RESULTS FROM PRIOR SUPPORT
Project Title: Collaborative Research: Crustal Evolution of the Bering Shelf-Chukchi Sea (Stanford P.I.'s
Simon Klemperer and Elizabeth Miller)
Dates: 03/01/94-8/31/97
Amount awarded: $903,000
Award Number: Continental Dynamics Division NSF EAR 9317087
The slightly submerged Bering Shelf-Chukchi Sea region comprises over 50% of the total U.S.
continental shelf area and forms a broad isthmus of continental crust connecting the North American and
Asian continents (Fig. 1). Although harsh climate and remoteness make this a difficult area to work in,
there has been much interest in the stratigraphic framework and evolution of sedimentary basins on this
shelf because of substantial oil and gas reserves in the region. However, the overall geologic and tectonic
evolution of the continental crust beneath this region, the continuity of geologic structures between North
America and Russia, and the plate-tectonic origin of the Arctic Ocean remain poorly known.
This project was carried out as part of a multidisciplinary, multi-institutional, international
collaborative effort with Russian scientists with the goal of better understanding the evolution of
continental crust beneath this region and thus addressing the questions above. Our efforts involved the
collection of two parallel seismic reflection profiles that imaged for the first time the deep crust and
mantle beneath the region, forming a crustal transect across the entire width of the region of submerged
continental crust connecting the North American and Asian continents. In addition, two full field seasons
of work were carried out which took ten separate field parties to points in northeast Russia and
westernmost Alaska. These field efforts were undertaken in order to place constraints on the geologic
interpretation of the seismic data. The project was similar in scope and impact to the U.S.G.S. TransAlaska Crustal Transect (TACT) in eastern Alaska. Together, the two efforts have provided the scientific
community with a wealth of new data and fresh insight into the make-up of the Alaskan part of the North
American continent and its westward link to the Arctic Russian part of the Asian continent. Data
collection went as planned, and the project was, on all counts, highly successful.
Our results, together with timely contributions by other workers in the region are published in
"Tectonic Evolution of the Bering Shelf-Chukchi Sea and Adjacent Landmasses", Geological Society of
America Special Paper 360. This volume focuses on the integration of the new data sets, assessment of
their relevance for the evolution of continental crust beneath the Bering-Chukchi region, the evidence for
continuity of structures and stratigraphy between the Arctic portion of the Asian and North American
continents and the implications of these data for the plate tectonic evolution of the Arctic. From the
contents of this volume, it is clear that this project provided an excellent opportunity for quite a number of
institutions and working groups to participate in the data collection and interpretation phases of the
original project. It should be noted that P.I. Jaime Toro of West Virginia University was a senior level
graduate student and post-doc at Stanford while The Bering Strait Project was conceived and carried out.
Our most interesting and exciting discoveries are listed briefly below:
1. The northern part of the seismic line images what appears to be intact Precambrian crust and its
overlying sedimentary cover, which possibly includes Late Precambrian as well as Paleozoic and
Mesozoic stratified sequences. This segment of the Chukchi Shelf may be representative of the crustal
fragment that rifted away from the Canadian Arctic margin during opening of the Canada Basin, one of
the main ocean basins of the Arctic Ocean. It is the first time the deeper part of this crust has been
imaged, and the data provide important constraints on plate tectonic reconstruction of the Arctic.
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2. The seismic data and our field data provide possible answers to why the Brooks Range, the northern
terminus of the North American Cordillera, diminishes in elevation and disappears westward towards
Russia. Tertiary-age extensional or transtensional basins provide evidence for thinning of the oncethickened crust of the Bering Shelf, and an older extensional event of Late Cretaceous age (described
below) also appears to have helped reduce the region to sea-level again.
3. From the Seward Peninsula to Saint Lawrence Island, the crust appears to have been extensively
modified by magmatism and crustal flow, possibly accompanied by extension. The details of this history
of magmatism help constrain the evolution of this crust through time (e.g. Amato and Wright, 1997).
Xenolith suites collected by K. Wirth as part of a supplemental NSF Research Opportunity Award
provide important insight into the age and nature of this crust and suggest that the effects of this magmatic
event are considerably more important with depth in the crust. Culminations of high-grade metamorphic
rocks, or gneiss domes, appear to be the consequence of this magmatic event and may have resulted from
flow of the crust while at elevated temperatures.
