Magmatic associations of the western part of the Aleutian island arc

Borsuk, A. M.; Tsvetkov, A. A.

doi:10.1080/00206818209452409

Cited by 13 publications

(9 citation statements)

References 19 publications

(13 reference statements)

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“…The Tertiary rocks of the western region, west of Bowers Ridge, include arc and back-arc or oceanic spreading-center rocks, as well as alkaline-series volcanic rocks (Gates and others, 1971;Borsuk and Tsvetkov, 1980;Rubenstone, 1984;DiLisio, 1984). Early mid-Tertiary (exact age uncertain) mafic and silicic plutons on Attu Island (173°E) are not calc-alkaline and may have formed at an oceanic spreading center (Shelton, 1986;Kay and others, 1986;Yogodzinski and others, 1988).…”

Section: Plutons Of the Western Regionmentioning

confidence: 99%

“…Early mid-Tertiary (exact age uncertain) mafic and silicic plutons on Attu Island (173°E) are not calc-alkaline and may have formed at an oceanic spreading center (Shelton, 1986;Kay and others, 1986;Yogodzinski and others, 1988). In contrast, younger plutons (Miocene: 8.5 to 12.5 Ma) in the Komandorski Islands (USSR) (167°E) are typical subduction-related calcalkaline granodiorites (Borsuk and Tsvetkov, 1980;DiLisio, 1984). Only in the Miocene did calc-alkaline magmatism occur along the entire Aleutian arc.…”

Section: Plutons Of the Western Regionmentioning

confidence: 99%

“…In the western region of the arc, Miocene calc-alkaline granitoid rocks exposed on the southern part of Medny Island in the Komandorski Islands have been described by Borsuk and Tsvetkov (1980). The outcrops consist of dikes and small granodiorite intrusives, the largest of which is about 10 km wide.…”

Section: Miocene Calc-alkaline Plutonismmentioning

confidence: 99%

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Calc-alkaline plutonism in the intra-oceanic Aleutian arc, Alaska

Kay

Kay²,

Citron³

et al. 1990

Geological Society of America Special Papers

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Some of the best developed calc-alkaline plutons in an oceanic island arc are found in the Aleutian arc, Alaska. These Tertiary plutons are similar in many ways to continental granodioritic I-type plutons, but are smaller and have isotopic ratios and Rb contents that reflect their oceanic setting. Some differences between Aleutian plutons occur, as exemplified by the higher K content and more oxidized, lower-temperature mineralogy in the Hidden Bay pluton (Adak Island) compared to the Captains Bay pluton (Unalaska Island). This variability implies regional differences in arc crust that may reflect the 20 m.y. of arc history, including thickening of the crust to a critical value, that preceded the onset of calc-alkaline magmatism. The plutons appear to have formed during the waning stages of volcanic periods, when the magmas were too cool and crystalline to erupt. Differentiation of the gabbroic to leucogranodioritic units occurred in the lower to mid-crust, followed by buoyant rise to mid-to upper-crustal magma chambers where final crystallization, and segregation of aplites occurred. Mafic dikes that intrude the plutons represent magmas that were able to fracture their way through the largely solidified pluton from below. Many gabbros and mafic diorite units in the plutons are crystal cumulates, and have no equivalents among volcanic rocks and dikes. In contrast, the predominant silicic plutonic units (58 to 63 percent SiC>2) and silicic volcanic rocks (or, in hybrid magmas, mixing end members) are similar. Whether these silicic magmas are deep-crustal differentiates of a high-AI basalt or high-temperature partial melts of older mafic arc volcanic rocks is difficult to discern because of the small chemical contrast between Aleutian magmas and country rock. Either model implies a large volume of lower-crustal mafic and ultramafic rock complementary to the observed upper-crustal plutons.

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Section: Plutons Of the Western Regionmentioning

confidence: 99%

Section: Plutons Of the Western Regionmentioning

confidence: 99%

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Calc-alkaline plutonism in the intra-oceanic Aleutian arc, Alaska

Kay

Kay²,

Citron³

et al. 1990

Geological Society of America Special Papers

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“… Histogram of published geochronologic data >3 Ma for the Aleutian Arc west of 164° W subdivided by existing K‐Ar (pink), 40 Ar/ 39 Ar (light blue), and U‐Pb (green) ages [ Carr et al , ; Cameron and Stone , ; von Huene et al , ; Marlow et al , ; DeLong and McDowell, 1975; Scholl et al , ; DeLong et al , ; Marvin and Cole , ; Hein and McLean, ; Citron et al ,; Borsuk and Tsvetkov, ; McLean et al , ; McLean and Hein, ; Wilson et al , ; Jicha et al , ; Layer et al , ; Cai et al , ] and the 40 Ar/ 39 Ar ages from this study (dark blue, Table 1).…”

