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The Uralian orogen is located along the western flank of a huge (>4000 km long) intracontinental Uralo-Mongolian mobile belt. The orogen developed mainly between the Late Devonian and the Late Permian, with a brief resumption of orogenic activity in the Lower Jurassic and Pliocene-Quaternary time. Although its evolution is commonly related to the Variscides of Western Europe, its very distinctive features argue against a simple geodynamic connection. To a first order, the evolution of Uralian orogen shows similarities with the 'Wilson cycle', beginning with epi-continental rifting (Late Cambrian-Lower Ordovician) followed by passive margin (since Middle Ordovician) development, onset of subduction and arc-related magmatism (Late Ordovician) followed by arc-continent collision (Late Devonian in the south and Early Carboniferous in the north) and continent-continent collision (beginning in the mid-Carboniferous). In detail, however, the Uralides preserve a number of rare features. Oceanic (Ordovician to Lower Devonian) and island-arc (Ordovician to Lower Carboniferous) complexes are particularly well preserved as is the foreland belt in the Southern Urals, which exhibits very limited shortening of deformed Mesoproterozoic to Permian sediments. Geophysical studies indicate the presence of 'cold', isostatically equilibrated root. Other characteristic features include a Silurian platinum-rich belt of subduction-related layered plutons, a simultaneous development of orogenic and rift-related magmatism, a succession of collisions that are both diachronous and oblique, and a single dominant stage of transpressive deformation after the Early Carboniferous. The end result is a pronounced bi-vergent structure. The Uralides are also characterized by Meso-Cenozoic post-orogenic stage and plume-related tectonics in Ordovician, Devonian and especially Triassic time. The evolution of the Uralides is consistent with the development and destruction of a Palaeouralian ocean to form part of a giant Uralo- Mongolian orogen, which involved an interaction of cratonic Baltica and Siberia with a young and rheologically weak Kazakhstanian continent. The Uralides are characterized by protracted and recurrent orogenesis, interrupted in the Triassic by tectonothermal activity associated with the Uralo-Siberian superplume.
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doi:10.1144/SP327.9
2009; v. 327; p. 161-195 Geological Society, London, Special Publications
Victor N. Puchkov
The evolution of the Uralian orogen
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The evolution of the Uralian orogen
VICTOR N. PUCHKOV
K. Marx st. 16/2, Institute of Geology, Ufimian Scientific Centre,
Russian Academy of Sciences, 450 000 Ufa, Russia
(e-mail: puchkv@anrb.ru)
Abstract: The Uralian orogen is located along the western flank of a huge (.4000 km long)
intracontinental Uralo-Mongolian mobile belt. The orogen developed mainly between the Late
Devonian and the Late Permian, with a brief resumption of orogenic activity in the Lower
Jurassic and PlioceneQuaternary time. Although its evolution is commonly related to the
Variscides of Western Europe, its very distinctive features argue against a simple geodynamic
connection. To a first order, the evolution of Uralian orogen shows similarities with the
‘Wilson cycle’, beginning with epi-continental rifting (Late CambrianLower Ordovician)
followed by passive margin (since Middle Ordovician) development, onset of subduction and
arc-related magmatism (Late Ordovician) followed by arc continent collision (Late Devonian
in the south and Early Carboniferous in the north) and continent continent collision (beginning
in the mid-Carboniferous). In detail, however, the Uralides preserve a number of rare features.
Oceanic (Ordovician to Lower Devonian) and islandarc (Ordovician to Lower Carboniferous)
complexes are particularly well preserved as is the foreland belt in the Southern Urals, which
exhibits very limited shortening of deformed Mesoproterozoic to Permian sediments. Geophysi-
cal studies indicate the presence of ‘cold’, isostatically equilibrated root. Other characteristic
features include a Silurian platinum-rich belt of subduction-related layered plutons, a simul-
taneous development of orogenic and rift-related magmatism, a succession of collisions that
are both diachronous and oblique, and a single dominant stage of transpressive deformation
after the Early Carboniferous. The end result is a pronounced bi-vergent structure. The Uralides
are also characterized by Meso-Cenozoic post-orogenic stage and plume-related tectonics in
Ordovician, Devonian and especially Triassic time. The evolution of the Uralides is consistent
with the development and destruction of a Palaeouralian ocean to form part of a giant Uralo-
Mongolian orogen, which involved an interaction of cratonic Baltica and Siberia with a
young and rheologically weak Kazakhstanian continent. The Uralides are characterized by
protracted and recurrent orogenesis, interrupted in the Triassic by tectonothermal activity
associated with the Uralo-Siberian superplume.
Introduction
The last general review of the structural and tectonic
evolution of the Uralian orogen was published in
English more than 10 years ago (Puchkov 1997).
Since then, the stimulus created by the international
EUROPROBE Uralides Project has resulted in con-
siderable advances in the understanding of the
geology of the Urals. However, most publications
in English are concerned with the evolution of the
Southern and Middle Urals (Brown et al. 2006a,
2008, and references therein). This publication pro-
vides an overview of the tectonic evolution of the
Uralian orogen as a whole, incorporating a wealth
of recently published data, and compares this evol-
ution with that of the European Variscides and
Mesozoic-Cenozoic orogens.
The Uralian orogen sensu stricto partly
coincides geographically with the young, neotec-
tonic (PlioceneQuaternary) Urals mountains, and
occurs between three former, Palaeozoic continents:
Baltica, Kazakhstania and Siberia (Fig. 1). In the
Early Palaeozoic, these continents were separated
by the Palaeouralian and Central Asian oceans.
The continents and oceans were partly inherited
from the Proterozoic (Vernikovsky et al. 2004;
Puchkov 2005). The Central Asian (or Palaeo-
Asian) ocean existed before the Late Neoproterozoic
as the portion of the Palaeo-Pacific Ocean, which
surrounded a considerable part of the Siberian conti-
nent. A complete separation of this continent from
Rodinia by 750 Ma resulted in the birth of the
Palaeo-Asian ocean (Li et al. 2008).
The ENE margin of Baltica was modified by
the Ediacarian deformational and accretionary
events of the Timanian orogeny (Puchkov 1997;
Gee et al. 2006). A close resemblance of Timanides
and Cadomides pointed out by the author (Puchkov
1997) has led to an idea of their immediate lateral
connection, supporting a notion of a supercontinent
(Pannotia, Dalziel 1992; or Panterra, Puchkov
2000), welded by Ediacarian orogenies. Several var-
iants of such a connection have been suggested,
depending on what side of Baltica was thought to
From:MURPHY, J. B., KEPPIE,J.D.&HYNES, A. J. (eds) Ancient Orogens and Modern Analogues.
Geological Society, London, Special Publications, 327, 161195.
DOI: 10.1144/SP327.9 0305-8719/09/$15.00 # The Geological Society of London 2009.
Fig. 1. Position and linkages of the Urals in the structure of the Central Eurasia.
V. N. PUCHKOV162
be attached to Gondwana (e.g. Linneman et al.
1998; Puchkov 2000; Cocks & Torsvik 2006).
Unfortunately the APWP of Baltica is still very
poorly constrained by existing palaeomagnetic
data and additional work is required to distinguish
between these hypotheses.
The Timanian/Cadomian orogeny was followed
by Late Cambrian Early Ordovician rifting and
passive margin development (Puchkov 2005;
Pease et al. 2008). These events led to the develop-
ment of the Palaeouralian ocean, which contained
some younger microcontinents (the continent that
rifted-away from Baltica is not identified yet). The
Mid- to Late Palaeozoic history of the Uralian
orogen can be described in terms of formation of
an island-arc crust (Late Ordovician Devonian)
and followed by Late Devonian Early Carbonifer-
ous accretion of the island-arcs and other microcon-
tinents with the continental margin of Baltica, which
by that time had merged with Laurentia to form
Laurussia (Brown et al. 1997, 2006ac). Kazakh-
stania formed in the OrdovicianSilurian as a
result of subduction-driven accretion of crust
around small Neoproterozoic microcontinents
(Puchkov 1996a). Its collision with the terranes pre-
viously accreted to the margins of Laurussia and
Siberia started in the Late Bashkirian, after the inter-
vening oceanic crust was completely subducted.
This continentcontinent collision continued into
Permian time, and resulted in the formation of
huge foldbelt, variously known as Uralo-Mongolian
(Muratov 1979) or Uralo-Okhotskian (Khain 2001)
belt, a fundamental event in the assembly of
Pangaea. The narrow western flank of the orogen
is known as the Uralides, and the more extensive
central and eastern flank of the belt is called the
Altaides (Sengo
¨
r et al. 1993). However the position-
ing of the Kazakhstanian continent as a separate
Mid-Palaeozoic structure (Figs 1 & 2) suggests
that the Kazakhstanides should be excluded from
the Altaides.
An attempt to formalize the term ‘Uralides’ was
made by Puchkov (2003), who noted that the north-
ern continuation of the western zones of the Urals is
represented by the Pay-Khoy-Novozemelian
foldbelt, which was the result of the younger
(Early Jurassic) collision between Laurussia and
Siberia. More southern parts of the Urals were
also deformed by this collision, though the intensity
and structural expression are not as prominent.
To the south, Late Palaeozoic collisional struc-
tures of the Urals continue in the south-southwest-
wards vergent fold-and-thrust belt of the Southern
Tyan-Shan. Like the Urals, this Late Palaeozoic
belt is bordered to the NE and north by the Early
Caledonides of Kazakhstania, where the Northern
Tyan-Shan occurs (Fig. 1). Attempts to trace Late
Palaeozoic structural features from the Uralides
into the Southern Tyan-Shan have been thwarted
by the higher degree of shortening and lack of
Devonian island arc development in the latter fold-
belt. However, palaeocontinental reconstructions
and modern structural connections (Figs 1 & 2)
suggest a genetic linkage. The evolution of Southern
Tyan-Shan is related to the subduction of the
Turkestanian ocean (Burtman 2006), that in the
Ordovician to Carboniferous time was a direct
continuation of the Palaeouralian ocean (Puchkov
2000; Didenko et al. 2001; YUGGEO 2002; Biske
2006). The Middle to Late Palaeozoic evolution of
the Uralian and Southern Tyan-Shan continental
margins has a striking resemblance (Puchkov
1996a). The end of orogenic activity in the Southern
Tyan-Shan is accompanied by Upper Permian and
Lower Triassic continental molasse followed by
the development of a stable platform in the whole
Tyan-Shan, which lasted until strong intra-plate
deformation of the PlioceneQuaternary age
propagated from the Alpine-Himalayan orogenic
system, resulting in renewed mountain building
(Burtman 2006; Biske 2006; Trifonov 2008).
Comparison between the Uralides,
Variscides and Appalachians
The development of the Ural orogenic belt has tra-
ditionally been interpreted to be one of the Late
Palaeozoic Variscide (or Hercynide) orogenic belts
(Shatsky 1965; International Committee 1982).
However, results of geological studies of the last
few decades, enhanced by EUROPROBE, have
shown such fundamental differences with the
Fig. 2. A tentative reconstruction of the Central Eurasia
for the Late Devonian (after YUGGEO2002, simplified).
THE EVOLUTION OF THE URALIAN OROGEN 163
Variscides that this interpretation is no longer con-
sidered valid (Brown et al. 2006a). Instead the
Urals is treated as a separate orogenic belt, the
main part of the Uralides.
