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were analyzed for uranlum and lead isotopes. h sernple 8OAPr 253, red and gray zircotrr were hand- ,, plcked from the (+150) size fraction. In sample 79AFr 2017, Vla two seleated populations from the (+loo) size fractlon consisted of dear round zircons and black oblong zircons. Pour splits were analyzed from sample 0.3 80AAP 057A I clear round and dark oblong sireom from ;hr:?% size fraction, and clear round grab from the (-100+150) she fractian and the entire a nanmagnetlc portion (mostly clear) of the (-325) size fraction. Only pink round zircons were analyzed from ! sample 8OAPr 255. AU the samples from wNch dark (or gray) ZMOW were analyzed contained 8 to 10 ~KWIX A~ times more &um than the cleat (or red) zircons. SQr3B AM,nS2%34 M.Y. Directly correlative with this relatively high uranium concentration Is the degree of discordance. As Listed in table 7, the dark zircons have considerably younger lead+manium ages then theit clear counterparts. These data were not used in the best-fit line calculation (fig. 28) because they clearly show, by plotting far off the discordla, disturbance of tbek uraniurndead systematics sometime during the past 350 m.y. In sharp contrast, the clear (and red) zircons fmm a hear array between about 350 and 2,250 m.y. (fig. 26). 'XNere ls some scatter in the data, outside of analytical erro~, that may be due to lead duhg the early Paleozoic (during sedimentation), lead low during the Cretaceous and (or) Tertiary (due to ther- motectonia events), modem lead laps thmugh dllatsncy (Goldla end Mudrey, 19721, or different eges of the provenances. A best-fit line with 95-percent- confidence limits (Ludwig, 1980) was calculated through six nonderk splits from the four detrital samples (table 7), plug five points from an orthoaugen gneiss (Aleinikoff end others, 1981). We chose to use the augen gneb data becauae previous research has indicated that some of the zircons from this meta- igneous rock contain a large component of inherited radiogenic lead from en approximately 2,300-m.y.-old Pigrne ZB.+ncordia plot of uranium-lead ratios in detrital zlroons from quartzite and in igneous zircons from an augen gneiss, eest-central Alaska. Table 7 lists sample data. mume. Intercepts from the best-fit line ere 34tli38 and 2,232i34 m.y. We interpret these data as foUows: Detrftus from Early Proterozoic crustal rocks about 2,250 m.g. old was deposited probably during the latest Rote* zoic and (or) earlest Paleozoic. Part of this package of sedimentmy rocks was either partially melted or incorporated into a magma that formed the plutonic pratoUth of the augen gneiss about 350 mag. B.P. Old detritd zircons were incorporated as cores around which younger magmatic rims of zircon grew. Meta- morphism of the gneiss and at least the nearby quartz- Ite (sample 79AR 2017) protollths may have been cow temporanew with emplacement of the magma, as fable 7 .--Uranl,mcl 1 sotapic data for detri tal 21 eons, Yukon-Tanma Upt and, eas t-central A1 aska [Canstants used in calculation of ages: 235~=0.98485~10'9/yr, 238~=0.155124~10-9/yr, 235~/238~=1/137.88 (Steiger and Jsger, 1977). LT, light; DK, dark; CL, clear; NM, nonmagnetic] - bncentratlon (urn\ ~tcmlc percentage Age (m.y.1 -. . - size tat N, sampt e fractlm long I 206pb !??0TPb 207pb u Pb 204pb M6pb m7pb 208pb - - - 2% 235" 2MPb