4. The seismic data indicate a rise in Moho depths beneath the basins of the Bering Shelf edge, indicating
that faulting or stretching related to basin development involves the entire crust. The data have
implications for why and how these basins formed, apparently shortly after the active margin jumped
southward from the Bering Shelf edge to the Aleutians.
5. Our new data indicate that both older and younger Paleozoic and Mesozoic stratigraphy and structure,
as well as superimposed Cretaceous structures and events, carry across the Bering Strait from Alaska to
Russia. This makes it highly improbable that a plate boundary or suture exists between Alaska and
Chukotka. Our evolving geological database is one of our more important contributions to understanding
the plate tectonic reconstructions of the Arctic.
Publications resulting from this award: The Stanford group produced 15 published papers, including
GSA Special Paper 360. In addition, 3 Ph.D. and 1 M.S. theses were produced at Stanford. See the
complete list of publications in the References section of this proposal.
Women and minorities involved: 1 female professor, 2 female graduate students in geophysics, 1 male
minority graduate student and 1 female Russian scientist; several undergraduate students at McCalester
University, Minnesota, under the direction of Karl Wirth (RUI supplement).
Collaborative Research: Does the Brooks Range Fold and Thrust Belt
Continue Into Arctic Russia?
Broader Scientific Context
We propose to improve geologic constraints on plate tectonic models of the Arctic region by
studying the tectonic evolution of Wrangel Island and coastal Chukotka, Russia. These two areas
serve as windows into the immense region of continental crust beneath the East Siberian Shelf which
comprises a large part of the Arctic Alaska-Chukotka plate. Our goals are 1) to establish with greater
certainty the kinematics and timing of Mesozoic deformation on Wrangel Island and northern
Chukotka and 2) to compare both the structural history and the stratigraphic successions of Wrangel
Island and Chukotka to those of the Brooks Range and North Slope Alaska. These studies will have
far-reaching implications because the Arctic Alaska-Chukotka plate plays a pivotal role in the mode
of formation of the Amerasian Basin of the Arctic Ocean. The Arctic Ocean Basin and surrounding
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continental shelves remain one of the least studied parts of the earth's crust. Two major sub-basins
exist, the Eurasian and Amerasian basins (Fig. 1). Well-developed magnetic anomalies in the
Eurasian Basin can be used to reconstruct the early Tertiary to recent sea floor spreading related to
the Gakkel Ridge, which is the extension of the North Atlantic spreading ridge into the Arctic (e.g.
Jackson and Gunnarson, 1990) (Fig. 1). In contrast, the origin of the Amerasian Basin, which
includes the Amerasian side of the Lomonov Ridge, the Makarov Basin, the Alpha-Mendeleev
Ridge, the Canada Basin and the Chukchi Borderland, is much more poorly understood (Fig. 2).
Despite extensive satellite and airborne magnetic and gravity surveys, the history of the Amerasian
Basin with its complex ridges, basins, and margins is still unknown. To compound the problem, this
basin is fringed on its south side by the immense East Siberian continental shelf, which is also
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virtually unexplored. Current thinking on the origin of the Amerasia Basin hinges on the existence of
the Arctic Alaska-Chukotka microplate. The Arctic Alaska-Chukotka plate includes all of northern
Alaska and Chukotka (a portion of NE Russia) as well as the offshore shelfal regions including
Wrangel Island and the East Siberia Shelf (Fig. 1).
