p.1
New Insights into Arctic Paleogeography and Tectonics from U-Pb Detrital
Zircon Geochronology
Elizabeth L. Miller1, Jaime Toro2, George Gehrels3, Jeffrey M. Amato4, Andrei
Prokopiev5, Marianna Tuchkova6, Vyacheslav V. Akinin7, Trevor A. Dumitru1, Thomas
E. Moore8, Ashton Embry9 and Michael P. Cecile9
1
Department of Geological and Environmental Sciences, Stanford Univ., Stanford, CA, USA
2
Department of Geology and Geography, West Virginia Univ., Morgantown, WV, USA
3
Department of Geosciences, Univ. of Arizona, Tucson, AZ, USA
4
Department of Geological Sciences, New Mexico State Univ., MSC 3AB, PO Box 30001,
Las Cruces, NM, USA
5
Diamond and Precious Metal Geology Institute, Russian Academy of Sciences, Yakutsk,
Russian Federation
6
Russian Academy of Sciences, Moscow, Russian Federation
7
Russian Academy of Sciences, Magadan, Russian Federation
8
U.S. Geological Survey, Menlo Park, CA, USA
9
Geological Survey of Canada, Calgary, Alberta, Canada
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ABSTRACT
In order to test existing models for the formation of the Amerasian Basin of the Arctic,
detrital zircon suites from 12 samples of Triassic sandstone from the circum-Arctic region
were dated by laser ablation-ICPMS. Triassic successions represent the last major phase of
regional deposition in the Arctic prior to the formation of the Amerasian Basin. Detrital
zircon samples from the northern Verkhoyansk fold-and-thrust belt (Siberia), from Chukotka
and Wrangel Island (NE Russia), and from northwestern Alaska have similar age
distributions distinguished by Carboniferous and Permo-Triassic peaks. In contrast, samples
from further east in Alaska and Canada (Sadlerochit Mts. and Sverdrup Basin) are dominated
by Cambro-Ordovician, or Proterozoic zircons. The samples from Chukotka most closely
resemble those from the Verkhoyansk. The current most popular reconstruction of the
Amerasian Basin involves counter-clockwise rotation of Arctic Alaska and Chukotka away
from the Canadian Arctic margin. Although this satisfies many stratigraphic and geophysical
constraints for the Alaska portion of the reconstruction, it places Chukotka a great distance
away from Siberia and it leads to considerable overlap of continental crust if Chukotka is
treated as a rigid block. To resolve these discrepancies we propose an alternative model for
formation of the Amerasian Basin where Chukotka originates closer to Siberia, but after
rotation with Alaska, moves further away from Siberia by extension and right-lateral strikeslip related to the subsequent opening of the Makarov Basin portion of the Amerasian Basin.
INDEX TERMS: 1165 Geochronology: Sedimentary geochronology; 8155 Tectonophysics:
Plate motions (3040); 8178 Tectonics and magmatism; 9315
Geographic Location:
Arctic region (0718, 4207)
KEYWORDS: Detrital Zircons, Canada Basin, Amerasian Basin, Chukotka, Triassic
p.3
1. Introduction
Despite an increased interest in the exploration of the Arctic Ocean for its role in
controlling the Tertiary climate history of Earth, we know remarkably little about its
formation and changing paleogeography through time. Sea floor spreading anomalies in the
Eurasian Basin (the northern continuation of the mid-Atlantic ridge system) constrain the
history of formation of the Arctic Ocean by rifting back to about 55 Ma, but the earlier
history of the adjacent Amerasian Basin (Figure 1) remains an unsolved plate tectonic puzzle.
The wide variety of proposed solutions to this puzzle was chronicled in Lawver et al. [1990].
Since then, increasingly sophisticated geophysical data sets and seismic based geologic
relations has lent support to the “rotational opening model”, often referred to as the
“windshield wiper” model (Figures 1 and 2). This model proposes that Early Cretaceous
rifting translated a small continental plate, known as the Arctic Alaska-Chukotka microplate,
southward from the Arctic margin of Canada. The plate rotated about a pole located in the
McKenzie Delta region, opening the Amerasian Basin by rifting while closing the
Angayucham and Anyui ocean basins to the south [e.g. Grantz et al., 1990] (Figure 2). Data
in support of this model include correlation of the upper Paleozoic-Mesozoic stratigraphy of
the North Slope of Alaska to the Sverdrup Basin of Arctic Canada [Grantz et al., 1990;
Embry et al., 1990; Toro et al., 2004], and magnetic and gravity anomalies that identify a
paleo-spreading center in part of the Amerasian Basin [Laxon and McAdoo, 1996; Brozena et
al., 2002]. Although the rotational model best satisfies geological and geophysical data from
the Canadian and Alaskan portion of the circum-Arctic, reconstructing the Russian portion of
the Arctic Alaska-Chukotka plate by this model creates a space problem. Geological
constraints suggest that the Arctic Alaska-Chukotka microplate extends as far west as the
New Siberian Islands and includes most of the immense and poorly known East Siberian
continental shelf (Figure 1). Restoring this piece of real estate against the Canadian Arctic
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and Barents margins with the rotation model produces significant overlap of continental crust
(Figure 2) [e.g. Drachev , 2004; Natal’in, 2004].
Understanding the development of the Amerasian Basin is required if we are to
understand the origin and evolution of the vast Russian continental shelves and basins as well
as the origin of several enigmatic bathymetric features in the Arctic Ocean such as the
continental Lomonosov Ridge, the Alpha-Mendeleev Ridge, and the Chukchi Borderland
(Figure 1). At present, land-based geologic efforts provide a straightforward and costeffective means of addressing this problem. In particular, data from NE Russia has the
potential for making significant contributions to our understanding. For instance, the
reconstruction shown in Figure 2 suggests Chukotka, Russia, should have depositional ties
with Arctic Canada and not Siberia. Here we present U-Pb dating of single grains from
detrital zircon populations from Triassic sandstones of the circum-Arctic, carried out in order
to better constrain the position of the different parts of the Arctic Alaska-Chukotka
microplate prior to the opening of the Amerasian basin. Recent advances in laser ablationmass spectrometry and ion microprobe technology have made the dating of large populations
of detrital zircon feasible and thus is a highly desired tool for provenance studies [e.g.
Gehrels et al.,
]. The utility of such studies for plate tectonic reconstructions and for our
understanding of frontier regions is just beginning to be demonstrated.
2. The Arctic Alaska-Chukotka Microplate
The key element in the plate tectonic evolution of the Amerasian Basin is the Arctic
Alaska-Chukotka microplate. Figure 1 portrays the microplate as a single elongate
continental sliver. Its northern boundary (present-day coordinates) is the Arctic Alaskan and
Russian outer shelf edges. Its southern boundary is defined by a belt of ophiolitic rocks that
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includes the Angayucham terrane of the southern Brooks Range [e.g. Moore et al., 1994] and
the South Anyui zone of western Chukotka [e.g. Sokolov et al., 2002].
Arctic Alaska-Chukotka is believed to be a unified continental fragment because of :
1) similar-age Neoproterozoic volcanic and plutonic basement rocks [Moore et al.,1994;
Amato et al., 2003; Kos’ko et al.,1993]; 2) An early Paleozoic carbonate succession with
Siberian faunal affinities that unconformably overlies this basement [Dumoulin et al., 2002;
Natalin et al., 1998; Kos’ko et al.,1993]; 3) A suite of Devonian plutons found in the Brooks
Range that have counterparts on the Seward Peninsula and along the north coast of Chukotka
[Moore et al., 1994; Toro et al., 2002; Kos’ko et al., 1993]; 4) Similarities in the nature and
age of Middle Jurassic-Early Cretaceous structural trends including ophiolite belts developed
by collision-related deformation along the southern side of the plate. These shorteningrelated structures appear to extend continuously from the Brooks Range to offshore Wrangel
Island and into the Chukotka fold belt (where they remain poorly dated) (Figure 1a).
