GEOLOGIC MAP OF THE PROTEROZOIC ROCKS OF THE CENTRAL … · nederland synform coal creek synform...
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36 35 36 5 82 30 65 43 36 36 40 47 42 30 31 20 33 44 9 35 50 2 37 42 28 12 23 78 34 45 36 31 37 10 39 29 17 18 31 26 56 59 48 82 SYNFORM ROWENA CARIBOU ANTIFORM CONEY LAKES SYNFORM THUNDERBOLT PEAK ANTIFORM NEDERLAND SYNFORM COAL CREEK SYNFORM CREEK COAL SYNFORM SYNFORM CENTRAL CITY SYNFORM ANTIFORM BALD MOUNTAIN DUMONT ANTIFORM ANTIFORM MOUNTAIN ARIZONA LAWSON SYNFORM LOCH LOMOND ANTIFORM MT. EVA ANTIFORM WITTER PEAK SYNFORM ROGERS ROGERS PASS PASS ANTIFORM SYNFORM 27 ? ? ? ANTIFORM SCAR TOP 5 PEWABIC MOUNTAIN ROGERS PASS FAULT JAMES PEAK FAULT FAULT BANCROFT MAMMOTH GULCH FAULT ROGERS FAULT SHEAR ZONE ZONE COPELAND ROGERS 60 68 Xfh 75 70 38 37 80 81 69 60 50 75 60 60 60 30 5 70 75 75 35 35 70 65 60 35 40 70 40 15 10 40 55 45 75 50 70 55 60 70 35 65 41 40 75 25 40 39 45 55 80 70 55 56 85 50 40 35 40 40 15 60 35 50 80 55 70 50 45 45 80 40 80 75 85 65 75 76 75 50 60 65 50 45 70 65 40 70 75 35 70 60 45 40 60 70 50 60 50 40 65 75 10 55 25 55 28 7 38 30 32 10 55 63 56 26 50 32 63 60 35 70 60 50 45 55 45 40 50 56 50 53 47 64 66 40 56 52 40 32 35 15 13 50 39 35 46 19 25 70 53 20 42 4 50 75 71 75 72 16 47 46 45 49 70 76 81 60 75 64 56 86 65 52 61 64 54 67 25 55 34 53 50 35 40 72 28 28 60 45 65 63 85 50 70 70 60 46 75 5 65 60 68 65 75 85 70 35 40 50 80 20 85 35 35 55 60 65 55 50 35 60 58 75 80 80 50 55 60 55 70 70 70 60 27 42 47 48 78 70 60 80 80 47 42 79 77 82 53 55 81 66 82 59 65 70 70 65 80 85 55 40 30 49 40 25 40 55 75 65 70 30 70 50 35 45 40 50 35 40 35 40 71 70 25 70 20 18 12 10 55 45 70 15 55 50 45 60 30 60 45 20 85 5 80 85 64 71 88 40 85 75 35 15 35 60 15 45 70 72 54 62 70 60 65 30 65 65 50 35 30 55 35 20 45 15 60 30 70 39 45 60 50 58 68 60 46 86 25 37 72 62 59 35 40 52 48 57 54 50 40 37 50 59 41 74 64 56 47 56 46 43 50 55 53 52 54 56 43 50 47 47 38 41 40 45 46 24 64 56 33 18 38 38 57 53 72 42 50 37 39 24 25 58 28 44 67 62 74 35 13 25 16 30 60 22 30 35 70 43 36 30 25 32 50 68 80 72 62 56 57 57 23 50 70 80 65 18 66 60 70 52 35 67 35 77 78 60 55 83 70 80 85 23 55 49 53 29 27 58 60 85 22 15 9 85 42 60 24 34 71 23 3 27 60 56 54 34 25 59 58 36 35 62 53 65 18 33 46 42 68 58 44 74 73 45 46 36 28 52 56 59 70 85 70 80 75 76 67 65 47 49 38 23 45 13 40 6 46 47 32 40 39 61 47 57 46 35 32 40 50 10 50 60 15 20 11 29 24 23 57 35 54 10 24 15 60 60 20 80 50 70 25 5 85 24 27 33 28 15 65 40 52 42 51 60 14 22 58 65 30 60 70 65 85 75 88 70 80 74 40 70 63 80 45 72 45 40 65 60 25 10 50 60 20 20 40 75 35 75 5 80 83 40 85 45 70 45 5 42 10 50 15 70 80 10 65 49 84 80 45 85 60 10 34 49 59 10 30 73 74 41 28 61 71 85 46 36 45 16 60 45 80 80 72 88 70 85 86 68 77 60 70 66 36 53 67 80 66 74 57 34 45 36 72 46 65 16 80 45 75 75 65 52 50 50 86 42 70 28 64 82 31 31 58 17 58 49 9 55 70 59 29 54 80 49 80 68 33 66 33 57 10 58 12 82 80 80 86 38 58 15 7 8 67 65 75 80 42 46 62 38 15 40 15 16 75 60 63 75 55 46 65 73 65 64 70 24 34 75 79 2 25 9 35 33 64 12 83 85 25 8 47 51 73 74 68 83 24 30 53 36 24 23 45 23 14 15 8 21 30 52 56 57 36 28 32 21 9 41 34 34 27 35 34 36 25 30 74 82 65 54 78 32 5 13 38 46 15 30 30 26 20 65 33 25 40 50 10 40 72 36 21 73 28 75 30 40 53 19 19 74 23 28 72 45 6 35 50 5 5 21 20 38 75 14 33 15 18 26 68 7 45 18 17 12 10 29 28 57 52 17 53 73 25 30 4 5 43 32 28 12 10 27 45 68 45 60 68 63 70 38 52 38 49 50 40 40 38 30 40 27 60 60 23 62 68 64 68 60 32 85 31 38 61 40 45 55 21 22 35 32 42 28 24 40 35 35 33 35 34 60 40 50 25 53 27 20 53 26 27 35 50 35 35 45 45 20 38 64 75 30 55 30 65 46 43 30 60 75 75 40 45 45 32 21 44 44 54 54 51 53 48 32 28 26 38 37 19 28 19 20 64 15 16 28 44 47 42 33 13 33 29 41 33 57 56 52 46 38 43 53 44 46 43 16 41 84 35 9 8 58 7 83 58 17 79 26 43 18 61 78 58 48 19 62 50 51 50 61 16 31 44 49 83 86 70 68 73 36 42 49 26 33 48 39 65 13 37 53 24 27 47 41 38 33 44 46 8 6 37 57 33 45 53 32 31 23 24 32 32 34 27 46 18 42 21 49 56 57 71 43 50 20 10 35 10 45 67 62 39 62 64 68 46 41 42 73 73 68 69 73 58 56 93 74 53 58 66 77 52 69 46 83 45 13 69 63 60 39 68 70 73 82 77 85 48 77 44 63 64 60 67 66 64 46 67 61 59 73 32 80 46 46 46 60 63 62 64 59 45 74 65 65 87 47 66 24 84 58 73 75 50 78 70 14 81 70 64 97 44 75 44 68 33 70 89 86 62 63 63 54 57 50 51 53 85 88 59 58 49 80 65 64 69 56 66 55 80 56 35 75 79 45 31 34 83 48 87 55 73 58 74 21 24 48 51 56 63 75 80 80 80 70 40 60 60 60 39 35 25 80 40 40 40 46 41 45 20 30 30 30 75 80 60 35 25 55 70 55 50 62 46 54 35 32 28 68 69 41 40 47 49 46 53 41 40 55 21 45 40 40 41 10 55 74 60 34 38 77 30 70 85 65 65 89 80 64 65 79 72 72 87 85 83 80 80 44 59 81 75 49 42 52 75 59 70 62 62 62 75 78 47 80 23 80 82 70 44 63 35 82 85 76 80 85 58 72 57 64 79 75 70 12 50 40 45 50 25 50 60 85 80 80 60 60 25 30 41 18 77 82 40 83 73 45 60 58 15 40 47 40 15 35 20 15 15 10 45 55 48 50 35 40 65 50 37 20 35 25 15 25 25 20 20 17 10 16 41 25 20 20 20 15 27 15 10 55 60 55 26 23 30 30 35 60 35 75 55 35 45 40 20 60 80 2 24 10 47 45 11 27 13 15 15 80 67 68 69 61 67 52 76 58 60 70 69 78 75 87 66 65 53 87 87 43 87 86 47 46 25 45 73 65 74 85 78 62 87 85 55 55 10 6 54 45 57 8 40 7 25 26 11 20 27 4 40 30 33 80 54 42 20 84 80 35 Qa Xgns 30 10 Xgnc Qa Qa 34 69 53 65 28 48 65 58 67 53 67 74 28 65 66 55 62 57 68 48 72 15 85 30 88 65 80 65 60 63 21 MAXWELL FAULT FAULT HOOSIER LIVINGSTON FAULT ARAPAHO PASS FAULT BERTHOUD PASS FAULT FAULT JUNCTION RANCH FAULT BLACK FAULT HAWK FAULT WAGONER- WILD JIM CREEK FAULT IDAHO SPRINGS- RALSTON FLOYD HILL FAULT ZONE KEN CARYL FAULT FLOYD HILL FAULT HURRICANE HILL FAULT FAULT RANCH CREEK FAULT APEX Qa ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? TKi TKi TKi TKi TKi Xgncs TKi TKi Xcb Xcb Xcb Xgncs Xgncs Xgncs Xgnca Xgnca Xgnca Xgnca Xqf Xrsq Xr Xgnca Xgg Xgnq Xgg Xgng Xgng Xgng Xgng Xr Xgmc Xgd Xgd Xgd Xgd Xgd Xgd Xgd Xgd Xhcs Xgd Xgd Xgnc Xgnc Xgnc Xgnc Xgnc Xgncs Qa Qa Qa Qa Qa Qa Qa Qa Qa QTg QTg QTg QTg Ypg Ypg Ypg Xmb Xmb Xmb Xmb Xmb Xmb Xmb Xmb Xmb Xma Xma Ypg Ypg Ypg