The role of serpentinite melanges in the unroofing of UHPM rocks: An example from the Western Alps of Italy

Blake, M. C.; Moore, Diane E.; Jayko, A. S.

doi:10.1017/cbo9780511573088.007

Cited by 43 publications

(72 citation statements)

References 14 publications

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“…Different interpretations have been suggested to explain it, the two principal being a tectonic mélange [36] and a meta-olistostrome or meta-debris flow [37,38]. In the M. Viso area a serpentinite mélange enclosing eclogites with different temperatures of equilibration has been interpreted [39,0] as formed in the mantle wedge during exhumation.…”

Section: Discussionmentioning

confidence: 99%

Different PT paths recorded in a tectonic mélange (Voltri Massif, NW Italy): implications for the exhumation of HP rocks

et al. 2007

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The Cascine Parasi Mélange (CPM) of the high-pressure, meta-ophiolitic Voltri Massif (Ligurian Western Alps), consists of a foliated chlorite-actinolite greenschist matrix enclosing lenses of metabasites and metasediments. The surrounding units consist of serpentinites not enclosing these metamorphic rocks. The matrix records three sets of folds: (i) Dm1/Dm2 (blueschist to greenschist-facies conditions), which can be correlated to folds in the metasedimentary blocks; (ii) Dm3, which are the most obvious in the field and which partially re-orient the previous structures. The metabasite lenses preserve internal High-Pressure (HP) schistosities unrelated to the matrix foliation. The lenses equilibrated at different peak metamorphic conditions (ranging from eclogite-to blueschist-facies) and some recorded the prograde transition from lawsonite-bearing assemblages to garnet blueschists. Individual lenses display different segments of typical subduction PT paths which apparently converge in the blueschist facies. A late stage greenschist-facies re-equilibration is particularly widespread at the rims of the HP lenses. These structural and metamorphic features suggest that the mélange was active during early phases of the structural evolution of the area, at least through the exhumation and emplacement of the HP blocks into shallower crustal levels at conditions transitional from blueschist-to greenschist-facies; the older history is only preserved inside the blocks.

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Section: Discussionmentioning

confidence: 99%

Different PT paths recorded in a tectonic mélange (Voltri Massif, NW Italy): implications for the exhumation of HP rocks

et al. 2007

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“…Exhumed oceanic crustal terranes such as the Monviso/Zermatt-Saas in the Alps contain km-cm scale blocks of metabasites within a sheared serpentinite matrix. The serpentinite appears to act as a low-density "carrier" for the higher density oceanic crustal eclogite blocks (Philippot and van Roermund, 1992;Blake et al, 1995;Schwartz et al, 2001).…”

Section: Hydration Weakeningmentioning

confidence: 99%

Exhumation of (ultra-)high-pressure terranes: concepts and mechanisms

Warren

2013

Solid Earth

113

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Abstract. The formation and exhumation of high and ultrahigh-pressure, (U)HP, rocks of crustal origin appears to be ubiquitous during Phanerozoic plate subduction and continental collision events. Exhumation of (U)HP material has been shown in some orogens to have occurred only once, during a single short-lived event; in other cases exhumation appears to have occurred multiple discrete times or during a single, long-lived, protracted event. It is becoming increasingly clear that no single exhumation mechanism dominates in any particular tectonic environment, and the mechanism may change in time and space within the same subduction zone. Subduction zone style and internal force balance change in both time and space, responding to changes in width, steepness, composition of subducting material and velocity of subduction. In order for continental crust, which is relatively buoyant compared to the mantle even when metamorphosed to (U)HP assemblages, to be subducted to (U)HP conditions, it must remain attached to a stronger and denser substrate. Buoyancy and external tectonic forces drive exhumation, although the changing spatial and temporal dominance of different driving forces still remains unclear. Exhumation may involve whole-scale detachment of the terrane from the subducting slab followed by exhumation within a subduction channel (perhaps during continued subduction) or a reversal in motion of the entire plate (eduction) following the removal of a lower part of the subducting slab. Weakening mechanisms that may be responsible for the detachment of deeply subducted crust from its stronger, denser substrate include strain weakening, hydration, melting, grain size reduction and the development of foliation. These may act locally to form narrow high-strain shear zones separating stronger, less-strained crust or may act on the bulk of the subducted material, allowing whole-scale flow. Metamorphic reactions, metastability and the composition of the subducted crust all affect buoyancy and overall strength. Future research directions include identifying temporal and spatial changes in exhumation mechanisms within different tectonic environments, and determining the factors that influence those changes.

