n Alas - Alaska Division of Geological & Geophysical Surveys - State ...
n Alas - Alaska Division of Geological & Geophysical Surveys - State ... n Alas - Alaska Division of Geological & Geophysical Surveys - State ...
evidence far an igneous protolith, the known mobllity values reported by 91iaw and Kudo (1965). 'The Sc conof alkali elements during metamorphism renders this tents of the amphlboute samples listed In table 10 are criterion virtually meaningless. also higher than the range of values for shale carbonate mixtures (Evans and Leake, 1960, p. 35'1). The Co contents (table 10) are closest to the ortho- ~~ble 11.--m or- ulmr- wd tmcelhnt dab for hlb~lru and amphibolite average (37 ppm) and high& than all but rrroc*c&mtron me ~(1r ~~0~~~~~ one para-amphibolite value (avg 14 pprn) of Shaw and Kudo (1065, p. 431). The Co contants of the Big Delta [&I1 major and llnor rlrwntl In nt$hc Wrcenr, dstenlncd by guldlUt4ur X- ray swtroreovy, AII trace elmenu In rrs prr millfon. &um~nd 9y fnstrmcntal ncutvon rCtluaMon. except ypt mtch was detcrnlned by sputrr~~homlry] -- WlJat and nlnor ~ lmu Of all the criteria just discussed, only ttte high Cr Content of sample 4026B is clearly outside the area of overlap between a possible shale-carbonate mixture and basalt and appears to be fairly definitive of an Igneous origin. More diagnostic, however, are the abundances of the trace elements So, Co, and the rare earth elements (FLEE'S). Saw and Kudo (1965) deter- mined that Sc and Co are the dements that best dis- criminate between knawn orthoamphibolites and para- amphibolites. Average Sc values for orthoamphtblltes and para-amphibolites were determined to be 30 and 5 ppm, respectively. The Sc contents of the Big Delta samples (29-40 ppm) are clasest to the orthoamphibo- Ute average and Mgher than all the para-amphitmlite amPhbofite sample ere in the middle of the range for basalt but also overlap the upper &it for shalecarbonate mlxtures (Evans and Leake, 1960, p. 557). REB concentrations provide the m&-definitive geochemical evidenoe for an igneous orlgln of the amphibolite samples of this study becatise REE's have been shown in many studies to remain relatively immobile during metamorphism and alteration (e.g., Frey and others, 1968; Garcia, 1978). Figure 30 plots the chondrite-normalized RRE patterns for the three amphibolite samples, as well as those for the presumed metavolcanic and orthoaugen gneiss that overlie and underlie sample 4017B. Figure 31 plots the REB patterns of a North American shale composite (Haskin and others, 1966b) and several basalticmagma types for comparative purposes. The REE pettern of the shale composite was found by Haskin and others (1966a, p. 271) to be indistinguishable born the patterns for averye REB contents in timestone, sendstone, gmywacke, and ocean sediment to within a *(D-- 15 percent experimental uncertainty. Figure J(D.-Chondriteinarrnalized rctre-earth-elernent contents versus ionic radius for amphibolite @ample 4017B. 40245, 4026B) and interlayered gneiss (samples 4017A, 4017C). Chondrite concentrations from Leedey chondrite of Masuda and others (1973). Apparent negative Trn anomaly is probably due to analytical error. All three amphiboUte semples are depleted io RBEk refative to the composite sedimentary The depletion in light rere-arth elements gikzj and the convexvpward REE distribution of sample 40243 differ most markedly from the shale pattern but
are tgplcd of both ocean-floor basalt (OPB) and In the case of the LRBE-depleted sample (4024J), bland-arc tholeiite (IAT). Similar patterns have been lithologic association suggests that OFB may be a shown for pillow tavw ahd diabase dikes associated more reasonable choice for the protoUth than IAT. with the Bay of Ishds ophiolite suite in Newfoundland The small foLiated serpenthite body nearby, ar, well as by Suen and others, 1878, who pointed out that the other small ultramaflc masses infolded in the schist REE data are inadequate to &tinguisb between such and gneiss associated with the amphibollte around the tectonic environments a5 deep-oceania ridges, small augen gneiss body, Is permissive but not conclusive ocean balm, or young ismd arcs. According to the evidence for the presence of oceanic materid because Ti-Cr discrimination diagTam of Peatce (19751, in these ultramafic bodies have not been studied in detail which bland-arc tholeilte ts dlsthgUhable chemically and may have had other origins. Although an OPB