Content uploaded by Christopher Juhlin
Author content
All content in this area was uploaded by Christopher Juhlin on Apr 25, 2018
Content may be subject to copyright.
Mountain building processes during continent–continent collision in the Uralides
D. Brown
a,
⁎, C. Juhlin
b
, C. Ayala
c
, A. Tryggvason
b
,F.Bea
d
, J. Alvarez-Marron
a
, R. Carbonell
a
, D. Seward
e
,
U. Glasmacher
f
, V. Puchkov
g
, A. Perez-Estaun
a
a
Institute of Earth Sciences “Jaume Almera”, CSIC, c/Lluís Solé i Sabarís s/n, 08028 Barcelona, Spain
b
Department of Earth Sciences, Uppsala University, Villavagen 16, SE-75236 Uppsala, Sweden
c
Department of Geology and Geophysics, IGME, C/ La Calera n. 1, 28760 Tres Cantos, Madrid, Spain
d
Department of Mineralogy and Petrology, Fuentenueva Campus, University of Granada, 18002 Granada, Spain
e
Geological Institute, Sonneggstrasse 5, ETH Zurich, 8092 Zurich, Switzerland
f
Institute of Geology and Palaeontology, University Heidelberg, Im Neuenheimer Feld 234, 69120 Heidelberg, Germany
g
Ufimian Scientific Center, Russian Academy of Sciences, ul. Karl Marx 16/2, Ufa 45000, Bashkiria, Russia
ABSTRACTARTICLE INFO
Article history:
Received 16 November 2007
Accepted 7 May 2008
Available online 17 May 2008
Keywords:
Uralides
mountain building processes
crustal architecture
Since the early 1990's the Paleozoic Uralide Orogen of Russia has been the target of a significant research
initiative as part of EUROPROBE and GEODE, both European Science Foundation programmes. One of the
main objectives of these research programmes was the determination of the tectonic processes that went
into the formation of the orogen. In this review paper we focus on the Late Paleozoic continent–continent
collision that took place between Laurussia and Kazakhstania. Research in the Uralides was concentrated
around two deep seismic profiles crossing the orogen. These were accompanied by geological, geophysical,
geochronological, geochemical, and low-temperature thermochronological studies. The seismic profiles
demonstrate that the Uralides has an overall bivergent structural architecture, but with significantly different
reflectivity characteristics from one tectonic zone to another. The integration of other types of data sets with
the seismic data allows us to interpret what tectonic processes where responsible for the formation of the
structural architecture, and when they were active. On the basis of these data, we suggest that the changes in
the crustal-scale structural architecture indicate that there was significant partitioning of tectonothermal
conditions and deformation from zone to zone across major fault systems, and between the lower and upper
crust. Also, a number of the structural features revealed in the bivergent architecture of the orogen formed
either in the Neoproterozoic or in the Paleozoic, prior to continent–continent collision. From the end of
continent–continent collision to the present, low-temperature thermochronology suggests that the evolution
of the Uralides has been dominated by erosion and slow exhumation. Despite some evidence for more recent
topographic uplift, it has so far proven difficult to quantify it.
© 2008 Elsevier B.V. All rights reserved.
Contents
1. Introduction .............................................................. 178
2. Geology of the South and Middle Urals ................................................. 179
2.1. Western foreland thrust and fold belt ............................................... 179
2.2. Main Uralian Fault........................................................ 179
2.3. Magnitogorsk–Tagil Zone .................................................... 179
2.4. East Uralian Zone ........................................................ 181
2.5. Trans-Uralian Zone ....................................................... 181
3. Crustal structure of South and Middle Urals ............................................... 181
3.1. Reflection seismic data...................................................... 181
3.1.1. The ESRU profile..................................................... 181
3.1.2. The URSEIS profile ................................................... 185
3.2. Velocity structure ........................................................ 185
3.3. Thermal structure along the URSEIS transect ........................................... 185
3.4. Density structure along the URSEIS transect ............................................ 188
Earth-Science Reviews 89 (2008) 177–195
⁎Corresponding author.
E-mail address: dbrown@ija.csic.es (D. Brown).
0012-8252/$ –see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.earscirev.2008.05.001
Contents lists available at ScienceDirect
Earth-Science Reviews
journal homepage: www.elsevier.com/locate/earscirev
3.5. Aeromagnetic anomaly in the South and Middle Urals ....................................... 188
3.6. Petrophysical modelling of crustal composition .......................................... 189
4. Low-temperature exhumation history .................................................. 189
5. Discussion ............................................................... 191
5.1. Structural architecture ...................................................... 191
5.2. Crustal composition along the URSEIS transect ........................................... 192
5.3. Low-temperature exhumation and uplift of the Ural Mountains................................... 192
6. Conclusions .............................................................. 193
Acknowledgements ............................................................. 193
References ................................................................. 193
1. Introduction
The Uralide Orogen (Fig. 1A) was one of the main orogenic edifices
built during the Paleozoic assembly of Pangaea (Hamilton,1970; Khain,
1975; Zonenshain et al., 1984, 1990). Unlike other orogens that
developed at that time, the Uralides has not been affected by later
plate break-up and dispersal and, at least in the south, has not been
extensively overprinted by post-orogenic processes (Alvarez-Marron,
2002). This, together with the large geological and geophysical database
that is currently available for the Uralides, provides an excellent
opportunity to study Paleozoic mountain building processes in an intact
orogen. For more than a century the Uralides has been a key area of
research by Russian Earth Scientists. By the end of 1960's, much of the
orogen had been mapped and a 1:200,000 scale map series had been
produced (Geology of the USSR 1:200,000 Urals Map Series). In the
1970's and 1980's the area became the focus of extensive geophysical
experiments, and a number of regional Deep Seismic Sounding (DSS)
profiles were acquired across the orogen, and potential field data were
collected (Semenov et al., 1983; Skripi and Iunusov, 1989; Tavrin and
Khalevin, 1990; Ryzhiy et al., 1992). Since the 1990's, a significant
Fig. 1. A) Lithotectonic map of the Uralides showing the tectonic and geographical subdivisions discussed in the text. B) Geological map of the South and Middle Urals. The locations of
the seismic profiles discussed in the text are shown. MK = Mikhailovsky.
178 D. Brown et al. / Earth-Science Reviews 89 (2008) 177–195
amount of new research has been carried out in the Uralides, in par-
ticular as partof EUROPROBE and GEODE (European Science Foundation
scientific programmes) (Ge e a nd Z eye n, 19 96; Bl und ell , 199 8). One of the
specific aims of these programmes was to study the tectonic processes
that were responsible for the formation of the Uralide Orogen.
Much of the recent research in the Uralides has been focused
around two deep seismic surveys, EUROPROBE's Seismic Reflection
Profiling in the Urals (ESRU) survey in the Middle Urals (e.g., Juhlin
et al., 1998; Kashubin et al., 2006) and the multicomponent Urals
Seismic Experiment and Integrated Studies (URSEIS) survey in the
South Urals (Berzin et al., 1996). These seismic experiments were
accompanied by a large number of geology, geochemistry, thermo-
chronology, and geochronology studies (e.g., Perez-Estaun et al.,
1997a; Brown et al., 2002a) that further helped to constrain the
tectonic evolution of the orogen. In this paper we present a reviewof a
broad range of these data, with the aim of extending our under-
standing of the tectonic processes that went into building the orogen
during the continent–continent collision that took place between
Laurussia and the Kazakhstan collage (which we here call Kazakh-
stania). The paper will focus geographically on the South and Middle
Urals (Fig. 1A), where the majority of the recent data collection took
place. The Devonian arc–continent collision history of the Uralides
was presented by Brown et al. (2006a), and the reader is referred there
for a detailed discussion of this process. In this paper we assume that
the Magnitogorsk and Tagil island arcs formed part of the Laurussia
margin by the time the continent–continent collision had started.
2. Geology of the South and Middle Urals
From west to east, the Uralides are divided geologically into the
western foreland thrust and fold belt, the Magnitogorsk–Tagil Zone,
the East Uralian Zone, and the Trans-Uralian Zone (Fig. 1A). These are
described below. Additionally, the Uralides are divided geographically
into the South, Middle, Northern, Cis-Polar and Polar Urals (Fig. 1A).
Finally, we use the term Ural Mountains when referring to the
topographic edifice.
2.1. Western foreland thrust and fold belt
The basement upon which the Paleozoic passive margin of
Laurussia was built consisted of Archean and Proterozoic gneisses
overlain by up to 12 km of Proterozoic sedimentary rocks that were
deposited in aulocogens (Kozlov et al., 1989; Maslov et al.,1997). These
rocks outcrop extensively along the South and Middle Urals, in the
Bashkirian and Kvarkush anticlines, respectively (Fig. 1B). Along the
eastern flanks of both these anticlines Precambrian rocks were affected
by a Neoproterozoic III (Vendian in the old timescale) to Early
Cambrian tectonothermal event that locally reached granulite and
eclogite facies metamorphism (Puchkov, 1997; Giese et al., 1999;
Glasmacher et al., 1999, 2001, 2004; Beckholmen and Glodny, 2004).
Unmetamorphosed Neoproterozoic III sediments along the western
flanks of both the Bashkirian and Kvarkush antiforms are thought to
have been deposited in a foreland basin setting to this tectonothermal
event (Brown et al., 1996; Puchkov, 1997). In the south, Ordovician or
Silurian clastic rocks unconformably overlie the basement locally,
whereas westward the Lower Devonian is unconformable on the
basement. In the South and Middle Urals, the shelf sediments of the
Paleozoic continental margin are made up of about 4000 m of
limestones with thin intercalations of clastics. The bathyal sediments
of the margin are preserved in allochthons overlying the shelf complex
and are represented by deep-water terrigenous and cherty rocks with,
locally, subordinate limestones (Puchkov, 2002). At the eastern margin
of the shelf, Ordovician, Silurian and Lower Devonian barrier reefs
were developed. To the west, the foreland basin is composed of more
than 3000 m of Late Carboniferous to Early Triassic syn-orogenic
sediments (Chuvashov and Diupina, 1973; Chuvashov et al., 1993).
In the South Urals, the continental margin sediments are
structurally overlain by an accretionary complex that is related to a
Late Devonian arc–continent collision that took place between the
Magnitogorsk island arc and the margin of Laurussia (Brown et al.,
1998; Brown and Spadea,1999; Brown et al., 2006a). The accretionary
complex is composed of weakly metamorphosed continental margin
sediments, Late Frasnian and Famennian syn-tectonic clastics,
ophiolite massifs, and high-pressure rocks. Along its southwest
flank, the syn-tectonic sediments of the accretionary complex are
conformably overlain by Lower Carboniferous sediments.
The foreland thrust and fold belt of the South and Middle Urals
developed during the Late Carboniferous through to the Late
Permian–Early Triassic (Kamaletdinov, 1974; Puchkov, 1997; Brown
et al., 1997, 2006b). It is overall a N–S trending, west-verging,
basement-involved thrust stack with a clear basal detachment
developed only in the frontal part (Brown et al., 2006b). Much of
the deformation in the thrust belt was achieved by reactivation of pre-
Uralide structures in the Bashkirian and Kvarkush anticlines (Perez-
Estaun et al., 1997b; Brown et al., 1999). Shortening in the thrust belt is
approximately 20 km (Brown et al., 1996; Perez-Estaun et al., 1997b;
Brown et al., 1997; Giese et al., 1999; Brown et al., 1999, 2006b).
