Bedrock geologic map of the Chulitna region, southcentral Alaska

Clautice, K. H.; Newberry, R. J.; Blodgett, Robert B.; Bundtzen, Thomas K.; Gage, B. G.; Harris, E. E.; Liss, S. A.; Miller, Mark M.; Clough, James G.; Pinney, D. S.

doi:10.14509/2768

Cited by 5 publications

(9 citation statements)

References 18 publications

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“…The crustal thickness and character of the suture zone proper (i.e., central section) does not vary greatly across the transects (Figures 4a–4d), suggesting that this region which broadens westward has experienced distributed deformation during Mesozoic collision and that deformation was likely not localized along a major discrete structure. This interpretation is consistent with geologic studies within the central section that document highly deformed, often isoclinally folded strata [ Reed and Nelson , 1980; Csejtey et al , 1992; Clautice et al , 2001; Eastham and Ridgway , 2002]. The presence of intracrustal discontinuities within the central section, the current crustal thickness, and geometry and relationship of the boundaries of this section with the former continental margin and allochthonous terrane, suggests that deformation was also accommodated within the middle and lower crust (Figures 4a–4d).…”

Section: Discussionsupporting

confidence: 89%

Crustal structure across the central Alaska Range: Anatomy of a Mesozoic collisional zone

Brennan

Gilbert

Ridgway

2011

Geochem Geophys Geosyst

102

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[1] A first-order process in the growth of continents is the collision and accretion of terranes against continental margins. Collision leads to the formation of a suture zone between the accreted terrane and the former continental margin. New insights on the suturing process are observed from two receiver function transects across the Mesozoic Alaska Range suture zone. Three distinct crustal sections are identified from observations of crustal thickness, intracrustal discontinuities, and Vp/Vs: a northern section with ∼27 km thick crust of felsic to intermediate composition, a central section that is ∼37 km thick that exhibits intracrustal discontinuities and has felsic to intermediate composition, and a southern section that is ∼30 km thick and has a more mafic composition. We interpret these sections to correspond with the former continental margin (Yukon composite terrane), the suture zone proper, and the allochthonous oceanic terrane (Wrangellia composite terrane). The boundary between the Yukon composite terrane and the suture zone appears to be a subhorizontal discontinuity that accommodated underthrusting of crust from the suture zone beneath the former continental margin. The boundary between the suture zone and the Wrangellia composite terrane, in contrast, appears to be a relatively discrete, vertical boundary. The observed variability in the crust across the Alaska Range suture zone is likely controlled by the differing compositions of the terranes involved, which influences how each section responds to precollisional, syncollisional, and postcollisional deformation.

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Section: Discussionsupporting

confidence: 89%

Crustal structure across the central Alaska Range: Anatomy of a Mesozoic collisional zone

Brennan

Gilbert

Ridgway

2011

Geochem Geophys Geosyst

102

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“…A model that invokes the initiation of back-arc rifting is consistent with evidence that strata were deposited within a rift basin. We fi nd no geochemical indication that these rocks are fl ood basalts, as would be expected if they were analogous to the Nikolai greenstones of the Wrangellia terrane (Clautice et al, 2001), although this could be a local variant where trace-element chemistry is infl uenced by subarc mantle. Based on this model of arc rifting, we interpret ultramafi c slivers and volcanics of the Devonian Chulitna basement as a suprasubduction ophiolite, similar to younger Upper Triassic mafi c and ultramafi c rocks between the Wrangellia composite terrane and North America in the Lake Clark region (Amato et al, 2007).…”

Section: Discussionmentioning

confidence: 52%

“…Tropical faunas from Triassic strata of the Chulitna terrane are consistent with an origin exotic to North America (Nokleberg et al, 1994) and suggest an affi nity with the Wrangellia composite terrane. The existence of a Paleozoic arc with a thick sequence of Late Triassic tholeiitic basalt shows a similarity to the stratigraphy of Wrangellia (Clautice et al, 2001). However, the existence of a Triassic red-bed sequence overlying basement along an unconformity is also observed in the Alexander terrane (Gehrels et al, 1996).…”