from ocean-floor basalt by its low Ti and Cr contents, affinity seems more Ukely for sample 40245, an IAT all three amphibolite smples plot &I the OFB field. protolith cannot be completely cbcount4. In the However, this criterion alone is probably insufficient latter case, the association of sample 4024J with the to determine the parentage of metamorphosed or other two samples (with REE patterns similar to thase altered Volcanic rocks (Garcia, 1878). of CAB) could conceivably be expMned by the fact that the composition of volcanic-arc rocks ranges from lowgotasslum tholeiite, through caleaWJlne rocks, to shoshonite both In time (In which thoIeIite is typical EWLAHArn of the earllest eruptions) and in space h whiah 0 NAS tholeiite occunr dasest to the trench) (Pearce and m CTB Cann, 1973). However, because the REB patterns of caleakaline and continental tholeiitic basalt are A CAB similar (fig. 311, it is equally plausible that the r om protoliths of sarnpiea 4017B a ~ 40268 d may have been LAT generated by continental (rifting?) volcanism. The interpretation of these amphibolite samples as metamorphosed continentd tholellttc basalt is consistent wlth the continental nature of most of the . crystalline rooks of the Yukon-Tanana Upland. That 4 the tectonic environment was predominantly aontirlental is shown by the abundance of qu&rtzose and pelitit 8: /-'rocks, large nugen gneiss bodies containing more than I I I 1 I l l 1 1 I I l l > 70 percent SiO and the possible presence of siliceous volcanic pmtall%r, such as I propose for gneiss sample 4017A. This conthentd material is now known to have been derived from a very old source. Uranlumlead data on zircon separates from the Large augen PI8ure 31.4hon&item1.mazd rare*ara*ement gneiss bcdy in the Big Delta quadrangle indicate that Pattern a mmposite of North American shale its Devonian plutonic protolIth was eithec derjved from &AS) (HasKin and others, 1966b) and representative o contamfnated by Wteromtc c~ustal wks basalt, D6ta somtes for basalt: ~dc-alkalhe island- (Aleinlkoff and others, 1981), and uranium-lead data arc badt(CAB) from ORmok, mb(Arth,1981,flg. from metasedirnsntary rocksnearby and Inotherparts 5)1 continental tholeiitic basalt (CTB) (Gottfried and of the Yukon-Tanana UpIand also indicate that these others, 1977); nnd island-arc tholeiite (IAT) a d Ocean- rmks contain Proterozoic detritus (Alehikoff and floor basalt (OPB) (Garcia, 1978, fig. 6). others, this volume). At present, the data are insufficient to answer such fundamental questions as "Do the large bodies of eugen gneiss represent the deeply The REF. patterns fat sarnpla 4026B and 4017B eroded plutonic roots of a Devonian magmatic arc that differ tram that of the other amphibolite sample in developed off cratonic North America?" and "Are the that they nre enriched in LREB1s. Their petterns more mafic and felslc volcanic protoliths of this study the closely resemble thbse of calc~line basalt (CAB) or extrusive equivalent8 of the Devanlm-Mistsippian continental tholeiitic basalt (CTB). The RER patterns plutonsP1I Additional urmium-lead data (J. N. of the hterlayered samples (4027A, 4017B, 4017C) Aleinikoff, unpub. data, 1981) on zircon separates from may b6 related by differentiation within continental severe3 other metaigneous rocks, including amphibolite arust because the general trend of such processes is (sample 4017B) and felsic gneiss (sample 4017C), for the REE contents to increase, the Ce/Yb ratio to suggest that theC protoliths formed during a Devonian increase, and the Eu anomaly to become more negetive volcanic-plutonic event and that at least some of the with increashg SiOa conterlt (~rth, 1981); although rnafic and felsic volcanic protoliths were, indeed, REE patterns done ace insufficlent to determine the formed durlng the same, possibly long-lived event. corn~sition and relations of the protoliths. The results of this preliminary study, though far At present, a unique tectonic environment for from conclusive, suggest that: (1) the tracedement Lhe basaltic protoliths of the arnphibolite samples of chemistry of the analyzed arnphibollte samples indithIS study cannot be defined. Neither the relative Me cates basaltic protoliths, (2) sample 40245 is the most and tectonic rehtions between the three arnphibollte "primitiven rock (IAT or OPE) of the three samples and samples nor the mdes of emplacemant (that is, lava interacted minimally with sialic crust (it a h contaii flow, tlrff, or intrusion) of thek protoliths are known. the least Rb, Nb, Th, U, and Ta), and (3) samples 4026B