In western Europe, tectonic events leading to the
development of the Variscan (also known as Hercy-
nian) orogenic belts (sensu stricto) occurred
between the Famennian and Late Carboniferous
(Fig. 3). Famennian flysch deposits, thought to rep-
resent the onset of orogenesis, continued until the
end of the Lower Carboniferous, and were followed
by molasse deposits which continued until the end
of the Carboniferous. Devono-Carboniferous tecto-
nothermal activity accompanied a pre-collisional
closure of the Rheic (Saxo-Thuringian) ocean,
collisional deformation, granitoid intrusions and
metamorphism (including HPLT type; Franke
2000; Ricken et al. 2000). Permian rocks are charac-
terized by rift-related magmatism and the formation
of ensialic basins within a wrench regime, and are
followed by Triassic terrigenous and evaporitic
deposits in graben structures. The PermianTriassic
events reflect post-orogenic extension (Schwab
1984; Ziegler 1999). The Alleghanian orogeny in
the southern Appalachians and Ouachita continued,
albeit in a weakened manner, into the Early Permian
(Engelder 2007). In the Triassic, the Variscide and
Appalachian orogenic belts were characterized by
horsts and grabens that strongly influenced the for-
mation of platform oil and gas deposits, especially
in the North Sea (Lu
¨
tzner et al. 1979; Beutler
1979; Schwab 1984; Ziegler 1999; Khain 2001;
Franke 2000).
The Uralides have a much more protracted
history of orogenesis than the Variscides, with tec-
tonic events continuing into the Jurassic. In the
southern Uralides, syn-orogenic flysch deposition
began in the Late Frasnian (Brown et al. 2006b).
Further to the north, collision started in the Visean
(Puchkov 2002a). This strongly diachronous
Fig. 3. To the left: correlation of orogenic and post-orogenic (intraplate) events in the Variscides and Uralides. To
the right: a comparison of idealized sections across the foreland flysch and molasse basins: Preuralian (Southern Urals)
after Puchkov (2000) and Central European Variscides, after Ricken et al. (2000). PUF, Preuralian foredeep; WUZ,
West Uralian zone; ZS, Zilair synclinorium, Stages; art, Asselian to Artinskian stages; v-s, Vizean and Serpukhovian
(¼ c. Lower Namurian); t, Tournaisian; fm, Famennian; fr-fm, Frasnian and Famennian; SVMB, Subvariscan molasse
basin; RHTB, Renohercynian turbidite basin; WC/D, Westphalian stage (¼ c. the Moscovian stage of the Urals) the
upper part; WA/B, Westphalian stage, the lower part; NA/B, Namurian stage (¼ c. Lower Bashkirian and
Serpukhovian stages of the Urals); NA, Namurian stage, the lower part (mostly Serpukhovian stage);
a
,
b
,
g
, the units of
the Upper Visean substage. Thick lines, the lower boundary of molasse.
V. N. PUCHKOV164
arc-continent collision was accompanied by HP
LT metamorphism (Brown et al. 2006b; Puchkov
2008, and references therein). In Bashkirian time,
continentcontinent (Laurussia Kazakhstania) col-
lision commenced and continued intermittently
until the end of the Permian. The early stage of this
collision was accompanied by flysch deposition,
periodically interrupted by relatively deep-water
sediments of a starved type. In the Kungurian
(Uppermost Priuralian), evaporite deposition
occurred in the southern to northern parts of the
Urals, but in its polar area the Kungurian deposits
filling the Preuralian foredeep are dominated by
flysch and coal-bearing sediments. Late Permian
strata are dominated by alluvial to lacustrine
molasse deposits and are weakly deformed in the
frontal part of the foreland fold-and-thrust belt
(Puchkov 2000). At the beginning of the Triassic,
tectonic movements connected with Large Igneous
Province (LIP) formation led to the accumulation
of molasse-like sediments. Voluminous mafic
magmatism began in the earliest Triassic, approxi-
mately at 250 Ma according to RbSr, Sm Nd
(Anderichev et al. 2005) and ArAr (Reichov
et al. 2007) age data, suggesting a correlation of
these events with the contemporaneous events in
Siberia and the hypothesis of a single Uralo-
Siberian superplume.
The latest collisional events in the Uralides took
place in the Early Jurassic, with increasing intensity
from the South to the North, and represents the term-
inal collision between Baltica (Laurussia) and
Siberia loose blocks united into Pangaea. The
effects of this collision are well exposed in the
Pai-Khoy Range, Novaya Zemlya islands and
Taymyr.
Tectonic zones of the Urals (Fig. 4)
The Uralides are divided into several northsouth
striking structural zones, giving the Urals a
general appearance of an approximately linear fold-
belt, in contrast to the more strongly oroclinal and
more mosaic chains of the European Variscides,
Alps or Kazakhstanides (Franke 2000; Khain
2001; Agard & Lemoine, 2005).
The Urals is divided into the following structural
zones, which are from west to east (Fig. 4; Puchkov
1997, 2000):
(1) A the Preuralian foredeep, which inherited
the western part of a bigger and long-living
orogenic basin. It is filled mostly by Permian
preflysch (deep-water condensed sediments),
flysch and molasse.
(2) B the West Uralian megazone, predomi-
nantly consisting of Palaeozoic shelf and
deep-water passive margin sediments. This
zone was affected by intense fold-and-thrust
Fig. 4. Tectonic zones of the Urals (explanations in the
text). Abbreviations: PBB, Platinum-bearing Belt;
MGA, Main Granitic Axis; MUF, Main Uralian Fault;
EMF, East Magnitogorsk Fault; SMF, SerovMauk
Fault; KRF, Kartaly (‘Troitsk’) Fault. URSEIS and
ESRUSB, lines of seismic profiles described in the text.
THE EVOLUTION OF THE URALIAN OROGEN 165
deformation, and includes klippe containing
easterly-derived ophiolites and arc volcanics
(Puchkov 2002a).
(3) C the Central Uralian megazone, where the
Precambrian (predominantly Meso- and Neo-
proterozoic) crystalline basement of the Urals
is exhumed. This basement is traced by geo-
physical data under the A, B and C megazones.
Basically, these megazones were formed as a
result of deformation of the continental
margin of Baltica, although some allochthons,
and partly the Ural-Tau antiform (UTA) were
derived from more eastern oceanic structures.
(4) D the TagiloMagnitogorskian megazone,
bordered to the west by serpentinitic
me
´
lange within the Main Uralian Fault zone
(MUF) and to the east by the East Magnito-
gorsk Fault (EMF) and Serov-Mauk Fault
zones (SMF). This megazone predominantly
consists of Ordovician Lower Carboniferous
complexes of oceanic crust and ensimatic
island arc, including the Platinum-bearing
Belt of layered basic-ultramafic massifs
(PBB), overlain by platformal carbonate and
rift-related volcanic rocks.
(5) E the East Uralian zone, bordered to the
west by the East Magnitogorskian me
´
lange
zone (EMF) and to the east by the Kartaly
(Troitsk) Fault (KRF) (Fig. 4). This zone
comprises Proterozoic gneisses and schists
overlain by weakly metamorphosed Ordovi-
cian to Devonian sedimentary clastic strata
and by tectonically emplaced sheets of
Palaeozoic (Ordovician Lower Carbonifer-
ous) oceanic and island arc complexes. The
East Uralian Zone is intruded by voluminous
Late Palaeozoic granite bodies which define
the Main Granitic Axis (MGA) of the Urals
(Puchkov et al. 1986).
(6) F the Transuralian zone, the easternmost
zone of the Urals has probably an accretionary
nature. It contains pre-Carboniferous com-
plexes which preserve a variety of tectonic
settings, including Proterozoic blocks of
gneisses, crystalline schists and weakly meta-
morphosed sediments, Ordovician rift (coarse
terrigenous and volcanic) and oceanic
(ophiolite) deposits, Silurian island-arc com-
plexes and Devonian deep-water deposits
overlain unconformably by the Lower Carbon-
iferous suprasubductional volcanogenic strata,
which form a post-accretionary overstep
complex.
Zones DF, together with MUF, are traditionally
interpreted to comprise of vestiges of the palaeo-
ceanic component of the Urals, relics of the
Palaeouralian ocean (Peyve et al. 1977; Puchkov
2000). As ophiolites with MORB signatures are
poorly preserved in most orogens, the abundance
of ophiolites in the eastern zones of the Uralian
orogen is a rather anomalous feature, compared to
many other orogens.
All megazones are either exposed or are near the
Earth’s surface only in the Southern Urals. To the
north, the easternmost zones are covered by
the Mesozoic and Cenozoic strata of the West
Siberian basin, and in the Northern and Polar areas
only the Preuralian foredeep, West Uralian,
Central Uralian and western part of the Tagil-
Magnitogorskian megazone are exposed.
Structural development of the Urals (Fig. 5)
In general, the Urals comprise the following
first-order structural stages: (1) Archaean
Palaeoproterozoic development of cratonic base-
ment; (2) Meso-Neoproterozoic rift and basin devel-
opment, followed by orogenesis that culminated
with the formation of Timanide orogen along
the periphery of Baltica; (3) PalaeozoicLower
Jurassic development of the Uralides; (4) Middle
JurassicPalaeogeneMiocene (platform); and
(5) PlioceneQuaternary (neo-orogenic) activity
which is a far-field effect of Alpine-Himalayan
orogenesis. In this paper we focus on the
Fig. 5. Structural stages of the Urals.
V. N. PUCHKOV166
PalaeozoicLower Jurassic stage as an example of a
full Wilson cycle leading to formation of the
Uralide orogen.
The Uralides (Fig. 6)
The Uralides consist of the following stages of
development: (1) rifting of Baltica continental
crust, composed of a cratonic crystalline basement
and the Neoproterozoic Timanide foldbelt;
(2) formation of an oceanic basin and micro-
continents; (3) subduction of the oceanic crust and
consequent arc generation; (4) arc-continent
collision, followed by (5) continentcontinent
(LaurussiaKazakhstania and then Laurussia
Siberia) collisions.
Rifting stage of the Uralides: a precursor of
the Palaeouralian ocean
On a global scale, rifting and development of the
Palaeouralian ocean episode was preceded by a
series of pene-contemporaneous collisions and oro-
genies (Cadomian, Timanian, Brasilian, Panafrican)
associated with the assembly of the supercontinent
Pannotia (or Panterra) in the Ediacarian time. The
Palaeouralian ocean was formed as a result of a
breakup of this supercontinent in the Late
CambrianOrdovician time (Puchkov 2000). Two
other possible scenarios for the origin of the ocean
have been suggested. According to Zonenshain
et al. (1990), a system of rifts formed in the Early
Ordovician at the eastern margin of East European
continent. Rifting gradually changed to oceanic
spreading and the generation of a series of micro-
continental fragments (Uvat-Khantymansian,
Uraltau, Mugodzharian) which formed adjacent to
the boundary between the new-formed Palaeoura-
lian ocean and the older, Asiatian ocean. Alterna-
tively, some researchers (Scarrow et al. 2001;
Samygin & Ruzhentsev 2003) maintain that
Palaeouralian ocean was inherited from the Protero-
zoic time, implying no distinction between the
development of the eastern and western flanks of
the Uralo-Mongolian orogenic belt in the Early
Palaeozoic. However, there are several strong argu-
ments against the latter interpretation. First, the con-
trasting orientation of the structural grain of the
Timanides and Uralides (especially in the North)
support the idea of a continental breakup preceding
the formation of the Uralian ophiolites. This
interpretation is supported by the pattern of strong
NW-trending magnetic anomalies of the Timan-
Pechora province, positive anomalies reflecting
vast fields of rift and island-arc volcanics, and nega-
tive anomalies associated with granites and meta-
morphic rocks (Fig. 7). These anomalies are
truncated by the N NE-trending magnetic
anomalies which correspond to the MUF and
palaeo-oceanic structures of the Uralides. Second,
the lower age limit of the ophiolites attributed to
the Palaeouralian ocean, as determined by recent
studies of conodonts, is ArenigLlandeilian (corre-
lated with two unnamed stages between Tremado-
cian and Darriwilian (Gradstein et al. 2004) and is
clearly younger than the Ediacarian Tremadocian
age that would be expected if there was uninter-
rupted ocean development (Puchkov 2005;
Borozdina et al. 2004; Borozdina 2006; Smirnov
et al. 2006). These ages are very different from
the relics of the Palaeoasian ocean in Altaides and
Kazakhstanides, where Cambrian ophiolites occur.