The preferred current working model for the formation of the Amerasian Basin calls upon
rotational opening by seafloor spreading about a pole near the McKenzie Delta which restores the
Arctic Alaska-Chukotka plate to a position alongside the Canadian Arctic margin (Figs. 2 and 3)
(Grantz et al., 1990; Lawver et al., 2002). This model best satisfies all stratigraphic and structural
data from the once-adjacent parts of Alaska and Canada (Fig. 2b) and is compatible with a set of
poorly developed and low amplitude magnetic anomalies within the Canada Basin itself (see
discussion in Grantz et al., 1990, 1994). Although there is wide variation in the way the geometry of
Arctic Alaska-Chukotka has been defined by different workers (as illustrated in figures 2 and 3), the
rotational model dictates 1) that the margin of the Amerasian Basin along the Lomonosov Ridge is a
right-lateral strike slip fault, and 2) that the Makarov Basin is the same age as the Canada Basin
(Lawver et al., 2002). These ideas in turn imply that the other major intrabasinal highs, such as the
Alpha-Mendeleev Ridge, are younger features, perhaps a hot-spot track (e.g. Forsyth and others,
1986). Discussions during this summer's NSF-sponsored workshop on the Amerasian Basin
(http://www.geo-prose.com/amerasian/info.html) emphasized how little is actually known about the
Amerasian Basin and how conflicting the interpretations are for the origin of these various parts of
the basin. Final discussions underscored the need, despite logistic difficulty and cost, for additional
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research to understand the origin and evolution of the various elements of the Amerasian Basin. This
will require detailed geophysical surveys and the establishment of sites for ocean drilling in order to
conclusively determine the age of basement and its overlying sedimentary cover. These conclusions
echoed recommendations made more than ten years ago by the 1991 National Academy of Science's
"Opportunities and Priorities in Arctic Geoscience" (//www.nap.edu/openbook/0309044855/html).
Geologists at the Amerasian Basin Workshop pointed out that, although several studies have
compared the stratigraphic and structural history of the northern Alaska to the Canadian Arctic (i.e.
Grantz et., 1979; Embry and Dixon, 1990; Sherwood, 1994; Toro et al., 2004), very little data is
available from the Russian portion of the Arctic Alaska-Chukotka plate to permit similar
correlations. It is clear that a very important step towards placing constraints on models for the
origin and evolution of the Amerasian Basin is to study key localities in Arctic Russia in order to
establish whether the geological history of these areas is compatible with what is known about the
North American portion of Arctic Alaska-Chukotka and whether there are stratigraphic matches
between the conjugate margins as predicted by the plate models.
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Questions concerning the structural integrity of the Arctic Alaska-Chukotka plate
The Brooks Range fold-and-thrust belt and its foredeep to the north, the North Slope Basin,
are the main structural elements of the Alaskan part of the Arctic Alaska-Chukotka plate (Fig. 4).
Deformation in the Brooks Range began with emplacement of ophiolites onto the passive margin of
Arctic Alaska in the Middle Jurassic and culminated with large-magnitude, thin-skinned thrust
faulting in the Early Cretaceous (Moore et al.,1994). Contractile structures are overprinted by a
strong extension-related metamorphic and deformational event along the southern flank of the
Brooks Range dated as 120-90 Ma (Miller and Hudson, 1991; Little et al., 1994; and Toro et al.,
2002). Although deformation in the Brooks Range began prior to the inferred time of opening of the
Canada Basin, the most intense shortening and maximum subsidence rates in the foredeep coincide
with the proposed timing of rotation of Arctic Alaska-Chukotka (135-120 Ma) (Grantz et al., 1990,
1994; Cole et al., 1997; Lawver et al., 2002). Episodic compressional deformation in the Brooks
Range resumed in the Late Cretaceous (summary in Moore et al., 2002) but these younger contractile
structures, related to far-field effects of Pacific margin convergence, die out westward and do not
occur in the westernmost Brooks Range (e.g. O'Sullivan et al., 1997).
In Chukotka, a broad belt of contractile structures, known as the Chukotka fold-belt, involves
rocks as young as Jurassic (Baranov, 1996). However, the exact timing of deformation is not known
as reported stratigraphic and cross-cutting igneous relations are conflicting (discussion in Miller et
al., 2002). Thus this fold belt may, or may not, be coeval with Brooks Range deformation.
Establishing the time relationship between these two fold-and-thrust belts will place constraints on
the timing, nature, and progression of internal deformation of the Arctic Alaska-Chukotka plate.
Although the match of the Alaskan North Slope margin to Arctic Canada proposed by the rotational
model is straightforward, the dimensions of the Chukotka portion of the plate require internal
deformation in order to restore it to the Canadian Arctic margin by simple rotation. Current plate
models use considerable freedom in reshaping Chukotka without taking into consideration the
structural history of the region (since it is not well-known). For example, Grantz et al. (1990b)
eliminated about 50% of the East Siberian Shelf in his restoration (Fig. 2). In the most updated
model, Lawver et al. (2002) arbitrarily sever the western-most part of Chukotka even though both
geological and geophysical data suggest that the plate continues to the west (Fig. 3).
