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Characteristics and Petrogenesis of Alaskan^Type Ultranaafic-Mafic Intrusions, Southeastern Alaska

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Characteristics and Petrogenesis of Alaskan^Type Ultranaafic-Mafic Intrusions, Southeastern Alaska Characteristics and Petrogenesis of Alaskan^Type«/ J: Ultranaafic-Mafic Intrusions, Southeastern Alaska U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1564 AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the current- year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" are no longer available. 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U.S. Geological Survey, Earth Science Information Center 101 Twelfth Ave., Box 12 Fairbanks, AK 99701 • STENNIS SPACE CENTER, Mississippi—Bldg. 3101 Characteristics and Petrogenesis of Alaskan-Type Ultramafic-Mafic Intrusions, Southeastern Alaska By Glen R. Himmelberg and Robert A. Loney U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1564 Field relations, petrography, rock chemistry, mineral chemistry, and interpretation of origin and emplacement of Alaskan-type intrusions UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1995 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director For sale by U.S. Geological Survey, Information Services Box 25286, Federal Center Denver, CO 80225 Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. Text and illustrations edited by Mary Lou Callas Graphics by authors Layout by Mary Lou Callas Library of Congress Cataloging-in-Publication Data Himmelberg, Glen R. Characteristics and petrogenesis of Alaskan-type ultramafic-maflc intrusions, southeastern Alaska / by Glen R. Himmelberg and Robert A. Loney. p. cm. — (U.S. Geological Survey professional paper : 1564) "Field relations, petrography, rock chemistry, mineral chemistry, and interpretation of origin and emplacement of Alaskan-type intrusions." Includes bibliographical references (p. - ). Supt. of Docs, no.: 119.16:1564 1. Intrusions (Geology)—Alaska. 2. Rocks, Ultrabasic—Alaska. 3. Geochemistry—Alaska. I. Loney, Robert Ahlberg, 1922- . II. Title. III. Series. QE611.5.U6H56 1995 551.8'8'097982-«ic20 95-2236 CIP CONTENTS Abstract ———————————————————————————————————————————— 1 Introduction —————————————————————————————————————————— 2 Regional setting and age——————————————————————————————————— 3 Field relations and petrography ——————————————————————————————— 3 Relation of Alaskan-type ultramafic intrusions to regional structure and metamorphism— 8 General statement ———————————————————————————————————— 8 Union Bay complex ——————————————————————————————————— 9 Kane Peak complex ——————————————————————————————————— 11 Blashke Islands complex ———————————————————————————————— 15 Rock chemistry ————————————————————————————————————————— 17 Major elements ————————————————————————————————————— 17 Trace elements —————————————————————————————————————— 19 Mineral chemistry —————————————————————————————————————— 26 Discussion —————————————————————————————————————————— 33 Crystallization conditions of ultramafic-mafie rocks ————————————————— 33 Nature of the parent magma —————————————————————————————— 39 Intrusive mechanism and zonal structure—————————————————————————— 41 Conclusions ————————————————————————————————————————— 42 References cited ——————————————————————————————————————— 43 FIGURES 1. Map of southeastern Alaska showing locations of Alaskan-type ultramafic-mafic intrusions and major tectonostratigraphic units——————————————————————————————————————————— 4 2. Geologic map of ultramafic complex at Red Bluff Bay ————————————————————————— 7 3. Geologic map of ultramafic complex at Union Bay ——————————————————————————— 10 4. Hypothetical cross section through ultramafic complex at Union Bay —————————————————— 11 5. Equal-area lower hemisphere plots of structural data in Union Bay area ———————————————— 12 6. Equal-area lower hemisphere plots of olivine X, Y, and Z axes in ultramafic complex at Union Bay -- 13 7. Geologic map of ultramafic complex at Kane Peak ——————————————————————————— ^ 8. Equal-area lower hemisphere plots of structural data in metaturbidites in Kane Peak area —————— 15 9. Equal-area lower hemisphere plots of olivine X, Y, and Z axes in ultramafic complex in Kane Peak area————————————————————————————————————————————————————— 16 10. Geologic map of ultramafic complex at Blashke Islands ————————————————————————— 18 11. Equal-area lower hemisphere plots of olivine X, Y, and Z axes in ultramafic complex at Blashke Islands ——————————————————————————————————————————————————— ^ 12. Rare-earth element patterns of ultramafic and gabbroic rocks of Alaskan-type intrusions at Blashke Islands, Kane Peak, Union Bay, Salt Chuck, and Port Snettisham ——————————————————— 22 13. Rare-earth element patterns of ultramafic xenoliths, plutonic gabbros, and a tholeiite flow associated with Aleutian island-arc volcanism ————————————————————————————————————— 23 III IV CONTENTS 14-18. Plots of chemical parameters of Alaskan-type intrusions: 14. Compositions of clinopyroxene and orthopyroxene in ultramafic rocks and gabbro ————————— 28 15. Weight percent A12O3 against Mg/(Mg+Fe2+) of clinopyroxene in ultramafic rocks and gabbro —— 29 16. Percent A1IV against weight percent TiO2 for clinopyroxene in clinopyroxenite and gabbro ———— 29 17. A1IV against cations in A-site for hornblende in ultramafic rocks and gabbro ———————————— 33 18. Cr/(Cr+Al+Fe3+) against Fe2+/(Mg+Fe2+) for chromian spinel in ultramafic rocks —————————— 33 TABLES 1. Major rock types and characteristics of Alaskan-type ultramafic-mafic bodies............................................ 6 2. Chemical compositions of Alaskan-type ultramafic and mafic rocks ........................................................... 20 3. Trace-element contents of Alaskan-type ultramafic and mafic rocks............................................................ 24 4-9. Analyses of minerals in Alaskan-type ultramafic and mafic rocks: 4. Olivine................................................................................................................................................... 27 5. Orthopyroxene...................................................................................................................................... 28 6. Clinopyroxene....................................................................................................................................... 30 7. Hornblende............................................................................................................................................ 34 8. Biotite.................................................................................................................................................... 36 9. Chromian spinel.................................................................................................................................... 37 10. Analyses of plagioclase in Blashke Islands Alaskan-type gabbro................................................................. 38 Characteristics and Petrogenesis of Alaskan-Type Ultramafic-Mafic Intrusions, Southeastern
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