USGS Professional Paper 1697 - Alaska Resources Library

cham oceans were closed, and the Chukotka (CH) and Arctic
Alaska terranes (AA) were accreted to Northeast Asia. During
accretion, the Chukotka metallogenic belt, which contains Au
and Sn quartz vein deposits, was formed. Also during accretion,
the major Nutesyn and Koyukuk island arcs and companion
subduction zones were thrust onto the continental-margin
Chukotka terrane (CH) and Arctic Alaska superterrane (AA)
in thrust sheets that are as much as 150 km wide in Northern
Alaska. The overthrust subduction-zone terranes include the
South Anyui (SA), Velmay (VE), Angayucham (AG), and
Goodnews (GD) terranes. The overthrust island arc terranes
include the Nutesyn (NU), Koyukuk (KY), and Togiak (TG)
terranes. A final stage of blueschist-facies metamorphism
of oceanic and continental-margin terranes occurred during
thrusting. The lack evidence of a huge Himalayan-type mountain
range in the Russian Northeast suggests that (1) strike-slip
translation was more dominant than rifting in formation of the
Canada Basin (Lane, 1994, 1997), and (or), (2) a major part
of the rift migration of the Russian Northeast away from the
Canada Basin was absorbed in the subduction zone associated
with formation of the Okhotsk-Chukotka arc.
(7) During accretion, the southern margin of the eastern
Chukotka terrane (CH), southern part of the Arctic Alaska
superterrane (AA), and the outboard Seward (SD), Coldfoot
(CO), Goodnews (GD), and Ruby (RB) terranes continued
to be intensely deformed and metamorphosed. At the end of
accretion, a period of extensional deformation occurred along
the southern margin of the Arctic Alaska superterrane (AA;
Miller and Hudson, 1991).
(8) Back-arc continental-margin sedimentation in Kuskokwim
Basin (kw) occurred in a dextral wrench-fault setting
(Bundtzen and Miller, 1997).
(9) The final stage of accretion of the Wrangellia superterrane
(WRA) was completed at about 95 Ma. Forming during
the final stage of accretion in Alaska were (a) the Yukon-
Tanana metallogenic belt (YT), which contains Au quartz vein
deposits, (b) the East-Central Alaska metallogenic belt (older
part, ECA), which contains granitic magmatism-related deposits,
and (c) the Wrangell Mountains metallogenic belt (WR),
which contains Cu-Ag quartz vein and Kennecott Cu deposits.
Several major geologic events are interpreted as caused by the
accretion of the Wrangellia superterrane: (a) The extensive
Gravina island arc, which formed along the leading edge of the
superterrane, and the Spences Bridge volcanic-plutonic belt
(sb) ceased activity after accretion. (b) The Kahiltna (kh) and
Gravina-Nutzotin-Gambier (gg) assemblages were thrust under
the North American continental margin (Stanley and others,
1990; McClelland and others, 1991, 1992a,b; Nokleberg and
others, 1994a) and were intensely deformed during a major
period of orthogonal convergence that replaced the previous
sinistral convergence. (c) The northeastern-most boundary of
the accreted Wrangellia superterrane became the locus of Late
Cretaceous high-grade metamorphism, plutonism, contractional
deformation, crustal thickening, uplift, and erosion that
characterizes the Coast Mountains of the Canadian Cordillera,
southeastern Alaska, and South-Central Alaska (McClelland
Early Late Cretaceous Metallogenic Belts (100 to 84 Ma; figs. 79, 80) 181
and others 1991, 1992a,b; Pavlis and others, 1993; Plafker and
Berg, 1994; Monger and Nokleberg, 1996). (d) A regional core
complex formed in the previously accreted Yukon-Tanana terrane
(part of the collage in present-day Alaska) and developed a
subhorizontal fabric, imbricate thrusting of large subhorizontal
nappes, and subsequent extension and removal of as much as
10 km of crust (Pavlis and others, 1993). (e) The southern part
of Gravina arc and companion subduction zone was doubled
during the latest stage of sinistral-slip faulting during accretion
of the Wrangellia superterrane (McClelland and others 1991,
1992a,b; Monger and others, 1994; Monger and Nokleberg,
1996). The Methow turbidite-basin terrane (MT), an Early and
mid-Cretaceous fore-arc part of the Gravina arc, and the companion
Bridge River (BR) and Easton (EA) subduction-zone
terranes were structurally imbricated behind the southern part
of the Gravina-Nutzotin-Gambier (gg) assemblage (Monger
and others, 1994). (f) The mainly orthogonal convergence and
accretion of the Wrangellia superterrane initiated eastward
thrusting of the North American Craton Margin (NAM) over
the North American Craton (NAC). (g) Coeval with thrusting,
and occurring along the axis of thrusting was intrusion of the
Omineca-Selwyn granitic belt (om), which occurs along the
length of Canadian Cordillera, Alaska, and the northern part
of the Russian Northeast. The belt was generated during an
intense period of anatectic melting, major regional thrusting,
and crustal shortening and thickening, all related to orthogonal
convergence. Continuing to form in or near the Omineca-
Selwyn granite belt were the Bayonne (BA), Cassiar (CA),
Selwyn (SW), and Whitehorse (WH) metallogenic belts, which
contain granitic-magmatism-related deposits. Alternatively,
the Wrangellia superterrane accreted far to the south at about
35° paleolatitude along the margin of Baja British Columbia
(latitude of present-day Baja California).
Metallogenic Belt Formed in Late Mesozoic Part
of East Sikhote-Aline Continental-Margin Arc,
Russian Southeast
Sergeevka Metallogenic Belt of Granitoid-
Related Au Deposits (Belt SG), Southern Part of
Russian Southeast
The Sergeevka metallogenic belt of granitoid-related Au
deposits (fig. 79; tables 3, 4) occurs in the southern part of
the Russian Far East. The Au deposits occur in or near Late
Cretaceous, postaccretionary granitoid plutons and dikes that
intrude gneissic gabbro and Cambrian metamorphosed sedimentary
rocks in the western part of the Sergeevka continental-margin
arc terrane of the Khanka superterrane (fig. 79).
The principal deposits are at Askold, Balykovskoe, Krinichnoe,
Porozhistoe, and Progress (table 4) (Nokleberg and others
1997a,b, 1998). The deposits are small and generally consist
of Au-bearing quartz veins with minor sulfides, mainly pyrite
and arsenopyrite. The deposits are generally small.