Third, the presence of the Ordovician rift complexes
along the margins of the former Baltica continent
from one side, and the microcontinent(s) incorpor-
ated into the East Uralian and Transuralian zones
support the former interpretation (Fig. 8).
A detailed description of the Uralian Early
Palaeozoic rift facies in the western slope of the
Urals is given in Puchkov (2002a, and references
therein). Typically, the rift facies consists of Upper-
most Cambrian Tremadocian to Middle Ordovi-
cian coarse terrigenous sediments (conglomerates,
sandstones, siltstones of very variable thickness,
combined with interlayered subalkaline flows and
tuffs). They overlie unconformably the crystalline
basement and are overlain either by shelf or deep-
water facies, reflecting the development of eastern
passive continental margin of Baltica. Although the
rift facies of the eastern zones of the Urals (Kliuzhina
1985; Snachev et al. 2006) resemble them lithologi-
cally, their age is restricted to the Middle Ordovician.
Alkaline carbonatite-bearing complexes (mostly
miaskites) in the western part of the Middle Urals
(Levin et al. 1997), originally thought to be a
manifestation of this rifting event (Samygin et al.
1998; Puchkov 2000) have been re-interpreted to
post-date rifting, on the basis of RbSr and UPb
isotopic data which indicate a latest Ordovician to
Silurian age (Puchkov 2006a; Nedosekova et al.
2006, and references therein). These intrusions are
oblique to the Uralian structural grain, and may be
analogous to the Early Cretaceous Monteregian
alkaline intrusions in eastern Canada or the more
or less contemporaneous hot spot tracks of Eastern
Brazil (Bell 2001; Cobbold ft al. 2001). Probable
Late OrdovicianEarly Silurian plume-related
complexes also occur in more northern parts of
the Urals (e.g. monzogabbro-syenite-porphyry as
indicated by the 447 + 8 Ma UPb (SHRIMP)
age of the Verkhneserebryansky complex (Petrov
2006) or REE-rich phases of subalkaline grani-
toids in the North of the Urals, dated as 420
460 Ma by Rb Sr and U Pb methods (Udoratina &
Larionov 2005).
THE EVOLUTION OF THE URALIAN OROGEN 167
Fig. 6. A tectonostratigraphic chart of the Uralides in the Southern Urals. All the formations are tentatively restored to their initial, autochthonous positions. Arrows show a
provenance of terrigenous material. (After Maslov et al. 2008, strongly modified.)
V. N. PUCHKOV168
Fig. 7. Magnetic anomalies of eastern Baltica (after Jorgensen et al. 1995, with data processed by CONOCO Inc.,
USA). White dotted line, Timanian deformation front; white solid line, Uralide deformation front; white dot-and-dash
line, the Main Uralian Fault.
THE EVOLUTION OF THE URALIAN OROGEN 169
The origin of the Palaeouralian
ocean ophiolites
The aforementioned continental rifting within
Baltica led to oceanic spreading and formation of
ophiolites. The unusual abundance of ophiolites is
a special feature of the Uralian orogen. Several
studies report on the petrology, geochemistry, struc-
ture and metallogeny of the Uralian ophiolites (e.g.
Savelieva 1987; Savelieva & Nesbitt 1996; Saveliev
1997; Melcher et al. 1999; Spadea et al. 2003;
Savelieva et al. 2006a, b). The general consensus
is that the ‘ideal’ section of the Uralian ophiolites
consists of (from top to bottom):
(1) Tholeiitic basalts (mostly pillow lavas) with
layers of pelagic sediments (typically cherts
containing relics of half-dissolved radiolar-
ians). The age of these basalts, constrained
by many occurrences of conodonts, is never
older than ArenigianLlandeilian (see
earlier comment). In the Tagil zone, ophiolitic
complexes are overlain by Upper Ordovician
island-arc formations, whereas in the Magni-
togorskian zone, the condensed oceanic sedi-
ments overlie OrdovicianLlandoverian
basalts, and persist until the onset of island
arc magmatism in the Early Devonian;
(2) Dyke-in-dyke sheeted complexes, which are
common in the Urals, in contrast to some
other orogens (e.g. the Alps);
(3) Alpine-type gabbro;
(4) Banded dunite-wehrlite-clinopyroxenite com-
plexes, interpreted to reflect a fossil MOHO
boundary; and
(5) Peridotite complexes, represented by lherzo-
lites, harzburgites and dunites in different pro-
portions and combinations.
However, in detail not all ophiolitic complexes
display this simple sequence. For example, Ishki-
nino, Ivanovka and Dergamysh NiCo-rich pyrite
deposits in the MUF zone are attributed to ocean-
floor black smokers and overlie and partly penetrate
peridotitic host-rock, devoid of the several ‘stan-
dard’ members of the ophiolite section. Similar
features occur in modern Atlantic thermal fields
(e.g. Logachev and Rainbow fields), although their
geodynamic setting may not support the direct
analogy. The deposits rather belong to the relics of
Magnitogorsk forearc (Jonas 2004; Melekesceva
2007).
Fig. 8. The position of the Early Palaeozoic rift/plume
related complexes. IVI, tectonic zones of the Urals
(correspond to A, B, C, D, E, F in Fig. 4, with the same
symbols); 1 8, localities where the Lower Palaeozoic
graben formations are developed; 1, Sakmarian;
Fig. 8. (Continued ) 2, Bardym; 3, Lemva; 4, Baydarata;
5, Samar; 6, Sargaza; Uvelka; 8, Mayachnaya.
Dashed-line ellipse, location of possible plume-related
alkaline complexes Vishnevogorsk and other).
V. N. PUCHKOV170
Savelieva et al. (2006a) classified the Uralian
ophiolites into three groups according to their
inferred geodynamic setting:
(1) Complete sections of ophiolites (e.g. Kempir-
say massif) or their fragments in the south of
Magnitogorsk, East Uralian or Denisovka
zones), include restite peridotite and overlying
succession of plutonic gabbro, parallel diabase
dyke complexes and tholeiitic lavas formed in
a MOR setting (Savelieva & Nesbitt 1996).
However, a supra-subduction geochemical
component has been documented in ophiolites
in the southern part of the Kempirsay massif
(Melcher et al. 1999);
(2) Massifs of a lherzolite type representing fairly
low depleted lithospheric mantle (e.g. Kraka,
Nurali) have a simple evolutionary history
consisting of enriched peridotite and dunite
associated with less abundant amphibole
gabbro (Savelieva 1987). These character-
istics are thought to reflect a low degree of
partial melting of a mantle diapir, followed
by rapid uplift, a scenario typical of rifting
that immediately precedes oceanic spreading.
Alternatively, Spadea et al. (2003) propose a
more dynamic history for these massifs, invol-
ving re-fertilization of a depleted mantle by
basaltic magma, by analogy with Lanzo
massif of Alps, which however is also
thought to be indicative of pre-spreading
rifting (Mu
¨
ntener et al. 2005); and
(3) According to the general geodynamic recon-
structions of Saveliev (1997), the huge Polar
Urals massifs such as Voykar-Synya, Ray-Iz
and Syum-Keu, are integrated into a system
of allochthons, composed of complexes of
two island arcs Tagil-Schuchya (O
3
–S
1
)
and Voykar (S
2
–D
3
). The restites in these
massifs are strongly depleted and preserve evi-
dence of interaction with basaltic magma. The
sections consist of multi-phase intrusions of
gabbro and diabase, interpreted by Savelieva
et al. (2006a) to reflect the development of a
marginal basin when an island arc rifted apart
in the Late Silurian-Early Devonian. Therefore
this spreading was related to the development
of a second island arc. This interpretation,
however, may be an over-simplification as
the presence of two island arcs suggests the
existence of older (OrdovicianLower Silur-
ian?) ophiolites corresponding to the older of
the two arcs. Indeed, Ar Ar data from the
banded complex of Voykar-Synya and
Khadata massifs (primary amphibole, fresh
plagioclase and clinopyroxene of gabbro)
yield 420490 Ma ages. In addition the
Khadata spreading dikes yield a c. 423 Ma
age and the Voykar sheeted dykes, described
by Remizov (2004) as island arc complex,
were dated at 426444 Ma (Didenko et al.
2001). Khain et al. (2004) dated zircons from
a plagiogranite dyke in the parallel dyke
complex of the Voykar-Synya massif at
490 + 7 Ma. The above data indicate that the
generation of these ophiolites is probably
more complicated than the current geody-
namic models purported to explain them.
This complicated scenario is highlighted by
recent age data (Gurskaya & Smelova 2003;
Savelieva et al. 2006a; Tessalina et al. 2005; Bata-
nova et al. 2007; Krasnobaev et al. 2008), which
yield NeoproterozoicEdiacarian (536885 Ma)
and some older dates for many of the ultramafic
and alpine-type gabbro complexes that were pre-
viously regarded as Palaeozoic. These data include
ReOs and Sm Nd mineral isochrons and UPb
analyses of zircons. In general, however, most of
published age data support also an Ordovician
Lower Devonian age of alteration processes for
most of the complexes (summarized by Puchkov
2000 and well illustrated by Krasnobaev et al.
2008). Two contrasting explanations have been pro-
posed. According to Tessalina et al. (2005), the
ultramafic complexes are Neoproterozoic ophiolites
and represent relics of the oceanic crust developed
during Timanide orogenesis. Alternatively,
Puchkov (2006b) suggests that the Neoproterozoic
dates in the Palaeozoic ophiolites reflect a relict sig-
nature preserved in the mantle part of the younger
ophiolites (peridotites and partly ex-eclogitic
mantle gabbro), notwithstanding the overprinting
during subsequent processes of ophiolite formation.
The possibility of preservation of ancient mantle
zircons and their contamination of younger MOR
and island arc volcanics has recently been under-
lined (Sharkov et al. 2004; Bortnikov et al 2005;
Puchkov et al. 2006).
Despite the above complexities, the age of
ophiolite basalts determined by conodonts, is
never older in the Urals than Arenigian Llandeilian
(see again the earlier comment).
The passive margin of the continent
Simultaneously with oceanic development, the con-
tinental margin of Baltica started to develop by
rifting in the Ordovician (Fig. 9). The identity of
the conjugate margin to this rift is not known. By
the end of the Silurian, Baltica had collided with
Laurentia to form Laurussia (Ziegler 1999). The
development of the margin is described in detail
by Puchkov (2002a), and only a general summary
is given here. Typically, the succession starts with
uppermost CambrianLower Ordovician coarse
terrigenous deposits, in some cases accompanied
THE EVOLUTION OF THE URALIAN OROGEN 171
by minor volcanic rocks (see above). The margin is
classified as a non-volcanic type (in a classification
of Geoffroy 2005).
Two facies were established early in the passive
margin development an inner (shelf) and an outer
(continental slope, grading to continental rise)
(Fig. 6). Generally, shelf sediments are represented
by shallow-water carbonates (limestones, dolomitic
limestones, dolomites) and terrigenous sediments
with west-derived (Smirnov 1957) oligomictic,
quartz sandstones. Regressions are marked by
barrier reefs at the outer margin of the shelf zone,
while the transgressions favour a formation of deep-
water, starved basins with condensed facies of marls
and oil shales (called ‘domanik’ in Russia),
surrounded by reefs and bioherms.
