Record Details
Geochemistry and geochronology of ancient southeast Indian and southwest Pacific seafloor
ScholarsArchive at Oregon State University
| Field | Value |
|---|---|
| Title | Geochemistry and geochronology of ancient southeast Indian and southwest Pacific seafloor |
| Names |
Pyle, D. G.
(creator) Christie, David M. (creator) Mahoney, J. J. (creator) Duncan, Robert A. (creator) |
| Date Issued | 1995-11-10 (iso8601) |
| Abstract | Within the Australian-Antarctic Discordance (AAD), a boundary exists between isotopically defined “Pacific-type” and “Indian-type” mid-ocean ridge basalt (MORB) erupted along the Southeast Indian Ridge (SEIR). This boundary has migrated westward beneath the easternmost AAD spreading segment at a minimum rate of 25 mm/yr since 4 Ma; however, its long-term history remains a matter of speculation. To determine if Pacific-type upper mantle has migrated westward beneath the eastern Indian Ocean basin as Australia and Antarctica drifted apart during the last 70 m.y., we present new Sr-Nd-Pb isotope data, combined with trace element and 40Ar-39Ar radiometric age determinations, for samples from Legs 28 and 29 of the Deep Sea Drilling Project (DSDP). Basaltic basement at these DSDP sites provides a record of their upper mantle source composition and shows regional variations consistent with upper mantle flow in this region. East of the South Tasman Rise, all DSDP basalts have 87SR/86SR (0.7025-0.7029) and 206Pb/204Pb (18.80-19.48) ratios typical of Pacific-type MORB indicating that Pacific-type upper mantle existed east of the Australian-Antarctic continental margin and beneath the Tasman Sea during the early stages of seafloor spreading in this region. Basalts from DSDP sites west of the AAD have high 87Sr/86Sr (0.7030-0.7035), low 206Pb/204Pb (17.99-18.10) and trace element characteristics typical of present day Indian-type SEIR MORB. Between these two regions, DSDP basalts recovered along the western margin of the South Tasman Rise have isotopic characteristics that are, in one case consistent with Indian-type MORB source (Site 280A) and, in the second case, transitional between Pacific-type and Indian-type mantle sources. The occurrence of seafloor basalts with transitional or Indian-type isotopic characteristics well to the east of the present Indian-Pacific MORB isotopic boundary within the AAD strongly implies that Pacific-type upper mantle has migrated westward into the region since the South Tasman Rise separated from Antarctica circa 40 Ma. |
| Genre | Article |
| Identifier | Pyle, D.G., Christie, D.M., Mahoney, J.J., and Duncan, R.A., 1995, Geochemistry and Geochronology of ancient southeast Indian and southwest Pacific seafloor. Journal of Geophysical Research, Vol. 100, Pg. 22,261–22,282. |
