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We present the first petrographic, lithogeochemical, and geochronological study of the Bayanteeg LCT pegmatite located in Idermeg terrane, central Mongolia, and interpret the findings within the geodynamic setting. The pegmatite extends over 140 m with a width of 1.3 m and unknown depth within Neoproterozoic gneiss. The pegmatite contains plagioclase, quartz, and lepidolite with minor K-feldspar, spodumene, muscovite, and topaz, and accessory amounts of cassiterite, amblygonite, columbite-tantalite, monazite, zircon, apatite, and fluorite. Locally, minor secondary quartz and lepidolite occur interstitially between plagioclase and quartz and along the edges of primary lepidolite, respectively, implying late-stage hydrothermal influence. Lithogeochemical data show that the pegmatite contains 0.3–1.12 wt% Li, 256–1285 ppm Cs, and 59–522 ppm Ta. Monazite U-Th-Pb geochronology yielded an age of 144.9 ± 2.8 Ma while cassiterite yielded a U-Pb age of 134.8 ± 1.4 Ma. Lepidolite yielded 40Ar/39Ar plateau age of 131.25 ± 0.3 Ma. These age results fall during the geodynamic evolution of an intracontinental extension accompanied by the exhumation of metamorphic core complexes and extensive magmatism in the eastern Central Asian Orogenic Belt. These events occurred due to a combination of gravitational collapse resulting from lithospheric delamination and asthenospheric upwelling. The geodynamic setting during the pegmatite emplacement implies abnormally hot conditions, ruling out the possibility of anatectic origin. The pegmatite dike with elevated concentrations of Be, Ga, Rb, Nb, Sn, Cs, Ta, and Tl supports a granitic origin with a hidden parental granite at depth. The fact that the Idermeg terrane contains several LCT pegmatites implies an important exploration target for Li exploration. 

Abstract Basaltic lavas from Harrat Uwayrid, Saudi Arabia, record the evolving magmatic and tectonic context of the Arabian Peninsula from at least the mid‐Miocene to the present day. New⁴⁰Ar/³⁹Ar ages spanning from the mid to late Miocene reveal that mid‐Miocene mafic volcanism formed a large, subalkaline volcanic plateau parallel to Red Sea rifts. Subsequent volumetrically subordinate late Miocene‐Quaternary alkaline volcanism erupted monogenetic cinder cones roughly orthogonal to the earlier volcanic field. The source region for all samples was affected by both fluid and silicate metasomatism; inferred mantle mineral assemblages include amphibole for mid‐Miocene lavas and phlogopite for late Miocene‐Quaternary samples. Calculated melting depths become shallower with time across the Miocene volcanic episode (∼20–15 Ma) but become deeper in the late Miocene to Quaternary (∼10–0 Ma), indicating melting pressures and temperatures significantly higher than those recorded in Miocene lavas despite progressive lithospheric thinning. We offer a two‐stage model for the formation of Harrat Uwayrid: (a) Early‐ and mid‐Miocene rifting associated with the Red Sea opening facilitated adiabatic melting of uppermost mantle lithosphere to form the early volcanic plateau and (b) Plate motion changes in the mid‐ and late‐Miocene initiated the Dead Sea Fault and destabilized a dense pyroxenitic lower lithosphere leading to foundering or lithospheric drip beneath Harrat Uwayrid that allowed deep lithospheric melting and formed the young volatile‐rich eruptives. 

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.