Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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intrusion in the Trout Creek area and Bickford and Boardman (1984) reported a U-Pb zircon age determination of 1,672 +/- 5 Ma from the southern part of the intrusion in the Cameron Mountain quadrangle. Two main areas of Proterozoic biotite granodiorite occur in the Maysville quadrangle: a large area of deformed, foliated biotite granodiorite (Xgdf) in the northwest quadrant and small, scattered intrusions of undeformed biotite granodiorite (Xgd) in the southwest quadrant. The foliated granodiorite is equivalent to Proterozoic foliated granodiorite (Xgdf) of Keller and others (2004) in the Buena Vista East quadrangle Xgdf Foliated augen granodiorite (Early Proterozoic) – Foliated augen granodiorite is present in an 18,000-ft long and 1,000- to 5,000-ft wide, east-northeast-trending zone crossing the southeast slopes of Mount Shavano (plate 1). It is medium to dark gray and medium to very coarse grained. It is composed of large (0.5 to 1.5 inch) microcline phenocrysts and augen in a medium-grained matrix of plagioclase, quartz and biotite, with accessory magnetite and sphene (fig. 27). The microcline crystals range from tabular, subhedral to euhedral, moderately aligned phenocrysts to more commonly highly stretched and flattened augen. Estimated modes include 20 to 25 percent quartz, 30 to 40 percent microcline, 30 to 35 percent plagioclase, and 8 to 12 percent biotite and magnetite. The foliated granodiorite is mineralogically variable and plots in the granite b field close to the quartz monzonite join (IUGS classification). Crawford (1913) provided a whole-rock chemical analysis of foliated granodiorite from Jennings Creek (Garfield quadrangle) that indicates a chemical classification (De la Roche and others, 1980) of granodiorite. The foliated granodiorite displays variable textural development of moderate to strong penetrative mylonitic deformation fabrics. It displays a weak to strong foliation with the preferential alignment of biotite and remnant alkali-feldspar phenocrysts that are locally drawn out to a well-developed augen structure. Overall, the fabrics are protomylonitic to orthomylonitic. Discrete mappable zones of stronger mylonitic fabrics were not identified but they are preferentially developed along contacts with Early Proterozoic gneiss. The foliated granodiorite intrudes older Early Proterozoic gneisses (Xag and 120
Xhig) along the southeastern contact and is intruded by the younger Tertiary Mount Princeton pluton (Tmpp) along the northwestern contact. The moderate to strong fabrics developed in the granodiorite are locally consistent but vary over larger areas of the body. Figure 27. Outcrop of Proterozoic foliated granodiorite (Xgdf) exhibiting mylonitic, augen textures. 121
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OPEN-FILE REPORT 06-10 Geologic Map
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TABLE OF CONTENTS Introduction…
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mylonitic, augen textures………
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INTRODUCTION LOCATION AND ACCESS Th
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SAWATCH RANGE RIFT-SHOULDER UPLIFT
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of the South Arkansas River (subseq
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EXPLANATION Rio Grande Rift Neogene
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in descriptions of the geologic uni
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During the Early and Middle Paleozo
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Mountains, and White River uplifts
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field are the largest remnants of t
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Figure 5. Detailed geologic-structu
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with the Colorado mineral belt (Boo
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Shannon, 2005). Widmann and others
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the Upper Arkansas graben (fig. 5)
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15-minute quadrangle, which is adja
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etween the northern and southern se
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on U.S. Forest Service color aerial
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We use fractional map units on the
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Qpt Pinedale till, undivided (late
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weathered, but Mount Princeton quar
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stratified, matrix-supported, bould
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as rockfalls, rock avalanches, rock
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stream-channel deposits of all pere
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Figure 10. View west up South Arkan
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Figure 11. View west up South Arkan
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valley near the eastern map boundar
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lithologies are variable and depend
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Arkansas River in parts of Redman C
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angular to subangular. Deposits gen
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elations, age constraints from foss
