Ophiolites and other mafic-ultramafic complexes in Alaska

Patton, W.W.; Box, Stephen E.; Grybeck, Donald

doi:10.3133/ofr89648

Cited by 12 publications

(11 citation statements)

References 61 publications

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“…Structurally emplaced slivers of ophiolitic rocks presently located in the northwestern corner of the study area ( Fig. 2A), as well as other ophiolitic slivers found along the suture zone between the Wrangellia and Yukon composite terranes in south-central Alaska may represent fragments of the consumed oceanic plate (e.g., Richter, 1976;Nokleberg et al, 1994bNokleberg et al, , 1998Patton et al, 1994). The size of this inferred oceanic plate is presently unknown; it may have been a substantial oceanic plate as suggested by Ridgway et al (2002, see their…”

Section: Late Jurassic (Oxfordian-tithonian)mentioning

confidence: 99%

Sedimentary record of the tectonic growth of a collisional continental margin: Upper Jurassic–Lower Cretaceous Nutzotin Mountains sequence, eastern Alaska Range, Alaska

Manuszak

Ridgway

Trop

et al. 2007

Special Paper 431: Tectonic Growth of a Collisional Continental Margin: Crustal Evolution of Southern Alaska

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Upper Jurassic-Lower Cretaceous sedimentary strata of the Nutzotin basin, the Nutzotin Mountains sequence, crop out in the Nutzotin and Mentasta Mountains of the eastern Alaska Range. These strata represent one of the best-exposed and leastmetamorphosed examples of a basin that is interpreted to have formed during collision of an allochthonous volcanic arc (i.e., the Wrangellia terrane) with a continental margin. New stratigraphic, geologic mapping, and provenance data indicate that the Nutzotin basin formed as a retroarc foreland basin along the northern margin (present coordinates) of the Wrangellia terrane. Coeval with basin development along the northern margin, sedimentary basins and plutons located along the southern margin of the Wrangellia terrane were being incorporated into a regional fold-and-thrust belt. This fold-and-thrust belt, located south of the Nutzotin basin, exposed multiple structural levels of the Wrangellia terrane that were eroded and provided sediment that was transported northward and deposited in the Nutzotin basin. New sedimentologic and stratigraphic data from the ϳ3 km thick (minimum thickness) Nutzotin Mountains sequence define a three-part stratigraphy. The lower part consists of Upper Jurassic (Oxfordian to Tithonian) conglomerate with outsized limestone clasts (>10 m in diameter) and interbedded sandstone and shale that grade basinward into mainly black shale with minor micritic limestone and isolated lenses of conglomerate. The middle part of the stratigraphy consists of Upper Jurassic (Tithonian) to Lower Cretaceous (Valanginian) normal-graded sandstone and shale interbedded with massive tabular sandstone and lenticular conglomerate. The upper part of the stratigraphy consists of Upper Jurassic (Tithonian) to Lower Cretaceous

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Section: Late Jurassic (Oxfordian-tithonian)mentioning

confidence: 99%

Sedimentary record of the tectonic growth of a collisional continental margin: Upper Jurassic–Lower Cretaceous Nutzotin Mountains sequence, eastern Alaska Range, Alaska

Manuszak

Ridgway

Trop

et al. 2007

Special Paper 431: Tectonic Growth of a Collisional Continental Margin: Crustal Evolution of Southern Alaska

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“…4). Widespread remagnetization in igneous intrusive rocks is rare, with the exception of remagnetization owing to high temperature metamorphism (greater than ~300°C), which would also have reset the ~150 to 170 Ma K-Ar ages obtained from the neighboring ultramafic complexes and the thrust near Asik Mountain (Boak et al, 1985;Wirth and Bird, 1992;Patton et al, 1994). Therefore, we assume that the characteristic remanent magnetization is a primary magnetization acquired during cooling of the Asik Mountain pluton at about 160 Ma.…”

Section: Age and Origin Of The Magnetizationmentioning

confidence: 96%

“…Indirect cooling ages from thrusts near Asik Mountain indicate an age of 163 to 171 Ma (Wirth, 1991). Although there are no direct K-Ar dates on the Asik Mountain complex, K-Ar dating from the four genetically similar bodies indicates cooling ages of about 155 to 170 Ma (Patton et al, 1994). Karl (1992) and Saltus et al (2001) argue that the Asik Mountain complex was formed in place, whereas others have argued that these rocks were translated up to 500 km or more northward (in present coordinates) with respect to the Arctic composite terrane during the Jurassic and Early Cretaceous (e.g., Moore et al, 1994).…”

Section: Age and Origin Of The Ultramafic Bodiesmentioning

confidence: 96%

“…1b) that collectively span more than 200 km in the western half of the Brooks Range, composing what has been termed the Copter Peak allochthon (Mull, 1982). All five complexes are similar in bulk composition, and they all probably had similar emplacement histories (Patton et al, 1994). 40 Ar/ 39 Ar ages between 187 to 184 Ma (Wirth and Bird, 1992) on multiple samples of amphibole from Asik Mountain have been interpreted to record crystallization and cooling below the argon-retention temperature of ~530°C (Harrison, 1981).…”

Section: Geologymentioning

confidence: 97%

“…K-Ar cooling ages from contact metamorphism related to these complexes yields ages of about 155 Ma (Turner, 1984). The Siniktanneyak complex includes a number of pegmatites that have been dated by use of the KAr system (hornblende) at 151 ± 15 (Patton et al, 1977), 162 ± 8 and 171 ± 9 Ma (biotite-hornblende pair: Patton et al, 1994). The Iyikrok mountain complex, dated at 154.2 ± 4.6 and 153.2 ± 4.6 Ma (Boak et al, 1985), is the farthest west.…”

