USGS Professional Paper 1697 - Alaska Resources Library

280 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
belts contain granitic-magmatism-related deposits and are
interpreted as forming during granitic plutonism associated
with subduction of the Pacific Plate.
(2) Rifting continues along the Gakkel Ridge (GK;
northern extension of mid-Atlantic Ridge) and the extension
of the ridge toward the Eurasian plate. The Gakkel Ridge
and its extension define the modern boundary between the
North American and Eurasian plates. Analysis of sea-floor
spreading anomalies in the Eurasia Basin (eb) suggest that
the Russian Northeast underwent extension from about 5 to
0.5 Ma (Moma rift episode as discussed by Fujita and others,
1990a,b, 1997; Savostin and Drachev, 1988a,b; Harbert
and others, 1990; Fujita and others, 1997). The youngest
change, a northward pole shift, occurred at about 0.5 Ma, as
indicated by resurgent or continued thrusting (Imaev, 1991).
Focal mechanism studies indicate that parts of this region are
undergoing compression (Cook and others, 1986; Parfenov
and others, 1989; Fujita and others, 1990a,b; Riegel and others,
1993). This compression is relieved by extrusion of the
Okhotsk block to the southeast (Riegel and others, 1993) and
by uplift and thrusting (Koz’min, 1984; Imaev and others,
1990; Koz’min and others, 1996). Sedimentation continues
in the Amerasia Basin (ab).
(3) Seismicity defines several new tectonic blocks, including
the Amur, Okhotsk, and Bering blocks (Riegel and others,
1993; Fujita and others, 1997; Mackey and others, 1997).
Boundaries between blocks are defined by epicenters located
by teleseismic and regional networks (Fujita and others, 1997).
(4) Marine and continental eruption of sparse, generally
small, highly dispersed flows of Bering Strait alkaline basalt
(bs) occurred in the Quaternary and Recent. This volcanism
may possibly be related to dextral-wrench faulting and tectonic
escape in this region. Rotation of the Bering block created
extension on the Seward Peninsula and on Chukotka (Mackey
and others, 1997), or the Bering block may have formed as the
back-arc with respect to the Aleutian-Wrangell arc.
(5) Tectonic escape (crustal extrusion) of terranes continues
along major dextral-slip faults, including the Denali (DE),
Nixon Fork (NF), Kaltag (KA), and companion faults (Scholl
and others, 1992, 1994), that may extend into the Bering Sea.
Dextral-wrench basins continue to form in association with
the dextral-slip faults and are still filling with continental
sediments. A thick sedimentary prism continues to form in the
Aleutian-Bowers Basin (atb) (Plafker and Berg, 1994). In interior
and southern Alaska, displacement continues along major
dextral-slip faults, such as the Denali (DE) Fault.
(6) The Pacific oceanic plate (PAC) continues to move
northwestward relative to the North American Plate. Along the
Aleutian megathrust (AL), plate convergence continues to vary
from orthogonal in the east to oblique to transform in the west.
(7) Intense tectonic disruption continues in the western
part of Aleutian-Wrangell arc along the western Aleutian
megathrust (AL), as a result of the transform coupling between
the Pacific oceanic plate (PAC) and the North American Plate
(Geist and others, 1988; Scholl and others, 1992, 1994). A
thick sedimentary prism continues to form in the Aleutian-
Bowers Basin (atb) that overlies a fragment of accreted Kula
oceanic plate (Plafker and Berg, 1994).
(8) Along the margin of southern Alaska, the eastern part
of the Aleutian-Wrangell arc continues activity. Associated
with the arc is mainly oblique subduction of the northern edge
of Pacific oceanic plate (PAC) along the Aleutian megathrust
(AL), continuing the formation of the younger part of the
Prince William terrane (PW). Continuing in the Aleutian-
Wrangell arc is the Alaska Peninsula and Aleutian Islands
(AP) metallogenic belt, which contains granitic-magmatismrelated
deposits and is hosted in the Aleutian volcanic belt.
The Yakutat terrane (YA) continues to migrate northwestward
and continues to underthrust the Prince William terrane (PW)
along the eastern part of the Aleutian megathrust (AL).
(9) Sea-floor spreading continues along the Juan de Fuca
oceanic ridge (JFR). Northward movement of the Pacific oceanic
plate (PAC) continues with transform displacement on the
Queen Charlotte transform fault (QC).
(10) The Cascade continental-margin arc continues to
form. Continuing in the Cascade arc was the Owl Creek (OC)
metallogenic belt that is hosted in the Cascade volcanic-plutonic
belt. Associated with the Cascade arc is subduction of
part of the Juan de Fuca oceanic plate (JF) and formation of a
subduction-zone complex along the Cascadia megathrust (CC;
Goldfinger and others, 1996, 1997; Fleuh and others, 1997).
Metallogenic Belts Formed in Late Tertiary and
Quaternary Continental-Margin Arcs,
Kamchatka Peninsula, Southern Alaska, and
Southern Canadian Cordillera
Sakhalin Island Metallogenic Belt of Silica-
Carbonate or Volcanic-Hosted Hg Deposits (Belt
SH). Sakhalin Island, Southeastern Part of
Russian Far East
The Sakhalin Island metallogenic belt of silica-carbonate
and volcanic-hosted Hg deposits occurs in the central and
southern part of Sakhalin Island, in and adjacent to the Aniva,
Nabilsky, and West-Sakhalin terranes (fig. 125; tables 3, 4)
(Nokleberg and others, 1997b, 1998). The Russian name for
the silica-carbonate Hg deposit type is listwandite. The silicacarbonate
Hg deposits occur along or adjacent to major faults
in faulted fragments of Late Cretaceous sedimentary rocks,
serpentinized and altered ultramafic rocks, and in postaccretionary
Neogene volcanic rocks. The significant deposits along
the In’ River, and at Inskoe, Svetlovskoe, Ostrinskoe, and Yasnoe
consist of cinnabar and native Hg in fracture zones along
contacts between gabbroic rocks and serpentinite, or in jasper,
basalt, and shale. The Hg minerals either replace quartz and
carbonate in listwandite or forms pods. Some of the Hg deposits,
as along the In’ River, occur in volcanic rocks but display
silica-carbonate alteration. Other deposits, as at Inskoe, are
hosted in altered quartzite and Neogene volcanic rock.