Constraints on the age and provenance of the Chugach accretionary complex from detrital zircons in the Sitka Graywacke near Sitka, Alaska

Haeussler, Peter J.; Gehrels, George E.; Karl, Susan M.

doi:10.3133/pp1709f

Cited by 11 publications

(15 citation statements)

References 29 publications

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“…Analyses interpreted to reflect metamorphic zircon growth were not included in probability plots and are shown in a lighter color. Data sources for reference strata: Gravina basin [ Kapp and Gehrels , ; Gehrels , ; Tochilin et al ., ; Yokelson et al , ], Bowser basin [ Evenchick et al ., ], Chugach accretionary complex [ Haeussler et al ., ; Amato and Pavlis , ; Garver and Davidson , ], and limited data from two detrital samples from the lower Hazelton Group with unimodal U‐Pb zircon age populations [ Cutts et al ., ].…”

Section: Resultsmentioning

confidence: 99%

“…However, our samples lack abundant Triassic dates that dominate DZ populations from the Bowser/Sustut retroarc basin [ Evenchick et al ., ] and have maximum depositional ages younger than Upper Jurassic to Lower Cretaceous sediments of the Gravina belt [ McClelland et al ., ; Kapp and Gehrels , ] (Figure ). Upper Cretaceous rocks of the southern Chugach accretionary complex, currently northwest of the Central Gneiss Complex, were derived from the Coast Mountains batholith, contain major age peaks that closely match our DZ populations, and are dominated in some samples by populations of Late Cretaceous ages very close to the depositional ages of the samples (Valdez Group) [ Haeussler et al ., ; Amato and Pavlis , ; Amato et al ., ; Kochelek et al ., ; Garver and Davidson , ]. Thus, partial underthrusting of accretionary complex rocks [ Ducea et al ., ], relamination of sediment at the plate interface [ Behn et al ., ; Hacker et al ., ], or intraarc burial may also be a viable hypothesis for the burial of these rocks beneath the Coast Mountains batholith.…”

Section: Discussionmentioning

confidence: 98%

“…Northwest of these terranes and ~300 km northwest of the Central Gneiss Complex, translated slivers of >205–125 Ma metamorphic rocks and 101–55 Ma clastic sedimentary rocks constitute the Chugach terrane [ Berg et al ., ; Amato et al ., ]. The Chugach terrane is an accretionary complex formed during east‐dipping subduction, largely outboard of the Coast Mountains batholith; the formation of this accretionary complex was coeval with major Late Cretaceous to early Cenozoic dextral translation along the Cordilleran margin [ Pavlis and Sisson , ; Cowan , ; Roeske et al ., ; Haeussler et al ., ; Pavlis and Roeske , ; Amato and Pavlis , ; Amato et al ., ; Gasser et al ., ; Kochelek et al ., ; Scharman and Pavlis , ; Garver and Davidson , ].…”

Section: Geological Settingmentioning

confidence: 98%

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Sediment underthrusting within a continental magmatic arc: Coast Mountains batholith, British Columbia

et al. 2017

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Though continental magmatic arcs are factories for new continental crust, a significant proportion of continental arc magmas are recycled from supracrustal material. To evaluate the relative contributions of retroarc underthrusting and trench side partial sediment subduction for introducing supracrustal rocks to the middle and lower crust of continental magmatic arcs, we present results from the deeply exposed country rocks of the Coast Mountains batholith of western British Columbia. Prior work demonstrates that these rocks underwent widespread partial melting that contributed to the Coast Mountains batholith. We utilize U‐Pb zircon geochronology, Sm‐Nd thermochronology, and field‐based studies to document the protoliths and early burial history of amphibolite and granulite‐facies metasedimentary rocks in the Central Gneiss Complex. U‐Pb detrital zircon data from the structurally highest sample localities yielded ~190 Ma unimodal age peaks and suggest that retroarc rocks of the Stikine terrane constitute a substantial portion of the Central Gneiss Complex. These supracrustal rocks underwent thrust‐related burial and metamorphism at >25 km depths prior to ~80 Ma. These rocks may also be underlain at the deepest exposed structural levels by Upper Cretaceous metasedimentary rocks, which may have been emplaced as a result of trench side underplating or intraarc burial. These results further our understanding of the mechanisms of material transport within the continental lithosphere along Cordilleran subduction margins.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 98%