Important along-strike differences in the stratigraphy of the microplate include the
varying nature of Triassic sedimentary successions. Northern Alaska is characterized by a
relatively thin, clastic passive margin succession, which includes chert and other pelagic
deposits in the south and more proximal thin platform sandstones in the north. In Chukotka,
the Triassic consists of thick turbidite sequences intruded by gabbroic dikes and sills at their
base [Gelman, 1963; Ivanov and Milov, 1975]. Thus, in contrast to Alaska, Chukotka was
paleogeographically linked to a major clastic source and probably experienced a Triassic
rifting event that formed the deep-water basins [Tuchkova et al., 2004].
3. Analytical Methods
We separated detrital zircons from twelve samples of Triassic sandstones (Table 1).
Zircons were mounted in epoxy and polished to expose the interior of the grains. Isotopic
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analyses were performed with a Micromass Isoprobe multicollector ICPMS with a laser
ablation system. Laser beam diameter was ~30 m and yielded ablation pits ~20 m deep.
Inter-element fractionation was monitored by analyzing fragments of a large concordant
zircon with a known (ID-TIMS) age of 564 ± 1 Ma (2 σ error). This standard was analyzed
once for every four unknowns. Grains were selected randomly from all sizes and
morphologies present, except for avoidance of grains with fractures or inclusion. The ablated
material is carried in argon gas into the plasma source of a Micromass Isoprobe, which is
equipped with a flight tube of sufficient width that U, Th, and Pb isotopes are measured
simultaneously. All measurements are made in static mode, using Faraday detectors for 238U,
232
Th, 208-206Pb, and an ion-counting channel for 204Pb. Ion yields are ~1 mv per ppm. Each
analysis consists of one 20-second integration on peaks with the laser off (for backgrounds),
20 one-second integrations with the laser firing, and a 30 second delay to purge the previous
sample and prepare for the next analysis.
Common Pb correction is made by using the measured 204Pb and assuming an initial Pb
composition from Stacey and Kramers [1975] (with uncertainties of 1.0 for 206Pb/204Pb and
0.3 for 207Pb/204Pb). Our measurement of 204Pb is unaffected by the presence of 204Hg
because backgrounds are measured on peaks (thereby subtracting any background 204Hg and
204
Pb), and because very little Hg is present in the argon gas.
Inter-element fractionation of Pb/U is generally <20%, whereas fractionation of Pb
isotopes is generally <5%. In-run analysis of fragments of a large zircon crystal (generally
every fifth measurement) with known age of 564 ± 4 Ma (2-sigma error) [G. Gehrels,
unpublished data] is used to correct for this fractionation. The uncertainty resulting from the
calibration correction (together with the uncertainty from decay constants and common Pb
composition) is generally 3% (2-sigma) for 206Pb/238U and >1.2 Ga 206Pb/207Pb ages.
Fractionation also increases with depth into the laser pit. The accepted isotope ratios are
p.7
accordingly determined by least-squares projection through the measured values back to the
initial determination. The complete measured isotopic ratios and ages are reported as tables in
the Supplementary Data Repository1. Errors are from the measurement of 206Pb/238U,
206
Pb/207Pb, and 206Pb/204Pb and are reported at the 1-sigma level. Additional errors that
affect all ages include uncertainties from (1) U decay constants, (2) the composition of
common Pb (assumed to be ±1.0 for 206Pb/204Pb and ±0.3 for 207Pb/204Pb), and (3) calibration
correction. These systematic errors add an additional 2% (1-sigma) uncertainty to 206Pb/238U
and >1.2 Ga 206Pb/207Pb ages.
Age interpretations for <1.2 Ga analyses are based largely on 206Pb/238U ages.
206
Pb/207Pb ages for these analyses are much less reliable given the low concentration of
207
Pb. Because of this, discordance on an individual grain basis cannot be assessed for grains
younger than 1.2 Ga.
For grains >1.2 Ga, 206Pb/207Pb ages are generally more precise than 206Pb/238U ages, and
are accordingly used in age interpretations. For the older grains, you can assess discordance
because the 207-206 ages are also precise. However, it should be noted that 206Pb/207Pb ages
underestimate the true age for discordant grains given that isotopic disturbance occurred in
the geologic past. To reduce the effect of discordance, only analyses that are less than 15%
discordant are included in age interpretations (applicable only to older grains). The
interpreted ages are presented in Table 2.
The U-Pb dates are plotted on a normalized relative-probability distribution diagrams
[Ludwig, 2003]. The relative height of the peaks corresponds to the significance of that
population of ages (Figure 3). Some analyses were not plotted because of one of two
reasons: 1) for ages <1000 Ma, the 206Pb/238U uncertainty was >10%; 2) for ages >1000 Ma,
1
Insert reference to Supplementary Data Repository here.
p.8
the 207Pb/206Pb uncertainty was >10% or the discordance between the 206Pb/238U and
207
Pb/206Pb ages was > 20%.
4. Geological Setting of Samples and Interpretation of Detrital Data
Triassic sandstones were selected for our study because they represent the youngest stage of
widespread marine deposition prior to the onset of rifting that led to the dispersal of terranes
during formation of the Amerasian Basin. Rifting started in the Late Jurassic along the
Alaskan margin [Grantz et al., 1990], but the major episode of sea floor spreading appears to
have occurred in the Early Cretaceous [Grantz et al., 1990, but see Drachev, 2004]. In
addition, compressional deformation also affected parts of Arctic Alaska starting as early as
the mid Jurassic when ophiolitic sequences were emplaced in Alaska and the Kolyma region
[Moore et al., 1998; Oxman et al., 1995]. Detrital age data from Triassic sedimentary rocks
along the length of the Arctic Alaska-Chukotka microplate were collected to test the integrity
and continuity of this crustal fragment and constrain its paleogeographic links to source
terranes. Three additional samples from the northern Verkhoyansk fold-and-thrust belt were
used to characterize a “Siberian source”, and two additional samples were dated from the
Sverdrup Basin to characterize a “Canadian source” (Figure 1).
Nearly all of the Triassic sandstones analyzed were derived from the erosion of
Paleozoic and early Mesozoic source terranes. Precambrian zircons are present in all samples
but only in limited amounts, with the exception of one sample from the southern Sverdrup
basin (Figure 3). Our discussion below focuses on the interpretation of the Phanerozoic ages
in the zircon populations because these are most easily interpreted with respect to possible
source areas making them useful for paleogeographic reconstructions. The samples are
discussed below from west to east.
The shallow marine Triassic succession of the Verkhoyansk (Figure 1) is part of an
immense passive-margin siliciclastic wedge that ranges in age from Carboniferous to Early
p.9
Jurassic [Khudoley and Guriev, 1994]. A major fluvial system connected the tectonically
active Baikal Mountain region to the Verkhoyansk Siberian margin via the long-lived Vilyui
graben system (Figure 1) and other distributary systems [e.g. Khudoley and Guriev, 1994].