2.2. Main Uralian Fault
The Main Uralian Fault is one of the most important structures in
the Uralides. It extends for more than 2000 km along the length of the
orogen, juxtaposing the pre-Middle Devonian Laurussia continental
margin rocks against the island arc rocks of the Magnitogorsk–Tagil
Zone (Fig. 1). In the South Urals, where it appears to represent the
original arc–continent suture of Late Devonian age (Brown et al., 1998,
2006a; Ayarza et al., 2000a), it is an up to 10 km wide mélange
consisting predominantly of serpentinite, but also containing material
that was tectonically eroded from the volcanic arc and the continental
margin, as well as a number of mantle fragments (e.g., Savelieva et al.,
1997). In the Middle to Northern Urals, the Main Uralian Fault is poorly
exposed and its outcrop characteristics are not well known.
2.3. Magnitogorsk–Tagil Zone
The Magnitogorsk–Tagil Zone represents at least two intra-oceanic
island arcs that developed during the Early Paleozoic in the paleo-
Uralian ocean, and which subsequently collided with the continental
margin of Laurussia during the Middle Devonian to Early Carboniferous
(Brown et al., 1998; Brown andSpadea, 1999; Brownet al., 2006a). In the
South Urals, the Early to Late Devonian Magnitogorsk arc (Fig. 1A), the
arc volcanic sequence begins with the Emsian-age Baimak-Buribai
Formation boninite-bearing arc-tholeiites in the forearc region, overlain
by the Emsian- to Eifelian-age Irendyk Formation arc-tholeiite to calc-
alkaline volcanism (Seravkin et al., 1992; Brown and Spadea, 1999;
Spadea et al., 2002). Rifting in the arcduring the Eifelian and Givetian led
to eruption of the Karamalytash Formation basalt, and rhyolite with
minor basaltic andesite and quartz andesite. These volcanic units form
the basement on which up to 5000 m of westward-thickening, Frasnian
to Famennian age forearc basin sediments were deposited (Maslov et al.,
1993; Brown et al., 2001). In the eastern part of the arc they are partly
substituted by volcanics of latest Frasnian and early Famennian age.
Lower Carboniferous shallow water carbonates unconformably overlie
the arc edifice. Locally, Lower Carboniferous granitoids intrude the arc.
Deformation in the Magnitogorsk volcanic arc is low, with only minor,
open foldingand minor thrusting (Brown et al., 2001).The metamorphic
grade barely exceeds seafloor metamorphism.
In the MiddleUrals, the Tagil arc (Fig.1A) has also been interpreted to
be an intra-oceanic island arc (Yazeva and Bochkarev, 1996; Bosch et al.,
1997) with predominantlySilurian andesiticmagmatic rocks overlain by
Lower Devonian trachytes and volcanoclasticsin the east. These volcanic
and volcanoclastic rocks are overlain by 2000 m of Lower and Middle
179D. Brown et al. / Earth-Science Reviews 89 (2008) 177–195
Fig. 2. A) Schematic map of the South and Middle Urals outlining the strike-slip fault system and the location of granitoids. U–Pb ages are from Bea et al. (2002). B) Continental-crust normalized REE plots of Early Carboniferous subduction-related
granitoids (from Bea et al., 2002). Circles represent diorites,dots represent granodiorites, andcrosses represent granites. C) Continental-crust normalized REE plots of Permian collision-related granitoids. Squares represent gabbros, circles represent
diorites,dots representgranodiorites, and crossesrepresent granites. For Dzhabyk,additionally, crossedsquares and open circles representMochagi and Rodnichki quartz–monzonitesrespectively (from Bea et al., 2002). D) ε
Nd
(t)vsε
Sr
(t) plot of Uralide
subduction granitoids (from Bea et al., 2002). Neither
87
Sr/
86
Sr(t)nor
143
Nd/
144
Nd(t) bear any relation with the age, but depend on the geographical longitude.E) ε
Nd
(t)vsε
Sr
(t) plot of Uralide continental granitoids (from Bea et al., 2002). The isotopic
signature of the Permian continental-type granitoids is very primitive, with
87
Sr/
86
Sr(t)and
143
Nd/
144
Nd(t) that match the subduction granites. This feature excludes continental materials older than Silurian as a possible protolith.
180 D. Brown et al. / Earth-Science Reviews 89 (20 08) 177–195
Devonian limestone that, in the east, is intercalated with calc-alkaline
volcanics (Antsigin et al., 1994; Yazeva and Bochkarev, 1996). The Tagil
arc forms an open synformal structure (e.g., Bashta et al., 1990; Ayarza
et al., 2000b) that has been metamorphosed to lower greenschist facies.
The Magnitogorsk–Tagil Zone is structurally juxtaposed against the
East Uralian Zone along the strike-slip to transpressional East
Magnitogorsk–Serov-Mauk fault system (Ayarza et al., 2000a; Brown
et al., 2002b)(Fig. 1). Along the entire 700 km length of this fault
system there is a significant jump in metamorphic grade from the low
grade volcanic arcs in the west to the upper greenschist to granulite
facies rocks of East Uralian Zone.
2.4. East Uralian Zone
The East Uralian Zone is a broad area of intensely deformed and
metamorphosed rocks that extends for more than 700 km along the
Uralides before it disappears beneath Mesozoic cover sediments in the
south and north (Fig. 1). Rocks in the East Uralian Zone were derived
from both Laurussia and Kazakhstania, as well as the intervening
ocean. We therefore suggest that it forms the suture zone (sensu lato)
between the two continental masses. It is characterized by a strike-
slip fault system that was active until late in the orogenic evolution,
and into which voluminous granitoids intruded during the Late
Carboniferous and Permian (Echtler et al., 1997; Friberg et al., 2002;
Hetzel and Glodny, 2002; Bea et al., 2002, 2005). Dating on one
segment of the strike-slip fault system indicates a Late Permian to
Early Triassic age (247–240 Ma) for the development of fault-related
mylonites (Hetzel and Glodny, 2002), and latest Carboniferous (305–
291 Ma) ages for associated metamorphic rocks (Echtler et al., 1997;
Eide et al., 1997). The regional metamorphic grade ranges from
greenschist to granulite facies, with generally Late Paleozoic meta-
morphic ages (e.g., Friberg et al., 2000; Scarrow et al., 2002a).
The East Uralian Zone contains numerous granitoids that range in
age from the Late Devonian to Early Permian (Fershtater et al., 1997;
Bea et al., 1997, 2002). A number of these appear to have formed in two
subduction zone settings that were active from the Late Devonian to
Late Carboniferous, prior to the onset of continent–continent collision
(Bea et al., 1997; Montero et al., 2000; Bea et al., 2002)(Fig. 2A). The
first subduction-related magmatism produced Andean I-type grani-
toids dated to about 370 Ma to 350 Ma (Bea et al., 2002). These
batholiths are generally enriched in K and trace elements of
continental affinity such as Rb, Ba, Th, U, Li, but with Sr and Nd
isotope compositions that are more characteristic of mantle than
crustal materials (Fig. 2B and D) (Bea et al., 2002). The continental
component in these granitoids has been interpreted to be the result of
east-dipping sub-continental subduction of oceanic crust beneath the
Kazakhstania margin (Bea et al., 2002). A second phase of subduction
magmatism took place from about 335 Ma to 315 Ma (Bea et al., 2002).
These batholiths are medium- to high-K, have lower
87
Sr/
86
Sr(t), but
higher
143
Nd/
144
Nd(t) than the Early Carboniferous batholiths in the
east, and are not as enriched in trace elements (Fig. 2B and D) (Bea
et al., 2002). This phase of magmatism is also thought to have been
related to an east-dipping subduction zone and the formation of
island arcs that may later have accreted to Kazakhstania, and to have
partly recycled the older continental arc material. Magmatic activity
directly related to subduction ended before the Permian.
During continent–continent collision, the strike-slip fault system
that currently defines the East Uralian Zone was extensively intruded
by latest Carboniferous and Permian granitoids; first in the southern
part (292 Ma to 280 Ma) and then in the northern part (270 Ma to
250 Ma) (Fig. 2A) (Bea et al., 1997; Montero et al., 2000; Bea et al.,
2002, 2005). In general, the granitoids have a high SiO
2
content, are
mildly peraluminous, with elevated Rb, Cs, Ba, Th and U (Fig. 2C), but
with an unusually primitive Sr and Nd isotopic composition (Fig. 2E).
The Sr and Nd isotope data are interpreted to indicate recycling of the
370–350 Ma granitoids that had formed on the active margin of
Kazakhstania (Fershtater et al., 1997; Bea et al., 1997; Montero et al.,
2000; Bea et al., 2002; Gerdes et al., 2002).
The eastern contact of the East Uralian Zone is only known in the
South Urals, where it is a mélange that, locally, contains relics of
harzburgite. In the area crossed by the URSEIS section (Fig. 1), the
mélange is intruded by a late, undeformed phase of the Dzhabyk
granite that has been dated at 291+4 Ma (Montero et al., 2000). The
late orogenic, dextral strike-slip Troisk Fault lies within the mélange.
2.5. Trans-Uralian Zone
The Trans-Uralian Zone is not well known due to its poor exposure;
it only outcrops along river beds in the South Urals. The best-known
units are Devonian and Carboniferous calc-alkaline volcano–plutonic
complexes that are composed predominately of volcanoclastics and
lava flows that are intruded by co-magmatic gabbro-diorite and
diorite plutons (e.g., Puchkov, 1997, 2000; Herrington et al., 2002,
2005). These rocks are generally thought to be the type section of the
Valerianovka arc, which formed on the continental margin of
Kazakhstania (e.g., Puchkov, 1997; 2000; Herrington et al., 2002,
2005). Ophiolite units and high-pressure rocks have also been
reported (Puchkov, 2000). The volcano–plutonic complexes are
overlain by terrigenous red-beds and evaporites. Deformation has
not been well studied, although it appears that the Devonian and
Lower Carboniferous units are affected by open to tight folds.
3. Crustal structure of South and Middle Urals
3.1. Reflection seismic data
Between 1993 and 2000 three deep reflection seismic profiles were
acquired in the Urals. These are the multicomponent URSEIS transect in
the South Urals (Berzin et al., 1996), and the Mikhailovsky (MK in
Fig. 1B) and ESRU transects in the Middle Urals (Kashubin et al., 2006)
(Fig. 1B). The URSEIS transect consisted of an explosion- and a
vibroseis-source (presented here) reflection profile, as well as a
wide-angle experiment (Berzin et al., 1996; Carbonell et al., 1996;
Echtler et al., 1996; Knapp et al., 1996). The western part of the ESRU
transect also coincides with the GRANIT DSS profile (Juhlin et al.,1996).
In addition, two reflection seismic profiles (R114 and R115) were
acquired across the arc–continent collision zone (Fig. 1B) by the
Bashkirskaya Geophysical Expedition in the 1980's, and were repro-
cessed from the original field tapes at Uppsala University (Brown et al.,
1998). Finally, the shallow Alapaev reflection profile, which crosses the
central part of the Middle Urals (Fig. 1B), was acquired by the Bazhenov
Geophysical Expedition and reprocessed at Cornell University (Steer
et al., 1995). Crustal images and velocity models derived from these
profiles have been presented elsewhere (Echtler et al., 1996; Knapp
et al., 1996; Carbonell et al., 1996; Juhlin et al., 1996, 1998; Steer et al.,
1998; Brownet al., 1998; Carbonell et al., 2000; Tryggvason et al., 2001;
Friberg et al., 2002; Brown et al., 2002b, 2006b; Kashubin et al., 2006)
and their acquisition parameters and processing flows can be found in
these publications. These experiments provide a large data set from
which we interpret the crustal architecture and velocity structure of
the Uralides. Here, we present only data fromthe ESRU (including part
of the GRANIT profile) and URSEIS transects, which provide crustal-
scale images across the entire Uralides.
