Geological and Geochemical Constraints on Oligo-Miocene Hypabyssal Intrusive Bodies From the Wrangell Arc, Alaska

Brueseke, Matthew E.; Benowitz, Jeff; Trop, Jeffrey M.; Berkelhammer, Samuel E.; Davis, Kailyn N.; Layer, Paul W.; Morter, Bethany K.; Mertzman, Stanley A.

doi:10.1130/abs/2017cd-292655

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“…30-20 Ma), reflecting one or more tectonic processes that we interpret to reflect anomalous heating of the Yakutat slab and/or mafic lower crust and variable production of fluids from the descending slab. Adakite-like affinities and ages that overlap with early SCVF volcanism also characterize hypabyssal units that are exposed ~40-100 km west of the SCVF (Weber et al, 2017). These intrusions and the SCVF likely represent the early initial extent of the WA, even though the SCVF was subsequently offset laterally along the Totschunda fault.…”

Section: ■ Conclusionmentioning

confidence: 90%

“…29-22 Ma along the northern flank of the WA (data shown in dashed field in Fig. 14C; Weber et al, 2017). The two Ptarmigan Creek high-Si adakites (15JB15LA and 15JB16LA) have high Sr/Y (15JB15LA has high La/Yb) and may represent a differentiated product of an adakite-like magma that formed via melting of a slab edge or lower crust during subduction initiation (Defant and Drummond, 1990;Sajona et al, 1993;Peacock et al, 1994) and then underwent mixing with another primitive mantle-wedge melt to produce the geochemical array of the Rocker Creek volcanics.…”

Section: Adakite-like Signature In Rocker Creek and Ptarmigan Creek Vmentioning

confidence: 99%

“…The location of the SCVF, as well as that of geochemically and temporally similar ca. 30-20 Ma hypabyssal rocks from the northern flank of the modern WA, designate the position of the WA at its initiation (Weber et al, 2017). These hypabyssal rocks and the SCVF define a <100-km-long, northwest-trending outcrop belt that is displaced by the Totschunda fault (Figs.…”

Section: Original Extent and Postemplacement Lateral Shuffling Of Thementioning

confidence: 99%

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Geochemical and geochronological records of tectonic changes along a flat-slab arc-transform junction: Circa 30 Ma to ca. 19 Ma Sonya Creek volcanic field, Wrangell Arc, Alaska

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The Sonya Creek volcanic field (SCVF) contains the oldest in situ volcanic products in the ca. 30 Ma–modern Wrangell Arc (WA) in south-central Alaska, which commenced due to Yakutat microplate subduction initiation. The WA occurs within a transition zone between Aleutian subduction to the west and dextral strike-slip tectonics along the Queen Charlotte–Fairweather and Denali–Duke River fault systems to the east. New 40Ar/39Ar geochronology of bedrock shows that SCVF magmatism occurred from ca. 30–19 Ma. New field mapping, physical volcanology, and major- and trace-element geochemistry, coupled with the 40Ar/39Ar ages and prior reconnaissance work, allows for the reconstruction of SCVF magmatic evolution. Initial SCVF magmatism that commenced at ca. 30 Ma records hydrous, subduction-related, calc-alkaline magmatism and also an adakite-like component that we interpret to represent slab-edge melting of the Yakutat slab. A minor westward shift of volcanism within the SCVF at ca. 25 Ma was accompanied by continued subduction-related magmatism without the adakite-like component (i.e., mantle-wedge melting), represented by ca. 25–20 Ma basaltic-andesite to dacite domes and associated diorites. These eruptions were coeval with another westward shift to anhydrous, transitional-tholeiitic, basaltic-andesite to rhyolite lavas and tuffs of the ca. 23–19 Ma Sonya Creek shield volcano; we attribute these eruptions to intra-arc extension. SCVF activity was also marked by a small southward shift in volcanism at ca. 21 Ma, characterized by hydrous calc-alkaline lavas. SCVF geochemical compositions closely overlap those from the <13 Ma WA, and no alkaline lavas that characterize the ca. 18–10 Ma eastern Wrangell volcanic belt exposed in Yukon Territory are observed. Calc-alkaline, transitional-tholeiitic, and adakite-like SCVF volcanism from ca. 30–19 Ma reflects subduction of oceanic lithosphere of the Yakutat microplate beneath North America. We suggest that the increase in magmatic flux and adakitic eruptions at ca. 25 Ma, align with a recently documented change in Pacific plate direction and velocity at this time and regional deformation events in southern Alaska. By ca. 18 Ma, SCVF activity ceased, and the locus of WA magmatism shifted to the south and east. The change in relative plate motions would be expected to transfer stress to strike-slip faults above the inboard margin of the subducting Yakutat slab, a scenario consistent with increased transtensional-related melting recorded by the ca. 23–19 Ma transitional-tholeiitic Sonya Creek shield volcano between the Denali and Totschunda faults. Moreover, we infer the Totschunda fault accommodated more than ∼85 km of horizontal offset since ca. 18 Ma, based on reconstructing the initial alignment of the early WA (i.e., 30–18 Ma SCVF) and temporally and chemically similar intrusions that crop out to the west on the opposite side of the Totschunda fault. Our results from the SCVF quantify spatial-temporal changes in deformation and magmatism that may typify arc-transform junctions over similar time scales (>10 m.y.).

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Section: ■ Conclusionmentioning

confidence: 90%

Section: Adakite-like Signature In Rocker Creek and Ptarmigan Creek Vmentioning

confidence: 99%

Section: Original Extent and Postemplacement Lateral Shuffling Of Thementioning

confidence: 99%

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Geochemical and geochronological records of tectonic changes along a flat-slab arc-transform junction: Circa 30 Ma to ca. 19 Ma Sonya Creek volcanic field, Wrangell Arc, Alaska

et al. 2019

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Geological and Geochemical Constraints on Oligo-Miocene Hypabyssal Intrusive Bodies From the Wrangell Arc, Alaska

Cited by 1 publication

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Geochemical and geochronological records of tectonic changes along a flat-slab arc-transform junction: Circa 30 Ma to ca. 19 Ma Sonya Creek volcanic field, Wrangell Arc, Alaska

Geochemical and geochronological records of tectonic changes along a flat-slab arc-transform junction: Circa 30 Ma to ca. 19 Ma Sonya Creek volcanic field, Wrangell Arc, Alaska

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