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| C. Alsrracr Microcline perthites from Precambrian pegmatites in the l'ront Range, Colorado, have been...orthoclase in a zone around a Tertiary intrusive stock. This stock, near the town of Eldor, is 2 miles across...sholvs fairly well exposed vertical contacts The microcline-orthoclase transition, the only major manifestation...five traverses. Outside the contact a.ureole and microcline commonly consists of clear crystals with typical...occasionally be observed. Both the nature of the microcline-orthoclase transition and its distance from the |
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| E , HORNBLENDE AND POTASSIUM FELDSPAR FROM ELDORA, COLORADO G L E N N W. B E R G E R 1 Geophysics Division...contact with the ~60 m.y. old Eldora stock in the Front Range of Colorado. The aim was to distinguish,...the time of the thermal overprinting. For the microcline 22500 (the sample number specifies the distance...original study of Hart [ 15] in the Eldora contact zone in Colorado. In essence then, one knows the timing...- S r whole-rock dates [16], intrusion of the Boulder Creek batholith and associated regional metamorphism |
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| TRANSFORI{ATION THE CONTACT AUREOLE OF THE ELDORA STOCK, COLORADO1 IN Tuouas L. Wnrcnr, U. S. Geologi...quartz monzonite stock near Eldora, Colorado, were transformed from maximum microcline to orthoclase by...greater distances perthites consisting of maximum microcline and low albite were unaffected, and at shorter...Hart place the upper stability limit of maximum microcline on the binary or-Ab solvus at 375'+ 50'C. A first-order...transformation is suggested by the absence of microcline of intermediate obliquity but a higher order |
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| r ages of hornblende from the Snowbank granitic stock near the contact with the Duluth Gabbro in Minnesota...the basis of the kinetic studies. The Snowbank stock is 2.60 billion (109) yr old and was transgressed...contact of the early Tertiary Eldora stock in the Front Range, Colorado. The effect of heating on Rb-Sr...ages from the 2.6-billion yr granitic Snowbank stock and the surrounding metasedimentary rocks near the...whereas the temperature of intrusion of the Eldora stock (quartz monzonite) was about 800°C (HART, 1964) |
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| Alkali Feldspar within the Rader Creek Pluton, Boulder Batholith, Montana1 by ROBERT I. TILLING U.S. Geological...general petrographic and mineralogic study of the Boulder batholith, a wide range of variation in microscopic...contains, in addition to orthoclase, grid-twinned microcline of varying obliquity. The perthitic structure...granodioritic Rader Creek pluton of the composite Boulder batholith contains microperthitic alkali feldspar...near-maximum microcline (obliquity = 0-75 — 1 -00); orthoclase with subordinate intermediate microcline (obliquity |
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| REGIONAL METAMORPHISM IN THE NORTHERN FRONT RANGE, COLORADO Abstract: Rubidium-strontium dating of wholerock...rocks give a concordant age of 1.71 ± 0.07 b.y. Microcline and plagioclase from a concretion pegmatite yield...A large part of the Precambrian terrane of the Colorado Front Range consists of schists and gneisses which...known rocks of the area (Fig. 1). West of Golden, Colorado, these were named the Idaho Springs Formation...andalusite, sillimanite-muscovite, and sillimanite-microcline zones have been recognized (Braddock, 1966). |
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| by BRUCE R. DOE U.S. Geological Survey, Denver, Colorado INTRODUCTION T H E isotopic composition of lead...within an individual magmatic complex such as the Boulder batholith, and by at least one isotope ratio that...shallow. A large triangular region comprising the Colorado Plateau and the Basin and Range province has not...Walcott Tuff (Re 3) Eldora stock, feldspar (Ta 1) Eldora stock, feldspar (Ta 1) Albion stock, feldspar (Ta...0-37 Pb I0> /Pb !0< 17-940 17-770 18090 18-742 Colorado 19156 19-508 19124 18-980 18-908 18-895 18-920 |
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| in the Santa Rosa Range, Nevada, and the Eldora area, Colorado, with emphasis on pelitic rocks. A consistent...S a n t a Rosa Range, Nevada, a n d the Eldora area, Colorado. A c o m p a n i o n study, dealing principally...Phyllite + 2,000 Whole rock 14.9 (1) Sawtooth stock, other samples SR0-24 + 2,000 Staurolite phyllite...Mineral ($O TM per mil 6 D per mil Santa Rosa stock S1~O-29F Granodiorite S1~O-29 A Migmatized hornfels...4• (2) 9.6• (2) 7.9 (I) 4.6 (1) -- 92 (1) Eldora traverse Biotite samples (HABT, 1964) C0A -- 5 |
