Isotopic heterogeneity of oceanic, arc and continental basalts and its implications for mantle dynamics

SUMMARY Previous studies have shown that a low viscosity upper mantle can impact the wavelength of mantle flow and the balance of plate driving to resisting forces. Those studies assumed that mantle viscosity is independent of mantle flow. We explore the potential that mantle flow is not only influenced by viscosity but can also feedback and alter mantle viscosity structure owing to a non-Newtonian upper-mantle rheology. Our results indicate that the average viscosity of the upper mantle, and viscosity variations within it, are affected by the depth to which a non-Newtonian rheology holds. Changes in the wavelength of mantle flow, that occur when upper-mantle viscosity drops below a critical value, alter flow velocities which, in turn, alter mantle viscosity. Those changes also affect flow profiles in the mantle and the degree to which mantle flow drives the motion of a plate analogue above it. Enhanced upper-mantle flow, due to an increasing degree of non-Newtonian behaviour, decreases the ratio of upper- to lower-mantle viscosity. Whole layer mantle convection is maintained but upper- and lower-mantle flow take on different dynamic forms: fast and concentrated upper-mantle flow; slow and diffuse lower-mantle flow. Collectively, mantle viscosity, mantle flow wavelengths, upper- to lower-mantle velocities and the degree to which the mantle can drive plate motions become connected to one another through coupled feedback loops. Under this view of mantle dynamics, depth-variable mantle viscosity is an emergent flow feature that both affects and is affected by the configuration of mantle and plate flow.

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Pn anisotropic tomography and mantle dynamics underneath the South China Sea and surrounding areas

Journal of Asian Earth Sciences ◽

10.1016/j.jseaes.2021.104796 ◽

2021 ◽

pp. 104796

Author(s):

Qi Mi ◽

Jianshe Lei ◽

Mofei Du ◽

Jing He ◽

Hongbin Lu ◽

...

Keyword(s):

South China Sea ◽

South China ◽

The South China Sea ◽

The South ◽

Mantle Dynamics ◽

China Sea ◽

Surrounding Areas

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Extreme isotopic heterogeneity in Samoan clinopyroxenes constrains sediment recycling

Nature Communications ◽

10.1038/s41467-021-21416-9 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Jenna V. Adams ◽

Matthew G. Jackson ◽

Frank J. Spera ◽

Allison A. Price ◽

Benjamin L. Byerly ◽

...

Keyword(s):

Mantle Source ◽

Magma Mixing ◽

Major And Trace Elements ◽

Mantle Heterogeneity ◽

Isotopic Data ◽

Nd Isotopes ◽

Isotopic Heterogeneity ◽

Total Variability ◽

High Silica ◽

Insight Into

AbstractLavas erupted at hotspot volcanoes provide evidence of mantle heterogeneity. Samoan Island lavas with high 87Sr/86Sr (>0.706) typify a mantle source incorporating ancient subducted sediments. To further characterize this source, we target a single high 87Sr/86Sr lava from Savai’i Island, Samoa for detailed analyses of 87Sr/86Sr and 143Nd/144Nd isotopes and major and trace elements on individual magmatic clinopyroxenes. We show the clinopyroxenes exhibit a remarkable range of 87Sr/86Sr—including the highest observed in an oceanic hotspot lava—encompassing ~30% of the oceanic mantle’s total variability. These new isotopic data, data from other Samoan lavas, and magma mixing calculations are consistent with clinopyroxene 87Sr/86Sr variability resulting from magma mixing between a high silica, high 87Sr/86Sr (up to 0.7316) magma, and a low silica, low 87Sr/86Sr magma. Results provide insight into the composition of magmas derived from a sediment-infiltrated mantle source and document the fate of sediment recycled into Earth’s mantle.

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Role of the transition zone and 660 km discontinuity in mantle dynamics

Physics of The Earth and Planetary Interiors ◽

10.1016/0031-9201(94)05058-9 ◽

1994 ◽

Vol 86 (1-3) ◽

pp. 5-24 ◽

Cited By ~ 70

Author(s):

A.E. Ringwood

Keyword(s):

Transition Zone ◽

Mantle Dynamics

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The Heterogeneous Tethyan Oceanic Lithosphere of the Alpine Ophiolites

Elements ◽

10.2138/gselements.17.1.23 ◽

2021 ◽

Vol 17 (1) ◽

pp. 23-28 ◽

Cited By ~ 1

Author(s):

Elisabetta Rampone ◽

Alessio Sanfilippo

Keyword(s):

Oceanic Lithosphere ◽

Passive Margin ◽

Crustal Material ◽

Crustal Accretion ◽

Mantle Dynamics ◽

Western Tethys ◽

Mantle Peridotites ◽

Slow Spreading ◽

Tethys Ocean ◽

Basaltic Crust

The Alpine–Apennine ophiolites are lithospheric remnants of the Jurassic Alpine Tethys Ocean. They predominantly consist of exhumed mantle peridotites with lesser gabbroic and basaltic crust and are locally associated with continental crustal material, indicating formation in an environment transitional from an ultra-slow-spreading seafloor to a hyperextended passive margin. These ophiolites represent a unique window into mantle dynamics and crustal accretion in an ultra-slow-spreading extensional environment. Old, pre-Alpine, lithosphere is locally preserved within the mantle sequences: these have been largely modified by reaction with migrating asthenospheric melts. These reactions were active in both the mantle and the crust and have played a key role in creating the heterogeneous oceanic lithosphere in this branch of the Mesozoic Western Tethys.

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