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Title: Experimental evidence supports mantle partial melting in the asthenosphere

Authors:
; ; ; ; ;  [1];  [2]
  1. UC
  2. (
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
NSFFOREIGN
OSTI Identifier:
1274758
Resource Type:
Journal Article
Resource Relation:
Journal Name: Science Advances; Journal Volume: 2; Journal Issue: 5
Country of Publication:
United States
Language:
ENGLISH

Citation Formats

Chantle, Julien, Manthilake, Geeth, Andrault, Denis, Novella, Davide, Yu, Tony, Wang, Yanbin, and CNRS-UMR). Experimental evidence supports mantle partial melting in the asthenosphere. United States: N. p., 2016. Web. doi:10.1126/sciadv.1600246.
Chantle, Julien, Manthilake, Geeth, Andrault, Denis, Novella, Davide, Yu, Tony, Wang, Yanbin, & CNRS-UMR). Experimental evidence supports mantle partial melting in the asthenosphere. United States. doi:10.1126/sciadv.1600246.
Chantle, Julien, Manthilake, Geeth, Andrault, Denis, Novella, Davide, Yu, Tony, Wang, Yanbin, and CNRS-UMR). 2016. "Experimental evidence supports mantle partial melting in the asthenosphere". United States. doi:10.1126/sciadv.1600246.
@article{osti_1274758,
title = {Experimental evidence supports mantle partial melting in the asthenosphere},
author = {Chantle, Julien and Manthilake, Geeth and Andrault, Denis and Novella, Davide and Yu, Tony and Wang, Yanbin and CNRS-UMR)},
abstractNote = {},
doi = {10.1126/sciadv.1600246},
journal = {Science Advances},
number = 5,
volume = 2,
place = {United States},
year = 2016,
month = 7
}
  • The partitioning behavior of U, Th, and Pb in the upper mantle has been investigated through the analysis of ultramafic nodules found in lava flows at two localities in the southwestern US. Most of the primary components have Nd, Pb, and Sr isotope ratios within the ranges observed in oceanic basalts. The {sup 238}U/{sup 204}Pb (mu) ratios of residual (i.e., type 1A) clinopyroxene separates analyzed in this study are generally high (60-120) and show an excellent positive correlation with {sup 147}Sm/{sup 144}Nd ratios. Because the latter are consistently greater than the chondritic ratio and because clinopyroxene contains most of themore » U in the nodules, the author suggests this mineral is a high-mu component in the upper mantle. Calculated whole rock U contents, based on analyses of purified separates of the major silicate minerals, are consistent with recent estimates for mid-ocean ridge basalt sources. Clinopyroxene/melt partition coefficients, based on the assumption that the lavas bearing the nodules are the melts with which the nodule minerals last equilibrated, decrease in the order D{sub U}{sup s/l} > D{sub Th}{sup s/l} > D{sub Pb}{sup s/l}, consistent with available experimental data. Sulfide is inferred to be a major Pb-bearing phase in the nodules. Bulk partition coefficients for Pb, Th, and U during melting are inferred to depend primarily on the abundance of clinopyroxene and sulfide in the residual mantle. On the basis of the model presented, the Pb paradox is explained as a direct consequence of melt depletion from the upper mantle.« less
  • For mantle regions of anomalously high electrical conductivity (greater than 0.1 S/m) the bulk conductivity is modeled by effective medium theory as a basalt melt fraction within a mainly olivine matrix. In order for the highly conducting melt to affect the bulk conductivity it must form interconnections, so that the very existence of mantle conductivity anomalies constitutes evidence for such interconnections. The inclusion of petrological data on the partial melting of peridotite strongly constrains the range of temperatures and melt fractions that can be used to yield an observed electrical conductivity. Thus from anomalous conductivities which are observed under riftmore » zones, volcanic belts, geothermal areas, and beneath the oceans, it is possible to estimate both the temperature and the degree of partial melting. While other mechanisms for mantle conductivity enhancement may exist, e.g., contributions from contaminated grain boundaries or high volatile contents, these explanations associate a chemical differentiation in the mantle with thermal manifestations and in most cases create conditions that favor melting.« less
  • Three source regions show evidence of a low-velocity layer that is less than 15 kilometers thick on top of the core-mantle boundary and require about a 3:1 ratio of shear-to-compressional velocity reduction, which is consistent with partial melt. Layer thickness is correlated with travel time residuals of the seismic phases that are most sensitive to the lowermost mantle velocity. These observations suggest that the layer is thinned beneath downwellings but is present everywhere along the core-mantle boundary. Low viscosity accompanying partial melt can localize the upwelling of warmed mantle, making the low-velocity layer a plausible source of mantle plumes.
  • A comprehensive study of mantle anisotropy along the Red Sea and across Saudi Arabia was performed by analyzing shear-wave splitting recorded by stations from three different seismic networks: the largest, most widely distributed array of stations examined across Saudi Arabia to date. Stations near the Gulf of Aqaba display fast orientations that are aligned parallel to the Dead Sea Transform Fault, most likely related to the strike-slip motion between Africa and Arabia. However, most of our observations across Saudi Arabia are statistically the same, showing a consistent pattern of north-south oriented fast directions with delay times averaging about 1.4 s.more » Fossilized anisotropy related to the Proterozoic assembly of the Arabian Shield may contribute to the pattern but is not sufficient to fully explain the observations. We feel that the uniform anisotropic signature across Saudi Arabia is best explained by a combination of plate and density driven flow in the asthenosphere. By combining the northeast oriented flow associated with absolute plate motion with the northwest oriented flow associated with the channelized Afar plume along the Red Sea, we obtain a north-south oriented resultant that matches our splitting observations and supports models of active rifting processes. This explains why the north-south orientation of the fast polarization direction is so pervasive across the vast Arabian Plate.« less
  • Mantle anisotropy along the Red Sea and across the Arabian Peninsula was analyzed using shear-wave splitting recorded by stations from three different seismic networks: the largest, most widely distributed array of stations examined across the Arabian Peninsula to date. Stations near the Gulf of Aqaba display fast orientations aligned parallel to the Dead Sea Transform Fault, most likely related to the strike-slip motion between Africa and Arabia However, most of our observations across Arabia are statistically the same (at a 95% confidence level), with north-south oriented fast directions and delay times averaging about 1.4 s. Since end-member models of fossilizedmore » anisotropy and present-day asthenospheric flow do not adequately explain these observations, we interpret them as a combination of plate and density driven flow in the asthenosphere. Combining northeast oriented flow associated with absolute plate motion with northwest oriented flow associated with the channelized Afar upwelling along the Red Sea produces a north-south resultant that matches the observations and supports models of active rifting.« less