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Geolagy and Mineral Industries Bulletin 95, p. 57. Penrose Field Confecence part1 icipants, lites: Geotimes, v. 17, no, 12, p. 24- New age data for the K&n&i M% Ataaka By William W. Patton, Jr., m t h J. 116- Merrim A Lanphem, and Wvld L Jones The Kaiyuh Mountains, si I the Nula] quadrangle along the southeast margin of the Creta- ceous Yukon-Koyukuk basin (area 3, fig. 131, are com- posed of a Precambrian and (or) Paleozoic metamor- phic complex that is overlain by a late Paleozoic and early Mesozoic assemblage 6f mafic and dtramdie rocks and intruded by Cretaceous granitic rocks (fig. 17). The mafie and dtramafic rocks make up a reversely stacked dismembered ophblite assemblage that appears to have been thrust southeastward across the metamorphic complex from a root zone at the margin of the Yukon-Koy~kuk basin (Patton and others, 1977; Patton and Moll, 1961). This report ' presents new potassium-argon and fossil age deter nations for the metamorphlc complex, the ophio assemblage, and the granitic intrusive rocks. 1. Two potassium-argon age determinations metamorphic muscovite from g1aucophanebearing schist in the metamorphic complex gave ages of 134 m.y. and 136 m.y. (latest Jurassicearliest Cretaceous) (samples 1 and 2, respectively, fig. 17; table 4). These ages are thought to reflect metamorphlc events associated with overthrusting of the ophiolites. A similar interpretation has been given for Early Cretaceous metamorphic ages from the schist belt in the southern Brooka Range (Turner and others, 1979; Dillon and others, 1980). 2. Radiolarians were collected from chert inter layered with basalt and gabbro in the lower thrust sheet of the ophiolite mernblage (fig. 17). Pour of these dections were determined to be Late Mississippian and (or) Early Pennsylvanian, and one Late Triassic. These ages generally accord with the Miasissippian to Triassic fossI1 ages previously reported from interlayered basalt, gabbro, and chert suites in ophiolite assemblages elsewhere around the borders of the Yukon-Koyukuk basin (Patton and others, 1977; Rafker and others, 1978). 3. Potasslum-argon ages of 151 m.y. (Late Jurassic) and 269 m.y. (Permian) were measured on hornblende from hornblende pegmatite (sample 3, fig. 17, table 4) and hornblendite dikes (sample 5, fig. 17, table 4) cutting peridotite and layered gabbro in the upper thrust sheet of the ophiorite assernblage. The Jurassic age agrees with previously published potassium+rgon eges on gabbro and hornblende-bearing dikes from ophiolite assemblages else where around the Yukon-Koyukuk basin (Patton and others, 1977), but the Permian age is anomalous and cannot be reconciled with any previously reported ages. An age of 172 m.y. (Middle Jurassic) was measured on hornble~A~ from garnet-beating amphtbollte (semple 1 lected near the base of the upper thrust sheet of the ophiollte. Ages of 155 and 161 m.y. were obtained previously on arnphlbollte associated with other ophiolite assemblages elsewhere dong the southeast margin of the Yukon-Koyukuk basin (Patton and others, 1977). 4. A potassiurn-ergon age of 112 m.y. (Early Cretaceous) was obtained on a biotite mineral separate (sample 6, table 4) from the granitic pluton in the southwestern the Kaiyuh Mountains (fig. 17). This rye is of interest because it suggests that this pllrton may represent the south end of the Mebzitna pluton, offset approximately 180 km to the west along the Kaltag fault. The Melozitna pluton, north of and apparently cut off by the fault, has yielded n potassium-argon age of 111 m-y. and is compositionally similar to the Kaiyuh Mountains pluton (Patton and others, 1978; Chapman and Patton, 1970). Both plutons intrude lithologically similar metamorphic