3.1.1. The ESRU profile
From km 0 to the Main Uralian Fault at about km 107, in the upper
crust, the ESRU reflection data images flat lying reflectivity of the
undeformed foreland basin and platform margin rocks (to c. km 35), and
disrupted to steeply east-dipping reflectivity of the foreland thrust and
fold belt (Fig. 3). These steeply dipping reflections lie above a shallowly
east-dipping zone of reflections at about 7 to 8 km depth that is thought
to be the basal detachment of the foreland thrust and fold belt (Brown
181D. Brown et al. / Earth-Science Reviews 89 (2008) 177–195
Fig. 4. A) Uninterpreted and, B) interpreted line drawings of the coherency filtered, depth-migrated URSEIS vibroseis data. See Fig.1B for location. The location of the URSEIS explosion-source reflection Moho (Steer et al., 1998) and the refraction
Moho (Carbonell et al., 1998) are shown.
183D. Brown et al. / Earth-Science Reviews 89 (2008) 177–195
et al., 2006b)(Fig. 3B). This reflectivity is abruptly truncated at about km
80, where the basal detachment is interpreted to ramp down into the
middle crust, and possibly even the lower crust. From km 78 to km 107,
the upper and middle crust are imaged as steeply east-dipping
reflectivitythat images deformation in the Precambrian-coredKvarkush
antiform. Below the undeformed foreland basin and the basal detach-
ment of the foreland thrust and fold belt, the middle crust contains
diffuse, sub-horizontal reflectivity down to approximately 30 km depth.
From 30 km to about 42 km depth, the lower crust contains moderately
coherent, sub-horizontal reflectivity. This middle and lower crustal
reflectivity images the Precambrian basement rocks of the Laurussia
margin. The similarity between the lower crustal reflectivity in the ESRU
and Mikhailovsky profiles (which extends farther westward across the
forelandthan ESRU) suggests that this part of the basementis unaffected
by the Uralide deformation (Brownetal.,2006b;Kashubinetal.,2006).
From about km 107 to km 150, the upper crust of the Tagil arc shows an
open synformal structure, whereas the middle crust is characterized by
patchy, generally gently east-dipping reflectivity interpreted to be
associated with the Precambrian rocks of the Kvarkush Anticline.From c.
km 260 to the end of the section, the upper 2 to 3 km are imaged as sub-
horizontal reflectivity interpreted to be related to sediments of the West
Siberian Basin, which cover this area. From km 150 to approximately km
315, the upper ~20 km of the East Uralian Zone crust is characterized by
moderately to steeply west-dipping, discontinuous reflectivity in the
west, to patchy, gently east- and west-dipping, weak reflectivity in the
easternpart of the section. Between c. 20 and 30 km depth, thewestern
part of the East Uralian Zone crust contains a cloud of roughly sub-
horizontal reflectivity that gives way to a less reflective area above the
lowermost crust. Eastward, the middle crust is imaged as patchy, weakly
coherent reflectivity. The lowermost crust, from c. 35 km depth to the
base of the crust at 42 to 45 km, contains a 5 to 10 km thick zoneof strong
sub-horizontal reflectivity. The location of the Troisk Fault in the Middle
Urals is not known from the surface geology because it is buried by the
Mesozoic sediments of the West Siberian Basin. However, the probable
extension of the Troisk Fault to the north can be made from the
aeromagnetic data (seeSection 3.5). The interpreted extension is located
on the ESRU reflection seismic data where it correlates with the onset of
the west-dipping reflectivity of the Trans-Uralian Zone at c. km 315.
From km 315 to the end of the section, the Trans-Uralian Zone crust
below the West Siberian Basin is imaged as irregular, generally
southwest-dipping,moderatelycoherent reflectivity that extends across
the entirecrust to the Moho. This southwest-dipping reflectivity extends
about 50 km beneath the East Uralian Zone.
In the ESRU data, the Moho is generally very well defined as an
abrupt change from highly reflective lower crust to nearly transparent
mantle. The crust thickens from about 45 km in both the west and east
to nearly 60 km beneath the eastern part of the foreland thrust and
fold belt. From west to east, there is a sharp deepening of the Moho at
about km 78, where a c. 10 km thick band of nearly continuous lower
crustal reflectivity appears to underthrust the highly reflective former
Fig. 5. A) P-wave velocity model of the GRANIT data plotted in the reference frame of the ESRU profile. B) P-wave velocity model of the URSEIS wide-angle data plotted in the
reference frame of the reflection profile. C) S-wave velocity model of the URSEIS wide-angle data plotted in the reference frame of the reflection profile.
184 D. Brown et al. / Earth-Science Reviews 89 (20 08) 177–195
Laurussia lower crust and Moho before shallowing eastward to about
45 km at km 140 where it becomes continuous with the lower crustal
reflectivity beneath the East Uralian Zone (Juhlin et al., 2007).
3.1.2. The URSEIS profile
From km 0 to the Main Uralian Fault at c. km 152, the URSEIS profile
images the western foreland thrust and fold belt of the South Urals
(Fig. 4). From km 0 to c. km 40, sub-horizontal, moderately coherent
reflectivity in the upper 5 km images weakly deformed foreland basin
and platform margin rocks (Brown et al., 2006b)(Fig. 4B). Below this, to
approximately 20 km depth, strongly coherent, horizontal reflectivity
images the undeformed Precambrian basement. The base of the
reflectivity here is thought to represent the unconformity between
undeformed Riphean sediments and the Archean crystalline basement,
which is not reflective (Echtler et al., 1996; Diaconescu et al., 1998).
Eastward, the upper and middle crust are imaged as weak, gently east-
dipping reflectivity that, between km 140 and the Main Uralian Fault is
openly concave downward. This reflectivity is associated with the
Precambrian rocks in the Bashkirian Anticline, part of whose deforma-
tion occurred prior to the Uralide orogeny. The base of the reflectivity is
interpreted to be the contact between Precambrian sediments and the
Archean crystalline basement, and to be the location of the basal
detachment (Tryggvason et al., 2001; Brown et al., 2006b)(Fig. 4B). The
lower crust beneath theforeland thrust andfold belt is weakly reflective
to unreflective. From the Main Uralian Fault to c. km 260, the
Magnitogorsk arc is only weakly reflective in the upper crust, with a
relatively transparent middle and lower crust. The contact between the
Magnitogorsk arc and the East Uralian Zone at c. km 258 (the East
Magnitogorsk Fault) is imaged by an abrupt change from nearly
transparent crust in the west to a highly reflective middle crust to the
east. In the East Uralian Zone, from km 258 to c. km 330, the crust is
nearly transparent down to about 8 km, corresponding to the Dzhabyk
granite. Below this, to a depth of about 20 km, the East Uralian Zone is
imaged as openly undulating, strongly to moderately coherent reflec-
tivity. The lower crust is overall transparent, except in the east, where
moderately west-dipping reflectivity appears to extend from the Trans-
Uralian Zone. The entire crust of the Trans-Uralian Zone is imaged as
moderately west-dipping, patchy, strongly coherent reflectivity that
appears to merge with the Moho. The boundary between the East
Uralian and Trans-Uralian zones is the Troisk Fault.
With the exception of the easternmost part of the profile, the Moho
is not imaged in the URSEIS vibroseis data (Fig. 4B). However, the
depth to the Moho and its geometry have been determined from
wide-angle data (see below) (Carbonell et al., 1998) and, in the west,
from the URSEIS explosion-source reflection data (Steer et al., 1998).
Beneath the Trans-Uralian Zone, the Moho is imaged as a sharp change
from moderately reflective lower crust to transparent mantle.
3.2. Velocity structure
In the Middle Urals, the GRANIT profile provides the Vp velocity
structure of the foreland thrust and fold belt, the Tagil arc, and the
western part of the East Uralian Zone (Fig. 5A). We would like to point
out, however, that the low resolution of the dataset may bias the
velocity model (Juhlin et al., 1996). Furthermore, the lower crustal
velocities are primarily constrained bytravel time differences for wide-
angle reflections off the top and bottom of the lower crust, although
short segments of P-wave rays through the lower crust can be coupled
to first arrivals in two shots, and are consistent with the calculated
velocity (Juhlin et al., 1996). Vp in the upper crust ranges from about
5.5 km s
−1
near the surface to around 6.4 km s
−1
at roughly 15 km depth
across the foreland thrust and fold belt, and about 10 km depth in the
Tagil and East Uralian zones. In the middle crust, Vp ranges from 6.4 up
to 6.8 km s
−1
at about 30 km depth across all tectonic units. Lower
crustal velocities reach as high as 7.6 km s
−1
in the lowermost crust
before reaching an upper mantle velocity greater than 8.0 km s
−1
.
Beneath the easternmost margin of the foreland thrust and fold belt,
and extending eastward beneath Tagil and East Uralian zones, the crust
thickens by approximately 10 km, reaching c. 60 km. Velocities in this
thickened zone increase from 7.6 to 7.8 km s
−1
before attaining mantle
velocities of greater than 8.0 km s
−1
. The lower crustal P-wave
velocities along the GRANIT profile are high compared to those in the
South Urals (Carbonell et al., 2000) and to the global average
(Christtensen and Mooney, 1995), but similar to those interpreted
from thickened crust in central Finland (Moisio and Kaikkonen, 2004).
In the South Urals, crustal P-wave (Vp) and S-wave (Vs) velocities are
constrained by the URSEIS wide-angle experiment. Details about the
acquisition, processing and generation of the velocity models are given
in Carbonell et al. (1996, 2000). The upper crust along the URSEIS
transect is characterized by Vp of up to 6.2 km s
−1
to a depth of
approximately 13 km in the foreland thrust and fold belt and
Magnitogorsk arc (Fig. 5B). Eastward, in the East and Trans-Uralian
zones, the upper crustal Vp reaches 6.2 to 6.3 km s
−1
at a depth of
between 15 and 18 km. Below these depths there is a gradual increase in
Vp to values of up to 6.7 km s
−1
. In the westernmost part of the foreland
thrust and fold belt, there is a jump in Vp from 6.5 to 6.7 kms
−1
at about
25 to 30 km depth that disappears eastward. From theMain Uralian Fault
eastward there is a velocity increase from 6.4 km s
−1
at the base of the
upper crust to between 6.6 and 6.8 km s
−1
at the top of the middle crust
and then a gradual increase up to 7.0 km s
−1
above the Moho. Vp in this
area also increases eastward to a maximum in the eastern part of the
Magnitogorsk arc and the western part of the East Uralian Zone, after
which it decreases again. The lowermost crust to the east of the Main
UralianFault is characterized by an eastward-thinning band of Vp of 7.0
to 7.1 km s
−1
. The crust–mantle boundary is marked by an increase in Vp
to N8.0 km s
−1
. Crustal thickness increases from c. 42 km in the west and
east to c. 53 km beneath the Magnitogorsk arc.
