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

The Strandja arc: anatomy of collision after long-lived arc parallel tectonic transport. Boris Natal’in, Gursel Sunal, and Erkan Toraman Istanbul Technical University.

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

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  1. The Strandja arc: anatomy of collision after long-lived arc parallel tectonic transport Boris Natal’in, Gursel Sunal, and Erkan Toraman Istanbul Technical University

  2. 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

  3. Late Carboniferous-early Permian kinematics of Eurasia

  4. Early Permian-Triassic kinematics of Eurasia

  5. 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?

  6. 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

  7. Tectonic setting of the Strandja massif

  8. cover basement 290 Ma 312 Ma 315 Ma 257 Ma

  9. Fabric of the Permian metagranites

  10. Permian granites in the Strandja/Balkan zone

  11. 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.

  12. Inherited ages • Long-lasted magmatic activity • There are no inherited zircons in the Permian granites

  13. 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.

  14. Negative anomaly of Nb - subduction zone component

  15. 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 Regional correlations Gondwanian blocks: Menderes massif - 570-520 Ma orthogneisses - 635-605 Ma inherited ages Strandja is a part of the Scytho-Turanian orogenic system

  16. Structural geology • D1 – Pre-Permian deformation • D2 – middle Jurassic-early Cretaceous deformation • D3 – pre-late Cretaceous

  17. Structural column is overturned basement cover cover basement • Moderate southern dips of the S2 foliation • Steep dips of bedding • Increase of metamorphism to the south

  18. L2 lineation

  19. Orientation of the L2 lineation

  20. Sg2 foliation indicates the latest top-to-north motions

  21. 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)

  22. 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.

  23. 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).

  24. 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.

  25. 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

  26. 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

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