Transcript 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
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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
Terrane Map:
Nokleberg et
al, 1998
Major collaborative effort to
compile geology of NE Russian
Widely accessible database
Progress: Pre-Late Cretaceous
Convergent Margin evolution
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Laboratory of Tectonics of Oceanic
and Perioceanic zones (Sokolov)
• Pekul’ney Range
• Koryak Highlands
• Taigonos Peninsula
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Transform-margin evolution in
Primoriye (Khanchuk)
Outline of Progress
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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
Modern extent of the Uda-Murgal
Arc
Late Jurassic –
Early Cretaceous
Margin
•Alaska-Aleutian or
Kamchatka-Kurile margin
analog
•Continental arc grades
offshore to island arc
Pekul’ney Segment
Island arc separated by back arc basin
Penzhina Segment
Island arc built on continental crust
Taigonos Segment
Island arc built on continental crust
Major contribution  understanding
character of subducting plate(s) via
multidisciplinary analysis of
accreted material
Cape Povorotniy
Accretionary Complex
•Basalt-chert associations
•Island Arc Volcanic unit
•Melange unit
Accreted Complexes are:
A record (relict fragments) of plate(s)
of the Pacific that are interacting with
the Asian continental margin.
34.4 ± 4.3 ºN
28.0 ± 3.5 ºN
These fragments carry rich
information regarding:
1)Pacific paleogeography
(biostratigraphy)
2)Plate boundaries (convergent,
divergent)
3)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
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.
Our study of the Mesozoic and Cenozoic tectonic
structures and rock complexes in the Northwest
Pacific Rim that took into account the Californiatype margin allowed us to establish the following
indications of the transform-margin regime:
1. Strike-slip faulting along the plate boundaries
occurring in the time interval under consideration.
2. 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.
3. 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.
Okhotsk-Chukotka Volcanic Belt
Okhotsk Chukotka Volcanic Belt
Outline of Progress
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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
Recent Analog Models
Back arc extension recognized as a important
process for decades….
Asymmetric back-arc spreading model
Schellart et al. (2003)
Existing models for the origin of the
Okhotsk Sea Basement
Okhotomorsk
Parfenov and Natalin, 1977
Oceanic Plateau
Bogdanov and Dobretsov, 2002
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
Reconstruction of the Late
Cretaceous – Early Tertiary margin
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
Outline of Progress
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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)
Comparative evolution of the
Lesnovsk Highlands and Sredinniy Range:
…But Sredinniy exposes metamorphic rocks up to granulite facies,
Lesnaya group is sub greenschist facies
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 postcollisional exhumation
Comparative evolution of the
Lesnovsk Highlands and Sredinniy Range:
…But Sredinniy exposes metamorphic rocks up to granulite facies,
Lesnaya group is sub greenschist facies
Simplified geologic map of the
Sredinniy Range
Kolpakova Gneiss: migmatite
Accumulation of protoliths
Arc-obduction and burial of the NE Russian margin
Outline of Progress
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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)
Cenozoic Geodynamic Associations of Kamchatka Peninsula
Cross-section of rapid anomalies along the Kurils-Kamchatka
subduction zone profile (according to Gordeyev and others.)
Paleogeodynamic scheme
of the Early Miocene
Northwest Pacific
(magnetic anomaly 6)
(according to Silvestrov,
1998, with add-ins)
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.
Outline of Progress
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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
Workshop objective
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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.
Discussion objectives
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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.
Discussion objectives
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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
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Origin of basement
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Time-space patterns of extensional basin formation and
strike-slip faulting
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Role of Pacific plate roll-back, strike-slip modification, and
Asian extrusion
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If the Sea of Okhotsk is a microplate, when did it achieve
the microplate character?
Discussion objectives
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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)