Earliest Triassic strata of the northern Verkhoyansk contain basalts and tuffs that are
believed to be coeval with Siberian Trap volcanism [Andrianova and Andrianov, 1970].
Triassic sandstones have petrographic characteristics of “recycled orogen” sources,
compatible with their inferred provenance. The age distribution of detrital zircon suites from
one Middle Triassic and two Upper Triassic sandstone samples are very similar and are
grouped in Figure 3 (a total of 281 ages). Post-Vendian peaks in the probability distribution
occur at 288, 482, 517 and 597 Ma. These ages are compatible with their inferred source in
the Baikal Mountain region along the southern margin of the North Asia craton, known to
have been an active Andean margin throughout the Paleozoic and early Mesozoic. Major
batholiths were intruded in the Carboniferous; Ordovican and Cambrian plutonic rocks are
present as well [Wickam et al., 1995; Yarmolyuk et al., 1997; Bukharov et al., 1992].
The Triassic of Chukotka is represented by up to 5 km of mostly distal turbidite
sequences that range upwards into shelf deposits of Upper Triassic (Norian) age [Tuchkova et
al., 2004]. Sandstones are mostly fine-grained with compositions varying from “continental
block” to “recycled orogen” [Tuchkova et al., 2004]. We analysed one Middle Triassic
(Carnian) and two Upper Triassic (Norian) samples. Zircon populations from these three
samples are very similar and are grouped in Figure 3 (285 grains). Zircon ages show peaks at
247, 299, 370, 440, and 494 Ma with older peaks at 575 and 650 Ma. It is notable that the
Paleozoic peak ages in these samples are very similar to those found in the Verkhoyansk
samples. The Permo-Triassic peak at 247 Ma lies within error of the age of well-dated
Siberian Trap magmatism (248-253 Ma) [e.g. Campbell et al., 1992; Venkatesan et al., 1997;
Renne and Basu, 1996]. Although Siberian Trap magmatism was dominantly basaltic, lesser
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silicic intrusions and tuffs have been described. In the Taymir Peninsula there are 249-241
Ma high level syenite-granite stocks that have been linked to the mantle plume which also
generated the Siberian Traps [Vernikovsky et al., 2003]. Tuffs and tuffaceous sediments are
also present in the Late Permian and earliest Triassic deposits of both the Verkhoyansk and
Chukotka [Andriavova and Andrianov, 1970; Chasovitin and Shpetnyi,1964; Belik and
Sosunov,1969; Sosunov and Tilíman, 1960] suggesting that magmatism related to the
Siberian Traps was the most likely origin for zircons of this age.
Wrangel Island lies between the sample sites in Chukotka and those in western Alaska
(Figure 1). The Triassic strata of Wrangel Island consist of proximal siliciclastic turbidites
[Kos’ko et al., 1993]. A single small Triassic sample from Wrangel Island (provided by
Mike Cecile of the Geological Survey of Canada) yielded 47 datable zircons (Figure 3).
Phanerozoic zircon age peaks at 253, 280, and 449 Ma are similar to the peaks seen in the
samples from Chukotka (to which Wrangel Island is linked, geographically, stratigraphically
and structurally) and the Verkhoyansk (which is quite distant) (Figure 3). A single grain
yielded an age younger than 200 Ma, but this is not considered to be statistically significant
given that concordance cannot be demonstrated (Figure 3) (Supplementary Data).
The westernmost sample site in Alaska is in the Lisburne Hills fold-and-thrust belt
which consists of lower Paleozoic to Mesozoic sedimentary rocks [e.g. Moore et al., 2002].
Two samples were collected from an unusual sandstone member of the Triassic Otuk
Formation which lies stratigraphically between the shale and chert members described by
Blome et al. [1988]. The sandstone is very fine to fine-grained, massive, and about 5 m thick.
Monotis fossils found in the sandstone suggest a Late Triassic age. The sandstone is lithic,
consisting of about 40 percent monocrystalline quartz, 20 percent altered feldspar, and 40
percent lithic fragments (argillite, chert, siltstone, granitic fragments and carbonate). The
Otuk is thought to represent condensed sedimentation in an outer shelf environment [Moore
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and others, 1994]. Although a predominantly sedimentary provenance is inferred for this
sandstone, the granitic grains suggest that it was shed from a source region that lay to the NW
in the offshore Chukchi platform region [K.W. Sherwood, 2000, written communication as
cited in Moore and others, 1994].
Because the age spectra of the two samples from the Lisburne Hills are similar, the
data are grouped in Figure 3 (187 zircons). Similarities and differences in the ages of the
detrital zircons from the Lisburne Hills and NE Russia are evident. A Permo-Triassic age
peak at 255 Ma is present in the Lisburne Hills Triassic which is also seen in samples from
Wrangel Island and Chukotka. Paleozoic peaks at 321, 362 and 431 Ma are similar to the
Russian samples. Differences include a younger Triassic (222 Ma) peak in the Lisburne Hills
sandstones. Its closeness in age to the depositional age of the sandstone suggests the presence
of an active magmatic source. The Lisburne Hills samples also lack the strong Cambrian
and Late Proterozoic peaks seen in the Chukotka samples.
A sample from the Early Triassic Ledge Member of the Ivishak Formation of the
Sadlerochit Mountains in northeastern Alaska (Figures 1, 2) shows the greatest difference in
provenance ages from the samples previously discussed. Sedimentary structures and burrows
indicate a shallow marine deltaic origin for the Ledge Member [Mariani, 1987]. This unit is
also notable because it is the main oil reservoir of the Prudhoe Bay field. Zircons from the
Ivishak Sandstone exhibit age peaks at 466, 531 and 564 Ma. Permo-Triassic and Late
Carboniferous to earliest Permian ages are conspicuously absent (Figure 3).
Despite their geographic proximity, two samples from the Triassic successions of the
Sverdrup Basin in Arctic Canada (Figure 1) have very different zircon age populations from
each other. Sample AE2 from Axel Heiberg Island on the northern flank of the Sverdrup
Basin has a zircon age distribution virtually identical to that of the Sadlerochit Mountains of
northeastern Alaska (Figure 3). This lends support to the rotational hypothesis for the
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opening of the Canada basin [Grantz et al., 1990], which would place these two samples in
close proximity prior to rifting (Figure 2). In contrast, sample AE1, from the southern flank
of the Sverdrup Basin on Ellesmere Island, is dominated by Proterozoic zircons with major
peaks at 1.2 and 1.78 Ga, plus a few zircons of Paleozoic age (Figure 3). An in depth
provenance study utilizing Sm-Nd isotopic data concluded that most of the sediments in the
Sverdrup basin were sourced from recycled Franklinian-Caledonian (Early Paleozoic)
sources [Patchett et al., 2004]. This is consistent with the detrital ages of sample AE2 and the
detrital zircon ages from the Triassic of the Sadlerochit Mountains. However, the zircons
dated in sample AE1 appear to represent the erosion of older crystalline rocks to the south
and east of the Sverdrup Basin, possibly related to uplift of Early Proterozoic and
Greenvillian age basement during the early stages of Atlantic rifting.
