Transcript Silurian to Devonian evolution of VMS

MIE
TECHNISCHE
UNIVERSITÄT
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BE R
AK ADE
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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)
IGCP 453 – Uralides / August 2nd – 12th, 2004
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 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
MOAS
Modern examples W Pacific –
Timor
no microcontinents involved
in arc-continent collision
subduction beneath NW Australian margin, Banda arc
approaching
island of Timor is emerged part of accretionary complex
Taiwan oblique 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
Good weather and fruitful discussions for our field trip!
Landscape of contact between Irendyk arc complexes (foreground)
and Karamalytash rocks (background) W of Sibai town