Circum-North Pacific tectonostratigraphic terrane map

The companion tectonostratigraphic terrane and overlap assemblage of map the Circum-North Pacific presents a modern description of the major geologic and tectonic units of the region. The map illustrates both the onshore terranes and overlap volcanic assemblages of the region, and the major offshore geologic features. The map is the first collaborative compilation of the geology of the region at a scale of 1:5,000,000 by geologists of the Russian Far East, Japanese, Alaskan, Canadian, and U.S.A. Pacific Northwest. The map is designed to be a source of geologic information for all scientists interested in the region, and is designed to be used for several purposes, including regional tectonic analyses, mineral resource and metallogenic analyses (Nokleberg and others, 1993, 1994a), petroleum analyses, neotectonic analyses, and analyses of seismic hazards and volcanic hazards. This text contains an introduction, tectonic definitions, acknowledgments, descriptions of postaccretion stratified rock units, descriptions and stratigraphic columns for tectonostratigraphic terranes in onshore areas, and references for the companion map (Sheets 1 to 5).

This map is the result of extensive geologic mapping and
associated tectonic studies in the Russian Far East, Hokkaido
Island of Japan, Alaska, the Canadian Cordillera, and the
U.S.A. Pacific Northwest in the last few decades. Geologic
mapping suggests that most of this region can be interpreted as
a collage of fault-bounded tectonostratigraphic terranes that
were accreted onto continental margins around the Circum-
. orth Pacific mainly during the Mesozoic and Cenozoic (Fujita
and ewberry, 1983; 1987; Parfenov, 1984, 1991; Howell,
1985; Watson and Fujita, 1985; Parfenov and Natal'in, 1984;
Jones and others. 1987; Monger and Berg, 1987, Fujita and
Cook. 1990; Zonenshain and others. 1990; Natal'in, 1991,
1993; Moore and others, 1992; Silberling and others, 1992;
Nokleberg and others. 1992, 1993, 1994a; Parfenov and
others. 1993; Plaflcer and Berg, 1994; Tabor, 1994).

This map is the result of extensive geologic mapping and
associated tectonic studies in the Russian Far East, Hokkaido
Island of Japan, Alaska, the Canadian Cordillera, and the
U.S.A. Pacific Northwest in the last few decades. Geologic
mapping suggests that most of this region can be interpreted as
a collage of fault-bounded tectonostratigraphic terranes that
were accreted onto continental margins around the Circum-
. orth Pacific mainly during the Mesozoic and Cenozoic (Fujita
and ewberry, 1983; 1987; Parfenov, 1984, 1991; Howell,
1985; Watson and Fujita, 1985; Parfenov and Natal'in, 1984;
Jones and others. 1987; Monger and Berg, 1987, Fujita and
Cook. 1990; Zonenshain and others. 1990; Natal'in, 1991,
1993; Moore and others, 1992; Silberling and others, 1992;
Nokleberg and others. 1992, 1993, 1994a; Parfenov and
others. 1993; Plaflcer and Berg, 1994; Tabor, 1994).

On the companion map and in the descriptions bel?w·
terranes are interpreted according to inferred tectonic
environments. These environments are (I) cratonai; (2)
passive continental margin; (3) metamorphosed continental
margin; (4) continental-margin arc; (5) island arc; (6) oceanic
crust, seamount, and ophiolite; (7) accretionary wedge and
subduction zone: (8) turbidite basin; and (9) metamorphic for
terranes that are too highly-deformed and metamorphosed to
de~ermine the original tectonic environment. For terranes with
complex geologic histories, the chosen color indicates the
tectonic environment most prevalent during this history of the
terrane. The tectonic environments inf~rred for igneous rocks
are both temporal and genetic. The temporal environments are
preaccretion and postaccretion. The genetic environments are
subduction-related, rift-related, and collisional (anatectic)-
related.

