La couverture océanique des ultrabasites de Lanzo (Alpes occidentales) : arguments lithostratigraphiques et pétrologiques

Lagabrielle, Yves; Fudral, Serge; Kiénast, Jean-Robert

doi:10.1080/09853111.1990.11105199

Cited by 29 publications

(21 citation statements)

References 1 publication

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“…Middle to Upper Jurassic exhumation to the seafloor is also indicated by relatively poor exposures of a Mesozoic sedimentary cover, consisting of meta-ophicarbonate, metabasalt, calcschist, quartzite, and monometamorphic gneiss locally resting upon serpentinized mantle in the central and northern Lanzo massif (Pelletier and Müntener, 2006). Further occurrences of riftrelated contacts between meta-sediments and ophiolitic basement have been reported from the western margins of the Lanzo massif (Lagabrielle et al, 1989). However, this poorly exposed area is located along a major late-Alpine brittle-ductile movement zone characterized by predominant strike slip kinematics (Balestro et al, 2009), preventing the unambiguous attribution of specific outcrops to the Lanzo Massif or to the neighboring Piemonte units.…”

Section: Lanzo Massifmentioning

confidence: 95%

Recognizing remnants of magma-poor rifted margins in high-pressure orogenic belts: The Alpine case study

Beltrando

Manatschal

Mohn

et al. 2014

Earth-Science Reviews

125

104

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This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. Magma-poor rifted margins are being increasingly recognized in present-day Atlantic-type systems. However, findings of fossil areas floored by exhumed mantle or hyper-extended crust are comparatively rare within orogenic belts that were originated through the inversion of pre-existing rifted margins. This discrepancy may be due to the common reactivation of lithological contacts during subduction/orogeny, potentially masking pre-orogenic relationships, and, most importantly, to the frequent lack of a preorogenic layer-cake architecture, hindering retro-deformation of multiply deformed tectonic units. This study outlines a methodology to detect sections of magma-poor, hyper-extended rifted margins without a layer-cake architecture in multiply deformed/metamorphosed terrains. This approach is defined by comparison to well studied examples of fossil analogues preserved in weakly deformed parts of Alpine orogens. In the latter domains, continental basement and hydrated peridotites were exhumed at the basin floor during Jurassic rifting along long-offset detachment systems. Extensional geometries locally resulted in tectonic sampling of laterally discontinuous slivers of allochthonous continental basement and pre-rift sediments from the hanging wall blocks. Lithostratigraphic associations consisting of continental basement rocks directly juxtaposed with syn-to post-rift meta-sediments and/or serpentinized subcontinental mantle are widespread within sections of Alpine-type orogenic belts that underwent high-to ultra-high-pressure metamorphism. However, similar associations may arise from a variety of processes other than rift-related lithospheric thinning in magma-poor environments, including subduction mélange dynamics or deposition of sedimentary mélanges along convergent/divergent margins. The partial preservation of rift-related lithostratigraphic associations may still be assessed, despite the lack of biostratigraphic evidence, by (1) the consistency of the lithostratigraphic architecture over large areas, despite pervasive Alpine deformation, which rules out chaotic mixing during subduction/ exhumation, (2) the presence of clasts of basement rocks in the neighboring meta-sediments, indicating the original proximity of the different lithologies, (3) evidence of brittle deformation in continental basement and ultramafic rocks pre-dating Alpine metamorphism, indicating that they were juxtaposed by fault activity prior to the deposition of post-rift sediments, and (4) the similar Alpine tectono-metamorphic evolution of ophiolites, continental basement and meta-sediments. A re-assessment of basement-cover relationships in...

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Section: Lanzo Massifmentioning

confidence: 95%

Recognizing remnants of magma-poor rifted margins in high-pressure orogenic belts: The Alpine case study

Beltrando

Manatschal

Mohn

et al. 2014

Earth-Science Reviews

125

104

View full text Add to dashboard Cite

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“…The massif is a portion of oceanic lithosphere preserving its oceanic structure (Debret et al, 2013a;Lagabrielle et al, 1989). It is composed of a central part of SSP surrounded by a serpentinite envelope of 3-5 km width.…”

Section: The Lanzo Massifmentioning

confidence: 99%

Evolution of Fe redox state in serpentine during subduction

Debret

Andréani

Muñoz

et al. 2014

Earth and Planetary Science Letters

101

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“…The Lanzo massif is considered a part of the lithospheric mantle exhumed at the ocean floor during opening of the Jurassic-Piedmont Ligurian ocean (Lagabrielle et al 1989;Pognante et al 1985). Recent studies demonstrate that the presence of a high-temperature mantle shear zone between the north and the central part of the massif is related to rapid mantle exhumation.…”

Section: Geological Settingmentioning

confidence: 99%

“…Additional gabbro dikes and basaltic rocks are compiled from Boudier (1972Boudier ( ), (1978, Pognante (1989) and Pelletier (2003) However, in less serpentinized areas gabbroic dikes were partially transformed into eclogites during Alpine subduction in Alpine times (Kienast and Pognante 1988;Pelletier and Müntener 2006). Locally the massif is overlain by minor ophicarbonates, MORB type volcanic rocks and metasediments (Lagabrielle et al 1989;Pelletier and Müntener 2006). The core of the Lanzo massif is dominated by fertile plagioclase lherzolite and minor volumes of spinel harzburgite and dunite (Boudier 1972(Boudier , 1978Piccardo et al 2004).…”

Section: Geological Settingmentioning

confidence: 99%

Trace element chemistry and U–Pb dating of zircons from oceanic gabbros and their relationship with whole rock composition (Lanzo, Italian Alps)

Kaczmarek

Müntener

Rubatto

2007

Contrib Mineral Petrol

145

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The U-Pb ages and the trace element content of zircon U-Pb along with major and trace element whole rock data on gabbroic dikes from the Lanzo lherzolitic massif, N-Italy, have been determined to constrain crustal accretion in ocean-continent transition zones. Three Fe-Ti gabbros were dated from the central and the southern part of the massif providing middle Jurassic ages of 161 ± 2, 158 ± 2 and 163 ± 1 Ma, which argue for magmatic activity over few millions of years. Zircon crystals are characterized by high but variable Th/U ratios, rare earth element patterns enriched in heavy rare earths, pronounced positive Ce and negative Eu-anomalies consistent with crystallization after substantial plagioclase fractionation. The zircon trace element composition coupled with whole rock chemistry was used to reconstruct the crystallization history of the gabbros. A number of gabbros crystallized in situ, and zircon precipitated from trapped, intercumulus liquid, while other gabbros represent residual liquids that were extracted from a cumulus pile and crystallized along syn-magmatic shear zones. We propose a model in which the emplacement mechanism of gabbroic rocks in oceancontinent transition zones evolves from in situ crystallization to stratified crystallization with efficient extraction of residual liquid along syn-magmatic shear zones. Such an evolution of the crystallization history is probably related to the thermal evolution of the underlying mantle lithosphere.

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La couverture océanique des ultrabasites de Lanzo (Alpes occidentales) : arguments lithostratigraphiques et pétrologiques

Cited by 29 publications

References 1 publication

Recognizing remnants of magma-poor rifted margins in high-pressure orogenic belts: The Alpine case study

Recognizing remnants of magma-poor rifted margins in high-pressure orogenic belts: The Alpine case study

Evolution of Fe redox state in serpentine during subduction

Trace element chemistry and U–Pb dating of zircons from oceanic gabbros and their relationship with whole rock composition (Lanzo, Italian Alps)

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