The variability of peridotite composition across a mantle shear zone (Lanzo massif, Italy): interplay of melt focusing and deformation

Kaczmarek, Mary-Alix; Müntener, Othmar

doi:10.1007/s00410-010-0500-8

Cited by 26 publications

(19 citation statements)

References 66 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For example, strain localization mostly starts with an early high‐temperature deformation (porphyroclastic fabrics) associated with synkinematic melt migration (e.g., Beni Bousera: Frets et al . []; Lanzo: Kaczmarek and Müntener [, ] and Kaczmarek and Tommasi []; Othris: Dijkstra et al . []; Lizard ophiolite; Allerton and Macleod []; and Josephine: Kelemen and Dick []), suggesting deformation in the vicinity of a thermal anomaly [ Vauchez et al ., ], a hypothesis which has recently been supported by geophysical surveys using SKS‐wave splitting in the active rift setting of the Afar (Ethiopia) region [ Hammond et al ., ].…”

Section: Discussionmentioning

confidence: 99%

Mechanical anisotropy control on strain localization in upper mantle shear zones

et al. 2016

View full text Add to dashboard Cite

Mantle rocks at oceanic spreading centers reveal dramatic rheological changes from partially molten to solid-state ductile to brittle deformation with progressive cooling. Using the crustal-scale Wadi al Wasit mantle shear zone (SZ, Semail ophiolite, Oman), we monitor such changes based on quantitative field and microstructural investigations combined with petrological and geochemical analyses. The spatial distribution of magmatic dikes and high strain zones gives important information on the location of magmatic and tectonic activity. In the SZ, dikes derived from primitive melts (websterites) are distributed over the entire SZ but are more abundant in the center; dikes from more evolved, plagioclase saturated melts (gabbronorites) are restricted to the SZ center. Accordingly, harzburgite deformation fabrics show a transition from protomylonite (1100°C), mylonite (900-800°C) to ultramylonite (<700°C) and a serpentine foliation (<500°C) from the SZ rim to the center. The spatial correlation between solid-state deformation fabrics and magmatic features indicates progressive strain localization in the SZ on the cooling path. Three stages can be discriminated: (i) Cycles of melt injection (dunite channels and websterite dikes) and solid-state deformation (protomylonites-mylonites; 1100-900°C), (ii) dominant solid-state deformation in harzburgite mylonites (900-800°C) with some last melt injections (gabbronorites) and ultramylonites (<700°C), and (iii) infiltration of seawater inducing a serpentine foliation (<500°C) followed by cataclasis during obduction. The change of these processes in space and time indicates that early dike-related ridge-parallel deformation controls the onset of the entire strain localization history promoting nucleation sites for different strain weakening processes as a consequence of changing physicochemical conditions.

show abstract

Section: Discussionmentioning

confidence: 99%

Mechanical anisotropy control on strain localization in upper mantle shear zones

et al. 2016

View full text Add to dashboard Cite

show abstract

“…11a). The Lanzo massif is composed of weakly to fully serpentinized peridotites, exhumed during the opening of the Jurassic Alpine Tethys ocean (Müntener and Piccardo, 2003;Kaczmarek and Müntener, 2008;Nicolas et al, 1972;Kaczmarek and Müntener, 2010).…”

Section: Italy)mentioning

confidence: 99%

The role of serpentinization and magmatism in the formation of decoupling interfaces at magma-poor rifted margins

Gillard

Tugend

Müntener

et al. 2019

Earth-Science Reviews

View full text Add to dashboard Cite

In spite of recent progress in the understanding of magma-poor rifted margins, the processes leading to the formation and evolution of the exhumed mantle domain and its transition toward steady state oceanic crust remain debated. In particular, the parameters controlling the progressive localization of extensional deformation and magmatic processes leading to the formation of an oceanic spreading center are poorly understood. In this paper, we highlight the occurrence of two major decoupling horizons controlling the structural and magmatic evolution of distal magma-poor rifted margins. They are marked by strong seismic reflectors located at about 1 sec TWTT (Upper Reflectors-UR) and 2 sec TWTT (Lower Reflectors-LR) below top basement in domains of exhumed mantle at several magma-poor rifted margins. Both reflection seismic observations and studies on the physical properties of serpentinized mantle suggest that the UR likely results from deformation localized along a rheological interface at about 3 km below top basement, associated with an abrupt change in the mechanical behavior of peridotites once they are serpentinized to ~15%. We suggest that this interface played a major role in successive fault reorganizations during formation of the exhumed mantle domain. The comparison of reflection seismic observations with Alpine field analogues suggests that the LR likely results from an interaction between magmatism, deformation and hydration reactions during final rifting. Based on our results, we suggest that during final rifting the strain distribution is controlled first by hydration and then by magmatic processes in the domain of exhumed mantle.