Ypg Xgns Xgns Xgns Xgns Xgns Xgns Xgns Xg Xgns Xgns Xgns Xgns Xgns Xgns Xgns Xgnb Xgnb Xgnb Xgg Xgnb Xhcs Xhcs Xhcs Xhcs Xgnh Xgnh Xgnh Xfh Xfh Xfh Xfh Xfh Xf Xf Xf Xf Xf Xf Xf Xf Xf Xf Xf Xf Xf Xf Xf Xqs Xq Xq Xq Xq Xam Xam Xam Xam Xqhd Xgd Xqhd Xqhd Xg Xqm Xqm Xqm Xqm Yspb Yspb Ysp Yspm Yspm Ysp Ysp Ysp Ysp Ysp Ysp Ysp Ysp Xgng Xgng PIKES Xf Xf Xqhd Xgns Xgncs Qa Xf Xf Xf Xf Xgns Xgnh TKi Ysp Xgnc Xgns Xgns Xgns Ysp Xgnh Xgnc Xgd Xgd Xf Xgns Xqm Xghd Xghd Xqhd Xgns Xgns Xam Xam Xam Xam Xg Xgnh Xgns Xgnh Xgd Xf Xgnc Qa Xgnh Xgns Xgnc Xgd Xgd Xfh Xgnb Xgd Qa Xgnc Ysp Ysp Ysp Ysp Xgnc Qa Xf Xfh Ysp Xgnc Xgnc TKi TKi TKi Ysp Ysp Ysp Ysp TKi Xgns Xqm Ysp Xqhd Xgns Xgnh Ysp Xqm Ysp Ysp Xqm Xgnc Xgns Xgnc Xhcs Xhcs BOULDER CREEK BATHOLITH Xqm Xfh Xgns Xfh Xf Xqm Xgnc Xgnc Xqhd Xq Qa Xqhd Xqs Xqs Xq Xgnb Xqhd Xgnh Xhcs Xhcs Xhcs Xhcs Qa Qa Qa Xhcs Xgng Xgnh TKi Xfh Xqhd Xgd Xgnh Xqhd Qa TKi Xam Xgnh Xgnh Xgnh Xam Xgnh Xgnh Xgns Xgnb Xgns Xgns Xgng Xgnh Xgd Xgd Xgnc Xgnc Xgncs Xf TKi TKi TKi Xgns TKi Xam Ysp Xgnb Xf Xqhd Xgnh Xfh Xgnc Xgnc Ysp Xhcs Xgnca Ysb Xqm Xf MOUNT EVANS BATHOLITH Qa Xq Xr Xgns Xf Xcb Xgnh Ysp Xhcs Xhcs Xgd Xqm Xgd Qa QTg Qa Qa Qa QTg Xgnca Xf Xfh Xfh Xf Xfh Xfh Xgnh Xhcs Xf Xfh Qa Xgnca Xgnb Xgnca Xf Xgg Xhcs Xgns Xhcs Xghd Xgns Xgns Xqm Xgnh Xqm Xhcs Xhcs Qa Xam Xgns Ysp Ysp Ypg Ypg Xmb Xgnb Xgnh Xgns Xgns Xgns Xgns Xam QTg Xgnh Qa Xgnh Xfh QTg Xgd Xgns BATHOLITH PEAK TKi Xf TKi TKi Xgnc Xfh Pf Pf Pf Pf Any use of trade names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey For sale by U.S. Geological Survey Information Services Box 25286, Federal Center, Denver, CO 80225 Manuscript approved for publication April 24, 1997 This map is also available as a PDF file at http://greenwood.cr.usgs.gov CONVERSION FACTORS Multiply By To obtain centimeters (cm) 0.3937 inches (in.) meters (m) 3.281 feet (ft) kilometers (km) 0.6214 miles (mi) GEOLOGIC MAP OF THE PROTEROZOIC ROCKS OF THE CENTRAL FRONT RANGE, COLORADO Compiled by Dolores J. Gable 2000 Base from U.S. Geological Survey Bailey, Denver West, 1983; Estes Park, 1984 Universal Transverse Mercator projection 1927 North American datum Geology compiled 1976–84 Additions in 1995, with assistance of William D. Johnson, Jr. Map digitized by Springfield and Springfield. Digital cartography by Denny Welp and Gayle Dumonceaux. Edited by F.C. Brunstein. 0 0 1 1 CONTOUR INTERVAL 50 METERS NATIONAL GEODETIC VERTICAL DATUM OF 1929 1 1 5 KILOMETERS 5 MILES 2 2 SCALE 1:100 000 3 4 4 3 TRUE NORTH MAGNETIC NORTH APPROXIMATE MEAN DECLINATION, 1999 12 ° 39°37'30" 30' 39°22'30" 105°30' 105° 22'30" 15' 40° 40°00' 52'30" 45' 7'30" 7'30" U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY 105°52'30" 45' 37'30" 40° 7'30" 40°00' 52'30" 45' 39°30' GEOLOGIC INVESTIGATIONS SERIES I–2605 37'30" 39°22'30" 105°30' 22'30" 15' 105°7'30" Printed on recycled paper 45° 37°30' CORRELATION OF MAP UNITS Qa QTg INTRUSIVE ROCKS SEDIMENTARY ROCKS Unconformity INTRUSIVE ROCKS TKi Pf Ypg Ysp Yspm Yspb Xqm Xgg Xgd Xg Xqhd Xq Xqs Xf Xfh Xgnb Xma Xmb Xgng Xgnq Xgnca Xgnc Xgns Xgncs Xr Xrsq Xqf METAMORPHIC ROCKS METASEDIMENTARY AND METAVOLCANIC ROCKS Xam Xgnh Xhcs Xcb Xgmc Interlayered lithologic units; no stratigraphic order implied Early Tertiary and Late Cretaceous Holocene and late Pleistocene QUATERNARY QUATERNARY AND TERTIARY TERTIARY AND CRETACEOUS MIDDLE PROTEROZOIC EARLY PROTEROZOIC PERMIAN AND PENNSYLVANIAN TKi Xgnb Xgns Xqm Ypg Ysp Yspm Xgg Xma Xcb Xqf Xrsq Xr Xgmc Xgncs Xgnc Xgnca Xgnq Xgng Xmb Xgd Xg Xqhd Xam Xq Xqs Xf Xfh Xgnh Xhcs Yspb QTg Qa Pf DESCRIPTION OF MAP UNITS SURFICIAL DEPOSITS Alluvium, colluvium, and glacial deposits (Holo- cene and late Pleistocene)—In northwest part of area (Strawberry Lake quadrangle), locally in- cludes Troublesome Formation (Miocene and Oligocene) adjacent to Proterozoic rock units Gravels (Quaternary and Tertiary)—Rounded to subangular pebbles, and boulders derived from metamorphic and igneous rocks mostly to the west of the map area. Patterned area consists of debris derived almost entirely from Precam- brian rocks and found on higher slopes above modern drainage channels EARLY TERTIARY AND LATE CRETACEOUS INTRUSIVE ROCKS Monzonite, granodiorite, and syenite—May in- clude minor amounts of mafic rocks, such as pyroxenite SEDIMENTARY ROCKS Fountain Formation (Permian and Pennsylvani- an)—Map unit locally includes Lykins Forma- tion (Triassic and Permian) and Lyons Sand- stone (Permian). Fountain Formation, predomi- nantly arkosic conglomerate and moderately coarse grained sandstone; Lykins Formation, red and light-green calcareous sandstone; Lyons Sandstone, red and pink fine-grained to very fine grained sandstone PROTEROZOIC INTRUSIVE ROCKS Pikes Peak Granite (Middle Proterozoic)—Biotite granite and biotite-hornblende granite, minor quartz syenite, fayalite granite, riebeckite gran- ite, and locally granodiorite and quartz monzon- ite. Rb-Sr age about 1,040 m.y. (Hedge, 1970) Silver Plume Granite (or Quartz Monzonite) of the Berthoud Plutonic Suite (Middle Proter- ozoic) Quartz monzonite and monzogranite—Mostly massive, gray to buff, fine- to medium-grained quartz monzonite or monzogranite displaying aligned tabular feldspar crystals and aligned bio- tite laths, especially along borders of plutons. U-Pb zircon age 1,400 m.y. (Aleinikoff and others, 1990) Monzodiorite to granodiorite facies—Medium- to coarse-grained, grayish-white and black, foli- ated monzodiorite to granodiorite. Exists locally in Mount Evans batholith. Contains 6–8 per- cent magnetite. U-Pb zircon age of 1,443 m.y. (Aleinikoff and others, 1990) Inclusions—Profuse inclusions mostly of biotite gneiss in Silver Plume Granite Quartz Monzonite (Early Proterozoic)—Light gray to light tan, leucocratic, and fine to medium grained. Includes Twin Spruce Quartz Monzon- ite of the Eldorado Springs area. Field evidence suggests Twin Spruce is both younger and the same age as the Boulder Creek Granodiorite. Patterned