Open AccessWeak thermal convection within tilted plume conduits
Author(s) -
Sleep Norman H.
Publication year - 2007
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2007gc001680
Subject(s) - plume , geology , convection , mantle convection , geophysics , electrical conduit , mantle plume , mantle (geology) , rayleigh number , stratification (seeds) , panache , thermal , convection cell , natural convection , mechanics , combined forced and natural convection , meteorology , seismology , physics , lithosphere , tectonics , engineering , biology , germination , mechanical engineering , seed dormancy , botany , dormancy
Shear from flow in the mantle tilts the conduits of mantle plumes. The density stratification at the top of the plume conduit is then unstable in cross section with cold material over hot. This stratification drives cross‐stream convection. Such convection including the Stokes' law rise of the plume conduit through the ambient mantle readily mixes isoviscous thermal plumes with their surroundings. Laboratory experiments by Kerr and Mériaux (2004) indicate that cross‐stream convection is weak within plumes with strongly temperature‐dependent viscosity and significant ∼56 viscosity contrasts. Analogy with stagnant‐lid convection provides scaling relationships with a Rayleigh number for cross‐stream convection within tilted plume conduits. Only material within a factor of a few e of the central viscosity of the plume convects significantly. The scaling analysis shows that the laboratory experiments by Kerr and Mériaux (2004) had the proper parameter range for the Hawaiian plume. The petrological conclusion that the plume conduit has been only mildly stirred by cross‐stream convection is reasonable. Cross‐stream convection is less likely for low‐flux plumes, like Galapagos, than high‐flux plumes and plumes in the deep mantle compared with those in the upper mantle.