Fig. 9. Major structural elements and complexes of Laurussia/Baltica passive margin involved into the Urals (from
Puchkov 2002, with minor changes).
V. N. PUCHKOV172
The outer, continental slope and rise (bathyal)
sections consist of thick westerly-derived quartz
sandstones, and thin, condensed units consisting of
shales, cherts and minor limestones (Puchkov
1979, 2000). Fauna are mostly pelagic: radiolarians,
conodonts, graptolites and rare goniatites. The
paucity of limestones indicate a transition to
abyssal conditions.
The upper strata of the outer facies consist of
polymictic, flysch deposits signifying a sharp
change of provenance that is connected with the
start of orogenesis (Puchkov 1979; Willner et al.
2002, 2004). This change of provenance is diachro-
nous: it is earlier in the east and south of the western
slope of the Urals; in the Southern Urals it occurs in
the uppermost Frasnian, but in the Polar Urals it
starts in the Early Visean.
Puchkov (1979) drew attention to the similarity
of these deposits with analogous geodynamic set-
tings in other orogens. For example, eastern Lauren-
tia was bordered by deep-water sediments in the
Ordovician that are preserved in the allochthons
formed during the generation of the Appalachian
orogen. In some cases (e.g. Ouachita), the deep-
water facies persisted, like in the Polar Urals,
through most of the Palaeozoic (from the lowermost
Ordovician until the Carboniferous).
Subduction of oceanic crust
The Urals is characterized by an exceptionally good
preservation of subduction complexes, which
permits reconstruction of the development of at
least three subduction zones in place and time:
Tagil (Late OrdovicianEarly Devonian), Magnito-
gorsk (EarlyLate Devonian) and Valerianovka
(TournaisianEarly Bashkirian) (Fig. 10).
The Late Ordovician Early Devonian Tagil
arc (Fig 10, to the left)
The oldest (Tagil) arc complexes are developed
in the Middle, Northern, Cis-Polar and Polar parts
of the Tagilo Magnitogorskian zone. The best sec-
tions, well constrained by conodonts, are preserved
in the southern part of the Tagil synclinorium
(synform). According to recent stratigraphic and
petrochemical studies (Narkissova 2005; Borozdina
2006), the oldest ensimatic island-arc succession is
predominately represented by the basaltic (O
3
),
basalt-plagiorhyolitic (O
3
) and basaltandesite
plagiodacite (S
1
) volcanic associations. The latter
two have calc-alkaline affinities (Narkissova
2005). The overlying Silurian association (S
1
ll
2
S
2
w
1
) is represented by flysch consisting of
interbedded black cherty siltstones, tuffites and
tuffaceous sandstones (arc slope deposits), overlain
by andesites, dacites, basalts and very abundant
tuffs. In the Wenlockian, the volcanic rocks are lat-
erally equivalent to reefal limestones (All-Russian
Committee 1993). These biohermal deposits per-
sisted until the Pridolian as an unstable, narrow car-
bonate shelf on the perimeter of the island arc. The
above Silurian complexes are substituted laterally
by a volcanic association (S
1
ll
3
–S
2
ld
1
), represented
by basalts, andesites and tuffs with rare layers of
cherty siltstones. After the Late Ludlovian, the
marine conditions partly changed to continental
conditions: the Pridolian association is represented
by predominant coarse-grained red-coloured poly-
mictic terrigenous-volcanogenic deposits with frag-
ments of the older rocks; such as volcanics, with
sublakalic and alkalic basalts being predominant.
The island arc succession is terminated by a very
specific association (S
2
prD
1
lh), preserved in the
axial part of the Tagil synform, which resembles
the underlying Pridolian association, and includes
shoshonitic mafic to intermediate volcanic rocks
(Narkissova 2005) and minor flysch-like volcani-
clastic deposits.
The volcanism of the Tagil arc evolved from a
uniformly tholeiitic affinity to a differentiated
calc-alkaline and then to subalkalic shoshonitic
affinity, suggesting deeper levels of partial
melting in mantle with time, a trend that is opposite
to the typical trend in rift and superplume zones
(Dobretsov et al. 2001). Geochemically, the vol-
canics are typical of ensimatic island arcs
(Narkissova 2005; Borozdina 2006). Basalts
retrieved from the superdeep SG-4 borehole
exhibit a distinct TaNb minimum. In general, the
volcanics are depleted in Nb,Ta, Zr, Ti, Y and
enriched in K, Rb, Ba, Pb relatively to NMORB.
The geochemical trends of contemporaneous volca-
nics suggest an eastward (in modern co-ordinates)
dipping subduction zone (Narkissova 2005).
The Tagil arc is also known for the presence of
gabbro-ultramafic massifs composing a gigantic
(c. 1000 km) linear, platinum-bearing belt (PBB
on Fig. 4). The concentric-zonal massifs consist of
dunites, clinopyroxenites, gabbro and plagiogra-
nites, and mafic rocks comprise up to 80% of the
belt. Disseminated platinum is hosted by dunites,
and industrial deposits are represented mostly by
modern (or reworked Meso-Cenozoic) placers.
The geodynamic significance of the belt is contro-
versial: models vary from a rift (Efimov 1993) to a
supra-subduction zone setting (Ivanov et al. 2006).
The age of the belt, determined by several
methods as 420 430 Ma, and the similarity of
petrogenetic-indicating trace and rare earth
elements with island-arc tholeiites (Ivanov et al.
2006) supports the supra-subduction zone model.
Such belts are rare in modern arc environments,
but possible analogues occur in the northern part
THE EVOLUTION OF THE URALIAN OROGEN 173
Fig. 10. The distribution of magmatism of three main stages of subduction: OrdovicianEarly Devonian (Tagil): Early
DevonianFamennian (Magnitogorsk); TournaisianEarly Bashkirian (Valerianovka and contemporaneous to it).
V. N. PUCHKOV174
of the circum-Pacific ring, and are known as
Alaskan type (Burns 1985).
OrdovicianEarly Devonian island-arc volcan-
ism was followed by the development of a relatively
stable carbonate shelf which caps the western part of
the island arc complexes. After that time the Tagil
arc was dismembered and by the Emsian, it was a
terrane that accreted to the Magnitogorsk island
arc, an event that coincided with the formation of
the Magnitogorsk arc itself (see below). The
location of the subduction zone changed and the
region became characterized by presence of two
sub-zones: the western, Petropavlovsk and the
eastern, Turyinsk sub-zones.
The Petropavlovsk sub-zone contains Lower to
Middle Devonian shallow-water limestones and
bauxite, followed in the Late Devonian by deep-
water cherty shales and polymictic terrigenous sedi-
ments. In the Turyinsk sub-zone, sedimentary strata
(shallow-water limestones, shales and cherty shales)
are interlayered with andesites, basalts, tuffs and
volcanogenic sandstones (All-Russian Committee
1993). Yazeva & Bochkarev (1993) point out that
these thick (up to 45 km) Devonian volcanic
layers occur with comagmatic intrusions in volcano-
plutonic complexes. Geochemical parameters (in
particular, Rb and Sr contents) indicate that the
thickness of the crust was c. 30 km (Yazeva &
Bochkarev 1993), which implies that the new arc
was ensialic, in contrast with the Ordovician
Lower Devonian ensimatic Tagil island arc.
Devonian Magnitigorsk arc (Fig. 10, centre)
The development of the Magnitogorsk arc in the
Southern Urals was more or less synchronous with
the dismemberment of the Tagil arc. The location
of the Turinsk zone of Tagil arc along the extension
of the Magnitogorsk arc suggests that the Magnito-
gorsk subduction zone was inherited from the Tagil
zone. The Middle Upper Devonian calc-alkaline
complexes can be traced northward to the Polar
Urals.
However, in the Southern Urals, island arc
development was preceded by a long period of
quiescence, expressed by the deposition of deep-
water oceanic cherts and carbonaceous cherty
shales accompanied by basalts in the Ordovician
and Llandoverian. Most of the Silurian is rep-
resented by 300 m of distal, condensed cherty
shales. They are considered to represent the
sedimentary cover of the ophiolites. Non-volcanic
sections of the Lower Devonian (Lochkovian
lowermost Emsian) are represented by either
deep-water terrigenous chert, argillaceous cherty
sediments of Masovo, Turatka, Ishkinino and other
formations or bioherm limestones (Artiushkova &
Maslov 2003; Fig. 6). This stratigraphic level
includes also olistostromes developed locally with
and within serpentinitic me
´
langes of the Main
Uralian fault. The bioherms and olistostromes are
local indicators of buckling of the oceanic crust at
the onset of subduction and are related to an early,
non-volcanic stage of subduction.
Volcanic complexes of the Magnitogorsk arc in
the Southern Urals are well studied (Brown et al.
2001, 2006b; Kosarev et al. 2005, 2006, and
references therein). The volcanic succession,
represented by a characteristic interlayering of tho-
leiitic basalts, bimodal basalt-rhyolite and regularly
differentiated basalt-andesite-dacite-rhyolite series,
comprises the following units (the local names
are partly shown in Figure 6, and numbered
correspondingly):
(1) A bimodal rhyolite-basalt series that overlies a
tholeiite-boninite unit (Emsian);
(2) Basalt-andesite-dacite-rhyolitic series (Upper
Emsian);
(3) Andesite-basalt series (uppermost Emsian
Lower Eifelian);
(4) Bimodal rhyolite-basalt series (Upper Eifelian);
(5) Basalt-andesite-dacite-rhyolite series (Givetian
Lower Frasnian);
(6) Basalt-andesite formation (Upper Frasnian);
(7) Local shoshonite-absarokite formation
(Famennian). In addition, subduction-related
370350 Ma granitoid intrusions of calc-
alkaline affinity are developed in the northern
part of Magnitogorsk synclinorium (Bea et al.
2002); and
(8) These intrusions are unconformably overlain
by Lower Carboniferous volcanics dominated
by tholeiitic basalt in the west and by
more widely developed subalkaline bimodal
basalt-rhyolite in the east. They are accom-
panied by a chain of coeval (335 315 Ma,
Bea et al. 2002) bimodal gabbro-granitoid
intrusions (Magnitogorsk-type plutons). Both
volcanic and intrusive bimodal series, accord-
ing to their field relationships, mineralogy and
geochemistry, suggest an extensional or
passive within-plate non-arc origin and are
probably produced by undepleted lherzolites
(Bochkarev & Yazeva 2000; Fershtater et al.
2006). This magmatism may be related to a
slab break-off of the Magnitogorsk subduction
zone which gave way to a melt from the less
depleted, deeper mantle under it (Kosarev
et al. 2006).
Notwithstanding differences in composition,
magmatic and tectonic affinities, all the Devonian
volcanic series share geochemical traits typical of
a supra-subduction zone origin, such as negative
Nb, Ta, Zr, Hf, Y anomalies, and elevated concen-
trations of large ion lithophile (LIL) elements
THE EVOLUTION OF THE URALIAN OROGEN 175
(K, Rb, Ba, Cs) and LREE. They show no signs
of contamination by continental crust and are
interpreted as ensimatic arc complexes.
There are many parallels with a development of
the Tagil arc, including the alkaline trend towards
the upper member of the succession. Trace
element abundances for contemporaneous volcanic
rocks are consistent with an eastward-dipping
subduction zone. To the west and east of the main
volcanic body of the arc, mostly in me
´
langes of
the MUF and EMF zones and associated alloch-
thons, condensed cherty-terrigenous series contem-
poraneous to the arc are developed, corresponding
to the forearc and backarc basins (Fig. 6).