Section: Geology Of the Chulitna Terranementioning

confidence: 75%

“…2). Jones et al (1980) described the Chulitna as unlike any other sequence in Alaska, whereas Clautice et al (2001) emphasized the similarities to parts of the Wrangellia composite terrane, given the existence of a mid-Paleozoic volcanic arc and a thick package of Triassic basalt with interbedded limestones. Much of the debate centers on the origin of these basalts.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, the basement of the Chulitna terrane has been referred to as either an ophiolite based on the occurrence of serpentinite, pillow basalts, and chert (Jones et al, 1980) or as an oceanic arc based on tholeiitic trend of basaltic andesites (Clautice et al, 2001). Red beds within the terrane have been cited as typical of Triassic deposition at lower latitudes (Jones et al, 1980) or as atypical of continental red beds (Clautice et al, 2001), though similar-aged red beds occur in the Alexander terrane (Butler et al, 1997). The occurrence of tropical fauna in limestones of the Chulitna suggests large latitudinal displacement in the Mesozoic and an exotic origin with respect to the Mesozoic margin of North America (Nokleberg et al, 1994).…”

Section: Introductionmentioning

confidence: 99%

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The Chulitna terrane of south-central Alaska: A rifted volcanic arc caught between the Wrangellia composite terrane and the Mesozoic margin of North America

2009

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The Chulitna terrane is an enigmatic, fault-bounded package of mid-Paleozoic to early Mesozoic sedimentary rocks and volcanics that are exotic to North America and show no clear affi nity with any of the other allochthonous terranes in southern Alaska. Geologic mapping and geochemical analyses of Triassic strata from the Chulitna terrane indicate Triassic rifting of a Devonian volcanic arc and development of an asymmetric basin that was later deformed in the Cretaceous within the broadly defi ned suture between the Wrangellia composite terrane and the Mesozoic margin of North America. The structure of the region consists of an overturned synclinorium that verges southeast, Triassic strata in the core of the syncline, and basement rocks exposed in the hanging walls of a series of out-of-syncline thrusts on the southeastern, upright limb. The basement of the complex consists of serpentinite, vesicular fl ows of basaltic andesite with minor pillow lavas, and volcanic debris with blocks of andesite and minor Devonian red chert. From southeast to northwest, there are systematic changes in the facies associated with Triassic strata that overlie this basement. To the southeast, the basement is unconformably overlain by bedded sedimentary breccias that consist of subangular clasts of basement lithologies, including red chert, serpentinite, and andesite. Further to the northwest, in the hanging wall of a more rearward thrust, the red-bed strata consist of conglomerate intermixed with siltstone and cross-bedded sandstone. In the northwest on the overturned limb of the syncline, the red beds are composed of siltstone and sandstone interfi ngered with limestone. There is an overall increase in the thickness of the red-bed unit from southeast to northwest. On the northwestern limb of the syncline, the red beds overlie a 1500-m-thick basalt sequence with columnar jointed fl ows and pillow basalts interbedded with limestone. Geochemical analyses of clinopyroxene phenocrysts in the basalts show similarities with island-arc basalts, suggesting that volcanism was related to early rifting of an oceanic arc. A marine sandstone unit overlies the entire red-bed package along a fl ooding surface and thins to the southeast. These results are consistent with Triassic deposition within a rifted volcanic arc, an upland erosion surface to the southeast, and increasing thickness of the Triassic section toward a basin-bounding fault in the northwest. This basin was initially ~18 km wide prior to accretion along the Mesozoic margin of North America, which resulted in southeast-vergent folding and 30% shortening.

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Tectonic Growth of the Late Paleozoic‐Middle Mesozoic Northwestern Margin of Laurentia and Implications for the Farewell Terrane: Stratigraphic, Structural, and Provenance Records From the Central Alaska Range

Keough

Ridgway

2021

Tectonics

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Bedrock geologic map of the Chulitna region, southcentral Alaska

Cited by 5 publications

References 18 publications

Crustal structure across the central Alaska Range: Anatomy of a Mesozoic collisional zone

Crustal structure across the central Alaska Range: Anatomy of a Mesozoic collisional zone

The Chulitna terrane of south-central Alaska: A rifted volcanic arc caught between the Wrangellia composite terrane and the Mesozoic margin of North America

Tectonic Growth of the Late Paleozoic‐Middle Mesozoic Northwestern Margin of Laurentia and Implications for the Farewell Terrane: Stratigraphic, Structural, and Provenance Records From the Central Alaska Range

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