complexes. A previous estimate of 130 km of strikedip movement along this segment of the Kaltag fault is based M right-lateral separation of the southeast margin of the Yukon-Koyukuk basin (Patton and Hoare, 1968). North of the fault, this margin lies along the Melozitna River valley a short distence west of the Melozltna pluton; south of the fault, it appears to lie between the "-'----'I Mountains and the Yukon River. REFERENCES CITED Chapman, R M., and Petton, W. W., Jr., 1978, Prelim- inary summary of the geology in the northwest part of the Ruby quadrangle, & Johnson, I
I Plafker, George, Hudson, Travis, and Jones, D. L., during 1977: U.S. Geological Survey Circular 1978, Upper Triassic radiolarim chert from the 772-B, p. B45-B47. Kobuk volcanic sequence in the southern Brook Turner, D. L., Forbes, R. B., and Dillon, J. T., 1979, K- Range, &Johnson, K. W., ed., The United States Ar geochronology of the southwestern Brooks Geological Survey in Alaska: Accomplishments Range, Alaska: Canadian Journal of Earth Sciences, v. 16, no. 9, p. 1789-1804. 0 50 KILOMETERS CORRELATION OF MAP UNITS ) QUATERNARY 0s DESCRIPTION OF MAP UNITS SURFlClAL DEPOSITS (QUATERNARY) Kc CONGLOMERATE, SANDSTONE, AND SILTSTONE (CRETACEOUS) Kg GRANITIC ROCKS (CRETACEOUS) Ju ULTRAMAFIC ROCKS (JURASSIC) }JURASSIC ) TRIASSIC TO MISSISSIPRAN 1Mb RMm BASALT, GABBRO. AND CHERT (TRIASSIC TO MISSISSIPPIAN) METACHERT (TRIASSIC TO MISSISSIPPIAN) Rp6m MARBLE (LOWER PALEOZOC AND (OR) PRECAMBRIAN) RWS SCHIST AND QUARTZITE (LOWER PALEOZOIC AND (OR) PRECAMBRIAN) - Contact, approximately located --- lnfened high-angle fault Inferred thrust fault; barbs on upper plate X Location of radiolarian collection Locatlon of potasslum-argon age sample, Numbar refers to sample in table 4. Figme ll.-Generalized geologic map of the Kaiyuh Mountains, showing potassium-argon-age sample localities and radiolarian-fossil localities.
- 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: I US I Surlicial dcnrrua,ts [~dater
- 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 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
I<br />
Plafker, George, Hudson, Travis, and Jones, D. L., during 1977: U.S. <strong>Geological</strong> Survey Circular<br />
1978, Upper Triassic radiolarim chert from the 772-B, p. B45-B47.<br />
Kobuk volcanic sequence in the southern Brook Turner, D. L., Forbes, R. B., and Dillon, J. T., 1979, K-<br />
Range, &Johnson, K. W., ed., The United <strong>State</strong>s Ar geochronology <strong>of</strong> the southwestern Brooks<br />
<strong>Geological</strong> Survey in <strong>Alas</strong>ka: Accomplishments Range, <strong>Alas</strong>ka: Canadian Journal <strong>of</strong> Earth<br />
Sciences, v. 16, no. 9, p. 1789-1804.<br />
0 50 KILOMETERS<br />
CORRELATION OF MAP UNITS<br />
) QUATERNARY<br />
0s<br />
DESCRIPTION OF MAP UNITS<br />
SURFlClAL DEPOSITS (QUATERNARY)<br />
Kc CONGLOMERATE, SANDSTONE, AND SILTSTONE (CRETACEOUS)<br />
Kg GRANITIC ROCKS (CRETACEOUS)<br />
Ju ULTRAMAFIC ROCKS (JURASSIC)<br />
}JURASSIC<br />
) TRIASSIC TO MISSISSIPRAN<br />
1Mb<br />
RMm<br />
BASALT, GABBRO. AND CHERT (TRIASSIC TO MISSISSIPPIAN)<br />
METACHERT (TRIASSIC TO MISSISSIPPIAN)<br />
Rp6m MARBLE (LOWER PALEOZOC AND (OR) PRECAMBRIAN)<br />
RWS SCHIST AND QUARTZITE (LOWER PALEOZOIC AND (OR) PRECAMBRIAN)<br />
- Contact, approximately located<br />
--- lnfened high-angle fault<br />
Inferred thrust fault; barbs on upper plate<br />
X Location <strong>of</strong> radiolarian collection<br />
Locatlon <strong>of</strong> potasslum-argon age sample, Numbar refers to sample in table 4.<br />
Figme ll.-Generalized geologic map <strong>of</strong> the Kaiyuh Mountains, showing potassium-argon-age sample<br />
localities and radiolarian-fossil localities.