TY - CHAP
T1 - Core-mantle boundary structures and processes
AU - Lay, Thorne
AU - Garnero, Edward
N1 - Funding Information:
Acknowledgements. We thank Geoff Davies, Brian Kennett, and Chris Hawkesworth for comments on the manuscript. This research was supported by NSF grants EAR-0125595 (TL). EAR-9996302 (EG). Contribution No. 466, Center for the Study of Imaging and Dynamics of the Earth, IGPP, UCSC.
Funding Information:
We thank Geoff Davies, Brian Kennett, and Chris Hawkesworth for comments on the manuscript. This research was supported by NSF grants EAR-0125595 (TL). EAR-9996302 (EG). Contribution No. 466, Center for the Study of Imaging and Dynamics of the Earth, IGPP, UCSC.
Publisher Copyright:
© 2004 by the American Geophysical Union.
PY - 2004
Y1 - 2004
N2 - Seismological and geodynamical observations have established the presence of a major thermo-chemical boundary layer (TCBL) in the lowermost mantle. This boundary layer plays a critical role in regulating heat flow through the core-mantle boundary, thereby influencing the dynamo-generating core flow regime. It also plays an important role in the mantle convection system, possibly serving as a source of boundary-layer instabilities and as a reservoir for long-lived geochemical heterogeneities. Two end-member conceptual models for the TCBL have emerged, both reconcilable with current observational constraints: a global, stably-stratified, chemically distinct layer may exist in the lowermost 250 km of the mantle (the global TCBL model), or this region may be a partially mixed boundary layer involving a composite of downwelling thermo-chemical anomalies such as oceanic lithospheric slabs or eclogitic oceanic crustal components and ancient dense chemical anomalies dynamically concentrated into large agglomerations beneath upwellings (the hybrid TCBL model). For the global TCBL model, laterally varying partial melt fractions within the layer are required to account for various seismological observations, and large dynamic topography on the upper boundary of this layer is expected: there is evidence for both of these attributes of the TCBL. The hybrid TCBL model requires additional complexity such as a phase transition or structural fabric transition to account for various seismological observations: some mineralogical candidates have been proposed. The outstanding challenge, requiring multi-disciplinary advances, is to discriminate between these competing conceptual models, as they differ in implications for thermal history, chemical processing, and dynamical behavior of the TCBL.
AB - Seismological and geodynamical observations have established the presence of a major thermo-chemical boundary layer (TCBL) in the lowermost mantle. This boundary layer plays a critical role in regulating heat flow through the core-mantle boundary, thereby influencing the dynamo-generating core flow regime. It also plays an important role in the mantle convection system, possibly serving as a source of boundary-layer instabilities and as a reservoir for long-lived geochemical heterogeneities. Two end-member conceptual models for the TCBL have emerged, both reconcilable with current observational constraints: a global, stably-stratified, chemically distinct layer may exist in the lowermost 250 km of the mantle (the global TCBL model), or this region may be a partially mixed boundary layer involving a composite of downwelling thermo-chemical anomalies such as oceanic lithospheric slabs or eclogitic oceanic crustal components and ancient dense chemical anomalies dynamically concentrated into large agglomerations beneath upwellings (the hybrid TCBL model). For the global TCBL model, laterally varying partial melt fractions within the layer are required to account for various seismological observations, and large dynamic topography on the upper boundary of this layer is expected: there is evidence for both of these attributes of the TCBL. The hybrid TCBL model requires additional complexity such as a phase transition or structural fabric transition to account for various seismological observations: some mineralogical candidates have been proposed. The outstanding challenge, requiring multi-disciplinary advances, is to discriminate between these competing conceptual models, as they differ in implications for thermal history, chemical processing, and dynamical behavior of the TCBL.
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U2 - 10.1029/150GM04
DO - 10.1029/150GM04
M3 - Chapter
AN - SCOPUS:33745898304
SN - 9780875904153
T3 - Geophysical Monograph Series
SP - 25
EP - 41
BT - The State of the Planet
A2 - Hawkesworth, C.J.
A2 - Sparks, R.S.J.
PB - Blackwell Publishing Ltd
ER -