5. Discussion
Despite the differences in the stratigraphic successions of Chukotka and Alaska,
Triassic sandstones in the Lisburne Hills have similar zircon populations to those of
Chukotka, Wrangel Island, and NE Russia, arguing for no major paleogeographic barriers
between the Russian and westernmost Alaskan parts of the Arctic Alaska-Chukotka
microplate in the Triassic. The greatest difference in source regions across Arctic AlaskaChukotka is found by a comparison of zircon suites from Triassic sandstones from western
versus eastern Alaska, even though this part of the microplate has well-documented structural
and stratigraphic continuity [e.g. Moore et al., 1994]. It appears that Caledonian-Franklinian
sources predominated in northeastern Alaska and northern Canada, while North Asian, or NE
Russian sources shed debris onto the western part of the microplate. Triassic strata of
Chukotka have the greatest similarities in ages of source regions with coeval rocks of the
Verkhoyansk belt of Siberia (Figure 3). However, Chukotka now lies a great distance from
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the northern Verkhoyansk and also from the Siberian Traps from which it may have received
its Permo-Triassic zircons (Figure 1). The preferred model for opening of the Amerasian
Basin (Figure 2) separates Chukotka from potential Siberian sources by a 1000-km wide
ocean. Furthermore, the rotational model restores Chukotka to a position adjacent to the
Sverdrup Basin, whose source regions for Triassic sandstones are the most dissimilar to those
of Chukotka.
As a means of addressing these questions, a hypothetical reconstruction of
Arctic Alaska-Chukotka that places Chukotka closer to Siberia, is presented in Figure 4a.
The model accepts the data in support of a rotational opening model for the Canada Basin
[Grantz, 1990] but restores Chukotka to a position closer to the northern Verkhoyansk, the
Taimyr Peninsula, and the Siberian Traps region by invoking a series of additional rotations
and internal deformation of the microplate. Any attempt to maintain the integrity of the
microplate from Alaska to Chukotka (as evidenced by geologic similarities) and also to
connect the Chukotka part of the plate to the Siberian margin results in a space problem that
is the opposite of that obtained by the rotation model—there is too much space between the
microplate and the Lomonosov Ridge. In our speculative model, this space problem is solved
by proposing that the Alpha-Mendeleev Ridge is underlain in part by thinned, stretched
continental crust that once helped fill this gap, and by proposing a younger opening of the
Makarov Basin (Figures 4b and c). Closing the Makarov Basin by extension sub-parallel to
the Lomonosov Ridge (as originally proposed by Taylor et al. [1981] and Vogt et al. [1982])
may be the main way to account for this gap. To do so would involve a change in the pole of
rotation of the Arctic Alaska-Chukotka plate relative to North America from a position in the
Mackenzie Delta region to one near the Canada/Greenland end of the Lomonosov Ridge
during the opening of the Makarov Basin. Rift opening of the Makarov Basin is supported by
the parallel systems of horsts and grabens along its border with the Lomonosov Ridge (Figure
p.14
1) but expected parallel magnetic anomalies are difficult to distinguish in the aeromagnetic
data [e.g. Brozena et al., 2002]. During this inferred opening, it is also hypothesized that
extension continued in continental crust beneath the East Siberia Shelf, increasing the region
in size, thus moving Chukotka further away from the Siberian margin. This motion might
have been bound by a transform-like feature that represents the western continuation of the
South Anyui Zone in the subsurface, characterized by a very strong set of linear positive
magnetic anomalies [Racey et al., 1996]. This motion may also be the possible cause of the
right-lateral sense bend of the trends of the northern Verkhoyansk (Figure 4c). The opening
of the Eurasian Basin in the Eocene is not shown as a step in Figure 4, but together with the
documented ~ 50% extension of continental crust beneath the Laptev Sea shelf [Drachev,
2004], Chukotka moves even further away from its initial position to its present location
(compare Figures 4, 1).
In addition to addressing the Siberian source region for Triassic sandstones in
Chukotka, Wrangel Island and westernmost Alaska, the reconstruction shown in Fig 4a
places Chukotka near the region of Siberia that was affected by a significant and widespread
Triassic rifting event [Aplotov,1988]. This helps explain the differences in its Triassic and
Jurassic stratigraphy compared to that of the adjacent Alaska portion of the Arctic AlaskaChukotka microplate.
Acknowledgements
This work builds on fieldwork and sampling in Arctic Russia and Alaska funded by
NSF (EAR-), Exxon-Mobil, Stanford University’s School of Earth Science McGuee funds,
and the Department of Geological Sciences at Stanford. Funding for the analyses presented
here was provided by the Exxon Mobil Corporation. Special thanks to Steve Creaney, Mike
Sullivan, Bob Ferderer, Ian Norton, and Pinar Ilmaz of ExxonMobil for their interest in
Arctic tectonics.
p.15
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Figure Captions
Figure 1. Circum-Arctic map showing the location of Triassic detrital zircon and main
tectonic features of the Arctic Basin. Bathymetry is from IBCAO [2002]. Sample locations
are shown as numbered circles. See Table 1 for sample data, and Figure 3 for zircon ages.
The Arctic Alaska-Chukotka microplate is bounded by a heavy dotted line. The fossil
spreading center for the Canada Basin is shown by a double line [Laxon and McAdoo, 1994]
flanked by magnetic anomalies (positive-thin solid line, negative-thin dashed line).
Abbreviations: AHI, Axel Heiberg Island, AN- Angayucham belt, AR- Alpha Ridge, BR-
p.20
Brooks Range, CB- Canada Basin, CH- Chukotka, CP- Chukchi Plateau, Cr- Chersky Range,
EI- Ellesmere Island, LR- Lomonosov Ridge, MB- Makarov Basin, MR- Mendeleben Ridge,
NSI- New Siberian Islands, SAZ- South Anyui Zone, SB- Sverdrup Basin, VG- Vilyui
Graben, WHA, Wrangel-Herald Arch, WI- Wrangel Island.
Figure 2. Early Cretaceous plate reconstruction of the Circum-Arctic region prior to opening
of the Amerasian Basin by simple rotation of Arctic Alaska-Chukotka (AAC) modified from
Lawver et al. [2002]. The area of overlap of continental crust that results if AAC is rotated as
a rigid plate is shown in black. The exposed area of the South Anyui Zone (SAZ) is
highlighted by a rulled pattern. Numbered circles are detrital zircon sample locations.
Abbreviations: AN- Angayucham belt, CR- Chersky range, KO- Kolyma-Omolon
superterrane, KY- Koyukuk arc.
Figure 3. Relative probability distribution diagrams for detrital zircon U-Pb ages from
Triassic sandstones in the Arctic. Sample locations shown in Figure 1. Height of peak is
proportional to the probability that these ages are present in the sample, with the area under
the curve = 1. On the left, spectra include all of the ages from each sample. On the right,
spectra include only ages <1000 Ma.
Figure 4. Speculative model of the evolution of the Amerasian Basin to account for U-Pb
single grain detrital grain ages in Triassic sediments. (a) Early Cretaceous restoration of the
Arctic region prior to opening of the Amerasian basin. Fragments of Arctic Alaska-Chukotka
which are treated semi-independently or independently in the model are outlined in grey.
Pink strip and thrust belt ticks with grey strip schematically represent an accreted arc and
ophiolite belt now represented by terranes in interior Alaska (Angayucham and correlatives)
and in the Kolyma region of Russia (Alazaya Arc and ophiolites of Oxman et al. [1995]) and
along the South Anyui Zone in Chukotka [Sokolov et al., 2002]. (b) Mid-Cretaceous stage
after opening of the Canada Basin by rotation about a pole in the McKenzie Delta
p.21
accompanied by large amounts of extensional thinning of continental crust represented by the
Chukchi Plateau region and the Alpha-Mendeleev Ridge. The New Siberian Islands block
remains attached to the Siberian margin at this stage and in close proximity to Chukotka as
well. (c) Latest Cretaceous stage during which the Makarov Basin opens by extension
seafloor spreading perpendicular to the Lomonosov Ridge accompanied by continental
extension of the western portion of the East Siberian Shelf . Note that the age assignments of
these stages of opening are not well constrained and could occur either closer in time and/or
together or even reversed in time.
