Megacrystic zircon with planar fractures in miaskite-type nepheline pegmatites formed at high pressures in the lower crust (Ivrea Zone, southern Alps, Switzerland)

2014 ◽  
Vol 100 (1) ◽  
pp. 83-94 ◽  
Author(s):  
U. Schaltegger ◽  
A. Ulianov ◽  
O. Muntener ◽  
M. Ovtcharova ◽  
I. Peytcheva ◽  
...  
Keyword(s):  
Lower Crust ◽  
High Pressures ◽  
Southern Alps ◽  
Ivrea Zone

Tectonometamorphic history of the Ivrea Zone and its relationship to the crustal evolution of the Southern Alps

1990 ◽  
Vol 182 (1-2) ◽  
pp. 169-192 ◽  
Author(s):  
A Zingg ◽  
M.R Handy ◽  
J.C Hunziker ◽  
S.M Schmid
Keyword(s):  
Southern Alps ◽  
Crustal Evolution ◽  
Ivrea Zone ◽  
History Of

Timing of crustal melting and magma emplacement at different depths: insights from the Permian in the Western Alps

2020 ◽  
Author(s):  
Paola Manzotti ◽  
Florence Bégué ◽  
Barbara Kunz ◽  
Daniela Rubatto ◽  
Alexey Ulianov
Keyword(s):  
Lower Crust ◽  
Western Alps ◽  
Southern Alps ◽  
The Other ◽  
Crustal Melting ◽  
Data Set ◽  
Alpine Orogeny ◽  
History Of ◽  
Different Depths ◽  
Magma Emplacement

<p>The pre-Alpine basement of the Adriatic plate in the Southern Alps exposes an exceptionally complete section across the continental crust (Ivrea Verbano: lower crust; Serie dei Laghi: upper crust). The section was weakly reworked during Jurassic extension and Cretaceous to Miocene Alpine shortening. The Insubric Line, an Alpine crustal-scale south-vergent backthrust, separates the Southern Alps from the Alpine nappe stack. The pre-Alpine basement of the Adriatic palaeomargin is intensely reworked in this stack, and is now part of the Sesia-Dent Blanche nappes (Manzotti et al. 2014) and other, smaller, Adria-derived units (e.g. Emilius).</p><p>The less deformed part of the Sesia-Dent Blanche nappes are the IIDK and Valpelline Series. Based on lithological similarities, they have been correlated with the Ivrea-Verbano Zone (Carraro et al. 1970). This equivalence has been confirmed by subsequent studies, including detailed U-Pb zircon ages of metamorphic (Kunz et al., 2018) and magmatic events. The other units of the Sesia-Dent Blanche nappes (the Arolla Series, the Gneiss Minuti, and the Eclogitic Micaschists) have been pervasively reworked during the Alpine orogeny, from greenschist to eclogite-facies. Identification of the age and nature of their pre-Alpine protoliths, and of the grade and age of their pre-Alpine metamorphism heavily relies on field and petrological data on key outcrops, supported by U-Pb dating.</p><p>If the IIDK and Valpelline Series represent the lower Adriatic crust, the other units may derive from the upper Adriatic crust, i.e. may be similar to the Serie dei Laghi in the Southern Alps. Alternatively, they may also represent pieces of the Adriatic lower crust that were pervasively re-hydrated during the Jurassic extension and/or the Alpine subduction (Engi et al., 2018), thus allowing re-equilibration at HP conditions during Alpine deformation.</p><p>This contribution will summarize a range of field, petrological, and geochronological data (obtained by LA-ICP MS on zircon, combined with in situ-oxygen isotope data measured by SIMS). This data set reveals significant differences in the timing of crustal melting, as well as magma emplacement at different depths. It can be concluded that the history of the Adriatic crust in the Alpine stack is comparable with that of the Southern Alps, with implications for the mechanical behaviour of the crust during the Alpine orogeny.</p><p> </p><p>Manzotti et al. (2014). Swiss Journal of Geosciences, 107, 309-336</p><p>Carraro et al. (1970). Memorie della Società Geologica Italiana, 9, 19-224</p><p>Kunz et al. (2018). International Journal of Earth Sciences, 107, 203-229</p><p>Engi et al. (2018). Geochemistry, Geophysics, Geosystems, 19, 865-881</p>