The Vs model (Fig. 5C) is an average of the north–south and the
east–west components of the S-wave velocity models (Carbonell et al.,
2000). Upper crustal Vs in the foreland thrust and fold belt reaches 3.5
to 3.6 km s
−1
at a depth of about 13 km, increasing in the Magnitogorsk
arc to 3.9 km s
−1
, and decreasing again to a maximum of 3.6 km s
−1
at
about 15 to 17 km depth in the East and Trans-Uralian zones. Below this
depth there is an increase in Vs to between 3.7 and 3.9 km s
−1
and then
a gradual increase from 3.9 to 4.0 km s
−1
at the Moho. Vs in the middle
and lower crust increases eastward to a maximum in the eastern part of
the Magnitogorsk arc and the western part of the East Uralian Zone,
after which it decreases again. The lowermost crust in the eastern part
of the Magnitogorsk arc and the westernpart of the East Uralian Zone is
marked by a high Vs in which velocities reach 3.9 to 4.0 km s
−1
. The
crust–mantle boundary is characterized by an increase from crustal
velocities of b4.0 km s
−1
to mantle velocities of N4.6 km s
−1
.
3.3. Thermal structure along the URSEIS transect
The South and Middle Urals is characterized by surface heat flow
densityvalues between 30 and40 mW m
−2
, with localhighs between 40
and 50 mW m
−2
, and a strong, short wavelength minimum (10mW m
−2
)
centered along the western margin of the Magnitogorsk arc and the
Main Uralian Fault (Fig. 6A). The heat flow density values in the South
and Middle Urals are low compared to those measured in other
Paleozoic orogens (between 45 and 68 mW m
−2
)(Pollack et al., 1993;
Jaupart and Mareschal, 2003). A thermal model of the surface heat flow
data (Fig. 6B) was presented by Brown et al. (2003) and the reader is
referred there for modelling parameters and assumptions. The short
wavelength low along the Main Uralian Fault is modeled using low heat
production values (k=2.5 to 2.6) below the Magnitogorsk arc. Despite
the low surface heat flow density, the root zone of the Uralides along the
URSEIS transect does not appear to be cold, with Moho temperature
reaching c. 600+ 50 °C at c. 50 km depth (Fig. 6C). The temperature-
depth function derived from the model is low compared to that derived
for average continental crust surface heat flow density (65 mW m
−2
)
185D. Brown et al. / Earth-Science Reviews 89 (2008) 177–195
186 D. Brown et al. / Earth-Science Reviews 89 (20 08) 177–195
Fig. 7. A) Bouguer gravity map of the Uralides. Data is courtesy of GETECH. B) Bouguer gravity map of the South and Middle Urals. C) Density model along the URSEIS transect (after
Kimbell et al., 2002). Numbers indicate density (Mg/m
3
). MUF Main Uralian Fault; ZF —Zuratkul fault. The location is shown in B.
Fig. 6. A) Heat flow map of the South and Middle Urals. Circles indicate the locations of measurements. From Kukkonen et al. (1997). B) Heat production (k) and conductivity (A) model
for the Uralides heat flow density data along the URSEIS transect. From Brown et al. (20 03). C) Geotherm model for the URSEIS transect. D) Average temperature-depth function along
the URSEIS transect (red). Gray lines represent temperature-depth functions for different heat flow regimes.
187D. Brown et al. / Earth-Science Reviews 89 (2008) 177–195
(Pollack et al., 1993)(Fig. 6D). We stress, however, that uncertainties in
the values of conductivity and heat production rate, as well as the lower
boundary conditions, mean that the temperatures calculated at 50 km
depth may be accurate to about +100 °C (Kukkonen et al., 1999).
3.4. Density structure along the URSEIS transect
The Bouguer anomaly in the South and Middle Urals is character-
ized by a low between −60 and −45 mGal across the foreland thrust
and fold belt that abruptly increases to between about 0 and −40 mGal
across the Magnitogorsk arc (Fig. 7A and B). The East Uralian Zone is
characterized by a low of −70 to −40 mGal, increasing again to
between −30 and −10 mGal across the East Uralian Zone. Along the
URSEIS transect, where a detailed gravity data set allows density
modelling to be carried out (Kimbell et al., 2002), the upper and
middle crust of the foreland thrust and fold belt have densities of
about 2.8 and 2.9 Mg/m
3
with small local variations to account for
short wavelength features (Fig. 7C). The lower crust is modelled with
higher densities of 2.98 and 3.02 Mg/m
3
. To the east of the Main
Uralian Fault, much of the upper crust can be modelled with densities
of between 2.71 and 2.8 Mg/m
3
, although densities are somewhat
higher in the Magnitogorsk arc. The middle crust (and part of the
upper crust in the Magnitogorsk arc) is modelled with densities of
between 2.92 and 2.95 Mg/m
3
. The lower crust is modelled with
densities of between 2.98 and 3.07 Mg/m
3
. The upper mantle, at the
depth shown, is modelled with a density of 3.34 Mg/m
3
.
3.5. Aeromagnetic anomaly in the South and Middle Urals
The true extent of the Uralide Orogen, especially in the poorly
exposed eastern region, is best seen in the regional aeromagnetic data
(Fig. 8A). Therefore, these data help to constrain the extent of several
important structures mapped at the surface and seen in the reflection
seismic data, but whose along-strike continuity is not clear because of
the poor exposure. In the South and Middle Urals the foreland thrust
and fold belt is characterized by long wavelength anomalies with
marked highs and lows that can be used to map the depth to the
magnetic crystalline basement (Fig. 8B) (Brown et al., 1999; Ayala
et al., 2000; Kimbell et al., 2002). The Main Uralian Fault is clearly
marked as an abrupt change from the long wavelength features of the
foreland thrust and fold belt to the roughly north-striking, high
amplitude, short wavelength features of the Magnitogorsk–Tagil Zone.
Kimbell et al. (2002) associate these high amplitude anomalies with
intrusions within the volcanic arcs. The East Magnitogorsk–Serov-
Mauk fault system is not clearly seen on the aeromagnetic data. The
East Uralian and Trans-Uralian zones are characterized by northeast-
Fig. 8. A) Aeromagnetic map of the Uralides. B) Detailed aeromagnetic map of the South and Middle Urals showing the location of the main faults discussed in the text.
188 D. Brown et al. / Earth-Science Reviews 89 (20 08) 177–195
trending, high amplitude, short wavelength anomalies. The boundary
between the two, the Troisk Fault, appears as a high amplitude
anomaly that extends from the South to the Middle Urals.
3.6. Petrophysical modelling of crustal composition
Brown et al. (20 03) and Brown (2007) presented a composition
model for the Uralide crust along the URSEIS transect by combining
the Vp, Vs (and their derivative Poisson's ratio), the potential field
data (gravity and magnetics), the reflection seismic data, heat flow,
and surface geology. The model was constructed using published
laboratory measurements of Vp, Vs, Poisson's ratio and density for
a variety of crustal rock types (Christtensen and Mooney, 1995).
These laboratory data were corrected for depth (pressure) and the
Uralides temperature-depth function using the heat flow data
(Section 3.3). In the model, the low velocities in the upper 5 km of
the western half of the profile are likely the result of cracks and
fluid, and therefore cannot be considered reliable for estimating
composition.
The average composition of the upper crust in the foreland thrust
and fold belt is best characterized by phyllite and perhaps slate and
mica quartz schist (Fig. 9). Granite and biotite gneiss both fall within
the acceptable values, but since neither fit the known geology of the
foreland thrust and fold belt they are discarded. The velocity and
density data for the foreland thrust and fold belt middle crust fall
outside the values for most of the measured rock types, although the
composition may be best characterized by mica quartz schist, felsic
granulite and paragranulite. The foreland thrust and fold belt lower
crust is likely composed of amphibolite and mafic granulite, which is
in keeping with the lithology of the Archean crystalline basement in
outcrop.
The composition of the upper part of the middle crust of the
Magnitogorsk arc is not well constrained by the velocity and density
data, but on the basis of surface geology is interpreted to consist of
zeolite to prehnite–pumpellyite facies basalt and its intrusive
equivalents (diabase, diorite, and tonalite) (Fig. 9). The lower part of
the middle crust fits the parameters for greenschist facies basalt,
amphibolite, and mafic granulite quite well. The Magnitogorsk arc
lower crust appears to be composed of gabbro-norite, mafic garnet
granulite or hornblendite.
The upper and middle crusts of the East Uralian and Trans-
Uralian zones are best characterized by low metamorphic grade
sediments, basalt, granite, and/or felsic gneiss (Fig. 9). The middle
crust in the East Uralian Zone, and extending into the lower crust in
the Trans-Uralian Zone, is best characterized by greenschist facies
basalt, amphibolite, and mafic granulite (and to a lesser extent
anorthosite and anorthositic granulite). The lower crust in the East
Uralian Zone, and the lowermost crust in the Trans-Uralian Zone are
best characterized by gabbro-norite, mafic garnet granulite and/or
hornblendite.
4. Low-temperature exhumation history
The low-temperature exhumation history of the South and Middle
Urals has been studied using zircon and apatite fission-track dating
(Seward et al., 1997, 2002; Glasmacher et al., 2002). Here we present
only the apatite fission-track (AFT) data. The foreland thrust and fold
belt, which directly correlates with the topography of the Ural
Mountains, yields average AFT ages of 245 +63 Ma (pooled ages
from the South Urals) (Glasmacher et al., 2002) and 223 +37 Ma
(central ages from the South and Middle Urals) (Seward et al., 2002)
(Fig. 10). In the Bashkirian Anticline there is a general trend with
younger ages in the middle of the anticline and older ages toward the
flanks. The Magnitogorsk–Tagil Zone yields central ages of 261+ 42 Ma
(Magnitogorsk) and 222+ 22 Ma (Tagil), and the East Uralian Zone
yields central ages of 222+32 Ma (Seward et al., 2002). These data
indicate that, with the exception of the Magnitogorsk arc, the South
and Middle Urals, including the topographically high foreland thrust
and fold belt, the majority of the analysed samples passed through the
AFT partial annealing zone in the Triassic to Early Jurassic. In the
Magnitogorsk arc, one sample, which yields an age of 349 Ma
represents a Lower Carboniferous dacite that has not been reset and
has a depositional age.
From the Uralides surface heat flow density modelling (see Section
3.4), the current average geothermal gradient in the upper crust is
calculated to be 16 °C/km (Fig. 10C). While it is possible that the
geothermal gradient in the Uralides has changed since the Triassic, we
suggest that the same heat producing lithologies were present in
much of the crust and it is, therefore, reasonable to assume the current
geothermal gradient when calculating the rate of exhumation since
the Triassic. Here, we take the AFT partial annealing zone to be
between 110 and 60 °C (Green et al., 1989; Corrigan, 1993),
corresponding to between 6 and 8 km depth and between 3 and
4 km depth, respectively (Fig. 10C). The topographic profile along the
URSEIS transect was taken from the digital elevation model (Fig. 10B).
Exhumation rates along the transect vary only slightly, from between
0.03 and 0.05 mm/yr, with the highest values corresponding the zone
of highest topography.
Fig. 9. Crustal composition model along the URSEIS transect determined from physical properties data. From Brown et al. (2003).
