Origin of the picrite blocks in the Marginal Border Group of the Skaergaard Intrusion,East Greenland |
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| Authors: | MA Kays AR McBirney |
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| Institution: | Department of Geology, University of Oregon, Eugene, OR 97403 USA |
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| Abstract: | New evidence shows that the picrite blocks in the margins of the Skaergaard intrusion, East Greenland are gabbro-contaminated xenoliths of ultramafic rock. Earlier studies suggested that the picrite blocks were cumulates formed in the Marginal Border Group or in the Hidden Zone. However, there are no known occurrences of undisturbed picrite or ultramafic rocks in the Skaergaard intrusion, and an extensive Hidden Zone is not supported by geophysical data. The picrite blocks are most abundant near a body of wehrlite in Precambrian rocks near Watkins Fjord. The wehrlite, which has a composition and mineralogy similar to the most mafic of the picrite blocks, lies structurally below the northern margin of the intrusion. It is possible that the refractory precursors of picrite in the Skaergaard intrusion may have been ultramafic xenoliths and are not representative of the earliest differentiated pan of the intrusion. |
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