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1. Inherited Upper-Plate Controls on Localized Arc Magmatism Since ca. 100Ma Along the Alaska Range Suture Zone

   https://doi.org/10.1002/9781394195947.ch19  

   Benowitz, Jeffrey A; Mann, Michael Everett (November 2024, Wiley)

   Ruppert, Natalia A; Jadamec, Margarete A; Freymueller, Jeffrey T (Ed.)

   Long-lived continental magmatic arcs may migrate large (hundreds of kilometers) trench perpendicular distances as convergent margin configurations and slab geometry vary over time; however, many arc-magmatic belts are spatially localized over tens of millions of years.We document, by compiling published crystallization geochronology data for southern Alaska (6,485 total bedrock and single-grain detrital ages combined), that since ca. 100 Ma, arc magmatism has been localized along the Alaska Range suture zone (in places within a 10km × 5km swath) and at times over 500km inboard. However, since ca. 100 Ma, incoming subducting slab characteristics and convergent margin configurations varied greatly and include both normal oceanic plate and oceanic plateau subduction, plate vector changes, oroclinal bending and reconfiguration of trench shape, terrane accretion, long-distance terrane translation, and a Paleocene slab break off/slab window event. Therefore, it is inferred that inherited upper-plate lithospheric thickness and thermal variations must control in part the geometry of the subducting slab below a mobile southern Alaskan margin through hydrodynamic mantle wedge “suction” forces. Additionally, crustal thickness heterogeneity may focus magma ascent through melt ponding along Moho offsets, and upper-plate lithospheric-scale strike-slip faults may be acting as passive and active conduits for arc magmatism. 

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2. Crustal bobbing in response to lithospheric foundering recorded by detrital proxy records from the central Andean Plateau

   https://doi.org/10.1130/G52455.1  

   Carrapa, B; Jepson, G; DeCelles, PG; George, SWM; Ducea, M; Campbell, C; Dawson_née_Canavan, RR (October 2024, Geology)

   Abstract Lithospheric foundering is an important mechanism of crustal deformation and recycling, basin subsidence, and surface uplift in orogenic systems. The Arizaro Basin, in the Puna region of NW Argentina, is a place where foundering was proposed to have taken place during the late Miocene. The Arizaro Basin has been described as a “bobber” basin produced by Miocene lithospheric foundering. The geometry, sedimentology, deformation, and paleoelevation history of the Arizaro Basin and surrounding arc suggest dynamic processes associated with lithospheric removal. Although analogue and numerical models support this hypothesis, the history of crustal thickness in response to lithospheric removal remains unconstrained. Here, we used a novel approach exploiting the geochemistry of detrital zircons from volcanic ashes intercalated within the Arizaro Basin stratigraphy to reconstruct the paleocrustal thickness of the neighboring magmatic sources throughout the Cenozoic. Our data indicate that the sources of volcanism for the Arizaro Basin were characterized by relatively thick crust (~53 km) since ca. 36 Ma. Thickening between ca. 20 and 13 Ma and thinning after ca. 13 Ma are consistent with formation and subsequent removal of a crustal root under the nearby arc and Aguas Calientes caldera. 

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3. Geochemical evidence for an orogenic plateau in the southern U.S. and northern Mexican Cordillera during the Laramide orogeny

   https://doi.org/10.1130/G47117.1  

   Chapman, James B.; Greig, Roy; Haxel, Gordon B. (November 2019, Geology)

   Abstract Previous studies of the central United States Cordillera have indicated that a high-elevation orogenic plateau, the Nevadaplano, was present in Late Cretaceous to early Paleogene time. The southern United States Cordillera and northern Mexican Cordillera share a similar geologic history and many of the same tectonic features (e.g., metamorphic core complexes) as the central United States Cordillera, raising the possibility that a similar plateau may have been present at lower latitudes. To test the hypothesis of an elevated plateau, we examined Laramide-age continental-arc geochemistry and employed an empirical relation between whole-rock La/Yb and Moho depth as a proxy for crustal thickness. Calculations of crustal thickness from individual data points range between 45 and 72 km, with an average of 57 ± 12 km (2σ) for the entire data set, which corresponds to 3 ± 1.8 km paleoelevation assuming simple Airy isostasy. These crustal thickness and paleoaltimetry estimates are similar to previous estimates for the Nevadaplano and are interpreted to suggest that an analogous high-elevation plateau may have been present in the southern United States Cordillera. This result raises questions about the mechanisms that thickened the crust, because shortening in the Sevier thrust belt is generally not thought to have extended into the southern United States Cordillera, south of ∼35°N latitude. 