It looks like the ophiolite basement of the
arc is mostly Ordovician in age, except the
Mugodzhary section, where the Emsian basalts
and cherts of Mugodzhary and Kurkuduk for-
mations overlie a large-scale Aktogay sheeted
dyke complex, gabbro and serpentinites, composing
a Lower Devonian ophiolite (Fig. 6). The ophiolite
is tentatively interpreted as a result of a backarc
spreading.
The collision of the Magnitogorsk arc with
the passive margin of Laurussia
The collision of the Magnitogorsk arc with the
passive margin of Laurussia (former Baltica) has
been described in several recent publications
(Brown & Puchkov 2004; Brown et al. 2006b, and
references therein) and is briefly summarized here
(Figs 11 & 12). Since the Early Devonian, an
island arc formed within the Uralian palaeocean
above an east-dipping subduction zone. Collision
of the arc with Laurussia occurred in the Late
Devonian and was accompanied by the following
events:
(1) scraping-up of the deep-water sediments of
the continental passive margin by the rigid
wedge (backstop) of the arc and the formation
of an accretionary prism;
(2) jamming of the subduction zone followed by a
jump in the location of the subduction zone;
(3) slab break-off and opening of a slab window
permitting the deeper, more fertile and hotter
mantle to produce subalkaline, non-
subduction volcanics;
(4) uplift of the buoyant continental part of the
slab, exhumation and erosion of UHP(?) and
HPLT metamorphic complexes and their
erosion;
(5) formation of the accretionary cordillera of
Uraltau antiform (comparable to accretionary
avolcanic arc of Indonesia) and two flysch
basins flanking both sides of it: forearc and
foredeep basins (Fig. 13); and
(6) formation of the suture zone of the Main
Uralian Fault, which divides the accretionary
prism on the continent from the remnant of
the island arc.
In summary, the Southern Urals Magnitogorsk
arc was formed in the Early Devonian upon
OrdovicianEarly Devonian oceanic crust
(Puchkov 2000; Snachev et al. 2006) and developed
until it collided with the passive continental margin
of Laurussia in the Late Devonian. Due to the
oblique orientation of the subduction zone relative
to the continental margin, collision at this time did
not take place along the whole length of the
passive margin of Laurussia continent. To the
north of the Ufimian promontory, the margin of
Laurussia shows no evidence of the Late Devonian
arccontinent collision.
Two remarkable Late Devonian events in the
Southern Urals can be regarded (along with direct
structural data) as important indicators of the tran-
sition from subduction to collision. The first is the
deposition of the Zilair greywacke flysch formation
of the eastern provenance (uppermost Frasnian
Famennian) which overlies Frasnian deep-water
and Famennian shallow-water deposits of the
continental margin of Laurussia. The second is a
culmination of a HPLT metamorphism at
372 378 Ma that provides additional evidence for
the end of subduction and the onset of collision.
As for the metamorphism, its age range in the
subduction zone should be broadly contempora-
neous with the subduction, and its oldest products
should be older than the supra-subductional volcan-
ism. However, it is not clear if the products of this
early metamorphism were preserved and then
exhumed or if they were completely entrained by
the slab. The Magnitogorsk arc appears to have
these products preserved and then exhumed. In the
serpentinitic me
´
lange of MUF, along the margin
of the Magnitogorsk arc, garnet pyroxenites (meta-
morphic basites) occur. The best documented occur-
rence where PT parameters of their origin are
determined as 1.5 2 GPa, 800 1200 8Cisinthe
Mindyak peridotite massif of MUF (Pushkarev
2001). Its age was determined by two methods:
Sm Nd isochron is 406 399 Ma (Gaggero et al.
1997); whereas UPb analysis of zircons yield an
age of 410 + 5 Ma, which is interpreted as a meta-
morphic age (Saveliev et al. 2001). A PbPb analy-
sis of zircon cores yield an age of 467 Ma, and is
interpreted as a protolith age (Gaggero et al.
1997). The age of garnet pyroxenite from the
Bayguskarovo occurrence is 416 + 6,1 U Pb
SHRIMP (Tretyakov et al. 2008). A series of
Ar Ar age determinations of phengite, whose
interpretation depends on mineral dimensions and
temperature conditions of equilibration, has been
V. N. PUCHKOV176
Fig. 11. Time/process evolutionary diagram for intra-oceanic subduction and arc-continent collision in the Southern
Urals (after Brown et al. 2006b, with added information given in bold).
THE EVOLUTION OF THE URALIAN OROGEN 177
done for a succession of samples across the contact
between eclogite and garnet glaucophane schist
from Maksiutovo complex. The age range of phen-
gites is from 400 Ma at c. 500 8Ctoc. 379 Ma at the
final closure temperature of the system (c. 370 8C).
The ArAr age of glaucophanes from the same
sample is 411389 Ma (Lepesin et al. 2006). The
peak of ArAr ages obtained from detrital phengites
of the Zilair series clusters around 400 Ma (Willner
et al. 2004). U Pb SHRIMP dating of zircons
from Maksiutovo eclogites yielded 388 + 4Ma
(Leech & Willingshofer 2004). These older
(Lower and Middle Devonian) dates of meta-
morphism are consistent with the cooling action of
the subducting slab, causing the closure of isotopic
systems.
The younger ages of the metamorphic rocks
cluster around 375380 Ma and probably are con-
sistent with the general exhumation of the HP LT
metamorphic rocks of the Southern Urals. The
rocks are divided into two units, established by
Zakharov & Puchkov (1994) and by many
later researchers.
The age of the start of general cooling and exhu-
mation (reviewed by Brown et al. 2006b) for the
eclogite facies metamorphism of the lower unit of
the Maksutovo Complex is thought to be Frasnian
in age, with a mean value of 378 + 6 Ma according
to many isotopic determinations (Matte et al. 1993;
Lennykh et al. 1995; Beane & Connelly 2000;
Hetzel & Romer 2000; Glodny et al. 1999, 2002).
The upper unit was metamorphosed together with
the lower unit, suggesting juxtaposition during
exhumation at a higher crustal level by
360 + 8 Ma (Rb Sr and ArAr methods; Beane
& Connelly 2000; Hetzel & Romer 2000).
In the Polar Urals, isotope dating of HP LT
metamorphism of the Marun-Keu complex of eclo-
gites and related metamorphic rocks was reviewed
recently by Petrov et al. (2005). According to
Shatsky et al. (2000), the SmNd isotopic analyses
of garnet, clinopyroxene and whole rock gave
366 + 8.5 Ma for the hornblende eclogite and
339 + 16 Ma for the kyanite eclogite. Rb Sr
whole-rock dating of the eclogites (Glodny et al.
1999) gave 358 + 3 Ma. According to the data of
Glodny et al. (2003, 2004), the concordant U Pb
age data for the metamorphic zircon domains are
between 353 and 362 Ma, coincident with the age
of metamorphism as inferred from RbSr internal
mineral isochrons (an average value of
355.5 þ 1.4 Ma).
The eclogite glaucophane Nerka-Yu and Parus-
Shor complexes in the southernmost Polar Urals
yielded 351 + 3.6 and 352 + 3.6 Ma (
40
Ar
39
Ar
ages, Ivanov et al. 2000). Sm Nd dating of glauco-
phane schists of the Salatim belt (Northern Urals)
gave 370 + 35 Ma. Taken together, these dates
characterize an Upper Famennian-Middle Tournai-
sian age of HPLT metamorphism and the begin-
ning of its exhumation. These data are supported
by the Lower Visean age of the oldest known
Palaeozoic easterly-derived polymictic sandstones
and conglomerates on the continental margin of
Laurussia, to the west of the Main Uralian Fault,
in the Polar and Northern Urals (Puchkov 2002a,
and references therein).
Developing the oblique collision model of
Puchkov (1996b), Ivanov (2001) calculated an
average rate of subduction, which led to a gradual
northward-shifting collision, of 2.752.80 cm.
However according to recent data, the diachroneity
of events at the end of the Devonian and beginning
of the Carboniferous show no gradual south north
Fig. 12. A model for development of the Magnitogorsk
arc and subduction zone (Kosarev et al. 2006, slightly
modified). Dotted lenses, supposed zones of melting of
initial magmas of different petrogenetic types: T,
tholeiitic; BON, boninitic; TMg, tholeiitic magnesial;
CA, calc-alkaline; ASh, absarokite-shoshonite; SA,
subalkaline. Stages of the Devonian: em, Emsian; ef,
Eifelian; gv, Givetian; f, Frasnian; fm, Famennian.
V. N. PUCHKOV178
pattern, implying that behaviour of the subduction
zone is more complex.
The collision of the Magnitogorsk arc with
Laurussia may have occurred in two discrete
stages (Fig. 14). First, collision in the Southern
Urals occurred by the Famennian, and a triangular-
shaped gap was left between the arc and the conti-
nent, similar to the modern Bengal Bay, Northwest
Australian Bay or the South China Sea. Second, in
the Early Carboniferous, the northern half of the
arc was bent to the west and docked to the conti-
nental margin. At this stage subduction in the
south virtually ceased, but in the north, increasing
velocity of subduction resulted in increasing inten-
sity of the HPLT metamorphism in the same
direction (from glaucophane schists of the
Salatim belt and Cis-Polar Urals to eclogites of
the Polar Urals). In the Middle Urals, these
events were immediately followed by intrusion of
Turgoyak-Syrostan group of granitoids (335
330 Ma), that was described by Fershtater et al.
(2006) as ‘granitoids connected with tensional
structures’. This group can be correlated by the
age with the Magnitogorsk within-plate gabbro-
granite series (see below).
Unfortunately there is no support for this model
from the data on the Early Carboniferous volcanism
in the northern part of the Magnitogorsk arc. But
the lack of data may be because the eastern limb
of this arc is concealed in the Northern to Polar
Urals under the Mesozoic Cenozoic cover of the
West Siberian plate.
The above-described Early Carboniferous
(Tournaisian Visean) stage of subduction was
followed in the Middle Urals by a Serpukhovian
stage, as indicated by the Verkhisetsk chain of
granitoids (320 Ma) (Fig. 10), related by Fershtater
et al. (2006) to another east-dipping subduction
zone.
Early Carboniferous-Bashkirian Valerianovka
subduction zone(s) (Fig. 10, to the right)
By the middle of the Lower Carboniferous, the
suture zone was established along the whole
length of the MUF (Puchkov 2000, 2002a). The
above-mentioned chain of 335 330 Ma (mid-
Visean) massifs (TurgoyakSyrostan group of
granites) intrude the suture zone (Fershtater et al.
2006) and therefore post-date the Magnitogorsk
subduction, providing an upper age limit for MUF.
This conclusion is supported by the age of the
Ufaley intrusion (concordant U Pb, 316 + 1 Ma,
Early Bashkirian), which seals the Main Uralian
Fault in the Northern part of the Ufimian promon-
tory (Hetzel & Romer 1999).
Fig. 13. Reconstructed geological section across the Magnitogorsk arc, in the Famennian time.
THE EVOLUTION OF THE URALIAN OROGEN 179
With the demise of the Magnitogorskian arc,
subduction did not terminate in the Urals as a
whole. Ensialic subduction (either island arc or
Andean-type or maybe two subduction zones of
different type) of uncertain polarity began in the
latest Devonian and lasted until the Mid-Bashkirian
in the eastern Urals. The Main Granitic Axis of the
Urals (Fig. 4) developed first as a chain of
suprasubductional tonalitegranodiorite massifs by
the end of the Famennian or the beginning of the
Tournaisian (c. 360 Ma), when the southern part
of the Magnitogorsk subduction zone ceased to
operate (Bea et al. 2002; Fershtater et al. 2006).