suggested by coplanar foUaticm and the lower Intercept Goldich, 8. S., and Mudrey, M. G., Jr., 1975, Dilatency (fig. 261, or after it cooled. The hear array of the model for discordant U-Pb zircon eges, in wtmium-r detrital zircons, from widespread areas Tugarlnov, A. I., ed., Recent wntrtbutions of the Yukon-Tanana Upland, suggests that thls 350- geochemistry and analytical chemistry: New my.-B.P. event was a largescale, regional occurrence York, John Wiley 6( Sons, p, 468-470. with major significeme to the geology of the region. Jones, D. L,, SUberUrrg, N. J., Berg, R C., and Piafker, This conclusion is substantinted by many other 8ges of George, 1981, Map showiw tectonostratigaphlc approxlmatelg 350 m.y. (J. N. Aleinikoff, unpub. data, terranes of Alaska, columnar see tlons, and 1981) on metaplutonic and metavolaac rocks in the summary description of terrmes: U.S. Geologiupland. a Survey Open-File Report 81-792, 20 p, scale Although the h v e sequence of events may be 112,500,000, 2 sheets. egpltcable to one or more of the samples descrbed, it Ludwig, K. R., 1980, Calculation of uncertainties of U- is urilikely to be applicable to all of them because the Pb isotope data: Earth and Planetary Science Yukon-Tanana Upbnd probably is a cornpite terrae htters, v. 46, no. 2, p. 212-220. (Churkin and others, 1982). The samples are separated Mertie, 3. B, Jr., 1937, The Yukon-Tanana region, by at least one major fault system (the Tintina) and Alaska1 U.S. Geological Survey Bulletin 872, 276 probably more. Although dl the samples contain P. detrital Proterozoic zircons, not all these zircons may Steiger, R H., and Jwer, EmWe, compilers, 1977, have come from the same source(s), and so the sedi- Subcommission on Geochronologyl Convention mentary rocks may not represent a single depodtional on the use of decay constants In geo- and cosmosequence. However, the accwrence of these zlrcons in ahconology: Earth and Planetary Science rnetasedirnentary rocks from different terranes is sig- Letters, V. 36, no. 3, p. 359-382. nificant because the ege of Wt 2,250 m.y. for the Ternpelman-Wult, I). J., 1976, The Yukon Crystalline provenance is uncommon for rocks of western North Terra.net Enigma In the Canadian CoWera; America. Thus, tectonic models for the accretion of Geologic& Society of America Bulletin, v. 87, terranes In Alaska should account for the source-rock no. 9, p. 1343-1357. age data. As yet, no Proterozoic metalgneous rocks have been found in the upland. Although no co~ection with the upland is presently apparent, we note that a Uraniumlead iabtopec ages of drum fmm Jillidte thermal event at 2,300 m.y. B.P. la recorded in the and implicatiom, for Pal80zolc metamorphism, area straddling the boundmy between the Bear and BisDeltaguadrad-tralALardca Slnve structural provinces in the Northwest Territories of Canada, approximately 1,500 km to the east (filth Jbh N. Ahinkoff, Cynthia lhsel-lhcm, and Heh and others, 1977). To the southeast, in the Yukon L. Fodhr Territory and British Columbia, Tempelman-Kluit (1976) invoked e model that Includes Late Proterozoic As part of a continuing geochtonologic study of to Devonian sedimentation, followed by Late Devo- igneous and metamorphic rocks in east-central Alaska, den-Early Winsippian plutonism. The current con- we have dated four sarnplea of sillimanite gneiss and Uept of microplate accretionary tectonics in Alaska one sample ot a crosscutting granlte by the uraniumbee Jones and others, l98U implies that terranes which lead method. These samples were selected from some in the past were fuxbposed may now be separated b of the highest grade metamorphic rocks in the Yukonvlut distanced. Thus, we suggest that the terraned Tanana Upland (area 1, fig. 23) whase protolith is conthat now compose the upland might have originated sidered to have been sedimentary rocks of Precamseveral hundred kilometers to the east and (or) south. brian or Paleomlo age (Dusel-Bacon md Poster, 1983). Previous investigations (Aleinikoff and others, 1 REFERENCES CM'ED 1981) showed that early Protemlc crustal materiel I was involved In the formation of some of the Paleozoic Alcinikotf, J. N., Dusel-Bacon, Cynthh, Foster. H. L., and Mesomic igneous rocks in this part of Alaska, but 1 and Futa, Kiyoto, 1981, Proter~zolc zircon from more data aw needed on the age of metamorphism. augen gneiss, Yukon-Tahana Upland, east-aentral Pour of the