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Abstract The Wrangell Arc in Alaska (USA) and adjacent volcanic fields in the Yukon provide a long-term record of interrelations between flat-slab subduction of the Yakutat microplate, strike-slip translation along the Denali–Totschunda–Duke River fault system, and magmatism focused within and proximal to a Cretaceous suture zone. Detrital zircon (DZ) U-Pb (n = 2640) and volcanic lithic (DARL) 40Ar/39Ar dates (n = 2771) from 30 modern river sediment samples document the spatial-temporal evolution of Wrangell Arc magmatism, which includes construction of some of the largest Quaternary volcanoes on Earth. Mismatches in DZ and DARL date distributions highlight the impact of variables such as mineral fertility and downstream mixing/dilution on resulting provenance signatures. Geochronologic data document the initiation of Wrangell Arc magmatism at ca. 30–17 Ma along both sides of the Totschunda fault on the north flank of the Wrangell–St. Elias Mountains in Alaska, followed by southeastward progression of magmatism at ca. 17–10 Ma along the Duke River fault in the Yukon. This spatial-temporal evolution is attributable to dextral translation along intra-arc, strike-slip faults and a change in the geometry of the subducting slab (slab curling/steepening). Magmatism then progressed generally westward outboard of the Totschunda and Duke River faults at ca. 13–6 Ma along the southern flank of the Wrangell–St. Elias Mountains in Alaska and then northwestward from ca. 6 Ma to present in the western Wrangell Mountains. The 13 Ma to present spatial-temporal evolution is consistent with dextral translation along intra-arc, strike-slip faults and previously documented changes in plate boundary conditions, which include an increase in plate convergence rate and angle at ca. 6 Ma. Voluminous magmatism is attributed to shallow subduction-related flux melting and slab edge melting that is driven by asthenospheric upwelling along the lateral edge of the Yakutat flat slab. Magmatism was persistently focused within or adjacent to a remnant suture zone, which indicates that upper plate crustal heterogeneities influenced arc magmatism. Rivers sampled also yield subordinate Paleozoic–Mesozoic DZ and DARL age populations that reflect earlier episodes of magmatism within underlying accreted terranes and match magmatic flare-ups documented along the Cordilleran margin.
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The Alaska Wrangell Arc: ~30 Ma of subduction‐related magmatism along a still active arc‐transform junction
Abstract The Oligocene to Present Wrangell Volcanic Belt (WVB) extends for ~500 km across south‐central Alaska (USA) into Canada at a volcanic arc‐transform junction. Previously, geochemistry documented mantle wedge and slab‐edge melting in <12 MaWVBvolcanic rocks; new geochemistry shows that the same processes characterized ~18–30 MaWVBmagmatism in Alaska. New40Ar/39Ar ages demonstrate thatWVBmagmatism in Alaska initiated at ~30 Ma due to flat‐slab subduction of the Yakutat microplate and that the dextral Totschunda fault was active at this time. Our results, together with prior studies, show that AlaskanWVBmagmatism occurred chiefly due to subduction and should be considered a volcanic arc (e.g. the Wrangell Arc). TheWVBprovides a long‐term geological record of subduction, strike‐slip and magmatism. Slab‐edge upwelling, flat‐slab defocused fluid‐flux and faults acting as magma conduits are likely responsible for the exceptionally large volcanoes and high eruption rates of the Wrangell Arc.
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- Award ID(s):
- 1450730
- PAR ID:
- 10462837
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Terra Nova
- Volume:
- 31
- Issue:
- 1
- ISSN:
- 0954-4879
- Page Range / eLocation ID:
- p. 59-66
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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