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Thomas K. Bundtzen

Publications and source records attributed to Thomas K. Bundtzen.

At least 19 recordsLinked to original sources
USGS2019

Effects of Cenozoic subduction along the outboard margin of the Northern Cordillera: Derived from e-book on the Northern Cordillera (Alaska and Western Canada) and adjacent marine areas

This article describes the regional effects of Cenozoic subduction along the outboard margin of the Northern Cordillera (Alaska, USA, and Western Canada), and thereby acquaints the reader with several chapters of the e-book Dynamic Geology of the Northern Cordillera (Alaska, Western Canada, and Adjacent Marine Areas) . This article and the e-book are written for earth-science students and teachers. The level of writing for the article and the source e-book is that of popular science magazines, and readers are encouraged to share this article with students and laypersons. The main thrust of the article is to present and describe a suite of ten regional topographic, bathymetric, and geologic maps, and two figures portraying deep-crustal sections that illustrate the regional effects of Cenozoic subduction along the outboard margin of the North American Cordillera. The regional maps and cross sections are described in a way that a teacher might describe a map to students. Cenozoic subduction along the margin of the Northern Cordillera resulted in the formation of the following: (1) underthrusting of terranes and oceanic lithosphere beneath Southern Alaska; (2) landscapes, including narrow continental shelves along Southern and Southeastern Alaska and Western Canada (the Canadian Cordillera) and continental-margin mountain ranges, including the Alaska Peninsula, Chugach Range, Saint Elias Mountains, and Cascade Mountains; (3) sedimentary basins; (4) an array of active continental strike-slip and thrust faults (inboard of subduction zones); (5) earthquake belts related to subduction of terranes and oceanic plates; (6) active volcanoes, including continental-margin arcs (the Aleutian, Wrangell, and Cascade Arcs) linked to subduction zones, and interior volcanic belts related to strike-slip faulting or to hot spots; (7) lode and placer mineral deposits related to continental margin arcs or subduction of oceanic ridges; (8) hot springs related to continental-margin arcs; (9) plate movements as recorded from GPS measurements; and (10) underthrusting of terranes and oceanic lithosphere beneath the Northern Cordillera.

Alaska, British Columbia, Idaho, Montana, Washingt↗
USGS2017

Regional patterns of Mesozoic-Cenozoic magmatism in western Alaska revealed by new U-Pb and 40Ar/39Ar ages

