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

tectonic erosion of the margins of terranes. In the case of dislocation, detailed analysis of each terrane with respect to in-place
overlap assemblages, passive continental-margin assemblages, and cratonal assemblages should provide the original site of origin.
In the case of lectonic erosion, as in the case of subduction-zone terranes, large parts of the original unit (such as an oceanic plate)
may have been thrust to great depths and thereby may essentially have disappeared.
An important interpretation in the metallogenic-tectonic model is that a succession of coeval single arcs and companion
subduction zones, and their contained, pre-accretionary metallogenic belts formed on or near the margins of the North Asian and
North American Plates. One consequence of this interpretation is that many of the complexities of the collage of accreted terranes
and contained metallogenic belts in the region are the results of oblique subduction and resultant strike-slip displacements within
active continental margins, rather than the migration of island-arc systems across ocean basins to accrete eventually to the margins
of plates. Substantiation of this interpretation will require: (1) determination of the facing directions of the arcs with respect to
cratons; (2) correlation of coeval arc and tectonically linked (companion) subduction zones to establish them as different parts of a
former, single, curvilinear arc/subduction-zone system; and (3) determination of the linkage of arcs to cratons. This interpretation
is reasonably well established for most of the Mesozoic and Cenozoic, but less so for the Paleozoic. For each time interval (stage)
in the metallogenic-tectonic model, specific (numbered) tectonic events are described in a clockwise order, according to similar
tectonic environments, starting with the area of the Russian Southeast and ending with the area of the southern Canadian
Cordillera. The time scale used for the tectonic model is from Palmer (1983).
Paleomagnetic Dilemma:
Loci of Accretion of Wrangellia Superterrane
A major paleomagnetic dilemma exists for the loci of accretion of superterranes to the margin of the North American
Craton in the mid-Cretaceous to early Tertiary. The dilemma consists of two conflicting hypotheses for the loci of accretion of the
Wrangellia superterrane, which constitutes most of the Insular superterrane, and the Intermontane superterrane which consists of
the Stikinia, Quesnellia, and Cache Creek terranes (Cowan. 1994; Cowan and others, 1997). One hypothesis, based on geologic
evidence, including magmatic, stratigraphic, and faunal ties, interprets the Wrangellia superterrane as accreting at a northerly
paleolatitude, approximately at its present latitude. The other hypothesis, based on paleomagnetic data for both continental
volcanic rocks and coeval plutonic rocks, interprets the Wrangellia superterrane and the western part of the Intermontane terrane
as accreting at a paleolatitude approximately 3,000 km farther south. This hypothesis is informally named the Baja British
Columbia controversy, in reference to accretion of the Wrangellia superterrane at the approximate latitude of Baja California
(Umhoefer, 1987; Cowan and others, 1997; Dickinson and Butler, 1998). For the synthesis of the tectonic evolution of the
Circum-North Pacific, these two hypothesis are called the northern-accretion interpretation and southern-accretion interpretation.
For the metallogenic analysis of the Wrangellia superterrane in the Mesozoic and early Cenozoic, only the northern-accretion
interpretation is considered. For additional information and references for both interpretations, please refer to the discussion and
references in Nokleberg and others (2000).
Proterozoic Metallogenic Belts
(2500 to 570 Ma; Figures 2, 3)
Overview
The major Proterozoic metallogenic belts in the Russian Far East, Alaska, and the Canadian Cordillera are summarized in
table 3 and portrayed on figures 2 and 3. The major belts (and their major mineral deposit types) are as follows. (1) In the central
and southeastern part of the Russian Northeast, are the Bilyakchan (BI) (basaltic Cu), Oroek (OK) (ironstone and sediment-hosted
Cu), Omolon (OM) (Ironstone (Superior Fe)), and Ulkan (UL) (Felsic Plutonic REE and related deposits) metallogenic belts.
These belts are interpreted as forming during incipient rifting of the passive continental margin of the North Asian Craton or
Craton Margin. (2) In the same region are the Lantarsky-Dzhugdzhur (LD) metallogenic belts of anorthosite-hosted apatite Ti-Fe
and gabbroic Cu-Ni-Co-PGE that is interpreted as forming during Mesoproterozoic rifting of passive continental margin of North
Asian Craton. (3) On the Seward Peninsula in Western Alaska, the Sinuk River (SR) metallogenic belt, which contains massive
sulfide-barite and stratabound Fe-Mn deposits, is hosted in Proterozoic or older metavolcanic and sedimentary rock. The belt is
interpreted as forming during marine volcanogenic rifling(?) of the North American Continental Margin. (4) In Southwestern
Alaska, the Kilbuck (KI) metallogenic belt, which contains mainly ironstone (Superior Fe) deposits, is hosted in the Kilbuck-
Idono cratonal terrane and is interpreted as forming during rifting of the North Asian Craton. (5) In the northern part of the
Canadian Cordillera is the Wernecke (WR) metallogenic belt of U-Cu-Fe (Au-Co) vein and breccia deposits. This belt is hosted in
the North American Craton Margin and is interpreted as forming during hydrothermal activity along a Paleoproterozoic passive
continental margin.