In addition to terranes, the map also depicts postaccretion
units that include: (I) Cenozoic and Mesozoic overlap
assemblages of sedimentary and volcanic rocks that are
deposited across two or more terranes that formed generally
after accretion of most terranes in the region; (2) Cenozoic and
Mesozoic basinal deposits that occur within a terrane or on the
craton; (3) plutonic rocks. The postaccretion igneous units are
identified by age-lithologic abbreviations and by name. These
overlap assemblages and basinal deposits formed mainly
during sedimentation and magmatism that occurred after
accretion of terranes to each other or to a continental margin.
Overlap assemblages provide minimum ages on the timing of
accretion of terranes. Some Cenozoic and Mesozoic overlap
assemblages and basinal deposits, as well as fragments of
terranes, are extensively offset by movement along
postaccretion faults. In addition, in onshore areas, the map
depicts major preaccretion plutonic rocks that are limited to
individual terranes. and in offshore areas. the map depicts
major oceanic plates,-ocean floor magnetic lineations. oceanic
spreading ridges, and seamounts.

The map consists of five sheets. Sheets I and 2 depict, at a
scale of I :5.000.000. the tectonostratigraphic terranes.
preaccretion plutonic rocks, and postaccretion Cenozoic and
Mesozoic overlap sedimentary, volcanic. and plutonic
assemblages, and basinal deposits for the Circum- orth Pacific
including the Russian Far East, northern Hokkaido Island of
Japan, Alaska. the Canadian Cordillera, part of the U.S.A.
Pacific Northwest. and adjacent offshore areas. Sheet 3
provides the list of map units for Sheets I and 2. Sheet 4 is a
index map showing generalized onshore terranes and overlap
assemblages for onshore parts of the Circum-North Pacific at a
scale of I: I 0,000,000. Sheet 4 is a guide to the more
complicated onshore features depicted on Sheets I and 2. Sheet
5 is an index map showing the major geographic regions for
the Circum-North Pacific.

Significant differences exist between the representation of
onshore and offshore geology on Sheets I and 2. These are: (I)
compared to the onshore part of the map, the offshore part is
depicted in a more schematic fashion because of more limited
data and because the offshore terranes and early Cenozoic and
older overlap assemblages generally are obscured by extensive
late Cenozoic sedimentary cover that is not shown unless
thicker than two kilometers; (2) marginal contacts of offshore
Cenozoic and Cretaceous sedimentary basins do not match
contacts of onshore Cenozoic and Cretaceous sedimentary units
because offshore basins are limited to those regions with
sediment thicknesses greater than two kilometers; (3)
stratigraphic columns, included at the end of this explanation.
are provided only for onshore terranes because the geology of
offshore terranes is generally less well-known; and (4) for
simplicity, the major onshore Cenozoic sedimentary basins are
generally not defined and described separately because the
onshore part of the map is designed to emphasize terranes and
overlap volcanic assemblages that are crucial for both for
tectonic and metallogenic analyses published elsewhere
(Nokleberg and others, 1993, 1994a).

Several key geologic sources were used in the compilation
of the map. For Alaska. the basic outcrop pattern for the map is
from Beikman (1980), Gehrels and Berg (1992, 1994). Barker
and others ( 1994). Brew (1994), and Moli-Stalcup and others
( 1994b). The distribution of terranes is from Jones and others
(1987) and Monger and Berg (1987), with modification by
Grantz and other (1991 ). Worall (199 1 ), okleberg and others
(1993, 1994a), the cited references, and the Alaskan co-authors
of this report. For the Canadian Cordillera. the basic outcrop
pattern is from Monger and Berg ( 1987), Wheeler and other
(1988). and Wheeler and McFeeley ( 1991) with modifications
by the Canadian authors. For the northern part of the Russian
Far East. the basic outcrop pattern is from So unov (1985) with
modifications by the Russian authors. For the outhern part of
the Russian Far East, the basic outcrop pattern is from Krasny
(1991) and Bazhanov and Oleinik ( 1986) with modification
by the Russian authors. The Russian Far East part of the map is
the first attempt to define and delineate terranes in that region.
In their compilation. the Russian authors utilized the
methodology of U.S.A. and Canadian geologists. Because this
map is the first attempt to display the terranes. Cenozoic and
Mesozoic overlap assemblages. basinal deposit , and plutonic
belts of the Russian Far East. the Russian author will
appreciate constructive sugge tions for improving the map.