| Title | Fossil subduction zone origin for magmas in the Ferrar Large Igneous Province, Antarctica: Evidence from PGE and Os isotope systematics in the Basement Sill of the McMurdo Dry Valleys |
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| Author | Choi, S H ;
Mukasa, S B; Ravizza, G; Fleming, T H; Marsh, B D; Bedard, J H J |
| Source | Earth and Planetary Science Letters vol. 506, 2019 p. 507-519, https://doi.org/10.1016/j.epsl.2018.11.027  Open Access |
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| Year | 2019 |
| Alt Series | Natural Resources Canada, Contribution Series 20200182 |
| Publisher | Elsevier |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Area | Antarctica |
| Subjects | general geology; Nature and Environment; Science and Technology; platinum; sills; igneous rocks; subduction zones; fossil zones; osmium; isotopes; Gondwanaland |
| Illustrations | location maps; block diagrams; stratigraphic columns; tables; plots |
| Released | 2018 11 27 |
| Abstract | Mantle plumes provide an attractive mechanism for generating short-duration, voluminous magmas in large igneous provinces (LIPS) while at the same time providing an explanation for the frequently
associated break-up of supercontinents. This model has also been invoked for the Ferrar large igneous province (FLIP) in Antarctica, which zircon and baddeleyite U-Pb dating shows was emplaced over a short duration at 182.7 +/- 0.5 Ma,
contemporaneously with fragmentation of the supercontinent Gondwanaland. Here, we present platinum-group-element (PGE) and Os-isotopic data for the Basement Sill in the McMurdo Dry Valleys - a part of the FLIP - that challenge the plume
interpretation. The Basement Sill samples studied are cumulate-textured gabbro to norite, and pyroxenite with minor ferroor leuco-lithofacies with MgO ranging from 2 to 19 wt%. The Os-187/Os-188 values range from 0.1609 +/- 0.003 (2 sigma) to 8.100
+/- 1.600 (2 sigma); the minimum value overlaps with a previously published estimated initial Os-187/Os-188 ratio for Ferrar magmas of 0.145 +/- 0.049 (2 sigma). The PGE abundance patterns for the Basement Sill define positive, convex-shaped slopes
between the IPGE (Os, Ir and Ru) and PPGE (Pt, Pd and Rh). The most significant feature of the entire data set is the extreme sub-chondritic Os/Ir ratios (<0.33), values which are atypical of plume-derived magmas. These low Os/Ir ratios are more
consistent with the alternative view that FLIP resulted from the decompression melting of mantle with a fossil subduction zone signature along the proto-Pacific margin of Gondwanaland, disaggregated by rifting related to plate rearrangements during
supercontinent break-up. We propose that hydrated fossil subduction zones elsewhere on Earth might account for other short-lived voluminous magmatic events that form LIPs. The remarkably short duration of these events may be due to rapid
decompression of hydrated mantle allowing instantaneous large-volume melting which then peters out quickly (<1 Myr) as H2O is expelled from the source rocks and into the melt. |
| GEOSCAN ID | 326594 |
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