Tables
Table 1. Sample Data for Sandstones Analysed for Detrital Zircons
Field
Number
Number on
Figures
00JT25
00JT26
00JT29
CH31B
CH26
CH265
C145741
94CL10
94CL53
96DH102
AE1
AE2
1
1
1
2
2
2
3
4
4
5
7
6
Area
Lat
Lon
Age
Unit
Verkhoyansk
Verkhoyansk
Verkhoyansk
Chukotka
Chukotka
Chukotka
Wrangel Island
Lisburne Hills
Lisburne Hills
Sadlerochit Mts.
Sverdrup Basin
Sverdrup Basin
65.450207
65.438062
65.336460
67.868222
68.061778
69.156528
71.031667
68.868667
68.861167
69.684330
79.566667
80.583333
126.897921
126.875138
126.343293
166.290222
166.412000
165.038222
179.216667
166.059667
166.014667
144.849000
83.333333
95.950000
M. Triassic
M. Triassic
U. Triassic
U. Triassic
U. Triassic
U. Triassic
Triassic
U. Triassic
U. Triassic
L. Triassic
L. Triassic
U. Triassic
Tolbon Fm
Tolbon Fm.
Khedalichen Fm.
Otuk Fm.
Otuk Fm.
Ivishak Fm.
Table 2. Interpreted Zircon Ages
Verkhoyansk
00JT25
Age (Ma)
256.0 ± 7.6
274.6 ± 15.2
291.7 ± 11.5
295.8 ± 8.9
310.0 ± 6.4
311.1 ± 26.1
321.6 ± 6.5
326.1 ± 14.4
328.5 ± 6.0
329.4 ± 7.9
336.0 ± 6.3
341.7 ± 5.4
353.9 ± 2.1
354.0 ± 10.8
363.6 ± 7.1
380.5 ± 6.9
381.1 ± 21.5
Verkhoyansk
00JT26
Age (Ma)
275.5 ± 7.3
280.5 ± 8.6
287.0 ± 12.2
287.1 ± 7.7
287.2 ± 5.3
290.6 ± 6.4
292.0 ± 8.7
293.5 ± 11.2
295.7 ± 10.1
302.2 ± 7.1
306.9 ± 10.3
308.9 ± 16.3
309.6 ± 10.3
315.1 ± 9.1
315.3 ± 16.0
317.1 ± 24.7
317.3 ± 23.0
Verkhoyansk
00JT29
Age (Ma)
269.2 ± 4.7
272.7 ± 6.3
285.5 ± 10.7
289.5 ± 7.5
290.4 ± 6.2
291.8 ± 5.6
308.4 ± 5.3
311.6 ± 7.2
312.4 ± 7.6
317.2 ± 11.3
339.3 ± 10.9
364.7 ± 10.7
364.9 ± 8.4
382.4 ± 17.8
409.8 ± 33.7
431.6 ± 7.6
442.6 ± 17.3
Chukotka
CH31B
Age (Ma)
235.8 ± 10.5
237.8 ± 2.6
241.6 ± 7.4
243.2 ± 7.6
243.8 ± 4.7
248.5 ± 9.3
248.7 ± 4.9
250.4 ± 7.7
252.7 ± 11.4
252.8 ± 9.4
253.1 ± 9.6
278.1 ± 6.8
284.4 ± 9.2
286.4 ± 7.2
292.8 ± 15.6
299.9 ± 8.0
312.2 ± 14.4
Chukotka
CH26
Age (Ma)
240.0 ± 8.4
246.2 ± 4.7
251.4 ± 7.7
252.9 ± 8.5
254.5 ± 8.7
263.2 ± 6.8
265.1 ± 16.5
271.2 ± 11.8
277.0 ± 14.3
280.9 ± 16.4
282.5 ± 5.3
283.0 ± 7.8
284.0 ± 6.2
284.1 ± 5.8
286.2 ± 6.5
287.6 ± 14.3
287.9 ± 6.3
Chukotka
CH265
Age (Ma)
253.7 ± 1.6
257.7 ± 9.4
264.7 ± 8.8
274.0 ± 10.7
274.9 ± 15.6
287.0 ± 3.6
287.8 ± 12.3
290.1 ± 8.0
293.9 ± 4.7
296.8 ± 4.8
298.4 ± 3.6
300.4 ± 7.7
301.1 ± 7.9
301.9 ± 9.1
302.0 ± 5.4
302.0 ± 5.1
302.2 ± 8.3
p.22
381.4 ± 13.9
388.2 ± 15.4
412.8 ± 10.6
413.7 ± 7.3
414.0 ± 6.9
417.5 ± 20.6
425.0 ± 15.7
428.8 ± 10.4
430.2 ± 14.1
442.1 ± 14.7
442.4 ± 34.9
444.8 ± 11.5
445.4 ± 15.2
449.9 ± 22.8
451.0 ± 11.6
455.0 ± 9.2
456.3 ± 10.8
464.3 ± 9.1
464.9 ± 13.9
466.8 ± 11.6
468.3 ± 12.7
469.4 ± 16.0
470.3 ± 13.4
474.1 ± 20.3
474.6 ± 14.8
478.7 ± 6.6
478.9 ± 10.8
480.5 ± 17.6
481.0 ± 13.8
481.7 ± 16.1
483.9 ± 12.4
484.1 ± 12.5
484.7 ± 28.8
485.5 ± 10.1
487.7 ± 16.0
489.1 ± 9.2
492.3 ± 6.3
493.6 ± 10.3
496.0 ± 18.6
501.8 ± 17.4
508.9 ± 13.6
518.4 ± 11.0
518.5 ± 7.6
521.5 ± 9.1
525.7 ± 7.8
538.6 ± 27.7
541.8 ± 23.7
555.6 ± 25.3
570.7 ± 36.3
578.3 ± 49.1
592.4 ± 15.9
594.5 ± 26.2
601.7 ± 20.2
652.7 ± 13.3
689.6 ± 23.6
826.5 ± 56.7
1754 ± 49
1800 ± 35
1804 ± 34
1839 ± 54
1862 ± 97
1864 ± 23
1888 ± 48
1922 ± 31
1948 ± 81
2028 ± 35
2069 ± 24
2073 ± 41
2501 ± 56
319.3 ± 14.8
320.2 ± 13.8
326.1 ± 9.1
337.5 ± 12.3
337.7 ± 10.6
361.0 ± 5.6
362.5 ± 12.5
367.2 ± 13.2
386.2 ± 5.2
426.1 ± 20.2
428.3 ± 10.5
429.4 ± 11.2
434.6 ± 8.7
440.1 ± 5.7
442.3 ± 8.7
443.2 ± 14.4
443.7 ± 10.8
452.9 ± 25.7
456.3 ± 20.2
460.3 ± 12.3
461.1 ± 8.4
465.3 ± 10.3
466.0 ± 19.1
476.1 ± 9.8
476.9 ± 12.5
478.7 ± 21.4
480.1 ± 11.1
481.7 ± 11.6
482.1 ± 24.1
482.6 ± 13.2
485.3 ± 7.4
487.1 ± 16.7
488.5 ± 20.2
488.9 ± 14.1
489.7 ± 28.8
489.9 ± 14.3
