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Geology of the Empire Quadrangle Grand, Gilpin, and Clear Creek Counties Colorado

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Geology of the Empire Quadrangle Grand, Gilpin, and Clear Creek Counties Colorado Geology of the Empire Quadrangle Grand, Gilpin, and Clear Creek Counties ColOrado. By WILLIAM A. BRADDOCK .,..,., GEOLOGICAL SURVEY PROFESSIONAL PAPER 616 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 78-650 226 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. .20402 CONTENTS Page Tertiary igneous rocks-Continued Page Abstract___________________________________________ 1 Monzonite group ______________________________ _ 22 Introduction_______________________________________ 1 Feldspathoidal hornblende-pyroxene monzonite_ 22 Geologic history______________________________ _ _ _ _ _ _ 2 Hornblende-pyroxene monzonite _____________ _ 26 Petrographic methods ______________________________ - 3 Porphyritic hornblende-pyroxene monzonite ___ _ 31 Precambrian metamorphic rocks _____________ --_-- __ -- 3 Monzonite porphyry _______________________ _ 32 Biotite gneiss___________________________________ 3 Quartz-bearing monzonite porphyry __________ _ 32 Migmatite ________________________ -- __ -- __ - 6 Leucocratic monzonite ______________________ _ 32 Calc-silicate gneiss ________________________ -- ___ - 6 Biotite quartz monzonite porphyry _______________ _ 33 Microcline gneiss (microcline-quartz-plagioclase-bio- Bostonite porphyry ____________________________ _ 33 ti te gneiss) _________ ._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 6 Sanidinite porphyry ____________________________ _ 35 Hornblende gneiss and amphibolite_______________ 8 Age and sequence of intrusion ___________________ _ 37 Origin of metamorphic rocks_____________________ 10 Petrology _____________________________________ _ 37 Nature of premetamorphic rocks______________ 10 Definition of rock series ____________________ _ 37 Metamorphic facies_________________________ 13 Calc-alkali series ___________________________ ~ 40 Precambrian igneous rocks___________________________ 14 Alkali-calcic series _________________________ _ Qua.rtz diorite of St. Marys Lake__________________ 14 41 Bo.ulder Creek Granite__________________________ 15 Undersaturated series ______________________ _ 43 Quartz diorite and hornblendite ______________ - _ _ _ _ 17 Summary of petrologic interpretations ________________ _ 45 Hornblende diorite and other metamorphosed basic Quaternary deposits ________________________________ _ 45 dikes________________________________________ 18 Structure _________________________________________ _ 45 Granite porphyry __________________________ - _ _ _ _ 18 Older deformation (B o) _________________________ _ 45 Silver Plume Granite____________________________ 19 Younger deformation (B ) ____________________ -- _ 49 Pegmatite_____________________________________ 19 11 Relations of intrusive rocks to deformations _______ _ 49 Tertiary igneous rocks_______________________________ 19 East-northeast-trending folds of unknown origin ___ _ 51 Granodiorite group_____________________________ 20 Faults ________________________________________ _ Hornblende granodiorite porphyry..:.___________ 20 51 References ________________________________________ _ Biotite granodiorite porphyry________________ 22 52 Granite aplite _________________________ - ___ - 22 Index ____________________________________________ _ 55 ILLUSTRATIONS .Page PLATE 1. Geologic map and sections of the Empire quadrangle _________________________________________________ In pocket 2. Index map of Tertiary igneous rocks in the Empire quadrangle, Grand, Gilpin, and Clear Creek Counties, Colo __ In pocket 3. Foliation and lineation diagrams__________________________________________________________________ In pocket FIGVRE 1. Index map showing location of the Empire quadrangle and the areas covered by other published geologic maps_ 2 2. Photomicrographs of muscovite in biotite gneiss________________________________________________________ 5 3. Photographs of migmatite, hornblende gneiss, and amphibolite _____________________________________ ------ 7 4. Triangular plot of quartz, plagioclase, and microcline in the granitic part of migmatite from biotite gneiss and from micro cline gneiss__________________________________________________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 8 5. Triangular plot of quartz, plagioclase, and microcline in microcline gneiss _______________ - _______ - ___ ------- 8 6. Graph showing comparison of the mineral composition of biotite gneiss with norms of quartz-rich igneous rocks and with mesonorms of sedimentary rocks _____________________________________________________ --__ 10 7. Triangular diagrams showing the comparison of modes of biotite gneiss and mesonorms of sedimentary rocks___ 12 8. Equilibrium curves related to metamorphism in the Empire quadrangle___________________________________ 14 9.