Wrangel Island is significant because it offers the best place to test the continuity of
structures from Arctic Alaska into Chukotka. It is also one of the few existing windows into the
geology of the immense East Siberian Shelf. The structure of Wrangel Island has been interpreted as
a north-vergent fold-and-thrust belt involving late Proterozoic though Triassic rocks (Kos'ko et al.,
1993) (Fig. 5). Although the general geometry of structures (north-vergent, folds with axial plane
cleavage, low metamorphic grade) has been described by Kos'ko et al. (1993), the exact age of
folding and thrust faulting is constrained only as post-Triassic. The limited seismic data available
from the Chukchi Sea together with satellite gravity data hints that the structures on the island
connect to those in the Lisburne Hills of Alaska via a basement high known as the Herald Arch (Fig.
4) (Grantz et al. 1990b). In U.S. waters, where more complete seismic coverage exists (e.g. Grantz
and May, 1987; Klemperer et al., 2002) the Herald Arch is underlain by a major thrust fault. This
fault is inferred to extend to the north of Wrangel Island. This connection is significant because
recent work (Moore et al., 2002) has shown that thrusting in the Lisburne Hills took place in the
Early Cretaceous, simultaneously with the main episode of deformation in the Brooks Range orogen.
We propose to test this link by dating the timing of deformation on Wrangel Island by apatite fission
track and 40Ar/39Ar thermochronology, the same techniques employed successfully by Moore et al.
(2002).
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There are important differences in the structural geology of Wrangel Island compared to that
of Alaska that would argue against connecting the two belts of deformation. First, Wrangel Island
does not exhibit the thin-skinned style of deformation seen in the northern Brooks Range and the
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magnitude of shortening appears to be much lower (Fig. 5) (Kos'ko et al 1993). Secondly, no
foredeep basin has been identified in Chukotka. This may be a function of the lack of knowledge of
the geology of the northern part of the East Siberian Shelf, or it may point to fundamental differences
in the tectonic history of Chukotka relative to Arctic Alaska. Our thermochronologic work will shed
light on the thickness of stratigraphic section that has been stripped by erosion from Wrangel Island
which may suggest an equivalent basin in the unexplored off-shore region. Third, in Chukotka there
are no ophiolite nappes in a structural position comparable to those of the Brooks Range.
Late-Stage Structural Features Cutting the Arctic Alaska-Chukotka Plate
The Hope Basin, a major early Tertiary feature of extensional to transtensional origin
occupies the continental shelf between Wrangel Island, the Chukotka mainland, and the western tip
of Alaska (Fig. 4) (Tolson, 1987; Elswick et al., 2003). The extent of the basin is revealed by a
prominent low in the satellite gravity (Fig. 4). Seismic data from the U.S. portion of the basin shows
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that basin formation was controlled by large NW-trending normal faults. The linear mountain front
along the south side of Wrangel Island might be controlled by an east-west-trending normal fault
associated with the northern margin of the western extent of the Hope Basin. A secondary objective
of our research will be to examine evidence for these faults and to determine, via fission-track
thermochronology, whether Tertiary tectonics play a significant role in the evolution of the island.
Stratigraphic Framework of Wrangel Island and Chukotka
Basement
Depositional basement to Paleozoic sequences is known only with certainty from Wrangel
Island where it consists of deformed Late Proterozoic clastic and volcaniclastic rocks with lesser
volcanic and intrusive components (Wrangel Complex of Kos'ko et al., 1993) (Fig. 5). Intrusive
rocks yielded U-Pb ages of 699± 2 Ma and felsic volcanic rocks yielded an age of 633 Ma (Kos'ko et
al., 1993). Similar U-Pb ages are reported from orthogneisses in the Nome Group of the Seward
Peninsula and from the Schist Belt of the southern Brooks Range, Alaska (e.g. Patrick and
McCleland, 1995; Amato, 1996; Karl et al., 1989). K-Ar ages from the Wrangel Complex range from
575 to 115 Ma (Kos’ko et al., 1993). This wide scatter is probably the result of Late Proterozoic
metamorphism overprinted by one or more younger thermal events. In Alaska, Late Proterozoic
rocks are so highly deformed and metamorphosed that their stratigraphic relationship to overlying
Paleozoic rocks is unclear. Wrangel Island is perhaps the only location in the entire Arctic AlaskaChukotka plate where the history of these basement rocks can be studied in sufficient detail to make
informed correlations with other Neoproterozoic successions of the circum-Arctic. It is also the only
place where their structural relationship to the overlying Paleozoic sequence can be observed.