496.5 ± 29.8
500.3 ± 17.0
503.6 ± 14.6
511.3 ± 22.7
512.8 ± 21.4
524.0 ± 12.5
526.9 ± 13.6
542.2 ± 9.7
545.6 ± 12.2
546.4 ± 19.4
550.7 ± 24.8
555.7 ± 24.1
576.3 ± 32.6
578.2 ± 10.0
591.3 ± 20.9
593.7 ± 13.8
595.0 ± 13.6
623.6 ± 10.9
634.7 ± 27.0
671.4 ± 24.4
810.0 ± 16.5
825.9 ± 13.0
988.6 ± 18.0
1801 ± 31
1832 ± 32
1845 ± 20
1888 ± 36
1911 ± 61
1931 ± 75
2014 ± 61
2021 ± 70
2044 ± 30
2445 ± 24
450.2 ± 12.8
450.6 ± 8.1
451.9 ± 40.2
453.8 ± 14.4
454.9 ± 13.8
455.3 ± 20.8
461.0 ± 9.9
463.1 ± 7.8
464.0 ± 7.4
464.1 ± 6.4
464.1 ± 8.8
465.9 ± 20.5
468.2 ± 13.0
470.6 ± 12.5
471.4 ± 14.5
472.8 ± 9.4
476.3 ± 11.6
479.1 ± 12.6
479.6 ± 18.0
485.1 ± 6.7
485.9 ± 16.4
487.1 ± 22.4
487.4 ± 12.2
487.9 ± 10.8
490.4 ± 13.3
490.8 ± 7.2
491.1 ± 7.0
513.8 ± 7.0
517.2 ± 7.2
518.0 ± 23.6
518.2 ± 7.7
518.5 ± 8.1
519.8 ± 24.8
526.9 ± 29.6
528.5 ± 12.6
528.6 ± 18.8
536.1 ± 19.4
549.3 ± 7.9
556.6 ± 14.1
567.3 ± 26.3
568.4 ± 23.3
585.9 ± 18.7
588.4 ± 33.1
594.8 ± 15.2
608.0 ± 28.7
611.4 ± 20.6
616.7 ± 45.7
623.9 ± 22.6
646.3 ± 53.1
652.6 ± 11.6
671.9 ± 26.3
688.9 ± 25.8
701.3 ± 29.7
754.0 ± 20.2
795.7 ± 18.1
1234 ± 90
1769 ± 38
1808 ± 18
1814 ± 33
1814 ± 32
1825 ± 9
1827 ± 50
1918 ± 51
1921 ± 50
1980 ± 30
2313 ± 7
2379 ± 9
2384 ± 9
2431 ± 5
318.3 ± 11.2
334.1 ± 14.0
370.2 ± 13.6
381.0 ± 7.3
386.5 ± 17.3
425.1 ± 12.1
426.9 ± 11.1
437.2 ± 14.3
451.8 ± 29.5
468.4 ± 6.5
477.4 ± 19.9
477.6 ± 37.3
482.3 ± 27.1
487.9 ± 9.4
495.0 ± 12.5
502.9 ± 12.2
512.2 ± 19.4
512.4 ± 15.5
512.9 ± 21.1
514.5 ± 8.9
515.7 ± 20.8
517.6 ± 15.6
525.1 ± 15.8
542.6 ± 21.5
544.6 ± 15.6
552.6 ± 10.1
553.5 ± 17.4
559.9 ± 19.5
560.1 ± 14.2
566.9 ± 16.5
568.2 ± 35.3
579.1 ± 14.6
582.5 ± 19.9
594.9 ± 11.8
604.4 ± 28.6
611.9 ± 19.5
676.8 ± 17.7
678.5 ± 24.9
683.1 ± 13.6
755.6 ± 25.1
792.1 ± 15.6
793.9 ± 42.7
819.4 ± 24.8
830.0 ± 59.2
862.5 ± 24.7
893.6 ± 20.3
911.2 ± 30.9
1061 ± 98
1093 ± 104
1110 ± 98
1123 ± 91
1170 ± 56
1185 ± 52
1203 ± 67
1426 ± 61
1442 ± 58
1449 ± 75
1606 ± 47
1609 ± 60
1610 ± 32
1626 ± 92
1634 ± 55
1638 ± 61
1645 ± 16
1649 ± 69
1655 ± 140
1662 ± 67
1691 ± 30
1758 ± 43
292.2 ± 12.0
294.8 ± 14.9
297.9 ± 8.8
299.2 ± 6.5
300.1 ± 13.6
326.6 ± 17.1
332.4 ± 13.1
344.6 ± 24.1
347.5 ± 11.2
350.9 ± 8.3
353.1 ± 12.7
359.9 ± 9.7
364.9 ± 5.8
366.7 ± 14.4
375.7 ± 9.5
377.1 ± 20.2
380.5 ± 17.4
385.3 ± 13.2
388.8 ± 12.7
389.8 ± 11.2
396.7 ± 31.0
436.3 ± 14.5
437.6 ± 19.0
439.4 ± 18.4
446.8 ± 13.9
447.6 ± 14.8
451.8 ± 7.8
453.4 ± 9.1
456.4 ± 12.9
459.9 ± 16.5
465.2 ± 18.2
482.9 ± 10.3
500.8 ± 37.7
503.7 ± 11.5
507.7 ± 20.9
517.6 ± 29.0
539.9 ± 13.5
543.3 ± 44.1
565.1 ± 28.9
566.9 ± 17.0
569.1 ± 14.3
576.5 ± 29.9
600.4 ± 11.4
614.6 ± 16.7
615.7 ± 27.0
620.5 ± 37.3
685.5 ± 16.2
723.4 ± 45.2
761.4 ± 18.9
774.8 ± 31.2
867.4 ± 27.2
1100 ± 71
1133 ± 65
1645 ± 22
1659 ± 79
1696 ± 77
1714 ± 109
1741 ± 109
1792 ± 94
1798 ± 20
1808 ± 12
1822 ± 26
1835 ± 33
1835 ± 12
1844 ± 15
1856 ± 58
1876 ± 38
1945 ± 29
1983 ± 116
304.5 ± 3.2
308.0 ± 3.6
309.4 ± 6.8
312.0 ± 7.1
312.8 ± 6.0
313.8 ± 11.4
314.7 ± 12.3
316.8 ± 6.7
319.0 ± 6.7
321.5 ± 7.6
329.5 ± 5.1
351.6 ± 9.4
368.7 ± 9.9
369.5 ± 14.0
378.9 ± 16.1
398.6 ± 15.9
444.4 ± 10.6
446.1 ± 19.7
455.6 ± 16.6
457.5 ± 8.4
460.5 ± 9.3
465.1 ± 11.8
471.2 ± 3.3
472.7 ± 16.4
474.4 ± 18.3
481.2 ± 15.6
492.6 ± 6.1
493.5 ± 14.8
495.5 ± 6.3
501.0 ± 7.7
502.1 ± 15.1
503.5 ± 11.9
503.7 ± 7.6
504.9 ± 19.3
510.4 ± 23.8
520.7 ± 17.9
522.7 ± 9.3
531.2 ± 25.0
544.5 ± 11.9
559.5 ± 23.5
560.3 ± 19.5
572.1 ± 17.1
587.3 ± 34.9
592.6 ± 10.5
602.1 ± 31.9
609.8 ± 13.8
621.7 ± 8.0
669.1 ± 9.0
729.6 ± 15.2
741.4 ± 27.7
755.9 ± 12.9
772.9 ± 16.2
794.1 ± 13.7
799.1 ± 22.5
799.8 ± 27.6
