USGS Professional Paper 1697 - Alaska Resources Library

(6) In the Paleocene (about 56 to 60 Ma), in the area of
the Bering Sea, major counter-clockwise rotation of the Pacific
oceanic plate (PAC) occurred (at about 30º to 50º paleolatitude;
Lonsdale, 1988). The rotation resulted from compression
between Eurasia and North America (Plafker and Berg,
1994). At the same time, the extension of dextral-slip faults
from the area of western Alaska into the Bering Sea resulted in
accretion and capture of a fragment of the Kula oceanic plate
(KULA; Scholl and others, 1992, 1994).
(7) In response to oblique subduction of the Kula oceanic
plate (KULA), the major Kluane continental-margin arc formed
(Plafker, 1994; Nokleberg and others, 2000). Parts of the arc
are preserved as the Kuskokwim Mountains volcanic-plutonic
belt (km) and Alaska Range-Talkeetna Mountains igneous
belt (at). The coeval Coast arc formed along the margin of the
North American Cordillera. Parts of this arc are preserved in
the Coast-North Cascade plutonic belt (cn) and the Kamloops
magmatic belt (kl). These continental-margin arcs overlapped
the previously accreted Wrangellia superterrane and adjacent
inboard terranes and extended for a distance of more than 3,200
km along the active continental margin of the North American
Cordillera. Associated with the Kluane continental-margin arc
was the subduction of the laterally extensive Chugach terrane
(CG) and the Pacific Rim terrane (PAR).
Forming in the Kluane arc in southern Alaska were the
East-Central Alaska (younger part; ECA), Southern Alaska
(SA), and Kuskokwim Mountains (KMT) belts, which are
hosted in the Kuskokwim Mountains sedimentary and volcanic
belt or the Alaska Range-Talkeetna Mountains igneous
belt. Forming in the Coast arc in southeastern Alaska and the
Canadian Cordillera were a large array of metallogenic belts,
which contain granitic-magmatism-related deposits, which are
hosted in or near the Coast-North Cascade plutonic belt. The
belts include the Catface (CF), central-southeastern Alaska
(CSE), Bulkley (BK), Fish Lake-Bralorne (FLB), Gambier
(GA), Nelson (NS), Skeena (SK), and Surprise Lake (SL)
belts. All these belts are interpreted as forming during subduction-related
granitic plutonism.
(8) Along the active margin of the North American Cordillera,
the rapid northward migration of the Kula oceanic plate
(KULA), which started to form at about 85 Ma (Englebretson
and others, 1985), resulted in formation of major dextral-slip
faults, including the Denali (DE), Tintina (TI), Ross Lake (RL),
and companion faults (Plafker and Berg, 1994). Oblique subduction
of the Kula-Farallon oceanic ridge occurred at about 50
to 60 Ma along the margin of southern Alaska (Bradley and others,
1993). The subduction of the oceanic ridge, locally partly
preserved in ophiolites in the Prince William Terrane (Lytwyn
and others, 1997; Kusky and Young, 1999), in the early Tertiary
is interpreted as causing (1) a regional metamorphic welt and
formation of anatectic granites (Plafker and others, 1989b;
1994), (2) rapid changes in components strike-slip movements
along the subduction zone bordering the early Tertiary continental
margin (Bradley and others, 1993), and (3) formation of belts
of early Tertiary granitic and mafic-ultramafic plutonic rocks of
the Sanak-Baranof plutonic belt (unit sab (Hudson, 1979; Moll-
Late Cretaceous and Early Tertiary Metallogenic Belts (84 to 52 Ma) (figs. 102, 103) 219
Stalcup and others, 1994) in Southern and southeastern Alaska,
which are interpreted as forming in a near-trench environment
during subduction of the Kula-Farallon oceanic ridge (Bradley
and others, 1993; Kusky and others, 1997).
In Southern and southeastern Alaska, several metallogenic
belts are interpreted as forming during oblique subduction
of the Kula-Farallon oceanic ridge under margin of
Southern and southeastern Alaska. These metallogenic belts
include the Baranof (BN), Chugach Mountains (CM), Juneau
(JU), Maclaren (MC), and Talkeetna Mountains (TM) metallogenic
belts, which contain Au quartz vein deposits, and the
Yakobi (YK) metallogenic belt, which contains gabbroic Ni-
Cu deposits. (9) Also in the same region, the Prince William
Sound (PW) metallogenic belt, which contains massive sulfide
deposits related to marine mafic volcanic rocks, is interpreted
as forming during sea-floor spreading along the Kula-Farallon
oceanic ridge before subduction of the ridge beneath the
margin of southern Alaska.
(9) Regional extension occurred in the southern Canadian
Cordillera and northeastern Washington. The extension
is interpreted as (1) the result of a change from transpression
to transtension at about 55 Ma (Parrish and others, 1988), (2)
caused by a change of obliquity of convergence of the oceanic
plate, and (or) (3) alternatively, but likely, collapse of overthickened
thrust units.
(10) The eastward thrusting of the North American Craton
Margin (NAM) over the North American Craton (NAC)
ended at about 60 Ma in the Canadian Cordillera.
Metallogenic Belt Formed in Late Mesozoic and
Early Cenozoic Olyutorka Island Arc, Russian
Northeast
Iruneiskiy Metallogenic Belt of Porphyry Cu
Deposits (Map Unit IR), Southern Kamchatka
Peninsula
The small Iruneiskiy metallogenic belt (IR) of porphyry
Mo deposits (Vlasov, 1977) occurs in the southern part of
the Kamchatka Peninsula in the Iruneiskiy island-arc terrane
(fig. 102; tables 3, 4) (Nokleberg and others, 1994c, 1997b,
c, 1998). The one economic porphyry Cu deposit in the belt
at Kirganik (Vlasov, 1977; A.V. Ignatyev, written commun.,
1980) consists of steeply dipping , metasomatically altered
zones of biotite and K-feldspar that occur in Late Cretaceous
siliceous volcanic rocks. The altered zones contain veinlets
and disseminations of pyrite, chalcopyrite, bornite, chalcocite,
hematite, and gold; the zone contain as much as 0.8 g/t
Au. The Late Cretaceous calc-alkalic volcanic rocks hosting
the zones grade upward into Maastrichtian shoshonite that is
intruded by dunite-clinopyroxenite-gabbro monzonite. The
porphyry Cu deposits are interpreted as being related to the
monzonite intrusions. The deposit has a K-Ar isotopic age of
75 to 65 Ma that is similar to that for the intrusion. The deposit
is of medium size, and average grades are 0.1 to 1 percent Cu