Simultaneously, immediately to the east, a wide
NNE-trending band of calc-alkaline and partly
within-plate volcanic rocks and associated plutonic
Fig. 14. A model for a two-stage Upper DevonianLower Carboniferous arc-continent collision in the Urals. 1,
continental crust; 2a, transitional crust; 2b, oceanic crust; 3, Tagil island arc; 4 and 5, Magnitogorsk island arc; 4;
ensialic (epi-tagilian); 5; ensimatic (Magnitogorsk arc sensu stricto); 6, subduction zone; 7, continent ocean boundary;
8, suture zone of the Main Uralian fault.
V. N. PUCHKOV180
complexes ranging up to mid-Bashkirian in age
were formed, suggesting a close affinity with the
massifs of the Main Granitic Axis (All-Russian
Committee 1993; Tevelev et al. 2005; Fershtater
et al. 2006). The Lower Carboniferous (320 Ma)
tonalite-granodiorite massifs occur in the Middle
Urals, situated to the east of the Serov-Mauk
suture zone (i.e. Verkhisetsk massif and others
located to the east of the former Magnitogorsk
volcano-plutonic arc).
According to Fershtater et al. (2006), increases in
K
2
O and REE abundances in the granodiorites to the
east indicate that subduction had an eastern polarity.
However, Kosarev & Puchkov (1999) point out that
K
2
O concentrations in the Lower Carboniferous vol-
canic rocks in the eastern Urals increase westward,
suggesting a western polarity for the subduction
zone. Of the same opinion are Tevelev et al. (2005)
for the Uralian Lower Carboniferous volcanics, but
they propose that the volcanism occurred in a
wrench regime and that the easternmost Valerya-
novka volcanic band belonged to Kazakhstanides
and developed over a separate subduction zone with
eastern polarity. Brown et al. (2006a) also suggest
two oppositely dipping subduction zones, whereas
Matte (2006) suggests a westerly dip for several sub-
duction zones. Such a difference in opinion is
explained by the complicated nature of the process,
involvement of wrench tectonics, and the rather
poor exposure of the complexes.
Calc-alkaline volcanic complexes in the Urals
abruptly stopped forming by the mid-Bashkirian,
signifying the end of a wide-scale subduction of
an oceanic crust and transition to a continent-
continent-type collision.
Continentcontinent collision and
formation of the orogen
The main Late Bashkirian to Permian
stage of collision
The collision between Laurussia and Kazakhstania
that resulted in mountain building in the southern
and middle Urals has been described recently by
Brownet al. (2006a),andits main eventsare summar-
ized here. The external (palaeogeographic and mag-
matic) expressions of the orogeny, including the
northern-to-polar and eastern (epi-Kazakhstanian)
regions are emphasized in this synthesis.
By the Mid-Bashkirian, subduction had ceased
and collisional processes between Laurussia and
Kazakhstania began first as a formation of linear
uplifts and basins, documented in the Southern
Urals (Puchkov 2000). In the Late Bashkirian and
Moscovian, widespread marine flysch were depos-
ited in troughs separated by more slowly subsiding
shelf zones and intensely eroded uplifted crustal
blocks. As uplift continued, the basins contracted
and inverted. By the Kasimovian time, the territory
east of MUF was dominated by erosion and subaer-
ial deposits. To the west of MUF, a deep-water
foredeep trough was filled by easterly-derived
flysch, prograding to the west (Puchkov 2000). A
westerly prograding foreland fold-and-thrust belt
was developed along the eastern margin of the fore-
deep, which deformed and uplifted flysch of its
eastern limb. The diachroneity of these processes
is documented by detailed studies of resedimented
conodonts within these strata (Gorozhanina &
Pazukhin 2007). In the Gzhelian Sakmarian, the
thrusting and crustal thickening created a hot
crustal root in the Southern Urals, which resulted
in generation of 305 290 Ma syn-collisional gran-
ites of the Main Granitic axis (Fig. 2), followed by
10 15 km of erosion (Fershtater et al. 2006).
Crustal thickness may reach 65 km (the modern
crust thickness of the East Uralian zone is up to
50 km; see below), similar to modern orogens.
Tuff layers in deep-water sections of Gzhelian to
Lower Kungurian preflysch and distal flysch of Pre-
uralian foredeep may represent volcanic equivalents
of this magmatic activity (Davydov et al. 2002).
Syn-collisional granite magmatism migrated
northward, and is thought to be a manifestation of
the oblique, diachronous character of collision
(305 290 Ma for the southern Uralian granites,
265 Ma for the Kisegach massif, 250 255 Ma for
Murzinka and Adui massifs of the Middle Urals,
Fershtater et al. 2006). The idea of the transpressive
character of orogenic deformation is supported by
structural studies (e.g. Pliusnin 1966; Znamensky
2007). A change from thrust-dominated tectonics
to sinistral transpression occurred in the Southern
Urals (Znamensky 2007), explaining the K-rich
concentric-zoned post-tectonic c. 283 Ma rift-
related granite-monzonite massifs at the northern
end of Magnitogorsk synclinorium (Ferstater et al.
2006) and the occurrence of c. 301310 Ma lam-
proite dykes in the Southern Urals (Pribavkin
et al. 2006).
Post-collisional granite magmatism in each
region was followed by uplift and erosion, and the
diachroneity of the magmatism is exemplified by
the presence of the Late Permian marine sediments
with Tethyan fauna in the Southern Urals that is
coeval with granite magmatism in the Middle
Urals (e.g. Chuvashov et al. 1984).
An interlude: LIP formation and
localized rifting
At the Permian Triassic boundary, the waning
effects of orogenesis were overprinted by the for-
mation of the vast Uralo-Siberian LIP, extending
THE EVOLUTION OF THE URALIAN OROGEN 181
from Taymyr in the north to the Kuznetsk and
Turgay basins in the south and from the Tunguska
basin in the east to the Urals in the west. Volcanism
started locally with alkaline basalts and minor rhyo-
lites. ArAr data (Ivanov et al. 2005) suggest that
the bulk of the volcanism initiated in Siberia at the
Permian Triassic boundary but probably continued
for 22 26 Ma, with several short surges. Recent
Ar Ar dates for plagioclase from basalts in the
Polar Urals (249.5 + 0.7 Ma) and in the east of
the Southern Urals (243.3 + 0.6 Ma) (Reichov
et al. 2007) support the simultaneous beginning of
the LIP formation over a vast region followed by a
more protracted period of reduced magmatism.
In contrast with eastern Siberia, the Early Trias-
sic history of the Urals is dominated by considerable
uplift, erosion and formation of thick coarse-grained
alluvial to proluvial sediments that resemble oro-
genic molasse but are attributed to the effects of
the Uralo Siberian distributed rifting and LIP
magmatism. Examples include the huge Triassic
KoltogorskUrengoy graben of Western Siberia,
the newly-identified Severososvinsky graben in the
subsurface of the Cis-Polar Urals (Ivanov et al.
2004), and the eastern parts of the LIP (Kurenkov
et al. 2002; Ryabov & Grib 2005).
The Cimmerian orogeny
A short pulse of orogeny occurred at the end of the
early Jurassic, and its effects differ along the strike
of the Uralides. The Triassic deposits of the
Southern Urals are affected by this orogeny only
in the Trans-Uralian zone (Chelyabinsk and other
graben-like depressions), where Upper Triassic
and older deposits are deformed by thrusting
(Rasulov 1982), followed by uplift and peneplana-
tion during the Middle and Upper Jurassic, and
deposition of Upper Cretaceous marine deposits.
In the Northern Urals, three ‘grabens’ (Mostovskoi,
Volchansky, Bogoslovsk-Veselovsky) (Tuzhikova
1973) containing Upper Triassic coal-bearing
sediments were complexly deformed. In the
Polar Urals, the Triassic deposits of the foredeep
and the Chernyshov and Chernov range are all
deformed, and are unconformably overlain by
Middle Jurassic strata. However, in the nearby
Severososvinsky graben to the east, Triassic and
Jurassic deposits are not deformed (Ivanov et al.
2004), attesting to the localized nature of Cimmer-
ian orogenic events.
The Pay-Khoy and Novozemelsky ranges were
formed in the Cimmerian (Korago et al. 1989;
Yudin 1994). Cimmerian orogenesis is attributed
to a large-scale intra-Pangaean strike-slip faulting,
accompanied by block rotation, possibly reflecting
lateral escape of Kazakhstania between Laurussia
and Siberia and an immediate collision of the
latter two (Fig. 1). According to palaeomagnetic
data (Kazansky et al. 2004), Siberia rotated 308
clockwise between the Triassic and the Late
Cretaceous.
Peneplain formation
Rapid uplift and erosion of the Uralide orogen
resulted in the formation of a Cretaceous-
Palaeogene peneplain (Papulov 1974; Sigov 1969;
Amon 2001), and by the Late Jurassic or Early Cre-
taceous, there was no topographic barrier dividing
Europe and Siberia. Buried river-bed deposits
along the eastern slope of the Southern and Middle
Urals have a north-eastern direction, as revealed
by a shallow prospecting drilling. For the Late Cre-
taceous and Eocene, the existence of short-lived
straits connecting the European and Siberian
marine basins is hypothesized.
Along the eastern slope of the Southern and
Middle Urals, thin marine sediments occur only
during maximal transgressions (in the Late Cretac-
eous and Middle Eocene); more generally, fluviatile
deposits occur. To the north, Upper Jurassic and
younger marine sediments occur adjacent to the
eastern foothills of the modern Ural mountains.
The difference between the southern and northern
parts of the modern Urals (as expressed by better
exposure of the eastern zones in the south), was
probably inherited from this time.
Neo-orogeny
In the PlioceneQuaternary time, a modern chain of
moderately high mountains was uplifted, forming a
natural drainage divide between Europe and Asia.
These mountains are formed in an intra-plate
setting, having no precursory suture zone. Conver-
gence is indicated by studies which show that
maximum stresses are oriented perpendicular to,
or at a high angle to, the strike of the belt and
by the identification of a zone with anomalously
low heat flow (Golovanova 2006). According to
Mikhailov et al. (2002), mountain building is
accompanied by westward-directed thrusting.
The timing of mountain building is controver-
sial. Until recently, there was a consensus that oro-
genesis began in the Late Oligocene and continued
into the Quaternary inclusive (Trifonov 1999;
Rozhdestvensky & Zinyakhina 1997) and that
ancient peneplains formed in the TriassicJurassic
were preserved (Sigov 1969; Borisevich 1992).
On the contrary, Puchkov (2002b) pointed out
that models proposing Late Oligocene uplift of the
Urals are inconsistent with: (1) the occurrence of
Miocene oligomictic quartz sands and sandstones
(Yakhimovich & Andrianova 1959; Kozlov 1976),
which indicate stable non-orogenic conditions of
V. N. PUCHKOV182
weathering, erosion and deposition in both foredeep
terrane and the Urals itself. The first appearance of
polymictic sediments, indicating more rapid uplift
and erosion, is Late Pliocene in age (Verbitskaya
1964); (2) deep Miocene river incision is best
explained by a drop of the Caspian sea level, Messi-
nian crisis, as well documented in the Mediterr-
anean (Milanovsky 1963), rather than by crustal
uplift; (3) no well-documented MioceneEarly
Pleistocene terraces occur in the river valleys of
the Urals; (4) no cave deposits older than
Middle-Upper Neopleistocene are found; and (5)
the velocities of the modern uplift of the Urals
surface are 5 7 mm a
21
, which is an order of mag-
nitude faster than the time needed to build the Urals
mountains since Oligocene.
On the other hand, fission-track (Seward et al.