803.6 ± 25.3
810.2 ± 6.0
820.2 ± 29.9
836.3 ± 16.5
1017 ± 43
1039 ± 84
1050 ± 82
1051 ± 14
1067 ± 87
1097 ± 50
1120 ± 44
1210 ± 94
1273 ± 59
1755 ± 12
p.23
2543 ± 53
2581 ± 18
2668 ± 5
2728 ± 67
2788 ± 17
2829 ± 21
2986 ± 19
2446 ± 31
2447 ± 28
2479 ± 23
2500 ± 13
2537 ± 12
2730 ± 18
2432 ± 11
2495 ± 10
2506 ± 12
2570 ± 8
2596 ± 18
2605 ± 20
2612 ± 21
2661 ± 12
2674 ± 11
2751 ± 10
1785 ± 54
1842 ± 83
1847 ± 72
2334 ± 69
2430 ± 35
2821 ± 20
2005 ± 35
2028 ± 19
2143 ± 23
2215 ± 23
2266 ± 16
2468 ± 13
2478 ± 13
3227 ± 19
1826 ± 15
1829 ± 45
1831 ± 24
1842 ± 26
1862 ± 78
1950 ± 25
1955 ± 25
1986 ± 39
2071 ± 10
2467 ± 11
2591 ± 10
2609 ± 10
2725 ± 24
Table 2 (cont.) Interpreted Zircon Ages
Wrangel Island
C145741
Age (Ma)
186.2 ± 4.9
237.9 ± 5.7
238.0 ± 9.2
250.6 ± 6.3
251.5 ± 15.8
252.7 ± 4.6
256.0 ± 20.8
270.6 ± 9.1
272.8 ± 23.2
274.8 ± 11.5
280.1 ± 20.9
283.1 ± 9.7
285.0 ± 2.6
292.6 ± 21.3
293.6 ± 9.6
294.4 ± 9.2
298.8 ± 17.8
303.3 ± 11.2
317.3 ± 18.9
323.9 ± 11.3
361.7 ± 5.8
375.2 ± 14.6
395.7 ± 7.1
397.8 ± 13.7
424.7 ± 14.1
435.5 ± 11.0
440.7 ± 14.4
443.3 ± 15.8
448.0 ± 11.8
454.6 ± 6.2
461.2 ± 21.0
510.7 ± 15.7
667.6 ± 17.7
751.5 ± 30.6
1059 ± 83
1084 ± 55
1110 ± 47
1188 ± 106
1613 ± 61
1699 ± 20
1717 ± 10
1832 ± 33
1892 ± 19
1926 ± 22
1947 ± 26
1977 ± 18
2129 ± 19
2384 ± 15
2435 ± 9
2454 ± 19
Lisburne Hills
94CL10
Age (Ma)
223.1 ± 4.6
224.7 ± 4.8
226.8 ± 12.2
232.2 ± 4.8
232.4 ± 11.7
237.4 ± 3.5
240.6 ± 4.6
251.5 ± 7.6
252.1 ± 6.0
253.1 ± 5.6
256.6 ± 4.2
258.0 ± 5.6
260.3 ± 7.8
260.4 ± 8.2
262.3 ± 6.9
267.7 ± 10.5
268.2 ± 9.4
269.3 ± 8.7
270.1 ± 7.6
272.7 ± 8.8
273.1 ± 8.2
276.8 ± 4.7
277.3 ± 3.7
317.9 ± 8.0
320.4 ± 9.9
321.2 ± 14.3
323.9 ± 11.9
324.2 ± 10.5
325.8 ± 8.2
327.4 ± 23.8
330.7 ± 9.4
332.0 ± 12.6
334.3 ± 11.4
336.5 ± 16.3
359.3 ± 14.4
359.8 ± 11.3
363.4 ± 11.6
365.0 ± 17.0
366.1 ± 19.6
369.2 ± 8.5
373.7 ± 12.6
374.3 ± 8.5
375.5 ± 11.8
406.4 ± 6.8
419.1 ± 6.1
423.0 ± 14.8
423.9 ± 14.9
425.1 ± 12.7
428.8 ± 10.1
429.4 ± 12.7
Lisburne Hills
94CL53
Age (Ma)
220.0 ± 6.7
224.1 ± 6.8
224.3 ± 11.5
232.4 ± 13.9
251.9 ± 6.4
256.9 ± 5.9
259.0 ± 7.2
260.7 ± 9.0
261.9 ± 9.7
275.8 ± 4.8
306.7 ± 15.5
306.9 ± 4.4
313.9 ± 5.9
313.9 ± 12.1
314.7 ± 3.6
317.4 ± 4.8
320.8 ± 9.5
321.5 ± 11.2
323.3 ± 11.1
325.8 ± 19.8
327.2 ± 14.3
327.9 ± 12.0
328.6 ± 8.6
339.8 ± 7.4
347.6 ± 10.5
356.9 ± 8.3
359.6 ± 8.5
359.7 ± 16.9
360.3 ± 9.3
361.3 ± 16.8
365.9 ± 13.8
368.0 ± 10.9
369.0 ± 14.3
381.4 ± 8.6
416.3 ± 19.7
421.9 ± 11.6
422.8 ± 18.0
423.4 ± 9.4
429.0 ± 12.6
430.4 ± 19.0
431.1 ± 16.4
431.7 ± 18.1
433.5 ± 35.7
434.1 ± 12.8
436.0 ± 19.1
439.2 ± 10.7
440.7 ± 14.5
443.6 ± 10.8
449.6 ± 19.6
452.4 ± 17.1
Sadlerochit
96DH102
Age (Ma)
415.9 ± 6.6
420.2 ± 12.5
433.1 ± 12.4
445.3 ± 14.6
452.7 ± 7.1
453.5 ± 26.3
464.7 ± 7.7
466.9 ± 11.4
467.4 ± 9.3
469.4 ± 11.4
472.8 ± 19.9
481.9 ± 22.3
488.2 ± 15.9
512.5 ± 28.6
518.1 ± 8.9
519.0 ± 10.1
520.7 ± 13.2
520.8 ± 11.9
520.9 ± 19.8
522.6 ± 23.2
523.0 ± 11.4
524.7 ± 10.8
524.9 ± 21.7
526.3 ± 10.6
526.7 ± 15.3
528.4 ± 16.1
528.9 ± 8.5
529.4 ± 13.8
531.3 ± 17.3
532.5 ± 12.7
533.6 ± 5.2
534.5 ± 17.6
539.7 ± 9.4
549.4 ± 17.3
550.0 ± 9.3
553.6 ± 38.9
554.3 ± 14.7
557.1 ± 21.9
558.8 ± 12.2
560.8 ± 17.5
560.8 ± 26.9
563.6 ± 9.1
564.1 ± 10.0
564.3 ± 23.8
564.7 ± 9.6
566.5 ± 17.2
568.0 ± 15.6
570.0 ± 10.3
572.2 ± 20.4
573.2 ± 8.7
Sverdrup
AE1
Age (Ma)
354.4 ± 10.1
362.1 ± 11.8
434.2 ± 4.1
450.2 ± 16.5
453.2 ± 7.3
456.8 ± 10.5
465.8 ± 14.8
465.9 ± 16.2
697.1 ± 58.2
1045 ± 60
1074 ± 88
1090 ± 68
1131 ± 37
1135 ± 60
1135 ± 30
1162 ± 24
1162 ± 35
1187 ± 56
1204 ± 47
1207 ± 25
1208 ± 32
1212 ± 79
1216 ± 13
1228 ± 62
1228 ± 31
