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General Geology and Petrology of the Precambrian Crystalline Rocks, Park and Jefferson Counties, Colorado

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General Geology and Petrology of the Precambrian Crystalline Rocks, Park and Jefferson Counties, Colorado General Geology and Petrology of the Precambrian Crystalline Rocks, Park and Jefferson Counties, Colorado GEOLOGICAL SURVEY PROFESSIONAL PAPER 608-B General Geology and Petrology of the Precambrian Crystalline Rocks, Park and Jefferson Counties, Colorado By C. C. HAWLEY and R. A. WOBUS GEOLOGY AND ORE DEPOSITS OF THE SOUTHERN TARRYALL REGION, PARK AND JEFFERSON COUNTIES, COLORADO GEOLOGICAL SURVEY PROFESSIONAL PAPER 608-B Metamorphic rocks in the Tarry all region were intruded by Precambrian igneous rocks in three distinct episodes 1.7, 1.46, and 1.04 billion years ago. Late phases of the final intrusion, the Pikes Peak Granite, were accompanied by beryllium-bearing greisens UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1977 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress Cataloging in Publication Data Hawley, Charles Caldwell, 1929- General geology and petrology of the Precambrian crystalline rocks, Park and Jefferson Counties. (Geology and ore deposits of the southern Tarryall region, Park and Jefferson Counties, Colorado) (Geological Survey Professional Paper 608-B) Bibliography: p. Includes index. Supt.ofDocs.no.: I 19:608-B 1. Geology, Stratigraphic Pre-Cambrian. 2. Geology-Colorado Park Co. 3. Geology Colorado Jefferson Co. 4. Granite- Colorado Park Co. 5. Granite Colorado Jefferson Co. I. Wobus, R. A., joint author. II. Title. III. Series. IV. Series: United States Geological Survey Professional Paper 608-B. QE75.P9 no. 608-B [QE653] 557.3'08s 76-608358 [552'.09788'59] For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock Number 024-001-02956-1 CONTENTS Page Pa,-*e Conversion to metric system......................................................... V General geology Continued Abstract......................................................................................... Bl Intrusive rocks Continued Introduction.................................................................................. 2 Pikes Peak Granite and associated rocks Continued Location and geography ....................................................... 2 Redskin Granite Continued Geologic investigations......................................................... 4 Rock description and classification Con. Acknowledgments.................................................................. 4 Granite-aplite dikes .................................. General geology............................................................................ 5 Summary.......................................................... 45 Precambrian rocks and their nomenclature.......................... 5 Structures in the Precambrian rocks.............................. 45 Layered gneiss........................................................................ 7 Foliation and cleavage............................................ 45 Sillimanitic biotite-muscovite gneiss and migmatite.... 7 Lineation................................................................. 45 Sillimanite-cordierite quartz gneiss ............................... 8 Folds........................................................................ 46 Fine-grained biotite gneiss............................................. 9 Faults.....................................................................1;. 46 Calc-silicate gneiss...................................................... - 9 Joints....................................................................... 48 Amphibolite........................................................................... 12 Rocks and deposits of Tertiary and Quaternary age..... 48 Derivation of the layered gneiss and amphibolite units ...... 14 Geologic history ............................................................. 50 Metamorphic reactions and conditions of metamorphism .. 15 Intrusive rocks....................................................................... 16 Chemical composition and petrology of the Pikes Peak Granite Boulder Creek(?) Granodiorite....................................... 17 and associated rocks............................................................ 51 Quartz diorite gneiss............................................... 17 Chemical composition........................................................... 51 Granodiorite gneiss................................................. 17 Pikes Peak Granite in the Tarryall Mountains Quartz monzonite gneiss......................................... 19 batholith...................................................................... 51 Mafic and metaigneous rocks......................................... 22 Redskin Granite ............................................................. 52 Quartz monzonite of Elevenmile Canyon...................... 22 Summary of trace elements in the Pikes Peak and Silver Plume(?) Quartz Monzonite................................. 23 Redskin Granites ........................................................ 52 Medium- to coarse-grained quartz monzonite........ 24 Chemical composition of biotite in the Pikes Peak and Fine- to medium-grained and fine-grained Redskin Granites ........................................................ 53 quartz monzonites................................................ 24 Petrologic interpretation of the Pikes Peak Granite Granite pegmatite of pre-Pikes Peak age ...................... 25 and associated rocks.................................................... 54 Pikes Peak Granite and associated rocks....................... 25 Origin and emplacement............................................... 54 Occurrence of the Pikes Peak Granite.................... 27 Some aspects of variation in the Pikes Peak magma.... 55 Age and correlation................................................. 27 Variation in the Pikes Peak Granite and Megascopic description........................................... 28 associated granodiorite..... ............................ 56 Quartz monzonite of the main Pikes Peak batholith....................................................... 28 Variation in the Pikes Peak Granite of Tarryall Rocks of the Tarryall Mountains batholith.... 28 Mountains batholith and Redskin Granite . 56 Coarse subequigranular granite............... 29 Grain size variation.......................................... 57 Coarse porphyritic granite........................ 31 Mineralogic variation ...................................... 57 Medium- to coarse-grained granite .......... 31 Chemical variation........................................... 58 Minor facies.............................................. 32 Summary .......................................................... 59 Granodiorite of Wellington Lake.................... 33 Causes of variation in the Pikes Peak and Redskin Gabbro and quartz monzonite......................... 33 Granites................................................................ 60 Redskin Granite...................................................... 35 Zoning..................................................................... 61 Age.................................................................... 35 Zoning and variation in some other granite series 63 Rock description and classification................. 35 Origin of fine-grained granite................................ 66 Granular granite....................................... 37 Relation of granites to ore deposits...................................... 67 Porphyritic granite................................... 39 Separation of hydrothermal fluids from magma........... 68 Fine-grained granite................................. 41 State of the hydrothermal fluid and greisenization....... 69 Granite-aplite............................................ 41 Summary......................................................................... 70 Granite-aplite of the Boomer and Selected references......................................................................... 70 China Wall cupolas .............................. 42 Index............................................................................................. 75 IV CONTENTS ILLUSTRATIONS Page PLATE 1. Geologic map (north half and south half) and section of the southern Tarryall region, Park and Jefferson Counties, Colo............................................................................................................................... In pocket FIGURE 1. Index map of the southern Tarryall region................................................................................................................................ B3 2. Generalized geologic map of the southern Tarryall region....................................................................................................... 6 3. Generalized map of the layered gneiss unit prior to intrusion of granitic rocks, Puma Hills................................................. 10 4. Generalized map showing distribution of silimanite-rich rocks................................................................................................. 11 5. Photograph of migmatitic sillimanitic biotite-muscovite gneiss............................................................................................... 12 6. Photograph of alined sillimanite crystals in sillimanitic biotite-muscovite gneiss................................................................... 12 7. Sample locality map...................................................................................................................................................................
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