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“…10a). These shear zones, particularly the LSZ, represent an example of network widening (in the sense of Schrank et al, 2008, for example) and not a subduction mélange formed by extensive mixing along the subduction interface (Blake et al, 1995;Guillot et al, 2004). The above description of deformation patterns within the Lago Superiore ophiolite thus suggests that caution is needed before interpreting former eclogite-facies shear zones as serpentinite mélanges, particularly in areas with limited surface exposures (e.g., Voltri; Brouwer et al, 2002;Federico et al, 2007).…”

Section: Implications For Km-scale Geodynamic Processes At the Subdumentioning

confidence: 99%

“…All the rocks of the massif show evidence for recrystallization under eclogite-facies conditions followed by retrogression under epidote-blueschist facies and greenschist facies (Lombardo et al, 1978;Blake et al, 1995). Ages for eclogitization of the ophiolite range between 50 and 40 Ma (Monié and Philippot, 1989;Duchêne et al, 1997;Cliff et al, 1998;Rubatto and Hermann, 2003).…”

Section: Introductionmentioning

confidence: 99%

“…Ages for eclogitization of the ophiolite range between 50 and 40 Ma (Monié and Philippot, 1989;Duchêne et al, 1997;Cliff et al, 1998;Rubatto and Hermann, 2003). Several studies suggested variable maximum P-T conditions for the Monviso ophiolite (from c. 450°C/12 kbar to 620°C/24 kbar; Blake et al, 1995;Messiga et al, 1999;Schwartz et al, 2001) and argued for the presence of a deep subduction mélange where tectonic slices detached from different depths accumulated in a weak serpentinized subduction channel (e.g., Guillot et al, 2004). However, Angiboust et al (2011) recently demonstrated that the Monviso ophiolite can be divided in two main coherent tectono-metamorphic units (Fig.…”

Section: Introductionmentioning

confidence: 99%

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Subduction interface processes recorded by eclogite-facies shear zones (Monviso, W. Alps)

Angiboust

Agard

Raimbourg

et al. 2011

Lithos

153

137

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The Monviso ophiolite Lago Superiore Unit constitutes a well-preserved, almost continuous upper fragment of oceanic lithosphere subducted at c. 80 km depth, thereby providing a unique opportunity to study mechanical coupling processes and meter-scale fluid-rock interactions occurring at such depths in present-day subduction zones. It is made of (i) a variably thick (50-500m) section of eclogitized basaltic crust (associated with minor calcschist lenses) overlying a 100-400m thick metagabbroic body and of (ii) a c. 1km thick serpentinite sole. We herein focus on the three major eclogite-facies shear zones found at the top of the unit, at the boundary between basalts and gabbros, and between gabbros and serpentinites, respectively. Strain

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The role of serpentinite melanges in the unroofing of UHPM rocks: An example from the Western Alps of Italy

Cited by 43 publications

References 14 publications

Different PT paths recorded in a tectonic mélange (Voltri Massif, NW Italy): implications for the exhumation of HP rocks

Different PT paths recorded in a tectonic mélange (Voltri Massif, NW Italy): implications for the exhumation of HP rocks

Exhumation of (ultra-)high-pressure terranes: concepts and mechanisms

Subduction interface processes recorded by eclogite-facies shear zones (Monviso, W. Alps)

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