Geophysical constraints on partial melt in the upper mantle

Deeply subducted carbonates likely cause low-degree melting of the upper mantle and thus play an important role in the deep carbon cycle. However, direct seismic detection of carbonate-induced partial melts in the Earth’s interior is hindered by our poor knowledge on the elastic properties of carbonate melts. Here we report the first experimentally determined sound velocity and density data on dolomite melt up to 5.9 GPa and 2046 K by in-situ ultrasonic and sink-float techniques, respectively, as well as first-principles molecular dynamics simulations of dolomite melt up to 16 GPa and 3000 K. Using our new elasticity data, the calculated VP/VSratio of the deep upper mantle (∼180–330 km) with a small amount of carbonate-rich melt provides a natural explanation for the elevated VP/VSratio of the upper mantle from global seismic observations, supporting the pervasive presence of a low-degree carbonate-rich partial melt (∼0.05%) that is consistent with the volatile-induced or redox-regulated initial melting in the upper mantle as argued by petrologic studies. This carbonate-rich partial melt region implies a global average carbon (C) concentration of 80–140 ppm. by weight in the deep upper mantle source region, consistent with the mantle carbon content determined from geochemical studies.

Download Full-text

A new model of upper mantle P-wave velocity below the Baltic Shield: indication of partial melt in the 95 to 160 km depth range

Tectonophysics ◽

10.1016/0040-1951(95)00057-7 ◽

1996 ◽

Vol 253 (3-4) ◽

pp. 227-245 ◽

Cited By ~ 44

Author(s):

E. Perchuć ◽

H. Thybo

Keyword(s):

Wave Velocity ◽

Baltic Shield ◽

Upper Mantle ◽

P Wave ◽

Depth Range ◽

New Model ◽

Partial Melt ◽

P Wave Velocity ◽

The Baltic

Download Full-text

Upper mantle seismic wave velocity: Effects of realistic partial melt geometries

Journal of Geophysical Research Atmospheres ◽

10.1029/2000jb900041 ◽

2000 ◽

Vol 105 (B5) ◽

pp. 10975-10986 ◽

Cited By ~ 254

Author(s):

William C. Hammond ◽

Eugene D. Humphreys

Keyword(s):

Wave Velocity ◽

Seismic Wave ◽

Upper Mantle ◽

Seismic Wave Velocity ◽

Partial Melt

Download Full-text

Upper Mantle Discontinuity Topography from Thermal and Chemical Heterogeneity

Science ◽

10.1126/science.1145962 ◽

2007 ◽

Vol 318 (5850) ◽

pp. 623-626 ◽

Cited By ~ 74

Author(s):

Nicholas Schmerr ◽

Edward J. Garnero

Keyword(s):

Upper Mantle ◽

Phase Changes ◽

Chemical Heterogeneity ◽

Multiple Reflections ◽

Partial Melt ◽

Tectonic Processes ◽

Seismic Discontinuities ◽

Mineralogical Phase ◽

Mantle Discontinuity ◽

Upper Mantle Discontinuity

Using high-resolution stacks of precursors to the seismic phase SS, we investigated seismic discontinuities associated with mineralogical phase changes approximately 410 and 660 kilometers (km) deep within Earth beneath South America and the surrounding oceans. Detailed maps of phase boundary topography revealed deep 410- and 660-km discontinuities in the down-dip direction of subduction, inconsistent with purely isochemical olivine phase transformation in response to lowered temperatures. Mechanisms invoking chemical heterogeneity within the mantle transition zone were explored to explain this feature. In some regions, multiple reflections from the discontinuities were detected, consistent with partial melt near 410-km depth and/or additional phase changes near 660-km depth. Thus, the origin of upper mantle heterogeneity has both chemical and thermal contributions and is associated with deeply rooted tectonic processes.

