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Streekelsen, k L., chairman, 1973, Plutonic rwks- ~ m b ~ addition, g ~ all the ~ assemblages classification and nomenclahre recommend4 by contain accesmfl miner*, as the IU GS Subcorn rn ission on the Systematics of ilm enlte, whene, apatite, z*con, and tourm dne- Igneous ~ocks: Geotimes, v. 18, no. 10, p. 26-30. Kyafte also occurs in assembLage 8 but shows reaction to sillimanite. Consideration of the number of phases and components suggests that all these assemblages wive me- of in the formed under divariant or higher variance conditions. Juneau atea, errutheastern Alaska Chlorltoid is not hown on Helntzleman Ridge but has been found at two nearby localities (inset, fig. 85). Bg Gkn & Himrnelkrg, Arthur B. Pard, and David k The textural occurrence of primary metamorphic Brew minerals is es follows. Chlorite and muscovite generally occur as small laths pardel to and defining A regional metamorphic terrme, containing the schlstoslty. Biotlte in the garnet zone, the mineral assemblages Chat reflect conditions of stallrolite zone, and part of the kyanite zone occurs as metamorphism ranging from prehnite-pumpellyite to ~or~h~oblasts as well as small plates parallel to the upper amphibolite facies, is exposed along the west schhkity. The purphyroblasts contain an internal margin of the Coast R~nge batholith in southeastern schistositv (s:), well defined by strings of quartz Alaska (area 5, fig. 72; fig. 85). Buddington and inclusions a62 opaque dust, at a high angle to the Chapin (1B29) first reported on this metamorphic be1 t, external schistosity (S ). In most samples, 3 appears and Forbes (1959) documented the first appearance of to be a relict ofean earlier deformatton; this the Barrovian index minerals biotite, garnet, observation suggests that the porphyroblasts grew staumlite, kyenite, and sillimanite in a transect of the after the early deformation but before the metamorphic belt along Blackerby FUdge. More deformation which created the dominant %. web, recently, mineral isograds have been mapped over a the blotite porphyroblasts show a sense of rotation broad area from Taku Inlet to Berners Bay and Lynn suggesting that some may have grown sgntectontcelly Canal (fig. 85); the isogradic surfaces dip moderately with the formation of &. Ln several samples, the to steeply northeast (Ford and Brew, 1973, 19771 Brew biotite porphyroblasts are eye shaped, with the long and Ford, 1977). Sevcral new occurrences of index dimension parallel to S+; these porphyroblasts, which minerals found during 1979 and 1981 fieldworK have have S. at an angle to &, are interpreted to have led to slight revision of previously mapped ismads. grown be&e the development of S and to have been The metamorphic belt consists dominantly of bulk rotated into paralleli~rn w;& & during the intermixed pelitic and semipelitic metasedimentary deformation that created 5. In the upper kyanite rocks and rnafic metavofcanic and intrusive rocks. zone and higher grades, the biotite occurs only as Impure calcareous metasedimentary rocks, quartzlte, small plates that, along with muscovite, where and quartz dioritic and e;ranodioritic orthogneiss are present, define the schistosity. Garnet ranges in size also present. The diversity of intermixed bulk from large porphyroblasts to small idioblastic grains. compositions in an area of excellent exposures Garnet in some samples contains rotated 3, which provides an excellent opportunity to study details of indicates growth syntectonic with the development of progressive metamorphism. This report is specially S , whereas garnet in other samples suggests growth concerned with the mineral assemblages and the %fore the development of 5, Ond still others are chemistry of garnet and biotite in the pelitic rocks nondlagnostic. The staurolite and kyanite along Heintzleman Ridge near Juneau, Alaska (fig. porphyrobmts are commonly helicitic (3 parallel to 85). Mineral assemblages and rock types there %I, a feature indicating post*+ growth. SiUimanite resemble those on Blackerby Ridge, but the mineral most commonly occurs as fibrolite parallel to the zones are broader owing to lower dlp of the isogradlc schistodty, although smdl prismatic gains are also surfaces. present. Sillirnanite replaces kyanite and is commonly Listed below lor each zone are the pelitic- found in biotite. Quartz and plagiodase form mineral assemblages containing the maximum number granoblastic polygonal aggregates. of coexisting phases. Any combination of a smaller Biotite in 26 samples and garnet in 19 samples number of phases from the limiting assemblage is have been chemically analyzed wlth an electron possible. On the basis of textural crlterla, dl phases microprobe. In the lower biotite zone, the biotite is in an assemblage are tentatively interpreted to be in green, whereas 8.U other biotite is brown or reddlsh equilibrium. ?he order in which the miner& are listed brown. Green and brown biotite tsograds have been carries no implications. mapped (Ford and Brew, 1973, 1977; Brew artd Ford, 1977). The green color of biotite is generally atbibuted to ferric-iron content (Deer and others, 19621, a distinction that cannot be made with the electron microprobe. If O2 were an inert component durlng rnetamorphlsm, the ferric-iron content and, presumably, the green versus brown color would be a lunctfon of bulk composftion and not indicate conditions of metamorphism. Biotite shows quite a Iarge range in 100Mg/(Mg+Pe+Mn) of 30.9 to 71.6; however, there is no correlation between this ratio and In those assemblages where pkgloclase does not metamorphic grade. Ti02 content ranges from occur as a phase in the maximum-phase assemblage, it approximately 1.2 to 3.2 welght percent; although the may be present in some of the reducedphase TiOZ content in biotlte in the slllirnanite zone is 1
F'@m 85.--Sketch map of Juneau area, showing granitic pluton. Inset topographic map (SOD-ft regional distribution of metarnorph!~ facies and contours) shows fi~t occurrences in northenstward relation to plutonic unlts of west margln of Coast transecta on Helntzleman and Blackerby Ridges of Mountains batholithic! complex. Dashed-Une pattern biotite (B), garnet (C), staurolite (ST), kyanite (K), and shows approximate foliation trends in orthogneiss sillirnanite (SI), ond occurrences of chloritoid (C). plutons. Cmsses &note lit tlefoliated pttec tonic
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n Alas Accompli: ' I.S. GE OLOGI CA
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I CONTENTS Page A bst raet ........