189D. Brown et al. / Earth-Science Reviews 89 (2008) 177–195
Fig. 10. A) Digital elevation model of the Ural mountains. B) Detailed digital elevation model of the South and Middle Urals showing apatite fission-track ages (in Ma). Red lines
indicate the main faults of the Uralides. Black lines indicate contours (in meters) of the base of the Upper Cretaceous (after Puchkov and Danukalova, 2004). C) Topographic profile and
depth section (note the change in scales) along the URSEIS transect (location shown in B) showing the 110° and 60° geotherms calculated from the Urals heat flow data. Inset shows
the temperature-depth function for the upper 10 km of crust. The calculated exhumation rate is given for the samples indicated on the topographic profile.
190 D. Brown et al. / Earth-Science Reviews 89 (2008) 177–195
5. Discussion
5.1. Structural architecture
The structural architecture of the Middle and South Urals crust as
imaged by the ESRU and URSEIS reflection seismic profiles is clearly
bivergent, with reflectivity in both the western and eastern flanks of
the orogen dipping toward its interior (Figs. 3 and 4). A bivergent
structural architecture has also been recognised in reflection seismic
data across other orogens formed by continent–continent collision,
and in these cases it is generally taken to represent tectonic processes
that took place during late- to post-collision (e.g., Hall et al., 1998;
Schmid and Kissling, 2000; Lüschen et al., 2006). However, in the case
of the Uralides we feel that many of the features may in fact be pre-
collisional, and some even post-collisional (Fig. 11). Therefore, several
key questions need to be answered before interpreting the meaning of
the bivergent reflection geometry. These include; 1) what are the
features causing the reflectivity, 2) what processes were involved in
their formation and, 3) when and where did these processes occur?
Along the western flank of the foreland thrust and fold belt,
deformation took place exclusively in the upper crust, above a sub-
horizontal to gently east-dipping basal detachment (Brown et al.,
2006b)(Fig. 11). Deformation above the basal detachment affects the
pre-orogenic Neoproterozoic III to syn-orogenic Permian to Early
Triassic sediments and must, therefore, have taken place during the
Late Paleozoic continent–continent collision that formed the Uralides.
The sub-horizontal middle crustal reflectivity appears to be related to
undeformed Precambrian sediments (Echtler et al., 1996; Diaconescu
et al., 1998), providing strong evidence that this area of the crust was
not affected by either the Uralide or the Neoproterozoic III deforma-
tion events. Eastward, the middle and lower crustal reflectivity is
truncated, suggesting that the basal detachment dips steeply down-
ward, involving almost the entire crust in the deformation. Although it
seems that the ramp down into the middle crust extends eastward, it
is not clear from any of the data whether or not there is a basal
detachment beneath either the Bashkirian or Kvarkush anticlines.
Reflectivity in this area images the Precambrian basement rocks that
were variably deformed during the Neoproterozoic III tectonothermal
event (Glasmacher et al., 2004), and much of the reflectivity is related
to that deformation event (Fig. 11A and B). However, geological
mapping has shown that a number of the faults that are related to the
Neoproterozoic III event were reactivated as thrusts during the Late
Paleozoic (Brown et al., 1997, 1999; Perez-Estaun et al., 1997a,b), so
reflectivity may to some degree be related to the Uralide deformation
event. The coincidence of the juxtaposition of the undeformed
basement across the ramp area with that deformed during the
Neoproterozoic III suggests that the ramp likely represents the
western limit of this deformation (Ayala et al., 2000). This implies
that during the continent–continent collision almost the entire crustal
column of the Laurussia margin underwent failure and reactivation in
areas where it had a strong pre-existing structural fabric. Where it did
not, only the uppermost crust deformed above a well-defined basal
detachment.
Both the Magnitogorsk and Tagil arcs had accreted to the Laurussia
continental margin by the Early Carboniferous, and so formed an
integral part of it by the onset of continent–continent collision. The
presence of these accreted volcanic arcs along the leading edge of the
Laurussia margin indicates that a wide area of extended continental
and transitional crust, such as is found in modern passive margins
(c. 150–300 km or more) (e.g., Haworth et al.,1994; Sayers et al., 2001;
Funck et al., 2004), did not exist at this time. Instead, it had a thickened
leading edge occupied by the volcanic arcs. This may account for the
differences in structural style and the amount of shortening between
the Uralide foreland thrust and fold belt and that of other orogens such
as the Rhenohercynian of central Europe (e.g., Oncken et al., 1999), or
the Varsicides of Spain (e.g., Perez-Estaun et al., 1988, 1994), where
imbrication of a thinned, extended continental margin resulted in
large amounts of shortening developed above a basal detachment. In
Fig. 11. Schematic interpretations of the ages and processes involved in the formation of reflectors imaged in A) the ESRU and, B) URSEIS transects.
191D. Brown et al. / Earth-Science Reviews 89 (2008) 177–195
the Uralides, the volcanic arcs behaved as rigid bodies that took up
very little strain by internal deformation (more in the Tagil arc than in
Magnitogorsk (Ayarza et al., 2000a)) (Brown et al., 2001). Instead,
stresses appear to have been transferred into the Precambrian
basement where pre-existing structures were reactivated, causing
uplift, but only minor shortening.
Along the eastern side of the orogen, in the Trans-Uralian Zone, the
crustal structure is interpreted solely from the geometry of the
reflectivity. In both the ESRU and URSEIS data, the entire crustappears
to contain moderately west-dipping, often patchy reflectivity, with a
number of thin, high amplitude reflections occurring throughout the
crust and which, in the lower crust, merge with the Moho (Figs. 3 and
4). Dipping crustal reflectivity that merges with the Moho has also
been recognised elsewhere in reflection seismic profiles across
collisional orogens, where it has been interpreted to be related to
crustal-scale thrusting that detaches at the Moho (e.g., Cook and
Varsek, 1994; Cook, 2002). A similar overall reflectivity character and
geometry to that of the Trans-Uralian Zone has been imaged in the
Southern Andes by the ANCORP seismic profile (ANCORP Working
Group, 2003). If we accept that during the Late Devonian to Late
Carboniferous, prior to continent–continent collision, the margin of
Kazakhstania involved in the collision with Laurussia was the site of a
sub-continental subduction zone (as in the Andes) and the resultant
formation of a continental arc (Bea et al., 2002; Herrington et al.,
2005), then it is possible that the reflectivity in the Trans-Uralian Zone
is related to this process (Fig. 11A and B). However, we stress that it is
difficult to place any time constraints on the development of the
reflectivity in the Trans-Uralian Zone since it cannot be directly related
to any outcropping geological features. Therefore it could, at least in
part, be related to the continent–continent collision.
In general, the upper and middle crustal reflectivity of the East
Uralian Zone can be characterized as patchy and locally vertically
truncated (especially apparent in the ESRUdata) against areas of weak
reflectivity that coincide with the location of strike-slip faults. In both
the ESRU and URSEIS data sets, the western margin of the East Uralian
Zone reflectivity is sharply truncated in the upper and middle crust
against the East Magnitogorsk–Serov-Mauk fault system. The seismic
reflection character of the East Uralian Zone crust is very different
from that to the west and east of it. This suggests strong partitioning of
the deformation across the East Magnitogorsk–Serov-Mauk fault
system, something that is also indicated by the significant increase
in metamorphic grade across it, and by the different geological
processes that were active in each zone at roughly the same time
(latest Carboniferous to Early Triassic). The East Uralian Zone was
affected by widespread and extensive strike-slip faulting that lasted
until at least the Early Triassic (Hetzel and Glodny, 2002), syn-
collisional melting together with ascent and emplacement of
granitoids during the Late Carboniferous and Permian (Bea et al.,
2002), and medium to high grade metamorphism and the subsequent
exhumation of these rocks until at least the latest Carboniferous
(Echtler et al., 1997; Eide et al., 1997). We therefore interpret the
reflectivity in the East Uralian Zone upper and middle crust to be due
to the Late Paleozoic strike-slip juxtaposition of the different
lithotectonic units found in this area (Fig. 11A and B). However, the
geometrical relationships between the upper and middle crustal
reflectivity and the band of lower crustal reflectivity imaged in the
ESRU data suggest that different processes were active in the lower
crust. Recently, Brown and Juhlin (2006) used a number of lines of
evidence to interpret the band of lower crustal reflectivity to be
associated with a flow channel in which material moved laterally
along the internal part of the orogen late in its tectonothermal
evolution (Fig. 11A). In this scenario, the lower crust was only weakly
coupled to the overlying middle crust. In both the ESRU and URSEIS
data sets, the Trans-Uralian Zone reflectivity extends several tens of
kilometers westward beneath the East Uralian Zone. We suggest that
during the approximately 50 My that continent–continent collision
was taking place in the Uralides, oblique convergence resulted in
Kazakhstania being underthrust beneath the East Uralian Zone.
Finally, the ESRU data indicate that a band of lower crustal
reflectivity with a well-defined Moho projects from the East Uralian
Zone westward beneath the foreland thrust and fold belt of the Middle
Urals (Fig. 3). This reflection package coincides with a deepening of the
Moho modeled with the GRANIT data. On the basis of these data,
Juhlin et al. (2007) suggested that East Uralian Zone crust has been
underthrust westward beneath the Tagil arc and Laurussia continental
crust and mantle, imbricating part of the upper mantle and the entire
crust (Fig. 11A). They further suggest that this underthrusting and
Moho imbrication is post-Uralide, possibly Jurassic, although it is
difficult to put an absolute age on it. Weak seismicity in the area
possibly indicates that it is currently active.
5.2. Crustal composition along the URSEIS transect
Further insight into the processes that went into the tectonic
evolution of the Uralides, especially in the middle and lower crust, is
provided by modelling the crustal composition. For example, it has
been suggested that eclogitised Laurussia margin lower crust makes up
the current root zone imaged in the Uralides, and that the presence of
this dense material has played a key role in the evolution of the
orogenic and its subsequent stabilisation to the present (Diaconescu
and Knapp, 2002). However, the presence of eclogite is not supported
by the petrophysical model presented above, or if eclogite is present, it
is in such small amounts that it is below the resolution of the data set
used in the modelling (Scarrow et al., 2002b; Brown et al., 2003;
Brown, 2007). The absence of eclogite in the Uralide lower crust may be
taken as evidence for intracrustal differentiation in which the eclogite
has delaminated and sunk into the mantle (e.g., Arndt and Goldstein,
1989; Austrheim, 1991; Kay and Mahlburg-Kay, 1991). However, there
is very little evidence, such as surface uplift, metamorphism or the
petrological signature of the granitoids to suggest that crustal thinning
occurred on a large enough scale to have affected the bulk composition
of the Uralide crust in this way. This point is further verified by the fact
that the physical properties indicate that the composition of the
Magnitogorsk Zone is basaltic or some derivative of it (e.g., diabase or
mafic granulite), in keeping with the basaltic source determined for its
volcanic suites on the basis of its geochemisty (Spadea et al., 2002).
This is in conflict with the andesitic bulk composition model
commonly proposed for the continental crust (Rudnick, 1995), and is
problematic with respect to the intracrustal differentiation model
in which the more mafic lower crust delaminates.
As outlined above (Section 2.4), geochemical and isotopic data
from the late-orogenic granitoids in the East Uralian Zone indicate that
they evolved from island arc crust (Gerdes et al., 2002) and/or the
remelting of earlier subduction-related granitoids (Bea et al., 2002)in
a thickened crust. The melting of arc crust (whose composition is
basaltic) to generate granitoids would likely result in an amphibolite
(+garnet), mafic (+garnet) granulite to mafic eclogite restite being
produced (Rapp and Watson, 1995). The physical properties of the East
and Trans-Uralian zone crust suggest a middle and lower crust made
up of amphibolite and/or mafic granulite, with garnet granulite,
gabbro-norite, or hornblendite at its base, consistent with this
petrological rationale. This would suggest that crustal differentiation
in the interior of the orogen occurred by melt extraction and not by
delamination.
