Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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Figure 36. Outcrop of Proterozoic amphibolite agglomerate (Xaa) with mixed mafic and felsic metavolcanic clasts. Note stretched, elongated clasts. 146
Xal Lineated amphibolite (Early Proterozoic) – Lineated amphibolite is present in one main area associated with the triangular-shaped lithologic-structural domain with the muscovite-sillimanite gneiss (Xmsg) in the eastern part of the Proterozoic terrane south of the South Arkansas River. The lineated amphibolite makes up a 4,000 ft by 4,000 ft by 5,000 ft triangular area in the eastern part of this domain that extends across Green Creek and beyond the southern edge of the quadrangle. It is poorly exposed with minor small outcrops and commonly found as concentrated float. The lineated amphibolite is dark gray to black and generally fine grained. The mineralogy is dominated by amphibole and plagioclase; the rocks lack quartz and micas and are generally nonmagnetic. Estimated modes are 50 to 70 percent hornblende and 30 to 50 percent plagioclase. In contrast to the well-layered amphibolite gneiss, the lineated amphibolite occurs as thick massive zones suggesting a more homogeneous protolith. The amphibolite is characterized by a moderate to strong penetrative lineation where the amphiboles are aligned, discontinuous rods (fig. 37). When viewed normal to the lineation the rock appears to have a strong foliation and when viewed parallel with the lineation the rock appears to be equigranular and non-foliated. The orientation of the lineation is consistently to the north-northeast (N10° to 35°E) with generally moderate, but locally shallow plunges (20° to 64°) to the northeast. Along the western contact with the muscovite-sillimanite gneiss a transitional zone of amphibolite gneiss (with minor interlayered hornblende intermediate gneiss and biotite-muscovite felsic gneiss) with gneissic layering is concordant to the contact and to the moderate to strong foliation in the muscovite-sillimanite gneiss (Xmsg). The gneisses in the transitional zone are generally oriented north-south with moderate dips (54° to 70°) to the east. In the central part of the lineated amphibolite sub-domain minor areas of the amphibolite are interlayered with hornblende intermediate gneiss (Xhig), biotite felsic gneiss (Xbfg), and calc-silicate gneiss (Xcs); these interlayers become more abundant and in larger sized areas to the southeast. The eastern boundary of the lineated amphibolite sub-domain is a major northwest trending fault zone that merges with or is truncated by the Willow Creek fault bounding the western edge of the South Arkansas graben. The distribution of Berthoud-type granite and pegmatite intrusions also changes across the 147
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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
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Volcanic Ash Figure 17. View of eas
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Figure 18. Close-up view of intense
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The western zone of brecciated Pale
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Tr Rhyolite dikes (early to late Ol
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as the overall N47°E trend of the
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One age determination on the rhyoli
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northwest-trending fault. Thus, fie
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on the North Fork leucogranite intr
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A small 400 by 400 foot body of Nor
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N12°E, 62°NW (about 6,000 ft sout
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The age of the quartz latite porphy
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Tma Mount Aetna quartz monzonite po
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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 and 120: endoskarn zones. The two widely sep
Page 121 and 122: Xhig) along the southeastern contac
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: samples) indicates they are compose
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
Page 171 and 172: graben and the Upper Arkansas Valle
Page 173 and 174: GEOLOGIC HAZARDS Potential geologic
Page 175 and 176: In addition, older landslides may h
Page 177 and 178: sparse vegetation. One such area is
Page 179 and 180: Table 7. Historical (pre-instrument
Page 181 and 182: 4262272N. ECONOMIC GEOLOGY Currentl
Page 183 and 184: A number of the larger pegmatite bo
Page 185 and 186: River placers near Buena Vista (Van
Page 187 and 188: The small mines and prospects along
Page 189 and 190: elatively recent (post-1970) explor
Page 191 and 192: contact of two Quaternary gravels (
Page 193 and 194: quadrangle. The first area is a clu
Page 195 and 196: 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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