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TitleLateral variation in slab window viscosity inferred from global navigation satellite system (GNSS)-observed uplift due to recent mass loss at Patagonia ice fields
AuthorRusso, R M; Luo, H; Wang, KORCID logo; Ambrosius, B; Mocanu, V; He, J; James, TORCID logo; Bevis, M; Fernandes, R
SourceGeology 2021 p. 1-5, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20210178
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf
AreaChile; Argentina
Lat/Long WENS -77.0000 -70.0000 -43.0000 -53.0000
Subjectstectonics; geophysics; surficial geology/geomorphology; Science and Technology; Nature and Environment; tectonic environments; subduction zones; mid-ocean ridges; rheology; viscosity; crustal uplift; deformation; isostasy; geodynamics; satellite geodesy; navigation satellites; glaciers; modelling; mantle; thermal analyses; Chile Ridge; Chile Triple Junction; Nazca Plate; Antarctic Plate; South America Plate; North Patagonia Ice Field; South Patagonia Ice Field; global navigation satellite systems (GNSS); Phanerozoic; Cenozoic
Illustrationsgeoscientific sketch maps; time series; 3-D models; profiles
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2021 10 08
AbstractThe geographic coincidence of the Chile Ridge slab window and the Patagonia ice fields offers a unique opportunity for assessing the effects of slab window rheology on glacial isostatic adjustment (GIA). Mass loss of these ice fields since the Little Ice Age causes rapid but variable crustal uplift, 12-24 mm/yr around the North Patagonia ice field, increasing to a maximum of 41 mm/yr around the South Patagonia ice field, as determined from newly collected or processed geodetic data. We used these observational constraints in a three-dimensional Maxwell viscoelastic finite element model of GIA response above both the subducting slab and slab window in which the upper-mantle viscosity was parameterized to be uniform with depth. We found that the viscosity of the northern part of the slab window, ~2 × 1000000000000000000 Pa·s, is lower than that of the southern part by approximately an order of magnitude. We propose that this along-strike viscosity contrast is due to late Cenozoic ridge subduction beneath the northern part of the slab window, which increases asthenospheric temperature and reduces viscosity.
Summary(Plain Language Summary, not published)
When mid-ocean ridge subducts, it creates a gap in the subducting slab called the slab window. Because slab window strongly affects changes in seismogenic behavior along a subduction zone, its mechanical properties are of great interest. Climatically induced ice melting at the Patagonia icefields causes rapid crustal uplift, and the rate of the uplift depends on the viscosity of the underlying Chile slab window. Using GPS observations of the uplift rates to constrain a 3-D model, we are able to estimate the viscosity values. We find that the younger northern part of the slab window is less viscous than the older southern part.

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