where unit contains numerous biotite gneiss inclusions Granodiorite (Early Proterozoic)—Gray to pink- ish-gray, medium- to coarse-grained gneissic granodiorite; weathers darker pinkish gray. Ex- ists locally at Mt. Morrison and in Clear Creek and Turkey Creek canyons. Isotopically fits the 1,700 m.y. isochron of the Boulder Creek Granodiorite (C.E. Hedge, oral commun., 1976) Boulder Creek Granodiorite and associated rocks of the Routt Plutonic Suite (Early Pro- terozoic)—Mottled grayish-white and black, medium- to very coarse grained, locally por- phyritic, predominantly granodiorite but in- cludes lenses and layers of gabbro, hornblende diorite, hornblendite, and quartz diorite. Rb-Sr determinations suggest the Boulder Creek is about 1,700 m.y. old (Peterman and others, 1968; Reed and others, 1987) Gabbro and related rocks (Early Proterozoic)— Dark-gray to pinkish-gray, black and white, massive, coarse-grained to very coarse grained rock ranging in composition from metagabbro to quartz diorite; contains intermediate plagio- clase and orthopyroxene and clinopyroxene Hornblende diorite, quartz-bearing hornblende diorite, quartz diorite, and hornblendite (Ear- ly Proterozoic)—Gray to black, medium- to fine-grained, gray to black hornblende-bearing rocks. Exists in small plutons, lenses, pods, and dikes EARLY PROTEROZOIC METAMORPHIC ROCKS [The mineralogy and modal, chemical, and quantitative analyses of the metamorphic rocks are given in Gable (1996).] Amphibolite—Dark-greenish-gray to black, fine- to medium-grained, nonlayered to poorly layered, weakly to strongly foliated rock, composed mostly of hornblende and plagioclase EARLY PROTEROZOIC METASEDIMENTARY AND METAVOLCANIC ROCKS Quartzite and quartz gneiss—Quartzite is white, gray, and pinkish or purplish gray, medium to coarse grained, and locally conglomeratic. In- terlayered with quartz-mica schist and some calc-silicate gneiss lenses. Quartzite along Coal Creek and in Eldorado Springs area is interlay- ered with conglomeratic quartzite. At some lo- calities, foliated quartz gneiss is conspicuously layered and contains variable amounts of gar- net, magnetite-ilmenite, and epidote Quartz-biotite-muscovite schist—Silver-gray to dark-gray, fine- to medium-grained, micaceous schist; locally contains porphyroblasts of anda- lusite, cordierite, and garnet and small amounts of staurolite and sillimanite. Mapped along mountain front in Ralston Buttes area Feldspar-rich gneiss—Light-gray, leucocratic, fine- to medium-grained, microcline-plagioclase- quartz-biotite gneiss. Conspicuously foliated; granitic in appearance. Locally garnetiferous and ubiquitously interlayered with conformable thin to thick layers and lenses of hornblende gneiss, amphibolite, biotite gneiss, and locally calc-silicate rock Interlayered feldspar-rich gneiss and hornblende gneiss—Feldspar-rich gneiss may contain horn- blende and is generally darker than the feld- spar-rich gneiss unit (Xf). Interlayered horn- blende gneiss is black, white, and dark gray or greenish gray and similar in composition to the hornblende gneiss in hornblende gneiss unit (Xgh). Layers and lenses of biotite gneiss, am- phibolite, calc-silicate rock, and biotite-quartz- plagioclase gneiss make up 10–30 percent of unit Hornblende gneiss and amphibolite—Black, black and white, and dark gray or greenish gray, fine to medium grained, and layered; has weak to strong foliation. Consists of hornblende-plagioclase- quartz gneiss or hornblende-clinopyroxene- quartz-feldspar gneiss; in places interlayered with amphibolite, calc-silicate gneiss, biotite-quartz- plagioclase gneiss, and minor quartzite Interlayered hornblende gneiss, calc-silicate gneiss, and amphibolite—Black and white, light gray, greenish gray, and yellowish green, fine to medium grained, layered; has moder- ate to good compositional layering and mod- erate to weak foliation. More leucocratic than hornblende gneiss (Xgnh) because individual gneiss layers are thicker and contain more fel- sic, calcic, and quartz-bearing layers. Contains minor cordierite-biotite gneiss and biotite- quartz-plagioclase gneiss Biotite gneiss—Dark-gray, fine- to medium- grained, foliated, biotite-quartz-plagioclase gneiss; locally garnetiferous and microcline- bearing, and interlayered with hornblende gneiss, calc-silicate gneiss, and sillimanite-bio- tite-quartz gneiss. Patterned areas contain pro- fuse lenses and layers of granite gneiss Biotite gneiss and amphibolite—Gray, fine- to medium-grained biotite-quartz-plagioclase gneiss interlayered and intergraded; includes profuse thin lenses and layers of amphibo- lite. Locally contains lenses and layers of hornblende-biotite-plagioclase gneiss, calc- silicate gneiss, quartzite, and profuse lenses and layers of granite gneiss and pegmatite Biotite-plagioclase gneiss—Interlayered and in- tergraded biotite-quartz-plagioclase gneiss and sillimanite-biotite-quartz-plagioclase gneiss; has profuse lenses and layers of granitic gneiss and pegmatite, and at some localities contains small lenses and layers of calc-silicate gneiss, amphibolite, and quartzite. Contains much less amphibole than the biotite gneiss and amphib- olite unit (Xma) Garnet-biotite gneiss—Exists as individual layers that grade into and are interlayered with minor units of biotite-quartz-plagioclase gneiss, garnet- sillimanite-biotite gneiss, and cordierite-garnet- sillimanite-biotite gneiss Quartz-plagioclase gneiss—Leucocratic, poorly fo- liated, and contains thin layers of biotite gneiss, feldspar-rich gneiss, quartzite, hornblende gneiss, and amphibolite. Only mapped along mountain front south of Morrison Cordierite-garnet-gedrite-biotite gneiss—Dark gray to black, medium to very coarse grained, foliated to massive. Interlayered with thinner layers of cordierite-biotite gneiss, garnet-bio- tite gneiss, and cordierite-garnet-sillimanite-bi- otite gneiss. K-feldspar is not present or is rare