In support of regional geologic framework studies, we obtained 50 new argon-40/argon-39 ( 40 Ar/ 39 Ar) ages and 33 new uranium-lead (U-Pb) ages from igneous rocks of southwestern Alaska. Most of the samples are from the Sleetmute and Taylor Mountains quadrangles; smaller collections or individual samples are from the Bethel, Candle, Dillingham, Goodnews Bay, Holy Cross, Iditarod, Kantishna River, Lake Clark, Lime Hills, McGrath, Medfra, Talkeetna, and Tanana quadrangles. A U-Pb zircon age of 317.7±0.6 million years (Ma) reveals the presence of Pennsylvanian intermediate igneous (probably volcanic) rocks in the Tikchik terrane, Bethel quadrangle. A U-Pb zircon age of 229.5±0.2 Ma from gabbro intruding the Rampart Group of the Angayucham-Tozitna terrane, Tanana quadrangle, confirms and tightens a previously cited Triassic age for this intrusive suite. A fresh mafic dike in Goodnews Bay quadrangle yielded a 40 Ar/ 39 Ar whole rock age of 155.0±1.9 Ma; this establishes a Jurassic or older age for the previously unconstrained (Paleozoic? to Mesozoic?) sandstone unit that it intrudes. A thick felsic tuff in the Gemuk Group in Taylor Mountains quadrangle yielded a U-Pb zircon age of 153.0±2.0 Ma, extending the age of magmatism in this part of the Togiak terrane back into the Late Jurassic. We report three new U-Pb zircon ages between 120 and 110 Ma—112.0±0.9 Ma from syenite in the Candle quadrangle, 114.9±0.3 Ma from orthogneiss assigned to the Ruby terrane in Iditarod quadrangle, and 116.6±0.1 Ma from a gabbro of the Dishna River mafic-ultramafic complex in Iditarod quadrangle. The latter result requires a substantial age revision, from Triassic to Cretaceous, for at least some rocks that have been mapped as the Dishna River mafic-ultramafic complex. A tuff in the Upper Cretaceous Kuskokwim Group yielded a U-Pb zircon (sensitive high-resolution ion microprobe, SHRIMP) age of 88.3±1.0 Ma; we speculate that the eruptive source was an arc along the trend of the Pebble porphyry copper deposit along the Gulf of Alaska continental margin. More than half of the new ages fall between 75 and 65 Ma, confirming the existence, based on conventional potassium-argon (K-Ar) ages, of a 70-Ma igneous flare-up across southwestern Alaska. Our new ages hint that during this pulse, the locus of magmatism shifted toward the Gulf of Alaska, that is, toward a more outboard position. This shift is consistent with the hypothesis that magmatism was the product of rollback of a subducted slab, which at that time would have been the Resurrection Plate. Intrusive rocks in the Taylor Mountains and Sleetmute quadrangles in the age range of 63 to 59 Ma were emplaced shortly before the onset of ridge subduction as dated by near-trench plutons in the adjacent part of the Chugach accretionary complex. Southwestern Alaska at this time would have been positioned above a very young subducted slab belonging to the Resurrection Plate; magmas, in this scenario, were generated near the edge of the slab window related to ridge subduction. A 56.3±0.2 Ma granite in Taylor Mountains quadrangle and a 54.7±0.7 Ma ashfall tuff in McGrath quadrangle were likely emplaced above the Resurrection-Kula slab window, which by this time is inferred to have entered the region. Another ashfall tuff in McGrath quadrangle, at 42.8±0.5 Ma, likely belongs to the Meshik Arc, the product of renewed subduction after inferred passage of the slab window. A 49.0±0.3-Ma rhyolite in Taylor Mountains quadrangle is about the age of the transition from slab window to renewed subduction. Two plutons in the western Alaska Range, at 31.8±0.4 and 30.9±0.6 Ma, belong to a suite of gabbro to peralkaline granite of unknown origin. Finally, a 4.6±0.1-Ma basalt from a flow in Taylor Mountains quadrangle belongs to the Neogene basaltic province of western Alaska. These rocks were erupted in a distal retroarc setting; the cause of magmatism is unknown.

Alaska↗
USGS2017

Tectonic evolution

The middle Paleozoic through Present tectonic evolution of the Northern Cordillera is portrayed in a series of 15 Tectonic Model figures. These figures depict the successive stages of formation and accretion of orogenic collages along the western margin of the North American Plate (craton and craton margin) and adjacent marine areas. The orogenic collages are composed of terranes and overlap assemblages. The terranes are tectonic (fault-bounded) fragments of island arcs and continental-margin arcs, subduction-zones, oceanic lithosphere, craton margins, and cratons. The overlap assemblages are sequences of mainly late Mesozoic and Cenozoic continental-margin-arc and sedimentary-basin assemblages that were deposited on subjacent terranes and on subjacent craton margin assemblages, following their tectonic assembly.

Book chapter↗
USGS2017

Geologic sources of energy

This chapter describes the exploration, development, and geologic setting of petroleum resources (including tar sands), coal resources (including coalbed methane), and geothermal energy resources of the Northern Cordillera.For petroleum resources, the chapter describes: (1) the history of petroleum development and production, first for Alaska and then for the Canadian Cordillera; and (2) generalized basin analysis geologic settings for the six major petroleum basins that are illustrated in summary maps and cross sections. Subsequent sections of the chapter describe the nature and geologic setting of tar sand resources, geothermal energy resources, and coal resources. The area distribution of the energy resources of the region are depicted in the Energy Resources Map that has multiple layers that can be displayed in various arrangements. Employing this map in a separate window while reading the text will be greatly beneficial. Many geographic names are employed in the descriptions throughout this chapter. While reading this chapter, viewing the Geographic Regions Layer of the Energy Resources Map, as needed, will be valuable.