Paleozoic
The oldest fossiliferous units on Wrangel Island are Upper Silurian to Lower Devonian
shallow marine shelf carbonates and siliciclastic strata (700 m). These are only locally exposed and
their basal contact with basement has not been mapped (Fig. 5). Lower to Upper Devonian marginal
marine to marine shelf sandstone, conglomerate and slate (up to 1200 m) rest directly on the Wrangel
Complex in several locations. Conglomerates at the base of the section contain clasts of the
underlying basement that display deformational fabrics that pre-date the enclosing sediments. The
relations on Wrangel Island provide excellent documentation of a latest Proterozoic to earliest
Paleozoic orogenic event in a continental or volcanic arc setting (Kos'ko et al., 1993). Lower
Carboniferous strata rest disconformably on Devonian strata but are difficult to differentiate because
they are similar in composition. Non-marine to shallow marine siliciclastic sandstone, slate,
conglomerate, minor carbonate and gypsum are present (350 m). Exposures of mafic and felsic
volcanic rocks, most likely part of the Carboniferous succession, were noted by Kos'ko et al. (1993).
The lower to upper Carboniferous consists of 500-1000m of distinctive shallow marine fossiliferous
limestone, slate and argillite. Lower to Upper Permian strata (750 m) are platformal to basinal
limestone, siliciclastic rocks and slate. There is an upwards progression to basinal facies and by Late
Permian, the carbonate platform was drowned.
The Paleozoic stratigraphic succession of mainland Chukotka (Figs. 6, 7) is similar to that of
Wrangel Island, although the oldest rocks mapped are Devonian shallow marine clastics and
carbonates. These are unconformably overlain by Carboniferous to Permian calcareous siltstones
and shales (700m) (Fig. 7).
Triassic
The Triassic successions of Chukotka are 3-5 km thick, and consist mostly of slate, siliceous argillite
and fine- to medium-grained quartz-rich sandstone, deposited in a basinal environment (Fig. 7).
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Across many hundreds of kilometers in Chukotka, the basal contact of the Triassic is mapped as
conformable with underlying Permian or disconformable on Carboniferous strata (Figs. 6, 7). The
lower part of the Triassic is notable in that it contains abundant gabbro/diorite sills and dikes. These
yielded conventional K-Ar whole rock ages ranging from 250-190 Ma, but have not been dated by
more precise methods (Bychkov and Gorodinsky, 1992; Gelman, 1963; Ivanov and Milov, 1975;
discussion in Miller et al., 2002). The Triassic of Wrangel Island is lithologically similar to that of
the mainland but considerably thinner (800-1500m) and lacks the gabbro sills and dikes.
The Triassic of Chukotka and Wrangel contrasts with the thinner Triassic of Alaska's Brooks
Range and North Slope. Beneath the North Slope, Triassic deposits are mainly shelfal to non-marine
clastics with minor carbonates and are less than 600 m thick (Moore et al., 1994). These units are
very well known as they include both the principal sandstone reservoir in the Prudhoe Bay oil field
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and an important petroleum source rock (the Shublik Fm.). In the Brooks Range, Triassic deposits
are chert and black shale characteristic of a starved basin setting (Moore et al., 1994). These
differences between the Triassic of Alaska and Chukotka have not been reconciled in terms of a
coherent paleogeographic model. In particular, the exact time of formation and plate tectonic setting
of Triassic basin development in Chukotka remain unexplained.