Corundum-rich dykes constraining Triassic alkaline magmatism in the Ivrea-Verbano Zone (Southern Alps): a zircon approach

2021 ◽  
Author(s):  
Mattia Bonazzi ◽  
Antonio Langone ◽  
Simone Tumiati ◽  
Edoardo Dellarole ◽  
Maurizio Mazzucchelli ◽  
...  
Keyword(s):  
High Pressures ◽  
Crustal Contamination ◽  
Weighted Average ◽  
Western Alps ◽  
Southern Alps ◽  
Accessory Mineral ◽  
Alkaline Magmatism ◽  
Mafic Complex ◽  
High Concentrations ◽  
Parental Melts

<p>Zircon is a common accessory mineral in evolved magmatic rocks and its investigation can provide unevaluable geochronological and geochemical information. The lower continental crust forming the Ivrea-Verbano Zone (IVZ, Southern Alps) locally shows the discordant intrusion of swarms of felsic dykes, which petrology was poorly constrained. Corundum-rich (Crn up to 55 vol.%) felsic dykes were sampled in two different outcrops along the Sabbiola valley (central IVZ). Besides corundum, they consist mainly of sodic plagioclase (An=5-10 %), biotite-siderophyllite, ±K-feldspar and ±hercynite. These dykes intrude granulites and Permian mafic intrusives, showing either pegmatite-like or porphyroclastic textures and contain abundant zircon. Trace elements concentration, as well as the isotopic U-Pb and Lu-Hf compositions of zircons have been determined by LA-ICP-(MC)MS to unravel emplacement ages and nature of parental melts. U-Pb weighted average ages point to Norian emplacement (ca. 224 Ma). Zircons are characterized by very high concentrations in REE, Th, U, Nb and Ta. REE patterns show marked negative Eu anomaly. These data, in association with the enrichments of Na in plagioclases and of Fe in micas and oxides, suggest that the parent melts were extremely evolved differentiates. Porphyroclastic texture developed in the frame of magmatic processes due to volatiles overpressure. Strongly positive Hf<sub>(</sub><sub>t)</sub> values (+13 on average) suggest a derivation of the parental melts from depleted to mildly enriched mantle sources. This observation and the corundum saturation (evidence for low silica activity) point to limited crustal contamination, which was favored by the high eutectic temperature of the host rocks. It is proposed that studied dykes segregated from peraluminous melts produced by exsolution processes affecting volatile-rich differentiates during alkaline magmatism (Bonazzi et al., 2020).</p><p>Triassic magmatic activity is largely documented throughout the Southern Alps, being related to different tectono-magmatic cycles. Nevertheless, before this study, the evidence of Triassic magmatism in IVZ was restricted only in its northernmost tip (Finero area, e.g. Zanetti et al., 2013; Schaltegger et al., 2015). This work provides robust constraints about the transition of the geochemical affinity of Southern Alps magmatism from orogenic-like to anorogenic during Norian, linked to a regional uprising of the asthenosphere and changes of tectonic regime.</p><p> </p><p>References</p><p>Bonazzi, M.; Langone, A.; Tumiati, S.; Dellarole, E.; Mazzucchelli, M.; Giovanardi, T.; Zanetti, A. Mantle-Derived Corundum-Bearing Felsic Dykes May Survive Only within the Lower (Refractory/Inert) Crust: Evidence from Zircon Geochemistry and Geochronology (Ivrea–Verbano Zone, Southern Alps, Italy). Geosciences 2020, 10, 281.</p><p>Schaltegger, U.; Ulianov, A.; Muntener, O.; Ovtcharova, M.; Peytcheva, I.; Vonlanthen, P.; Vennemann, T.; Antognini, M.; Girlanda, F. Megacrystic zircon with planar fractures in miaskite-type nepheline pegmatites formed at high pressures in the lower crust (Ivrea Zone, southern Alps, Switzerland). Am. Miner. 2014, 100, 83–94.</p><p>Zanetti, A.; Mazzucchelli, M.; Sinigoi, S.; Giovanardi, T.; Peressini, G.; Fanning, C.M. SHRIMP U-Pb Zircon Triassic Intrusion Age of the Finero Mafic Complex (Ivrea-Verbano Zone, Western Alps) and its Geodynamic Implications. J. Pet. 2013, 54, 2235–2265.</p>

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