Zircon U-Pb and 40Ar/39Ar results from dikes collected within the Bruin Bay fault zone, lower Cook Inlet

This data release presents zircon U-Pb LA-ICP-MS geochronology from igneous rocks exposed in a coastal exposure at Ursus Head, Iliamna C-2 Quadrangle. Sills and dikes exposed in a coastal exposure at Ursus Head are deformed within the Bruin Bay fault zone. Common dikes intruding late Triassic Kamishak Formation strata composing the hanging-wall of the Bruin Bay fault are cut by numerous small-scale, low-angle, bedding-parallel, and high angle contractional faults. Sample 09MAW006A collected from one of many dikes deformed in the fault zone produced a uni-modal distribution of zircon ages of with a weighted mean of 206.92 +/-0.96 (2 sigma, n=47) and an MSWD of 1.1. Sample 09BG020C collected from a sill of more mafic...

Tags: 40Ar/39Ar, Age Dates, Analyses, Analyses and Sampling, Analytical Lab Results, All tags... Analytical Results, Ar-Ar, Bedrock, Bedrock Geology, Contact Point, Cook Inlet, Cook Inlet Basin, Fault Displacement, Geochronology, Geologic, Geology, Igneous, Iliamna Quadrangle, Isotopes, Lab Methods, Lead, Methods, Naknek, Plagioclase, Rocks, Sample Location, Stratigraphy, Structural Geology, Structure, Tectonics, U-Pb, Uranium, Ursus Head, Volcanic, Volcanic Rocks, Zircon, geoscientificInformation, Fewer tags

Zircon U-Pb and 40Ar/39Ar results from dikes collected within the Bruin Bay fault zone, lower Cook Inlet

This data release presents 40Ar/39Ar step-heating geochronology results from rocks collected roughly 7 km southwest of Contact Point, Iliamna B-3 Quadrangle. Samples obtained from a felsic dike intruding the principal Bruin Bay fault plane near Contact Point produced biotite and plagioclase 40Ar/39Ar ages of 36.5 +/- 0.8 Ma and 31.5+/-0.7 Ma, respectively. The age dates inform stratigraphic, structural, and geochronologic studies along the western margin of lower Cook Inlet basin. The accompanying report also presents zircon U-Pb LA-ICP-MS geochronology results for dikes near Ursus Head.

Tags: 40Ar/39Ar, Age Dates, Analyses, Analyses and Sampling, Analytical Lab Results, All tags... Analytical Results, Ar-Ar, Bedrock, Bedrock Geology, Contact Point, Cook Inlet, Cook Inlet Basin, Fault Displacement, Geochronology, Geologic, Geology, Igneous, Iliamna Quadrangle, Isotopes, Lab Methods, Lead, Methods, Plagioclase, Rocks, Sample Location, Stratigraphy, Structural Geology, Structure, Tectonics, U-Pb, Uranium, Ursus Head, Volcanic, Volcanic Rocks, Zircon, geoscientificInformation, Fewer tags

40Ar/39Ar data from the Tok River area, Tanacross A-5 and A-6 quadrangles and adjoining areas, eastern Alaska Range

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...

Tags: 40Ar/39Ar, Amphibolite, Analyses, Analyses and Sampling, Analytical Lab Results, All tags... Analytical Results, Basalt, Bedrock, Crystals, Exploration, Faulting, Geochronology, Geologic, Geology, Gneiss, Granite, Granodiorite, Greenschist, Hornblende, Igneous, Isotopes, Metamorphic, Metamorphic Rocks, Metamorphism, Methods, Mica, Mineral Composition, Mineral Prospect, Mineralogy, Minerals, Muscovite, Noah Prospect, Plagioclase, Plutonic, Rocks, Sample Location, Sericite, Shalosky Prospect, Tanacross Quadrangle, Tok, Tok Mining District, Tok River, geoscientificInformation, Fewer tags