The timing of the Middle Triassic magmatism in the Dolomites area (Southern Alps, Italy)

Autor(en): Nicolò Nardini, Federico Casetta, Ryan B. Ickert, Lorenzo Tavazzani, Disha C. Okhai, Stefano Peres, Elio Dellantonio, Theodoros Ntaflos, Massimo Coltorti
Abstrakt: The Middle Triassic magmatic event in the Southern Alps (Italy) is characterised by the emplacement and eruption of multiple magma batches with different geochemical affinities in a short time span. In this work, we present the first geochemical and geochronological data on highly differentiated alkaline dykes (phonolites) exposed in and near the Middle Triassic Predazzo magmatic complex (Southern Alps, Italy) and a first complete geochronological survey of the Predazzo pluton. The phonolites, cutting the Middle Triassic volcanic sequences, are sodalite- and aegirine-bearing and have titanite, apatite and magnetite as accessory phases. Their trace element concentration reflects a geochemical signature similar to the orogenic-like signature typical of the Middle Triassic magmatic rocks of the Predazzo complex. New in situ U–Pb dating on titanite from the phonolite dykes and U–Pb dating on zircon separates from all the magmatic units of the Predazzo pluton show that the phonolite dykes were emplaced between 233.8 ± 3.1 Ma and 238.1 ± 4.5 Ma, i.e., overlapping to and postdating the emplacement and crystallisation of plutonic rocks, which yield ages ranging from 237.97 ± 0.15 Ma to 238.31 ± 0.13 Ma. The ages obtained for the diverse suites of the pluton are in good agreement with previous dating and show that silica-saturated to -undersaturated rocks were placed within the same context in a short time span. Thermometry and hygrometry on titanite, clinopyroxene and K-feldspar revealed that phonolites represent volatile- and REE-rich (H₂O = 8 ± 0.6 wt%) highly differentiated alkaline melts intruding at relatively low T (752–868 °C), which easily caused the spatially related Cu–W mineralisation. Comparisons with sub-volcanic rocks exposed in the Central (Edolo) and Western Alps (Finero mafic complex) indicate that the phonolites still preserve the orogenic signature of the Middle Triassic event in the Southalpine, that characterise all magmas emplaced before the opening of the Alpine Tethys in the Late Triassic. These new geochronological constraints on the Predazzo pluton and phonolite dykes enable us to outline the complete sequence of magmatic events associated with the emplacement of the Predazzo volcano-plutonic complex during Mid-Triassic and to speculate about the genesis of Cu–W mineralisation.
Organisation(en): Department für Lithosphärenforschung
Externe Organisation(en): Universitá degli studi di Ferrara, Purdue University, Eidgenössische Technische Hochschule Zürich, Museo Geologico delle Dolomiti, Istituto Nazionale di Geofisica e Vulcanologia (INGV) Sezione di Palermo
Journal: Lithos
Band: 494-495
ISSN: 0024-4937
DOI: https://doi.org/10.1016/j.lithos.2024.107894
Publikationsdatum: 02-2025
Peer-reviewed: Ja
ÖFOS 2012: 105105 Geochemie, 105127 Geochronologie
Schlagwörter
ASJC Scopus Sachgebiete: Geology, Geochemistry and Petrology
Link zum Portal: https://ucrisportal.univie.ac.at/de/publications/924fefa4-6b1a-40b0-bb96-ad1b4f79062e

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