5.3. Low-temperature exhumation and uplift of the Ural Mountains
Care must be taken when interpreting AFT values since the cooling
histories of the apatite grains may be more complex than a simple
one-stage exhumation event. Nevertheless, it appears that since the
Late Triassic the Uralides have undergone only slow exhumation with
little or no other thermal overprint since then (Seward et al., 1997,
192 D. Brown et al. / Earth-Science Reviews 89 (2008) 177–195
2002; Glasmacher et al., 2002). Exhumation of the apatite grains
through the partial annealing zone seems to be in agreement with the
widespread evidence that parts of the Uralides were peneplaned by
the Late Jurassic (Borisevich, 1992; Bachmanov et al., 2001). However,
the AFT data seem to point to long-term stability of the Ural Mountain
topography, with only slow erosion having taken place since its
Paleozoic formation.
This leads us to one of the tantalising questions still surrounding
the Uralides; when did the topographic feature that we call the Ural
Mountains form? The geomorphology of the Ural Mountains is
generally mature, being dominated by a system of smooth, north–
south trending ridges that, in the South Urals, locally reach up to
1600 m. The topography of the Ural Mountains is almost exclusively
associated with the foreland thrust and fold belt and there is a strong
correlation of topography with Uralide-age thrusts that lie in the
valleys. Yet, some features, such as deeply incised river valleys and
elevated river terraces hint at recent uplift (Borisevich, 1992;
Bachmanov et al., 2001). A recent study carried out by Puchkov and
Danukalova (2004) shows that the base of the Upper Cretaceous
sediments in the South Urals is currently at progressively higher
altitudes towards the mountains (Fig. 10B), further suggesting a more
recent development of the topography than the Paleozoic. Also,
topographic levelling carried out over a number of years in the South
Urals indicates uplift rates of up to 6 mm/yr (Bachmanov et al., 2001).
Finally, Juhlin et al. (2007) suggested that the apparent Moho
imbrication imaged in the ESRU data can, in fact, be a post-Uralide
feature. If this is so, then it could account for the recent uplift of the
Ural Mountains. However, if the formation of the Ural Mountain
topography is more recent than the Mesozoic it appears to still not
have acquired sufficient denudation to be recorded by AFT data.
6. Conclusions
On the basis of the data presented here, we suggest that the changes
in the crustal-scale structural architecture as imaged by the ESRU and
URSEIS reflection seismic data across the Uralides indicate that there
was partitioning of tectonothermal conditions and deformation from
zone to zone across major fault systems. In the western thrust belt
deformation appears tohave been strongly controlled by the presence of
a pre-existing fabric. In the previously undeformed foreland only upper
crustal deformation took place above a basal detachment. At the same
time, along the margin of Kazakhstania, the reflection seismic data
suggest a different deformation style, with the whole crust being
imbricated along faults that appear to merge with the Moho. With
advanced continent–continent collision the interior part of the orogen
(the East Uralian Zone) underwent extensive strike-slip faulting,
metamorphism, melt generation and emplacement, compositional
differentiation, and exhumation of middle and lower crust rocks. In
the Middle Urals, the ESRU data indicate that there was partitioning of
the deformation between the lower and middle crust in East Uralian
Zone, and the possible development of a lower crustal flow channel.
Some of the features to whichreflectivity in the western foreland thrust
and fold belt and in the Trans-Uralian Zone is related formed prior to
being juxtaposed during continent–continent collision (Neoproterozoic
III and Devonian, and Early to Late Paleozoic, respectively), by different
tectonic processes, and on distinct tectonic plates. Therefore, the
bivergent architecture of the Uralides is not entirely due to tectonic
processes that took place during continent–continent collision. The
post-Paleozoic evolution of the Ural Mountains appears to have been
dominated by slow exhumation. Despite there being some evidence for
more recenttopographicuplift, it has so far provendifficult to quantify it.
Acknowledgements
This work was in part funded by MCyT projects BTE2001-5002-E
and BTE2002-04618-C02-02, DGCYT grant PB97-1141 and by the EEC
research network URO (ERBFMRXCT960009). The Swedish Research
Council (VR) is gratefully acknowledged for early funding of seismic
studies in the Urals. GETECH is thanked for the gravity data in Fig. 7.R.
Herrington and R. Van der Voo are thanked for their reviews.
References
Alvarez-Marron, J., 2002. Tectonic processes during collisional orogenesis from
comparison of the Southern Urals with the Central Variscides. In: Brown, D., Juhlin,
C., Puchkov, V. (Eds.), Mountain Building in the Uralides: Pangea to Present.
Geophysical Monograph, vol. 132. American Geophysical Union, pp. 83–100.
ANCORP Working Group, 2003. Seismic imaging of a convergent continental margin and
plateau in the central Andes (Andean Continental Research Project 1996 (ANCORP'96)).
Journal of Geophysical Research 108, 3–1–3-25. doi:10.1029/2002JB001771.
Antsigin, N.I., Zoloev, K.K., Kluzina, M.L., Nasedkina, V.A., Popov, B.A., Chuvashov, B.I.,
Shurigina, M.V., Sherbakov, O.A., Iackusev, V.M., 1994. Descriptions of the
Stratigraphic Schemes of the Urals. Urals Stratigraphic Commitee, Ekaterinburg.
Arndt, N.T., Goldstein, S.L., 1989. An open boundary between lower continental crust
and mantle: its role in crust formation and crustal recycling. Tectonophysics 161,
201–212.
Austrheim, H., 1991. Eclogite formation and dynamics of crustal roots under continental
collision zones. Terra Nova 3, 492–499.
Ayala, C., Kimbell, G.S., Brown, D., Ayarza, P., Menshikov, Y.P., 2000. Magnetic evidence
for the geometry and evolution of the eastern margin of the East European Craton
in the southern Urals. Tectonophysics 320, 31–44.
Ayarza, P., Brown, D., Alvarez-Marron, J., Juhlin, C., 20 00a. Contrasting tectonic history of
the arc–continent suture in the Southern and Middle Urals: implications for the
evolution of the orogen. Journal of the Geological Society 157, 1065–1076.
Ayarza, P., Juhlin, C., Brown, D., Beckholmen, M., Kimbell, G., Pechning, R., Pevzner, L.,
Pevzner, R., Ayala, C., Bliznetsov, M., Glushkov, A., Rybalka, A., 2000b. Integrated
geological and geophysical studies in the SG4 borehole area (Tagil volcanic arc —
Middle Urals): location of seismic reflectors and source of the reflectivity. Journal of
Geophysical Research 105, 21,333–21,352.
Bachmanov, D.M., Govorova,N.N., Skobelev, S.F., Trifonov, V.G., 2001.Neotectonics of the
Urals (problems and solutions). Geotectonics 35, 389–402.
Bashta, E.G., Kushkov, V.N., Shatornaya, L.N., Glushkov, A.N., Sergeev, V.A., 1990. First
results from the drilling and investigations of the Urals superdeep borehole (SG-4).
Mineral Geology SSSR 19–30.
Bea, F., Fershtater, G., Montero, P., Smirnov, V., Zin'kova, E., 1997. Generation and
evolution of subduction-related batholiths from the central Urals: constraints on
the P–T history of the Uralian orogen. Tectonophysics 276, 103–116.
Bea, F., Fershtater, G., Montero, P., 2002. Granitoids of the Urals: implications for the
evolution of the orogen. In: Brown, D., Juhlin, C., Puchkov, V. (Eds.), Mountain
Building in the Uralides: Pangea to Present. Geophysical Monograph, vol. 132.
American Geophysical Union, pp. 211–232.
Bea, F., Fershtater, G.B., Montero, P., Smirnov, V.N., Molina, J.F., 2005. Deformation-
driven differentiation of granitic magma: the Stepninsk pluton of the Uralides,
Russia. Lithos 81, 209–231.
Beckholmen, M., Glodny, J., 2004. Timanian blueschist-facies metamorphism in the
Kvarkush metamorphic basement, Northern Urals, Russia. In: Gee, D.G., Pease, V.
(Eds.), The Neoproterozoic Timanide Orogen of Eastern Baltica. Memoirs, vol. 30.
Geological Society, London, pp. 125–134.
Berzin, R., Oncken, O., Knapp, J.H., Perez-Estaun, A., Hismatulin, T., Yunusov, N., Lipilin,
A., 1996. Orogenic evolution of the Ural Mountains: results from an integrated
seismic experiment. Science 274, 220–221.
Blundell, D.J., 1998. The new European Research Programme on Ore Deposits—GEODE.
SGA Newsletter No. 6, November 1998, pp. 2–5.
Borisevich, D.V., 1992. Neotectonics of the Urals. Geotectonics 26, 41–47.
Bosch, D., Krasnobayev, A.A., Efimov, A., Savelieva, G., Boudier, F., 1997. Early Silurian
ages for the gabbroic section of the mafic–ultramafic zone from the Urals. In:
Oxburgh, E.R. (Ed.), EUG 9. Terra Nova. Cambridge Publications, Strasbourg, p. 121.
Brown, D., 2007. Modal mineralogy and chemical composition of the Uralide lower crust
determined from physical properties data. Tectonophysics 433, 39–51.
Brown,D., Spadea, P.,1999. Processesof forearc and accretionary complexformationduring
arc–continent collision in the Southern Ural Mountains. Geology 27, 649–652.
Brown, D., Juhlin, C., 2006. A possible lower crustal flow channel in the Middle Urals
based on reflection seismic data. Terra Nova 18,1–8.
Brown, D., Puchkov, V., Alvarez-Marron, J., Perez-Estaun, A., 1996. The structural
architecture of the footwall to the Main Uralian Fault, southern Urals. Earth-Science
Reviews 40, 125–147.
Brown, D., Alvarez-Marron, J., Perez-Estaun, A., Gorozhanina, Y., Baryshev, V., Puchkov,
V., 1997. Geometric and kinematic evolution of the foreland thrust and fold belt in
the southern Urals. Tectonics 16, 551–562.
Brown, D., Juhlin, C., Alvarez-Marron, J., Perez-Estaun, A., Oslianski, A., 1998. Crustal-
scale structure and evolution of an arc–continent collision zone in the southern
Urals, Russia. Tectonics 17, 158–171.
Brown, D., Alvarez-Marron, J., Perez-Estaun, A., Puchkov, V., Ayala, C., 1999. Basement
influence on foreland thrust and fold belt development: an example from the
southern Urals. Tectonophysics 308, 459–472.
Brown,D.,Alvarez-Marron,J.,Perez-Estaun,A.,Puchkov,V.,Ayarza,P.,Gorozhanina,Y.,2001.
Structure and evolution of the Magnitogorsk forearc basin: identifying upper crustal
processes during arc–continent collision in the Southern Urals. Tectonics 20, 364–375.
Brown, D., Juhlin, C., Puchkov, V.N., 2002a. Mountain Building in the Uralides: Pangeato
Present. Geophysical Monograph, vol. 132. American Geophysical Union.
