Petrology, trace element and Sr, Nd, Hf isotope geochemistry of the north lanzo peridotite massif (Western Alps, Italy)

Luisa Guarnieri, Eizou Nakamura, Giovanni B. Piccardo, Chie Sakaguchi, Nobumichi Shimizu, Riccardo Vannucci, Alberto Zanetti

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

Field, petrographic-structural and geochemical data are reported for spinel and plagioclase peridotites from the northern domain of the Lanzo peridotite massif (Western Alps).The North Lanzo peridotites are extremely heterogeneous in terms of mineral mode, texture and chemistry. They can be referred to four major groups: (1) spinel harzburgites with coarse granular to porphyroclastic structures; (2) pyroxene-depleted spinel harzburgites recording olivine-forming or pyroxene-consuming microtextures; (3) spinel lherzolites with porphyroclastic to foliated and banded structures; (4) plagioclaseenriched spinel lherzolites. Major and trace element characterization of whole-rocks and their constituent minerals allows reconstruction of the complex series of pre- to syn-rift events this mantle sector underwent. Sr, Nd and Hf isotope data provide information on the nature of infiltrating melts and time constraints. More depleted harzburgites represent refractory protoliths that after melt extraction, possibly in the presence of residual garnet, underwent a first episode of refertilization by enriched mid-ocean ridge basalt (E-MORB)-like melts, whereas harzburgites and spinel lherzolites with ocean island basalt (OIB) signatures document the successive migration of alkaline melts. The most noticeable feature of this group of rocks is their Nd-Hf decoupling, specifically the very high 176Hf/ 177Hf coupled with very low 143Nd/ 144Nd. Lu-Hf data for these peridotites define an ~260Ma errorchron that is interpreted as evidence of mixing during relatively recent times between old (most probably Proterozoic) refractory subcontinental mantle and OIB-type melts. This event most probably occurred during extension (Triassic times) or during the onset of exhumation (Liassic times). Plagioclase peridotites document the last refertilization episode, involving the shallow-level impregnation of harzburgite mantle by evolved MORB melts before its sea-floor emplacement. This MiddleJurassic event caused the almost complete resetting of the original trace element and 87Sr/ 86Sr composition. The combination of structural, petrological and geochemical information for a north- south Lanzo traverse, from the North Massif to the South Massif, notwithstanding the effects of the alpine orogeny, allows the study of the complete evolution of a sector of old (Proterozoic?) mantle since the early stages of melt removal and allows reconstruction of the tectonic and magmatic events during continental extension leading to the opening of the Jurassic Ligurian-Piedmontese basin. North Lanzo fundamentally preserves the record of pre-syn-rift ancient episodes, whereas South Lanzo better highlights the processes that deeply modified and refertilized the older lithosphere during subsequent lithosphere extension. Slow to very slow extension led to sea-floor exposure of the subcontinental lithospheric mantle (North Lanzo) at a marginal position, close to the Adria continental margin, and of the deeply melt-modified lithospheric mantle (Lanzo South) in a more distal setting of the basin. In this respect, the Lanzo traverse is closely similar to the ocean-continent transition in slow- or ultraslow-spreading oceanic basins, such as the North Atlantic.

Original languageEnglish
Article numberegs049
Pages (from-to)2259-2306
Number of pages48
JournalJournal of Petrology
Volume53
Issue number11
DOIs
Publication statusPublished - Nov 2012

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Petrology
petrology
Geochemistry
peridotite
Trace Elements
geochemistry
trace elements
Italy
Isotopes
spinel
Earth mantle
isotopes
trace element
melt
isotope
mantle
basalt
oceans
refractories
plagioclase

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Petrology, trace element and Sr, Nd, Hf isotope geochemistry of the north lanzo peridotite massif (Western Alps, Italy). / Guarnieri, Luisa; Nakamura, Eizou; Piccardo, Giovanni B.; Sakaguchi, Chie; Shimizu, Nobumichi; Vannucci, Riccardo; Zanetti, Alberto.

In: Journal of Petrology, Vol. 53, No. 11, egs049, 11.2012, p. 2259-2306.