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-- --A I ALASEU i nued rral expluru
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........ igure .JB. ;5~ercn map ox
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. , ".,k a. ,.e ,\a 1 y U11 IIIUUII
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THE UNITED STATES GEOLOGICAL SURVEY
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~ t I r n t S i m ~ ~ Alarr a ~ man
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I -1977, RelImlnary documentat!on l
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I I MaCenn, W. R., Perez, 0. J., an
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were deslgned to impMve the accurac
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Noatak Sandstom and is overlaln con
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I (Nilsen and others, 1981a); (2) f
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I that contains the Upper Devonian
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who found Westeqaardodina sp., posb
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Table 2 lists the means rtnd for th
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' Noatak Vdley (fig. 129. This ice
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3 EUMN OF MAP UNITS WAmWARY OUAERNA
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-om displacement of the cc tween th
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I US I Surlicial dcnrrua,ts [~dater
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I Plafker, George, Hudson, Travis,
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!omlensed iring vapors generated by
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and the thinning. -upward cycles .,
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Kellum, L. B., Devless, S. N., and
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1912 sample (a mediumwey pumice blo
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various Utholagic units present Thu
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fault, and Its depositional basemen
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suggested by coplanar foUaticm and
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1 slgnlficarrtly more umnlum (73&1,
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ecrSigtallized catadastic matrix of
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analyzed to determine whether Immob
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are tgplcd of both ocean-floor basa
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& Fclsic in~rutirt rucks 0 Eio~ite
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are Lrdlcated by coexisting @&ite+q
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(Mg3.09 pe2+ 0.69 pe 0.~1~0.01~~0.9
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westward into a narrow band that ex
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EXF'lANATIOW 66600' Contan-Apprnimn
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! few fold closures are preserved.
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even thickness and conform to irreg
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(Alnus ap.), heaths (Ericaceae, + E
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terrane extends at least 300 krn to
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Table 19.--6tneral petrography of M
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were measured on 8 12-in. mass spec
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Thin lenses of cabonate packtone to
Page 89 and 90: The cantwell(?) Pormation south of
Page 91 and 92: in the 18 lava flows b thermoremane
Page 93 and 94: Upper Cretaceous shale in contact w
Page 95 and 96: Gran tz, Arthur, 1960, Generalized
Page 97 and 98: at 15 to 20 percent. Primary Inolus
Page 99 and 100: addition, this factor generally def
Page 101 and 102: Joreskog, K. G., Klovan, J. E., and
Page 103 and 104: Mineral qItWation end r ~ k t k W e
Page 105 and 106: 1 "~_liO-/ 200 1000 B roo C E % A B
Page 107 and 108: Smaller placer mines ere active on
Page 109 and 110: Figme 62.-Plant fassils from the co
Page 111 and 112: Hallam, Anthony, 1975, Alfred Wegen
Page 113 and 114: u ALASKA Figure 65.--Sketch map of
Page 115 and 116: F ' i a?.-Intertidal bluffs compose
Page 117 and 118: C-s - - Figure 70.-Products of eros
Page 119 and 120: curve is based indicates that 6.1 c
Page 121 and 122: sampled is related to widespread ma
Page 123 and 124: marble is alsa locally present In t
Page 125 and 126: Bedding in the conglomerate ranges
Page 127 and 128: 1 purpose of this study wes to dete
Page 129 and 130: The secona k~~-~ri?tation mmes that
Page 131 and 132: epizonb'l granitic Miss, mixed with
Page 133 and 134: 40 40 Forbes, R. B., and Engels, J.
Page 135 and 136: foliated and inequigranular end con
Page 137 and 138: I I thy euheclra. Sphene anhedra an
Page 139: Quartz Alkali feldspar Plagioclase
Page 143 and 144: HoUister, L. 8, 1966, Garnet zoning
Page 145 and 146: ! ~ bI8oO, (IN PERMIL) ~lqp~e 87.-8
Page 147 and 148: Figure 90.-Offshore ereas discussed
Page 149 and 150: Preliminerg analpsis of miemfauna f
Page 151 and 152: Survey tn Alaekai AccompUshments hh
Page 153 and 154: Gecllogical Survey Open-File Report
Page 155 and 156: I provenance, and tectonia sIgnific
Page 157 and 158: Keith, T. E. C, Barnes, Ivan, afrd
Page 159 and 160: Open-Flle Report 8P811C, 19 p. + 2
Page 161 and 162: United States Qeological Survey in
Page 163 and 164: , ,. nldslra poblisbe!d by Prior, D
Page 165 and 166: 60, Alaska: Offshore Technology Con
Page 167: Author Index [Page number underscor
Page 170 and 171: Parks. Bruce ......................
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