Sandstone petrographic evidence and the Chugach-Prince, William terrane boundary in southern Alaska

Dumoulin, Julie A.

doi:10.1130/0091-7613(1988)016<0456:speatc>2.3.co;2

Cited by 38 publications

(30 citation statements)

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“…A critical result from this study is the major difference in rock uplift centered on the Contact fault system, which has been the subject of debate as to whether it is a structure that has accommodated Miocene to recent deformation (Dumoulin, 1988;Bol and Gibbons, 1992). AHe and AFT ages decrease by 50% (Fig.…”

Section: Exhumation Of the Western Chugach Mountains And Northern Primentioning

confidence: 93%

“…To the south, the arcuate Contact fault system separates the Valdez and Orca Groups and is the southern boundary between the Chugach and Prince William terranes. The kinematics and location of the Contact fault in this area are contentious because of uncertainties in dating, lack of fossils for correlation, structural complexity, and the similarity of metamorphism and lithology (Dumoulin, 1988;Bol and Gibbons, 1992). This study addresses the location of the Contact fault system and possible phases of major displacement.…”

Section: Geomorphic and Structural Settingmentioning

confidence: 99%

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Focused exhumation in the syntaxis of the western Chugach Mountains and Prince William Sound, Alaska

Arkle

Armstrong

Haeussler

et al. 2013

Geological Society of America Bulletin

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The western Chugach Mountains and Prince William Sound are located in a syntaxial bend, which lies above fl at-slab subduction of the Yakutat microplate and inboard of the Yakutat collision zone of southern Alaska. The syntaxis is characterized by arcuate fault systems and steep, high topography, which suggest focused uplift and exhumation of the accretionary prism. We examined the exhumation history with low-temperature thermochronometry of 42 samples collected across the region. These new apatite (U-Th)/He, apatite fi ssion-track, zircon (U-Th)/He, and zircon fi ssion-track ages, combined with ages from surrounding regions, show a bull'seye pattern, with the youngest ages focused on the western Chugach syntaxis. The ages have ranges of ca. 10-4 Ma, ca. 35-11 Ma, ca. 33-25 Ma, and ca. 44-27 Ma, respectively. The youngest ages are located on the south (windward) side of the Chugach Mountains and just north of the Contact fault. Sequentially higher closure temperature systems are nested across Prince William Sound in the south, the Chugach Mountains, and the Talkeetna Mountains to the north. Computed exhumation rates typically are 0.2 mm/yr across Prince William Sound, increase abruptly to ~0.7 mm/yr across and adjacent to the Contact fault system, and decrease to ~0.4 mm/yr north of the core of the Chugach Mountains. The abrupt age and exhumation rate changes centered on the Contact fault system suggest that it may be a critical structural system for facilitating rock uplift. Our data are most consistent with Yakutat fl at-slab subduction starting in the Oligocene, and since then ~11 km of rock uplift north of the Contact fault and ~4-5 km of rock uplift in Prince William Sound to the south. These data are consistent with a deformation model where the western Chugach core has approached long-term exhumational steady state, though exhumation rates have probably increased in the last ~5 m.y. We interpret that rock uplift in the overriding wedge has been driven dominantly by underplating, with long-term vertical displacement concentrated at the southern edge of the Chugach Mountains and centered on the Contact fault system. Though our data do not unequivocally differentiate between Pliocene tectonic-or climate-related causes for increased exhumation in the last ~5 m.y., we interpret the increased rates to be due to increased infl ux of underplated sediments that are derived from erosion in the Saint Elias orogen collision zone.

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Section: Exhumation Of the Western Chugach Mountains And Northern Primentioning

confidence: 93%

Section: Geomorphic and Structural Settingmentioning

confidence: 99%

Focused exhumation in the syntaxis of the western Chugach Mountains and Prince William Sound, Alaska

Arkle

Armstrong

Haeussler

et al. 2013

Geological Society of America Bulletin

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“…12). In Prince William Sound (Dumoulin, 1987(Dumoulin, , 1988 sandstones of Stage 1 (Valdez Group and inboard part of the Orca Group) contain abundant volcanic lithic clasts, locally abundant grains of pyroxene and amphibole, and little quartz. They were derived from a progressively unroofi ng magmatic arc with increasing input from subduction-complex sources through time.…”

Section: Late Cretaceous-early Tertiary Deep-marine Sedimentationmentioning

confidence: 99%

Geologic signature of early Tertiary ridge subduction in Alaska

Bradley¹,

Kusky²,

Haeussler³

et al. 2003

Geology of a Transpressional Orogen Developed During Ridge-Trench Interaction Along the North Pacific Margin