Research output: Contribution to journalArticle

Guarnieri, Luisa ; Nakamura, Eizou ; Piccardo, Giovanni B. ; Sakaguchi, Chie ; Shimizu, Nobumichi ; Vannucci, Riccardo ; Zanetti, Alberto. / Petrology, trace element and Sr, Nd, Hf isotope geochemistry of the north lanzo peridotite massif (Western Alps, Italy). In: Journal of Petrology. 2012 ; Vol. 53, No. 11. pp. 2259-2306.
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abstract = "Field, petrographic-structural and geochemical data are reported for spinel and plagioclase peridotites from the northern domain of the Lanzo peridotite massif (Western Alps).The North Lanzo peridotites are extremely heterogeneous in terms of mineral mode, texture and chemistry. They can be referred to four major groups: (1) spinel harzburgites with coarse granular to porphyroclastic structures; (2) pyroxene-depleted spinel harzburgites recording olivine-forming or pyroxene-consuming microtextures; (3) spinel lherzolites with porphyroclastic to foliated and banded structures; (4) plagioclaseenriched spinel lherzolites. Major and trace element characterization of whole-rocks and their constituent minerals allows reconstruction of the complex series of pre- to syn-rift events this mantle sector underwent. Sr, Nd and Hf isotope data provide information on the nature of infiltrating melts and time constraints. More depleted harzburgites represent refractory protoliths that after melt extraction, possibly in the presence of residual garnet, underwent a first episode of refertilization by enriched mid-ocean ridge basalt (E-MORB)-like melts, whereas harzburgites and spinel lherzolites with ocean island basalt (OIB) signatures document the successive migration of alkaline melts. The most noticeable feature of this group of rocks is their Nd-Hf decoupling, specifically the very high 176Hf/ 177Hf coupled with very low 143Nd/ 144Nd. Lu-Hf data for these peridotites define an ~260Ma errorchron that is interpreted as evidence of mixing during relatively recent times between old (most probably Proterozoic) refractory subcontinental mantle and OIB-type melts. This event most probably occurred during extension (Triassic times) or during the onset of exhumation (Liassic times). Plagioclase peridotites document the last refertilization episode, involving the shallow-level impregnation of harzburgite mantle by evolved MORB melts before its sea-floor emplacement. This MiddleJurassic event caused the almost complete resetting of the original trace element and 87Sr/ 86Sr composition. The combination of structural, petrological and geochemical information for a north- south Lanzo traverse, from the North Massif to the South Massif, notwithstanding the effects of the alpine orogeny, allows the study of the complete evolution of a sector of old (Proterozoic?) mantle since the early stages of melt removal and allows reconstruction of the tectonic and magmatic events during continental extension leading to the opening of the Jurassic Ligurian-Piedmontese basin. North Lanzo fundamentally preserves the record of pre-syn-rift ancient episodes, whereas South Lanzo better highlights the processes that deeply modified and refertilized the older lithosphere during subsequent lithosphere extension. Slow to very slow extension led to sea-floor exposure of the subcontinental lithospheric mantle (North Lanzo) at a marginal position, close to the Adria continental margin, and of the deeply melt-modified lithospheric mantle (Lanzo South) in a more distal setting of the basin. In this respect, the Lanzo traverse is closely similar to the ocean-continent transition in slow- or ultraslow-spreading oceanic basins, such as the North Atlantic.",
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T1 - Petrology, trace element and Sr, Nd, Hf isotope geochemistry of the north lanzo peridotite massif (Western Alps, Italy)

AU - Guarnieri, Luisa

AU - Nakamura, Eizou

AU - Piccardo, Giovanni B.