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| 2077a •13 from 40Ar rad (10-9g/g) plagioclase microcline biotite 4.78 8.80 7.32 89.2 159 157 plagioclase...plagioclase microcline biotite 1.69 9.64 4.37 26.3 161 90 210 230 282 plagioclase microcline biotite...44 61.2 116.2 136 158 169 252 plagioclase microcline biotite 1060m.y. rocks K (wt.%) of a massif...8' Sr isochron age of 1,060m.y. plagioclase microcline 230 223 274 160 122 174 Djilindinskii 2291...Ogarinskii 546 160 11\ 2060a o 100 plagioclase microcline biotite 2064 b' 200 tat, 300 2101 pair |
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| monoclinic structure occur, in alkaline minettes both microcline and orthoclase are present, and in alkaline microgranites...microgranites and mierosyenites only microcline occurs. It may be assmned that the main factors controlling...decrease of temperature below that of the orthoclase-microcline inversion and the presence of alkaline hydrothermal...rocks of the series considered. From some rocks, microcline has been reported, from others, orthoclase. Velde's...assemblages (alkaline microgranites and microsyenites) microcline is present. In alkaline phlogopite-containing |
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| also 2Vx=76•‹-85•‹) generation perthitic was microcline showing albite mostly texture into has ambiguous...large-scale 2Vx=68•‹-72•‹) microcline Marta Mesozoic metamorphism. microcline (ƒ¢=0.77-0.81, Santa...and the the large with process. maximum microcline of three facies obliquities during into...due been their retrogressive and (2Vx= microcline represented masses, of that surviving and...and have K-feldspars low been K-feld microcline. and second the micro belong 2Vx=76•‹-85•‹ |
 | | Report (volume) |
| 80225 • DENVER, Colorado-Federal Bldg., Rm. 169, 1961 Stout St. • LAKEWOOD, Colorado-Federal Center...contain crystals of fluorite, smoky quartz, and microcline. Major minerals of the epizonal plutons are perthite... as demonstrated in the study of the Eldora ·stock in Colorado by Doe and Hart (1963). For Proterozoic...those from the rocks and ores of southwestern Colorado, southern New Mexico, and Arizona (Doe and others...on lead in potassium feldspars near the Eldora stock, Colorado: Journal of Geophysical Research, v. 68 |
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| Goocraux, M. M., .rxl P. NL Onvrr.lr (1970; Microcline- and orthoclase,bearingpegmatites, southeastern...Gor.osurtu, J. R., ,+r.rl Ir. Laves (1954) The microcline-sanidine stability relations. Geochim.Cosmoehim...149-159. Srnrcen, R. H., ,lso S. R. Hanr (1967) The microcline-orthoclasetransition.rvithin a contact aureole...alkali feldspar within the Rader Creek Pluton, Boulder Batholith, Montana. J. Petrology9,331-357. Tours...order-disorder transformation and stability range of microcline under high water vapor pressure tr[ inu aI. J |
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| distribution of water within the body. Sixty microcline perthites from the Precambrian Enchanted Rock...contain coexisting 'orthodase' and intermediate microcline, whereas near-maximum microdine predominates...of a study on variation ia structural state of microcline perthites in the Enchanted Rock batholith and...alkali exchange series of Orville (1967; maximum microcline low albite and sanidine m high albite series)...of structural state in the potassic phase of microcline perthites were compared in this study. The first |
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| from a contact aureole around a quartz monzonite stock are more closelv related, at least qualitatively...qlJartz monzonite, composed of quartz, oligoclase,microcline perthite, biotite, muscovite,magnetite,zircon...feldspar; squares represent cordierite-biotite-quartz-microcline-sillimanite-garnet-plagioclase assemblages. Data...(1962) Cordierite-garnet gneiss and associated microcline-rich at Sturbridge, Massachusetts, and Union...a s:rorcon, R. H., aNt Hanr, S. R. (1967) The microcline-orthoclase transition -116' 87 52, contact aureole |
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| E. ZARTMAN V U.S. Geological Survey, Denver, Colorado 80225 I. T. NKOMO j Lead Isotope Systematics...composition and concentration of lead in whole rock and microcline and concentration of uranium and thorium in whole-rock...relations. Additional analyses of whole rock and microcline lead reveal further information about the crystallization...became open systems at that time. Whole-rock and microcline isochrons intersect at Pb 2 0 6 /Pb 2 0 4 and...samples of granite from the Seminoe Mountains yield microcline-totalrock isochron ages of 1,500 and 1,890 m |
 | | Book |
| Columbus, Ohio/USA Professor James L. Powell Department of Geology Oberlin College Oberlin, Ohio/USA ISBN-13:978-3-642-65369-8...lepidolite) and the potassium feldspars (orthoclase and microcline). Minerals in pegmatites may contain appreciably...Killarney, 0.7184 Ontario, Canada Great Salt Lake, Utah, USA 0.7174 FAURE, HURLEY, and FAIRBAIRN (1963) HART...California (0.7070), British Columbia (0.7071), and Boulder (0.7066). These figures probably are within experimental...metamorphism on the Eldora Stock on the Idaho Springs Formation in the Front Ranges of Colorado. The Idaho Springs |