1233 ± 82
1234 ± 93
1250 ± 91
1265 ± 45
1271 ± 24
1290 ± 59
1306 ± 21
1374 ± 30
1376 ± 43
1396 ± 43
1609 ± 96
1610 ± 38
1641 ± 24
1643 ± 17
1646 ± 37
1653 ± 52
1666 ± 28
1666 ± 49
1667 ± 19
1673 ± 25
1696 ± 19
1708 ± 17
1711 ± 31
1723 ± 21
1730 ± 27
Sverdrup
AE2
Age (Ma)
376.3 ± 11.4
387.9 ± 10.8
426.2 ± 11.2
432.4 ± 8.2
447.8 ± 12.8
452.6 ± 29.7
464.2 ± 12.6
472.1 ± 14.7
473.9 ± 5.8
478.3 ± 11.7
504.2 ± 14.3
509.0 ± 7.4
509.5 ± 17.4
511.7 ± 9.0
511.7 ± 11.9
516.1 ± 18.3
530.5 ± 11.5
531.4 ± 8.6
534.7 ± 9.6
536.3 ± 13.1
536.5 ± 8.8
540.0 ± 9.6
543.7 ± 9.7
548.0 ± 10.6
549.8 ± 26.3
549.9 ± 22.6
550.3 ± 20.2
551.3 ± 13.3
551.9 ± 26.2
552.8 ± 13.5
554.3 ± 20.4
554.7 ± 10.5
556.4 ± 24.9
558.3 ± 12.3
559.6 ± 13.3
559.7 ± 11.7
561.3 ± 17.5
562.2 ± 12.0
563.1 ± 32.5
566.5 ± 11.5
567.1 ± 27.4
567.1 ± 11.2
567.6 ± 21.7
567.6 ± 18.6
569.2 ± 16.1
569.4 ± 26.1
570.9 ± 6.0
572.2 ± 10.5
572.2 ± 12.4
572.2 ± 17.2
p.24
2492 ± 20
429.6 ± 12.3
431.6 ± 8.0
438.7 ± 12.9
439.9 ± 16.8
440.0 ± 11.7
440.3 ± 12.0
442.3 ± 8.0
445.6 ± 13.4
450.7 ± 23.7
450.9 ± 30.5
452.3 ± 12.5
456.3 ± 9.2
459.6 ± 17.5
490.5 ± 10.4
518.0 ± 11.6
553.5 ± 11.7
581.9 ± 23.7
600.5 ± 9.7
615.1 ± 17.9
638.5 ± 16.6
644.6 ± 23.7
646.7 ± 16.1
662.3 ± 25.8
739.0 ± 40.0
751.7 ± 30.7
805.3 ± 28.9
815.8 ± 46.8
909.1 ± 23.0
928.4 ± 20.6
1228 ± 66
1292 ± 57
1715 ± 47
1722 ± 66
1747 ± 18
1767 ± 89
1834 ± 36
1876 ± 31
1953 ± 41
2051 ± 23
2063 ± 71
2136 ± 32
2166 ± 16
2302 ± 18
2674 ± 12
453.0 ± 17.4
453.7 ± 11.5
481.5 ± 17.2
536.6 ± 19.0
537.9 ± 19.4
544.2 ± 14.7
561.3 ± 19.4
569.0 ± 33.6
598.4 ± 7.8
611.1 ± 21.1
611.2 ± 20.0
677.6 ± 7.7
799.4 ± 21.5
817.4 ± 13.6
867.2 ± 14.3
870.7 ± 23.2
904.5 ± 20.6
908.3 ± 26.8
974.5 ± 34.0
1066 ± 84
1204 ± 66
1227 ± 69
1243 ± 62
1277 ± 50
1362 ± 69
1454 ± 55
1499 ± 71
1846 ± 48
1862 ± 46
1903 ± 11
1955 ± 49
1963 ± 42
1977 ± 26
1986 ± 39
2033 ± 12
2149 ± 25
2274 ± 21
2329 ± 47
2352 ± 17
2490 ± 15
2512 ± 7
2536 ± 37
2555 ± 24
577.3 ± 24.0
579.2 ± 14.3
582.7 ± 18.2
585.8 ± 22.0
589.8 ± 24.7
590.3 ± 24.3
595.2 ± 12.5
599.3 ± 15.7
614.2 ± 28.0
615.7 ± 7.7
616.7 ± 20.5
623.5 ± 30.0
679.1 ± 21.0
681.1 ± 10.1
684.8 ± 27.1
874.1 ± 12.2
882.1 ± 20.4
883.4 ± 10.2
893.9 ± 23.2
895.8 ± 31.5
916.1 ± 30.6
950.3 ± 39.9
1049 ± 22
1058 ± 37
1065 ± 11
1069 ± 22
1095 ± 77
1097 ± 73
1140 ± 50
1160 ± 38
1195 ± 62
1204 ± 48
1218 ± 54
1228 ± 45
1239 ± 57
1607 ± 19
1654 ± 36
1765 ± 41
1849 ± 9
1970 ± 21
1985 ± 47
2609 ± 21
2636 ± 15
2638 ± 28
2681 ± 33
1742 ± 18
1744 ± 20
1751 ± 43
1754 ± 35
1763 ± 22
1764 ± 34
1775 ± 18
1776 ± 21
1779 ± 29
1786 ± 21
1799 ± 19
1803 ± 17
1841 ± 52
1847 ± 21
1870 ± 24
1904 ± 84
1919 ± 25
1932 ± 28
1933 ± 20
1937 ± 19
1945 ± 23
1986 ± 13
1993 ± 17
2020 ± 19
2024 ± 19
2397 ± 33
2432 ± 18
2476 ± 26
2488 ± 40
2599 ± 16
2695 ± 17
2724 ± 16
2736 ± 17
2834 ± 18
2938 ± 16
3184 ± 16
572.5 ± 16.7
574.6 ± 17.2
574.7 ± 15.4
575.3 ± 16.7
578.4 ± 12.9
578.4 ± 14.7
578.5 ± 10.0
585.8 ± 16.2
587.1 ± 16.1
587.5 ± 17.8
589.6 ± 20.6
590.7 ± 20.2
600.3 ± 20.4
607.4 ± 25.3
608.3 ± 20.8
619.5 ± 12.7
621.4 ± 32.4
629.5 ± 38.7
662.1 ± 12.9
663.0 ± 17.9
675.1 ± 24.0
751.1 ± 15.9
906.3 ± 39.3
921.2 ± 9.0
1021 ± 65
1058 ± 28
1076 ± 83
1115 ± 56
1129 ± 28
1170 ± 51
1210 ± 82
1211 ± 43
1257 ± 42
1265 ± 50
1277 ± 34
1354 ± 75
1473 ± 20
1610 ± 68
1612 ± 33
1657 ± 18
1693 ± 44
1832 ± 17
1833 ± 17
1845 ± 47
1858 ± 25
1883 ± 37
Uncertainties are at the 95% confidence interval.
Interpreted ages for grains <1.2 Ga are 206Pb/238U ages.
Interpreted ages for grains >1.2 Ga are 206Pb/207Pb ages.
The complete isotopic and age data can be found in the Supplementary Data Repository.