Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

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y the North Fork leucogranite (Tnfg) about 400 ft west of the Maysville quadrangle west boundary. The Mount Princeton pluton is generally discordant to foliation and gneissic layering in Proterozoic rocks and to bedding in Paleozoic sedimentary rocks. Shannon (1988) reviewed the overall attitude of contacts along the margin of the pluton. Most of the pluton contacts are steep with the exception of the northern and southern margins, which plunge moderately to shallowly north and moderately south, respectively. The southeastern contact, including the segment crossing the northwest corner of the Maysville quadrangle, is nearly vertical to steeply inward (northwest) dipping. Within the Mount Princeton pluton (largely preserved in the Mount Aetna cauldron collapse structure in the St. Elmo quadrangle), low dips of broad, internal textural and compositional units suggest that the pluton had a relatively broad, flat roof that was gently tilted southward during collapse of the Mount Aetna cauldron. Many previous workers have noted textural and compositional variations in the Mount Princeton pluton (Crawford, 1913; Dings and Robinson, 1957; Limbach, 1975; Sharp, 1976; R.P. Smith, 1979, unpublished reconnaissance map and 1981, personal communication; Shannon, 1988; Toulmin and Hammarstrom, 1990; and McCalpin and Shannon, 2005). Shannon (1988) described and delineated a number of systematic textural and compositional variations in the pluton. The pluton was divided into a border unit with three subunits and an interior unit with three subunits. The Mount Princeton border unit is mostly preserved in the Mount Aetna cauldron collapse structure in the southern part of the St. Elmo quadrangle. The genetic relations of compositional-textural units along the roof of the Mount Princeton pluton have been variably interpreted and are problematic. The Mount Pomeroy quartz monzonite was interpreted as a separate earlier intrusion by Crawford (1913) and Dings and Robinson (1957). It is mainly preserved in the Mount Aetna cauldron collapse structure, in a 7 mile long and 0.5 to 1.5 mile wide, N60°E-trending zone. Toulmin (1976), Shannon (1988) and Toulmin and Hammarstrom (1990) suggested that the Mount Pomeroy quartz monzonite is a roof facies of the Mount Princeton pluton. Shannon (1988) suggested that the Mount Princeton border unit be defined as the broad zone of heterogeneous textures and compositions along the roof zone, and locally along 96
the margins of the pluton, including the Mount Pomeroy quartz monzonite. He recommended abandoning the formal name Mount Pomeroy quartz monzonite and applied the name Mount Princeton inner roof border subunit. The Mount Pomeroy quartz monzonite problem is important to the geology of the Maysville quadrangle because it is the main textural unit of the Mount Princeton pluton in the quadrangle. New observations on the Mount Princeton pluton during mapping of the Buena Vista West quadrangle (McCalpin and Shannon, 2005) and during this study indicate that the Mount Pomeroy quartz monzonite problem is more complicated than initially interpreted (Shannon, 1988). New descriptions of the Mount Princeton pluton along the northern contact zone, in the Buena Vista West quadrangle, were given in McCalpin and Shannon (2005). The marginal border zone exposed in the Buena Vista West quadrangle includes minor zones of alkali feldspar and plagioclase porphyritic subunits. The latter subunit has the same appearance, mineralogy, and texture as Mount Pomeroy quartz monzonite (Tmpp subunit). An attempt was made to simplify the nomenclature of Mount Princeton pluton units and subunits (McCalpin and Shannon, 2005). The Mount Princeton includes the following units: the Mount Princeton border unit (Tmpb); and the interior subunits -- Mount Princeton finer-grained quartz monzonite (Tmpf), Mount Princeton porphyritic K- feldspar (Tmpk), and Mount Princeton quartz monzonite (Tmpm); and the Mount Pomeroy subunit (Tmpp). Observations from this study raise additional questions about the relationship between the Mount Princeton pluton and the Mount Pomeroy subunit. First, there is much more Mount Pomeroy subunit that occurs outside the southeastern margin of the Mount Aetna cauldron than previously recognized by Shannon (1988). It is in direct intrusive contact with Proterozoic rocks without evidence of other intervening border subunits. Secondly, another Tertiary intrusion (Tqm) in the west part of the Maysville quadrangle is similar to, and may be related to, the Mount Pomeroy subunit. The resolution of this problem is beyond the scope of this study, however, it is clear that a full understanding of the distribution of the Mount Pomeroy subunit and additional petrologic and geochemical studies are required. Consequently, in this report the Mount Pomeroy quartz monzonite is treated as a mappable unit and is referred to as the Mount Pomeroy subunit (Tmpp) of the 97
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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
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: Mount Aetna ring dikes (Tma), one i
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 and 146: samples) indicates they are compose
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Xal Lineated amphibolite (Early Pro
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of the Proterozoic metamorphic rock
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that the present structural configu
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elated to rotation of domain blocks
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sometimes terminate at a cross stru
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limestone that is exposed in a wind
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quadrangle are intimately associate
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of the quadrangle. The north-northw
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quartz monzonite ring dikes (Tma).
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that truncates the Upper Arkansas g
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as at the mouth of Squaw Creek. How
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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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