Depleted and enriched mantle processes under the Rio Grande rift: spinel peridotite xenoliths |
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| Authors: | Y Kil R F Wendlandt |
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| Institution: | (1) Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80401, USA;(2) New Ventures, Korea National Oil Corporation, 1588-14 Gwanyang-dong, Dongan-gu, Anyang, Gyeonggi-do, 431-711, South Korea |
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| Abstract: | Upper mantle xenoliths from the southern Rio Grande rift axis (Potrillo and Elephant Butte) and flank (Adam’s Diggings) have
been investigated to determine chemical depletion and enrichment processes. The variation of modal, whole rock, and mineral
compositions reflect melt extraction. Fractional melting is the likely process. Fractional melting calculations show that
most spinel peridotites from rift axis locations have undergone <5% melting versus 7–14% melting for xenoliths from the rift
shoulder, although the total range of fractional melting overlaps at all three locations. In the rift axis, deformed (equigranular
and porphyroclastic texture) spinel peridotites are generally characterized by significantly less fractional melting (2–5%)
than undeformed (protogranular) xenoliths (up to 16%). This difference may reflect undeformed xenoliths being derived from
greater depths and higher temperatures than deformed rocks. Spinel peridotites from the axis and shoulder of the Rio Grande
rift have undergone mantle metasomatism subsequent to melt extraction. Under the rift shoulder spinel peridotites have undergone
both cryptic and patent (modal) metasomatism, possibly during separate events, whereas the upper mantle under the rift axis
has undergone only cryptic metasomatism by alkali basaltic magma. |
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