in these rocks Cordierite-garnet-sillimanite-biotite gneiss ± K- feldspar ± plagioclase—Generally gray to very dark gray, fine to medium grained, and foliated. Foliation or layering disrupted by pegmatite, gar- net, fibrolitic sillimanite, and clusters of cordierite and biotite. May be finely interlayered with one or more of the following types of gneiss: garnet- sillimanite-biotite, cordierite-biotite, garnet-biotite, cordierite-garnet-biotite, cordierite-sillimanite-biotite, magnetite-sillimanite-biotite, and cordierite-magnet- ite-sillimanite-biotite Sillimanite-biotite gneiss—Banded light gray, very dark gray, or black; at some localities interlay- ered with biotite-quartz-plagioclase gneiss and layers and lenses of amphibolite, biotite gneiss, calc-silicate gneiss, and garnet-biotite gneiss. South of the Idaho Springs-Ralston shear zone, primary muscovite and trace amounts of cor- dierite present in unit. Pattern shows area that contains profuse pods and lenses of Silver Plume Granite (Ysp) Cordierite-magnetite-sillimanite-biotite gneiss and minor magnetite-sillimanite-biotite gneiss—Light gray to nearly black, fine to me- dium grained, compositionally layered. In pla- ces layers discontinuous due to stringers and clots of pegmatite and knots of cordierite, silli- manite, biotite, and magnetite. Both rock types gradational into cordierite-garnet-sillimanite-bio- tite gneiss (Xgnc) and sillimanite-biotite gneiss (Xgns) Cordierite-sillimanite-biotite gneiss—Light-gray, medium-grained, foliated biotite gneiss. Map- ped only in Evergreen-Squaw Pass area Calc-silicate gneiss—Variable gray, green, white, or black and fine to coarse grained. Color de- pends on the type and quantity of minerals present, such as hornblende, diopside, biotite, calcic-plagioclase, scapolite, and quartz. Folia- tion poor but compositional layering good Rutile-bearing, sillimanite-quartz gneiss and bio- tite-quartz gneiss—Light gray, fine to medium grained, and commonly interlayered with bio- tite-quartz gneiss and sillimanite-quartz gneiss. Exists as thin lenses in the Evergreen-Squaw Pass area Sillimanite-quartz gneiss containing accessory rutile lenses—Light gray to gray, fine to medium grained, and foliated. Exists only as thin lenses 15 cm to 30 m wide in the Evergreen and Squaw Pass quadrangles; most are of limited extent but one is 6 km long Augen gneiss—Fine-grained, sheared gneiss contain- ing small, pink feldspar augen in a well-foliated bi- otitic matrix. Mapped only in Ralston Buttes area Contact—Approximately located, dotted where concealed; queried where inferred Fault or fracture zone—Dashed where approxi- mately located; dotted where concealed; quer- ied where uncertain. Arrows show apparent di- rection of relative movement. Pattern indicates broad zone of brecciation Fault zone—Shown where map unit is fractured and not identifiable Zone of closely spaced shears Boundary of Idaho Springs-Ralston shear zone Folds—Showing approximate trace of axial plane and direction of plunge. Dotted where con- cealed; queried where inferred Antiform Overturned antiform Synform Overturned synform Small-scale linear and planar features Bearing and plunge of axis of minor folds— Symbols show plan view of minor folds Strike and dip of foliation Inclined Vertical Bearing and plunge of lineation—Lineations de- fined by aligned minerals, mineral streaks, and fold axes or intersection of planar elements. Symbol may be combined with foliation symbol IDAHO SPRINGS EVERGREEN MORRISON CONIFER INDIAN HILLS BAILEY PINE PLATTE CANYON KASSLER SQUAW PASS ISOLATION PEAK ALLENS PARK STRAWBERRY LAKE MONARCH LAKE WARD GOLD HILL BOULDER EAST PORTAL NEDERLAND TUNGSTEN ELDORADO SPRINGS EMPIRE CENTRAL CITY BLACK HAWK RALSTON BUTTES GOLDEN SHADOW MOUNTAIN 40°15' 7'30" 40°00' 105°00' 7'30" 15' 22'30" 30' 37'30" 45' 105°52'30" 52'30" 45' 37'30" 30' 39°22'30" 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 1. Pearson (1980) 2. Pearson (1980) 3. Pearson (1980) 4. Wrucke and Wilson (1967) 5. Gable (1980) 6. Gable and Madole (1976) 7. Pearson (1980) 8. Schroeder (1995) 9. Young (1991) 10. Gable (1969) 11. Gable (1972) 12. Wells (1967) 13. Van Horn (1972) 14. Sheridan and others (1967) 15. Taylor (1976) 16. Sims and Gable (1967) 17. Braddock (1969) 18. Moench and others (1962) Moench (1964) Hawley and Moore (1967) 19. Sheridan and Marsh (1976) 20. Sheridan and others (1972) 21. Gable (1968) 22. Bryant and others (1973) 23. Bryant (1974a) 24. Bryant (1976) 25. Bryant (1974b) 26. Peterson (1964) 27. Scott (1963) SOURCES OF GEOLOGIC DATA COLORADO MAP LOCATION Map area Mountain Front REFERENCES CITED Aleinikoff, J.N., DeWitt, Ed., Reed, J.C., Jr., and Walter, Marianne, 1990, The Mount Evans batholith—an anomalous 1.4 Ga pluton in the Front Range, Colorado [abs.]: Geological Society of America Abstracts with Programs, v. 22, no. 6, p. 1. Braddock, W.A., 1969, Geology of the Empire quadrangle, Grand, Gilpin, and Clear Creek Counties, Colorado: U.S. Geological Survey Professional Paper 616, 56 p. Bryant, B.H., 1974a, Reconnaissance geologic map of the Conifer quadrangle, Jefferson County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF–597, scale 1:24,000. ———1974b, Reconnaissance geologic map of the Pine quadrangle, Jefferson County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF–598, scale 1:24,000. ———1976, Reconnaissance geologic map of the Bailey quadrangle, Jefferson and Park Counties, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF–816, scale 1:24,000. Bryant, B.H., Miller, R.D., and Scott, G.R., 1973, Geologic map of the Indian Hills quadrangle, Jefferson County, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–1073, scale 1:24,000. Gable, D.J., 1968, Geology of the crystalline rocks in the western part of the Morrison quadrangle, Jefferson County, Colorado: U.S. Geological Survey Bulletin 1251–E, 45 p. ———1969, Geologic map of the Nederland quadrangle, Boulder and