IGCP 453 Uralides conference and fieldtrip:

Arc-continent collision

Organisers:

Dennis Brown, Instituto de Ciencias de la Tierra, Barcelona, Spain (dbrown@ija.csic.es)

Victor Puchkov, Institute of Geology, Ufimian Geoscience Center, Ufa, Russia (puchkv@anrb.ru)

When: August 3rd to 12th, 2004

Where: A one day conference will be held on 3rd August in the city of Ufa. The field excursion will leave from and return to Ufa. See the schedule below.

Duration: 10 days after arrival in Ufa

Cost: $700US (based on a minimum of 10 participants. The cost will be reduced with more people). Cost includes accomodation after arrival in Ufa, meals, transportation, etc.

Travel to Ufa: There are a number of flights a day from Moscow to Ufa, leaving either from the international airport Sheremetovo-I or the national airport Domodedovo. There is one flight a day from the international airport. This flight is IATA rated and operated by Aeroflot. Tickets can be bought in most travel agencies. The flight leaves Moscow at 01:30 and arrives Ufa at 05:30 (a two hour flight with a two hour time change). The return flight leaves Ufa at 07:00 and arrives Moscow at 07:00. There are currently 2 or 3 flights a day from Domodedovo to Ufa. These are operated by Bashkirian Airlines and tickets cannot be bought outside of Russia.

Visas: All non-Russians will need to have a visa. In the past few years a visa support has been needed from the office of the Russian Federation in Ufa which you then take to the Russian embassy when you fill out the visa application. This will have to be done about three months before the fieldtrip since it can take a long time getting through the beaurocratic red tape in Ufa. Victor Puchkov will take care of this. A reminder will be sent to everyone in April.

Background

IGCP 453 Uralides conference and fieldtrip will take place in the southern Urals of Bashkiria in August of 2004 (Fig. 1). The meeting and fieldtrip will take 10 days, depending on when people want to return to Moscow at the end. See the schedule below. The aim of IGCP 453 in the Uralides is to see first hand the well preserved arc-continent collision that occurred from the Middle Devonian to the Earliest Carboniferous and two sections of the foreland thrust and fold belt that developed from the Late Carboniferous to the Early Triassic.

Fig. 1. Geological map of the southern Uralides outlining the volcanic arc, the accretionary complex and the foreland thrust and fold belt. The route to be taken on the fieldtrip is marked.

The southern Uralides of Russia (Fig. 1) constitute part of a collisional orogenic belt that developed during two distinct deformation events. From the Late Devonian to Early Carboniferous, continental lithosphere of the East European craton was subducted beneath the Magnitogorsk arc, resulting in the development and emplacement of an accretionary wedge over the subducting slab and suturing of the arc to the continental margin along the Main Uralian fault zone (Puchkov, 1997; Brown et al., 1998; Brown and Spadea, 1999) (Fig. 2). From the Late Carboniferous through the Late Permian-Early Triassic, the ocean to the east of the accretted Magnitogorsk arc closed, resulting in it and its accretionary wedge being thrust westward along with the East European craton Precambrian basement and its Paleozoic preorogenic platform cover, to form a foreland thrust and fold belt and a largely carbonate foreland basin (Brown et al., 1997).

Fig. 2. Model schematically outlining the evolution of the collision between the East European Craton and the Magnitogorsk arc from the Middle Devonian to the Early Carboniferous.

The accretionary complex (Figs. 1 and 2) is composed of Ordovician to Middle Devonian continental slope and platform sedimentary rocks (Suvanyak Complex and Timirovo thrust system) that were detached from the East European craton, and are overthrust by ~5 km of the Uppermost Frasnian and Famennian syncollisional volcanoclastic turbidites sourced from the Magnitogorsk arc (Zilair nappe) (e.g., Puchkov, 1997; Brown et al., 1998). These units are flanked to the east by eclogite- and blueschist-bearing gneisses of the Maksutovo Complex that record a peak metamorphic age of ca. 380–370 Ma (Matte et al., 1993; Lennykh et al., 1995; Glodny et al., 2002). The highest structural level in the accretionary wedge is the Kraka lherzolite massif (Savelieva et al., 1997). The accretionary wedge is sutured to the Magnitogorsk arc along the east-dipping Main Uralian fault zone, a melange that is up to ~10 km that contains several km-scale ultramafic fragments.

