The identification of radial velocity anomalies in the lower mantle using an interference method

Wright, C.; Lyons, J. A.

doi:10.1016/0031-9201(79)90153-5

Cited by 10 publications

(2 citation statements)

References 7 publications

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“…P wave discontinuity observations. The initial indications that a velocity discontinuity exists in D″ were based on rather subtle P wave slowness analyses [e.g., Wright, 1973;Wright and Lyons, 1975, 1979 that did not compel broad acceptance; the nature of the P velocity structure remains enigmatic. Ironically, this may be a factor compatible with pPv occurrence, as discussed below.…”

Section: Abrupt Increases or Decreases In Seismic Velocity With Incrementioning

confidence: 99%

Reconciling the post-perovskite phase with seismological observations of lowermost mantle structure

Lay

Garnero

2007

Geophysical Monograph Series

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The discovery of post-perovskite (pPv), the high pressure polymorph of (Mg x ,Fe 1-x )SiO 3 perovskite (Pv), may have profound implications for the thermal, chemical and dynamical structure of the deep Earth, if it can be demonstrated that pPv currently exists in the lower mantle. The requisite basis for such a demonstration is seismological observation of elastic velocity and density structures diagnostic of or at least compatible with the expected properties of pPv occurrence in a realistic lower mantle chemical and thermal environment. A critical assessment of seismological observations versus predictions for a lower mantle model with pPv is undertaken, with the limitations and robust attributes of the seismological data being summarized. The existence of a seismic velocity discontinuity several hundred kilometers above the core-mantle boundary is a primary line of evidence for the presence of a Pv-pPv phase change. However, some attributes of the discontinuity, such as localized P wave reflections from a large P velocity increase and the sharpness of observed P and S velocity increases, reveal inconsistencies with expected properties of a Pv-pPv phase transition. Lateral variations in temperature can produce complex phase boundary structure that explains variable S wave observations, but such elastic heterogeneity intrinsically complicates testing the pPv hypothesis. The combination of rapidly expanding seismological data sets and new high resolution data analysis procedures reveal multiple seismic discontinuities near the base of the mantle; in some cases these may be consistent with forward and reverse Pv-pPv transformations, bounding a pPv layer or lens in D″ above the CMB. Other phase changes or compositional contrasts could also be involved. At present, existence of pPv in the deep Earth is quite plausible, but not yet conclusively demonstrated. Future seismological and mineral physics research directions for further testing the hypothesis that pPv is present in the lower mantle are suggested.

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Section: Abrupt Increases or Decreases In Seismic Velocity With Incrementioning

confidence: 99%

Reconciling the post-perovskite phase with seismological observations of lowermost mantle structure

Lay

Garnero

2007

Geophysical Monograph Series

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“…Complex locally layered seismic structures have also been detected on the mantle side of the CMB at both the top and bottom of the D" region. The shallower structure, typically from 150 to 350 km above the CMB, was first detected by array analysis of P waves [Wright and Lyons, 1979;Wright et al, 1985;Weber and Davis, 1990] and by analysis of profiles of S waves [Lay and Helmberger, 1983;Young and Lay, 1987b;Young and Lay, 1990]. Wysession et al [1998] review the many subsequent studies that characterize this feature as a rapid increase in seismic velocity with depth, over a depth extent of 0-30 km, with 2-3% shear velocity increase and 0.5-3% compressional velocity increase.…”

Section: Local Stratification Of the Boundary Layermentioning

confidence: 99%

Core-mantle boundary structures and processes

Lay

Garnero

2004

Geophysical Monograph Series

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The past two decades have witnessed tremendous progress in seismological, geodynamical, geomagnetic, and mineral physics efforts to quantify deep Earth processes. Our understanding of structures and processes in the lowermost mantle has advanced accordingly, and there is now widespread agreement that some form of major thermo-chemical boundary layer (TCBL) exists on the mantle side of the core-mantle boundary (CMB), extending at least several hundred kilometers upward into the lower mantle. Boundary layers play critical roles in heat transport and dominant length scales of thermal convection systems, so there is a concerted effort to understand the lowermost mantle boundary layer. The endmember conceptual models now being considered for the TCBL at the base of the mantle are reviewed here along with Book Title Book Series 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. CORE-MANTLE BOUNDARY STRUCTURE AND PROCESSES

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Evidence for P wave velocity discontinuities at depths greater than 650 km in the mantle

Muirhead

Hales

1980

Physics of the Earth and Planetary Interiors

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The identification of radial velocity anomalies in the lower mantle using an interference method

Cited by 10 publications

References 7 publications

Reconciling the post-perovskite phase with seismological observations of lowermost mantle structure

Reconciling the post-perovskite phase with seismological observations of lowermost mantle structure

Core-mantle boundary structures and processes

Evidence for P wave velocity discontinuities at depths greater than 650 km in the mantle

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