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Arctic margin. Strike-slip faults are clearly Siberia
exposed on Ellesmere Island and record a Figure 4. Schematic Mesozoic
paleogeographic reconstruction
complex history of post-Carboniferous to showing the role of the Canadian
Eocene sinistral and dextral displacement SAZ ESB Arctic transform system (CATS) in
opening of the Canada Basin and
(Piepjohn et al., 2013). These structures large magnitude extension in the
record reactivation of the Paleozoic trans- Chukotka PB Lomonosov Ridge Amerasian Basin. Modified after
Patrick and McClelland (1995),
form margin. West of Ellesmere Island to the CBL AMR MB Dickinson (2009), Miller et al.
Yukon-Alaska mainland, the structural his- SAR (2018), and Døssing et al. (2020).
AMR—Alpha-Mendelev Ridge;
tory of the Canadian margin is in question. CB CATS CB—Canada Basin; CBL—Chuk-
Although conventionally interpreted as Arctic Alaska Laurentia chi Borderland; ESB—East Sibe-
representative of Mesozoic extension, pub- rian basins (see Nikishin et al.,
2021); MB—Makarov basin; PB—
lished seismic reflection profiles across the Podvodnikov basin; SAR—south
northern boundary of the Sverdrup basin Amerasia ridge; SAZ—South Anyui
suture zone. Extent of thin crust
(Embry and Dixon, 1990) show the bound- (<10 km) is from Lebedeva-Ivanova
ary to be disrupted by near-vertical faults Crustal thickness <10 km convergent plate boundary et al. (2019).
more reasonably interpreted as strike-slip Strike-slip / transform fault normal fault
faults. The faults separate blocks with sub-
stantial differences in thickness of Late
Jurassic and Early Cretaceous sedimentary much more limited extent of oceanic crust displacement along the Arctic margin
rocks. The faults cut and are locally sealed (Chian et al., 2016), and interpretation of geo- (Piepjohn et al, 2013) and the Porcupine shear
by Late Cretaceous clastic rocks that indi- physical lineaments as transform structures zone marks reactivation of the central and
cate displacement into the late Mesozoic. has produced models invoking strike-slip western segments of the CATS, respectively.
Along Prince Patrick Island, the faults trun- faults within the Canada Basin (Hutchinson et Activity on the western CATS was linked
cate Paleozoic and Mesozoic stratigraphic al., 2017). These new models will be greatly with continued evolution of the Cordilleran
and structural trends at a high angle to the improved by incorporating the CATS. In fact, strike-slip orogen (Murphy, 2019).
margin (Harrison and Brent, 2005). Local the recent transform model of Døssing et al.
evidence of extensional deformation is (2020) explicitly requires sinistral translation CONCLUDING REMARKS
described along Banks Island (Fig. 1; Helwig on the Porcupine shear zone. Many uncertain- Available field evidence strongly supports
et al., 2011) in a segment of the boundary ties remain regarding the crustal composition the presence of a long-lived strike-slip fault
characterized by a slight deflection in strike and the timing and magnitude of extension extending from North Greenland westward to
consistent with an extensional step in a within the Canada Basin and broader Alaska along the northern Laurentian margin.
sinistral transcurrent fault system (Fig. 4). Amerasian Basin (Lebedeva-Ivanova et al., Onshore and offshore observations are con-
Seismic sections west of Banks Island doc- 2019), but tectonic models place the region in sistent with Paleozoic translation of arc ter-
ument near-vertical structures that truncate a back arc setting relative to the Mesozoic ranes and crustal fragments along the CATS,
the continental margin along the Tuk trans- Cordilleran margin (Miller et al., 2018). followed by Mesozoic reactivation to accom-
form (Helwig et al., 2011). Integrating our land-based observations of modate regional extension of continental and
The Porcupine shear zone, separated from translation with the offshore geophysics pro- hybrid crust (Miller et al., 2018) during trans-
the Tuk transform to the east by a series of vides a realistic geodynamic model for the lational opening of the Canada Basin.
north-striking Cenozoic faults that record Cretaceous opening of the Canada Basin in Ongoing geochronologic and kinematic stud-
east-west contraction and disrupt the simple this setting (Fig. 4). The greater Amerasian ies of fault rocks will provide additional
continuation of the CATS, is essential to Basin is best viewed as a domain of large- insight on the magnitude, timing, and direc-
translation models for opening of the Canada magnitude extension in response to slab roll- tion of displacement along the length of the
Basin. Preliminary structural studies sup- back on the paleo-Pacific margin that is bound boundary. Pre-Devonian terrane translation
ported Late Jurassic to Early Cretaceous by strike-slip displacement on the Laurentian complicates restorations based on age or litho-
sinistral transpression along the Porcupine and Siberian margins (Miller et al., 2018). logic similarities since many correlations are
shear zone (Oldow and Avé Lallemant, Transforms on the Siberian margin and within non-unique. In addition, extension within the
1993). Recent studies have demonstrated that the Canada Basin are commonly accepted as Canada Basin accommodated by transform
reactivation of the Porcupine shear zone components of the rotational model (Amato et boundaries on the Canadian and Chukchi
involved Jurassic and Cretaceous rocks (von al., 2015; Doré et al., 2016). Sinistral reactiva- Borderland margins does not preclude block
Gosen et al., 2019). Although the magnitude tion of the CATS on the Laurentian margin rotation within the basin, leading to hybrid
and timing of Mesozoic displacement on the similarly bounds the extensional domain to models (Miller et al., 2018).
Porcupine shear zone is not well documented the south. Block rotation of northern Alaska The rotation model for opening of the
at present, sinistral translation associated related to opening of the Canada Basin is Canada Basin has long rested on stratigraphic
with opening of the Canada Basin is clear. permissible but no longer required. arguments (e.g., Embry, 1990). Early struc-
Marine geophysical data have long been Cenozoic reactivation of the CATS is tural analysis recognized translation of units
interpreted in support of the rotation model, recorded along its length. Displacement on with different Paleozoic and Mesozoic defor-
particularly satellite gravity data that was the de Geer transform during opening of the mation histories (Oldow et al., 1987, 1989), but
inferred to represent a spreading center Eurasian Basin records reactivation at the the necessary kinematic and timing con-
(McAdoo et al., 2008). New data suggest a eastern end (Doré et al., 2016). Dextral straints were missing, thus allowing the

8 GSA Today | July 2021