193D. Brown et al. / Earth-Science Reviews 89 (2008) 177–195
Brown, D., Juhlin, C., Tryggvason, A., Steer, D., Ayarza, P., Beckholmen, M., Rybalka, A.,
Bliznetsov, M., 2002b. The crustal architecture of the Southern and Middle Urals
from the URSEIS, ESRU, and Alapaev reflection seismic surveys. In: Brown, D., Juhlin,
C., Puchkov, V. (Eds.), Mountain Building in the Uralides: Pangea to Present.
Geophysical Monograph, vol. 132. Ameri can Geophysical Union, pp. 33–48.
Brown, D., Carbonell, R., Kukkonen, I., Ayala, C., Golovonova, I., 2003. Composition of the
Uralide crust from seismic velocity (Vp, Vs), heat flow, gravity, and magnetic data.
Earth and Planetary Science Letters 210, 333–349.
Brown, D., Spadea, P., Puchkov, V., Alvarez-Marron, J., Herrington, R., Willner, A.P.,
Hetzel, R., Gorozhanina, Y., 2006a. Arc–continent collision in the Southern Urals.
Earth-Science Reviews, 79, 261–287.
Brown, D., Juhlin, C., Tryggvason, A., Friberg, M., Rybalka, A., Puchkov, V., Petrov, G.,
2006b. Structural architecture of the Southern and Middle Urals foreland from
reflection seismic profiles. Tectonics 25. doi:10.1029/2005TC001834.
Carbonell, R., Perez-Estaún, A., Gallart, J., Diaz, J., Kashubin, S., Mechie, J., Stadtlander, R.,
Schulze, A., Knapp, J.H., Morozov, A., 1996. A crustal root beneath the Urals: wide-
angle seismic evidence. Science 274, 222–224.
Carbonell, R., Lecerf, D., Itzin, M., Gallart, J., Brown, D., 1998. Mapping the Moho beneath
the Southern Urals. Geophysical Research Letters 25, 4229–4233.
Carbonell, R., Gallart, J., Perez-Estaun, A., Diaz, J., Kashubin, S., Mechie, J., Wenzel, F.,
Knapp, J., 2000. Seismic wide-angle constraints on the crust of the southern Urals.
Journal of Geophysical Research 105, 13,755–13,777.
Christtensen, N.I., Mooney, W.D.,1995. Seismic velocity structure and composition of the
continental crust: A global view. Journal of Geophysical Research 100, 9761–9788.
Chuvashov, B.I., Diupina, G.V., 1973. The Upper Paleozoic Terrigenous Sediments of the
Western Slope of the Middle Urals. Nauka. 208 p.
Chuvashov,B.I., Chermynkh, V.A., Chernykh, V.V., Kipin, V.J., Molin, V.A., Ozhgibesov, V.P.,
Sofronitsky, P.A., 1993. The Permian system: guides to geological excursions in the
Uralian type localities. Part 2 —Southern Urals. Occasional Publications ESRI, New
Series, no. 10.
Cook, F.A., 2002. Fine structure of the continental Moho. Geological Society of America
Bulletin 114, 64–79.
Cook, F.A., Varsek, J.L., 1994. Orogen-scale décollements. Reviews of Geophysics 32,
37–60.
Corrigan, J.D.,1993. Apatite fission-track analysis of Oligocene strata in South Texas, U.S.A.
Testing annealing models. Chemical Geology 104, 227–249.
Diaconescu, C.C., Knapp, J.H., 2002. Role of a phase-change Moho in stabilization and
preservation of the Southern Uralide Orogen, Russia. In: Brown, D., Juhlin, C.,
Puchkov, V. (Eds.), Mountain Building in the Uralides: Pangea to Present.
Geophysical Monograph, vol. 132. Ameri can Geophysical Union, pp. 67–82.
Diaconescu, C.C., Knapp, J.H., Brown, L.D., Steer, D.N., Stiller, M., 1998.Precambrian Moho
offset and tectonic stability of the East European platform from the URSEIS deep
seismic profile. Geology 26, 211–214.
Echtler, H.P., Stiller, M., Steinhoff, F., Krawczyk, C.M., Suleimanov, A., Spiridonov, V.,
Knapp, J.H., Menshikov, Y., Alvarez-Marron, J., Yunusov, N., 1996. Preserved
collisional crustal architecture of the Southern Urals-Vibroseis CMP-profiling.
Science 274, 224–226.
Echtler, H.P., Ivanov, K.S., Ronkin, Y.L., Karsten, L.A., Hetzel, R., Noskov, A.G., 1997. The
tectono-metamorphic evolution of gneiss complexes in the Middle Urals, Russia: a
reappraisal. Tectonophysics 276, 229–251.
Eide, E.A., Echtler, H.P.,Hetzel, R., Ivanov, K.,1997. Cooling agediachroneity and Paleozoic
orogenic processes in the Middle and Southern Urals. Abstract Supplement 1, Terra
Nova 9, 119.
Fershtater, G.B., Montero, P., Borodina, N.S., Pushkarev, E.V., Smirnov, V., Zin'kova, E.,
Bea, F., 1997. Uralian magmatism: an overview. Tectonophysics 276, 87–102.
Friberg, M., Larionov, A., Petrov, G.A., Gee, D.G., 2000. Paleozoic amphibolite–granulite
facies magmatic complexes in the hinterland of the Uralide Orogen. International
Journal of Earth Science 89, 21–39.
Friberg, M., Juhlin, C., Beckholmen, M., Petrov, G.A., Green, A.G., 2002. Paleozoic tectonic
evolution of the Middle Urals in light of the ESRU seismic experiments. Journal of
the Geological Society 159, 295–306.
Funck, T., Jackson, H.R., Louden, K.E., Dehler, S.A., Wu, Y., 2004. Crustal structure of the
northern Nova Scotia rifted continental margin (eastern Canada). Journal of
Geophysical Research 109. doi:10.1029/2004JB003008.
Gee, D., Zeyen, H.J., 1996. EUROPROBE 1996 –Lithosphere Dynamics: Origin and
Evolution of Continents. EUROPROBE Secretatiate, Uppsala University. 138 pp.
Gerdes, A., Montero, P., Bea, F., Fershtater, G., Borodina, N., Osipova, T., Shardakova, G.,
2002. Peraluminous granites frequently with mantle-like isotope compositions: the
continental-type Murzinka and Dzhabyk batholiths of the eastern Urals. Interna-
tional Journal of Earth Science 91, 1–17.
Giese, U., Glasmacher, U., Kozlov, V.I., Matenaar, I., Puchkov, V.N., Stroink, L., Bauer, W.,
Ladage, S., Walter, R., 1999. Structural framework of the Bashkirian anticlinorium,
SW Urals. Geologische Rundschau 87, 526–544.
Glasmacher, U.A., Reynolds, P., Alekseev, A., Puchkov, V.N., Taylor, K., Gorozhanin, V.,
Walter, R., 1999.
40
Ar/
39
Ar thermochronology west of the Main Uralian Fault,
Southern Urals, Russia. Geologische Rundschau 87, 515–525.
Glasmacher, U.A., Bauer, W., Giese, U., Reynolds, P., Kober, B., Puchkov, V.N., Stroink, L.,
Alekseev, A., Willner, A., 2001. The metamorphic complex of Beloretzk, SW Urals,
Russia —a terrane with a polyphase Meso- to Neoproterozoic thermo-dynamic
evolution. Precambrian Research 110, 185–213.
Glasmacher, U.A., Wagner, G.A., Puchkov, V.N., 2002. Thermotectonic evolution of the
western fold-and-thrust belt, southern Urals, Russia, as revealed by apatite fission-
track data. Tectonophysics 354, 25–48.
Glasmacher, U.A., Bauer, W., Clauer, N., Puchkov, V.N., 2004. Neoproterozoic meta-
morphism and deformation at the southeastern margin of the East European Craton
Uralides, Russia. International Journal of Earth Science 93, 921–944.
Green, P.F., Duddy, I.R., Laslett, G.M., Hegarty, K.A., Gleadow, A.J.W., Lovering, J.F., 1989.
Thermal annealing of fission-tracks in apatite, 4. Quantitative modelling techniques
and extension to geological time scales. Chemical Geology 79, 155–182.
Hall, J., Marillier, F., Dehler, S., 1998. Geophysical studies of the structure of the
Appalachian orogen in the Atlantic borderlands of Canada. Canadian Journal of
Earth Sciences 35, 1205–1221.
Hamilton, W.,1970. The Uralides and the motion of the Russian and Siberian platforms.
Geological Society of America Bulletin 81, 2553–2576.
Haworth, R.T., Keen, C.E., Williams, H., 1994. Transects of the ancient and modern
continental margins of eastern Canada. In: Speed, R.C. (Ed.), Phanerozoic Evolution
of North America Continent–Ocean Transitions. DNAG Continent–Ocean Transect
Volume. Geological Society of America, pp. 87–127.
Herrington, R.J., Armstong, R.N., Zaykov, V.V., Maslennikov, V.V., Tessalina, S.G., Orgeval,
J.-J., Taylor,R.N., 20 02. Massive sulfide deposits in the south Urals: geological setting
within the framework of the Uralide Orogen. In: Brown, D., Juhlin, C., Puchkov, V.
(Eds.), Mountain Building in t he Uralides: Pangea to Present. Geophysical
Monograph, vol. 132. American Geophysical Union, pp. 155–182.
Herrington, R.J., Zaykov, V.V., Maslennikov, V.V., Brown, D., Puchkov, V.N., 2005. Mineral
deposits of the Urals and links to geodynamic evolution. In: Hedenquist, J.W.,
Thompson, J.F.H., Goldfarb, R.J., Richards, J.P. (Eds.), Economic Geology 100
Anniversary Volume, pp. 1069–1095.
Hetzel, R., Glodny, J., 2002. A crustal-scale, orogen parallel strike-slip fault in the Middle
Urals: age, magnitude of displacement, and geodynamic significance. International
Journal of Earth Science 91, 231–245.
Jaupart, C., Mareschal, J.-C., 2003. Constraints on crustal heat production from heat flow
data. In: Rudnick, R.L. (Ed.), Treatise on Geochemistry, vol. 3. Elsevier, Amsterdam,
pp. 66–84.
Juhlin, C., Knapp, J.H., Kashubin, S., Bliznetzov, M., 1996. Crustal evolution of the Middle
Urals based on seismic reflection and refraction data. Tectonophysics 26, 21–34.
Juhlin, C., Friberg, M., Echtler, H., Green, A.G., Ansorge, J., Hismatulin, T., Rybalka, A.,
1998. Crustal structure of the Middle Urals: results from the (ESRU) EUROPROBE
Seismic Reflection Profiling in the Urals Experiments. Tectonics 17, 710–725.
Juhlin, C., Brown, D., Rybalka, A., Petrov, G., 20 07. Moho imbrication in the Middle Urals.
Terra Nova 19, 189–194.
Kamaletdinov, M.A., 1974. The Nappe Structures of the Urals. Nauka, Moscow. 228pp.
Kashubin, S., Juhlin, C., Friberg, M., Rybalka, A., Petrov, G., Kashubin, A., Bliznetsov, M.,
Steer, D., 2006. Crustal structure of the Middle Urals based on reflection seismic
data. In: Gee, D., Stephenson, R. (Eds.), European Lithosphere Dynamics. Memoirs,
vol. 32. Geological Society, London, pp. 427–442.
Kay, R.W., Mahlburg-Kay, S., 1991. Creation and destruction of the lower continental
crust. Geologische Rundschau 80, 259–278.
