IGCP 453 – Uralides / August 2nd – 12th, 2004IGCP 453 – Uralides / August 2nd – 12th, 2004

T E C H N IS C H EU N IV E R SIT Ä TB

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GA K A D E

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RE I B E R

GEvolution of the Evolution of the

Magnitogorsk oceanic arc system Magnitogorsk oceanic arc system (Devonian, southern Urals) (Devonian, southern Urals)

Bernd Buschmann (TU Bergakademie Freiberg)Bernd Buschmann (TU Bergakademie Freiberg)

based on major cooperation with:based on major cooperation with:Peter Jonas (Freiberg)Peter Jonas (Freiberg)Victor Puchkov (Ufa)Victor Puchkov (Ufa)Valery Maslennikov, Victor Zaykov (Miass)Valery Maslennikov, Victor Zaykov (Miass)

Major tectonostratigraphic-structural zones Major tectonostratigraphic-structural zones of the southern Uralsof the southern Urals

Tectonostratigraphic-structural zones Tectonostratigraphic-structural zones related to arc-continent accretionrelated to arc-continent accretion

Scheme of Scheme of arc-continent arc-continent

collision collision in the southern in the southern

UralsUrals

(from Matte 1998, after (from Matte 1998, after Chemenda et al. 1997)Chemenda et al. 1997)

GeneralizedGeneralizedgeological mapgeological map

of the of the Magnitogorsk ZoneMagnitogorsk Zone

Schematic tectonostratigraphic column for N part of Magnitogorsk ZoneSchematic tectonostratigraphic column for N part of Magnitogorsk Zone

Schematic cross section of N part of MOAS in Early Frasnian time Schematic cross section of N part of MOAS in Early Frasnian time (onset of arc-continent docking)(onset of arc-continent docking)

2D scheme of evolution of the MOAS2D scheme of evolution of the MOAS

Some major points to discussSome major points to discuss

environment responsible for generation of boninitic rocks in initial arc complex

vergency of subducting slab during oceanic arc growth

geotectonic environment of formation of Famennian calc-alkaline volcanics a eastern margin of Magnitogorsk Zone

structure development of the accretionary complex by

1. arc-continent docking

2. subsequent compression (hypercollision - wrench tectonics)

Some arguments against W-vergent subduction at eastern margin of Some arguments against W-vergent subduction at eastern margin of MOASMOAS

Southern Urals situation

mineral closing ages (garnet, sphene, phengite) in HP-rocks of subducted continental margin 380-370 Ma

requires presence of E-vergent subducted slab at western board of MOAS before 370 Ma

contemporaneous W-vergent subduction at eastern margin of MOAS (if feasible at all) should have resulted in strong extension in overriding plate – no signs for such extension

Some arguments against W-vergent subduction at eastern margin of Some arguments against W-vergent subduction at eastern margin of MOASMOAS

Modern examples W Pacific – no microcontinents involved in arc-continent collision

Timor subduction beneath NW Australian margin, Banda arc approaching island of Timor is emerged part of accretionary complex

Taiwan oblique arc-continent collisionaccretionary complex first to emerge in front of docking arc

Timor + Taiwan – shelfal sea between emerged accretionary complex and continental coastline- seastrait between emerged accretionary complex

and extinct arc

Landscape of contact between Irendyk arc complexes (foreground) Landscape of contact between Irendyk arc complexes (foreground) and Karamalytash rocks (background) W of Sibai townand Karamalytash rocks (background) W of Sibai town

Good weather and fruitful discussions for our field trip!