1,721,011 research outputs found
Deformation-metamorphism relationships in the eclogitised serpentinites and rodingites of the Zermatt-Saas Zone – Western Alps (Upper Valtournenche – Aosta Valley – Italy)
No full textInteraction of deformation and metamorphism during subduction and exhumation of hydrated oceanic mantle : insights from the Western Alps
No full textPetrological investigations supported by multi-scale structural analysis of eclogitized serpentinite in the Zermatt–Saas Zone of the Western Alps allows for the determination of mineral assemblages related to successive fabrics, upon which the P–T–d–t path of these hydrated mantle rocks can be inferred. Serpentinites of the upper Valtournanche, with lenses and dykes of metagabbro and meta-rodingite, display an Alpine polyphase metamorphic evolution from eclogite to epidote-amphibolite facies conditions associated with three successive foliations having different parageneses in these rocks. Serpentinite mainly consists of serpentine with minor magnetite; however, where S1 and S2 foliations are pervasive, metamorphic olivine, together with Ti-clinohumite and clinopyroxene, are also found. The mineral assemblage associated with D1 includes serpentine1, clinopyroxene1, opaque minerals, titanite ± olivine1, Ti-clinohumite1 and ilmenite; the D2 assemblage is the same (±chlorite) but minerals have different compositions. The assemblage associated with D3 comprises serpentine3, opaque minerals, ±chlorite3, ilmenite and amphibole3. Ti-clinohumite is associated with veins that are older than D2 and pre-date D3. Veins that post-date D3 are characterized by amphibole + chlorite or by serpentine. P–T conditions for S2 parageneses evaluated using two pseudosections for different bulk compositions suggest that these rocks experienced pressures >2.5 ± 0.3 GPa at temperatures slightly higher than 600 °C. The late epidote–amphibolite facies re-equilibration associated with D3 and D4 developed during late syn-exhumation deformation related to folding and testifies to a small temperature decrease. These results, which were integrated in the regional framework, suggest that different portions of the Zermatt–Saas Zone registered different P–T peak conditions and underwent different exhumation paths. In addition, the inferred P–T–d–t path suggests that the Valtournanche serpentinites re-equilibrated close to the UHP conditions registered by the Cignana meta-cherts. These results imply that tectonic slices exhumed after UHP metamorphism might be wider than previously reported or that small-size UHP units, tectonically sampled during the Alpine convergence, are more abundant than those that have been detected to date
The subducted Tethys in the Aosta Valley (Italian Western Alps
No full textPre-congress Field trip guide-book B0
Deformation-metamorphism relationships in the eclogitised serpentinites and rodingites of the Upper Valtournenche (Zermatt-Saas Zone, Italy)
No full textCl-rich amphiboles from continental and oceanic crust : a microstructural and microchemical study
No full textEclogitised rodingites of the Zermatt-Saas Zone : unravelling their evolution through deformation–metamorphism relationships
No full textThe interplay between deformation and metamorphism during Alpine eclogitisation of pre-Alpine amphibolites in the Sesia-Lanzo Zone (Italian Western Alps)
No full textDeformation history of ultra high-pressure ophiolitic serpentinites in the Zermatt-Saas zone, Créton, upper Valtournanche (Aosta Valley, Western Alps)
No full textDetailed multiscale structural analyses and mapping (1:20 scale) integrated with petrological investigation were used to study a portion of the Zermatt-Saas serpentinites that crop out in upper Valtournanche (north-western Italy). Results are synthesized in a foliation trajectory map that displays the transposed original lithostratigraphy of a serpentinite body exposed at Créton. The serpentinite body comprises magnetite sheets and rare, decimetre-thick, diopsidite layers and lenses. Moreover, veins and aggregates of Ti-chondrodite and Ti-clinohumite, olivine-rich layers and lenses, veinlets of olivine, and layers of dark pyroxenite are embedded in the serpentinites. Serpentinites and associated rocks record three relative age groups of ductile structures: D1 consists of rare folds and S1 foliation; D2 is a group of isoclinal folds and a very pervasive foliation (S2), which is the dominant structure; D3 includes a crenulation and shear zones affecting S2. The detailed meso-structural and microstructural analyses allowed individuating the metamorphic environment of successive deformation stages and correlating the resulting tectono-metamorphic investigation with those already inferred in surrounding areas. In addition, metre- to submillimetre-sized pre-D2 structural, mineralogical, and textural relics have been clearly identified in spite of the strong transposition imposed during the development of S2 high pressure - ultra-high pressure foliation
An eclogitized, oceanic paleohydrothermal field from the St. Marcel Valley (Italian Western Alps).
No full textThe eclogite-facies Servette metaophiolites (St. Marcel Valley, Italian Western Alps) belong to the Piedmont Nappe. They are glaucophanite, chloriteschists,
talcschists and associated mineralised quartzite derived from different types of hydrated Tethyan oceanic crust affected by sea-floor and sub-sea
floor hydrothermal alteration. We first describe the geology and lithology of the Servette metaophiolites and their chemical signature, and then we focus on
the estimation of the Alpine subduction-related peak P-T metamorphic conditions and associated microstructures. Estimation of the peak P-T conditions was
performed via calculations of pseudosections representing the equilibrium assemblages in the studied rocks using THERMOCALC. These calculations yielded
relatively uniform values for the high-pressure metamorphic equilibration, with temperatures of 550 ± 60°C and pressures of 2.1 ± 0.3 Gpa, higher than the
previously estimated P-T in the St. Marcel Valley (T max = 500°C and P max = 1-4 GPa), but lower than those obtained in other localities of the Zermatt-Saas
zone (T up to 550-600° C and P up to 2.5-3.0 GPa). Comparison with similar rocks from the Zermatt-Saas zone helps to constrain the peculiar conditions at
the P peak of these hydrated rocks within the Alpine subduction slab
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