Eastward, in the immediate hanging wall of the Main Uralian fault, the oldest island arc unit found in the Magnitogorsk forearc is the Emsian (ages determinations in the Magnitogorsk arc are from conodont data of Maslov et al., 1993) high-Mg basaltic andesite to andesitic Baimak-Buribai Formation in which basic-intermediate boninitic lavas, dikes, and shallow intrusive rocks have been described (Spadea et al., 1998). Locally, the Baimak-Buribai Formation is overlain by a condensed section of Eifelian to Famennian cherts, tuffaceous sandstones, and conglomerates, followed upwards by the Zilair Formation. Its eastern margin is overthrust by Emsian to Eifelian Irendyk Formation, which consists of andesitic basalts, hyaloclastic flows, agglomerates, and intercalations of volcaniclastic sandstones. The Irendyk Formation is overlain by the predominantly dacitic volcanics of the Eifelian to Givetian Karamalytash Formation or by contemporaneous condensed cherts of the Yarlykapovo formation. The Magnitogorsk arc volcanic rocks all have oceanic island-arc geochemical and isotopic signature.

Fig. 3. Upper crustal cross section across the accretionary complex and the Magnitogorsk arc.

The volcanic units form the basement on which as much as 5000 m of westward-thickening forearc basin sediments were deposited. Givetian Bugulygir jaspers that directly overlie the volcanic units are widespread in the basin. These are everywhere stratigraphically overlain by Givetian to Lower Frasnian volcanoclastic sandstones, microconglomerates, and tuffaceous cherts of the Ulutau Formation. This is followed by the Mukas Formation varying in composition from condensed cherty shale to a rather thick cherty flysch. The stratigraphically highest unit is the Frasnian to Famennian Zilair Formation which consists of turbiditic volcanoclastic sandstones, siliceous siltstones, and interbedded cherts. Synsedimentary deformation and olistostromes are common in the forearc sediments, but are especially widespread in the Zilair Formation, where olistostromes of several tens of square kilometers are developed. Regionally, the Zilair Formation is correlated with the volcanoclastic sandstones that are in the Zilair nappe. Shallow-water Lower Carboniferous carbonates and bimodal subalkaline volcanics unconformably overlie the openly folded arc.

The southern Uralide foreland thrust and fold belt developed during the Late Carboniferous through to the Late Permian-Early Triassic (Kamaletdinov, 1974; Puchkov, 1997; Brown et al., 1997). North of approximately 53º N, the foreland thrust and fold belt is a ~150 km wide, west vergent thrust wedge made up of Precambrian basement, the Late Devonian accretionary complex, Paleozoic platform, and foreland basin sediments (Fig. 1). Paleozoic shortening in this part of the thrust belt is small in comparison to other mountain belts, approximately 20 km or less (e.g., Giese et al., 1999; Perez-Estaun et al., 1997; Brown et al., 1996, 1997, 1999). It also exhibits a high degree of along strike structural variation and basement involvement, which has been interpreted to have been caused by pre-existing structures in the basement (Perez-Estaun et al., 1997; Brown et al., 1999). South of 53º N the southern Uralide foreland is dominated by the accretionary complex (Brown et al., 1998; Alvarez-Marron et al., 2000) (Fig. 1). Another major difference between the two segments of the thrust belt is the Paleozoic stratigraphy. To the north of approximately 53º N, the Ordovician and Silurian sediments consist of thin units of clastics and subordinate carbonates (locally up to 750 m) deposited in shallow, laterally discontinuous rift basins that disappear westward. The Devonian to Upper Carboniferous sediments consist of < 3000 m of mostly shallow water carbonates that were deposited on a passive platform margin (e.g., Brown et al., 1997; Puchkov, 2002). Southward, the Ordovician to Middle Devonian consists of a thin veneer (c. 1000 m) of clastics and subordinate carbonates similar to that in the north, but the Upper Devonian is dominated by the Zilair Fm. (e.g., Alvarez-Marron et al., 2000) which is in turn overlain by Late Devonian to Early Carboniferous sediments. The Zilair formation completely disappears from the western slope of the Urals north of the 56º N.

