Marco Filippi
email: marco.filippi@unimi.it

Davide Zanoni

Massimo Tiepolo

Michel Corsini

Gisella Rebay

Jean-Marc Lardeaux

Maria Iole Spalla

High-Nb alkaline mafic dykes in the central Alps witness to the Triassic evolution of the Adria passive margin

Keywords:

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Introduction

The Permian-Triassic period in the Alpine domains is characterized by extension and lithospheric thinning, which led HT (high-temperature) metamorphism in the basement rocks and mantle-derived magmatism [START_REF] Lardeaux | From granulites to eclogites in the Sesia zone (Italian Western Alps): a record of the opening and closure of the Piedmont Ocean[END_REF][START_REF] Rebay | Emplacement at granulite facies conditions of the Sesia-Lanzo metagabbros: an early record of Permian rifting?[END_REF][START_REF] Roda | What drives Alpine Tethys opening? Clues from the review of geological data and model predictions[END_REF][START_REF] Roda | Metamorphic remnants of the Variscan orogeny across the Alps and their tectonic significance[END_REF][START_REF] Schuster | Permian metamorphic event in the Alps[END_REF][START_REF] Spalla | The transition from Variscan collision to continental break-up in the Alps: insights from the comparison between natural data and numerical model predictions[END_REF]. The extensional tectonics has persisted continuously for a hundred million years leading to the Jurassic oceanization [START_REF] Marotta | Thermo-mechanical numerical model of the transition from continental rifting to oceanic spreading: the case study of the Alpine Tethys[END_REF][START_REF] Roda | What drives Alpine Tethys opening? Clues from the review of geological data and model predictions[END_REF], despite the volcano-sedimentary basins display diachronous stages of subsidence and exhumation [START_REF] Berra | Subsidence history from a backstripping analysis of the Permo-Mesozoic succession of the Central Southern Alps (Northern Italy)[END_REF] and the volumes of emplaced mafic igneous rocks decrease over time.

In the western Alps, Permian metamorphism is extensively recorded in the Austroalpine and Southalpine domains [START_REF] Lardeaux | From granulites to eclogites in the Sesia zone (Italian Western Alps): a record of the opening and closure of the Piedmont Ocean[END_REF][START_REF] Manzotti | Permian magmatism and metamorphism in the Dent Blanche nappe: constraints from field observations and geochronology[END_REF][START_REF] Rebay | Emplacement at granulite facies conditions of the Sesia-Lanzo metagabbros: an early record of Permian rifting?[END_REF] and, in the latter, the thermal perturbation also characterized the Triassic evolution [START_REF] Guergouz | Zircon and monazite petrochronologic record of prolonged amphibolite to granulite facies metamorphism in the Ivrea-Verbano and Strona-Ceneri zones[END_REF][START_REF] Klötzli | Duration of igneous activity in the Sesia magmatic system and implications for high-temperature metamorphism in the Ivrea-Verbano deep crust[END_REF][START_REF] Peressini | Duration of a large mafic intrusion and heat transfer in the lower crust: a SHRIMP U-Pb zircon study in the Ivrea-Verbano Zone (Western Alps, Italy)[END_REF][START_REF] Smye | Episodic heating of continental lower crust during extension: a thermal modeling investigation of the Ivrea-Verbano Zone[END_REF]. In apparent contrast, a substantial portion of the Variscan basement in Southalpine domain of central and eastern Alps escaped the Permian-Triassic HT metamorphism because it had already been exhumed at the end of the Variscan evolution [START_REF] Spalla | Deciphering the geologic memory of a Permian conglomerate of the Southern Alps by pebble P-T estimates[END_REF][START_REF] Zanoni | Vestiges of lost tectonic units in conglomerate pebbles? A test in Permian sequences of the Southalpine Orobic Alps[END_REF][START_REF] Zanoni | The Variscan evolution in basement cobbles of the Permian Ponteranica formation by microstructural and petrologic analysis[END_REF]Filippi et al., 2021 and ref. therein), with the exception of the Triassic Dervio Olgiasca unit (Fig. 1, [START_REF] Diella | Contrasting thermomechanical evolutions in the Southalpine metamorphic basement of the Orobic Alps (central Alps, Italy)[END_REF][START_REF] Bertotti | Deformation and metamorphism associated with crustal rifting: the Permian to Liassic evolution of the Lake Lugano-Lake Como area (Southern Alps)[END_REF][START_REF] Di Paola | Contrasting tectonic records in pre-Alpine metabasites of the Southern Alps (Lake Como, Italy)[END_REF][START_REF] Spalla | The role of structural and metamorphic memory in the distinction of tectono-metamorphic units: the basement of the Como lake in the Southern Alps[END_REF][START_REF] Real | Carboniferous-Triassic tectonic and thermal evolution of the middle crust section of the Dervio-Olgiasca Zone (Southern Alps)[END_REF]. In these crustal levels, lithospheric thinning is evidenced by transtensional to extensional faulting accomodating the deposition of Carboniferous to Mesozoic sedimentary covers [START_REF] De Graciansky | The Western Alps, from Rift to Passive Margin to Orogenic Belt: An Integrated Geoscience Overview[END_REF][START_REF] Zanchi | Low-angle normal faults record early Permian extensional tectonics in the Orobic Basin (Southern Alps, N Italy)[END_REF] and Permian-Triassic volcanoclastites and dykes [START_REF] Beltrán-Triviño | Triassic magmatism on the transition from Variscan to Alpine cycles: evidence from U-Pb, Hf, and geochemistry of detrital minerals[END_REF][START_REF] Berra | U-Pb zircon geochronology of volcanic deposits from the Permian basin of the Orobic Alps (Southern Alps, Lombardy): chronostratigraphic and geological implications[END_REF][START_REF] Cassinis | Permian to Triassic geodynamic and magmatic evolution of the Brescian Prealps (eastern Lombardy, Italy)[END_REF][START_REF] Schaltegger | Crustal-scale magmatic systems during intracontinental strike-slip tectonics: U, Pb and Hf isotopic constraints from Permian magmatic rocks of the Southern Alps[END_REF][START_REF] Storck | Timing and evolution of Middle Triassic magmatism in the Southern Alps (northern Italy)[END_REF]. Xenoliths of Permian granulites within Oligocene trachytes [START_REF] Sassi | HT-LP crustal syntectonic anatexis as a source of the Permian magmatism in the Eastern Southern Alps: evidence from xenoliths in the Euganean trachytes (NE Italy)[END_REF] are indirect evidence of HT Permian-Triassic metamorphism in the eastern Southalpine domain.

