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Scientific Investigations Map 3335

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# 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 are components of a Paleozoic to Early Tertiary oceanic volcanic arc  complex, including sedimentary and volcanic rocks that were deposited on and  adjacent to the arc complex, deformed, and accreted. The arc complex consists  of greenschist to amphibolite facies Paleozoic metavolcanic and metasedimentary  rocks overlain by lower-grade Triassic metasedimentary and metavolcanic rocks  and intruded by Jurassic calc-alkaline plutons. The Paleozoic rocks correlate  well in age and lithology with rocks of the Sicker and Buttle Lake Groups of  the Wrangellia terrane on Vancouver Island and differ from rocks of the Skolai  Group that constitute basement to type-Wrangellia in the Wrangell Mountains.  The Jurassic intrusive rocks are correlative with plutons that intrude the  Wrangellia terrane on Vancouver Island but are lacking in the Wrangell  Mountains. The rocks accreted beneath the arc complex are referred to as the Baranof  Accretionary Complex in this report and are correlated with the Chugach  Accretionary Complex of southern and southeastern Alaska and with the Pacific  Rim Complex on Vancouver Island. Stratigraphic correlations between upper- and  lower-plate rocks on Baranof Island and western Chichagof Island with rocks on  Haida Gwaii and Vancouver Island, in addition to correlative ages of intrusive  rocks and restorations of the Fairweather-Queen Charlotte, Chatham Strait, and  Peril Strait Faults that define the Baranof-Chichagof block, suggest Baranof  Island was near Vancouver Island at the time of initiation of arc magmatism in  the Early Jurassic. Early Eocene plutons that intruded the accretionary complex  outboard of the arc on Baranof Island are attributed to anatectic melting of  trench sediments resulting from subduction of a spreading center. Oligocene  intrusive rocks on Baranof Island correlate in age and composition with  intrusive rocks in the Kano Plutonic Suite on Haida Gwaii, and similar magmatic  sources are inferred. | First posted July 29, 2015
- **Pamphlet** PDF (1 MB)
- **Map Sheet** PDF (18 MB) 
-  **Map GIS** ZIP (14.7 MB)  Contains: geospatial database. Refer to the Readme and Metadata files for more information. 
-  **Table 1** XLS (47 kB)  Geochronologic data for the Geologic Map of Baranof Island, Southeastern Alaska 
-  **Table 4** XLS (28 kB)  Geochemical data for the Geologic Map of Baranof Island, Southestern Alaska 

**For additional information, contact:**Alaska Science Center staff U.S. Geological Survey4210 University Dr.Anchorage, AK 99508Alaska Science Center 

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### 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, pamphlet 82 p., scale 1:200,000, https://dx.doi.org/10.3133/sim3335.

ISSN 2329-132X (online)

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### Pamphlet Contents

Abstract

Introduction

Previous Investigations

Geology of Baranof Island

Deformation and Metamorphism

Faults

Hot Springs

Summary and Discussion

Acknowledgments

Description of Map Units

References

Figures (3)

Tables (4)

AccessibilityFOIAPrivacyPolicies and Notices

U.S. Department of the Interior |            U.S. Geological Survey           	URL: *http://pubsdata.usgs.gov/pubs/sim/3335/index.html*            Page Contact Information: GS Pubs Web Contact           	Page Last Modified: Thursday, 01-Dec-2016 17:33:30 EST