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4. Record of Crustal Thickening and Synconvergent Extension from the Dajiamang Tso Rift, Southern Tibet

   https://doi.org/10.3390/geosciences11050209  

   Burke, William; Laskowski, Andrew; Orme, Devon; Sundell, Kurt; Taylor, Michael; Guo, Xudong; Ding, Lin (May 2021, Geosciences)

   Carosi, Rodolfo; da Costa Campos Neto, Mario; Fossen, Hakkon; Montomoli, Chiara; Simonetti, Matteo; Martinez-Frias, Jesus (Ed.)

   North-trending rifts throughout south-central Tibet provide an opportunity to study the dynamics of synconvergent extension in contractional orogenic belts. In this study, we present new data from the Dajiamang Tso rift, including quantitative crustal thickness estimates calculated from trace/rare earth element zircon data, U-Pb geochronology, and zircon-He thermochronology. These data constrain the timing and rates of exhumation in the Dajiamang Tso rift and provide a basis for evaluating dynamic models of synconvergent extension. Our results also provide a semi-continuous record of Mid-Cretaceous to Miocene evolution of the Himalayan-Tibetan orogenic belt along the India-Asia suture zone. We report igneous zircon U-Pb ages of ~103 Ma and 70–42 Ma for samples collected from the Xigaze forearc basin and Gangdese Batholith/Linzizong Formation, respectively. Zircon-He cooling ages of forearc rocks in the hanging wall of the Great Counter thrust are ~28 Ma, while Gangdese arc samples in the footwalls of the Dajiamang Tso rift are 16–8 Ma. These data reveal the approximate timing of the switch from contraction to extension along the India-Asia suture zone (minimum 16 Ma). Crustal-thickness trends from zircon geochemistry reveal possible crustal thinning (to ~40 km) immediately prior to India-Eurasia collision onset (58 Ma). Following initial collision, crustal thickness increases to 50 km by 40 Ma with continued thickening until the early Miocene supported by regional data from the Tibetan Magmatism Database. Current crustal thickness estimates based on geophysical observations show no evidence for crustal thinning following the onset of E–W extension (~16 Ma), suggesting that modern crustal thickness is likely facilitated by an underthrusting Indian lithosphere balanced by upper plate extension. 

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5. Outboard Onset of Ross Orogen Magmatism and Subsequent Igneous and Metamorphic Cooling Linked to Slab Rollback during Late-Stage Gondwana Assembly

   https://doi.org/10.3390/geosciences13040126  

   Paulsen, Timothy; Encarnación, John; Grunow, Anne; Benowitz, Jeffrey; Layer, Paul; Deering, Chad; Sliwinski, Jakub (April 2023, Geosciences)

   Changes in magmatism and sedimentation along the late Neoproterozoic-early Paleozoic Ross orogenic belt in Antarctica have been linked to the cessation of convergence along the Mozambique belt during the assembly of East-West Gondwana. However, these interpretations are non-unique and are based, in part, on limited thermochronological data sets spread out along large sectors of the East Antarctic margin. We report new 40Ar/39Ar hornblende, muscovite, and biotite age data for plutonic (n = 13) and metasedimentary (n = 3) samples from the Shackleton–Liv Glacier sector of the Queen Maud Mountains in Antarctica. Cumulative 40Ar/39Ar age data show polymodal age peaks (510 Ma, 491 Ma, 475 Ma) that lag peaks in U-Pb igneous crystallization ages, suggesting igneous and metamorphic cooling following magmatism within the region. The 40Ar/39Ar ages are similar to ages in other sectors of the Ross orogen, but younger than detrital mineral 40Ar/39Ar cooling ages indicative of older magmatism and cooling of unexposed inboard areas along the margin. Detrital zircon trace element abundances suggest that the widespread onset of magmatism in outboard localities of the orogen correlates with a ~560–530 Ma decrease in crustal thickness. The timing of crustal thinning recorded by zircon in magmas overlaps with other evidence for the timing of crustal extension, suggesting that the regional onset of magmatism with subsequent igneous and metamorphic cooling probably reflects slab rollback that coincided with possible global plate motion changes induced during the final assembly of Gondwana. 

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