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

Sung Hi Choi, Samuel B. Mukasa, Greg Ravizza, Thomas H. Fleming, Bruce D. Marsh, Jean H.J. Bédard

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

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 ferro- or leuco-lithofacies with MgO ranging from 2 to 19 wt%. The 187Os/188Os values range from 0.1609 ± 0.003 (2σ) to 8.100 ± 1.600 (2σ); the minimum value overlaps with a previously published estimated initial 187Os/188Os ratio for Ferrar magmas of 0.145 ± 0.049 (2σ). 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.

Original languageEnglish (US)
Pages (from-to)507-519
Number of pages13
JournalEarth and Planetary Science Letters
Volume506
DOIs
StatePublished - Jan 15 2019

Bibliographical note

Funding Information:
The authors are indebted to journal editor Professor Tamsin Mather and two anonymous reviewers for their constructive comments which improved this manuscript. Our pMELTS calculations benefited from discussions with Marc Hirschmann and Mary Peterson to whom we are most grateful. The work presented here was supported by US National Science Foundation (NSF) award OPP-0603729 to S. B. M.

Publisher Copyright:
© 2018 Elsevier B.V.

Keywords

  • Antarctica
  • Basement Sill
  • Ferrar LIP
  • PGE
  • fossil subduction zone

Fingerprint

Dive into the research topics of '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'. Together they form a unique fingerprint.

Cite this