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GRAINS AND TERRANES: WHERE The terranes of Svalbard, Pearya, and Laurentian signature of the North Slope sub-
DID THEY COME FROM? North Slope show clear evidence of terrane and Franklinian basin. Terranes with
Evidence for terrane displacement along Mesoproterozoic and older material consis- this signature are assigned origins adjacent
the Arctic margin can be evaluated by com- tent with derivation from Laurentia but dis- to Baltica or Siberia (e.g., Beranek et al.,
paring detrital zircon data from the Paleozoic tinct from passive margin units in the 2013; White et al., 2016), consistent with fau-
passive margin to terranes thought to have Franklinian basin. The Precambrian signa- nal (Soja and Antoshkina, 1997) and paleo-
moved along it. Critical components include ture of the North Slope subterrane is most magnetic (Bazard et al., 1995) data.
(1) variation in detrital zircon signatures compatible with northeastern Laurentia Ordovician to Silurian arc magmatism
across northern Laurentia; (2) the ca. 970 Ma (Greenland), making a strong case for large- observed in the Arctic terranes indicates
signature of the convergent margin external scale translation of a peri-Laurentian frag- that they largely represent displaced arc
to Rodinia; (3) Neoproterozoic magmatic ment along the Arctic margin (Gibson et al., fragments. The age of individual peaks var-
ages; and (4) Ordovician, Silurian, and 2021). The Tonian (ca. 970 Ma) signature of ies by terrane, and Hf isotopes range from
Devonian arc magmatism common to many the Pearya, Svalbard, Arctic Alaska, and juvenile (>+5 ɛHf ) to evolved (<–5 ɛHf )
t
t
of the displaced terranes. Tracking detrital Farewell terranes clearly distinguishes these settings (Fig. 2B), tracking differences in
zircons in combination with their Hf isotopic crustal fragments from the Franklinian mar- arc basement and proximity to active con-
signatures demonstrates significant differ- gin (Fig. 2). The Tonian signature is subtle to vergent boundaries. For example, Ordovician
ences in provenance history between Arctic absent in the Alexander and Yukon-Tanana signatures are dominant in the Pearya,
terranes and the Laurentian margin. For terranes, making it a useful discriminant as Alexander, Farewell, and Arctic Alaska ter-
example, Proterozoic to Devonian units of well. Evidence for Neoproterozoic–early ranes, but lacking in Svalbard and portions
Svalbard remain similar throughout their Paleozoic (710–520 Ma) magmatism coeval of the Yukon-Tanana terrane. Silurian mag-
evolution, whereas Proterozoic to Silurian with activity in the Timanide orogen of east- matic rocks are absent from Pearya and the
components of the Alexander terrane are ern Baltica (Fig. 3) appears in the Pearya, North Slope subterrane although both regions
highly variable but coalesce to a common Arctic Alaska, Farewell, and Alexander ter- record influx of Silurian detrital compo-
signature in the Devonian (Fig. 2A). ranes, but is notably missing from the nents. The εHf signatures for Ordovician and
t

20
A Precambrian input B
Paleozoic input Depleted Mantle Array
-0.4 Sv P Sv SS CWp SS SS P ATb F P3 15 (DM)
Paleoproterozoic Neoproterozoic 0.0 Dim 2 ATb P F YTs ATb P ATn N F YTs D ATb ATs ATn WMA Ordovician Silurian εHf t -5 5 0 Chondritic Uniform
ATn
10
Sv
ATs
F
D
CW
N
Reservoir
N
(CHUR)
0.4
FB
-10
ATs
FB
-15
-0.4 0.0 Dim 1 0.4
Depositional Age εHf -20 ATs Sv N
ATn
Devonian-Carboniferous > +5 ATb P F SS
D
Silurian +5 to -5 -25
Ordovician < -5 Devonian Silurian Ordovician
Proterozoic-Cambrian no data -30
340 350 360 370 380 390 400 410 420 430 440 450 460 470 480 490 500
Age(Ma)
Figure 2. (A) Two-dimensional multidimensional scaling (MDS) plot (Saylor et al., 2017; Kolmogorov-Smirnov comparison of probability density plots, metric
squared test = 0.137) and (B) age-εHf plot of detrital zircon data from units involved in translation along the Canadian Arctic transform system. Annotations
t
on (A) show general detrital age trends reflected in the MDS plot. Alexander terrane data in (B) is plotted as contoured density maps of bivariate kernel
density estimates with contours of 68% (1σ) and 95% (2σ) of peak density and cool to hot color gradient reflecting increasing peak density (Sundell et al.,
2019). Data from Svalbard (Sv); Franklinian basin (FB); Pearya terrane (P; P3—Succession 3); Canadian Arctic Islands clastic wedge (CW; CWp—Parry Islands
Formation); Arctic Alaska terrane (N—North Slope subterrane; SS—southwestern subterranes; D—Doonerak; WMA—Whale Mountain Allochthon); Farewell
terrane (F); Alexander terrane (AT: ATn—northern, St. Elias; ATs—southern, Prince of Wales Island; ATb—Banks Island assemblage); the Yukon-Tanana ter-
rane (YTs) in southeastern Alaska is presented in additional plots and references in the supplemental material . 1

1 Supplemental Material. Probability plots, Shepard plot, and sources of U/Pb data in Figure 2A. Go to https://doi.org/10.1130/GSAT.S.14442635 to access the supplemental
material; contact editing@geosociety.org with any questions.

6 GSA Today | July 2021