Vertical and lateral heterogeneity of the upper mantle

Mercier, J.

doi:10.1016/0040-1951(79)90032-5

Cited by 3 publications

(4 citation statements)

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“…This agreement is not surprising for the following reasons. (1) The subgrain‐size piezometer of Mercier [] was calibrated using the measurements from standard, undecorated thin sections, in which detection of very low angle boundaries is difficult. (2) The subgrain‐size piezometer of Karato et al .…”

Section: Resultsmentioning

confidence: 78%

“…Subgrain size piezometric relationships generally have a similar form to equation , given by

σ_{normalo normall} = \frac{C}{d_{s g}^{p}},

where the subscript ol indicates the property averaged among olivine grains, d sg is the subgrain size, and C and p are empirically derived constants. Such a relationship has been calibrated by various authors based on both experimentally and naturally deformed olivine‐rich rocks [ Goetze , ; Mercier , ; Durham et al ., ; Toriumi , ; Karato et al ., ].…”

Section: Resultsmentioning

confidence: 99%

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Quantifying the effect of pyroxene on deformation of peridotite in a natural shear zone

Hansen

Warren

2015

JGR Solid Earth

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The influence of pyroxene on upper mantle viscosity remains unclear but may occur either through its difference in strength relative to olivine or through its effect on olivine microstructure. To determine the role of pyroxene in moderating peridotite viscosity, we analyzed microstructures in paired harzburgites and dunites from a natural shear zone exposed in the Josephine Peridotite. Olivine crystallographic textures evolve similarly in harzburgites and dunites with increasing strain, indicating the operation of similar deformation mechanisms in olivine. The mean olivine grain sizes are~1.5 times larger in dunites than in harzburgites, whereas the mean olivine subgrain sizes are a factor of~1.2 smaller in dunites than in harzburgites. The average stresses in olivine, estimated with a subgrain-size piezometer, are inversely correlated with pyroxene volume fraction and directly correlated with the mean olivine grain size. The calculated ratio of pyroxene viscosity to olivine viscosity for each harzburgite/dunite pair varies from 1.2 to 3.3. Notably, our data indicate that olivine viscosity is non-Newtonian with a finite grain-size sensitivity. We suggest that at the conditions of the shear zone, pyroxene is more viscous than olivine but that the increase in aggregate strength with larger pyroxene fractions is offset by correspondingly smaller olivine grain sizes. Thus, major rheological weakening associated with pyroxene content may only be possible if (1) temperatures are higher than those characterizing this shear zone, increasing the viscosity contrast between olivine and pyroxene or (2) stresses are high enough that grain-size reduction promotes a transition to a deformation mechanism with extreme grain-size sensitivity, such as diffusion creep.

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Section: Resultsmentioning

confidence: 78%

“…Subgrain size piezometric relationships generally have a similar form to equation , given by

σ_{normalo normall} = \frac{C}{d_{s g}^{p}},

Section: Resultsmentioning

confidence: 99%

Quantifying the effect of pyroxene on deformation of peridotite in a natural shear zone

Hansen

Warren

2015

JGR Solid Earth

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“…Because the mylonitic structures result from high-strain-high-stress deformations, we suggest that they formed when the asthenospheric material arrived near the surface, where steep thermal gradients are expected between the ascending material and the surrounding lithosphere. Such conditions are expected in a rift environment (Mercier, 1977;Boudier and Nicolas, 1985) or where the stretched lithosphere has just reached the oceanic accretion stage.…”

Section: Origin Of the Hole 637a Peridotitesmentioning

confidence: 97%

Structural Analysis of Plagioclase-Bearing Peridotites Emplaced at the End of Continental Rifting: Hole 637A, ODP Leg 103 on the Galicia Margin

