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Age and geochemistry of magmatism on the oceanic Wallaby Plateau and implications for the opening of the Indian Ocean
Swedish Museum of Natural History. (NordSIMS)ORCID iD: 0000-0001-9018-6862
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2015 (English)In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 43, no 11, p. 971-974Article in journal (Refereed) Published
Abstract [en]

The temporal relationship between tectonic and volcanic activity on passive continental margins immediately before and after the initiation of mid-ocean ridge spreading is poorly understood because of the scarcity of volcanic samples on which to perform isotope geochronology. We present the first accurate geochronological constraints from a suite of volcanic and volcaniclastic rocks dredged from the 70,000 km2 submerged Wallaby Plateau situated on the Western Australian passive margin. Plagioclase 40Ar/39Ar and zircon U-Pb sensitive high-resolution ion microprobe ages indicate that a portion of the plateau formed at ca. 124 Ma. These ages are at least 6 m.y. younger than the oldest oceanic crust in adjacent abyssal plains (minimum = 130 Ma). Geochemical data indicate that the Wallaby Plateau volcanic samples are enriched tholeiitic basalt, similar to continental flood basalts, including the spatially and temporally proximal Bunbury Basalt in southwestern Australia. Thus, the Wallaby Plateau volcanism could be regarded as a (small) flood basalt event on the order of 104–105 km3. We suggest that magma could not erupt prior to 124 Ma because of the lack of space adjacent to the plateau. Eruption was made possible at 124 Ma via the opening of the Indian Ocean during the breakup of Greater India and Australia along the Wallaby-Zenith Fracture Zone. The scale of volcanism and the temporal proximity to breakup challenges the prevailing theory that the Western Australian margin formed as a volcanic passive margin. Given that the volume of volcanism is too small for typical flood basalts associated with volcanic passive margins, we suggest that the two end members, magma-poor and volcanic passive margins, should rather be treated as a continuum.

Place, publisher, year, edition, pages
2015. Vol. 43, no 11, p. 971-974
National Category
Natural Sciences
Research subject
The changing Earth
Identifiers
URN: urn:nbn:se:nrm:diva-3545DOI: 10.1130/G37044.1OAI: oai:DiVA.org:nrm-3545DiVA, id: diva2:1375222
Conference
12/4/2019
Available from: 2019-12-04 Created: 2019-12-04 Last updated: 2019-12-04

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Publisher's full texthttps://doi.org/10.1130/G37044.1

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merle, Renaud E.
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