Evolution of the Pacific Margin: Progress and Future

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Evolution of the Pacific Margin Progress and
Future

• Jeremy Hourigan, Yale University
• Sergei D. Sokolov, GIN-RAS Moscow
• Aleksandr I. Khanchuk, FEGI-RAS, Vladivostok

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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

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Terrane Map Nokleberg et al, 1998
Major collaborative effort to compile geology of
NE Russian Widely accessible database
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Progress Pre-Late Cretaceous Convergent Margin
evolution

• Laboratory of Tectonics of Oceanic and
  Perioceanic zones (Sokolov)
• Pekulney Range
• Koryak Highlands
• Taigonos Peninsula
• Transform-margin evolution in Primoriye
  (Khanchuk)

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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

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Modern extent of the Uda-Murgal Arc
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• Late Jurassic
• Early Cretaceous Margin
• Alaska-Aleutian or Kamchatka-Kurile margin analog
• Continental arc grades offshore to island arc

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Pekulney Segment Island arc separated by back
arc basin
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Penzhina Segment Island arc built on continental
crust
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Taigonos Segment Island arc built on continental
crust
Major contribution ? understanding character of
subducting plate(s) via multidisciplinary
analysis of accreted material
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• Cape Povorotniy
• Accretionary Complex
• Basalt-chert associations
• Island Arc Volcanic unit
• Melange unit

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• 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
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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.
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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
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• 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. 

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Okhotsk-Chukotka Volcanic Belt
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Okhotsk Chukotka Volcanic Belt
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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

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Recent Analog Models
Back arc extension recognized as a
important process for decades. Asymmetric
back-arc spreading model Schellart et al. (2003)
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Existing models for the origin of the Okhotsk Sea
Basement
Okhotomorsk
Oceanic Plateau
Bogdanov and Dobretsov, 2002
Parfenov and Natalin, 1977
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Structure of the Exterior OCVB

• So flat itll 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

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Reconstruction of the Late Cretaceous Early
Tertiary margin
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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

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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

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• 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)

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Comparative evolution of the Lesnovsk Highlands
and Sredinniy Range
But Sredinniy exposes metamorphic rocks up to
granulite facies, Lesnaya group is sub
greenschist facies
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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
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Comparative evolution of the Lesnovsk Highlands
and Sredinniy Range
But Sredinniy exposes metamorphic rocks up to
granulite facies, Lesnaya group is sub
greenschist facies
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Simplified geologic map of the Sredinniy Range
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Kolpakova Gneiss migmatite
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Accumulation of protoliths
Arc-obduction and burial of the NE Russian margin
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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)

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Cenozoic Geodynamic Associations of Kamchatka
Peninsula
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Cross-section of rapid anomalies along the
Kurils-Kamchatka subduction zone profile
(according to Gordeyev and others.)
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Paleogeodynamic scheme of the Early Miocene
Northwest Pacific (magnetic anomaly 6) (according
to Silvestrov, 1998, with add-ins)
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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.  
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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

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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.

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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.

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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?

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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)