Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

More documents

Recommendations

Info

(Xmsg) with minor amphibolite gneiss in the western part and lineated amphibolite (Xal) in the eastern part. The two lithologies form a coherent structural block where the contacts between the units appear concordant and the foliations and lineations are similar and dip to the east and east-northeast. The muscovite-sillimanite gneiss forms a roughly north-south-trending, crescent-shaped zone that is about 11,000 ft long and up to 3,000 ft wide; this zone extends from Green Creek north-northwest across Willow Creek. It is poorly to moderately well exposed and locally makes good, continuous ledge outcrops. The muscovite-sillimanite gneiss varies from a white to a mostly light- to medium-orangeish-brown color. The orangeish-brown color is related to a weak to moderate, pervasive limonite staining that generally increases to the south. Most of the muscovite-sillimanite gneiss is nonmagnetic and the limonite stain may be related to pervasive oxidation of disseminated magnetite. It is fine to medium grained (locally coarse grained) and moderately to strongly foliated. The muscovite-sillimanite gneiss generally lacks gneissic layering but is characterized by small (0.25 to 1.0 inch) eyes, lenses, or flattened nodules consisting of fine-grained sillimanite-quartz-muscovite (fig. 33). The amount, size, and composition of the eyes vary within the unit. Minor zones within the muscovite-sillimanite gneiss lack the eyes and other areas have small (0.25 to 0.5 inch) muscovite porphyroblasts. The eyes tend to be the same size in any given area and the size and abundance gradationally varies from place to place. Local gneissic structures are produced by discontinuous layers of medium- to coarse-grained microcline and quartz. A study of two thin sections shows 35 to 40 percent quartz, 20 to 25 percent microcline, 5 to 15 percent plagioclase, 10 to 15 percent muscovite, 10 to 12 percent sillimanite, 3 to 10 percent biotite, with accessory zircon. On the basis of estimated modes the rock has a granitic composition that would plot near the join between the granite a and granite b fields (IUGS classification). The sillimanite tends to be concentrated in the eyes and occurs as very fine-grained bundles of needles that are locally intergrown with muscovite. The sillimanite and muscovite locally fringe each other, but textures usually suggest that sillimanite replaces the muscovite. Both thin sections show evidence of larger microcline grains with well-developed perthitic textures that appear to be pegmatitic segregations. The microcline grains are locally extensively 136
eplaced by muscovite. The western margin of the muscovite-sillimanite gneiss (Xmsg)/lineated amphibolite (Xal) domain is bounded by a north-northwest-trending fault that separates it from the domain to the west that contains the muscovite-cordierite schist (Xmc) unit. The eastern margin of the domain is bounded by a northwest-trending fault. The two faults that bound the domain are major faults with suspected thousands of feet of offset. The southern part of the domain is open and the muscovite-sillimanite gneiss and amphibolite extend beyond the south margin of the Maysville quadrangle. Figure 33. Hand sample, billet and slab of muscovite-sillimanite gneiss (Xmsg). Eyes are composed of sillimanite-quartz-muscovite. Billet is stained showing irregular distribution of alkali feldspar (upper right). The muscovite-sillimanite gneiss and lineated amphibolite have highly contrasting compositions that are suggestive of a mafic-felsic bimodal relationship. Further support for a conformable structural relationship is indicated by a long, narrow (about 100 ft thick) amphibolite gneiss body that is interlayered with the muscovite-sillimanite gneiss 137
Page 1 and 2:
OPEN-FILE REPORT 06-10 Geologic Map
Page 3 and 4:
TABLE OF CONTENTS Introduction…
Page 5 and 6:
mylonitic, augen textures………
Page 7 and 8:
INTRODUCTION LOCATION AND ACCESS Th
Page 9 and 10:
SAWATCH RANGE RIFT-SHOULDER UPLIFT
Page 11 and 12:
of the South Arkansas River (subseq
Page 13 and 14:
EXPLANATION Rio Grande Rift Neogene
Page 15 and 16:
in descriptions of the geologic uni
Page 17 and 18:
During the Early and Middle Paleozo
Page 19 and 20:
Mountains, and White River uplifts
Page 21 and 22:
field are the largest remnants of t
Page 23 and 24:
Figure 5. Detailed geologic-structu
Page 25 and 26:
with the Colorado mineral belt (Boo
Page 27 and 28:
Shannon, 2005). Widmann and others
Page 29 and 30:
the Upper Arkansas graben (fig. 5)
Page 31 and 32:
15-minute quadrangle, which is adja
Page 33 and 34:
etween the northern and southern se
Page 35 and 36:
on U.S. Forest Service color aerial
Page 37 and 38:
We use fractional map units on the
Page 39 and 40:
Qpt Pinedale till, undivided (late
Page 41 and 42:
weathered, but Mount Princeton quar
Page 43 and 44:
stratified, matrix-supported, bould
Page 45 and 46:
as rockfalls, rock avalanches, rock
Page 47 and 48:
stream-channel deposits of all pere
Page 49 and 50:
Figure 10. View west up South Arkan
Page 51 and 52:
Figure 11. View west up South Arkan
Page 53 and 54:
valley near the eastern map boundar
Page 55 and 56:
lithologies are variable and depend
Page 57 and 58:
Arkansas River in parts of Redman C
Page 59 and 60:
angular to subangular. Deposits gen
Page 61 and 62:
elations, age constraints from foss
Page 63 and 64:
elated to the inferred Squaw Creek
Page 65 and 66:
Figure 14. Crude bedding in coarse
Page 67 and 68:
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 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: the north side of all three segment
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
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
Page 197 and 198:
quadrant of the Maysville quadrangl
Page 199 and 200:
the large Paleozoic rock outlier) i
Page 201 and 202:
WATER RESOURCES Water resources on
Page 203 and 204:
water near Maysville is being produ
Page 205 and 206:
to Rudy C. Epis: Colorado School of
Page 207 and 208:
University, M.Sc. thesis, 50 p. Din
Page 209 and 210:
Hutchinson, R.M., and Hedge, C.E.,
Page 211 and 212:
Litsey, L.R., 1958, Stratigraphy an
Page 213 and 214:
County, Colorado, in Berg, R.R., an
Page 215 and 216:
Stark, J.T., and Barnes, F.F., 1935
Page 217 and 218:
Tweto, O., 1987, Rock units of the
Page 219 and 220:
quadrangle, Colorado: U.S. Geologic
Page 221 and 222:
94A 391996 4263422 Prospect YXp;Xbf
Page 223 and 224:
336A 396189 4274961 Prospect Xgdf B
Page 225:
854 391849 4268852 42 Adit; Geochem
show all

Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?