Abstract
Abstract Silicic segregation veins in the Basement Sill, Dry Valleys, Antarctica, represent fracture-filling liquids differentiated from mid-Jurassic Ferrar tholeiitic basalt magmas. Geochemical and mineralogical characterizations for several of these veins and for their host gabbros within centimeters of sharp contacts with the veins provide information about silicic liquid produced from basalt in closed systems. The Basement Sill silicic veins are coarse- to pegmatite-textured diorites (∼60 wt% SiO2; 1.6%–2.6% MgO) composed of Fe-rich clinopyroxene (cpx; Fs20-60) and orthopyroxene (and pigeonite), ∼An50-60 plagioclase, and ∼20–30 vol% mesostases of micrographic quartz + alkali feldspar (∼Or80-90). The host gabbros (52–54 wt% SiO2; 5.5%–9.2% MgO) within ∼2 cm of veins contain pyroxene and feldspar with compositions that range from overlapping those in the diorite veins to those closer to characteristic of gabbro (e.g., cpx ∼Fs20; ∼An60-80) but unlike the more primitive mineral compositions representing t...
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