Metallogenesis and Tectonics of the Russian Far East, Alaska, and ...

metallogenic belt (SP) which contains Sn skarn and related deposits, and the West-Central Alaska metallogenic belt (WCA) which
contains porphyry Cu deposits.
(4) Between the areas of the Russian Far East and Alaska, continental-margin arcs and companion subduction zones in
each region were connected by a major transform fault. In the area of Western Alaska, tectonic escape (crustal extrusion) of
terranes occurred along major dextral-slip faults, including the Denali (DE), Iditarod-Nixon Fork (NF), Kaltag (KA), and
companion faults (Scholl and others, 1992. 1994). In association with movement on these major dextral-slip faults, dextral-wrench
sedimentary basins formed, including the Kuskokwim basin (kw; Plafker and Berg, 1994; Bundtzen and Miller, 1997). The crustal
extension and wrench faulting were associated with a major period of extension in Interior Alaska according to the interpretation
of Miller and Hudson (1991). The middle and Late Cretaceous extension is interpreted as forming warm, thin continental crust
which was favorable for crustal extrusion and dext~al-wrench faulting (Scholl and others, 1992, 1994).
(5) By the early Tertiary, in the region of the Amerasia (ab), Canada (cb) and Eurasia (eb) Basins, sea-floor spreading
and associated rifting was completed (Grantz and others, 1990, 1991, 1998), and sedimentation continued in the large Arnerasia
(ab), Canada (cb) and Eurasia (eb) Basins. The formation of the Alpha and Mendeleev Ridges (am), which are interpreted as large
piles of hot-spot basalt and associated deposits, was completed (Grantz and others, 1990, 1991, 1998).
(6) In the Paleocene (about 56 to 60 Ma), in the area of the Bering Sea, major counter-clockwise rotation of the Pacific
Ocean plate (PAC) occurred (at about 30" to 50" 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 Ocean plate (KULA; Scholl and
others, 1992, 1994).
(7) In response to oblique subduction of the Kula Ocean 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
(krn) 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 krn 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-Takeetna 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 Ocean 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 (To, 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, 2000), in the early Tertiary is interpreted as causing: (I) 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 (sab; Hudson, 1979; Moll-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 either 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, 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.