Continental material in the shallow oceanic mantle - How does it get there?

Publication Type  Journal Article
Year of Publication  2006
Authors  Class, C.; le Roex, A. P.
Journal Title  Geology
Volume  34
Issue  3
Pages  129-132
Journal Date  Mar
ISBN Number  0091-7613
Accession Number  ISI:000235959300002
Key Words  mantle plume; lithosphere; recycling; craton; geodynamics; south-atlantic; northwestern namibia; geochemistry; beneath; isotope; basalts; ridge; petrogenesis; lithosphere; constraints

Unusual compositions of some oceanic basalts have been attributed to their sources containing continental lithosphere detached during the breakup of Gondwana. However, the processes of how such continental lithospheric material is detached and transported into the ocean basin have not been constrained. Here we identify Walvis Ridge, where it has been argued that Deep Sea Drilling Project (DSDP) Site 525A contains continental material, as a unique location to constrain these processes. Absolute plate motion (relative to the Tristan mantle plume) and relative plate motion (between Africa and South America) of the African plate are oblique to one another, such that tectonic detachment versus hotspot-related thermal erosion should sample spatially separated continental units of different age. We present isotopic compositions of xenoliths representing the neoProterozoic lithosphere at the inferred site for tectonic detachment during continental breakup and show that this process does not explain the Walvis Ridge DSDP Site 525A mantle source. Rather, thermal erosion of ancient cratonic mantle by the Tristan mantle plume is indicated. A convective return flow is required to transport the eroded subcontinental lithospheric mantle to the site of plume activity some similar to 50 m.y. later and provides constraints on the direction and velocity of mantle flow in the upper mantle.


021CBTimes Cited:3Cited References Count:28

URL  <Go to ISI>://000235959300002
DOI  Doi 10.1103/G21943.1