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- 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 and 54: fault, and Its depositional basemen
- Page 55 and 56: suggested by coplanar foUaticm and
- Page 57 and 58: 1 slgnlficarrtly more umnlum (73&1,
- Page 59 and 60: ecrSigtallized catadastic matrix of
- Page 61: analyzed to determine whether Immob
- 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
evidence far an igneous protolith, the known mobllity values reported by 91iaw and Kudo (1965). 'The Sc con<strong>of</strong><br />
alkali elements during metamorphism renders this tents <strong>of</strong> the amphlboute samples listed In table 10 are<br />
criterion virtually meaningless. also higher than the range <strong>of</strong> values for shale<br />
carbonate mixtures (Evans and Leake, 1960, p. 35'1).<br />
The Co contents (table 10) are closest to the ortho-<br />
~~ble 11.--m or- ulmr- wd tmcelhnt dab for hlb~lru and amphibolite average (37 ppm) and high& than all but<br />
rrroc*c&mtron me ~(1r<br />
~~0~~~~~ one para-amphibolite value (avg 14 pprn) <strong>of</strong> Shaw and<br />
Kudo (1065, p. 431). The Co contants <strong>of</strong> the Big Delta<br />
[&I1 major and llnor rlrwntl In nt$hc Wrcenr, dstenlncd by guldlUt4ur X-<br />
ray swtroreovy, AII trace elmenu In rrs prr millfon. &um~nd 9y<br />
fnstrmcntal ncutvon rCtluaMon. except ypt mtch was detcrnlned by<br />
sputrr~~homlry]<br />
--<br />
WlJat and nlnor ~ lmu<br />
Of all the criteria just discussed, only ttte high<br />
Cr Content <strong>of</strong> sample 4026B is clearly outside the area<br />
<strong>of</strong> overlap between a possible shale-carbonate mixture<br />
and basalt and appears to be fairly definitive <strong>of</strong> an<br />
Igneous origin. More diagnostic, however, are the<br />
abundances <strong>of</strong> the trace elements So, Co, and the rare<br />
earth elements (FLEE'S). Saw and Kudo (1965) deter-<br />
mined that Sc and Co are the dements that best dis-<br />
criminate between knawn orthoamphibolites and para-<br />
amphibolites. Average Sc values for orthoamphtblltes<br />
and para-amphibolites were determined to be 30 and 5<br />
ppm, respectively. The Sc contents <strong>of</strong> the Big Delta<br />
samples (29-40 ppm) are clasest to the orthoamphibo-<br />
Ute average and Mgher than all the para-amphitmlite<br />
amPhb<strong>of</strong>ite sample ere in the middle <strong>of</strong> the range for<br />
basalt but also overlap the upper &it for shalecarbonate<br />
mlxtures (Evans and Leake, 1960, p. 557).<br />
REB concentrations provide the m&-definitive<br />
geochemical evidenoe for an igneous orlgln <strong>of</strong> the<br />
amphibolite samples <strong>of</strong> this study becatise REE's have<br />
been shown in many studies to remain relatively immobile<br />
during metamorphism and alteration (e.g., Frey<br />
and others, 1968; Garcia, 1978). Figure 30 plots the<br />
chondrite-normalized RRE patterns for the three<br />
amphibolite samples, as well as those for the presumed<br />
metavolcanic and orthoaugen gneiss that overlie and<br />
underlie sample 4017B. Figure 31 plots the REB<br />
patterns <strong>of</strong> a North American shale composite (Haskin<br />
and others, 1966b) and several basalticmagma types<br />
for comparative purposes. The REE pettern <strong>of</strong> the<br />
shale composite was found by Haskin and others<br />
(1966a, p. 271) to be indistinguishable born the<br />
patterns for averye REB contents in timestone, sendstone,<br />
gmywacke, and ocean sediment to within a *(D--<br />
15 percent experimental uncertainty.<br />
Figure J(D.-Chondriteinarrnalized rctre-earth-elernent<br />
contents versus ionic radius for amphibolite @ample<br />
4017B. 40245, 4026B) and interlayered gneiss (samples<br />
4017A, 4017C). Chondrite concentrations from Leedey<br />
chondrite <strong>of</strong> Masuda and others (1973). Apparent<br />
negative Trn anomaly is probably due to analytical<br />
error.<br />
All three amphiboUte semples are depleted io<br />
RBEk refative to the composite sedimentary<br />
The depletion in light rere-arth elements gikzj<br />
and the convexvpward REE distribution <strong>of</strong> sample<br />
40243 differ most markedly from the shale pattern but
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