Geologic map of western Chichagof Island, southeastern Alaska

Decker, John

doi:10.3133/ofr80150

Cited by 25 publications

(11 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…3) that were metamorphosed during the Early Jurassic, as summarized, for example, by Dusel-Bacon et al (1993). The next belt is an argillite-matrix melange containing blocks and fault slices of Triassic to middle Cretaceous chert and basalt, undated graywacke, rare Permian limestone, and a few Triassic-Jurassic ultramafi c-mafi c complexes (Uyak Complex, McHugh Complex, and Kelp Bay Group;Connelly, 1978;Bradley and Kusky, 1992;Decker, 1980). Small near-trench plutons and numerous dikes intrude these rocks.…”

Section: Geologic Settingmentioning

confidence: 98%

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

105

View full text Add to dashboard Cite

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.

show abstract

Section: Geologic Settingmentioning

confidence: 98%

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

105

View full text Add to dashboard Cite

show abstract

“…Plafker and others (1976;1977) the Uyak Complex, the McHugh Complex, and the melange facies of the Yakutat Group, which together they interpreted as the melange facies of a subduction complex accreted to the continental margin along the Border Ranges fault system. Recent detailed mapping (Decker, 1980a;Decker and Johnson, 1980) has confirmed or reinforced the general conclusions of the earlier workers through documented field relationships and additional age information. Radiolarian age determinations from the Kelp Bay Group west of the Border Ranges fault establish that some of these rocks are as young as Early Cretaceous (Plafker and others, 1976;Decker, 1980a) and isotopic age determinations on metamorphic minerals from units west of the fault establish the intermediate to high pressure metamorphism associated with accretion as being of mid-Cretaceous (106 to 91 m.y.)…”

Section: Previous Workmentioning

confidence: 71%

Radiometric age file for Alaska: A section in <i>The United States Geological Survey in Alaska: Accomplishments during 1980</i>

Shew¹,

Wilson²

1982

Circular

View full text Add to dashboard Cite

“…Three accreted rock units recognized on the basis of age, rock type, and structural style are germane to the present paper. From landward to seaward and from west to east: (1) The Uyak Complex (Connelly, 1978), McHugh Complex (Clark, 1973), and Kelp Bay Group (Decker, 1980) are mélanges consisting of an argillaceous matrix and more competent blocks of graywacke, greenstone, tuff, Triassic to middle Cretaceous chert, gabbro, plus rare ultramafi c rocks and Permian limestone. (2) The Campanian-Maastrichtian Shumagin Formation (Moore, 1973), Kodiak Formation (Nilsen and Moore, 1979), Valdez Group (Nilsen and Zuffa, 1982), and Sitka Graywacke (Decker, 1980) consist of siliciclastic turbidites thought to have originated as trenchfi ll deposits derived from uplift of the Coast Plutonic Complex Figure 1.…”

Section: Geologic and Tectonic Settingmentioning

confidence: 99%

Brittle deformation along the Gulf of Alaska margin in response to Paleocene-Eocene triple junction migration

Haeussler¹,

Bradley²,

Goldfarb³

2003

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

View full text Add to dashboard Cite

A spreading center was subducted diachronously along a 2200 km segment of what is now the Gulf of Alaska margin between 61 and 50 Ma, and left in its wake near-trench intrusions and high-T, low-P metamorphic rocks. Gold-quartz veins and dikes, linked to ridge subduction by geochronological and relative timing evidence, provide a record of brittle deformation during and after passage of the ridge. The gold-quartz veins are typically hosted by faults, and their regional extent indicates there was widespread deformation of the forearc above the slab window at the time of ridge subduction. Considerable variability in the strain pattern was associated with the slab window and the trailing plate. A diffuse network of dextral, sinistral, and normal faults hosted small lode-gold deposits (<50,000 oz) in south-central Alaska, whereas crustal-scale dextral faults in southeastern Alaska are spatially associated with large gold deposits (up to 800,000 oz).We interpret the gold-quartz veins as having formed above an eastward-migrating slab window, where the forearc crust responded to the diminishing infl uence of the forward subducting plate, the increasing infl uence of the trailing plate, and the thermal pulse and decreased basal friction from the slab window. In addition, extensional deformation of the forearc resulted from the diverging motions of the two oceanic plates at the margins of the slab window. Factors that complicate interpretations of fault kinematics and near-trench dike orientations include a change in plate motions at ca. 52 Ma, northward translation of the accretionary complex, oroclinal bending of the south-central Alaska margin, and subduction of transform segments. We fi nd the pattern of syn-ridge subduction faulting in southern Alaska is remarkably similar to brittle faults near the Chile triple junction and to earthquake focal mechanisms in the Woodlark basin-the two modern sites of ridge subduction. Therefore, extensional and strike-slip deformation above slab windows may be a common occurrence.

show abstract

Geologic map of western Chichagof Island, southeastern Alaska

Cited by 25 publications

References 0 publications

Geologic signature of early Tertiary ridge subduction in Alaska

Geologic signature of early Tertiary ridge subduction in Alaska

Radiometric age file for Alaska: A section in <i>The United States Geological Survey in Alaska: Accomplishments during 1980</i>

Brittle deformation along the Gulf of Alaska margin in response to Paleocene-Eocene triple junction migration

Contact Info

Product

Resources

About