USGS Professional Paper 1697 - Alaska Resources Library

Viliga (VL) passive continental-margin terrane and the Omolon
(OM) and Avekova (AK) cratonal terranes. The Kony-Murgal
terrane (KM) contains Triassic, Jurassic, and Neocomian
Boreal fauna (Dagis and others, 1979; Dagis and Dagis, 1984;
Zakharov and others, 1984). The Viliga terrane contains Carboniferous,
Permian, Triassic, and Jurassic Boreal fauna.
(3) The Alazeya arc, consisting of the Alazeya (AL)
and Khetachan (KH) island-arc terranes, continued activity
and moved toward the Omulevka Ridge. Associated with the
Alazeya arc was subduction of part of the Ancestral Pacific
Ocean to form the Aluchin (AC) and Argatas (ARG) accretionary-wedge
terranes. These terranes can be traced by magnetic
anomalies under extensive Cenozoic deposits of the Russian
Northeast (Parfenov and others, 1999). Behind the arc were
fragments of prior Devonian to Pennsylvanian island arcs,
including the Beryozovka turbidite-basin (BE) and the Oloy
(OL) and Yarakvaam (YA) island-arc terranes.
(4) The Kotel’nyi passive continental-margin terrane
(KT) was accreted and became part of the Taimyr Peninsular
collage (TA). Within the Angayucham, Goodnews, and
Seventymile Oceans were previously rifted terranes, including
the Kilbuck-Idono cratonal (KI) and the combined Nixon
Fork-Dillinger-Mystic passive continental-margin terrane
(NX, DL, MY). During this time span, before accretion to
the North American continent, the Dillinger, Mystic, and
Nixon Fork terranes may have experienced several post-rifting
events that formed additional units, such as the Triassic
basaltic rocks that occur in the Tatina River area. Coeval
mafic-ultramafic sills and dikes and cogenetic alkali-olivine
basalt flows host gabbroic Ni-Cu-PGE deposits of the Farewell
(FW) metallogenic belt.
(5) The complex Stikinia-Quesnellia island arc and
associated subduction zones were active. The Stuhini Group is
preserved in the Stikinia (ST) terrane, whereas the Takla and
Nicola Groups are preserved in the Quesnellia (QN) terrane.
Forming with the Stikinia-Quesnellia island arc were the Copper
Mountain (North; CMN), Copper Mountain (South; CMS),
Galore (GL), Guichon (GU), and Texas Creek (TC) belts,
which contain granitic magmatism-related deposits. Also in
the Stikinia island arc terrane is the Sustut (SU) metallogenic
belt of basaltic Cu deposits that is interepreted as forming in in
the upper oxidized parts of an island arc volcanic pile during
shallow burial metamorphism and diagenesis. The Stikinia-
Quesnellia arc is interpreted as forming stratigraphically on the
Yukon-Tanana (YT) and Kootenay (KO) terranes, previously
rifted fragments of the North American Craton Margin (NAM;
Mihalynuk and others, 1994). On the outboard side of the arcs
was subduction of part of the Cache Creek oceanic plate to
form the Cache Creek terrane (CC). The Cache Creek terrane
and similar subduction-zone assemblages, which were tectonically
linked to the Talkeetna and Bonanza arcs, along with the
Chugach (CG), possibly Bridge River (BR), and Baker (BA)
terranes, all contain exotic Permian Tethyan faunas in carbonate
blocks in matrices of mainly early Mesozoic age. The
Cache Creek terrane contains detritus probably derived from
the Stikinia-Quesnellia arc (Monger and Nokleberg, 1996).
Late Triassic Metallogenic Belts (230 to 208 Ma; fig. 32) 83
(6) Parts of the Seventymile (SV) and Slide Mountain
(SM; Anvil Ocean of Templeman-Kluit, 1979) oceanic plates
were obducted onto the Yukon-Tanana (YT) and Kootenay
(KO) terranes, and onto the North American Craton Margin
(NAM). Part of the obduction occurred by the Late Triassic
and (or) Early Jurassic, when granitic plutons of the Stikinia-
Quesnellia arc intruded across an intervening fault.
(7) The beginning of dextral-slip imbrication of the
Stikinia-Quesnellia arc occurred along the Tally Ho shear zone
(Hansen and others, 1990; Hart, 1995; inset, fig. 34). Alternatively,
the present-day configuration of the Stikinia-Quesnellia
island-arc and associated subduction zone terranes may have
formed by oroclinal warping and counter-clockwise rotation
of the Stikinia-Quesnellia arc in response to a combination of
oblique convergence and arc migration toward the companion
subduction zone of the Cache Creek terrane (fig. 34) (Mihalynuk
and others, 1994). Migration of the Stikinia-Quesnellia
arc and associated terranes toward North America was accomplished
by subduction and (or) obduction of the Seventymile
terrane along the continental margin.
(8) The Talkeetna and Bonanza arcs formed along the
length of the Wrangellia superterrane. Forming with the
arcs were (a) the Kodiak Island and Border Ranges (KOD)
metallogenic belt, which contains podiform Cr deposits and
is interpreted as forming in the roots of the arc, (b) the eastern
and western Alaska Range (EAR) metallogenic belt, which
contains gabbroic Ni-Cu, Besshi massive sulfide, and related
deposits, and (c) the Alexander (AX) metallogenic belt, which
contains deposits related to felsic to mafic marine volcanism.
The Talkeetna arc is preserved in the Late Triassic(?) and
Jurassic Talkeetna Formation and coeval granitic plutonic
rocks of the Peninsular sequence (PE) of the Wrangellia
superterrane (WRA), and the Bonzana arc is preserved in the
Cadwallader island-arc terrane (CD). Associated with the
island arcs was subduction of part the Cache Creek oceanic
plate to form the Chugach (CG), possibly Bridge River (BR),
and Baker (BA) terranes. These terranes locally contain early
Mesozoic blueschist (Plafker and others, 1994).
(9) During subduction of the Cache Creek oceanic plate
to form the Talkeetna, Bonanza, and Stikinia-Quesnellia arcs,
limestone blocks containing mainly Permian Tethyan faunas
were accreted, locally in thick and extensive blocks in the subduction-zone
complexes of the Chugach (CG) and Cache Creek
(CC) terranes (Monger and Berg, 1987; Monger and Nokleberg,
1996). Tethyan faunas are generally interpreted as being
derived from the late Paleozoic and early Mesozoic Tethys
Ocean, remnants of which occur in the present-day Mediterranean
region, Middle East, Himalayas, Southeast Asia, eastern
China, Russian Southeast, and Japan (Monger and Ross, 1971;
Monger and others, 1972; Stevens and others, 1997).
(10) In the Wrangellia superterrane (WRA), back-arc
rifting or hot-spot activity formed the widespread basalt fields
of the Nikolai Greenstone and Karmutsen Formation (Barker
and others, 1989; Richards and others, 1991; Lassiter and
others, 1994). The mafic magmatism forming those rocks was
first interpreted as forming in a rift setting (Barker and others,