Gilpin Counties, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–833, scale 1:24,000. ———1972, Geologic map of the Tungsten quadrangle, Boulder, Gilpin, and Jefferson Counties, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–978, scale 1:24,000. ———1980, Geologic map of the Gold Hill quadrangle, Boulder County, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–1525, scale 1:24,000. ———1996, Mineralogy, geochemistry, metamorphism, and provenance of the early Proterozoic metamorphic rocks of the central Front Range, Colorado: U.S. Geological Survey Open-File Report 96-522, 2 sheets, map scale 1:100,000. Gable, D.J., and Madole, R.F., 1976, Geologic map of the Ward quadrangle, Boulder County, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–1277, scale 1:24,000. Gable, D.J., and Sims, P.K., 1969, Geology and regional metamorphism of some high-grade cordierite gneisses, Front Range, Colorado: Geological Society of America Special Paper 128, 87 p. Hawley, C.C., and Moore, F.B., 1967, Geology and ore deposits of the Lawson- Dumont-Fall River district, Clear Creek County, Colorado: U.S. Geological Survey Bulletin 1231, 92 p. Hedge, C.E., 1970, Whole-rock Rb-Sr age of the Pikes Peak batholith, Colorado: U.S. Geological Survey Professional Paper 700–B, p. B86–B89. Lovering, T.S., and Goddard, E.N., 1950 [1951], Geology and ore deposits of the Front Range, Colorado: U.S. Geological Survey Professional Paper 223, 319 p. Marsh, S.P., and Sheridan, D.M., 1976, Rutile in Precambrian sillimanite-quartz gneiss and related rocks, east-central Front Range, Colorado: U.S. Geological Survey Professional Paper 959–G, 17 p. Moench, R.H., 1964, Geology of Precambrian rocks, Idaho Springs district, Colorado: U.S. Geological Survey Bulletin 1182–A, 70 p. Moench, R.H., Harrison, J.E., and Sims, P.K., 1962, Precambrian folding in the Idaho Springs-Central City area, Front Range, Colorado: Geological Society of America Bulletin, v. 73, p. 35–58. Pearson, R.C., 1980, Mineral resources of the Indian Peaks study area, Boulder and Grand Counties, Colorado, with a section on Interpretation of aeromagnetic data, by Gordon Johnson: U.S. Geological Survey Bulletin 1463, 109 p. Peterman, Z.E., Hedge, C.E., and Braddock, W.A., 1968, Age of Precambrian events in the northeastern Front Range, Colorado: Journal of Geophysical Research, v. 73, no. 6, p. 2277–2296. Peterson, W.L., 1964, Geology of the Platte Canyon quadrangle, Colorado: U.S. Geological Survey Bulletin 1181–C, 23 p. Reed, J.C., Jr., Bickford, M.E., Premo, W.R., Pallister, J.S., and Aleinikoff, J.N., 1987, Evolution of the Early Proterozoic Colorado Province—constraints from U-Pb geochronology: Geology, v. 15, no. 9, p. 861–865. Schroeder, D.A., 1995, Geologic map of the Strawberry Lake quadrangle, Grand County, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–1764, scale 1:24,000. Scott, G.R., 1963, Bedrock geology of the Kassler quadrangle, Colorado: U.S. Geological Survey Professional Paper 421–B, p. 71–125. Sheridan, D.M., and Marsh, S.P., 1976, Geologic map of the Squaw Pass quadrangle, Clear Creek, Jefferson, and Gilpin Counties, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–1337, scale 1:24,000. Sheridan, D.M., Maxwell, C.H., and Albee, A.L., 1967, Geology and uranium deposits of the Ralston Buttes district, Jefferson County, Colorado, with a section on Paleozoic and younger sedimentary rocks, by Richard Van Horn: U.S. Geological Survey Professional Paper 520, 121 p. Sheridan, D.M., Reed, J.C., Jr., and Bryant, B.H., 1972 [1973], Geologic map of the Evergreen quadrangle, Jefferson County, Colorado: U.S. Geological Survey Miscellaneous Geologic Investigations Series Map I–786–A, scale 1:24,000. Sims, P.K., and Gable, D.J., 1967, Petrology and structure of Precambrian rocks, Central City quadrangle, Colorado: U.S. Geological Survey Professional Paper 554–E, 56 p. Taylor, R.B., 1976, Geologic map of the Black Hawk quadrangle, Gilpin, Jefferson, and Clear Creek Counties, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–1248, scale 1:24,000. Tweto, Ogden, 1987, Rock units in the Precambrian basement in Colorado: U.S. Geological Survey Professional Paper 1321–A, p. A1–A54. Van Horn, Richard, 1972, Surficial and bedrock geologic map of the Golden quadrangle, Jefferson County, Colorado: U.S. Geological Survey Folio of the Golden quadrangle, Colorado, Map I–761–A, scale 1:24,000. Wells, J.D., 1967, Geology of the Eldorado Springs quadrangle, Boulder and Jefferson Counties, Colorado: U.S. Geological Survey Bulletin 1221–D, 85 p. Wrucke, C.T., and Wilson, R.F., 1967, Geologic map of the Boulder quadrangle, Boulder County, Colorado: U.S. Geological Survey Open-file report, scale 1:24,000. Young, E.J., 1991, Geologic map of the East Portal quadrangle, Boulder, Gilpin, and Grand Counties, Colorado: U.S. Geological Survey Miscellaneous Investigations Series Map I–2212, scale 1:24,000.
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Xgnc
Xfh
P f
P f
P f
P f
Any use of trade names in this publication is fordescriptive purposes only and does not implyendorsement by the U.S. Geological Survey
For sale by U.S. Geological Survey Information ServicesBox 25286, Federal Center, Denver, CO 80225
Manuscript approved for publicationApril 24, 1997
This map is also available as a PDF file athttp://greenwood.cr.usgs.gov
CONVERSION FACTORS
Multiply By To obtain
centimeters (cm) 0.3937 inches (in.)meters (m) 3.281 feet (ft)kilometers (km) 0.6214 miles (mi)
GEOLOGIC MAP OF THE PROTEROZOIC ROCKS OF THE CENTRAL FRONT RANGE, COLORADO
Compiled byDolores J. Gable
2000
Base from U.S. Geological SurveyBailey, Denver West, 1983; Estes Park, 1984
Universal Transverse Mercator projection1927 North American datum
Geology compiled 1976–84Additions in 1995, with assistanceof William D. Johnson, Jr. Map digitizedby Springfield and Springfield. Digitalcartography by Denny Welp and GayleDumonceaux. Edited by F.C. Brunstein.