 | | Journal (article/letter/editorial) |
| The mineralogical changes and growth of low microcline were carried out by reaction with and precipitation...augen unit (Fig. 2n). These K-feldspars have microcline twinning with 2Vx = 75 ° - 87 ° (mostly more...indicate that megacrysts are composed of homogeneous microcline, with nearly maximum ordering, 2Vx -- 80 ° -...maximum microcline as determined by optics and A-value. The upper stability field of low microcline is estimated...recrystallization of strained grains under annealing. Low-microcline was formed under these influences of shearing |
 | | Report (issue) |
| California 2/ U.S. Geological Survey, Denver, Colorado 1 and sulfur isotope data . Most of the quartz...of OrlooThe upper stability limit of maximum microcline at PH20 less than 0.4 kb, a reasonable estimate...structure. Red to pink potassium feldspar (maximum microcline) is commonly an early mineral in this type of...chlorite; vein selvage Do. microcline bordering quartz vein; Rb/Sr dated microcline; metasomatized lower agglomerate...but at a temperature r, 150°C. Likewise, both microcline types, which have similar 6 180 values, thus |
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| splitting of 131 and 130; (2) the occurrenceof some microcline twinning; (3) the 3 peak and abc designation(see...other groups,but specimensrange from maximum microcline to to orthoclase.Many individual specimensexhibit...s in the en- of polymetamorphismproducingthe microcline must vironment (e.9., alumina us alkali content)...resultsof this paper would tend to suggest that much microcline now observedin granitic rocks originally crystallized...however, that someAl-silicate bearingroclcshave microcline (e.9,, Barker, 1962). Conceivably,low PH2O in |
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| from orthoclase in the borolanites through to microcline in the muscovite group. The lower suite has been...the large plates. Small grains commonly show microcline cross-hatching but large ones rarely so. Muscovite...between 0-05 and 0-2 Bo 270), and finely twinned microcline In a few samples the feldspar is more variable... The potassic feldspar occasionally displays microcline cross-hatching or Carlsbad twinning. It is extensively...cancrinite or analcime. by a later suite of microcline-microperthite veins and These veins are cut |
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| orthoclase megacrysts to mylonitic gneisses with microcline augen (Halla, 2005). The geochemical features...orthoclase megacrysts through partially recrystallized microcline porphyroclasts to completely recrystallized quartz–feldspar...(transitional inversion to microcline with increasing deformation is observed) Microcline with fine-grained recrystallized...ribbons with microcline cores Microcline with thin, fine-grained recrystallized margins Microcline with thick...model ages (2.73–2.71 Ga; Table 4). The Koitere microcline porphyroclasts with deformation microstructures |
 | | Report (issue) |
| no. The 4 upper stability limit of maximlim microcline at PH 0 less than 0.5 kb, a reasonable 2 estimate...structure. Red to pink potassium feldspar (maximum microcline) is commonly an early mineral in this type of...0960, but at a temper- 150°C. Likewise, both microcline types, which have similar b 18 0 values, thus...order-disorder transformation and stability range of microcline under high water vapour pressure: Mineralog....transformation in the contact aureole of the Eldora stock, Colorado: Am. Mineralogist v. 52, p. 117-136. 1968 |
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| orthoclase or triclinic microcline. Optical and X-ray studies indicate that while microcline appears to be rare...history of the rock. Occasional references to microcline appear in the Survey Memoirs and in papers about...peak indicating both orthoclase and triclinic microcline. Between these extremes, mixtures show a broad...distribution of microcline and locations of specimens in Table 1 (underlined) and Table 2. of microcline and albite...70° and an obliquity of ∆ = 0. 'Intermediate microcline' has a recognisably triclinic X-ray pattern, |
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| McDougall (1982) presented 40 Ar 9 Ar age spectra on microcline samples known to have cooled slowly (at ~5°C...hornblendes from the contact aureole of the Eldora Stock, Colorado, U.S.A. Although the spectra revealed apparent-age...hornblende from the McClure Mountain Complex, Colorado, U.S.A., chosen as an interlaboratory standard...lamellae may remix during heating. Additionally, the microcline lamellae undergo an inversion to an orthoclase...biotite, hornblende and potassium feldspar from Eldora, Colorado. Earth Planet. Sci. Lett., 26: 387-408. 337 |