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elated to the inferred Squaw Creek
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Figure 14. Crude bedding in coarse
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microcline, and muscovite. The latt
Page 69 and 70: Volcanic Ash Figure 17. View of eas
Page 71 and 72: Figure 18. Close-up view of intense
Page 73 and 74: The western zone of brecciated Pale
Page 75 and 76: Tr Rhyolite dikes (early to late Ol
Page 77 and 78: as the overall N47°E trend of the
Page 79 and 80: One age determination on the rhyoli
Page 81 and 82: northwest-trending fault. Thus, fie
Page 83 and 84: on the North Fork leucogranite intr
Page 85 and 86: A small 400 by 400 foot body of Nor
Page 87 and 88: N12°E, 62°NW (about 6,000 ft sout
Page 89 and 90: The age of the quartz latite porphy
Page 91 and 92: Tma Mount Aetna quartz monzonite po
Page 93 and 94: of the Maysville quadrangle and the
Page 95 and 96: Mount Aetna ring dikes (Tma), one i
Page 97 and 98: the margins of the pluton, includin
Page 99 and 100: Shannon (1988). The average of seve
Page 101 and 102: indicating a granite b composition
Page 103 and 104: analysis by Crawford (1913), two an
Page 105 and 106: locally tanish to pinkish gray. It
Page 107 and 108: quadrangle (tables 1 and 3) were fr
Page 109 and 110: slices of Paleozoic sedimentary roc
Page 111 and 112: south-southwest of Maysville is a 9
Page 113 and 114: There is one additional Paleozoic s
Page 115 and 116: near the southwest margin of the qu
Page 117 and 118: eastern contact of the diorite intr
Page 119: endoskarn zones. The two widely sep
Page 123 and 124: Xgd Granodiorite (Early Proterozoic
Page 125 and 126: Hybrid granodiorite is locally deve
Page 127 and 128: Xcs Calc-silicate gneiss (Early Pro
Page 129 and 130: Many of the calc-silicate gneiss zo
Page 131 and 132: typically expressed by intermittent
Page 133 and 134: The field relations and characteris
Page 135 and 136: the north side of all three segment
Page 137 and 138: eplaced by muscovite. The western m
Page 139 and 140: sillimanite-quartz-muscovite that a
Page 141 and 142: sillimanite gneiss (Xmsg) and the m
Page 143 and 144: Figure 35. Outcrop of Proterozoic h
Page 145 and 146: samples) indicates they are compose
Page 147 and 148: Xal Lineated amphibolite (Early Pro
Page 149 and 150: of the Proterozoic metamorphic rock
Page 151 and 152: that the present structural configu
Page 153 and 154: elated to rotation of domain blocks
Page 155 and 156: sometimes terminate at a cross stru
Page 157 and 158: limestone that is exposed in a wind
Page 159 and 160: quadrangle are intimately associate
Page 161 and 162: of the quadrangle. The north-northw
Page 163 and 164: quartz monzonite ring dikes (Tma).
Page 165 and 166: that truncates the Upper Arkansas g
Page 167 and 168: as at the mouth of Squaw Creek. How
Page 169 and 170: adjacent to the southwestern edge o
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graben and the Upper Arkansas Valle
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GEOLOGIC HAZARDS Potential geologic
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In addition, older landslides may h
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sparse vegetation. One such area is
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Table 7. Historical (pre-instrument
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4262272N. ECONOMIC GEOLOGY Currentl
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A number of the larger pegmatite bo
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River placers near Buena Vista (Van
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The small mines and prospects along
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elatively recent (post-1970) explor
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contact of two Quaternary gravels (
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quadrangle. The first area is a clu
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y Sharp (1976) to be a fault slice
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quadrant of the Maysville quadrangl
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the large Paleozoic rock outlier) i
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WATER RESOURCES Water resources on
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water near Maysville is being produ
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to Rudy C. Epis: Colorado School of
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University, M.Sc. thesis, 50 p. Din
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Hutchinson, R.M., and Hedge, C.E.,
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Litsey, L.R., 1958, Stratigraphy an
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County, Colorado, in Berg, R.R., an
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Stark, J.T., and Barnes, F.F., 1935
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Tweto, O., 1987, Rock units of the
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quadrangle, Colorado: U.S. Geologic
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94A 391996 4263422 Prospect YXp;Xbf
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336A 396189 4274961 Prospect Xgdf B
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854 391849 4268852 42 Adit; Geochem
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Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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