Paleomagnetic timing of Mesozoic Mongol-Okhotsk Ocean closure by

1. EGU General Assembly 2012 – Vienna, Austria, April 22-27, 2012 Paleomagnetic timing of Mesozoic Mongol-Okhotsk Ocean closure by J.P. Cogné1, D. Gapais2, Y. Daoudene2 and V.A. Kravchinsky3 1Université Paris Diderot, IPGP, UMR CNRS 7154, 75238 Paris Cedex 05, France 2Université de Rennes 1, Géosciences Rennes, UMR CNRS 6118, 35042 Rennes Cedex, France 3University of Alberta, Edmonton, AB, T6G2J1, Canada

3. Mongol-Okhotsk foldbelt Geological background: - Occurrence of hyperbasites, ophiolites, intrusions of gabbro-tonalites and plagiogranites comparable with island-arc granitoïds... remains of a Paleozoic ocean separating Siberia in the north from Amuria (or Mongolia) in the south. - Younging ages of felsic intrusives all along the suture, from late Carboniferous in the west, to early Cretaceous in the east.. suggests a progressive, scissor-like, closure of this ocean... Zonenshain et al. (1976, 1990), Kuzmin & Filipova (1979), Parfenov (1984), Sorokin (1992)....

5. 8 Permo-Carboniferous (C2-P2) poles 9 Jurassic (J2-3) poles 13 Early Cretaceous (K1) poles

6. 1. Late Paleozoic (data)

7. 1. Late Paleozoic 1. Late Paleozoic (data)

8. 1. Late Paleozoic (palaeolatitudes)

9. 1. Late Paleozoic (data)

10. 1. Late Paleozoic 1. Late Paleozoic (data)

11. 1. Late Paleozoic (palaeolatitudes)

12. 1. Late Paleozoic (palaeolatitudes)

13. 1. Late Paleozoic (palaeolatitudes)

14. 1. Late Paleozoic (rotations - 1)

15. 1. Late Paleozoic (rotations - 1)

16. 1. Late Paleozoic (rotations - 1)

17. 1. Late Paleozoic (rotations - 2) local tectonic rotations due to early Cretaceous MO closure and/or Cenozoic India collision..?

18. 2. Middle-Late Jurassic (data)

19. 2. Middle-Late Jurassic (data)

20. 2. Middle-Late Jurassic (average Siberian poles) allowing some poles to rotate about their site location

21. 2. Middle-Late Jurassic (data)

22. 2. Middle-Late Jurassic (average Mongolian poles) allowing some poles to rotate about their site location

23. 2. Middle-Late Jurassic (Palaeolatitudes)

24. 2. Middle-Late Jurassic (Palaeolatitudes)

25. 2. Middle-Late Jurassic (rotations)

26. 2. Middle-Late Jurassic (rotations)

27. 3. Early Cretaceous (data)

28. 3. Early Cretaceous (data)

29. 3. Early Cretaceous (palaeolatitudes)

30. 3. Early Cretaceous (data)

31. 3. Early Cretaceous (palaeolatitudes)

32. 3. Early Cretaceous (palaeolatitudes)

33. 3. Early Cretaceous (mean paleopoles) allowing some poles to rotate about their site location

34. 3. Early Cretaceous (mean paleopoles) allowing some poles to rotate about their site location

35. 3. Early Cretaceous (mean paleopoles)

36. 4. Age of MO ocean closure: Latitude evolution of a reference point currently located on the Mongol-Okhotsk suture

37. 4. Age of MO ocean closure: Latitude evolution of a reference point currently located on the Mongol-Okhotsk suture at {51°N, 112°E} after paleopoles from: North of the suture – (Siberia) South of the suture – (Amuria)

38. 4. Age of MO ocean closure: Latitude evolution of a reference point currently located on the Mongol-Okhotsk suture at {51°N, 112°E} Not before 150 Ma... after paleopoles from: North of the suture – (Siberia) South of the suture – (Amuria) and APWP's for: Eurasia(Besse & Courtillot, 2002) NCB(Gilder & Courtillot, 1997)

39. 4. Age of MO ocean closure: Latitude evolution of a reference point currently located on the Mongol-Okhotsk suture at {51°N, 112°E} ... rather at ~130 Ma ... at ~130 Ma or somewhat later ?... after paleopoles from: North of the suture – (Siberia) South of the suture – (Amuria) and APWP's for: Eurasia(Besse & Courtillot, 2002) NCB(Gilder & Courtillot, 1997) ?

40. 5. Evaluation of closure velocity Middle-Late Jurassic Permo-Carboniferous Early Cretaceous

41. 5. Evaluation of closure velocity: Latitude evolution of a reference point currently located on the Mongol-Okhotsk suture at {51°N, 112°E} based on actual paleomagnetic data from both sides of the suture...

42. 5. Evaluation of closure velocity: Latitude evolution of a reference point currently located on the Mongol-Okhotsk suture at {51°N, 112°E} 40 to 75 myrs 33° to 48° a 33° to 48° latitudinal convergence in 40 to 75 myrs implies a relative velocity of: 4.9 to 13.3 cm/yr or = 9.1 ± 4.2 cm/yr

43. EGU General Assembly 2012 – Vienna, Austria, April 22-27, 2012 Conclusions: Paleomagnetic poles obtained from both sides of the Mongol-Okhotsk geosuture unambiguously reveal that: 1. A wide ocean separated Siberia craton from Asian terranes in the Mesozoic. 2. This ocean was as large as more than 5000 km in latitude in the late Permian, and more than 3000 km in the middle-late Jurassic, at a present-day longitude of ~110° E. 3. Closure of this ocean took place in a scissor-like manner, beginning at the permo-triassic boundary, and was achieved no later (but not earlier, as well..!) than 130 to 110 Ma, by the beginning of the Cretaceous. 4. This history indeed casts some questions about its relationships to ~N/S crustal extension in Mongolia and North China, which begins as early as ~130 Ma.... (see next talks..!). Paleomagnetic timing of Mesozoic Mongol-Okhotsk Ocean closure. J.P. Cogné, D. Gapais, Y. Daoudene and V.A. Kravchinsky.