Page 7 - i1052-5173-31-7

SIBERIA
SIBERIA
~370 Ma SIBERIA subterrane along the Laurentian continental
Figure 3. Schematic Devo- margin, with the rest of Arctic Alaska and
W F nian paleogeographic recon-
30°N AT Ch T Timanides struction showing terrane Alexander located farther outboard. Final
d d
PALEO-PACIFIC YTs SS D Sv translation on the Canadian contraction in the northern Caledonides, rep-
Arctic transform system
OCEAN CATSTS N (CATS). Modified after Torsvik resented by ultrahigh-pressure metamor-
CA
CATS
BAL
BALTICATICA
incipient YTn BALTICA and Cocks (2017). AT—Alex- phism at 360 Ma in North-East Greenland,
subduction
ST ST S ST P Caledonides ander terrane; Ch—Chukotka; was accompanied by sinistral and dextral
0° S-K D—Doonerak arc; F—Fare- translation that accommodated margin-
PROTO-TETHYS well; N—North Slope sub-
terrane; P—Pearya terrane;
LAURENTIAURENTIAURENTIA
LA OCEAN S-K—Sierra-Klamath ter- parallel escape from the orogen (Gilotti and
LA
ranes; SS—southwestern McClelland, 2007). This intra-Caledonian
Arctic Alaska subterranes; strike-slip system was truncated by the
30°S GONDW ST—Stikinia; Sv—Svalbard; CATS, effectively transferring Caledonian
GONDWANAANA
GONDWANA
W—Wrangellia; YTn—Yukon-
~1000 km RHEIC OCEAN Tanana terrane in Yukon; rocks of Svalbard to the Arctic margin
YTs—Yukon-Tanana terrane
(Fig. 3). The eastern continuation of CATS
in southeastern Alaska.
orogenic belt subduction zone transform ridge projects toward the truncated margin of
northern Scandinavia marked by the
Trollfjord- Komagelva fault system, requir-
Silurian zircon in most terranes, ranging PALEOZOIC EVOLUTION OF THE ing an Ordovician–Devonian strike-slip
from +5 to –15, record evolution in settings NORTHERN LAURENTIAN MARGIN history on this or an outboard structure along
with variable input from older continental The variations in zircon age and εHf sig- the Timanide-Baltica suture.
t
sources, either from the arc basement or natures in circum-Arctic and Cordilleran The amalgamated terranes translated
influx of continentally derived sedimentary terranes record changes in Paleozoic arc along the Arctic margin shed detritus with
material. In stark contrast, the southern magmatism that broadly represent a north- characteristic juvenile isotopic signatures
Alexander terrane on Prince of Wales Island, ern continuation of the arc system associated (e.g., Anfinson et al., 2012) southward into
along with the Doonerak arc and Whale with closure of Iapetus and the subsequent the Canadian Arctic Island clastic wedge
Mountain allochthon of Arctic Alaska, con- Silurian collision of Baltica with Laurentia (Fig. 1). Middle Devonian arc magmatism
sistently have a juvenile signature that indi- (Fig. 3; Strauss et al., 2017). These arc com- developed in Arctic Alaska simultaneously
cates evolution in an intraoceanic setting iso- plexes are best viewed as age equivalent to with clastic wedge deposition. This activity
lated from any continental input throughout subduction-related rocks preserved in the was contemporaneous with Uralian arc mag-
their pre-Devonian history (Fig. 2). thrust sheets of the Caledonides. Svalbard matism on the Baltican margin, but the two
Devonian–Carboniferous detrital zircon represents a Caledonian signature; however, systems were separated by the CATS. The
signatures define amalgamation of terranes the other circum-Arctic terranes are arc Late Devonian marks a transition to subduc-
and juxtaposition with the Arctic margin. The complexes that extended beyond the tion initiation along the western margin of
Devonian clastic wedge in the Canadian Caledonides and are characterized by a mix- Laurentia with granitic magmatism present
Arctic Islands records deposition on Laurentia ture of juvenile intraoceanic fragments (e.g., in the North Slope subterrane to the north
from a more juvenile source emplaced along southern Alexander terrane, Doonerak) and and Yukon-Tanana, Stikinia, Quesnellia,
the Franklinian margin (Patchett et al., 1999). arc fragments with continental substrates Kootenay, and Sierra-Klamath terranes to
Late Devonian units (e.g., Parry Islands (e.g., Pearya, northern Alexander terrane). the south (Fig. 3). The CATS effectively
Formation) at the top of the wedge are domi- Translation associated with the CATS initi- accommodated migration of Paleozoic arcs
nated by Neoproterozoic to Devonian grains ated as Ordovician and Silurian subduction active outboard of the Laurentian margin
with juvenile εHf (Anfinson et al., 2012). This migrated along the northern Laurentian mar- into the paleo-Pacific realm. Latest stages of
t
shift in signature is consistent with recycling gin. Subduction-related rocks inboard of Ellesmerian shortening and translation on
of Silurian units from the Pearya, Farewell, Pearya are inferred to record transpressional the northern margin coincide with the start
northern Alexander, and Arctic Alaska ter- collapse of the Ordovician arc against the of Yukon-Tanana magmatism in the northern
ranes (Fig. 2). The εHf values for Ordovician Franklinian margin, with Silurian arc activity Cordillera (Colpron and Nelson, 2009).
t
to Early Devonian grains in many terranes are continuing offshore as subduction migrated
markedly juvenile but show a sharp pull down westward. The location of Siberia and its role MESOZOIC TRANSLATION AND
in the Late Devonian (Fig. 2), which reflects in the transfer of circum-Arctic terranes to the OPENING OF THE CANADA BASIN
increased crustal involvement due to contrac- Cordilleran margin is poorly understood, but Despite lithologic, sedimentologic, and
tion and perhaps collision. The Banks Island relative motion between Baltica, Siberia, and structural arguments for translation of Arctic
and northern (St. Elias) units of the Alexander the Arctic terranes likely increased after the Alaska along the northern Laurentian mar-
terrane (Fig. 1) show a transition from strongly Silurian Baltica–Laurentia collision. Silurian gin (Patrick and McClelland, 1995; Oldow et
evolved in Ordovician–Silurian grains to translation placed several crustal fragments al., 1987, 1989; Dickinson, 2009), Early
dominantly juvenile values—a signature that and arc terranes along the Arctic margin. Cretaceous counterclockwise rotation of
is more consistent with the southern Alexander Silurian to Early Devonian arc activity con- Alaska is the generally accepted model for
terrane (Fig. 2). This transition, combined tinued in outboard terranes destined to opening of the Canada Basin (Grantz et al.,
with the similarity in detrital zircon patterns, approach the Cordilleran realm. 2011). The rotation model persists in large
suggests Devonian amalgamation of the dis- Devonian displacement on the CATS part due to a perceived lack of evidence for
parate Alexander fragments. emplaced Pearya and the North Slope Mesozoic displacement on the Canadian
www.geosociety.org/gsatoday 7