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The Dais Intrusion in upper Wright Valley is a spectacular layered intrusion connected to Bull Pass by the Basement Sill, the connection of which can be traced along the south wall of Wright Valley, with the layering becoming more distinct and cleaner with distance to the Dais. The Dais Intrusion is relatively small for a body as well layered as this: it is perhaps 1,000 m thick but only the upper half is visible. The lower half of the visible section is coarse grained ultramafic orthopyroxenite with 20 wt.% MgO, containing several periodic meter-thick anorthosite layers, which are lobate in nature, perhaps reflecting formation by avalanching slurries. The upper half of the Dais Intrusion is more tholeiitic in bulk composition, and the transition between top and bottom is dramatic, marking event horizons, much like the transition between mantle and oceanic crust for Earth as a planet. The style of layering becomes more delicate upwards in the section. Because the body cooled relatively quickly many annealing processes have been quenched prior to full completion. These are clearly textural processes that actively operate in many larger bodies but are never seen because of strong long term annealing effects.
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