Girardeau¹,

Evans²,

Beslier³

1988

Proceedings of the Ocean Drilling Program

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A ridge of peridotite, 100 km long and a few kilometers wide, borders the western edge of the Galicia passive continental margin (Spain) at the contact with oceanic crust. This ridge was drilled at Hole 637A during ODP Leg 103. The peridotites are serpentinized diopside-rich spinel-or spinel + plagioclase-bearing harzburgites and lherzolites that underwent only limited melt extraction during their ascent within the lithosphere.The foliation in the peridotites shows a nearly constant attitude; dip is constant (20°-30°) to the east-northeast in the upper 50 m of the section and increases to 70° in the deepest 20 m. The stretching lineation is generally downdip (i.e., nearly east-west) except locally, where it is at 45° to the downdip direction. The peridotite, initially coarse grained, displays a mylonitic disrupted texture. It has been plastically deformed in a rotational regime (simple shear), under high-stress conditions (~ 180 MPa), at high but decreasing temperatures (from up to 1000° to 850°C), and probably at very shallow depths (<7 km). High strain intensities (7 = 12) are estimated for the mylonite formation. After ductile shearing, the peridotite underwent some brittle deformation, allowing for complete serpentinization and the opening of fractures that are now filled by serpentine and calcite. Some fracturing continued after the calcite injection.The Hole 637A peridotites probably represent asthenospheric material emplaced in a stretched continental margin during the first stage of ocean accretion. The geometry and kinematics of the peridotite emplacement are consistent with a roughly east-west opening of the Atlantic Ocean.

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“…Coarse orthopyroxene grains may contain clinopyroxene lamellae. Olivine and clinopyroxene sometimes appear as inclusions in orthopyroxene (e.g., NPY1311, NFL1324, and NFK1123), leading to poikilitic textures (Mercier, ). Spinel inclusions in olivine suggest grain growth (Mercier & Nicolas, ).…”

Section: Petrography and Microstructuresmentioning

confidence: 99%

Lateral and Vertical Heterogeneity in the Lithospheric Mantle at the Northern Margin of the Pannonian Basin Reconstructed From Peridotite Xenolith Microstructures

et al. 2019

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This study analyzes the microstructures and deformational characteristics of spinel peridotite xenoliths from the Nógrád-Gömör Volcanic Field (NGVF), located on the northern margin of a young extensional basin presently affected by compression. The xenoliths show a wide range of microstructures, bearing the imprints of heterogeneous deformation and variable degrees of subsequent annealing. Olivine crystal preferred orientations (CPOs) have dominantly [010]-fiber and orthorhombic patterns. Orthopyroxene CPOs indicate coeval deformation with olivine. Olivine J indices correlate positively with equilibration temperatures, suggesting that the CPO strength increases with depth. In contrast, the intensity of intragranular deformation in olivine varies as a function of the sampling locality. We interpret the microstructures and CPO patterns as recording deformation by dislocation creep in a transpressional regime, which is consistent with recent tectonic evolution in the Carpathian-Pannonian region due to the convergence between the Adria microplate and the European platform. Postkinematic annealing is probably linked to percolation of metasomatism by mafic melts through the upper mantle of the NGVF prior to the eruption of the host alkali basalt. Elevated equilibration temperatures in xenoliths from the central part of the volcanic field are interpreted to be associated with the last metasomatic event, which only shortly preceded the ascent of the host magma. Despite well-developed olivine CPOs in the xenoliths, which imply a strong seismic anisotropy, the lithospheric mantle alone cannot account for the shear wave splitting delay times measured in the NGVF, indicating that deformation in both the lithosphere and the asthenosphere contributes to the observed shear wave splitting.

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Vertical and lateral heterogeneity of the upper mantle

Cited by 3 publications

References 0 publications

Quantifying the effect of pyroxene on deformation of peridotite in a natural shear zone

Quantifying the effect of pyroxene on deformation of peridotite in a natural shear zone

Structural Analysis of Plagioclase-Bearing Peridotites Emplaced at the End of Continental Rifting: Hole 637A, ODP Leg 103 on the Galicia Margin

Lateral and Vertical Heterogeneity in the Lithospheric Mantle at the Northern Margin of the Pannonian Basin Reconstructed From Peridotite Xenolith Microstructures

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