The Zircon-Bearing Chromitites of the Phlogopite Peridotite of Finero (Ivrea Zone, Southern Alps): Evidence and Geochronology of a Metasomatized Mantle Slab

Grieco, G.; Ferrario, A.; Quadt, Albrecht von; Koeppel, V.; Mathez, E. A.

doi:10.1093/petrology/42.1.89

Cited by 108 publications

(74 citation statements)

References 20 publications

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“…The surrounding magmatic rocks are early Paleozoic (533 F 20 Ma for the amphibole peridotite and 549 F 12 Ma for the layered internal zone- Lu et al, 1997b), but ages obtained on the peridotite range from 293 to 163 Ma (Hunziker, 1974;Voshage et al, 1987;Hartmann and Wedepohl, 1993;Lu et al, 1997b;Grieco et al, 2001). This suggests that the peridotite experienced multiple metasomatic events that seemingly spanned tens of millions of years.…”

Section: Geology and Petrographymentioning

confidence: 99%

“…Agrinier et al, 1993;Arai and Yurimoto, 1994;Johnson et al, 1996;McPherson et al, 1996;Ionov et al, 1999;McInnes et al, 2001), there has been little investigation of how these processes relate to PGE mineralization. The Finero complex, where the dunite and chromitite appear to have formed by reaction of peridotite and melt (Grieco et al, 2001), offers a good opportunity to explore the influence of metasomatism on PGE mineralization.…”

Section: Introductionmentioning

confidence: 99%

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The effect of metasomatism on the Cr-PGE mineralization in the Finero Complex, Ivrea Zone, Southern Alps

Grieco

Ferrario

Mathez

2004

Ore Geology Reviews

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The magmatic metasomatism that was responsible for producing chromitite -dunite bodies in the unusual phlogopite peridotite of the Finero Complex in Permian to Triassic times also influenced the Cr-platinum group elements (PGE) mineralization. At least the end stages of this metasomatism are recorded in compositional zoning of chromite grains in the podiform chromitite. Metasomatic melt, with or without vapor, reacted with chromite to produce core-to-rim Cr enrichment of extant chromite grains and was concurrent with pyroxene crystallization. Under conditions of lower melt/rock ratio, metasomatism resulted in core-to-rim Al enrichment in chromite and crystallization of amphibole between chromite and clinopyroxene. This early, high-temperature metasomatism is unrelated to the later and pervasive K-metasomatism that crystallized phlogopite and was associated with the intrusion of clinopyroxenite dikes that cut the peridotite. Much later, serpentinization of olivine locally depleted chromite in Al and enriched it in Fe and formed minor amounts of magnetite.The PGE, which are present mainly as laurite inclusions in chromite, were remobilized by the early metasomatism. This resulted in substantial variation in the PGE contents of chromitites and imposed a characteristic PGE pattern in which chondritenormalized Os, Ir, Ru and Rh contents are high but Pt and Pd contents are low. The slopes of PGE chondrite-normalized concentration patterns are systematically related to absolute PGE abundance and to rock mode. Chromitites with low modal orthopyroxene, clinopyroxene, and amphibole exhibit negative PGE slopes and contain relatively high PGE concentrations, whereas chromitites rich in these silicate minerals have positive slopes and low PGE contents.

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Section: Geology and Petrographymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The effect of metasomatism on the Cr-PGE mineralization in the Finero Complex, Ivrea Zone, Southern Alps

Grieco

Ferrario

Mathez

2004

Ore Geology Reviews

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“…This mineral is presented in high amounts in the granites, diorites, nepheline syenites, lamproites, carbonatites and alkaline metasomatic rocks, more rarely it occurs in the gabbros, eclogites, kimberlites, minettes, lamproites, carbonatites, gneisses, amphibolites and other metamorphic rocks. Recently, the zircons were found in ultramafites from some mantle xenoliths in alkali basalts in several provinces of China and Russia [73,74], in ore chromitites occurring among phlogopite-bearing peridotites of Finero massif (Southern Alps) [75], as well as in dunites and ore chromitites of Voykar-Syn'insky massif (Polar Urals, Russia) [76,77]. In the latter case, as the authors assume, zircons crystallized from the residual portions of fractionated basic melts that infiltrated into peridotites.…”