1997; Glasmacher et al. 2002) and unpublished
U/Th He data show that the relief of the axial
part of the Southern Urals was not completely
stabilized by the Late Cretaceous. Puchkov &
Danukalova (2004) demonstrated that the altitudes
of the base of shallow marine Upper Cretaceous
deposits increase progressively in the direction of
the mountain ridge, disappearing at elevations of
500 m. Therefore no Triassic Jurassic planation
surfaces can be preserved in the modern surface.
The depth of erosion since the Cretaceous is
between 1000 and 2000 m (depending on the
thermal gradient), and these numbers are several
times greater than the previous estimates.
The deep structure of the Urals
The main milestones of the study
Fifteen regional deep seismic survey (DSS) profiles,
made between 1961 and 1993 permit the definition
of the Moho surface beneath the Urals and demon-
strated its layered seismic structure and the anoma-
lous character of its crust. In particular, these
surveys suggest the presence of a crustal ‘root’
under the Tagil Magnitogorsk zone and a
complex compositional transition zone in the
lower crust, with V
p
velocities between 7.2 and
7.8 km/s (Druzhinin et al. 1976). Puchkov & Sve-
tlakova (1993) placed these results into a plate tec-
tonic context for the first time, by interpreting a
DSS profile in the Middle Urals as an indicator of
the bi-vergent character of the Uralian orogen.
Reflection profiles made between 1964 and the
early 1990s in the Magnitogorsk and Tagil zones
(e.g. Menshikov et al. 1983; Sokolov 1992) revealed
the inclined reflectors that define synclinoria and
anticlinoria, and along-strike variations in the mor-
phology of the Main Uralian fault. In the 1980s,
state oil company surveys along the western slope
of the Urals (e.g. Skripiy & Yunusov 1989;
Sobornov & Bushuev 1992), combined with drilling,
helped to solve some structural problems in the
Uralian foreland. In 1993, the commencement of
the EUROPROBE Programme ‘Uralides’, involved
acquisition and interpretation of seismic data along
two regional profiles (the Southern and Middle
Urals) and re-interpretation of some existing
shorter profiles. A combined geological and multi-
component geophysical URSEIS-95 project in the
Southern Urals (Berzin et al. 1996; Carbonell et al.
1996; Echtler et al. 1996; Knapp et al. 1996;
Suleimanov 2006), included a c. 500 km-long
seismic reflection line across most of the orogen at
a latitude of Kraka and Gebyk massifs. The
ESRU-SB profile, ultimately c. 440 km long,
crossed the Middle Urals where the ‘superdeep’
SG-4 borehole (currently c. 5.5 km deep) is located
(Kashubin et al. 2006, and references therein).
The URSEIS profile (Fig. 15)
The interpretation given here is based on combined
(vibroseis and explosion) seismic section along the
geotraverse profile, after Suleimanov (2006), Spets-
Geofizika. The coherency-filtered, depth-migrated
vibroseis data by Tryggvason et al. (2001) were
also used as an alternative source of information
for the upper and middle crust. Along with generally
accepted conclusions (Brown et al. 2008, and refer-
ences therein), the following interpretations contain
some latest original inferences of the author.
From 500 km (in the Preuralian foredeep), to the
Main Uralian Fault at c. 275 km, the survey charac-
terizes the structure of the foreland fold-and-thrust
belt (Fig. 15). From 500 c. 420 km, subhorizontal,
moderately coherent reflectivity in the upper 5 km
corresponds to weakly deformed Palaeozoic fore-
land basin (foredeep) and platform margin shelf
rocks of Ordovician Lower Permian age (Brown
et al. 2006b). Below this, to approximately 20 km
depth, strongly coherent, subhorizontal reflectivity
is interpreted to represent undeformed Meso- and
Neoproterozoic strata of the SSE prolongation of
the Kama-Belsk aulacogen. The base of the reflec-
tivity here is thought to represent the unconformity
between undeformed and low-metamorphic
Mesoproterozoic strata and the non-reflective
Archaean-Palaeoproterozoic crystalline basement
(Dianconescu et al. 1998; Echtler et al. 1996). The
sedimentary prism, almost 20 km thick, has a
convex lens-like shape, consistent with the
interpretation that the prism represents an inverted
aulacogen. Beneath the crystalline basement, at
c. 430 km the Moho is cut by Makarovo normal
(?) fault, with up to 5 km of amplitude probably
related to the rift nature of the aulacogen (Fig. 15).
To the east, the upper and middle crust has weak,
gently east-dipping reflectivity that, between
THE EVOLUTION OF THE URALIAN OROGEN 183
Fig. 15. (a) Uninterpreted combined (vibro- and explosion) seismic section along the URSEIS geotraverse profile (the seismic data after Suleimanov 2006, SpetsGeofizika).
(b) Geological interpretation, overlain on the profile. See Figure 4 for location.
V. N. PUCHKOV184
420 km and the MUF is concave downward. This
reflectivity is associated with the Precambrian
rocks in the Bashkirian Anticlinorium which, in its
eastern part, was deformed during the Timanide
orogeny (Puchkov 2000). The base of the reflectiv-
ity is usually interpreted to be the basal detachment
contact between Mesoproterozoic strata and the
Archaean Palaeoproterozoic crystalline basement.
However, according to structural studies, large
anticlines of the central and eastern part of the
Bashkirian anticlinoria have detached blocks of
the crystalline basement beneath them, close to the
surface. Taratash anticline in the north exposes
such Precambrian core in the surface.
The lower crust beneath the foreland
fold-and-thrust belt is weakly- to non-reflective,
though the Moho boundary can be traced by
explosion seismic data further to the east, towards
the MUF. Close to the MUF, the deep-seated
Uraltau antiform is clearly imaged and the MUF
fault is traced as a gently concave structure,
mainly by a loss of reflections from the Precambrian
rocks and assuming that the base of the island-arc
complex in the hanging wall of MUF is transparent.
The Zilair synform and Uraltau antiform immedi-
ately to the west of the MUF form a dynamic
couple, with the antiform making a tectonic wedge
downthrusted to the west under the antiform.
From the MUF to c. 180 km, the Magnitogorsk
arc is almost non-reflective in the upper crust,
though the east-vergent Kizil thrust is clearly
imaged in the coherency-filtered vibroseis data
(Tryggvason et al. 2001) and its interpretation is
supported by deep drilling and recent short seismic
reflection profiles. The middle and lower crust
is relatively transparent. The contact between
the Magnitogorsk arc and the East Uralian Zone
at c. 180 km (the East Magnitogorsk Fault and
suture zone) is imaged by a sharp change from
almost transparent crust in the west to coherent,
highly reflective, middle crust to the east. In the
East Uralian Zone, from c. 180100 km, the upper
crust is nearly transparent down to about 8 km,
corresponding to the Gebyk granite. Below this, a
series of short east-dipping and subhorizontal
reflectors are descending into the middle crust.
The lower crust is almost transparent or semi-
transparent, except in the east, where a zone
with strong west-dipping reflectivity extends
downward and westward from the Trans-Uralian
Zone (a continuation of Kartaly reflections; see
below).
The crust of the Trans-Uralian Zone is imaged as
west-dipping, strongly coherent reflectivity called
the Kartaly Reflection Sequence (KRS, Fig. 15),
which merges with the Moho in a system of
thrusts; in this region the Moho appears as a near-
horizontal detachment fault. The boundary
between the East Uralian and Trans-Uralian zones
is thought to be a regional fault called Kartaly or
(wrongly) Troitsk fault located immediately to the
east of Dzhabyk massif and traced in the SSW and
NNE directions where it is interpreted as a wrench
fault of a considerable amplitude.
In the western and eastern parts of the profile, the
Moho is imaged in the URSEIS combined (vibro-
and dynamite) reflection data to a depth of
c. 50 km but cannot be traced in the deeper,
central portion of the profile. The Moho has been
determined from wide-angle data to occur at a
maximum depth of 55 km (Carbonell et al. 1998).
Although there is some bias between the wide-angle
and CDP data, a cloudy reflection under this depth
at c. 250 km, can be tentatively interpreted as a
wedge of the lower crust protruding into the
mantle (compare with a much better imaged
wedge of the lower crust in the ESRU-SB profile,
see below) (Fig. 16).
The ESRU-SB profile (Fig. 16)
The latest interpretation of crustal structure of the
Middle Urals at latitude 56 628 based on seismic
reflection data obtained by yearly installments
since 1993 (ESRU-SB profile) was given recently
by Kashubin et al. (2006), Rybalka et al. (2006)
and Brown et al. (2008). From 100 km in the Pre-
ruralian foredeep to c. 25 km in the east, the upper
crust has a flat-lying reflectivity, interpreted to rep-
resent an undeformed foredeep orogenic basin and
platformal deposits (up to c. 65 km). In contrast,
to the east, the steeply east-dipping shallow reflec-
tivity of the ‘thin-skinned’ fold-and-thrust foreland
occurs (Fig. 16). Both undeformed and steeply-
dipping reflections are underlain by a gently east-
dipping zone of reflections at a depth of c. 5–8 km
that is interpreted as a low-angle unconformity
surface between the platform cover of Ediacarian
and Palaeozoic age and the older Neoproterozoic
(Upper Riphean), that is transformed in the east
into a basal detachment of the fold-and-thrust belt
(Brown et al. 2006c). At c. 25 km this reflectivity
is abruptly truncated by a series of steep east-
dipping concave reflectors corresponding probably
to listric-like faults, traced into the middle crust to
a depth of 2530 km. This type of reflectivity
persists from a distance mark of 25 km to the
MUF zone. The zone is characterized by several
pronounced closely-spaced reflectors dipping to
the east at angles of 458 –608 between 0 and
10 km, imaging an imbrication zone of the
strongly deformed margin of Laurussia continent.
From 2010 km, the steeply east-dipping reflec-
tors represent ‘thick-skinned’ deformation in the
Precambrian-cored Kvarkush anticlinorium and
Early Palaeozoic hanging wall.
THE EVOLUTION OF THE URALIAN OROGEN 185
Fig. 16. Seismic cross-sections (a) Uninterpreted, and (b) Interpreted line drawings of the coherency filtered, depth-migrated ESRU-SB data (Kashubin et al. 2006 Rybalka
et al. 2006). See Figure 4 for location. Abbreviations in the Figure A: MUFZ, Main Uralian Fault zone; SMZ, Serov-Mauk Fault zone; MAMC, Murzinka-Aduy
metamorphic complex.
V. N. PUCHKOV186
Below the undeformed foreland basin and the
basal detachment of the fold-and-thrust belt, the
middle crust exhibits wave-like concave to convex
reflectivity down to approximately 25 km depth.
From 25 km to c. 42 km depth, the lower crust is
characterized by more coherent and strong, sub-
horizontal reflectivity. The middle crustalreflectivity
probably imagesthe Neoproterozoicand Mesoproter-
ozoic sedimentary rocks, and the lower crustal
reflectivity images ArchaeanPalaeoproterozoic
crystalline basement rocks of the Laurussian
margin, though there is a striking difference
between the reflectance character of the crystalline
basement here and in the URSEIS. The character
of crustal reflectivity in the deep part of the
section suggests that it is unaffected by the
Uralide deformation which also makes a difference
between the profiles (Brown et al. 2006c; Kashubin
et al. 2006). On the other hand, the reflectivity
pattern of the middle crust suggests that at 100
to c. 20 km, the 15 or more kilometre-thick
Meso- and Neoproterozoic strata form a large
synform that is underthrust by an antiformal tectonic
wedge composed of the rocks of the same age. The
structure is characteristic of a Timanian foreland
deformation, but also resembles the wedge-like
relationships between the Uraltau antiform and
Zilair synform imaged by URSEIS, though their
relationships had been formed by the Uralide
orogeny.
