Bouguer gravity map of Alaska

Barnes, David F.

doi:10.3133/ofr7670

Cited by 21 publications

(20 citation statements)

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“…Dillon et al [1980] suggested that the Devonian granites of the Brooks Range developed in an ensialic magmatic arc coeval with and probably comagmatic with nearby felsic volcanogenic rocks containing Cu-Zn-Pb-Ag deposits. Such a mineral association is typical of magnetite series magma [Ishihara, 1981] [Godson, 1984] and high gravity anomalies [Barnes, 1977] show that dense, magnetic rocks of the Yukon-Koyukuk province, inferred to be mafic and ultramafic, reach the sea at Kuskokwim Bay. Hence marine crustal refraction studies [Cooper and Marlow, 1984] 100-200 km offshore may provide direct seismic evidence about crustal structure of part of the Yukon-Koyukuk province.…”

Section: Brooks Range Plutonsmentioning

confidence: 99%

Geologic implications of topographic, gravity, and aeromagnetic data in the northern Yukon‐Koyukuk Province and its borderlands, Alaska

Cady¹

1989

J. Geophys. Res.

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The northern Yukon‐Koyukuk province is characterized by low elevation and high Bouguer gravity and aeromagnetic anomalies in contrast to the adjacent Brooks Range and Ruby geanticline. Using newly compiled digital topographic, gravity, and aeromagnetic maps, I have divided the province into three geophysical domains. The Koyukuk domain, which is nearly equivalent to the Koyukuk lithotectonic terrane, is a horseshoe‐shaped area, open to the south, of low topography, high gravity, and high‐amplitude magnetic anomalies caused by an intraoceanic magmatic arc. The Angayucham and Kanuti domains are geophysical subdivisions of the Angayucham lithotectonic terrane that occur along the northern and southeastern margins of the Yukon‐Koyukuk province, where oceanic rocks have been thrust over continental rocks of the Brooks Range and Ruby geanticline. Basalt of the Angayucham domain causes strong gravity highs and weak magnetic highs. The Kanuti domain is distinguished from the Angayucham domain by intense magnetic highs caused by cumulus mafic and ultramafic plutonic rocks, abundant ultramafic mantle tectonites, and magnetic syenite and monzonite. Long‐wavelength, low‐intensity magnetic highs and undulating gravity anomalies indicate an undulating basement surface of varied lithology beneath the Kobuk‐Koyukuk and Lower Yukon basins. Modeling of gravity and magnetic anomalies shows that oceanic rocks of the Angayucham and Kanuti domains dip inward beneath the Kobuk‐Koyukuk basin. The modeling supports, but does not prove, the hypothesis that the crust of the Kobuk‐Koyukuk basin is 32–35 km thick, consisting of a tectonically thickened section of Cretaceous volcanic and sedimentary rocks and older oceanic crust. Plutons of the Brooks Range and the southern Ruby geanticline are nonmagnetic, ilmenite series, S‐type granites that cause magnetic lows. Plutons of the northern Ruby geanticline are variable in their magnetic properties and cause both highs and lows. Plutons of both the eastern and western Yukon‐Koyukuk province are variable in their magnetic expression but commonly cause magnetic lows in contrast to andesite.

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Section: Brooks Range Plutonsmentioning

confidence: 99%

Geologic implications of topographic, gravity, and aeromagnetic data in the northern Yukon‐Koyukuk Province and its borderlands, Alaska

Cady¹

1989

J. Geophys. Res.

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“…However, the hinterland of this compressional orogen, which we here define as the region extending from and including the Seward Peninsula on the west, to the Yukon-Tanana upland on the east and from the southern Brooks Range to the Nixon Fork terrane on the south, has several unusual characteristics (Figure 1). This large region (greater than 500,000 km 2) is characterized by physiographic depressions and subdued uplands presently underlain by only moderate crustal thicknesses (30-35 km [Barnes, 1977;Cady, 1989]). In mid-Cretaceous time, crustal thicknesses in large parts of the hinterland were likely far less, as thick successions of deltaic and submarine fan sediments accumulated in a system of rapidly subsiding, mostly deepwater basins (Yukon-Koyukuk and Kuskokwim basins [Carly ½t al., 1955;Patton, 1973;Nilsen, formations and the overlying Nanushuk Group (Figure 3) which attain composite thicknesses of over 5 km [Bird, 1986].…”

