IGCP 453 – Uralides / August 2nd – 12th, 2004 Evolution of the Magnitogorsk oceanic arc system (Devonian, southern Urals) Bernd Buschmann (TU Bergakademie Freiberg) based on major cooperation with: Peter Jonas (Freiberg) Victor Puchkov (Ufa) Valery Maslennikov, Victor Zaykov (Miass)

Major tectonostratigraphic-structural zones of the southern Urals

Tectonostratigraphic-structural zones related to arc-continent accretion

Scheme of arc-continent collision in the southern Urals (from Matte 1998, after Chemenda et al. 1997)

Generalized geological map of the Magnitogorsk Zone

Schematic tectonostratigraphic column for N part of Magnitogorsk Zone

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

2D scheme of evolution of the MOAS

Some 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 MOAS Southern Urals situation mineral closing ages (garnet, sphene, phengite) in HP-rocks of subducted continental margin 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 MOAS 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 Taiwanoblique arc-continent collision accretionary 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) and Karamalytash rocks (background) W of Sibai town Good weather and fruitful discussions for our field trip!