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Geologic Map of Baranof Island, Southeastern Alaska

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Geologic Map of Baranof Island, Southeastern Alaska Geologic Map of Baranof Island, Southeastern Alaska By Susan M. Karl, Peter J. Haeussler, Glen R. Himmelberg, Cathy L. Zumsteg, Paul W. Layer, Richard M. Friedman, Sarah M. Roeske, and Lawrence W. Snee Pamphlet to accompany Scientific Investigations Map 3335 2015 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette M. Kimball, Acting Director U.S. Geological Survey, Reston, Virginia: 2015 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit http://www.usgs.gov/ or call 1–888–ASK–USGS (1–888–275–8747). For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod/. To order USGS information products, visit http://store.usgs.gov/. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Karl, S.M., Haeussler, P.J., Himmelberg, G.R., Zumsteg, C.L., Layer, P.W., Friedman, R.M., Roeske, S.M., and Snee, L.W., 2015, Geologic map of Baranof Island, southeastern Alaska: U.S. Geological Survey Scientific Investigations Map 3335, 82 p., 1 sheet, http://dx.doi.org/10.3133/sim3335. ISSN 2329-132X (online) ii Contents Abstract .......................................................................................................................................................................... 1 Introduction ..................................................................................................................................................................... 2 Previous Investigations ................................................................................................................................................... 3 Geology of Baranof Island .............................................................................................................................................. 4 Paleozoic Rocks ......................................................................................................................................................... 5 Mesozoic Rocks .......................................................................................................................................................... 8 Cenozoic Rocks ........................................................................................................................................................ 14 Deformation and Metamorphism .................................................................................................................................. 17 M1: Pre-Late Triassic Regional Deformation and Amphibolite to Greenschist Facies Metamorphism ...................... 18 M2: Early Jurassic Thermal Metamorphism Related to Pluton Emplacement (~192 Ma) ......................................... 18 M3: Middle to Late Jurassic Metamorphism Related to Pluton Emplacement (~173–155 Ma) ................................. 18 M4: Early Late Jurassic Deformation and Greenschist Facies Metamorphism (≥155 Ma) ........................................ 19 M5: Late Jurassic-Early Cretaceous Deformation and Metamorphism (144 Ma) ...................................................... 19 M6: Middle Cretaceous Deformation and Blueschist-Greenschist Facies Metamorphism (91–109 Ma) ................... 20 M7: Late Cretaceous Prehnite-Pumpellyite Facies Metamorphism (≥74 Ma) ........................................................... 21 M8: Early Eocene Deformation and Amphibolite Facies Metamorphism................................................................... 21 M9: Late Early Eocene Thermal Metamorphism (~50 Ma) ........................................................................................ 22 M10: Middle Eocene to Early Oligocene Thermal Metamorphism (~43 Ma) ............................................................. 23 M11: Late Oligocene Thermal Metamorphism Related To Pluton Emplacement (~26 Ma) ...................................... 24 Faults ............................................................................................................................................................................ 25 Border Ranges Fault ................................................................................................................................................. 25 Peril Strait Fault ........................................................................................................................................................ 26 Chatham Strait Fault ................................................................................................................................................. 27 Fairweather-Queen Charlotte Fault ........................................................................................................................... 27 Patterson Bay Fault .................................................................................................................................................. 28 Neva Strait-Silver Bay Fault ...................................................................................................................................... 29 Hot Springs ................................................................................................................................................................... 29 Summary and Discussion ............................................................................................................................................. 29 Acknowledgments ........................................................................................................................................................ 33 Description of Map Units............................................................................................................................................... 34 Stratigraphic Map Units ............................................................................................................................................. 34 Baranof Accretionary Complex .............................................................................................................................. 38 Wrangellia Terrane ................................................................................................................................................ 51 Intrusive Rock Units .................................................................................................................................................. 57 Alexander Terrane................................................................................................................................................. 63 Wrangellia Terrane ................................................................................................................................................ 64 References Cited .......................................................................................................................................................... 67 Figures Figure 1. Map showing generalized tectonostratigraphic terranes of Alaska .............................................................. 5 Figure 2. Generalized tectonostratigraphic terrane map of southeastern Alaska showing faults that bound the Baranof-Chichagof block. ............................................................................................................................ 6 iii Figure 3. Trace-element geochemical diagrams comparing the chemistry of the Triassic greenstone on Baranof Island to the chemistry of the Goon Dip Greenstone on Chichagof Island, the Nikolai Greenstone in the Wrangell Mountains, and the Karmutsen Formation on Vancouver Island .................... 9 Tables Table 1. Geochronologic data ......................................................................................................................... web only Table 2. Geochronologic data for detrital zircon samples. Data from Haeussler and others (2006) ......................... 80 Table 3. Paleontologic data ...................................................................................................................................... 82 Table 4. Geochemical data ............................................................................................................................. web only iv Geologic Map of Baranof Island, Southeastern Alaska By Susan M. Karl, Peter J. Haeussler, Glen R. Himmelberg, Cathy L. Zumsteg, Paul W. Layer, Richard M. Friedman, Sarah M. Roeske, and Lawrence W. Snee Abstract This map updates the geology of Baranof Island based on fieldwork, petrographic analyses, paleontologic ages, and isotopic ages. These new data provide constraints on depositional and metamorphic ages of lithostratigraphic rock units and the timing of structures that separate them. Kinematic analyses and thermobarometric calculations provide insights on the regional tectonic processes that affected the rocks on Baranof Island. The rocks on Baranof Island consist of Paleozoic to Cenozoic volcanic, sedimentary, and intrusive igneous rocks that are part of a volcanic island arc. Detailed mapping, petrologic
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