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This report presents 40Ar/39Ar step-heating geochronology results for igneous and metamorphic rocks from the Alaska Division of Geological & Geophysical Surveys' (DGGS) Wrangellia Mineral Assessment project, part of a multi-year effort focusing on improving the publicly available geoscientific information for the western Wrangellia terrane. The samples described in this report were selected and analyzed to improve our understanding of the geology and structural history of the Wrangellia Mineral Assessment project area. A metagabbro rock sample returned a Late Triassic crystallization age consistent with regional ages for Nikolai Greenstone-related magmatism; however, the two amphibole separates ages do not overlap,...
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Variability in sediment properties with depth and the thickness of individual sedimentary layers are critical determinants of seabed acoustic response. The New England Mud Patch (NEMP), located south of Cape Cod, is an unusual feature on the U.S. Continental Shelf in that it is composed of fine-grained sediment layers containing a relatively-homogeneous mix of sand, silt, and clay-sized particles bounded by more typical sandy shelf sediments. The unique characteristics and nature of this deposit is due to a derivation of sediments that have been transported to, and deposited in, a basal bowl-shaped depression since the last glacial maximum. Ninety-two piston, vibra-, and gravity cores with a maximum length of 8.2...
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This report presents 40Ar/39Ar step-heating geochronology results for igneous and metamorphic rocks from the Alaska Division of Geological & Geophysical Surveys' (DGGS) geologic mapping project in the Tanacross A-5 and A-6 quadrangles and adjoining areas. Our results indicate the Hona granodiorite pluton intruded the area in the Late Cretaceous between 76 and 71 Ma. We determined Cretaceous metamorphic ages from 126 to 121 Ma for hornblende, biotite, sericite and muscovite from multiple samples of upper greenschist to amphibolite grade rocks. This is consistent with regional argon results that imply this area is in the upper plate of the Yukon Tanana Terrane (Hansen and Dusel-Bacon, 1998). Basaltic andesite dikes...


    map background search result map search result map 40Ar/39Ar data from rocks collected in the 2015 Wrangellia mineral assessment project area, Mount Hayes A-5, Mount Hayes B-6, and Talkeetna Mountains D-2 quadrangles, Alaska 40Ar/39Ar data from the Tok River area, Tanacross A-5 and A-6 quadrangles and adjoining areas, eastern Alaska Range Raw X-ray diffraction data of cores from the New England Mud Patch collected on USGS Field Activity 2016-001-FA Raw X-ray diffraction data of cores from the New England Mud Patch collected on USGS Field Activity 2016-001-FA 40Ar/39Ar data from the Tok River area, Tanacross A-5 and A-6 quadrangles and adjoining areas, eastern Alaska Range 40Ar/39Ar data from rocks collected in the 2015 Wrangellia mineral assessment project area, Mount Hayes A-5, Mount Hayes B-6, and Talkeetna Mountains D-2 quadrangles, Alaska