Cretaceous magmatism
An immense belt of Jura?-Cretaceous plutons and volcanic rocks extends across most of
Chukotka (Gorodinski, 1980). In northern Chukotka this belt is represented by older, syn- to postfolding, compositionally heterogeneous plutons and dike swarms. Unconformably overlying,
gently-dipping silicic to mafic volcanic rocks and associated dikes of the Okhotsk-Chukotka belt are
younger. The age span, geochemistry, and tectonic affinity of the older plutonic rocks are not well
known. These data are of critical importance because they will help to date structural events in
Chukotka and will help determine the plate tectonic setting of this magmatism (i.e. mantle-derived
vs. crustal melts; subduction vs. hot-spot origin). The Okhotsk-Chukotka volcanic belt is generally
regarded as related to subduction along the Pacific plate boundary (Belyi, 1977a, 1977b, 1978). It is
important in the context of this proposal because it stitches the Arctic Alaska-Chukotka plate to the
rest of Northeast Russia (Fig. 1). New 40Ar/39Ar ages from the southern portion of the belt indicate
that the majority of the volcanic sequence was erupted between 85.5 ± 1.3 Ma and 73.6 ± 0.7 Ma
(Hourigan and Akinin, 2004). This age-range is 15 Ma younger than the Albian to Early
Cenomanian age range accepted in the Russian literature on the basis of fossil flora (i.e. Fig. 7).
Thus, carrying out modern geochronology and geochemistry on the older cross-cutting plutons and
the overlapping volcanic rocks in Chukotka will improve the constraints on both the timing of
deformation in Chukotka and the arrival of Chukotka to its present position.
Methodology
Dating regional folding and thrust-faulting
A wide spectrum of stratigraphic, geochronologic and thermochronologic tools are available
to help date structures and fabrics formed during specific deformational events. Of these,
stratigraphic and sedimentologic relations with fossil age control or cross-cutting relationships with
igneous rocks are the most robust, but in the absence of straightforward relations such as these, a
variety of radiometric dating techniques can date regional deformational events indirectly. These
methods include U-Pb dating of zircon and monazite for high grade rocks; 40Ar/39Ar dating of
hornblende, muscovite, biotite, and K-feldspar for intermediate to low-grade rocks; and fission-track
dating of apatite for low-temperature events. These techniques date the time a particular mineral
cooled below the temperature at which radioactive daughter isotopes are retained (closure
temperature). These ages can be used to set limits on the age deformation particularly when growth
of specific minerals can be linked to a particular event. Successful application of these
thermochronologic techniques requires a sampling strategy that takes advantage of the exposure of
different crustal levels across an orogen or map-scale structure and uses multiple mineral systems
with different closure temperatures . Good examples of previous studies by the PI's and their
collaborators that have used these different techniques to date deformation in western Alaska and the
Bering Strait region are those of Moore et al. (2002), Toro et al. (2002), Amato et al. (2002 ), and
Akinin and Calvert (2002). See the Facilities section for a description of the geochronological
laboratories available for this project.
In the area of our proposed field work in coastal Chukotka, sedimentary, volcanic, and
volcanoclastic units ranging from late Paleozoic to Late Cretaceous have been mapped. Their degree
of deformation will provide a good stratigraphic bracket for regional folding in the Chukotka
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foldbelt. In addition, cross-cutting granitic to gabbroic plutons and dikes have been mapped but
never dated. The cross-cutting relationships of these igneous rocks with structures is likely to
provide reliable control on the time-span of regional deformation. Igneous rocks will be dated with a
combination of U-Pb zircon and 40Ar/39Ar hornblende methods if appropriate. We will also examine
reported higher grade rocks and migmatites of the Velitkinai massif (Fig. 6) to determine if the there
is a link between the igneous-metamorphic fabrics and the regional deformation.
On Wrangel Island there are no stratigraphic relations that bracket deformation except that it
post-dates deposition of Triassic sediments which are involved in folding and thrusting (Fig. 5). In
addition, no cross-cutting intrusive rocks have been mapped, therefore we must rely entirely on
thermochronologic techniques. Apatite fission-track thermochronology is a method for
reconstructing the time-temperature history of rock samples within the temperature window of 60125°C (e.g. Dumitru, 2000). Assuming a nominal geothermal gradient of ~25°C/km, this
temperature window is equivalent to a depth window of ~2-5 km beneath the earth's surface. A
complete thermal history can be determined because fission tracks, are generated continuously, but
are erased rapidly near 125 degrees, and very slowly near 60°C. The length distribution of fission
tracks in a sample can be modeled to determine the possible cooling histories experienced by the
rock. On Wrangel Island, where 5-10 km of structural section is exposed due to the southward tilt of
units, the fission-track method can provide information on the timing of thrust burial and subsequent
erosional exhumation back towards the earth's surface. This approach, was successfully used by T.