Book chapter↗
USGS2010

Methodology of a combined regional metallogenic and tectonic analysis for northeast Asia, Chapter 2 in Metallogenesis and tectonics of northeast Asia

The major purposes of this chapter are to provide (1) an overview of the regional geology, tectonics, and metallogenesis of Northeast Asia for readers who are unfamiliar with the region, (2) a general scientific introduction to the succeeding chapters of this volume, and (3) an overview of the methodology of metallogenic and tectonic analysis used in this study. We also describe how a high-quality metallogenic and tectonic analysis, including construction of an associated metallogenic-tectonic model will greatly benefit other mineral resource studies, including synthesis of mineral-deposit models; improve prediction of undiscovered mineral deposit as part of a quantitative mineral-resource-assessment studies; assist land-use and mineral-exploration planning; improve interpretations of the origins of host rocks, mineral deposits, and metallogenic belts, and suggest new research. Research on the metallogenesis and tectonics of such major regions as Northeast Asia (eastern Russia, Mongolia, northern China, South Korea, and Japan) and the Circum-North Pacific (the Russian Far East, Alaska, and the Canadian Cordillera) requires a complex methodology including (1) definitions of key terms, (2) compilation of a regional geologic base map that can be interpreted according to modern tectonic concepts and definitions, (3) compilation of a mineral-deposit database that enables a determination of mineral-deposit models and clarification of the relations of deposits to host rocks and tectonic origins, (4) synthesis of a series of mineral-deposit models that characterize the known mineral deposits and inferred undiscovered deposits in the region, (5) compilation of a series of metallogenic-belt belts constructed on the regional geologic base map, and (6) construction of a unified metallogenic and tectonic model. The summary of regional geology and metallogenesis presented here is based on publications of the major international collaborative studies of the metallogenesis and tectonics of Northeast Asia that have been led by the U.S. Geological Survey (USGS). These studies have produced two broad types of publications (1) a series of regional geologic, mineral-deposit, and metallogenic-belt maps, with companion descriptions of the region, and (2) a suite of metallogenic and tectonic analyses of the same region. The study area consists of eastern Russia (most of eastern Siberia and the Russian Far East), Mongolia, northern China, South Korea, Japan, and adjacent offshore areas. The major cooperative agencies are the Russian Academy of Sciences; the Academy of Sciences of the Sakha Republic (Yakutia); VNIIOkeangeologia and Ministry of Natural Resources of the Russian Federation; the Mongolian Academy of Sciences; the Mongolian University of Science and Technology; the Mongolian National University; Jilin University, Changchun, People?s Republic of China, the China Geological Survey; the Korea Institute of Geosciences and Mineral Resources; the Geological Survey of Japan/AIST; the University of Texas, Arlington, and the U.S. Geological Survey (USGS). This study builds on and extends the data and interpretations from a previous project on the Major Mineral Deposits, Metallogenesis, and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera conducted by the USGS, the Russian Academy of Sciences, the Alaska Division of Geological and Geophysical Surveys, and the Geological Survey of Canada. The major products of this project were summarized by Naumova and others (2006) and are described in appendix A.

