IGCP-480 Structural and Tectonic Correlation across the Central Asia Orogenic Collage: Implications for Continental Growth and Intracontinental Deformation Activity in 2005-2006

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IGCP-480Structural and Tectonic Correlation
across the Central Asia Orogenic Collage
Implications for Continental Growth and
Intracontinental DeformationActivity in 2005-2006

• Boris A. Natalin, Istanbul Technical University

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Orogenic collages in Central Asia

• Each orogenic collage evolved according its own
  plate tectonic scenario (e.g. Sengör and
  Natalin, 1996).
• The term Central Asian Orogenic Belt has
  geosynclinal connotation. It was vaguely defined
  for structures of similar ages of the main
  folding that are located between the Siberian
  craton, Tarim, and North China (Yanshin et al.,
  1965).

Modified after Sengör and Natalin (1996)
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Objectives of the IGCP-480 project

• Detailed structural studies of relationships of
  tectonic units
• Tectonic nature and exhumation of metamorphic
  complexes
• Tectonic setting of ophiolites and their
  significance for paleotectonic reconstructions
• Paleogeographic positions of tectonic units
• Late Paleozoic and Mesozoic tectonics and the
  origin of large sedimentary basins.
• Far-field effects of Indo-Asian collision
• Mantle plumes

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Two competing tectonic hypotheses

• Continuous growth of the continental crust due to
  the formation of large subduction-accretion
  complexes. This process was synchronous to the
  duplication of arc and forearc fragments via
  large-scale strike-slip systems during subduction
• Multiple frontal collisions and collapses of
  back-arc basins

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Irkutsk, Russia, 2005
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Mongolia, 2006
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Planned workshops and field trips
2009
2005
2008
2006
2007
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The Second workshop in Ulaanbaatar, Mongolia

• The workshop was organized by the Institute of
  Geology and Mineral Recourses of the Mongolian
  Academy of Sciences and the School of Geology and
  Petroleum of the Mongolian University of Science
  and Technology
• Professor O. Tomurtogoo and Dr. D. Tomurhuu

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• Abstract volume and a Field Excursion Guidebook
  (Tomurhuu et al., 2006)
• The workshop was attended by 92 scientists and
  students from twelve counties who made thirty
  oral and eight poster presentations

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Field trips to Khangai-Khantey Zone
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Tectonic interpretations of the Khangai-Khantey
zone

• Back-arc basin filled with a thick (10 km) pile
  of Paleozoic turbidites and underlain by
  continental crust (Zonenshain, 1973)
• Paleozoic to Triassic subduction-accretion
  complex (Sengör et al., 1993 Sengör and
  Natalin, 1996 Zorin, 1999 ),
• Passive continental margin (Bucham et al., 2001
  Badarch et al., 2002 Tomurtogoo et al., 2005)
• Continental block overlain by a thick sedimentary
  cover (Jahn et al., 2004 Kovalenko et al., 2004
  Herrington et al., 2005)

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Coherent bedding in turbidites, Khangai-Khantey
accretionary wedge
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Sheared turbidites in the Khangai-Khantey
accretionary wedge
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Pelagic cherts in the Gorhi Formation,, near
Ulaanbaatar. Note asymmetric boudinage with
vertical elongations of boudin. Sinistral sense
of shear
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Seamount limestone in the Shohoi Tsagaan Bulag
quarry
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Basaltic tuff containing clasts of limestones,
Shohoi Tsagaan Bulag quarry
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• Tectonic nature of the Khangai-Khantey zone
• The Khangai-Khantey zone is the
  subduction-accretion complex
• Kurihara et al. (2006) reconstructed the oceanic
  plate stratigraphy of the downgoing slab in the
  MongolOkhotsk ocean, confirmed its extensive
  width, and constrained the age of subduction to a
  date as young as the Carboniferous
• Permian radiolarite reported by Tomurtogoo
  (2005) suggests an even younger age of subduction.

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Field trips to the Bayanhongor Zone
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Dyke with chilled margin
Dykes and volcanic rocks vary from N-MORB through
E-MORB to OIB basalts suggesting their backarc
(Buchan et al., 2001) or oceanic origin (Tomurhuu
and Munkh-Erdene, 2006).
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Dyke-in-dyke (plan view)
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Two direction of dykes in the Bayanhongor
ophiolites
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Sheeted dyke complex in the Altan-Am gorge. View
to the north. Western dips of the dyke indicate
rotation
E
W
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Bayanhongor ophiolites, Stop 6. Pillow lavas
indicating NE-ward younging direction
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• Our observations
• Ophiolite thrust sheets are steeply dipping and
  overturned to the NE
• This style is consistent across our transect
• Clockwise rotation of dykes and shear zones imply
  dextral NW-trending shearing

Simple imbricate stack of NE-vergent thrusts
(Buchan et al., 2001)
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Other evidence for dextral orogen-parallel
shearing
Steeply dipping Lower Cambrian phyllonites at
station 9
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N
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Augen gneisses at St. 9. Lineation is horizontal
dextral shearing
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High temperature mylonite (gabbro) with sinistral
orogen-parallel sense of shear
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Bayanhongor problem

• Jiang Ping and his coauthors reported 300240 Ma
  ages from porphyric dykes and ophiolite cumulates
• These ages contradict to ages of main
  deformations to between 540 and 450 Ma (Badarch
  et al., 2002)
• Almost all rocks from ophiolites are in clasts of
  low strained Ordovician conglomerate

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Section in the Taats River valley
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Welcome to China!

• Workshop in Beijing - 60 participants from
  Australia, China, Israel, Kazakhstan, Mongolia,
  Poland, Russia, Taipei, Turkey, Switzerland,
  USA- 25 oral and 4 poster presentations
• Field trip to Inner Mongolia

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Special thanks

• Prof. Shuwen Dong
• Prof. Dunyi Liu
• Prof. Ping Jiang
• Prof. Alfred Kroener
• Mr. Wang Weiand Chinese team representing the
  Beijing SHRIMP-Centre, the Institute of Geology
  of the Chinese Academy of Geological Sciences,
  and the China National Committee for IGCP