Schedule

August 2nd

Arrive in Ufa (Aeroflot flight leaves Moscow International airport terminal 1 at 01:30 and arrives Ufa at 05:30. A two hour direct flight. You will be met at the airport.)

In the evening there will be a reception and icebreaker followed by dinner.

August 3rd

A full day of talks and poster presentations.

August 4th

Leave Ufa by bus to the first field camp (approximately 6 to 7 hour drive). Along the way there will be a stop to view one of the Permian reefs of the Shikans.

The camp will be already set up on arrival in the town of Kugarchi, near the frontal structure of the foreland thrust and fold belt.

Plate 1. Typical field camp in the southern Urals.

August 5th

A section through the foreland thrust and fold belt. In this section faulted and folded Carboniferous sediments and Permian sediments of the foreland basin are seen. The day will end with structures at the base of the accretionary complex.

Plate 2. Photograph of overturned Upper Carbonierous and Lower Permian sediments along the frontal structure of the foreland thrust and fold belt near Kugarchi.

In the evening, there will be an around the campfire discussion of the transition from a passive to an active margin and the development of the foreland thrust and fold belt.

August 6th

Leave the camp in Kugarchi heading east across the accretionary complex. Stops will include the volcanoclastic turbidites of the Zilair Formation, phyllites and metaquartzites of the Suvanyak Complex, high pressure rocks of the Maksutovo Complex, and the arc-continent suture (the Main Uralian fault). Arrive in the town of Sibay in the evening and stay in a hotel.

Plate 3. Upright folds in the Zilair Fm. Along the eastern flank of the Zilair Nappe.

Plate 4. High pressure blueschist and eclogite of the Maksutovo Complex.

August 7th

A section through the Magnitogorsk island arc beginning in the boninitic arc tholiites up through the volcanic pile to the andesites and dacites. For those who are interested it may be possible to organise a seprate visit to the Sibay open pit mine.

In the evening there wil be a roundtable discussion of the formation of a volcanic arc and arc-continent collision.

Plate 5. Pillow lavas in Baimak-Buribai Fm. The pillow rims are bonititic.

August 8th

A section through the sediments overlying the Magnitogorsk arc volcanics. These sediments register the arc-continent collision.

August 9th

Leave Sibay and head west across the accretionary complex. This will provide a better oportunity to see the Suvanyak Complex.

Field camp in Starosubkhangulovo.

August 10th

Exceptional exposures of a calc-mylonite developed at the base of the accretionary complex and the frontal structures within the Zilair Nappe and the basal contact of the Kraka lherzolite massif which sits within the accretionary complex.

Plate 6. Base of the Zilair Nappe in Starosubkhangulovo. To the right are the Zilair sediments and to the left is a calc-mylonite.

Plate 7. Tailed clast in the calc-mylonite at the base of the accretionary complex.

In the evening there will be an around the campfire discussion of arc-continent collision through geological time.

August 11th

Leave Starosubkhangulovo and drive north along the Kraka massif and into the metamorphic basement rocks of the Bashkirian anticline. These rocks were deformed and metamorphosed in a late Vendian tectonothermal event, and reactivation of pre-exisitng structures during the Uralide orogeny had a significant influence on the architecture of the foreland thrust and fold belt.

Field camp near the town of Beloretsk.

In the evening there will be an around the campfire discussion of the influence of pre-exisiting basement structure on the evolution of a foreland thrust and fold belt.

August 12th

Return to Ufa crossing the Precambrian basement rocks in Bashkirian anticlinorium and the Paleozoic platform sediments and the foreland basin along its western flank.

Hotel in Ufa

August 13th

Flight leaves for Moscow at 07:00 and arrives Moscow International airport at 07:00 local time (there is two hour time difference)

Suggested references (in English)

Alvarez-Marron, J., D. Brown, A. Perez-Estaun, V. Puchkov, and Y. Gorozhanina, Accretionary complex structure and kinematics during Paleozoic arc-Continent collision in the southern Urals, Tectonophysics, 325, 175-191, 2000.

