CIRCUM-NORTH PACIFIC TECTONOSTRATIGRAPHIC TERRANE MAP By Warren J. Nokleberg1, Leonid M. Parfenov2, James W.H. Monger3, and Boris V. Baranov2,Stanislav G. Byalobzhesky2, Thomas K. Bundtzen4, Tracey D. Feeney3, Kazuya Fujita5, Steven P. Gordey3, Arthur Grantz1, Alexander I. Khanchuk2,
Boris A. Natal'in2, Lev M. Natapov6, Ian O. Norton7,William W. Patton1, Jr., George Plafker1, David W. Scholl1,
Sergei D. Sokolov2, Gleb M. Sosunov6, David B. Stone8, Rowland W. Tabor1, Nickolai V. Tsukanov2,
Tracy L. Vallier1, and Koji Wakita9
1 U.S. Geological Survey, 2 Russian Academy of Sciences, 3 Geological Survey of Canada, 4 Alaska Division of Geological and Geophysical Surveys, 5 Michigan State University, 6 Russian Committee on Geology, 7 Exxon Production Research Company,
8 University of Alaska, 9 Geological Survey of Japan
INTRODUCTION 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-North Pacific mainly during the Mesozoic and Cenozoic (Fujita and Newberry, 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; Plafker and Berg, 1994; Tabor, 1994).
A key definition for the map is tectonostratigraphic terrane which is defined below, along with other key terms, as a fault-bounded geologic entity or fragment that is characterized by a distinctive geologic history that differs markedly from that of adjacent terranes (Jones and others, 1983; Howell and others, 1985). A tectonostratigraphic terrane (hereafter referred to as terrane) is a fault-bounded, stratigraphically coherent assemblage that formed before accretion, i.e. tectonic juxtaposition, to adjacent units. A few terranes are fault-bounded structural complexes, mainly subduction zone or accretionary-wedge complexes. The terranes are bounded by various types of major faults or fault zones, termed sutures. Paleontologic, stratigraphic, and paleomagnetic evidence suggests that some terranes were originally widely separated from one another, or from the cratons of either North America or North Asia by distances of as much as thousands of kilometers Plafker and Berg, 1994). But other terranes are interpreted to be displaced from one another or from a another loci on the same continent by distances of only hundreds of kilometers or less.
On the companion map and in the descriptions below, terranes are interpreted according to inferred tectonic environments. These environments are (1) cratonal; (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 determine 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 inferred 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: (1) 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 1 and 2 depict, at a scale of 1:5,000,000, the tectonostratigraphic terranes, preaccretion plutonic rocks, and postaccretion Cenozoic and Mesozoic overlap sedimentary, volcanic, and plutonic assemblages, and basinal deposits for the Circum-North 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 1 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 1:10,000,000. Sheet 4 is a guide to the more complicated onshore features depicted on Sheets 1 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 1 and 2. These are: (1) 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 Moll-Stalcup and others (1994b). The distribution of terranes is from Jones and others (1987) and Monger and Berg (1987), with modifications by Grantz and others (1991), Worall (1991), Nokleberg 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 others (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 Sosunov (1985) with modifications by the Russian authors. For the southern part of the Russian Far East, the basic outcrop pattern is from Krasny (1991) and Bazhanov and Oleinik (1986) with modifications 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 deposits, and plutonic belts of the Russian Far East, the Russian authors will appreciate constructive suggestions for improving the map.