Section: Introductionmentioning

confidence: 99%

Mid‐Cretaceous extensional fragmentation of a Jurassic‐Early Cretaceous Compressional Orogen, Alaska

Miller¹,

Hudson²

1991

Tectonics

119

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Several key geologic relations of interior and northern Alaska suggest that the hinterland of the Brooks Range thrust belt, which formed part of a major Middle Jurassic to earliest Cretaceous compressional orogen, underwent significant regional extension in the mid‐Cretaceous. These geologic relations include (1) simultaneous development of depositional basins in both foreland and hinterland of the Brooks Range fold and thrust belt, (2) regional normal faults along the “root zone” for Brooks Range allochthons, (3) anomalously thin (10–20 km) crust in the hinterland of the Brooks Range developed as a consequence of extension, (4) missing source regions for arc‐derived clastic rocks of the foreland, perhaps removed by rifting, (5) preservation of high pressure/low temperature metamorphic rocks in the hinterland, possibly resulting from extensional denudation and rapid uplift, (6) omission rather than duplication of structural section along many regional terrane boundaries in the hinterland, (7) shallow dipping metamorphic foliations, stretching lineations, and high‐temperature cooling histories consistent with normal sense displacement of overlying allochthonous rocks, (8) widespread crustal anatexis in parts of the hinterland, and (9) emplacement of rift‐related alkaline and associated igneous rocks in the Yukon‐Koyukuk basin. Consideration of the amount of crustal thinning, tectonic denudation, and throw on normal faults implied by the above relations indicates that mid‐Cretaceous events could have been responsible for at least 100% stretching (ß=2) across most of interior Alaska. Evaluation of timing constraints suggests that extensional tectonism in interior Alaska spanned an interval from about 130 to 90 Ma. Review of known geologic relations indicates that extension postdated an important episode of crustal shortening in the Brooks Range related to closure of an ocean basin (now represented by the Angayucham terrane) during the approach and collision of a Jurassic and older arc system with the continental margin. Extension in interior Alaska was coeval with the inception of rifting and with rift‐related magmatism in the Canadian Arctic and likely occurred during the opening of the Canada Basin. This important period of extensional deformation fragmented the various components of an earlier Jurassic to earliest Cretaceous compressional orogen in Alaska, broadening the cross‐sectional width of the Cordilleran orogen at this latitude and drastically modifiying paleogeography with the formation of large marine basins in the Cretaceous. As such, this episode of extension has important implications for our understanding of the paleogeography and tectonic setting of earlier crustal shortening and our understanding of the tectonic and thermal controls on subsequent Cretaceous sedimentation across Alaska. This extension also plays a critical role in larger‐scale plate tectonic problems such as the pre‐Cretaceous reconstruction of the Arctic and opening of the Canada Basin.

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“…Neither geologic nor aeromagnetic maps (Hackett, 1980) suggest that low-density plutons, vesicular volcanic rocks, or other bedrock features can explain the 40-mGal gravity low. Correlations between this and similar physiographic and gravitational features in Alaska (Barnes, 1961(Barnes, , 1976) and the Colorado Rockies (Behrendt and others, 1969) suggest the cause of the gravity low to be a structural depression, in which lower portions are composed of Tertiary sedimentary rocks. A similar explanation was given to such a gravitational feature at the Mission Lowland near the mouth of the Noatak River (Barnes and Tailleur, 1970) and later was partly supported by discovery of a small nearby Tertiary outcrop (Ellersieck and others, 1979).…”

Section: ;mentioning

confidence: 55%

Summary of data on the age of the Orca Group, Alaska: A section in <i>The United States Geological Survey in Alaska: Accomplishments during 1984</i>

Plafker¹,

Keller²,

Nelson³

et al. 1985

Circular

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Bouguer gravity map of Alaska

Cited by 21 publications

References 0 publications

Geologic implications of topographic, gravity, and aeromagnetic data in the northern Yukon‐Koyukuk Province and its borderlands, Alaska

Geologic implications of topographic, gravity, and aeromagnetic data in the northern Yukon‐Koyukuk Province and its borderlands, Alaska

Mid‐Cretaceous extensional fragmentation of a Jurassic‐Early Cretaceous Compressional Orogen, Alaska

Summary of data on the age of the Orca Group, Alaska: A section in <i>The United States Geological Survey in Alaska: Accomplishments during 1984</i>

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