Download Full-text

Sea Bottom EM Field of M2 Tidal to Probe Upper Mantle Conductivity

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.683.828 ◽

2013 ◽

Vol 683 ◽

pp. 828-831

Author(s):

Yan Xu ◽

Jun Xu ◽

Wen Hu Zhang

Keyword(s):

Upper Mantle ◽

Period Range ◽

Partial Melt ◽

The Earth ◽

Ionospheric Source ◽

Sea Bottom ◽

Mantle Conductivity ◽

Em Field ◽

Recent Laboratory

Recent laboratory experiments demonstrate that electrical conductivity of upper mantle (UM) minerals is greatly increased by small amounts of water or by partial melt. Determination of deep conductivity using electromagnetic (EM) methods can thus provide constraints on the presence of volatiles and melting processes in UM. Probing conductivity at UM depths requires EM data with periods of a few to one cycle per day. This is a challenging period range for EM studies due to the spatially complex ionospheric source that dominates at these periods. The idea of exploiting tidal signals for EM studies of the Earth is not new, but so far it was used only for interpretation of inland and transoceanic electric field data due to M2. Emphasis in this work is made on a discussion of sea bottom magnetic field of the same origin.

Download Full-text

A BRIEF SUMMARY OF OUR PRESENT DAY UNDERSTANDING OF THE EFFECT OF VOLATILES AND PARTIAL MELT ON THE MECHANICAL PROPERTIES OF THE UPPER MANTLE

High-Pressure Research ◽

10.1016/b978-0-12-468750-9.50007-3 ◽

1977 ◽

pp. 3-23 ◽

Cited By ~ 50

Author(s):

C. GOETZE

Keyword(s):

Mechanical Properties ◽

Upper Mantle ◽

Partial Melt

Download Full-text

Modelling clinopyroxene/melt partition coefficients for higher upper mantle pressures

10.5194/egusphere-egu21-12478 ◽

2021 ◽

Author(s):

Julia Marleen Schmidt ◽

Lena Noack

Keyword(s):

Trace Elements ◽

Trace Element ◽

Thermodynamic Model ◽

Upper Mantle ◽

Partition Coefficients ◽

Trace Element Partitioning ◽

Partial Melt ◽

Element Partitioning ◽

Incompatible Trace Elements ◽

Free Element

When partial melt occurs in the mantle, redistribution of trace elements between the solid mantle material and partial melt takes place. Partition coefficients play an important role when determining the amount of trace elements that get redistributed into the melt. Due to a lower density compared to surrounding solid rock, partial melt that was generated in the upper mantle will rise towards the surface, leaving the upper mantle depleted in incompatible trace elements and an enriched crust. Studies investigating trace element partitioning in the mantle typically rely on constant partition coefficients throughout the mantle, even though it is known that partition coefficients depend on pressure, temperature, and composition. Between the pressures of 0-15 GPa, partition coefficients vary by two orders of magnitude along both, solidus and liquidus. Since partition coefficients exhibit a parabolic relationship in an Onuma diagram, a similar variation is expected for all trace element partition coefficients that can be derived from the sodium partition coefficients.In this study, we developed a thermodynamic model for sodium in clinopyroxene after Blundy et al. (1995). With the thermodynamic model results, we were able to deduce a P-T dependent equation for sodium partitioning that is applicable up to 12 GPa between the peridotite solidus and liquidus. Because sodium is an almost strain-free element in jadeite, it can be used as a reference to model partition coefficients for other elements, including heat producing elements like K, Th, and U. This gives us the opportunity to insert P-T dependent partition coefficient calculations of any trace element into mantle melting models, which will have a big impact on the accuracy of elemental redistribution calculations and therefore, if the partitioning of the heat producing elements is taken into account, also the evolution of the mantle and crust.Blundy, J. et al. (1995): Sodium partitioning between clinopyroxene and silicate melts, J. Geophys. Res., 100, 15501-15515.Schmidt, J.M. and Noack, L. (2021): Parameterizing a model of clinopyroxene/melt partition coefficients for sodium to higher upper mantle pressures (to be submitted)

Download Full-text