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Evolution of the Pacific Margin: Progress and Future

Evolution of the Pacific Margin: Progress and Future. Jeremy Hourigan, Yale University Sergei D. Sokolov, GIN-RAS Moscow Aleksandr I. Khanchuk, FEGI-RAS, Vladivostok. Outline of Progress. Pre-Late Cretaceous Pacific Convergent Margin Sea of Okhotsk Olyutorsky Arc-Collision zone, Kamchatka

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Evolution of the Pacific Margin: Progress and Future

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  1. Evolution of the Pacific Margin: Progress and Future Jeremy Hourigan, Yale University Sergei D. Sokolov, GIN-RAS Moscow Aleksandr I. Khanchuk, FEGI-RAS, Vladivostok

  2. Outline of Progress • Pre-Late Cretaceous Pacific Convergent Margin • Sea of Okhotsk • Olyutorsky Arc-Collision zone, Kamchatka • Neotectonics - upper crustal response to plate margin processes • Geophysics - structure of the modern subduction zone

  3. Terrane Map:Nokleberg et al, 1998 Major collaborative effort to compile geology of NE Russian Widely accessible database

  4. Progress: Pre-Late Cretaceous Convergent Margin evolution • Laboratory of Tectonics of Oceanic and Perioceanic zones (Sokolov) • Pekul’ney Range • Koryak Highlands • Taigonos Peninsula • Transform-margin evolution in Primoriye (Khanchuk)

  5. Outline of Progress • Uda-Murgal Arc evolution • Improved understanding of Pacific plate geometry and kinematics from the record far-traveled material in accretionary prism (geochemistry, radiolarian stratigraphy, and paleomagnetic) • Tectonic reconstruction of Pre-mid Cretaceous NE Russian Margin

  6. Modern extent of the Uda-Murgal Arc

  7. Late Jurassic – • Early Cretaceous Margin • Alaska-Aleutian or Kamchatka-Kurile margin analog • Continental arc grades offshore to island arc

  8. Pekul’ney Segment Island arc separated by back arc basin

  9. Penzhina Segment Island arc built on continental crust

  10. Taigonos Segment Island arc built on continental crust Major contribution  understanding character of subducting plate(s) via multidisciplinary analysis of accreted material

  11. Cape Povorotniy • Accretionary Complex • Basalt-chert associations • Island Arc Volcanic unit • Melange unit

  12. Accreted Complexes are: • A record (relict fragments) of plate(s) of the Pacific that are interacting with the Asian continental margin. • These fragments carry rich information regarding: • Pacific paleogeography (biostratigraphy) • Plate boundaries (convergent, divergent) • Terrane transport magnitude (paleomagnetism, radiolarian stratigraphy) • Data on the origin and transport history of accreted material complemented by studies within the magmatic belt (geochronologic, geochemical and structural) provide a better understanding of NE Russian arc systems 34.4 ± 4.3 ºN 28.0 ± 3.5 ºN

  13. Extension of transform margins takes about 8% of the total length of the current continental margins that makes this type of plate boundaries important. However, all the geodynamic reconstructions that have been published until presently use the subduction model for all the boundaries between oceanic and continental plates, even those made for the areas where shifting of an oceanic plate at the sharp angle or parallel to an adjacent continental margin is suggested. This is obviously due to the lack of criteria for distinguishing a transform-margin setting among others occurred during the geological history.

  14. Our study of the Mesozoic and Cenozoic tectonic structures and rock complexes in the Northwest Pacific Rim that took into account the California-type margin allowed us to establish the following indications of the transform-margin regime:

  15. Strike-slip faulting along the plate boundaries occurring in the time interval under consideration. • Formation of basins with avalanche-type sedimentation of arkosic turbidites along plate boundary. This turbidite is distinguished from those of passive continental margins by that the subductionary rock complexes laterally replace them. Well-known strike-slip basins filled with terrigenous deposits associated with volcanics are characteristic of the continental parts of transform margins. • Volcanic rocks associated with the strike-slip basins are distributed very irregularly and combine geochemical characteristics of the subductionary, intraplate and, where and when a spreading center submerges beneath the transform margin, MORB sources.