Khain, V.E., 1975. Structure and main stages in the tectono-magmatic development of
the Caucasus: an attempt at geodynamic interpretation. American Journal of
Science 275, 131–156.
Kimbell, G.S., Ayala, C., Gerdes, A., Kaban, M.K., Shapiro, V.A., Menshikov, Y.P., 2002.
Insights into the architecture and evolution of the southern and middle Urals
from gravity and magnetic data. In: Brown, D., Juhlin, C., Puchkov, V. (Eds.),
Mountain Building in the Uralides: Pangea to Present. Geophysical Monograph
Ser. AGU, pp. 49–66.
Knapp, J.H., Steer, D.N., Brown, L.D., Berzin, R., Suleimanov, A., Stiller, M., Lüschen, E.,
Brown, D., Bulgakov, R., Rybalka, A.V., 1996. A lithosphere-scale image of the
Southern Urals from explosion-source seismic reflection profiling in URSEIS '95.
Science 274, 226–228.
Kozlov, V.I., Krasnobaev, A.A., Larionov, N.N., Maslov, A.V., Sergeeva, N.D., Bibikova, E.V.,
Genina, L.A., Ronkin, Yu.L., 1989. The Lower Riphean of the Southern Urals. Nauka,
Moscow. 208 p.
Kukkonen, I.T., Golovanova,I.V., Khachay, Y., Druzhinin, V.S., Kosarev,A.M., Schapov, V.A.,
1997. Low geothermal heat flow of the Urals fold belt —implication of low heat
production, fluid circulation or palaeoclimate. Tectonophysics 276, 63–86.
Kukkonen, I.T., Jokinen, J., Seipold, U., 1999. Temperature and pressure dependencies of
thermal transport properties of rocks: implications for uncertainties in thermal
lithosphere models and new laboratory measurements of high-grade rocks in the
Central Fennoscandian Shield. Surveys in Geophysics 20, 33–59.
Lüschen, E., Borrini, D., Gebrande, H., Lammerer, B., Millahn, K., Neubauer, F., Nicolich, R.,
2006. TRANSALP —deep crustal vibroseis and explosive seismic profiling of the
Eastern Alps. Tectonophysics 414, 9–38.
Maslov, V.A., Cherkasov,V.L., Tischchenko, V.T., Smirnova, I.A., Artyushkova, O.V., Pavlov,
V.V., 1993. On the Stratigraphy and Correlation of the Middle Paleozoic Complexes
of the Main Copper–Pyritic Areas of the Southern Urals. Ufimsky Nauchno Tsentr,
Ufa. 129 pp.
Maslov, A.V., Erdtmann, B.-D., Ivanov, K.S., Ivanov, S.N., Krupenin, M.T., 1997. The main
tectonic events, depositional history, and the paleogeography of the southern Urals
during the Riphean –Early Paleozoic. Tectonophysics 276, 313–335.
Moisio, K., Kaikkonen, P., 2004. The present day rheology, stress field and deformation
along the DSS profile FENNIA in the central Fennoscandian Shield. Journal of
Geodynamics 38, 161–184.
Montero, P., Bea, F., Gerdes, A., Fershtater, G., Zinkova, E., Borodina, N., Osipova, T.,
Smirnov, V., 2000. Single-zircon evaporation ages and Rb–Sr dating of four major
Variscan batholiths of the Urals —a perspective of the timing of deformation and
granite generation. Tectonophysics 317, 93–108.
Oncken, O., von Winterfeld, C., Dittmar, U., 1999. Accretion of a rifted passive margin:
the Late Paleozoic Rhenohercynian fold and thrust belt (Middle European
Variscides). Tectonics 18, 75–91.
Perez-Estaun, A., Bastida, F., Alonso, J.L., Marquinez, J., Aller,J., Alvarez-Marron, J., Marcos,
A., Pulgar, J.A., 1988. A thin-skinned tectonics model for an arcuate fold and thrust
belt: The Cantabrian Zone (Variscan Ibero-Armorican Arc). Tectonics 7, 517–537.
194 D. Brown et al. / Earth-Science Reviews 89 (2008) 177–195
Perez-Estaun, A., Pulgar, J.A., Banda, E., Alvarez-Marron, J., ESCI-NResearch Group, 1994.
Crustal structure of the external Variscides in northwestern Spain from deep
seismic reflection profiling. Tectonophysics 232, 91–118.
Perez-Estaun, A., Brown, D., Gee, D., 1997a. EUROPROBE's Uralides Project. Tectono-
physics 276.
Perez-Estaun, A., Alvarez-Marron, J., Brown, D., Puchkov, V., Gorozhanina, Y., Baryshev,
V., 1997b. Along-strike structural variations in the foreland thrust and fold belt of
the southern Urals. Tectonophysics 276, 265–280.
Pollack, H.N., Hurter, S.J., Johnson, J.R., 1993. Heat flow from the Earth's interior: analysis
of the global data set. Reviews of Geophysics 31, 267–280.
Puchkov, V.N., 1997. Structure and geodynamics of the Uralian orogen. In: Burg, J.-P.,
Ford, M. (Eds.), Orogeny Through Time. Special Publication, vol. 121. Geological
Society, pp. 201–236.
Puchkov, V.N., 2000. Paleogeodynamics of the Central and Southern Urals. Ufa Pauria,
145p.
Puchkov, V., 2002. Paleozoic evolution of the East European continental margin
involved in the Uralide orogeny. In: Brown, D., Juhlin, C., Puchkov, V. (Eds.),
Mountian Building in the Uralides: Pangea to Present, American Geophysical Union.
Geophysical Monograph, 132, pp. 9–32.
Puchkov, V.N., Danukalova, G.A., 2004. New data on the character of tectonic
deformations of the Cretaceous–Paleogene peneplain in the Southern Urals. In:
Puchkov, V.N. (Ed.), Geological SBORNIK N4. Information Materials of the Institute
of Geology. Institute of Geology, Ufimian Geoscience Center, Russian Academy of
Science, Ufa, pp. 183–184.
Rapp, R.P., Watson, E.B., 1995. Dehydration melting of metabasalt at 8–32 kbar:
implication for continental growth and crust–mantle recycling. Journal of Petrology
36, 891–931.
Rudnick, R.L., 1995. Making continental crust. Nature 378, 571–578.
Ryzhiy, B.P., Druzhinin, V.S., Yunusov, F.F., Ananyin, I.V., 1992. Deep structure of the Urals
region and its seismicity. Physics of the Earth and Planetary Interiors 75, 185–191.
Savelieva, G.N., Sharaskin, A.Y., Saveliev, A.A., Spadea, P., Gaggero, L., 1997. Ophiolites of
the Southern Uralides adjacent to the East European continental margin.
Tectonophysics 276, 117–138.
Sayers, J., Symonds, P.A., Direen, N.G., Bernardel, G., 2001.Nature of the continent–ocean
transition on the non-volcanic rifted margin of the central Great Australian Bight.
In: Wilson, R.C.L., Whitmarsh, R.B., Taylor, B., Froitzheim, N. (Eds.), Non-volcanic
Rifting of Continental Margins: A Comparison of Evidence from Land and Sea.
Special Publication, vol. 187. The Geological Society, London, pp. 51–76.
Scarrow, J., Ayala, C., Kimbell, G.S., 2002a. Insights into orogenesis: Getting to the root of
the continent–ocean–continent collision in the southern Urals, Russia. Journal of
the Geological Society 159, 659–672.
Scarrow, J.H., Hetzel, R., Gorozhanin, V.M., Dinn, M., Glodny, J., Gerdes, A., Ayala, C.,
Montero, P., 2002b. Four decades of geochronological work in the Southern and
Middle Urals: A review. In: Brown, D., Juhlin, C., Puchkov, V. (Eds.), Mountain
Building in the Uralides: Pangea to Present. Geophysical Monograph, vol. 132.
American Geophysical Union, pp. 233–256.
Schmid, S.M., Kissling, E., 2000. The arc of the western Alps in light of geophysical data
on deep crustal structure. Tectonics 19, 62–85.
Seward, D., Perez-Estaun, A., Puchkov, V., 1997. Preliminary fission-track results from
the southern Urals –Sterlitamak to Magnitogorsk. Tectonophysics 276, 281–290.
Seward, D., Brown, D., Hetzel, R., Friberg, M., Gerdes, A., Petrov, G.A., Perez-Estaun, A.,
2002. The syn- and post-orogenic low temperature events in the southern and
middle Urals: Evidence from fission-track analysis. In: Brown, D., Juhlin, C.,
Puchkov, V. (Eds.), Mountain Building in the Uralides: Pangea to Present.
Geophysical Monograph, vol. 132. American Geophysical Union, pp. 257–272.
Semenov, B.G., Anan'yeva, Ye.M., Yekidina, N.Y., Berland, N.G., Kassin, G.G., Tsvetkova, A.
A., 1983. Deep crustal structure of the Urals and the adjoining area. Geotectonics 17,
288–295.
Seravkin, I., Kosarev, A.M., Salikhov, D.N., 1992. Volcanism of the Southern Urals. Nauka,
Moscow, Russia. 195 pp.
Skripi, A.A., Iunusov, H.K., 1989. Tension and compression structures in the Articulation
zone of the Southern Urals and the East European Platform. Geotectonics 23,
515–522.
Spadea, P., D' Antonio, M., Kosarev, A., Gorozhanina, Y., Brown, D., 2002. Arc–continent
collision i n the Southern Urals: petrogenetic aspects of the forearc complex. In:
Brown, D., Juhlin, C., Puchkov, V. (Eds.), Mountain Building in the Uralides:
Pangea to Present. Geophysical Monograph , vol. 132. Amer ican Geophysical
Union, pp. 101–134.
Steer, D.N., Knapp, J.H., Brown, L.D., Rybalka, A.V., Sokolov, V.B., 1995. Crustal structure
of the Middle Urals based on reprocessing of Russian seismic reflection data.
Geophysical Journal International 123, 673–682 1995.
Steer, D.N., Knapp, J.H., Brown, L.D., Echtler, H.P., Brown, D.L., Berzin, R., 1998. Deep
structure of the continental lithosphere in an unextended orogen: an explosive-
source seismic reflection profile in the Urals (Urals Seismic Experiment and
Integrated Studies (URSEIS 1995)). Tectonics 17, 143–157.
Tavrin, I.F., Khalevin, N.I., 1990. Geophysical models for the Urals crust. Geotectonics 24,
223–230.
Tryggvason, A., Brown, D., Perez-Estaun, A., 2001. Crustal architecture of the southern
Uralides from true amplitude processing of the URSEIS vibroseis profile. Tectonics
20, 1040–1052.
Yazeva, R.G., Bochkarev, V.V., 1996. Silurian island arc of the Urals: structure, evolution
and geodynamics. Geotectonics 29, 478–489.
Zonenshain, L.P., Korinevsky, V.G., Kazmin, V.G., Pechersky, D.M., Khain, V.V.,
Mateveenkov, V.V., 1984. Plate tectonic model of the south Urals development.
Tectonophysics 109, 95–135.
Zonenshain, L.P., Kuzmin, M.I., Natapov, L.M., 1990. Uralian foldbelt. In: Page, B.M. (Ed.),
Geology of the USSR: A Plate-tectonic Synthesis, Geodynamic Series, vol. 21.
American Geophysical Union, Washington, D.C., pp. 27–54.
195D. Brown et al. / Earth-Science Reviews 89 (2008) 177–195