The Moho surface is traced here as a gently east-
dipping boundary between highly reflective lower
crust and almost transparent mantle at a depth of
42 45 km. From about c. 1050 km, the upper
crust of the Tagil arc is imaged as an open
synform, thrust to the west over the Meso-
Neoproterozoic rocks of Kvarkush aniclinorium.
The Tagil synform is asymmetric, and its eastern
limb is limited by a serpentinite me
´
lange of the
Serov-Mauk fault zone, separating the synform
from the Salda metamorphic complex. The
me
´
lange zone is transparent and its western bound-
ary can be traced along abrupt truncations of Tagil
reflectors, suggesting a westerly dip of the zone at
an angle of 608. The zone can be traced tentatively
into the lower crust along weak and diffuse reflec-
tors, changing the steep western dip of the zone to
a gentler 308 close to Moho surface.
The Salda metamorphic complex of probable
island-arc nature (Rybalka et al. 2006), situated
between 55 and 103 km, is characterized by a
series of west-dipping reflections, which can be
traced under the Tagil synform and Central
Uralian zone together with the Serov-Mauk fault.
This portion of the crust, correlated with the Salda
zone, is wedge-like, protruding down into the
mantle under the western slope of the Urals to a
depth of 60 km.
The next zone to the east, Murzinka-Adui zone
(103 120 km), is represented at the surface by Neo-
proterozoic metamorphic rocks and Permian gran-
ites, and together with the Salda zone belongs to
the East Uralian megazone. The character of its
reflectivity in the upper crust is incoherent and
patchy, and does not permit recognition of its
detailed structure. Further east, from 120180 km
within the Trans-Uralian zone, the upper crustal
structure is more difficult to interpret owing to
both poor surface exposure and the almost complete
absence of coherent reflectors in the upper 10-km of
the profile.
From c. 180 km to the end of the profile
(260 km), the platformal Cretaceous and Cenozoic
strata of the West Siberian Basin appear to be
characterized by a zone of good subhorizontal
reflectivity which thickens to the east up to 1.5 km
at 260 km. The details of the profile imaged
by Rybalka et al. (2006) show a relief of the
PalaeozoicCretaceous unconformity surface,
which is strongly uneven probably due to pre-
Cretaceous grabens, flexures and river-bed
incisions. Under the platformal cover, the structure
of the Trans-Uralian zone reveals a series of west-
dipping reflectors, merging with the Moho at a
depth of c . 40 km, in a manner similar to that seen
in the KRS of the URSEIS profile, although not
as bright.
In general, the Moho is very well defined along
the whole profile as a sharp boundary between
highly reflective lower crust and an almost transpar-
ent mantle. The crust thickens from c. 42 43 km in
both the west and east to nearly 60 km beneath the
Central Uralian zone. The above-mentioned wedge
of the lower crust protruding into the mantle gives
here the impression that the eastern limb of the
orogen is thrust under the former Laurussian lower
crust and Moho.
Discussion
The development of the Uralides in the Palaeozoic
preserves many of the characteristics of a full
Wilson cycle. However, if the concept of such a
cycle is restricted to a classical ‘accordion-type’
development, wherein the continent that rifted
away returns back to collide (as it was in the case
of Rheic ocean), then the development of the Ura-
lides does not conform with the idea. According to
palaeomagnetic data and geodynamic reconstruc-
tions (e.g. Puchkov 2000; Kurenkov et al. 2002;
Svyazhina et al. 2003; Levashova et al. 2003),
between Ordovician and Early Permian time, the
microcontinents of the East Uralian zone and Kok-
chetav block of Kazakhstania were transported at
least 2000 km from north to south parallel to the
margin of Baltica. Kazakhstania as a whole
THE EVOLUTION OF THE URALIAN OROGEN 187
intervened between Siberia and Baltica in the Devo-
nian, and Siberia rotated clockwise at 908 prob-
ably because of the arrival of Kazakhstania.
Kazakhstania was squeezed between accreted
margins of Siberia and Laurussia, forming a pro-
nounced horseshoe-like orocline (Fig. 1). It looks
more like a rock’n’roll dance than an accordion-like
motion. On the other hand, only a minority of
orogens belongs to the regular ‘accordion’ type,
and therefore we prefer to follow to a more liberal
understanding of Wilson cycle.
The rift processes at the beginning of the cycle
are demonstrated by a profound difference
between the strikes of Timanide structures and the
Main Uralian Fault to the north of the Poliud
Range (Fig. 7). The accompanying sedimentary
deposits are characterized by irregularly distributed
coarse-grained polymictic to arkosic sediments
unconformably overlying the basement and
accompanied by subalkaline basaltic volcanism.
Similar formations on the sialic blocks of the East
Uralian and Transuralian zones are c. 15 20 Ma
younger than those in the Western zones, indicating
that the East Uralian microcontinent was not pre-
viously detached from the same place where it
finally docked.
The suggested Early Palaeozoic plume magma-
tism described above is considerably younger than
the rifting event, and is only indirectly connected,
possibly in an analogous manner to the relationship
between the transverse chain of the Cretaceous
Monteregian alkaline with carbonatite intrusions
of eastern North America and the Mesozoic rifts
along the margin of the Atlantic Ocean.
Widespread development of ophiolite com-
plexes, almost unprecedented among the Palaeozoic
or earlier foldbelts, is one of the most important
characteristics of the Uralides. Ophiolites appear
to represent anomalous portions of the oceanic
tract (Aden and Red sea-type, supra-subduction
zone basalts, Lanzo-type mantle blocks) whereas
most typical MORB appears to have been almost
eliminated by subduction. Island-arc complexes
are also widely spread in the Uralides, and sub-
sequent uplift and erosion offers a rare possibility
of studying the deeper structure of an island arc,
than is available for study in modern island arcs.
The internal structure of the arcs exhibits a moderate
strain (Brown et al. 2001). According to Alvarez-
Marron (2002) the Uralides ‘may be seen as a
factory for “making” new continental crust in con-
trast to the Variscides which is a factory for “recy-
cling” existing continental crust’.
One of the possible explanations for the excep-
tionally good preservation of oceanic complexes
in the Uralides is the low rigidity of the Kazakhsta-
nian plate, which became continental crust only in
the Silurian (Puchkov 1996a). The deep-seated
deformation of the whole crust with the Moho as a
detachment, in the young, eastern limb of the Ura-
lides (see above), absorbed a considerable part of
strain. The preservation of ophiolites may depend
on strain. In zones of higher strain, ophiolites are
squeezed from sutures as allochthonous sheets
aided by the formation of rheologically weak ser-
pentinites which may also have acted as a lubricant.
This interpretation is supported by experiments that
demonstrate the rheological weakness of serpenti-
nite (e.g. Escartin et al. 1997; Hilairet et al. 2007)
and by structural studies in the foreland
fold-and-thrust belt of the Southern and Middle
Urals, where shortening deduced from balanced
geological sections is anomalously low (14 17%,
Brown et al. 1997). Shortening increases to the
north, and in the Mikhailovsk and Serebryansk pro-
files it is c. 30% (calculated after Brown et al.
2006c). In the Cis-Polar and Polar Urals, however,
shortening can be still much greater, judging by
the upper section of figure 4 in Puchkov (1997);
see also Yudin (1994). This may be explained by
the wedging-out of Kazakstania to the north,
where two rigid cratons, Laurussia and Siberia,
come into contact.
Modern analogies to the arc-continent collision
in the Urals include the Indonesian, Taiwan,
Tyrrhenian and Greater Antilles arcs. The evolution
is similar to that proposed for the Taconian arc in
the Appalachian orogen, and the mid-Devonian
arc collision with Baltica along the margins of the
Rheic Ocean.
Another striking feature of the Uralides, is a long
duration and recurrence of orogenic events from
the Devonian until the Early Jurassic, which is com-
parable to the duration of Appalachian orogenic
activity. The oblique, transpressive character and
the diachroneity of the continentcontinent col-
lision in the Urals is similar to that of the Alleghe-
nian orogeny (Engelder 2007). But the absence of
Caledonian collisions, from the Ordovician to the
Middle Devonian, is another striking feature of the
Uralides.
The characteristics of two regional profiles trans-
ecting the orogen, confirm the bi-vergent symmetry
of it. Alternatively, uniformly vergent orogens may
be part of a bigger, bi-vergent one, that has been dis-
membered and dispersed by subsequent tectonic
events (e.g. Greenland and Scandinavian Caledo-
nides) or its lacking limb overlain by a younger
orogen (e.g. a Variscan basement of Alps).
In the western Uralides, where the foreland is
cratonic (i.e. ancient and characterized by a thick
and rigid lithosphere), the crystalline basement
and Moho surface are not affected, or only partly
affected, by the main Uralide orogenesis. In the
eastern Uralides, however, the Moho is interpreted
as a detachment, and the crust is deformed to great
V. N. PUCHKOV188
depths, an interpretation which supports the idea of
a comparative weakness of the Palaeozoic crust and
lithosphere as a whole.
In the west, the regional and local profiles show
an abrupt transition from ‘thin-skinned’ to
thick-skinned tectonics along a sharp ramp due to
an abrupt change in the plasticity of the rocks. In
the east we do not see any ‘thin-skinned’ tectonics
at all. This may reflect the incompleteness of the
eastern part of the profiles (URSEIS had been
stopped at a state border with Kazakhstan and
ESRU in swamps of Siberia) (Fig. 4). On the
other hand, Late Palaeozoic orogenic processes
reached much farther to the east than the initial
boundary between Uralides and Kazakhstanides
(Fig. 1). In the Central Kazakhstanian Caledonides,
orogenic processes are documented by Permian
deformation of different styles, voluminous Late
Palaeozoic syn-orogenic granite and deposition of
the contemporaneous molasse in huge intermontane
basins such as Chu-Sarysu and Teniz (YUGGEO
2002). Where the Upper Palaeozoic epi-Caledonian
sedimentary cover is preserved, as in the Greater
Karatau, the east-vergent ‘thin-skinned’ tectonics
was developed during the Upper Carboniferous
and Permian (Alekseiev 2008).
Concluding remarks
Extremely good preservation of oceanic and
island-arc complexes and low degree of shortening
in the foreland belt are unprecedented in the Palaeo-
zoic orogens and give the Uralides a real individua-
lity. Many other features of the Urals are also rare,
such as its well-preserved bi-lateral structure,
island-arc related platinum-bearing belt, demonstra-
tive arc-continent collision, diachroneity of col-
lisions, a combination of orogenic and rift-related
magmatism in a single stage of transpressive defor-
mation of the lithosphere, and the preservation of a
heavy, relatively ‘cold’, isostatically equilibrated
root. On a plate scale, however, the history of the
Uralides follows the main stages of a Wilson
cycle, modified somewhat by episodes of plume-
related tectonics and magmatism in the Early
Palaeozoic and Triassic.
Fieldwork campaigns, workshops and informal discus-
sions in more than a decade of co-operation with prominent
European and American geologists during the activity of
the EUROPROBE Commission in the Urals have consider-
ably stimulated the work of the author. The author
acknowledges also the importance of his participation in
the IGCP-453 Uniformitarianism revisited: a comparison
between modern and ancient orogens’, which ultimately
inspired him to write this paper. The financial support of
the Department of Earth’s Sciences of the Russian
Academy of Sciences, Program No. 10 The Central
Asian mobile belt: geodynamics and stages of the
Earth’s crust formation must be also highly appreciated.
The last, but not the least of my expression of gratitude
is to the reviewers, V. Ramos and R. Ernst and to
B. Murphy, the editor, who helped greatly at the last
stages of the work.
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THE EVOLUTION OF THE URALIAN OROGEN 191
interpolated transcurrent deformations of the