show abstract

“… Müntener and Piccardo [2003] proposed that it represents a subcontinental lithospheric mantle modified by thermochemical erosion in an extensional, preoceanic setting. Widespread interaction with mid‐ocean ridge basaltic (MORB‐type) melts is recorded in the Lanzo massif by formation of pyroxene‐depleted reactive spinel peridotites, plagioclase‐enriched impregnated peridotites, and replacive spinel harzburgite‐dunite channels; all lithologies were later intruded by MORB‐type gabbroic dykes [ Boudier , 1972; Bodinier et al , 1991; Müntener and Piccardo , 2003; Piccardo et al , 2007a; Kaczmarek and Müntener , 2010].…”

Section: The Lanzo Massif: Large‐scale Structuresmentioning

confidence: 99%

“…Increasing deformation from porphyroclastic to mylonitic peridotites is associated with more homogeneous compositions (Al 2 O 3 , TiO 2 , Na 2 O, NiO, Yb, Sm) and a general tendency for enrichment in basaltic components [ Kaczmarek and Müntener , 2010]. The evolution of trace element contents of the peridotites within the studied area is reproduced by refertilization models where an E‐MORB produced by melting of a spinel‐peridotite percolates a depleted peridotite [ Kaczmarek and Müntener , 2010]. Rare earth elements (REE) contents also indicate a less enriched composition of the northern body relative to the central body.…”

Section: The Lanzo Massif: Large‐scale Structuresmentioning

confidence: 99%

Anatomy of an extensional shear zone in the mantle, Lanzo massif, Italy

Kaczmarek

Tommasi

2011

Geochem. Geophys. Geosyst.

View full text Add to dashboard Cite

[1] Analysis of the microstructures in the km-scale mantle shear zone that separates the northern and the central parts of the Lanzo peridotite massif provides evidence of an evolution in time and space of deformation processes accommodating shearing in the shallow mantle within an extensional setting. This shear zone displays an asymmetric distribution of deformation facies. From south to north, gradual reorientation of the foliation of coarse porphyroclastic plagioclase-bearing peridotites is followed by development of protomylonites, mylonites, and mm-scale ultramylonite bands. A sharp grain size gradient marks the northern boundary. Early deformation under near-solidus conditions in the south is recorded by preservation of weakly deformed interstitial plagioclase and almost random clinopyroxene and plagioclase crystal orientations. Feedback between deformation and melt transport probably led to melt focusing and strain weakening in the shear zone. Overprint of melt-rock reaction microstructures by solid-state deformation and decrease in recrystallized grain size in the protomylonites and mylonites indicate continued deformation under decreasing temperature. Less enriched peridotite compositions and absence of ultramafic dykes or widespread melt-impregnation microstructures north of the shear zone and clinopyroxene and amphibole enrichment in the mylonites and ultramylonites suggest that the shear zone acted as both a thermal barrier and a high-permeability channel for late crystallizing fluids. These observations, together with chemical data indicating faster cooling of central Lanzo relative to the northern body, corroborate that this shear zone is a mantle detachment fault. All deformation facies have crystal preferred orientations consistent with deformation by dislocation creep with dominant activation of the (010)[100] and (100)[001] systems in olivine and orthopyroxene, respectively. Dynamic recrystallization produces dispersion of olivine CPO but not a change of dominant deformation mechanism. Evidence for activation of grain boundary sliding is limited to mm-scale ultramylonite bands, where solid-state reactions produced very fine grained polymineralic aggregates. Except for these latest stages of deformation, strain localization does not result from the microstructural evolution; the grain size decrease is a consequence of the need to deform a rock volume whose strength continuously increases because of decreasing temperature conditions. Strain localization in the intermediate levels thus essentially results from the more localizing behavior of both the deep, partially molten, and shallow parts of this extensional shear zone distribution.

show abstract

The variability of peridotite composition across a mantle shear zone (Lanzo massif, Italy): interplay of melt focusing and deformation

Cited by 26 publications

References 66 publications

Mechanical anisotropy control on strain localization in upper mantle shear zones

Mechanical anisotropy control on strain localization in upper mantle shear zones

The role of serpentinization and magmatism in the formation of decoupling interfaces at magma-poor rifted margins

Anatomy of an extensional shear zone in the mantle, Lanzo massif, Italy

Contact Info

Product

Resources

About