0
01
1
CONTOUR INTERVAL 50 METERSNATIONAL GEODETIC VERTICAL DATUM OF 1929
1
1 5 KILOMETERS
5 MILES2
2
SCALE 1:100 0003 4
43
TRU
E N
OR
TH
MA
GN
ETIC
NO
RTH
APPROXIMATE MEANDECLINATION, 1999
12 °
39°37'30"
30'
39°22'30"
105°30'
105°
22'30" 15'
40°
40°00'
52'30"
45'
7'30"
7'30"
U.S. DEPARTMENT OF THE INTERIORU.S. GEOLOGICAL SURVEY
105°52'30" 45' 37'30"
40°7'30"
40°00'
52'30"
45'
39°30'
GEOLOGIC INVESTIGATIONS SERIESI–2605
37'30"
39°22'30"
105°30' 22'30" 15' 105°7'30"
Printed on recycled paper
45° 37°30'
CORRELATION OF MAP UNITS
Qa
QTg
INTRUSIVE ROCKS
SEDIMENTARY ROCKS
UnconformityINTRUSIVE ROCKS
TKi
P f
Ypg
Ysp Yspm Yspb
Xqm Xgg Xgd Xg Xqhd
Xq Xqs
Xf Xfh
Xgnb Xma Xmb
Xgng Xgnq
Xgnca Xgnc
Xgns
Xgncs
Xr Xrsq Xqf
METAMORPHIC ROCKS
METASEDIMENTARY ANDMETAVOLCANIC ROCKS
Xam
Xgnh Xhcs
Xcb
Xgmc
Interlayeredlithologic units;no stratigraphicorder implied
Early Tertiaryand
Late Cretaceous
Holocene andlate Pleistocene QUATERNARY
QUATERNARYAND TERTIARY
TERTIARY ANDCRETACEOUS
MIDDLEPROTEROZOIC
EARLYPROTEROZOIC
PERMIAN ANDPENNSYLVANIAN
TKi
Xgnb
Xgns
Xqm
Ypg
Ysp
Yspm
Xgg
Xma
Xcb
Xqf
Xrsq
Xr
Xgmc
Xgncs
Xgnc
Xgnca
Xgnq
Xgng
Xmb
Xgd
Xg
Xqhd
Xam
Xq
Xqs
Xf
Xfh
Xgnh
Xhcs
Yspb
QTg
Qa
P f
DESCRIPTION OF MAP UNITS
SURFICIAL DEPOSITSAlluvium, colluvium, and glacial deposits (Holo-
cene and late Pleistocene)—In northwest part of area (Strawberry Lake quadrangle), locally in-cludes Troublesome Formation (Miocene and Oligocene) adjacent to Proterozoic rock units
Gravels (Quaternary and Tertiary)—Rounded to subangular pebbles, and boulders derived from metamorphic and igneous rocks mostly to the west of the map area. Patterned area consists of debris derived almost entirely from Precam-brian rocks and found on higher slopes above modern drainage channels
EARLY TERTIARY AND LATE CRETACEOUSINTRUSIVE ROCKS
Monzonite, granodiorite, and syenite—May in-clude minor amounts of mafic rocks, such as pyroxenite
SEDIMENTARY ROCKSFountain Formation (Permian and Pennsylvani-
an)—Map unit locally includes Lykins Forma-tion (Triassic and Permian) and Lyons Sand-stone (Permian). Fountain Formation, predomi-nantly arkosic conglomerate and moderately coarse grained sandstone; Lykins Formation, red and light-green calcareous sandstone; Lyons Sandstone, red and pink fine-grained to very fine grained sandstone
PROTEROZOIC INTRUSIVE ROCKSPikes Peak Granite (Middle Proterozoic)—Biotite
granite and biotite-hornblende granite, minor quartz syenite, fayalite granite, riebeckite gran-ite, and locally granodiorite and quartz monzon-ite. Rb-Sr age about 1,040 m.y. (Hedge, 1970)
Silver Plume Granite (or Quartz Monzonite) of the Berthoud Plutonic Suite (Middle Proter-ozoic)
Quartz monzonite and monzogranite—Mostly massive, gray to buff, fine- to medium-grained quartz monzonite or monzogranite displaying aligned tabular feldspar crystals and aligned bio-tite laths, especially along borders of plutons. U-Pb zircon age 1,400 m.y. (Aleinikoff and others, 1990)
Monzodiorite to granodiorite facies—Medium- to coarse-grained, grayish-white and black, foli-ated monzodiorite to granodiorite. Exists locally in Mount Evans batholith. Contains 6–8 per-cent magnetite. U-Pb zircon age of 1,443 m.y. (Aleinikoff and others, 1990)
Inclusions—Profuse inclusions mostly of biotite gneiss in Silver Plume Granite
Quartz Monzonite (Early Proterozoic)—Light gray to light tan, leucocratic, and fine to medium grained. Includes Twin Spruce Quartz Monzon-ite of the Eldorado Springs area. Field evidence suggests Twin Spruce is both younger and the same age as the Boulder Creek Granodiorite. Patterned where unit contains numerous biotite gneiss inclusions
Granodiorite (Early Proterozoic)—Gray to pink-ish-gray, medium- to coarse-grained gneissic granodiorite; weathers darker pinkish gray. Ex-ists locally at Mt. Morrison and in Clear Creek and Turkey Creek canyons. Isotopically fits the 1,700 m.y. isochron of the Boulder Creek Granodiorite (C.E. Hedge, oral commun., 1976)
Boulder Creek Granodiorite and associated rocks of the Routt Plutonic Suite (Early Pro-terozoic)—Mottled grayish-white and black, medium- to very coarse grained, locally por-phyritic, predominantly granodiorite but in-cludes lenses and layers of gabbro, hornblende diorite, hornblendite, and quartz diorite. Rb-Sr determinations suggest the Boulder Creek is about 1,700 m.y. old (Peterman and others, 1968; Reed and others, 1987)
Gabbro and related rocks (Early Proterozoic)— Dark-gray to pinkish-gray, black and white, massive, coarse-grained to very coarse grained rock ranging in composition from metagabbro to quartz diorite; contains intermediate plagio-clase and orthopyroxene and clinopyroxene
Hornblende diorite, quartz-bearing hornblende diorite, quartz diorite, and hornblendite (Ear-ly Proterozoic)—Gray to black, medium- to fine-grained, gray to black hornblende-bearing rocks. Exists in small plutons, lenses, pods, and dikes
EARLY PROTEROZOIC METAMORPHIC ROCKS [The mineralogy and modal, chemical, and quantitative analyses of the metamorphic rocks are given in Gable
(1996).]Amphibolite—Dark-greenish-gray to black, fine- to
medium-grained, nonlayered to poorly layered, weakly to strongly foliated rock, composed mostly of hornblende and plagioclase
EARLY PROTEROZOIC METASEDIMENTARY AND METAVOLCANIC ROCKS
Quartzite and quartz gneiss—Quartzite is white, gray, and pinkish or purplish gray, medium to coarse grained, and locally conglomeratic. In-terlayered with quartz-mica schist and some calc-silicate gneiss lenses. Quartzite along Coal Creek and in Eldorado Springs area is interlay-ered with conglomeratic quartzite. At some lo-calities, foliated quartz gneiss is conspicuously layered and contains variable amounts of gar-net, magnetite-ilmenite, and epidote
Quartz-biotite-muscovite schist—Silver-gray to dark-gray, fine- to medium-grained, micaceous schist; locally contains porphyroblasts of anda-lusite, cordierite, and garnet and small amounts of staurolite and sillimanite. Mapped along mountain front in Ralston Buttes area
Feldspar-rich gneiss—Light-gray, leucocratic, fine- to medium-grained, microcline-plagioclase-quartz-biotite gneiss. Conspicuously foliated; granitic in appearance. Locally garnetiferous and ubiquitously interlayered with conformable thin to thick layers and lenses of hornblende gneiss, amphibolite, biotite gneiss, and locally calc-silicate rock
Interlayered feldspar-rich gneiss and hornblende gneiss—Feldspar-rich gneiss may contain horn-blende and is generally darker than the feld-spar-rich gneiss unit (Xf). Interlayered horn-blende gneiss is black, white, and dark gray or greenish gray and similar in composition to the hornblende gneiss in hornblende gneiss unit (Xgh). Layers and lenses of biotite gneiss, am-phibolite, calc-silicate rock, and biotite-quartz-plagioclase gneiss make up 10–30 percent of unit
Hornblende gneiss and amphibolite—Black, black and white, and dark gray or greenish gray, fine to medium grained, and layered; has weak to strong foliation. Consists of hornblende-plagioclase- quartz gneiss or hornblende-clinopyroxene- quartz-feldspar gneiss; in places interlayered with amphibolite, calc-silicate gneiss, biotite-quartz-plagioclase gneiss, and minor quartzite