Dumitru in the Lisburne Hills of Alaska (Moore et al., 2002) and will be applied again to our samples
from Chukotka and Wrangel Island. Dumitru's CV and the description of Stanford's fission-track
analytical facilities are included under Supplementary Documents and Analytical Facilities.
On the Chukotka mainland, appropriate samples collected from various parts of the
stratigraphic succession across regional anticlinal structures and dated with both fission track (at
shallow structural levels) and with 40Ar/39 Ar methods (at deeper levels) will provide good controls
on the age of deformation. On Wrangel Island, Paleozoic and Triassic rocks are described mostly as
slates. Rocks of this grade are difficult to date, but metamorphic basement rocks do have
metamorphic white micas (Kos'ko et al., 1993). The available K-Ar ages from the Wrangel Complex
range from Neoproterozoic to Early Cretaceous. We will use modern 40Ar/39Ar thermochronology on
metamorphic white micas (closure temperature 35050C, McDougall and Harrison, 1988) and
igneous K-feldspar in order to resolve the timing of the different thermal events. A carefully
designed step-heating experiment of a K-feldspar sample can reveal a complete thermal history for
the sample from above 400 to less than 200C because of the existence of multiple diffusion
domains in the mineral (Lovera et al., 1997).
Geochemistry and Geochrology of Igneous Rocks
A wide variety of dikes, sills, and intrusive bodies ranging from granite to gabbro have been
mapped in our target field areas of the Chukotka mainland (Fig. 6). There has been little or no
modern geochemistry or geochronology on any of these igneous rocks. Are the plutons of the
Chukotka fold belt related to mantle-derived magmatism? Are they related to subduction along the
South Anyui margin of the Arctic Alaska-Chukotka plate as implied by the plate reconstructions
shown in Figs. 2 and 3? Or are they related to the onshore continuation of the Alpha-Mendeleev
Ridge, a postulated Cretaceous hot-spot track (e.g. Lawver et al., 2002)? In order to answer these
questions we will carry out U-Pb zircon dating of the major intrusive bodies accessible from our
transects using the USGS/Stanford SHRIMP-RG. This work will be lead by our Russian collaborator
Dr. V. V. Akinin, who is an experienced petrologist (see Supplementary Documents). We will also
characterize the major and trace element composition of the Velitkinai granite massif and other
selected intrusive bodies, and investigate their Sm, Nd, Sr, and Pb isotopic composition by thermal
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ionization mass spectrometry to help determine source region characteristics for the magmas in order
to help constrain their tectonic setting.
Circum-Arctic Paleogeographic Correlations with the help of U-Pb geochronology
A more in depth geochronologic study of Neoproterozoic, Paleozoic, and Triassic strata of
Wrangel Island and Chukotka will provide a better basis for comparisons of the Russian part of the
Arctic Alaska-Chukotka plate to other circum-Arctic regions and will help to test whether Chukotka
was once connected to the Canadian margin. Work on this aspect of the project will be carried out
by Dr. Victoria Pease at no cost to NSF. She has experience working in the Russian Taymir, Nova
Zemlaya, and the Siberian Islands (see letter of support and interest in Supplementary Documents).
Field observations, together with U-Pb geochronology provides the best means of comparing the
history of basement rocks from these different places. In addition, dating of detrital zircon suites
from sedimentary rocks can provide information-rich data sets on the age and nature of source
regions for clastic rocks, thus allowing linkage of basins to a particular continental mass (e.g. North
America, Siberia, Eurasia).