Professional Paper↗
USGS2005

Metallogenesis and tectonics of the Russian Far East, Alaska, and the Canadian Cordillera

The Proterozoic and Phanerozoic metallogenic and tectonic evolution of the Russian Far East, Alaska, and the Canadian Cordillera is recorded in the cratons, craton margins, and orogenic collages of the Circum-North Pacific mountain belts that separate the North Pacific from the eastern North Asian and western North American Cratons. The collages consist of tectonostratigraphic terranes and contained metallogenic belts, which are composed of fragments of igneous arcs, accretionary-wedge and subduction-zone complexes, passive continental margins, and cratons. The terranes are overlapped by continental-margin-arc and sedimentary-basin assemblages and contained metallogenic belts. The metallogenic and geologic history of terranes, overlap assemblages, cratons, and craton margins has been complicated by postaccretion dismemberment and translation during strike-slip faulting that occurred subparallel to continental margins. Seven processes overlapping in time were responsible for most of metallogenic and geologic complexities of the region (1) In the Early and Middle Proterozoic, marine sedimentary basins developed on major cratons and were the loci for ironstone (Superior Fe) deposits and sediment-hosted Cu deposits that occur along both the North Asia Craton and North American Craton Margin. (2) In the Late Proterozoic, Late Devonian, and Early Carboniferous, major periods of rifting occurred along the ancestral margins of present-day Northeast Asia and northwestern North America. The rifting resulted in fragmentation of each continent, and formation of cratonal and passive continental-margin terranes that eventually migrated and accreted to other sites along the evolving margins of the original or adjacent continents. The rifting also resulted in formation of various massive-sulfide metallogenic belts. (3) From about the late Paleozoic through the mid-Cretaceous, a succession of island arcs and contained igneous-arc-related metallogenic belts and tectonically paired subduction zones formed near continental margins. (4) From about mainly the mid-Cretaceous through the present, a succession of continental-margin igneous arcs (some extending offshore into island arcs) and contained metallogenic belts, and tectonically paired subduction zones formed along the continental margins. (5) From about the Jurassic to the present, oblique convergence and rotations caused orogen-parallel sinistral, and then dextral displacements within the plate margins of the Northeast Asian and North American Cratons. The oblique convergences and rotations resulted in the fragmentation, displacement, and duplication of formerly more continuous arcs, subduction zones, passive continental margins, and contained metallogenic belts. These fragments were subsequently accreted along the margins of the expanding continental margins. (6) From the Early Jurassic through Tertiary, movement of the upper continental plates toward subduction zones resulted in strong plate coupling and accretion of the former island arcs, subduction zones, and contained metallogenic belts to continental margins. In this region, the multiple arc accretions were accompanied and followed by crustal thickening, anatexis, metamorphism, formation of collision-related metallogenic belts, and uplift; this resulted in the substantial growth of the North Asian and North American continents. (7) In the middle and late Cenozoic, oblique to orthogonal convergence of the Pacific Plate with present-day Alaska and Northeast Asia resulted in formation of the present ring of volcanoes and contained metallogenic belts around the Circum-North Pacific. Oblique convergence between the Pacific Plate and Alaska also resulted in major dextral-slip faulting in interior and southern Alaska and along the western part of the Aleutian- Wrangell arc. Associated with dextral-slip faulting was crustal extrusion of terranes from western Alaska into the Bering Sea.

Professional Paper↗
USGS2001

Dynamic computer model for the metallogenesis and tectonics of the Circum-North Pacific

The digital files on this report consist of a dynamic computer model of the metallogenesis and tectonics of the Circum-North Pacific, and background articles, figures, and maps. The tectonic part of the dynamic computer model is derived from a major analysis of the tectonic evolution of the Circum-North Pacific which is also contained in directory tectevol. The dynamic computer model and associated materials on this CD-ROM are part of a project on the major mineral deposits, metallogenesis, and tectonics of the Russian Far East, Alaska, and the Canadian Cordillera. The project provides critical information on bedrock geology and geophysics, tectonics, major metalliferous mineral resources, metallogenic patterns, and crustal origin and evolution of mineralizing systems for this region. The major scientific goals and benefits of the project are to: (1) provide a comprehensive international data base on the mineral resources of the region that is the first, extensive knowledge available in English; (2) provide major new interpretations of the origin and crustal evolution of mineralizing systems and their host rocks, thereby enabling enhanced, broad-scale tectonic reconstructions and interpretations; and (3) promote trade and scientific and technical exchanges between North America and Eastern Asia.