Interlayered hornblende gneiss, calc-silicate gneiss, and amphibolite—Black and white, light gray, greenish gray, and yellowish green, fine to medium grained, layered; has moder-ate to good compositional layering and mod-erate to weak foliation. More leucocratic than hornblende gneiss (Xgnh) because individual gneiss layers are thicker and contain more fel-sic, calcic, and quartz-bearing layers. Contains minor cordierite-biotite gneiss and biotite-quartz-plagioclase gneiss
Biotite gneiss—Dark-gray, fine- to medium-grained, foliated, biotite-quartz-plagioclase gneiss; locally garnetiferous and microcline-bearing, and interlayered with hornblende gneiss, calc-silicate gneiss, and sillimanite-bio-tite-quartz gneiss. Patterned areas contain pro-fuse lenses and layers of granite gneiss
Biotite gneiss and amphibolite—Gray, fine- to medium-grained biotite-quartz-plagioclase gneiss interlayered and intergraded; includes profuse thin lenses and layers of amphibo-lite. Locally contains lenses and layers of hornblende-biotite-plagioclase gneiss, calc-silicate gneiss, quartzite, and profuse lenses and layers of granite gneiss and pegmatite
Biotite-plagioclase gneiss—Interlayered and in-tergraded biotite-quartz-plagioclase gneiss and sillimanite-biotite-quartz-plagioclase gneiss; has profuse lenses and layers of granitic gneiss and pegmatite, and at some localities contains small lenses and layers of calc-silicate gneiss, amphibolite, and quartzite. Contains much less amphibole than the biotite gneiss and amphib-olite unit (Xma)
Garnet-biotite gneiss—Exists as individual layers that grade into and are interlayered with minor units of biotite-quartz-plagioclase gneiss, garnet-sillimanite-biotite gneiss, and cordierite-garnet-sillimanite-biotite gneiss
Quartz-plagioclase gneiss—Leucocratic, poorly fo-liated, and contains thin layers of biotite gneiss, feldspar-rich gneiss, quartzite, hornblende gneiss, and amphibolite. Only mapped along mountain front south of Morrison
Cordierite-garnet-gedrite-biotite gneiss—Dark gray to black, medium to very coarse grained, foliated to massive. Interlayered with thinner layers of cordierite-biotite gneiss, garnet-bio-tite gneiss, and cordierite-garnet-sillimanite-bi-otite gneiss. K-feldspar is not present or is rare in these rocks
Cordierite-garnet-sillimanite-biotite gneiss ± K-feldspar ± plagioclase—Generally gray to very dark gray, fine to medium grained, and foliated. Foliation or layering disrupted by pegmatite, gar-net, fibrolitic sillimanite, and clusters of cordierite and biotite. May be finely interlayered with one or more of the following types of gneiss: garnet- sillimanite-biotite, cordierite-biotite, garnet-biotite, cordierite-garnet-biotite, cordierite-sillimanite-biotite, magnetite-sillimanite-biotite, and cordierite-magnet-ite-sillimanite-biotite
Sillimanite-biotite gneiss—Banded light gray, very dark gray, or black; at some localities interlay-ered with biotite-quartz-plagioclase gneiss and layers and lenses of amphibolite, biotite gneiss, calc-silicate gneiss, and garnet-biotite gneiss. South of the Idaho Springs-Ralston shear zone, primary muscovite and trace amounts of cor-dierite present in unit. Pattern shows area that contains profuse pods and lenses of Silver Plume Granite (Ysp)
Cordierite-magnetite-sillimanite-biotite gneiss and minor magnetite-sillimanite-biotite gneiss—Light gray to nearly black, fine to me-dium grained, compositionally layered. In pla-ces layers discontinuous due to stringers and clots of pegmatite and knots of cordierite, silli-manite, biotite, and magnetite. Both rock types gradational into cordierite-garnet-sillimanite-bio-tite gneiss (Xgnc) and sillimanite-biotite gneiss (Xgns)
Cordierite-sillimanite-biotite gneiss—Light-gray, medium-grained, foliated biotite gneiss. Map-ped only in Evergreen-Squaw Pass area
Calc-silicate gneiss—Variable gray, green, white, or black and fine to coarse grained. Color de-pends on the type and quantity of minerals present, such as hornblende, diopside, biotite, calcic-plagioclase, scapolite, and quartz. Folia-tion poor but compositional layering good
Rutile-bearing, sillimanite-quartz gneiss and bio-tite-quartz gneiss—Light gray, fine to medium grained, and commonly interlayered with bio-tite-quartz gneiss and sillimanite-quartz gneiss. Exists as thin lenses in the Evergreen-Squaw Pass area
Sillimanite-quartz gneiss containing accessory rutile lenses—Light gray to gray, fine to medium grained, and foliated. Exists only as thin lenses 15 cm to 30 m wide in the Evergreen and Squaw Pass quadrangles; most are of limited extent but one is 6 km long
Augen gneiss—Fine-grained, sheared gneiss contain-ing small, pink feldspar augen in a well-foliated bi-otitic matrix. Mapped only in Ralston Buttes area
Contact—Approximately located, dotted where concealed; queried where inferred
Fault or fracture zone—Dashed where approxi-mately located; dotted where concealed; quer-ied where uncertain. Arrows show apparent di-rection of relative movement. Pattern indicates broad zone of brecciation
Fault zone—Shown where map unit is fractured and not identifiable
Zone of closely spaced shears
Boundary of Idaho Springs-Ralston shear zone
Folds—Showing approximate trace of axial plane and direction of plunge. Dotted where con-cealed; queried where inferred
Antiform
Overturned antiform
Synform
Overturned synform
Small-scale linear and planar features
Bearing and plunge of axis of minor folds— Symbols show plan view of minor folds
Strike and dip of foliationInclined
Vertical
Bearing and plunge of lineation—Lineations de-fined by aligned minerals, mineral streaks, and fold axes or intersection of planar elements. Symbol may be combined with foliation symbol
IDAHO S
PRINGS
EVER
GREEN
MORRIS
ON
CONIFER
INDIA
N HILL
S
BAILEY
PINE
PLATT
E CANYO
N
KASSLER
SQUAW PA
SS
ISOLA
TION
PEAK
ALLEN
SPA
RK
STRAW
BERRY
LAKE
MONARCH
LAKE
WARD
GOLD H
ILL
BOULDER
EAST P
ORTAL
NEDER
LAND
TUNGSTE
N
ELDORADO
SPRINGS
EMPIR
E
CENTR
AL CIT
Y
BLACK H
AWK
RALSTO
NBUTT
ES
GOLDEN
SHADOWM
OUNTAIN
40°15'
7'30"
40°00'
105°00'
7'30"
15'22'30"
30'37'30"45'105°52'30"
52'30"
45'
37'30"
30'
39°22'30"
1 2 3
45678
9 10 11 12
1314151617
18 19 20 21
2223
24 25 2627
1. Pearson (1980) 2. Pearson (1980) 3. Pearson (1980) 4. Wrucke and Wilson (1967) 5. Gable (1980) 6. Gable and Madole (1976) 7. Pearson (1980) 8. Schroeder (1995) 9. Young (1991)10. Gable (1969)11. Gable (1972)12. Wells (1967)13. Van Horn (1972)14. Sheridan and others (1967)15. Taylor (1976)16. Sims and Gable (1967)
17. Braddock (1969)18. Moench and others (1962) Moench (1964) Hawley and Moore (1967)19. Sheridan and Marsh
(1976)20. Sheridan and others
(1972)21. Gable (1968)22. Bryant and others (1973)23. Bryant (1974a)24. Bryant (1976)25. Bryant (1974b)26. Peterson (1964)27. Scott (1963)
SOURCES OF GEOLOGIC DATA
COLORADO
MAP LOCATION
Map area
Mountain
Front
REFERENCES CITED
Aleinikoff, J.N., DeWitt, Ed., Reed, J.C., Jr., and Walter, Marianne, 1990, The Mount Evans batholith—an anomalous 1.4 Ga pluton in the Front Range, Colorado [abs.]: Geological Society of America Abstracts with Programs, v. 22, no. 6, p. 1.