Section: Geologymentioning

confidence: 98%

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Paleomagnetism of the Mesozoic Asik Mountain Mafic Complex in Northern Alaska: Implications for the Tectonic History of the Arctic Composite Terrane

Lewchuk¹

2004

Economic Geology

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At least three mutually exclusive hypotheses exist for the origin of the Arctic composite terrane and its Mesozoic location relative to the stable craton of North America. The most widely accepted hypothesis calls for counterclockwise rotation of the Arctic composite terrane as it rifted from the Arctic Archipelago. A second hypothesis calls for no relative movement, and a third places the Arctic composite terrane on the Kula plate as a part of a separate ribbon-shaped microcontinent. All three hypotheses predict unique positions for the Arctic composite terrane with respect to rotation and translation since the middle of the Mesozoic. Paleomagnetic and susceptibility studies were conducted on rocks from 15 sites in the ~160 Ma (K-Ar cooling age) Asik Mountain mafic to ultramafic complex in the western part of the Arctic composite terrane. Coherent data from 11 sites yielded a direction of dec = 255.1°, inc = 82.1°, = 19.3, 95 = 9.6°, 63 = 5.6°. Contact and fold tests were not possible but the direction differs distinctly from the modern magnetic direction. The anisotropy of magnetic susceptibility revealed a well-developed oblate fabric of variable orientation. The orientation of the fabric was not related to the regional stress regime, so we conclude that the rocks were not deformed and metamorphosed during thrusting, and thus the magnetic remanence direction obtained is most likely primary. The direction yields a pole position at long = 166.8°E, lat = 59.8°N, A 95 = 18.4°, A 63 = 10.7°that is discordant to the expected 160 Ma reference direction for North America. Counterclockwise rotation of the Arctic composite terrane would yield a perfect fit to the 160 Ma reference pole with an allowance for up to 5°of northward translation. This result, combined with previous paleomagnetic data, makes a convincing argument that the Arctic composite terrane has not remained fixed in its current orientation with respect to North America. However, the data are not sufficient to differentiate between the two hypotheses that suggest movement of the Arctic composite terrane relative to North America.

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Thin, low‐velocity crust beneath the southern Yukon‐Tanana Terrane, east central Alaska: Results from Trans‐Alaska crustal transect refraction/wide‐angle reflection data

Beaudoin¹,

Fuis²,

Mooney³

et al. 1992

J. Geophys. Res.

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A seismic refraction/wide-angle reflection survey for the Trans-Alaska Crustal Transect program reveals a thin, reflective crust beneath the southern Yukon-Tanana terrane (YTT) in east central Alaska. These data are the first detailed refraction survey of the southern YTT and compose a 130-km-long reversed profile along the Alaska and Richardson highways. Results from this study indicate that low-velocity (-• 6.4 km/s) rocks extend to approximately 27 km in depth. Based on these low velocities and an average Poisson's ratio of 0.23 determined for depths of -• 27 km, an overall silicic composition is interpreted for this portion of the crust beneath the Yukon-Tanana terrane. From approximately 8 to 27 km depth the crust exhibits an increase in reflectivity. This middle to lower crustal reflectivity is modeled as alternating high-and low-velocity lamellae with an average velocity of 6.1 km/s at 10 km depth to an average velocity of 6.4 km/s at 27 km depth. Beneath these reflective, low-velocity rocks a 3-to 5-km-thick, 7.0 km/s basal crustal layer produces a prominent reflection that extends to offsets of up to 280 km. The crust-mantle boundary, modeled at an average depth of 30 km, produces a variable PmP reflection, which may indicate lateral heterogeneity of this boundary, and a weak and emergent Pn refraction with a velocity of 8.2 km/s. We interpret the crustal section as follows: the low-velocity rocks of the southern YTT extend from the surface to depths of approximately 10 km; underthrust Mesozoic flysch of the Kahiltna terrane, rocks of the Gravina arc, and basement of the Wrangellia(?) terrane extend from 10 to 27 km depth; a 3-to 5-km-thick layer of mantle-derived mafic rocks, relic oceanic crust, or Wrangellia(?) terrane lower crust extends from 27 to approximately 30 km depth; a tectonically young Moho beneath the southern YTT is found at an average depth of 30 km; and it is underlain by a mantle that may be relatively cool and/or olivine rich. In this interpretation, the Yukon-Tanana terrane is a thin-skinned terrane. Our results indicate that tectonic, and possibly magmatic, underplating has played a significant role in crustal growth for central

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Ophiolites and other mafic-ultramafic complexes in Alaska

Abstract: This report is preliminary and has not been reviewed for conformity with U.S.

Cited by 12 publications

References 61 publications

Sedimentary record of the tectonic growth of a collisional continental margin: Upper Jurassic–Lower Cretaceous Nutzotin Mountains sequence, eastern Alaska Range, Alaska

Sedimentary record of the tectonic growth of a collisional continental margin: Upper Jurassic–Lower Cretaceous Nutzotin Mountains sequence, eastern Alaska Range, Alaska

Paleomagnetism of the Mesozoic Asik Mountain Mafic Complex in Northern Alaska: Implications for the Tectonic History of the Arctic Composite Terrane

Thin, low‐velocity crust beneath the southern Yukon‐Tanana Terrane, east central Alaska: Results from Trans‐Alaska crustal transect refraction/wide‐angle reflection data

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