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A mid-Paleocene to early Eocene encounter between an oceanic spreading center and a subduction zone produced a wide range of geologic features in Alaska. The most striking effects are seen in the accretionary prism (Chugach-Prince William terrane), where 61 to 50 Ma near-trench granitic to gabbroic plutons were intruded into accreted trench sediments that had been deposited only a few million years earlier. This short time interval also saw the genesis of ophiolites, some of which contain syngenetic massive sulfi de deposits; the rapid burial of these ophiolites beneath trench turbidites, followed immediately by obduction; anomalous high-T, low-P, near-trench metamorphism; intense ductile deformation; motion on transverse strike-slip and normal faults; gold mineralization; and uplift of the accretionary prism above sea level. The magmatic arc experienced a brief fl are-up followed by quiescence. In the Alaskan interior, 100 to 600 km landward of the paleotrench, several Paleocene to Eocene sedimentary basins underwent episodes of extensional subsidence, accompanied by bimodal volcanism. Even as far as 1000 km inboard of the paleotrench, the ancestral Brooks Range and its foreland basin experienced a pulse of uplift that followed about 40 million years of quiescence.All of these events-but most especially those in the accretionary prism-can be attributed with varying degrees of confi dence to the subduction of an oceanic spreading center. In this model, the ophiolites and allied ore deposits were produced at the soon-to-be subducted ridge. Near-trench magmatism, metamorphism, deformation, and gold mineralization took place in the accretionary prism above a slab window, where hot asthenosphere welled up into the gap between the two subducted, but still diverging, plates. Deformation took place as the critically tapered accretionary prism *dbradley@usgs.gov on June 7, 2015 specialpapers.gsapubs.org Downloaded from 20 D. Bradley et al.

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“…The plutons intrude the Cretaceous Valdez Group, which in the area is a thick sequence of turbiditic sandstone and shale with some minor granule conglomerate and calcareous siltstone (Dumoulin, 1987(Dumoulin, , 1988Kusky and Young, 1999). The Valdez Formation is locally transposed into a mélange (Iceworm mélange) (Kusky et al, 1997b) consisting of blocks of graywacke in a phacoidally cleaved argillite matrix.…”

Section: Magmatic and Tectonic Foliations In The Granite Of Harding Imentioning

confidence: 99%

Controls on intrusion of near-trench magmas of the Sanak-Baranof Belt, Alaska, during Paleogene ridge subduction, and consequences for forearc evolution

Kusky¹,

Bradley²,

Donely³

et al. 2003

Geology of a Transpressional Orogen Developed During Ridge-Trench Interaction Along the North Pacific Margin

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A belt of Paleogene near-trench plutons known as the Sanak-Baranof belt intruded the southern Alaska convergent margin. A compilation of isotopic ages of these plutons shows that they range in age from 61 Ma in the west to ca. 50 Ma in the east. This migrating pulse of magmatism along the continental margin is consistent with North Pacifi c plate reconstructions that suggests the plutons were generated by migration of a trench-ridge-trench triple junction along the margin. On the Kenai Peninsula the regional lower greenschist metamorphic grade of the turbiditic host rocks, texture of the plutons, contact-metamorphic assemblage, and isotopic and fl uid inclusion studies suggest that the plutons were emplaced at pressures of 1.5-3.0 kbars (5.2-10.5 km) into a part of the accretionary wedge with an ambient temperature of 210-300 °C. The presence of kyanite, garnet, and cordierite megacrysts in the plutons indicates that the melts were generated at a depth greater than 20 km and minimum temperature of 650 °C. These megacrysts are probably xenocrystic remnants of a restitic or contact metamorphic phase entrained by the melt during intrusion. However, it is also possible that they are primary magmatic phases crystallized from the peraluminous melt.Plutons of the Sanak-Baranof belt serve as time and strain markers separating kinematic regimes that predate and postdate ridge subduction. Pre-ridge subduction structures are interpreted to be related to the interaction between the leading oceanic plate and the Chugach terrane. These include regional thrust faults, NE-striking map-scale folds with associated axial planar foliation, type-1 mélanges, and an array

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Sandstone petrographic evidence and the Chugach-Prince, William terrane boundary in southern Alaska

Cited by 38 publications

References 0 publications

Focused exhumation in the syntaxis of the western Chugach Mountains and Prince William Sound, Alaska

Focused exhumation in the syntaxis of the western Chugach Mountains and Prince William Sound, Alaska

Geologic signature of early Tertiary ridge subduction in Alaska

Controls on intrusion of near-trench magmas of the Sanak-Baranof Belt, Alaska, during Paleogene ridge subduction, and consequences for forearc evolution

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