The ophiolitic Voltri Group in the eastern part of the Ligurian Alps (NW Italy) is made up of a number of thrust sheets emplaced during Alpine collision. These thrust sheets include (1) the Voltri-Rossiglione calcschist unit of Mesozoic high-pressure calcareous micaschists, metavolcanics and slices of serpentinite, overlain by (2) the Beigua serpentinite unit, of mainly antigorite serpentinite and eclogitic metagabbro, in turn overlain by (3) the Erro-Tobbio peridotites. In the northern part of the Voltri Massif, a conspicuous melange-type lithology occurs along the contact of the Beigua serpentinite unit and the Voltri-Rossiglione calcschist unit. In the vicinity of the contact, the structure in the hanging-wall serpentinites is dominated by kink-type crenulations. Towards the base of the serpentinite nappe these crenulations become intense, and veins and patches of talc + chlorite + tremolite + carbonate replace the original antigorite-dominated assemblage. The thrust itself is marked by a layer, at least several tens of metres thick, of intensely deformed and foliated antigorite-bearing talc-chlorite-tremolite schist, enclosing rounded and lense-shaped (phacoid) blocks, up to 25 metres across, of retrogressed eclogitic metagabbro, antigorite serpentinite, metabasic rock, calcschist and schistose micaceous marble. The main features of this chaotic lithology meet the descriptive criteria of a tectonic melange. The structures and assemblages in the wall rock units and those in the melange indicate that the melange lithology developed at a relatively late stage of greenschist facies ductile thrusting, emplacing the Beigua unit onto the rocks of the Voltri-Rossiglione unit. The structures indicate that the blocks and lenses were formed during localized deformation in a relatively narrow zone along the thrust plane via intense stretching and boudinage of the various lithologies in the foot- and hanging wall. The development of talc-chlorite-tremolite-carbonate assemblages at the expense of the overriding antigorite serpentinites require significant calciummetasomatism, hence extensive fluid activity, whilst the microstructures in the melange matrix suggest that the talc-chlorite-tremolite-carbonate assemblage was mechanically weak. It is suggested that both fluid activity and the associated metamorphic reactions strongly facilitated ductile to semi-brittle deformation along the thrust, leading to progressive fragmentation and mixing of the different lithologies and development of a tectonic melange.

Greenschist

Lithology

Ultramafic rock

Phyllite

Tremolite

10.4454/ofioliti.v26i1.129

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Citations (8)

Some constraints on the kinematics of the Tertiary Piemonte Basin (northwest Italy)

Tectonophysics (1991)

Eilard H. Hoogerduijn Strating W.A. van Wamel Reinoud L.M. Vissers

Culmination

Basement

Marine transgression

10.1016/0040-1951(91)90130-k

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Citations (16)

On the Hellenic subduction zone and the geodynamic evolution of Crete since the late Middle Miocene

Tectonophysics (1988)

J.E. Meulenkamp M. J. R. Wortel W.A. van Wamel Wim Spakman Eilard H. Hoogerduijn Strating

Eclogitization

Volcanic arc

10.1016/0040-1951(88)90091-1

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Citations (332)

Shear zones in the upper mantle: A case study in an Alpine Iherzolite massif

Geology (1991)

Reinoud L.M. Vissers Martyn R. Drury Eilard H. Hoogerduijn Strating D. van der Wal

Research Article| October 01, 1991 Shear zones in the upper mantle: A case study in an Alpine Iherzolite massif R.L.M. Vissers; R.L.M. Vissers 1Institute of Earth Sciences, P.O. Box 80.021, Utrecht, Netherlands Search for other works by this author on: GSW Google Scholar M. R. Drury; M. R. Drury 1Institute of Earth Sciences, P.O. Box 80.021, Utrecht, Netherlands Search for other works by this author on: GSW Google Scholar E. H. Hoogerduijn Strating; E. H. Hoogerduijn Strating 1Institute of Earth Sciences, P.O. Box 80.021, Utrecht, Netherlands Search for other works by this author on: GSW Google Scholar D. van der Wal D. van der Wal 1Institute of Earth Sciences, P.O. Box 80.021, Utrecht, Netherlands Search for other works by this author on: GSW Google Scholar Geology (1991) 19 (10): 990–993. https://doi.org/10.1130/0091-7613(1991)019<0990:SZITUM>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation R.L.M. Vissers, M. R. Drury, E. H. Hoogerduijn Strating, D. van der Wal; Shear zones in the upper mantle: A case study in an Alpine Iherzolite massif. Geology 1991;; 19 (10): 990–993. doi: https://doi.org/10.1130/0091-7613(1991)019<0990:SZITUM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Erro-Tobbio upper-mantle lherzolite of northwest Italy, emplaced in the Alpine suture zone during collision of the European and Adriatic plates, has preserved a set of major shear zones formed at temperatures in the range 800-1040 °C during the period of Jurassic rifting and breakup and development of the Piemonte-Ligurian oceanic basin. These structures clearly demonstrate localization of the deformation in the Piemonte-Ligurian upper mantle during lithosphere stretching and breakup. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Massif