Wrangel Island Field Work
Fieldwork on Wrangel Island will be carried out by members of the geologic team aboard the
Oden at no cost to NSF. Our first objective is to study the structural style of deformation in the
Triassic and Paleozoic part of the section which will involve measuring structural fabrics in the field
and determining single or multiple phases of deformation. Our second objective is to collect a suite
of samples for fission track apatite dating so that we can place good constraints on the age of folding
and thrusting on Wrangel Island. The rationale for this sampling transect is described under
methodology and several possible sample transect locations are shown on Fig. 5. The south dip of
units along the southern side of Wrangel Island affords the greatest structural relief: 5-10 km of
structural section are exposed over 10-20 km. About 15-20 samples will be collected across one of
these transects. The base of the Paleozoic stratigraphic section and the underlying Wrangel Complex
are described as containing various amounts of metamorphic white mica, which are appropriate
targets to sample for 40Ar/39Ar dating to complement the fission track dating. Our final objectives are
to collect Paleozoic sandstone and conglomerate for single-grain zircon provenance studies and
determine more certainly the deformational, metamorphic and intrusive history of the Wrangel
Complex, collecting samples that will provide data to match these rocks to other sequences along the
margins of the Amerasian Basin. This work will be carried out mainly by our Swedish colleagues.
Chukotka Field Work
During July and August of 2005, one of the P.I.’s (Toro) together with chief Russian
collaborator Dr. V. V. Akinin, and two graduate students will study two areas of the Arctic coast of
Chukotka making use of a Russian all-terrain track vehicle (Fig.7). They will first conduct a
structural and thermochronologic transect of about 100 km across the Sheiagskiy Range starting from
the town of Pevek to the Arctic coast (Fig. 7). Here, folded Devonian to Triassic clastic sedimentary
rocks are exposed and their deformational history can be studied. They will collect samples across
this transect for apatite fission track and 40Ar/39Ar dating. The apatite fission track analyses will help
constrain the history of cooling and erosion to help place limits on the timing of folding in the
Chukotka foldbelt. 40Ar/39Ar thermochronology, together with structural measurements and
petrographic studies, will help establish the age of metamorphism, its relationship to the plutons
exposed in the area, and whether it is syn-or post-folding or both. In the process of achieving these
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objectives, the basic stratigraphic units of this region will be described and sampled for fossils,
sedimentologic studies, and detrital zircon geochronology in order to better understand their
correlation to other sequences of this age across Chukotka, on Wrangel Island and in Alaska After
completing this work, Toro and Akinin will continue east to the large Velitkinai granitic massif in
order to study the extensive contact metamorphism described in the Russian literature, the higher
grade rocks and migmatites in the core of the massif, and key stratigraphic relationships between the
Late Cretaceous volcanic and volcaniclastic rocks of the Okhotsk-Chukotka belt and the underlying
deformed Devonian to Triassic strata. The Pevek Transect is designed to complement and augment
simultaneous helicopter-based work from the Swedish icebreaker Oden on Wrangel Island and to a
few points on the Chuktoka coastline.
Work Plan and Time Table
Approximate
Dates/Location
Personnel
Task
Year 1 March1, 2005-February 28, 2006
Jan 2005
Spring 2005
/Magadan
Spring 2005
July-August
2005/Arctic
July-August
2005/Chukotka
August 2005
/Stanford
Sept.-Dec.
2005
Dec. 2005
/Stanford
Toro, Akinin, Sokolov
Akinin
Begin logistic preparation and permitting for 2005 field work.
GIS Russian maps and photos in preparation for 2005 field work.
Miller, Sokolov
Miller, Sokolov
Preparation for Oden Icebreaker Beringia 2005 Expedition
Participation in Oden Icebreaker Beringia 2005 Expedition to
Wrangel Island and north coast of Chukotka (no cost to NSF)
American participants travel to Magadan to meet Akinin. All travel
to Pevek for 2005 transects.
Oden Icebreaker Beringia 2005 Expedition ends in Nome Alaska,
Miller and Sokolov return to Stanford for wrap-up
Preparation of 2005 samples for geochemistry, geochronology, and
thermochronology and compilation of field data.
Project Meeting at Stanford, presentation of preliminary results at
AGU, analytical work at Stanford
Toro, grad. students,
Akinin
Miller, Sokolov
All participants
Miller, Toro, 2 Russian
collaborators
Year 2 February 1, 2006-January 31, 2007
Jan- July 2006
All participants
Sept.-Dec.
2007
Dec. 2007
/Stanford
All participants
Miller, Toro, 2 Russian
collaborators
Geochronology/thermochronology, petrology, geochemistry and
sedimentology of selected samples.
Final study of samples and data analysis /thermochronology,
petrology/geochemistry and sedimentology. Outline final papers
Project Meeting at Stanford, presentation of final results at AGU,
any remaining analytical work at Stanford, manuscript work.
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