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

Federico, Laura; Crispini, Laura; Scambelluri, Marco; Capponi, Giovanni

doi:10.3166/ga.20.3-19

Cited by 21 publications

(13 citation statements)

References 29 publications

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“…The low Ti content of the BEIG zircon rims is in line with growth at T ≤ 650°C [ Watson et al , 2006]. Petrological evidence shows that the Voltri‐Rossiglione Unit, during its metamorphic evolution (from burial to exhumation), never experienced temperatures in excess of ∼550°C [ Cimmino and Messiga , 1979; Hoogerduijn Strating , 1991; Federico et al , 2007a] (see also this study). The euhedral shape and the sharp boundaries with the magmatic zircon core suggest that the rims represent new growth and not recrystallized domains.…”

Section: Discussionsupporting

confidence: 61%

“…1. D 1 ‐M 1 stage corresponds to peak metamorphism under blueschist to eclogitic facies conditions [e.g., Liou et al , 1998; Brouwer et al , 2002; Vignaroli et al , 2005; Federico et al , 2007a, 2007b], which is assigned to the time interval between ∼34 and ∼50 Ma [see also Rubatto and Scambelluri , 2003; Federico et al , 2005, 2007b]. The D 1 fabric has been extensively overprinted and no structural/kinematics data could be obtained.…”

Section: Discussionmentioning

confidence: 99%

“…Numbers refer to the following: 1, Rubatto and Scambelluri [2003]; 2, Hoogerduijn Strating [1991]; 3, Barbieri et al [2003]; 4, Carrapa et al [2004]; 5, Charrier et al [1964] and Gelati et al [1993]; 6, Di Biase and Pandolfi [1999]; 7, Federico et al [2005]; 8, Gelati and Gnaccolini [1998]; 9, Bertotti et al [2006]; 10, Federico et al [2007b]. (c–f) Proposed tectonic models for exhumation in the Voltri Massif, simplified and redrawn after Messiga and Scambelluri [1991] (Figure 2c), Federico et al [2007a] (Figure 2d), Hoogerduijn Strating [1994], with permission from Elsevier (Figure 2e), and Vignaroli et al [2008] (Figure 2f). The asterisk indicates the supposed position of the Voltri Massif.…”

Section: Geological Background Of the Voltri Massifmentioning

confidence: 99%

“…Peak metamorphic conditions are represented by relicts of garnet, paragonite, sodic amphibole and zoisite together with Si 4+ ‐rich phengite (Si 4+ > 3.5 atoms per formula unit (a.p.f.u. )), all preserved in low‐strain domains indicating temperatures of 450°C–550°C and pressures of 12–18 kbar [e.g., Cimmino and Messiga , 1979; Hoogerduijn Strating , 1991; Federico et al , 2007a]. The polyphase decompression event involves a transition from blueschist facies conditions to greenschist facies conditions, as revealed by the occurrence of chloritoid, albite, chlorite, titanite and lower Si 4+ phengite assemblages [ Cimmino and Messiga , 1979; Hoogerduijn Strating , 1991].…”

Section: Geological Background Of the Voltri Massifmentioning

confidence: 99%

“…In the Erro‐Tobbio Unit, both presubduction [e.g., Vissers et al , 1991; Borghini et al , 2007] and subduction related structures have been observed [e.g., Hoogerduijn Strating et al , 1993; Scambelluri et al , 1995; Hermann et al , 2000]. The deformation history is best preserved in the metasedimentary sequence of the Voltri‐Rossiglione Unit, where the polyphase fabric shows evidence of progressively refolded mylonitic zones with superimposed brittle deformation features [e.g., Hoogerduijn Strating , 1994; Capponi and Crispini , 2002; Federico et al , 2007a; Vignaroli et al , 2009a], attesting for evolution of deformation during exhumation path.…”

Section: Geological Background Of the Voltri Massifmentioning

confidence: 99%

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Pressure-temperature-deformation-time (P-T-d-t) exhumation history of the Voltri Massif HP complex, Ligurian Alps, Italy