Section: Discussionmentioning

confidence: 99%

Eocene to Pleistocene magmatic evolution of the Delarof Islands, Aleutian Arc

Schaen

Jicha

Kay

et al. 2016

Geochem Geophys Geosyst

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The Delarof Islands in the Aleutian Arc near 179º W record ∼37 million years of discontinuous arc magmatism along a SW‐NE cross‐arc transect from near the trench to the active volcanic front. Geochemical and geochronologic data from the pre‐Pleistocene volcanic record in this region are limited and the 40Ar/39Ar, isotopic, and trace element data presented here are the first from units older than the Pleistocene‐Holocene volcanoes (Tanaga, Gareloi). Twenty‐two new 40Ar/39Ar ages establish a temporal framework for geochemical data and reveal that magmatism in the Delarof region was coincident with two arc‐wide magmatic flare ups in the late Eocene/early Oligocene and latest Miocene/Pliocene. Mafic lavas and plutons in the southern Delarofs give 40Ar/39Ar plateau ages ranging from 36.8 ± 0.2 to 26.9 ± 0.6 Ma on Amatignak Island and 37.0 ± 0.2 to 29.3 ± 1.0 Ma on Ulak Island. To the north 25 km, 40Ar/39Ar ages from the central Delarof Islands, Kavalga, Ogliuga, and Skagul are late Miocene (6.28 ± 0.04 Ma) to Pliocene (4.77 ± 0.18 Ma) with younger ages to the northeast. A significant transition in arc chemistry occurs in the Pleistocene where lavas from active volcanoes Gareloi and Tanaga exhibit higher sediment and hydrous fluid signatures (Th/La, Cs/Ta, La/Sm, LILE abundances) and lower 143Nd/144Nd than older Delarof Island units closer to the trench. Similar findings from Eocene‐Miocene lavas from Amchitka to Adak suggest that a previously minor sediment melt component became more pronounced in the Quaternary.

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“…On Attu Island (173øE), however, some 100 km west of the dredge site, the youngest known volcanic rocks have been dated as being between 5.9 and 7.4 Ma [Delong and McDowell, 1975]. Farther west in the Komandorsky (Commander) Islands (167øE), the westernmost islands of the Aleutian chain, the youngest known volcanic rocks have been dated between 8.5 and 12.5 Ma [Scholl et al, 1976;Borsuk and Tsvetkov, 1982]. Since these ages were determined by whole-rock analysis, however, Scholl et al [1976] suggest that they are minimum age estimates and, on the basis of diatom flora within associated sedimentary rocks, conclude that the age of extrusion was sometime between 9 and 14 Ma.…”

Section: Introductionmentioning

confidence: 99%

The geometry of Aleutian subduction: Three‐dimensional kinematic flow model

Creager¹,

Boyd²

1991

J. Geophys. Res.

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We construct a steady state kinematic model of slab flow along the Aleutian Arc assuming the slab's geometry is known. The slab geometry is constrained by local network data where the slab is seismically active and by P wave residual‐sphere analysis of 11 earthquakes and one nuclear explosion where it is aseismic. The slab is approximated by a thin Newtonian sheet subducting in a less viscous and incompressible mantle. Particles enter the trench at known rates of relative plate motion and are required to subduct along the predefined slab geometry. For discrete, but small (0.1 m.y.) time steps, we determine the speed and direction of each slab particle that minimizes dissipation power as the spherical shell (oceanic lithosphere) deforms to obtain the observed slab shape. Because the dip of the slab in the central Aleutians is steep relative to the radius of curvature of the trench, the slab must stretch along arc to obtain its present configuration. Our kinematic model represents one internally consistent flow that results in the observed geometry. Furthermore, it provides a lower bound on the total amount of internal in‐plane deformation required by the shape and an estimate of stream lines and of the orientation and spatial distribution of the deformation rate. The predicted in‐plane strain rate field is dominated by along arc extension, reaching values as large as 10−15s−1 in the central Aleutians and decaying by an order of magnitude to the east and west. The slab accumulates an in‐plane strain of 10% by the time it reaches the depth of the seismicity cutoff. Along‐arc variations in both the magnitude and orientation of calculated strain rates are consistent with the spatial distribution of seismic moment release and source mechanism orientations of intermediate‐depth earthquakes, suggesting that in order to understand intermediate‐focus earthquakes one must consider along‐arc deformation. Three‐dimensional analyses of subduction in a spherical geometry, such as the present study, are required to model along‐arc effects. Relative plate motions along the trench vary from nearly normal in the eastern Aleutians to transform farther west. Coincident with this change, the maximum depth of seismicity within the descending slab decreases from 250 to 50 km and active andesitic volcanism ceases. The kinematic flow model predicts that the slab subducted obliquely along the central portion of the Aleutian Arc is transported laterally westward producing cold slab material to a depth of at least 300 km along the entire arc after only 15 m.y. of subduction. The lack of volcanic activity in the western Aleutians is apparently related to the lateral transport of the slab, perhaps indicating that the slab is dehydrated and incapable of producing the volatiles necessary for arc magmatism. The along‐arc variation in the maximum depth of seismicity can be explained thermally. We construct temperature estimates within the slab using a quasi three‐dimensional finite difference scheme, including entrained mantle flow, stream lines f...

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Magmatic associations of the western part of the Aleutian island arc

Cited by 13 publications

References 19 publications

Calc-alkaline plutonism in the intra-oceanic Aleutian arc, Alaska

Calc-alkaline plutonism in the intra-oceanic Aleutian arc, Alaska

Eocene to Pleistocene magmatic evolution of the Delarof Islands, Aleutian Arc

The geometry of Aleutian subduction: Three‐dimensional kinematic flow model

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