Evidence of Early Permian extension during the post-Variscan evolution of the central Southern Alps (N Italy)

Locchi, Sofia; Zanchetta, Stefano; Zanchi, Andréa

doi:10.1007/s00531-022-02220-2

Cited by 5 publications

(1 citation statement)

References 76 publications

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“…In addition, in the last few years, a series of new studies about the late Variscan hydrothermalism of Lombard Southern Alps have been published (e.g. Servida et al, 2010;Martin et al, 2017;Locchi et al, 2022;Zanchetta et al, 2022), underlining a renewed scientific interest in these deposits.…”

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confidence: 99%

The base metal sulfide and Ni–Co arsenide-bearing veins of Valsassina, Lombardy, Italy: a preliminary study

Vergani,

Moroni,

Gentile

et al. 2024

MinMag

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Valsassina (Lombardy, Northern Italy) is located in the Lombard Southern Alps and is characterised by the presence of a metamorphic basement, by a major late Variscan intrusive complex and by Carboniferous–Permian volcano-sedimentary cover units. These rocks host a pervasive system of inadequately studied mineralised veins. These veins are characterised by base metal (Pb, Zn, Cu and Fe) and complex polymetallic assemblages. In this study, we have investigated the ore textures, mineral compositions of sulfides and sulfosalts (by EMPA–WDS and LA–ICP–MS analyses), and stable isotopes (C and O) in carbonate gangue minerals of various mineralised veins to determine the conditions of deposition of these ore deposits. Two different vein families can be recognised in Valsassina: NNW–SSE veins characterised by a complex polymetallic sulfide–sulfosalt assemblage, also with Ni–Co–Fe arsenides and other Ag–Bi-bearing minerals; and NE–SW veins with a simpler, base metal sulfide assemblage. The Ni–Co-bearing NNW–SSE veins have some distinctive features of the ‘five-element vein’ type deposits, with the Ni–Co–Fe arsenide ore stage pre-dating a sulfide-tetrahedrite-dominated ore stage. LA–ICP–MS data for pyrite and sphalerite, and stable isotopic compositions (C and O) of the carbonate gangue minerals, show no clear differences between the two families of veins, which are probably linked genetically. The isotopic compositions of the Valsassina vein carbonates are closely comparable with the signature of several major five-element ore districts. Preliminary temperature estimates for the Valsassina vein systems were based on the sphalerite composition, applying the GGIMFis geothermometer. The estimated temperatures for the sulfide-dominated ore stage post-dating the Ni–Co minerals precipitation range between 100 and 250°C. The crosscutting relationships, observed for all the veins with the host rocks, suggest a possible late to post Variscan (late Permian) age, making these vein systems comparable with other late–post Variscan polyphase hydrothermal events affecting large sectors of the Southern Alpine domain.

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Section: Introductionmentioning

confidence: 99%

The base metal sulfide and Ni–Co arsenide-bearing veins of Valsassina, Lombardy, Italy: a preliminary study

Vergani,

Moroni,

Gentile

et al. 2024

MinMag

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The Permian-Triassic succession of the Montagnola Senese Ridge (Middle Tuscan Ridge, Italy): a perspective for late Palaeozoic magmatism and continentalisation in the western Tethys

Brogi

Regoli

Spina

et al. 2023

International Geology Review

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The Val Biandino Intrusive Suite (central Southern Alps, N Italy): new geochronological and geochemical data on the Early Permian magmatic activity in the Southalpine Domain

Zanchetta,

Crippa,

Zanchi

et al. 2024

Swiss J Geosci

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The Early Permian in the present-day Europe area was a time when a major tectonic shift occurred, leading from the tectonic collapse of the Variscan orogeny to the crustal extension and thinning that characterized the Early Permian times. Crustal extension was associated with extensive magmatism at different crustal levels: from gabbro in the lower crust or at the mantle/crust transition to subaerial high-SiO2 volcanic activity. In the whole Southalpine Domain, the Early Permian intrusive bodies occur from the west (e.g. Ivrea-Verbano Complex and “Graniti dei Laghi”) to the east (Ifinger, Brixen and Cima d’Asta intrusive complexes). Among these, in the central Southern Alps (comprised between the Giudicarie Belt and the Lake Como), minor intrusive complexes also occur. The Val Biandino Intrusive Suite consists of two magmatic units: the Val Biandino Quartz-Diorite (VBQD) and the Valle di San Biagio Granite (VSBG). The first of them consists of gabbro-diorite to granodiorite bodies associated with leucocratic cordierite-bearing granitic dikes that intruded the pre-Permian basement. To the west, a W-dipping normal fault of Permian age represents the boundary between this unit and the Valle di San Biagio porphyric granite. All rock varieties of the Val Biandino Intrusive Suite display a high-K calc-alkaline affinity with metaluminous to peraluminous character. Field crosscutting relationships point to a late generation of the cordierite granites of the Val Biandino Quartz-Diorite unit with respect to the more mafic types. SHRIMP U–Pb zircon dating provided an age of 285.2 ± 1.9 Ma for a cordierite granite of the Val Biandino Quartz-Diorite unit and 283.2 ± 1.9 Ma for the porphyric Valle di San Biagio Granite. Geochemical data suggest that gabbro-diorite, quartz-diorite, granodiorite and leucogranite are not co-magmatic. The existing gaps in term of SiO2 wt% and the higher HREE contents in mafic and intermediate rocks with respect to granite coupled with similar LREE in all rocks support this hypothesis. The high Rb/Sr ratios (> 1) in leucogranite, together with the occurrence of white mica and cordierite point to a significant contribution of crustal partial melting in their genesis. The Val Biandino Intrusive Suite was likely formed through the interaction of magma genesis at the mantle/crust transition and partial melting of the heterogeneous pre-Permian basement of the Southalpine Domain. This scenario explains the strong heterogeneity displayed by the relatively small intrusive complex and the strong crustal signature exhibited by all the magmatic types of the Val Biandino Intrusive Suite.

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Evidence of Early Permian extension during the post-Variscan evolution of the central Southern Alps (N Italy)

Cited by 5 publications

References 76 publications

The base metal sulfide and Ni–Co arsenide-bearing veins of Valsassina, Lombardy, Italy: a preliminary study

The base metal sulfide and Ni–Co arsenide-bearing veins of Valsassina, Lombardy, Italy: a preliminary study

The Permian-Triassic succession of the Montagnola Senese Ridge (Middle Tuscan Ridge, Italy): a perspective for late Palaeozoic magmatism and continentalisation in the western Tethys

The Val Biandino Intrusive Suite (central Southern Alps, N Italy): new geochronological and geochemical data on the Early Permian magmatic activity in the Southalpine Domain

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