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7 - Dais Layered Intrusion

Published online by Cambridge University Press:  17 February 2023

Bruce Marsh
Affiliation:
Johns Hopkins University
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Summary

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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Publisher: Cambridge University Press
Print publication year: 2023

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  • Dais Layered Intrusion
  • Bruce Marsh, Johns Hopkins University
  • Book: Magmatism in the McMurdo Dry Valleys, Antarctica
  • Online publication: 17 February 2023
  • Chapter DOI: https://doi.org/10.1017/9781009177078.008
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  • Dais Layered Intrusion
  • Bruce Marsh, Johns Hopkins University
  • Book: Magmatism in the McMurdo Dry Valleys, Antarctica
  • Online publication: 17 February 2023
  • Chapter DOI: https://doi.org/10.1017/9781009177078.008
Available formats
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Save book to Google Drive

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

  • Dais Layered Intrusion
  • Bruce Marsh, Johns Hopkins University
  • Book: Magmatism in the McMurdo Dry Valleys, Antarctica
  • Online publication: 17 February 2023
  • Chapter DOI: https://doi.org/10.1017/9781009177078.008
Available formats
×