Braddock, W.A., 1969, Geology of the Empire quadrangle, Grand, Gilpin, and Clear Creek Counties, Colorado: U.S. Geological Survey Professional Paper 616, 56 p.
Bryant, B.H., 1974a, Reconnaissance geologic map of the Conifer quadrangle, Jefferson County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF–597, scale 1:24,000.
———1974b, Reconnaissance geologic map of the Pine quadrangle, Jefferson County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF–598, scale 1:24,000.
———1976, Reconnaissance geologic map of the Bailey quadrangle, Jefferson and Park Counties, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF–816, scale 1:24,000.
Bryant, B.H., Miller, R.D., and Scott, G.R., 1973, Geologic map of the Indian Hills quadrangle, Jefferson County, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–1073, scale 1:24,000.
Gable, D.J., 1968, Geology of the crystalline rocks in the western part of the Morrison quadrangle, Jefferson County, Colorado: U.S. Geological Survey Bulletin 1251–E, 45 p.
———1969, Geologic map of the Nederland quadrangle, Boulder and Gilpin Counties, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–833, scale 1:24,000.
———1972, Geologic map of the Tungsten quadrangle, Boulder, Gilpin, and Jefferson Counties, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–978, scale 1:24,000.
———1980, Geologic map of the Gold Hill quadrangle, Boulder County, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–1525, scale 1:24,000.
———1996, Mineralogy, geochemistry, metamorphism, and provenance of the early Proterozoic metamorphic rocks of the central Front Range, Colorado: U.S. Geological Survey Open-File Report 96-522, 2 sheets, map scale 1:100,000.
Gable, D.J., and Madole, R.F., 1976, Geologic map of the Ward quadrangle, Boulder County, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–1277, scale 1:24,000.
Gable, D.J., and Sims, P.K., 1969, Geology and regional metamorphism of some high-grade cordierite gneisses, Front Range, Colorado: Geological Society of America Special Paper 128, 87 p.
Hawley, C.C., and Moore, F.B., 1967, Geology and ore deposits of the Lawson-Dumont-Fall River district, Clear Creek County, Colorado: U.S. Geological Survey Bulletin 1231, 92 p.
Hedge, C.E., 1970, Whole-rock Rb-Sr age of the Pikes Peak batholith, Colorado: U.S. Geological Survey Professional Paper 700–B, p. B86–B89.
Lovering, T.S., and Goddard, E.N., 1950 [1951], Geology and ore deposits of the Front Range, Colorado: U.S. Geological Survey Professional Paper 223, 319 p.
Marsh, S.P., and Sheridan, D.M., 1976, Rutile in Precambrian sillimanite-quartz gneiss and related rocks, east-central Front Range, Colorado: U.S. Geological Survey Professional Paper 959–G, 17 p.
Moench, R.H., 1964, Geology of Precambrian rocks, Idaho Springs district, Colorado: U.S. Geological Survey Bulletin 1182–A, 70 p.
Moench, R.H., Harrison, J.E., and Sims, P.K., 1962, Precambrian folding in the Idaho Springs-Central City area, Front Range, Colorado: Geological Society of America Bulletin, v. 73, p. 35–58.
Pearson, R.C., 1980, Mineral resources of the Indian Peaks study area, Boulder and Grand Counties, Colorado, with a section on Interpretation of aeromagnetic data, by Gordon Johnson: U.S. Geological Survey Bulletin 1463, 109 p.
Peterman, Z.E., Hedge, C.E., and Braddock, W.A., 1968, Age of Precambrian events in the northeastern Front Range, Colorado: Journal of Geophysical Research, v. 73, no. 6, p. 2277–2296.
Peterson, W.L., 1964, Geology of the Platte Canyon quadrangle, Colorado: U.S. Geological Survey Bulletin 1181–C, 23 p.
Reed, J.C., Jr., Bickford, M.E., Premo, W.R., Pallister, J.S., and Aleinikoff, J.N., 1987, Evolution of the Early Proterozoic Colorado Province—constraints from U-Pb geochronology: Geology, v. 15, no. 9, p. 861–865.
Schroeder, D.A., 1995, Geologic map of the Strawberry Lake quadrangle, Grand County, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–1764, scale 1:24,000.
Scott, G.R., 1963, Bedrock geology of the Kassler quadrangle, Colorado: U.S. Geological Survey Professional Paper 421–B, p. 71–125.
Sheridan, D.M., and Marsh, S.P., 1976, Geologic map of the Squaw Pass quadrangle, Clear Creek, Jefferson, and Gilpin Counties, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–1337, scale 1:24,000.
Sheridan, D.M., Maxwell, C.H., and Albee, A.L., 1967, Geology and uranium deposits of the Ralston Buttes district, Jefferson County, Colorado, with a section on Paleozoic and younger sedimentary rocks, by Richard Van Horn: U.S. Geological Survey Professional Paper 520, 121 p.
Sheridan, D.M., Reed, J.C., Jr., and Bryant, B.H., 1972 [1973], Geologic map of the Evergreen quadrangle, Jefferson County, Colorado: U.S. Geological Survey Miscellaneous Geologic Investigations Series Map I–786–A, scale 1:24,000.
Sims, P.K., and Gable, D.J., 1967, Petrology and structure of Precambrian rocks, Central City quadrangle, Colorado: U.S. Geological Survey Professional Paper 554–E, 56 p.
Taylor, R.B., 1976, Geologic map of the Black Hawk quadrangle, Gilpin, Jefferson, and Clear Creek Counties, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ–1248, scale 1:24,000.
Tweto, Ogden, 1987, Rock units in the Precambrian basement in Colorado: U.S. Geological Survey Professional Paper 1321–A, p. A1–A54.
Van Horn, Richard, 1972, Surficial and bedrock geologic map of the Golden quadrangle, Jefferson County, Colorado: U.S. Geological Survey Folio of the Golden quadrangle, Colorado, Map I–761–A, scale 1:24,000.
Wells, J.D., 1967, Geology of the Eldorado Springs quadrangle, Boulder and Jefferson Counties, Colorado: U.S. Geological Survey Bulletin 1221–D, 85 p.
Wrucke, C.T., and Wilson, R.F., 1967, Geologic map of the Boulder quadrangle, Boulder County, Colorado: U.S. Geological Survey Open-file report, scale 1:24,000.
Young, E.J., 1991, Geologic map of the East Portal quadrangle, Boulder, Gilpin, and Grand Counties, Colorado: U.S. Geological Survey Miscellaneous Investigations Series Map I–2212, scale 1:24,000.
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