Leg 187: Mantle reservoirs and migration associated with Australian-Antarctic rifting (16 November 1999-10 January 2000)

• Main Authors: Christie, David, Pedersen, Rolf, Miller, Jay, Balzer, Vaughn, Einaudi, Florence, Gee, Mary, Hauff, Faulkmar, Kempton, Pamela, Liang, Wen Tsong, Lysnes, Kristine, Pyle, Douglas, Russo, Christopher, Sato, Hiroshi, Thorseth, Ingunn, MEYZEN, CHRISTINE MARIE
• Other Authors: Meyzen, CHRISTINE MARIE, Pyle, Dougla
• Format: Book
• Language: English
• Published: Ocean Drilling Program 2001
• Subjects: Ocean Drilling Australian-Antarctic Discordance Basalt Mantle; Antarctic; Pacific; Indian; Australian-Antarctic Discordance; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/11577/3146981; https://doi.org/10.2973/odp.proc.ir.187.2001; http://www-odp.tamu.edu/publications/prelim/187_prel/187toc.html

Leg 187 undertook to trace the boundary between Indian and Pacific, ocean-scale mantle provinces across 10- to 30-Ma seafloor of the Southeast Indian Ocean between Australia and Antarctica. The boundary is sharply defined on young seafloor within the Australian Antarctic Discordance (AAD), where it is migrating to the west at ~40 mm/yr. The leg was built around a responsive drilling strategy in which real-time shipboard geochemical analyses from one site were used to guide the selection of subsequent sites from a slate of preapproved targets. This strategy proved highly effective, allowing us to maximize our time on site and to focus on sites that could potentially yield the best definition of the boundary configuration. Using Ba and Zr contents of basalt glasses referenced to our database of younger (0-7 Ma) lavas from the AAD and Zone A (east of the AAD), we were able to assign each of the 23 holes drilled at 13 sites to an Indian, Pacific, or Transitional-Pacific upper mantle type. At three sites we encountered lavas from two of these three mantle types, indicating mixed or transitional mantle sources. From these shipboard identifications of mantle domain, three fundamental observations can be made: No Indian-type mantle occurs east of the regional residual depth anomaly. Pacific- and especially Transitional-Pacific-type mantle occurs throughout the depth anomaly in the study area. Between ~28 and 14 Ma, Indian and Pacific mantle types alternated in western Zone A on a time scale of a few million years. These observations lead to the following tentative conclusions which require careful testing as isotopic data become available. A discrete mantle boundary comparable to the present-day boundary in the AAD cannot be mapped through the entire 14- to 28-Ma time interval encompassed by Leg 187 sites, although comparable boundaries have existed for relatively short, discrete time intervals. We conclude that, in the long term, the eastern limit of the Indian mantle province corresponds closely to the eastern edge of ...