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| Structure | Volcanics | Refl. Seismic | Thickness | Heat Flow |
Volcanic evidence
Abundant post-Eocene mafic volcanic rocks are exposed in the Ross Embayment region, and volcanism continues to the present at locales such as Mount Erebus on Ross Island. Based on major element chemistry, some of these volcanics are classified as near-primary, meaning that they were derived in a nearly pristine state directly from the mantle. Figure 9 shows the occurrence of these volcanics (labeled McMurdo Volcanics).
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| Figure 9. Map showing the distribution of post-Eocene volcanic rocks in the Ross Embayment Region. Rocholl et al., 1995. | ||||
The isotopic composition of these volcanics is consistent with mantle derivation in a rift setting. In general, the data plot near the MORB field in Nd-Sr space, but with slight enrichment trends (Figure 10).
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| Figure 10. Sr and Nd initial isotopic ratios for mafic post-Eocene volcanics in North Victoria Land. MM- Mount Melbourne. MBL- Marie Bird Land. MORB- Mid-Ocean Ridge Basalt. Other mantle isotopic fields explained in Rocholl et al., 1995. | ||||
Locales on the rift flank in the TAM are more enriched than those in the center part of the rift (Figure 11).
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| Figure 11. Isotopic ratios from different locations across the TAM rift. RSR- Ross Sea Rift. MBL- Marie Byrd Land. TAM- Transantarctic Mountains. Rocholl et al., 1995. | ||||
The volcanics show a trend toward more primitive compositions with decreasing age (Figure 12). The isotopic data are permissive of an interpretation of a mantle plume source for the youngest lavas.
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| Figure 12. Variation of Nd initial isotopic ratios with crystallization age of volcanics. Trend is toward more MORB-like compositions with decreasing age. Rocholl et al., 1995. | ||||
Based on aeromagnetic data, Behrendt et al., (1994) infer the presence of a large volume of late Cenozoic volcanics beneath the ice of Marie Byrd Land and the Ross Ice Shelf. They suggest that a mantle plume may be responsible for the large volume of volcanics in this area. Aeromagnetic data from this region shows the presence of linear features, interpreted to be horsts and grabens, and circular features, interpreted to be volcanic centers (Figure 13).
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| Figure 13. Aeromagnetic data from the Ross Ice Shelf region. Behrendt et al., 1994. | ||||
Figure 14 shows a map of the Ross Embayment area with a compilation of known and inferred late Cenozoic volcanic centers. The outline of the inferred mantle plume is also shown.
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| Figure 14. Map showing locations of known and infered Late Cenozoic volcanic centers, and the outline of the inferred mantle plume that may be responsible for the volcanic centers. Behrendt et al., 1994. | ||||