et al. 2010

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[1] An integrated structural, petrological, and geochronological/thermochronological study was undertaken to constrain the tectonic controls on the exhumation of the Voltri Massif high-pressure (HP) complex, located in the Ligurian portion of the Western Alps (Italy). Petrotextural analyses were performed to identify the pressure-temperature interval of (1) peak metamorphism (the D 1 -M 1 stage) to eclogitic/blueschist facies conditions and (2) the main retrogressive event (the D 2 -M 2 stage) to greenschist facies conditions. U-Pb SHRIMP dating on a zircon rim (33.8 ± 0.8 Ma) and titanite grains (29 ± 5 Ma), coupled with 40 Ar-39 Ar analyses on phengite (∼64 Ma to ∼34 Ma) placed temporal constraints on the exhumation path from the D 1 -M 1 to the D 2 -M 2 stages at the Eocene-Oligocene boundary. Apatite fission track thermochronology, with older ages of 23.9 ± 4.9 Ma, confirms the existence of a regional, Late Oligocene to Miocene cooling/exhumation event for the Voltri Massif (the D 3 -M 3 stage). The compilation of this pressure-temperature-deformation-time path supports a change in the exhumation history: (1) an initial stage, from the D 1 -M 1 to the D 2 -M 2 , which was nearly isothermal with highly variable exhumation rates, and (2) a second stage, from D 2 -M 2 to upper crustal levels, which was accomplished by cooling and moderate exhumation rates of ∼1-2 mm yr −1 . This two-stage path can be reconciled with the dominant tectonic mechanisms responsible for exhumation of HP rocks in the Voltri Massif area. At the regional scale, this path is consistent with major geodynamic reorganization in the Mediterranean region at the Eocene-Oligocene time boundary, which involved a switch from synorogenic events during transpressive kinematics at the Alpine-Apennine plate boundaries, to postorogenic processes related to crustal thinning and opening of back-arc basins. Citation: Vignaroli, G.,

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Section: Discussionsupporting

confidence: 61%

Section: Discussionmentioning

confidence: 99%

Section: Geological Background Of the Voltri Massifmentioning

confidence: 99%

Section: Geological Background Of the Voltri Massifmentioning

confidence: 99%

Section: Geological Background Of the Voltri Massifmentioning

confidence: 99%

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Pressure-temperature-deformation-time (P-T-d-t) exhumation history of the Voltri Massif HP complex, Ligurian Alps, Italy

et al. 2010

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Controls on development of different mineral assemblages in gabbro and basalt during subduction metamorphism

Kang

Fornash

2020

Contrib Mineral Petrol

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Coexisting fine-grained (meta-volcanic) and coarse-grained (meta-plutonic) mafic rocks in a high-pressure (P)/low-temperature (T) complex (Sivrihisar, Turkey) preserve different prograde, peak, and retrograde mineral assemblages, providing an opportunity to evaluate controls on mineral assemblages in metabasites that experienced the same P-T conditions. Finegrained metabasalts are garnet-bearing lawsonite blueschist and eclogite with similar assemblages that vary on a mm-to cm-scale in mode of glaucophane vs. omphacite. In contrast, metagabbro consists of a disequilibrium mineral suite of relict igneous clinopyroxene partially replaced by omphacite or hydrous phases (lawsonite + tremolite or glaucophane) in a matrix of fine-grained lawsonite, omphacite, tremolite, white mica, very rare garnet, and retrograde minerals (e.g., epidote, albite, and titanite), with later chlorite and calcite. Pseudosection modeling predicts similar peak P-T conditions (490-530 °C, 1.8-2.0 GPa) for both glaucophane-rich (blueschist) and omphacite-rich (eclogite) layers of the metabasalt and similar to slightly higher conditions (490-600 °C, 1.9-2.5 GPa) for metagabbro. The range of modelled H 2 O content at peak P-T conditions in metabasalt (2.0-5.4 wt%) is significantly lower than in metagabbro (6.4-8.7 wt%) due to the higher modal abundance of hydrous minerals in the latter. At the relatively similar peak P-T conditions, metagabbro experienced different reaction histories from coexisting metabasalt, thereby developing distinctive HP/LT mineral assemblages and modes (e.g., scarce garnet) owing to its more Mg-rich bulk composition (X Mg = 0.58-0.84 vs. 0.50), higher H 2 O content, and coarser grain-size. This study is the first petrologic analysis of Sivrihisar metagabbro and the first systematic study of H 2 O content in metabasites from this locality, which is one of the best-preserved examples of lawsonite eclogite and blueschist in the world.

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Exhumation dynamics of high-pressure metamorphic rocks from the Voltri Unit, Western Alps: constraints from phengite Rb–Sr geochronology

Smye

Seman

Scambelluri

et al. 2021

Contrib Mineral Petrol

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

Cited by 21 publications

References 29 publications

Pressure-temperature-deformation-time (P-T-d-t) exhumation history of the Voltri Massif HP complex, Ligurian Alps, Italy

Pressure-temperature-deformation-time (P-T-d-t) exhumation history of the Voltri Massif HP complex, Ligurian Alps, Italy

Controls on development of different mineral assemblages in gabbro and basalt during subduction metamorphism

Exhumation dynamics of high-pressure metamorphic rocks from the Voltri Unit, Western Alps: constraints from phengite Rb–Sr geochronology

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