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

Origin of and Tectonic Controls for
Yakobi Metallogenic Belt
The gabbroic Ni-Cu deposits and host mafic and ultramafic rocks in the Yakobi metallogenic belt formed during
intrusion into the Oligocene La Perowe Plutonic Suite into highly-deformed and low-grade, regionally metamorphosed rocks of
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the Chugach accretionary wedge and subduction-zone tenane (Woodsworth and others, 1991; Brew, 1993, 1994; Moll-Stalcup
and others, 1994). Intrusion occurred in the early Tertiary diw cessation of accretion and suMuctioa ofthe Chugach terrane in the
earliest Tertiary. The early Tertiary La Perouse Plutonic Suite is interpreled as forming during final spreading along the Kula-
P
Farallon oceanic ridge during ridge subduction at about 50 lo 60 Ma along he margin of southern end Southeastern Alaska
(Bradley and others, 1993; Kusky and others, 1997). The early Tertiary subduction of the spreading oceanic ridge, locally partly
preserved in ophiolites in the Prince Winiam terme (Lyhvyn and olhers, 1997; Kusky and Young, 2000, in press), is interpreted
as causing: (1) a regional metamorphic welt and formation of anateclic granites (Ptafkcr and others, 1989b; 1994); (2) rapid
change in component of strike-slip movements aiong the subduction zone bordering the early Tertiary continental margin (Bradley
and others, 1993); and (3) intrusion of the early Tertiary pmitic and rnafic-ultramafie plutonic rock of the Sanak-Baranof plutonic
belt (Hudson, 1979; Moll-Stalcup and others, 1994) in Southem and Southeastern Alaska. The intrusions are interpreted as
forming in a near-trench environmenl during subduction of the Kula-Farallon oceanic ridge (Bradley and others, 1993; Kusky and
others, 1997). Because of temporal and spatial proximity to subduction of the Kula-Farallon oceanic ridge Pkrng h margin of
Southeastern Alaska from about 50 to 60 Ma, the Oligocene La Perouse Plutonic Suite and amwiated plebbroic Ni-Cu &pita of
the Yakobi metallogenic belt are interpreted as forming either: (1) during the last gasp of oceanic ridge mafic plutonnm (&is
article); or (2) possibly slightly later in association wilh strike-slip disnu-ent of a cmtinental-mugin ue (GoW. md
others, 1997, 1998; Goldfarb, 1997).
( Za%rhPCtCu(Cbnarmn
0.5 paFaent
1 Mi-
Contact
0 MOM
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Figure 117. Brady Glacier gabbroic Ni-Cu deposit, Yakobi metallogenic belt, Southeastern Alaska. Schematic southwt--st
cross section. Adapted from Himmelberg and Loney (1 981).