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10.1130/0091-7613(1991)019<0990:szitum>2.3.co;2

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Citations (104)

Dehydration-induced fracturing of eclogite-facies peridotites: Implications for the mechanical behaviour of subducting oceanic lithosphere

Tectonophysics (1991)

Eilard H. Hoogerduijn Strating Reinoud L.M. Vissers

Peridotite

Mylonite

10.1016/0040-1951(91)90014-j

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Citations (42)

173. Microstructures in Low- and High-Temperature Serpentinite Mylonites

Princeton University Press eBooks (1998)

Eilard H. Hoogerduijn Strating Reinoud L.M. Vissers

Mylonite

10.1515/9781400864935.578

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Citations (0)

Subsolidus Emplacement of Mantle Peridotites during Incipient Oceanic Rifting and Opening of the Mesozoic Tethys (Voltri Massif, NW Italy)

Journal of Petrology (1993)

Eilard H. Hoogerduijn Strating Elisabetta Rampone Giovanni B. Piccardo Martyn R. Drury Reinoud L.M. Vissers

The Erro–Tobbio (ET) peridotite (Voltri Massif, NW Italy) represents a fragment of subcontinental mantle, emplaced at high crustal levels during rifting and opening of the Piemonte–Ligurian ocean, the Alps–Apennine part of the Mesozoic Tethys. The ET peridotite is dominated by spinel-bearing lherzolites, with minor dunites, spinel websterites and plagioclase-bearing lherzolites. Granular spinel lherzolites in the ET peridotite are transected by five generations of shear zone structures: porphyroclastic spinel-bearing tectonites, plagioclase-, hornblende- and chlorite-bearing peridotite mylonites, and serpentinite mylonites. There is a systematic correlation between the microstructures and the composition of the constituent mineral phases. These compositional trends are related to changing conditions of P and T during the pertinent stages of syntectonic recrystallization in the shear zones. Geothermobarometry shows that the shear zone structures developed at progressively lower P and T conditions. The P–T path obtained for the ET peridotite indicates subsolidus uplift, from deep levels in the subcontinental mantle towards the ocean floor. Uplift is associated with limited 'wet' partial melting. This subsolidus trajectory is particularly consistent with the thermal history expected for the footwall of a lithosphere-scale, dipping extensional shear zone, and differs from those of more oceanic peridotites showing an adiabatic uplift history at much higher temperatures presumably related to convective upwelling. The shear zone structures in the ET peridotites are therefore interpreted as fragments of an extensional detachment system. This interpretation is consistent with the overall asymmetric architecture of the coeval passive margins bordering the Piemonte–Ligurian ocean. It is suggested that the uplift of the ET peridotites occurred by tectonic denudation, in a slightly to strongly asymmetric oceanic rift.

Peridotite

Tectonite

Mylonite

Massif

10.1093/petrology/34.5.901

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Citations (123)

Structures in natural serpentinite gouges

Journal of Structural Geology (1994)

Eilard H. Hoogerduijn Strating Reinoud L.M. Vissers

Fault gouge

Mylonite

Cataclastic rock

Massif

Pyroxene

10.1016/0191-8141(94)90064-7

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Citations (32)

The structure of the Bracco Ophiolite complex (Ligurian Apennines, Italy): a change from Alpine to Apennine polarity

Journal of the Geological Society (1989)

Eilard H. Hoogerduijn Strating W.A. van Wamel

The Bracco ophiolite complex, exposed in the area studied as the Bracco Subunit of the Melange Nappe, is tectonically intercalated between the underlying Canetolo Nappe and the overlying Lavagna Nappe. Detailed structural analysis and mapping in these units reveals a multi-phase deformation history. In the Bracco Subunit and the Lavagna Nappe, this history is characterized by a change, from SW (i.e. ‘Alpine’) directed folding of the ophiolitic basement and its sedimentary cover, to NE (i.e. ‘Apennine’) directed folds and thrusts. The Canetolo Nappe only shows Apennine vergent structures. The Alpine vergent structures are considered to be developed during the Late Cretaceous to Palaeocene in an accretionary wedge associated with an east-dipping subduction zone. The first Apennine directed structures are low-angle extensional faults and cascading folds, indicating that the change to Apennine polarity resulted from gravitational collapse of the accretionary wedge during the Palaeocene to Eocene. Gravitational instability is considered to have resulted from a drastic decrease of subduction rate during the Palaeocene, which has led to extension and uplift of the wedge. The rapid decompression under isothermal to slightly decreasing temperature conditions of the high-pressure terrains in the Voltri Massif concurs well with this tectonic scenario.

Polarity (international relations)

10.1144/gsjgs.146.6.0933

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Citations (15)