

From north to south, the main terranes are character-

ized as follows.

Hebridean Terrane

In north-west Scotland, the Hebridean Terrane forms

the foreland to the Caledonian belt and is limited to

the east by the Moine Thrust Zone. The oldest com-

ponent is the Archaean–Palaeoproterozoic Lewisian

Gneiss Complex, which is correlated with Laurentian

basement in south-east Greenland. The unconform-

ably overlying continental Torridonian sedimentary

rocks were deposited from 1200–1000 Ma and com-

prise two successions separated by an angular uncon-

formity. The Lewisian and Torridonian rocks are

overstepped by a highly distinctive succession of

Cambrian–Ordovician shallow-marine quartzites

and limestones, which accumulated on the Lauren-

tian margin of Iapetus and correlate closely with

similar sequences in north-western Newfoundland

and eastern Greenland.

Northern Highland Terrane

The Northern Highland Terrane is bounded in north-

western Scotland by the Moine Thrust Zone and the

Great Glen Fault. The terrane is dominated by the

Early Neoproterozoic Moine Supergroup, a thick suc-

cession of strongly deformed and metamorphosed

marine sediments that were deposited in an intracra-

tonic rift within the Laurentian sector of the Rodinia

Supercontinent at 1000–870 Ma. Early deformation

and metamorphism during a Knoydartian tecto-

nothermal event at 800 Ma may have resulted from

rift closure. Inliers of Archaean orthogneisses, vari-

ably reworked at 1000 Ma during the Grenville or-

ogeny, represent the basement on which the Moine

sediments were unconformably deposited.

Grampian Terrane

In Scotland and north-western Ireland, the Grampian

Terrane occurs between the Great Glen Fault and the

Fair Head–Clew Bay Line or Highland Boundary

Fault. The terrane is dominated by the Dalradian

Supergroup, a thick succession of variably deformed

and metamorphosed metasandstones, metasiltstones,

and metalimestones with minor contemporaneous

mafic igneous rocks. The duration of sedimentation

is uncertain, but it probably spanned at least the

period 750–520 Ma. Tillites have been correlated

with the widespread Sturtian and Varangerian glacial

events. The Dalradian succession shows a transition

from shallow-water to deep-water sedimentation,

EUROPE/Caledonides of Britain and Ireland 59

Elsevier Encyclopedia of Geology - vol I A-E

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