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The Tungnárhraun basalts in southern Iceland record a transcrustal magma system formed during Holocene deglaciation. These large-volume (>1 km3) Early through Mid-Holocene lavas contain ubiquitous plagioclase feldspar macrocrysts that are too primitive to have grown from the host lavas. Thermobarometry based on plagioclase melt and clinopyroxene melt equilibrium reveals a transcrustal structure with at least three distinct storage regions. A lower-crustal mush zone at ~14–30 km is fed by primitive, low 87Sr/86Sr magmas with diverse Ti/K and Al/Ti signatures. Plagioclase feldspar growth is controlled by an experimentally determined pseudoazeotrope where crystals develop inversely correlated An and Mg contents. The rapid ascent of magmas to mid-crustal levels (~8–9 km) allows the feldspar system to revert to conventional thermodynamic phase constraints. Continued plagioclase growth releases heat, causing olivine and pyroxene to be resorbed and giving the magmas their characteristic high CaO/Al2O3 values (~0.8–1.0) and Sc contents (~52 ppm in matrix material). Mid-Holocene MgO-rich lavas with abundant plagioclase feldspar macrocrysts erupted directly from this depth, but both older and younger magmas ascended to a shallow-crustal storage chamber (~5 km) where they crystallized olivine, clinopyroxene, and plagioclase feldspar and evolved to lower MgO contents. The Sr isotope differences between the plagioclase macrocrysts and their carrier melts suggest that the fractionation involves the minor assimilation of country rock. This model does not require the physical disruption of an established and long-lived gabbroic cumulate mush. The transcrustal structures documented here existed in south Iceland at least throughout the Holocene and likely influenced much of Icelandic magmatism. 

Abstract Practitioners and researchers in geoscience education embrace collaboration applying ICON (Integrated, Coordinated, Open science, and Networked) principles and approaches which have been used to create and share large collections of educational resources, to move forward collective priorities, and to foster peer‐learning among educators. These strategies can also support the advancement of coproduction between geoscientists and diverse communities. For this reason, many authors from the geoscience education community have co‐created three commentaries on the use and future of ICON in geoscience education. We envision that sharing our expertise with ICON practice will be useful to other geoscience communities seeking to strengthen collaboration. Geoscience education brings substantial expertise in social science research and its application to building individual and collective capacity to address earth sustainability and equity issues at local to global scales The geoscience education community has expanded its own ICON capacity through access to and use of shared resources and research findings, enhancing data sharing and publication, and leadership development. We prioritize continued use of ICON principles to develop effective and inclusive communities that increase equity in geoscience education and beyond, support leadership and full participation of systemically non‐dominant groups and enable global discussions and collaborations. 

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.