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Dwight C. Bradley

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The Farewell terrane is an exotic continental fragment in interior Alaska that during the early Paleozoic was the site of a passive margin. We report a 238U/206Pb zircon age of 432.9±3.0 Ma from a Farewell terrane ash in Mt. McKinley quadrangle, Alaska. This age overlaps with prominent detrital zircon age maxima reported from Silurian and Devonian strata from the Farewell, Arctic Alaska-Chukotka, White Mountains, Alexander, and Yreka terranes, and from parautochtonous Silurian and Devonian foreland-basin strata along the Laurentian margin in the Canadian Arctic and Alaska. These findings can be explained in terms of refinements to the extrusion model of Colpron and Nelson (2011). In the original model, the Farewell...
Categories: Publication; Types: Citation; Tags: Professional Paper
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Onshore evidence suggests that a plate is missing from published reconstructions of the northeastern Pacific Ooean in Paleocene- Eocene time. The Resurrection plate, named for the Resurrection Peninsula ophiolite near Seward, Alaska, was located east of the Kula plate and north of the Farallon plate. We interpret coeval near-trench magmatism in southern Alaska and the Cascadia margin as evidence for two slab windows associated with trench-ridge-trench (TRT) triple junctions, which formed the western and southern boundaries of the Resurrection plate. In Alaska, the Sanak-Baranof belt of near-trench intrusions records a west-to-east migration, from 61 to 50 Ma, of the northern TRT triple junction along a 2100-km-long...
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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This map and associated digital databases are the result of a compilation and reinterpretation of published and unpublished 1:250,000- and limited 1:125,000- and 1:63,360-scale mapping.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...
Categories: Publication; Types: Citation; Tags: Open-File Report
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The Kuskokwim mineral belt of Bundtzen and Miller (1997) forms an important metallogenic region in southwestern Alaska that has yielded more than 3.22 million ounces of gold and 400,000 ounces of silver. Precious-metal and related deposits in this region associated with Late Cretaceous to early Tertiary igneous complexes extend into the Taylor Mountains 1:250,000-scale quadrangle. The U.S. Geological Survey is conducting geologic mapping and a mineral resource assessment of this area that will provide a better understanding of the geologic framework, regional geochemistry, and may provide targets for mineral exploration and development. During the 2004 field season 137 rock samples were collected for a variety of...
Categories: Publication; Types: Citation; Tags: Open-File Report
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This report is a companion to the new Geologic Map of Mauritania (Bradley and others, 2015; referred to herein as “Deliverable 51”) and the new Structural Geologic Map of Mauritania (Bradley and others, 2015a; referred to herein as “Deliverable 52”). Section 1 contains explanatory information for these two digital maps. Section 2 covers the analytical methods used in obtaining new U-Pb ages from 9 igneous rock samples, new detrital zircon ages from 40 sedimentary or metasedimentary rock samples, and new 40Ar/39Ar ages from 12 samples of metamorphic rocks and veins. Sections 3 through 6 present the new geochronological results, organized by region. In Section 7, we discuss implications of the new ages for the regional...
Categories: Publication; Types: Citation; Tags: Open-File Report
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