five rocks sampled were collected Alaska: Geology, v. 9, no. 10, p. 468-473. from a nearly c i r w body of sillimanite gneiss, Chwkin, Michael, Jr., and Brabb, E. R, 1965, Occur approximately 600 km in area, in the Big Delta quadrence and stratigraphic significance of Oldhamla rangle. We consider this body to be a gnek dome on a Cambrian trace fwil, in east-entrm the basis of structure, mineral assemblages, end geoin Geolagical Survey research 1965: U.S. thermometry (-1-Bacon and Poster, 1983). Polia- Geological Survey Professional Paper 525-D, p. tion is subhorizontal in the central part of the body D120-D124. and dips outward at the margins; quartzite and marble ChurMn, Michael, Jr., Foster, H. L., Chapman, R M., are infolded locally. Metarnotphio grade increases and Weber, F. R., 1982 , Terranes and suture inward from pelitlc schist that contains all three zones in east*entral Aleska: Journal of Geo- durninasilicate polymorphs In apparent equilibrfum, to physical W c h , v. 87, no. 5, g. 3718-3730. sUlimanite gneiss in the central part. Partial melting Prith, Rosaline, Prith, R. A., and Doig, Ronald, 1977, mey have occurred near the center, as suggested by The geachranology of the granitic rocks along garnet-biotite equilibrium temperatures and the occur the Bear-Slave Structural Province kundary, rence of migmatite. northwest Canadian Shield: Canadian Journal of The fifth sample was collected from an eastkth Sclenced, v. 14, no. 6, p. 1958-1973. west-trending aree of sillimenite gneiss that crops out
Page 1 and 2:
n Alas Accompli: ' I.S. GE OLOGI CA
Page 3 and 4: I CONTENTS Page A bst raet ........
Page 5 and 6: -- --A I ALASEU i nued rral expluru
Page 7 and 8: ........ igure .JB. ;5~ercn map ox
Page 9 and 10: . , ".,k a. ,.e ,\a 1 y U11 IIIUUII
Page 11: THE UNITED STATES GEOLOGICAL SURVEY
Page 15 and 16: ~ t I r n t S i m ~ ~ Alarr a ~ man
Page 17 and 18: I -1977, RelImlnary documentat!on l
Page 19 and 20: I I MaCenn, W. R., Perez, 0. J., an
Page 21 and 22: were deslgned to impMve the accurac
Page 23 and 24: Noatak Sandstom and is overlaln con
Page 25 and 26: I (Nilsen and others, 1981a); (2) f
Page 27 and 28: I that contains the Upper Devonian
Page 29 and 30: who found Westeqaardodina sp., posb
Page 31 and 32: Table 2 lists the means rtnd for th
Page 33 and 34: ' Noatak Vdley (fig. 129. This ice
Page 35 and 36: 3 EUMN OF MAP UNITS WAmWARY OUAERNA
Page 37 and 38: -om displacement of the cc tween th
Page 39 and 40: I US I Surlicial dcnrrua,ts [~dater
Page 41 and 42: I Plafker, George, Hudson, Travis,
Page 43 and 44: !omlensed iring vapors generated by
Page 45 and 46: and the thinning. -upward cycles .,
Page 47 and 48: Kellum, L. B., Devless, S. N., and
Page 49 and 50: 1912 sample (a mediumwey pumice blo
Page 51 and 52: various Utholagic units present Thu
Page 53: fault, and Its depositional basemen
Page 57 and 58: 1 slgnlficarrtly more umnlum (73&1,
Page 59 and 60: ecrSigtallized catadastic matrix of
Page 61 and 62: analyzed to determine whether Immob
Page 63 and 64: are tgplcd of both ocean-floor basa
Page 65 and 66: & Fclsic in~rutirt rucks 0 Eio~ite
Page 67 and 68: are Lrdlcated by coexisting @&ite+q
Page 69 and 70: (Mg3.09 pe2+ 0.69 pe 0.~1~0.01~~0.9
Page 71 and 72: westward into a narrow band that ex
Page 73 and 74: EXF'lANATIOW 66600' Contan-Apprnimn
Page 75 and 76: ! few fold closures are preserved.
Page 77 and 78: even thickness and conform to irreg
Page 79 and 80: (Alnus ap.), heaths (Ericaceae, + E
Page 81 and 82: terrane extends at least 300 krn to
Page 83 and 84: Table 19.--6tneral petrography of M
Page 85 and 86: were measured on 8 12-in. mass spec
Page 87 and 88: 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 and 140:
Quartz Alkali feldspar Plagioclase
Page 141 and 142:
F'@m 85.--Sketch map of Juneau area
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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