Beane, R., J. Connelly, ⁴⁰Ar/³⁹Ar, U-Pb, and Sm-Nd constraints on the timing of metamorphic events in the Maksytov Complex, southern Ural Mountains, J. Geol. Soc. of London, 157, 811-822, 2000.

Brown, D., R. Hetzel, and J.H. Scarrow, Tracking arc-continent collision subduction zone processes from high pressure rocks in the southern Urals, J. Geol. Soc. of London, 157, 901-904, 2000.

Brown, D., and P. Spadea, Processes of forearc and accretionary complex formation during arc-continent collision in the southern Ural Mountains, Geology, 27, 649-652, 1999.

Brown, D., J. Alvarez-Marron, A. Perez-Estaun, Y. Gorozhanina, V. Baryshev, V. Puchkov, Geometric and kinematic evolution of the foreland thrust and fold belt in the southern Urals, Tectonics, 16, 551-562, 1997.

Brown, D., C. Juhlin, J. Alvarez-Marron, A. Perez-Estaun, and A. Oslianski, Crustal-scale structure and evolution of an arc-continent collision zone in the southern Urals, Russia, Tectonics, 17, 158-171, 1998.

Brown, D., J. Alvarez-Marron, A. Perez-Estaun, V. Puchkov, Y. Gorozhanina, P. Ayarza, Structure and evolution of the Magnitogorsk forearc basin: Identifying upper crustal processes during arc-continent collision in the southern Urals, Tectonics, 20, 364-375, 2001.

Brown, D., C. Juhlin, V. Puchkov (editors), Mountain Building in the Uralides: Pangea to Present, American Geophysical Union Geophysical Monograph 132, 2002.

Giese, U., U. Glasmacher, V. Kozlov, I. Matenaar, V. Puchkov, L. Stroink, W. Bauer, S. Ladage, R. Walter, Structural framework of the Bashkirian anticlinorium, SW Urals, Geol. Rundsch, 87, 526-544, 1999.

Glasmacher, U.A., G.A. Wagner, V.N. Puchkov, Thermotectonic evolution of the western forld-and-thrust belt, southern Uralides, Russia, as revealed by apatite fission track data, Tectonophysics, 354, 25-48, 2002.

Glasmacher, U.A., W. Bauer, U. Giese, P. Reynolds, B. Kober, V. Puchkov, L. Stroink, A. Alekseyev, A.P. Willner, The metamorphic complex of Beloretzk, SW Urals, Russia – a terrnae with polyphase Meso- to Neoproterozoic thermo-dynamic evolution, Precambrian Research, 110, 185-213, 2001.

Glodny, J., B. Bingen, H. Austrheim, J. Molina, A. Rusin, Precise eclogitization ages deduced from Rb/Sr mineral systematics: The Maksyutov complex, southern Urals, Russia, Geochimica et Cosmochimica Acta, 66, 1221-1235, 2002.

Hetzel, R., H. Echtler, W. Seifert, B. Schulte, K. Ivanov, Subduction- and exhumation-related fabrics in the Paleozoic high-pressure – low-temperature maksyutov Complex, Antingan area, southern Urals, Russia, Geol, Soc. Am. Bull., 110, 916-930, 1998.

Hetzel, R., Geology and geodynamic evolution of the high-P/low-T Maksyutov Complex, southern Urals, Russia, Geol. Rundsch, 87, 577-588, 1999.

Perez-Estaun, A., D. Brown, D. Gee (editors), EUROPROBE’s Uralides Project, Tectonophysics, 276, 1997.

Puchkov, V.N., Structure and geodynamics of the Uralian orogen, in Orogeny Through Time, edited by J.-P. Burg and M. Ford, Geol. Soc. of London, Spec. Publ. 121, 201-236, London, 1997.

Spadea, P., L.Y. Kabanova, and J.H. Scarrow, Petrology, geochemistry and geodynamic significance of Mid-Devonian boninitic rocks from the Baimak-Buribai area [Magnitogorsk Zone, southern Urals), Ofioliti, 23, 17-36, 1998.

Tryggvason, A., D. Brown, A. Pérez-Estaún, Crustal architecture of the southern Uralides from true amplitude processing of the URSEIS vibroseis profile, Tectonincs, 20, 1040-1052, 2001.