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This dataset accompanies planned publication 'Near-Ridge Magmatism Constrained Using 40Ar/39Ar Dating of Enriched MORB from the 8°20' N Seamount Chain'. The Ar/Ar data are for samples that record the volcanic history of the area. The geochronology provides time constraints for the eruption of rocks studied in the manuscript. Samples were collected from the 8°20' N seamount chain by Molly Anderson (University of Florida), who sent them to the USGS Denver Argon Geochronology Laboratory for Ar/Ar analysis. 

Constraining the subsurface structural geometry of the central Himalaya continues to prove difficult, even after the 2015 Gorkha earthquake and the resulting insights into the trajectory of the Main Himalayan thrust (MHT). To this end, we apply a thermokinematic model to evaluate four possible balanced cross section geometries based on three estimates of the MHT in central Nepal. We compare the effect of different décollement and duplex geometries on predicted cooling ages and compare these to new and published ages. We find that the best‐fit geometry able to reproduce the cooling ages at the surface is a hinterland‐dipping duplex, which has been translated over a mid‐crustal ramp located ~110 km north of the Main Frontal thrust. We find that the temporal evolution of the duplex and MHT mid‐crustal ramp both play an integral role in producing the observed cooling ages, implying that the common assumption that the active décollement and ramp geometry solely control the distribution of cooling ages is incorrect. Furthermore, results indicate that the Ramgarh‐Munsiari thrust was emplaced between 17 and ~10 Ma, followed by the Trishuli thrust. Duplex growth occurs between 6.5 and 0.75 Ma, with its constituent thrust sheets moving at variable rates between 10 and 42 mm/yr. Young out‐of‐sequence thrusting (5 km of displacement) in the hinterland produces a slightly improved fit to the cooling ages. Finally, the resulting thermal field modeled from our best‐fit geometry suggests a possible basis for the nucleation and rupture characteristics of the Gorkha earthquake.

 

Abstract The 40Ar/39Ar dating method is among the most versatile of geochronometers, having the potential to date a broad variety of K-bearing materials spanning from the time of Earth’s formation into the historical realm. Measurements using modern noble-gas mass spectrometers are now producing 40Ar/39Ar dates with analytical uncertainties of ∼0.1%, thereby providing precise time constraints for a wide range of geologic and extraterrestrial processes. Analyses of increasingly smaller subsamples have revealed age dispersion in many materials, including some minerals used as neutron fluence monitors. Accordingly, interpretive strategies are evolving to address observed dispersion in dates from a single sample. Moreover, inferring a geologically meaningful “age” from a measured “date” or set of dates is dependent on the geological problem being addressed and the salient assumptions associated with each set of data. We highlight requirements for collateral information that will better constrain the interpretation of 40Ar/39Ar data sets, including those associated with single-crystal fusion analyses, incremental heating experiments, and in situ analyses of microsampled domains. To ensure the utility and viability of published results, we emphasize previous recommendations for reporting 40Ar/39Ar data and the related essential metadata, with the amendment that data conform to evolving standards of being findable, accessible, interoperable, and reusable (FAIR) by both humans and computers. Our examples provide guidance for the presentation and interpretation of 40Ar/39Ar dates to maximize their interdisciplinary usage, reproducibility, and longevity. 

Understanding, and ideally quantifying, the relative roles of climatic and tectonic processes during orogenic exhumation is critical to resolving the dynamics of mountain building. However, vastly differing opinions regarding proposed drivers often complicate how thermochronometric ages are interpreted, particularly from the hinterland portions of thrust belts. Here we integrate three possible cross‐section geometries and kinematics along a transect through the eastern Bhutan Himalaya with a thermal model (Pecube‐D) to calculate the resulting thermal field and predict potential ages. We compare predicted ages to a suite of new and published cooling ages. Our results argue for ramp‐focused exhumation of the Main Central thrust from 16 to 14 Ma at shortening rates of 40–55 mm/year, followed by slower rates (25 mm/year) during the last 50 km of Main Central thrust displacement and growth of the Lesser Himalayan duplex from 14 to 11 Ma. Emplacement of frontal Lesser Himalayan thrust sheets occurred rapidly (55–70 mm/year) between ~11 and 9 Ma, followed by a decrease in shortening rates to ~10 mm/year during motion on the Main Boundary thrust. Modern shortening rates (17 mm/year) and out‐of‐sequence motion on the Main Boundary thrust from 0.5 Ma to present reproduce the young cooling ages near the Main Boundary thrust. We show that the dominant control on exhumation patterns in a fold‐thrust belt results from the evolution of ramps and emphasize that the geometry and kinematics of structures driving hinterland exhumation need to be evaluated with their linked foreland structures to ensure the viability of the proposed geometry, kinematics, and thus cooling history.