· Photomicrographs of the quartz diorite of St. Marys Lake_______________________________________________ 16 10. Triangular plot of plagioclase, quartz, and microcline in the Boulder Creek Granite_________________________ 17 11. Triangular plot of plagioclase, quartz, and microcline in the Silver Plume Granite___________________________ 19 12. Diagrams showing modal compositions of rocks of the Empire stock_______________________________________ 23 13. Photomicrographs of feldspathoidal hornblende-pyroxene monzonite of the Empire stock____________________ 24 14. Photomicrographs of hornblende-pyroxene monzonite, Empire stock_______________________________________ 30 III IV CONTENTS Page FIGURE 15. Photomicrographs of leucocratic monzonite, bostonite porphyry, and sanidinite porphyry____________________ 34 16. Diagram showing the known sequence of intrusion of Tertiary igneous rocks in the Empire quadrangle________ 37 17. Diagram showing relation between normative anorthite and normative quartz or nepheline in Tertiary igneous rDcks-------------------------------------------------------------------------------------------- 38 18. Larsen plot of analyses of Tertiary igneous rocks_______________________________________________________ 39 19. Triangular plot of the calc-alkali series_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 40 20. Phase diagrams for the anorthite-albite-orthoclase system compared with the trends of the alkali-calcic and calc-alkali' series__________________________________________________________________________________ 41 21. Triangular plot of aJkali-calcic series~ _______ --- ______ -________________________________________________ 42 22. Triangular plot of the anorthite-poor members of the alkali-calcic series___________________________________ 43 23. Diagram of quaternary nepheline-anorthite-kalsilite-silica system showing the position of the ternary feldspar plane---~-------------------------------------------------------------------------------------- 44 24. Addition and subtraction diagram used in testing a theory about the origin of feldspathoidal hornblende-pyroxene monzonite-------------------------------------------------------------------------------------- 45 25. Index map of folds and faults in the Empire and Central City quadrangles and adjacent areas---------------- 47 26. Synoptic diagram showing major maximums of foliation and lineation______________________________________ 48 27. Photomicrographs of cataclastically deformed rocks_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 50 28. Diagram showing the strike of large faults and small faults and veins_______________________________________ 52 TABLES Page TABLE 1. Mineral assemblages in several varieties of biotite gneiss__________________________________________________ 4 2. Modes of microcline gneiss ________ ~___________________________________________________________________ 9 3. Modes of amphibolite________________________________________________________________________________ 9 4. Chemical and spectrographic analyses of hornblende from amphibolite_____________________________________ 10 5. Mesonorms of sedimentary rocks ________________________________________ ·______________________________ 11 6. Probable sedimentary parents of biotite gneisses_________________________________________________________ 13 7. Modes of quartz diorite of St. Marys Lake______________________________________________________________ 15 8. Modal compoEition of Boulder Creek Granite___________________________________________________________ 17 9. Modal compositions of Silver Plume Granite____________________________________________________________ 19 10. Correiation of Tertiary igneous rock names as used by Wells ( 1960) and in this report______ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 20 11. Chemical and spectrographic analyses and CIPW norms of hornblende granodiorite porphyry, biotite granodiorite porphyry, biotite quartz monzonite porphyry, and granite aplite_______________________________________ 21 12. Chemical and spectrographic analyses and CIPW norms of feldspathoidal hornblende-pyroxene monzonite______ 26 13. Chemical and spectrographic analyses and CIPW nornis of hornblende-pyroxene monzonite, porphyritic horn- blende-pyroxene monzonite, and monzonite porphyry_________________________________________________ 27 14. Chemical and spectrographic analyses of pyroxene and amphibole from hornblende-pyroxene monzonite of the Empire stock ___________ ._ _
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