Section: Geological Settingmentioning

confidence: 98%

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Sediment underthrusting within a continental magmatic arc: Coast Mountains batholith, British Columbia

et al. 2017

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“…Comparison of U‐Pb ages and Hf isotope values of detrital zircons from the Gravina belt (this study) with reference fields for detrital zircons from the Alexander terrane in SE Alaska (C. White, written communication, 2015; n = 2288), the Yukon‐Tanana (M. Pecha, written communication, 2015), and Taku (D. Giesler, written communication, 2015) terranes ( n = 2761), detrital zircons from the Chugach terrane [ Haeussler et al ., ; Amato and Pavlis , ; Garver and Davidson , ] ( n = 1968) and plutons of the eastern (inboard) and western (outboard) segments of the CMB [ Cecil et al ., ]. Note that age‐distribution curves have variable exaggeration of >800 Ma ages.…”

Section: U‐pb Geochronologic and Hf Isotope Geochemical Resultsmentioning

confidence: 99%

U-Pb and Hf isotope analysis of detrital zircons from Mesozoic strata of the Gravina belt, southeast Alaska

et al. 2015

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The Gravina belt consists of Upper Jurassic through Lower Cretaceous marine clastic strata and mafic-intermediate volcanic rocks that occur along the western flank of the Coast Mountains in southeast Alaska and coastal British Columbia. This report presents U-Pb ages and Hf isotope determinations of detrital zircons that have been recovered from samples collected from various stratigraphic levels and from along the length of the belt. The results support previous interpretations that strata in the western portion of the Gravina belt accumulated along the inboard margin of the Alexander-Wrangellia terrane and in a back-arc position with respect to the western Coast Mountains batholith. Our results are also consistent with previous suggestions that eastern strata accumulated along the western margin of the inboard Stikine, Yukon-Tanana, and Taku terranes and in a fore-arc position with respect to the eastern Coast Mountains batholith. The history of juxtaposition of western and eastern assemblages is obscured by subsequent plutonism, deformation, and metamorphism within the Coast Mountains orogen, but may have occurred along an Early Cretaceous sinistral transform system. Our results are inconsistent with models in which an east-facing subduction zone existed along the inboard margin of the Alexander-Wrangellia terrane during Late Jurassic-Early Cretaceous time.

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“…However, even with transform offsets, the possible plate geometry is limited for any Kula‐Farallon ridge interaction with North America using the updated plate motion models of Doubrovine and Tarduno [2008] and Müller et al [2008] (Figure 7a). With these updated models, we reproduce possible plate geometries based on the Alaska‐British Columbia border velocity diagram (Figure 6d), since several provenance studies indicate the Coast Mountains as a source for the Chugach terrane accretionary prism material [e.g., Plafker et al , 1994; Haeussler et al , 2004; Kochelek et al , 2011]. Figure 7shows the two end‐member arrangements of ridge and transform segments to accommodate 350 km of triple junction migration in 2 m.y.…”

Section: Plate Velocity Modelsmentioning

confidence: 99%

Kinematics of the Chugach metamorphic complex, southern Alaska: Plate geometry in the north Pacific margin during the Late Cretaceous to Eocene

Scharman

Pavlis

2012

Tectonics

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1] The Paleogene plate geometry of the north Pacific margin is poorly constrained because all of the plates involved, except the trailing Pacific plate, have been subducted. However, the kinematic history of the Chugach metamorphic complex in southern Alaska constrains plate configurations because of its link to ridge-subduction. We synthesize recent regional mapping of the complex, finite strain data, and geochronology to show that progressive deformation records the Paleogene triple junction interaction occurred over a period of less than 2 m.y. across $350 km of the margin. We document that 140-190 km of distributed dextral shear occurred across the complex during the latest phase of deformation in the complex. This analysis suggests dextral motion of at least 70-95 mm/yr which can account for most, or all, of the margin parallel plate motion during a brief period of the Eocene. We use these results to compare and evaluate possible plate configurations based on older and newer plate motion models. Using modern plate motion models it is difficult to reconcile a Kula-Farallon ridge-subduction model with the available data, but our preferred plate geometry model involving a Kula-Resurrection ridge provides a reasonable explanation for our observations. Citation: Scharman, M. R., and T. L. Pavlis (2012), Kinematics of the Chugach metamorphic complex, southern Alaska: Plate geometry in the north Pacific margin during the Late Cretaceous to Eocene, Tectonics, 31, TC4014,

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Constraints on the age and provenance of the Chugach accretionary complex from detrital zircons in the Sitka Graywacke near Sitka, Alaska

Cited by 11 publications

References 29 publications

Sediment underthrusting within a continental magmatic arc: Coast Mountains batholith, British Columbia

Sediment underthrusting within a continental magmatic arc: Coast Mountains batholith, British Columbia

U-Pb and Hf isotope analysis of detrital zircons from Mesozoic strata of the Gravina belt, southeast Alaska

Kinematics of the Chugach metamorphic complex, southern Alaska: Plate geometry in the north Pacific margin during the Late Cretaceous to Eocene

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