Paleogene anatexis along the Gulf of Alaska margin

Hudson, Travis; Plafker, George; Peterman, Zell E.

doi:10.1130/0091-7613(1979)7<573:paatgo>2.0.co;2

Cited by 92 publications

(42 citation statements)

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“…Felsic plutons of Cretaceous to early Tertiary age intrude the accretionary wedge that borders the Gulf of Alaska, far from the coeval volcanic arc (Hudson et al, 1979;Hill et al, 1981;Barker et al, 1992;Pavlis et al, 1988). These plutons have been interpreted to be largely to entirely anatectic in origin, with melting being induced by heating associated with crustal thickening (Hudson et al, 1979), basaltic influx (Barker et al, 1992), or shear heating along deep faults (Barnett et al, 1993).…”

Section: Origins Of the Blue Ridge Magmas And Their Relationship To Smentioning

confidence: 96%

Low-potassium, trondhjemitic to granodioritic plutonism in the eastern Blue Ridge, southwestern North Carolina-northeastern Georgia

Miller¹,

Fullagar²,

Sando³

et al. 1997

The Nature of Magmatism in the Appalachian Orogen

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Plutons and dikes of the eastern Blue Ridge, North Carolina and northeasternGeorgia, were emplaced syntectonically ca. 400 Ma in the evolving southern Appalachian orogen. These intrusive rocks are uniformly felsic and peraluminous, ranging continuously from trondhjemitic to granodioritic in composition with no associated mafic or intermediate rocks. The trondhjemites are very low in K and in incompatible and high field strength trace elements; are rich in Al, Na, and Sr; and have low 87 Sr/ 86 Sr and δ 18 O and high ε Nd . Granodiorites are less extreme, having elemental and isotopic compositions that are more typical of continent margin granitoids.Their compositions require that the rocks near the trondhjemitic end of the spectrum had a relatively mafic source that was young and derived from depleted mantle. Trace-element modeling and isotopic constraints suggest that this source had the geochemical characteristics of a primitive arc basalt, and that the residue of melting was garnet amphibolite. The granodiorite end of the compositional continuum was derived in large part from the Proterozoic continental basement of the region. The most plausible genetic model involves development of an early Paleozoic magmatic arc, underthrusting of arc rocks during subsequent orogeny, heating of the deep crust as a consequence of crustal thickening, and anatexis within a heterogeneous lower crust. Magmas generated within this crust ranged from trondhjemite to granodiorite, depending upon the source rock, and coalesced in the source region or during ascent to yield the observed compositional continuum.

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Section: Origins Of the Blue Ridge Magmas And Their Relationship To Smentioning

confidence: 96%

Low-potassium, trondhjemitic to granodioritic plutonism in the eastern Blue Ridge, southwestern North Carolina-northeastern Georgia

Miller¹,

Fullagar²,

Sando³

et al. 1997

The Nature of Magmatism in the Appalachian Orogen

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“…The latter present an intriguing problem, but are younger than events of interest here. The Paleocene to early Eocene plutons include granodiorite, granite, tonalite, and gabbro (Hudson et al, 1979;Hudson, 1983). Swarms of basaltic to rhyolitic dikes, known or inferred to be of the same range of ages as the Paleocene to early Eocene plutons, have been mapped along some sectors of the margin.…”

Section: Near-trench Intrusive Rocksmentioning

confidence: 98%

“…The track of a migrating trench-ridgetrench triple junction is suggested, however, by the near-trench plutons in Alaska. As will be shown, ridge subduction provides the most reasonable explanation for these plutons, which defi ne the Sanak-Baranof plutonic belt of Hudson et al (1979). If the Great Magnetic Bight is a smoking gun, the near-trench plutons would then be the bullet holes.…”

Section: Introductionmentioning

confidence: 95%

“…In Plafker and Berg's 1994 Decade of North American Geology synthesis of Alaskan tectonic evolution, they likewise showed no ridge intersecting the Alaskan margin during the time in question. Various alternative explanations for the near-trench plutons-published and unpublished-have been put forth: They were emplaced along an arc that had jumped to an extreme trenchward position (Kienle and Turner, 1976); they record anatectic melting of a thick pile of recently subducted fl ysch (Hudson et al, 1979); the trench overrode a hotspot; very adjusted its shape to changes in the bathymetry of the incoming plate, changes in the convergence direction before and after ridge subduction, and changes in the strength of the prism as it was heated and then cooled. In this model, events in the Alaskan interior would have taken place above more distal, deeper parts of the slab window.…”

Section: Introductionmentioning

confidence: 99%

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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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“…(2) A belt of near-trench intrusions along Alaska's Pacifi c margin has been interpreted as having formed during ridge subduction, and thus they mark the migrating site of the elusive trench-ridge-trench triple junction (Marshak and Karig, 1977;Hill et al, 1981;Helwig and Emmet, 1981;Moore et al, 1983;Bradley et al, 1993;Pavlis and Sisson, 1995;Harris et al, 1996). These intrusions, collectively referred to as the Sanak-Baranof belt (Hudson et al, 1979), extend for 2200 km from Sanak Island on the west to Baranof Island on the east (Fig. 1).…”

Section: Evidence For Ridge Subduction Beneath Southern Alaskamentioning

confidence: 96%

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

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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.

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Paleogene anatexis along the Gulf of Alaska margin

Cited by 92 publications

References 0 publications

Low-potassium, trondhjemitic to granodioritic plutonism in the eastern Blue Ridge, southwestern North Carolina-northeastern Georgia

Low-potassium, trondhjemitic to granodioritic plutonism in the eastern Blue Ridge, southwestern North Carolina-northeastern Georgia

Geologic signature of early Tertiary ridge subduction in Alaska

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

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