Open-File Report↗
USGS1999

Alaska resource data file: McGrath quadrangle

The unnamed occurrence was investigated by the reporter in 1978 during a 1:63,360 scale geologic mapping effort for the Alaska Division of Geological and Geophysical Surveys in the McGrath quadrangle (Bundtzen and Laird, 1983). Two grab samples from the mineralized zone contained up to 222 ppm copper, 0.6 grams/tonne silver, and 100 ppm lead.

Alaska↗
USGS1998

Geologic map of central (interior) Alaska

Introduction: This map and associated digital databases are the result of a compilation and reinterpretation of published and unpublished 1:250,000- and limited 1:125,000- and 1:63,360-scale mapping. The map area covers approximately 416,000 sq km (134,000 sq mi) and encompasses 25 1:250,000-scale quadrangles in central Alaska. The compilation was done as part of the U.S. Geological Survey National Surveys and Analysis project, whose goal is nationwide assemble geologic, geochemical, geophysical, and other data. This map is an early product of an effort that will eventually encompass all of Alaska, and is the result of an agreement with the Alaska Department of Natural Resources, Division of Oil And Gas, to provide data on interior basins in Alaska. A paper version of the three map sheets has been published as USGS Open-File Report 98-133. Two geophysical maps that cover the identical area have been published earlier: 'Bouguer gravity map of Interior Alaska' (Meyer and others, 1996); and 'Merged aeromagnetic map of Interior Alaska' (Meyer and Saltus, 1995). These two publications are supplied in the 'geophys' directory of this report.

Alaska↗
USGS1998

Summary terrane, mineral deposit, and metallogenic belt maps of the Russian Far East, Alaska, and the Canadian Cordillera

This report is part of a project on the major mineral deposits, metallogenesis, and tectonics of the Russian Far East, Alaska, and the Canadian Cordillera. The project is to provide critical information for collaborators and customers on bedrock geology and geophysics, tectonics, major metalliferous mineral resources, metallogenic patterns, and crustal origin and evolution of mineralizing systems for the Russian Far East, Alaska, and the Canadian Cordillera.

Open-File Report↗
USGS1998

Stratiform zinc-lead mineralization in Nasina assemblage rocks of the Yukon-Tanana Upland in east-central Alaska

The Yukon-Tanana Upland of east-central Alaska and Yukon comprises thrust sheets of ductilely deformed metasedimentary and metaigneous rocks of uncertain age and origin that are overlain by klippen of weakly metamorphosed oceanic rocks of the Seventymile-Slide Mountain terrane, and intruded by post-kinematic Early Jurassic, Cretaceous and Tertiary granitoids. Metamorphosed continental margin strata in the Yukon-Tanana Upland of east-central Alaska are thought to be correlative, on the basis of stratigraphic similarities and sparse Mississippian U-Pb zircon and fossil ages (Mortensen, 1992), with middle Paleozoic metasedimentary and metavolcanic rocks in the eastern Alaska Range and in western and southeastern Yukon. Furthermore, rocks in the northern Yukon-Tanana Upland may correlate across the Tintina fault with unmetamorphosed counterparts in the Selwyn Basin (Murphy and Abbott, 1995). Volcanic-hosted (VMS) and sedimentary exhalative (sedex) massive sulfide occurrences are widely reported for these other areas (green-colored unit of fig. 1) but, as yet, have not been documented in the Alaskan part of the Yukon-Tanana Upland. Recent discoveries of VMS deposits in Devono-Mississippian metavolcanic rocks in the Finlayson Lake area of southeastern Yukon (Hunt, 1997) have increased the potential for finding VMS deposits in rocks of similar lithology and age in the Yukon-Tanana Upland of Alaska. Restoration of 450 km of early Tertiary dextral movement along the Tintina fault juxtaposes these two areas.

Alaska↗