AU - Sakaguchi, Chie

AU - Shimizu, Nobumichi

AU - Vannucci, Riccardo

AU - Zanetti, Alberto

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N2 - Field, petrographic-structural and geochemical data are reported for spinel and plagioclase peridotites from the northern domain of the Lanzo peridotite massif (Western Alps).The North Lanzo peridotites are extremely heterogeneous in terms of mineral mode, texture and chemistry. They can be referred to four major groups: (1) spinel harzburgites with coarse granular to porphyroclastic structures; (2) pyroxene-depleted spinel harzburgites recording olivine-forming or pyroxene-consuming microtextures; (3) spinel lherzolites with porphyroclastic to foliated and banded structures; (4) plagioclaseenriched spinel lherzolites. Major and trace element characterization of whole-rocks and their constituent minerals allows reconstruction of the complex series of pre- to syn-rift events this mantle sector underwent. Sr, Nd and Hf isotope data provide information on the nature of infiltrating melts and time constraints. More depleted harzburgites represent refractory protoliths that after melt extraction, possibly in the presence of residual garnet, underwent a first episode of refertilization by enriched mid-ocean ridge basalt (E-MORB)-like melts, whereas harzburgites and spinel lherzolites with ocean island basalt (OIB) signatures document the successive migration of alkaline melts. The most noticeable feature of this group of rocks is their Nd-Hf decoupling, specifically the very high 176Hf/ 177Hf coupled with very low 143Nd/ 144Nd. Lu-Hf data for these peridotites define an ~260Ma errorchron that is interpreted as evidence of mixing during relatively recent times between old (most probably Proterozoic) refractory subcontinental mantle and OIB-type melts. This event most probably occurred during extension (Triassic times) or during the onset of exhumation (Liassic times). Plagioclase peridotites document the last refertilization episode, involving the shallow-level impregnation of harzburgite mantle by evolved MORB melts before its sea-floor emplacement. This MiddleJurassic event caused the almost complete resetting of the original trace element and 87Sr/ 86Sr composition. The combination of structural, petrological and geochemical information for a north- south Lanzo traverse, from the North Massif to the South Massif, notwithstanding the effects of the alpine orogeny, allows the study of the complete evolution of a sector of old (Proterozoic?) mantle since the early stages of melt removal and allows reconstruction of the tectonic and magmatic events during continental extension leading to the opening of the Jurassic Ligurian-Piedmontese basin. North Lanzo fundamentally preserves the record of pre-syn-rift ancient episodes, whereas South Lanzo better highlights the processes that deeply modified and refertilized the older lithosphere during subsequent lithosphere extension. Slow to very slow extension led to sea-floor exposure of the subcontinental lithospheric mantle (North Lanzo) at a marginal position, close to the Adria continental margin, and of the deeply melt-modified lithospheric mantle (Lanzo South) in a more distal setting of the basin. In this respect, the Lanzo traverse is closely similar to the ocean-continent transition in slow- or ultraslow-spreading oceanic basins, such as the North Atlantic.

AB - Field, petrographic-structural and geochemical data are reported for spinel and plagioclase peridotites from the northern domain of the Lanzo peridotite massif (Western Alps).The North Lanzo peridotites are extremely heterogeneous in terms of mineral mode, texture and chemistry. They can be referred to four major groups: (1) spinel harzburgites with coarse granular to porphyroclastic structures; (2) pyroxene-depleted spinel harzburgites recording olivine-forming or pyroxene-consuming microtextures; (3) spinel lherzolites with porphyroclastic to foliated and banded structures; (4) plagioclaseenriched spinel lherzolites. Major and trace element characterization of whole-rocks and their constituent minerals allows reconstruction of the complex series of pre- to syn-rift events this mantle sector underwent. Sr, Nd and Hf isotope data provide information on the nature of infiltrating melts and time constraints. More depleted harzburgites represent refractory protoliths that after melt extraction, possibly in the presence of residual garnet, underwent a first episode of refertilization by enriched mid-ocean ridge basalt (E-MORB)-like melts, whereas harzburgites and spinel lherzolites with ocean island basalt (OIB) signatures document the successive migration of alkaline melts. The most noticeable feature of this group of rocks is their Nd-Hf decoupling, specifically the very high 176Hf/ 177Hf coupled with very low 143Nd/ 144Nd. Lu-Hf data for these peridotites define an ~260Ma errorchron that is interpreted as evidence of mixing during relatively recent times between old (most probably Proterozoic) refractory subcontinental mantle and OIB-type melts. This event most probably occurred during extension (Triassic times) or during the onset of exhumation (Liassic times). Plagioclase peridotites document the last refertilization episode, involving the shallow-level impregnation of harzburgite mantle by evolved MORB melts before its sea-floor emplacement. This MiddleJurassic event caused the almost complete resetting of the original trace element and 87Sr/ 86Sr composition. The combination of structural, petrological and geochemical information for a north- south Lanzo traverse, from the North Massif to the South Massif, notwithstanding the effects of the alpine orogeny, allows the study of the complete evolution of a sector of old (Proterozoic?) mantle since the early stages of melt removal and allows reconstruction of the tectonic and magmatic events during continental extension leading to the opening of the Jurassic Ligurian-Piedmontese basin. North Lanzo fundamentally preserves the record of pre-syn-rift ancient episodes, whereas South Lanzo better highlights the processes that deeply modified and refertilized the older lithosphere during subsequent lithosphere extension. Slow to very slow extension led to sea-floor exposure of the subcontinental lithospheric mantle (North Lanzo) at a marginal position, close to the Adria continental margin, and of the deeply melt-modified lithospheric mantle (Lanzo South) in a more distal setting of the basin. In this respect, the Lanzo traverse is closely similar to the ocean-continent transition in slow- or ultraslow-spreading oceanic basins, such as the North Atlantic.

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