  16. Okhotsk-Chukotka Volcanic Belt

  17. Okhotsk Chukotka Volcanic Belt

  18. Outline of Progress • Sea of Okhotsk • Sredinniy Range (eastern edge of Okhotsk Sea microplate?) • Seasat gravity dataset • Analog modeling asymmetric back arc extension • S-wave tomography of sub-Okhotsk mantle • Thermochronologic constraints for extension in the Magadan Basin

  19. Recent Analog Models Back arc extension recognized as a important process for decades…. Asymmetric back-arc spreading model Schellart et al. (2003)

  20. Existing models for the origin of the Okhotsk Sea Basement Okhotomorsk Oceanic Plateau Parfenov and Natalin, 1977 Bogdanov and Dobretsov, 2002

  21. Structure of the Exterior OCVB • So flat it’ll drive you to drink • Dips of rhyolite and basalt units generally less than 5 degrees • Volcanic section preserved in its entirety – only minor fluvial incision

  22. Reconstruction of the Late Cretaceous – Early Tertiary margin

  23. Surface Wave Diffraction Tomography • Prominent back-arc low-velocity anomaly typical of all back-arc in the western Pacific • Thermal age of the mantle can be calculated (based on T-dependence of mantle velocity and age dependence of Temp.) • Thermal age of the mantle beneath the Sea of Okhotsk is Eocene to Miocene

  24. Outline of Progress • Olyutorsky arc-continent collision zone • New timing constraints for arc-continent collision (Soloviev, Garver and Brandon) • High-grade roots of the Collision zone in the Sredinniy Range

  25. Arc-continent collision between Late K – Paleocene Olyutorsky Arc and the northeast Russian continental margin • Timing constrained by fission-track grain-age stratigraphy and biostratigraphy from marginal sandstone units in the lower plate • Timing estimates: 55 – 45 Ma • Cross-cutting granite and overlapping Kinkil volcanic rocks of the West Kamchatka Belt: 45 Ma (U/Pb zircon TIMS, Garver, 2001)

  26. Comparative evolution of the Lesnovsk Highlands and Sredinniy Range: …But Sredinniy exposes metamorphic rocks up to granulite facies, Lesnaya group is sub greenschist facies

  27. Lesnovsk Highlands Late K upper plate sediments (radiolaria, Inoceramus) Late K – Eocene lower plate sediments (Detrital zircon FT, nanofossil) Stitching intrusion and overlapping volcanic rocks - 45 ± 1 Ma (U/Pb zircon) Partially resent AFT  insignificant post-collisional exhumation

  28. Comparative evolution of the Lesnovsk Highlands and Sredinniy Range: …But Sredinniy exposes metamorphic rocks up to granulite facies, Lesnaya group is sub greenschist facies

  29. Simplified geologic map of the Sredinniy Range

  30. Kolpakova Gneiss: migmatite

  31. Accumulation of protoliths Arc-obduction and burial of the NE Russian margin

  32. Outline of Progress • Neotectonics • Tephrachronologic, marine terrace record of vertical motion along coastal Kamchatka (Bourgeois group) • Accretion history of Cape Terranes (Mann and co-workers; Gaedicke and others)

  33. Cenozoic Geodynamic Associations of Kamchatka Peninsula

  34. Cross-section of rapid anomalies along the Kurils-Kamchatka subduction zone profile (according to Gordeyev and others.)

  35. Paleogeodynamic scheme of the Early Miocene Northwest Pacific (magnetic anomaly 6) (according to Silvestrov, 1998, with add-ins)

  36. The Mesozoic-Cenozoic development of the Northwest Pacific margins occurred as alternation of episodes while either subduction or transform geodynamic regime predominated. Predomination of one of the two regimes was controlled by system of motions between the plates adjacent to the Eurasian plate, as well as mutual orientation of the Eurasian plate edges at the location studied.

  37. Outline of Progress • Geophysics – Modern subduction zone structure • SEKS experiment (Side-Edge of the Kamchatka Slab) • Crustal Structure of Kamchatka and Mainland Russia • Mantle velocity structure beneath the Sea of Okhotsk

  38. Workshop objective • Establish links between geodetic, neotectonic, structural, thermochronologic, and geophysical disciplines to understand the evolution of the Pacific margin at a range of time and length scales.

  39. Discussion objectives • Establish links between geodetic, neotectonic, structural, thermochronologic, and geophysical disciplines to understand the evolution of the Pacific margin at a range of time and length scales  cross-disciplinary approach.

  40. Discussion objectives • The southern continuation  Understanding linkages with Mongol-Okhotsk Belt and Sikhote-Alin Margin • Radiation of angiosperms – climatic and paleobotanical implications (EARTHTIME Iniative) The Sea of Okhotsk • Origin of basement • Time-space patterns of extensional basin formation and strike-slip faulting • Role of Pacific plate roll-back, strike-slip modification, and Asian extrusion • If the Sea of Okhotsk is a microplate, when did it achieve the microplate character?

  41. Discussion objectives • Kamchatka • Cross disciplinary projects that address the evolution of the Aleutian Kamchatka junction • Evolution of high grade metamorphic rocks in a collage of low-grade accreted terranes (Sredinniy, Ganal and Khavyven Ranges)

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