The Strandja arc: anatomy of collision after long-lived arc parallel tectonic transport

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The Strandja arc anatomy of collision after
long-lived arc parallel tectonic transport

• Boris Natalin, Gursel Sunal, and Erkan Toraman
• Istanbul Technical University

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• The basement of the Turan and Scythian platform
  consists of Permo-Triassic arc (red)-forearc
  (green) fragments bounded by dextral strike-slip
  faults
• They belonged to the south-facing Silk Road arc
  evolving along the southern margin of Eurasia

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Late Carboniferous-early Permian kinematics of
Eurasia
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Early Permian-Triassic kinematics of Eurasia
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Problems

• How far Asiatic structures can be traced in the
  west?
• How large-scale strike-slip displacements were
  compensated in the western corner of the
  Paleo-Tethys?

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Main topics

• The Strandja massif is a long-lived
  Paleozoic-Triassic magmatic arc
• The Strandja massif reveals a similarity with the
  tectonic units of the Scytho-Turanian orogenic
  system
• Middle Jurassic-Early Cretaceous deformations
  record a passage of a triple junction and change
  of dextral motions to thrusting

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Tectonic setting of the Strandja massif
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315 Ma
257 Ma
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Fabric of the Permian metagranites
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Permian granites in the Strandja/Balkan zone
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Detrital zircons from metasediments

• The source area was characterized by exposure of
  magmatic rocks of heterogeneous ages (460 to 1273
  Ma) that is characteristic for a deeply eroded
  continental region.

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Inherited ages

• Long-lasted magmatic activity
• There are no inherited zircons in the Permian
  granites

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• Chemical compositions of Carboniferous and
  Permian metagranite. Abbreviations VAG-
  volcanic-arc granitoids, syn-COLG-
  syn-collisional granitoids, WPG- within plate
  granitoids, ORG- ocean-ridge granitoids.

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Negative anomaly of Nb - subduction zone
component
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Regional correlations
Gondwanian blocks Menderes massif - 570-520 Ma
orthogneisses - 635-605 Ma inherited ages

• Caucasus (Somin, 2000)-460-400 Ma-320-310
  Ma-305-280 Ma-medial Carboniferous-Permian
  intermediate volcanics

• Kunlun (Pan et al., 1996)-540-400
  Ma-intermediate to mafic Carboniferous tuff and
  lava-260-200 Ma

Strandja is a part of the Scytho-Turanian
orogenic system
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Structural geology

• D1 Pre-Permian deformation
• D2 middle Jurassic-early Cretaceous deformation
• D3 pre-late Cretaceous

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• Moderate southern dips of the S2 foliation
• Steep dips of bedding
• Increase of metamorphism to the south

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L2 lineation
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Orientation of the L2 lineation
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Sg2 foliation indicates the latest top-to-north
motions
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Age of S2 foliation and L2 lineation

• 40Ar/39Ar (muscovite and biotite) 151-167 Ma
• Rb-Sr (muscovite) 149-162 Ma
• Rb-Sr (biotite) 136-148 Ma
• The Bathonian-Berriasian (middle Jurassic-early
  Cretaceous) time interval according to the
  International Stratigraphic Chart (UNESCO-IUGS,
  2000)

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Triple junction T of convergent plate boundaries.
Oblique convergence of the plate B causes the
development of NW-trending lineation l1 at point
L lying on the plate A.
Migration of the triple junction from T0 to T1
brings the plate C into interaction with the
plate A. NE-trending lineation l2 forms
immediately after the passage of the triple
junction across point L.
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The plate A is Eurasia. The plate B is the
Tethyan ocean The boundary AC is the Balkan
fold-and-thrust belt. It has the northern
vergence. The boundary CB is the Jurassic-early
Cretaceous Mandritsa arc (Bonev and Stampfli,
2003).
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The NW-trending lineation must be older than NE
and north-south trending lineations. Preservations
of two lineations- at L1 earlier lineation
will be destroyed- point L2 represents the
Strandja case- at point L3 discrete shear zones
produced by thrusting cut earlier penetrative
lineation. The shear zone boundaries are sharp.
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Conclusions

• The Strandja massif represents a Paleozoic
  magmatic arc.
• Inherited zircons in the Carboniferous
  orthogneisses record magmatic activity at 330-355
  Ma and 420-440 Ma. Detrital zircons record
  magmatic activity between 460 and 650 Ma
• The Strandja arc is a part of the Scytho-Turanian
  orogenic system

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Conclusions

• Similar to the Scytho-Turanian orogenic system
  the Strandja arc presents evidence for the
  arc-parallel tectonic transport
• Arc-parallel displacements terminated with
  collision of the Mandritsa arc in the medial
  Jurassic-early Cretaceous
• Collisional deformation records a migration of
  the triple junction