Section: Zirconsmentioning

confidence: 99%

“…In these rocks the accessory zircons are much rarer present and in much smaller quantities than in most other varieties of magmatic and metamorphic rocks, so they are still the least studied with respect to the geochemistry of REE and other trace elements. Thus, in this concern there have been recently studied in detail the zircons from peridotites forming massifs in the Northern Tibet [88] and Sulu provinces (China) [89], from ultramafic xenoliths in kimberlites of Gibeon province (Southern Namibia), as well as from ultramafic xenoliths of some diatremes of Hinyang province (North China) [75]. According to the research, in the zircons from Hinyang province the total REE contents, except for Tb and Tm, vary in the range from 435 to 1483 ppm.…”

Section: Zirconsmentioning

confidence: 99%

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Consistent patterns of rare earth element distribution in accessory minerals from rocks of mafic-ultramafic complexes

Lesnov

2013

Open Geosciences

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This paper summarizes analytical data accumulated in the world literature and other materials about the regularities of the REE distribution in minerals contained in ultramafic and mafic rocks as accessory phases. These minerals are tentatively divided into two groups. The first includes garnets, zircons, apatites and perovskites, which can accumulate increased amounts of REE in their structure. The second consists of minerals whose structure can accumulate only limited contents of these trace elements. These are chrome-spinels, ilmenites, and micas. These minerals, in respect of REE geochemistry, are studied to a varying degree because of the different levels of accumulations of these elements, different degrees of occurrence in rocks, tiny sizes of their grains and other reasons. The analytical database formed on their basis includes about 600 original analyses. The overwhelming majority of presently available data on REE geochemistry in accessory minerals from ultramafic and mafic rocks have been published only in the recent 15 years. The studies became possible due to the development and introduction of new highly sensible microprobe analyses allowing detection of REE and many other trace elements in minerals grains directly in thin sections. The greatest numbers of these analyses were performed for garnets and zircons, fewer for apatites, and the fewest for chrome-spinels, ilmenites, micas, and perovskites. In general, the regularities of REE distribution in these minerals from ultramafic and mafic rocks are less studied compared to the rock-forming minerals from ultramafic and mafic rocks. Among the analytical methods, which were used to study the REE composition of accessory minerals, the most efficient was the mass-spectrometry with inductively coupled plasma (ICP-MS).Keywords: REE distribution • ultramafic and mafic rocks • accessory minerals © Versita Sp. z o.o.

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The deformation record of olivine in mylonitic peridotites from the Finero Complex, Ivrea Zone: Separate deformation cycles during exhumation

Matysiak

Trepmann

2015

Tectonics

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Mylonitic peridotites from the Finero complex are investigated to detect characteristic olivine microfabrics that can resolve separate deformation cycles at different metamorphic conditions. The heterogeneous olivine microstructures are characterized by deformed porphyroclasts surrounded by varying amounts of recrystallized grains. A well-developed but only locally preserved foam structure is present in recrystallized grain aggregates. This indicates an early stage of dynamic recrystallization and subsequent recovery and recrystallization at quasi-static stress conditions, where the strain energy was reduced such that a reduction in surface energy controlled grain boundary migration. Ultramylonites record a renewed stage of localized deformation and recrystallization by a second generation of recrystallized grains that do not show a foam structure. This second generation of recrystallized grains as well as sutured grain and kink band boundaries of porphyroclasts indicate that these microstructures developed during a stage of localized deformation after development of the foam structure. The heterogeneity of the microfabrics is interpreted to represent several (at least two) cycles of localized deformation separated by a marked hiatus with quasi-static recrystallization and recovery and eventually grain growth. The second deformation cycle did not only result in reactivation of preexisting shear zones but instead also locally affected the host rock that was not deformed in the first stage. Such stress cycles can result from sudden increases in differential stress imposed by seismic events, i.e., high stress-loading rates, during exhumation of the Finero complex.

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The Zircon-Bearing Chromitites of the Phlogopite Peridotite of Finero (Ivrea Zone, Southern Alps): Evidence and Geochronology of a Metasomatized Mantle Slab

Cited by 108 publications

References 20 publications

The effect of metasomatism on the Cr-PGE mineralization in the Finero Complex, Ivrea Zone, Southern Alps

The effect of metasomatism on the Cr-PGE mineralization in the Finero Complex, Ivrea Zone, Southern Alps

Consistent patterns of rare earth element distribution in accessory minerals from rocks of mafic-ultramafic complexes

The deformation record of olivine in mylonitic peridotites from the Finero Complex, Ivrea Zone: Separate deformation cycles during exhumation

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