The Permian-Triassic HT metamorphism is coeval with mafic magma emplacements at various depths along the Adria passive margin and these rocks exhibit a consistent compositional evolution over time. After the emplacement of voluminous tholeiitic gabbros in the Permian, the scattered middle Triassic magmatism shifted from calc-alkaline to shoshonitic, later transitioning to alkaline and carbonatitic in the late Triassic (Casetta et al., 2018a(Casetta et al., , 2018b[START_REF] Casetta | The alkaline lamprophyres of the Dolomitic Area (Southern Alps, Italy): markers of the late Triassic change from orogenic-like to anorogenic magmatism[END_REF][START_REF] De Min | Triassic magmatism in the European Southern Alps as an early phase of Pangea break-up[END_REF][START_REF] Denyszyn | A bigger tent for CAMP[END_REF][START_REF] Lustrino | Origin of Triassic magmatism of the Southern Alps (Italy): constraints from geochemistry and Sr-Nd-Pb isotopic ratios[END_REF][START_REF] Quick | Magmatic plumbing of a large Permian caldera exposed to a depth of 25 km[END_REF][START_REF] Sloman | Triassic shoshonites from the dolomites, northern Italy: alkaline arc rocks in a strike-slip setting[END_REF][START_REF] Storck | Timing and evolution of Middle Triassic magmatism in the Southern Alps (northern Italy)[END_REF][START_REF] Tribuzio | Petrology, mineral and isotope geochemistry of the Sondalo gabbroic complex (central Alps, Northern Italy): implications for the origin of post-Variscan magmatism[END_REF].

In this study, we present a field, petrological, geochemical, and geochronological study of the Edolo diabase, which consists of a swarm of mafic dykes emplaced into the Variscan basement in the central Southalpine domain and intersecting the sequence of syn-metamorphic Variscan structures. This study aims to enhance the record of the Permian-Triassic magmatism along the Adria passive margin and to compare the features of the Edolo diabase dykes with those of coeval magmatic rocks in other portions of the Southalpine domain.

Geological setting

The metamorphic basement of the central Southalpine domain retains contrasting Variscan P-T (pressuretemperature) evolutions allowing for contouring of tectono-metamorphic units. Among them, the Passo Calvalcafiche, Domaso-Cortafò, and Tre Valli Bresciane Massif units (Fig. 1) retain the effects of superposed thermal states compatible with early Variscan burial and collision [START_REF] Spalla | Influence of deformation partitioning and metamorphic re-equilibration on P-T path reconstruction in the pre-Alpine basement of central Southern Alps (Northern Italy)[END_REF]di Paola et al., 2001 and ref. therein), whereas the Val Vedello, Monte Muggio, and Aprica units (Fig. 1) only record the Barrovian metamorphic imprint of the Variscan collision [START_REF] Diella | Contrasting thermomechanical evolutions in the Southalpine metamorphic basement of the Orobic Alps (central Alps, Italy)[END_REF][START_REF] Gosso | International ophiolite symposium field excursion guide-continental rifting to ocean floor metamorphism (21st-23rd September 1995): first day: HT/LP metamorphism and structures in the South-Alpine basement near Lake Como, Orobic Alps; intracontinental imprints of the Permo-Triassic rifting[END_REF]. These tectono-metamorphic units were already exposed at surface in Permian times, according to the metamorphic evolution recorded in the clasts of the lower Permian sequences capping the Variscan basement and interesecting all the Variscan structures [START_REF] Spalla | Deciphering the geologic memory of a Permian conglomerate of the Southern Alps by pebble P-T estimates[END_REF][START_REF] Zanoni | Vestiges of lost tectonic units in conglomerate pebbles? A test in Permian sequences of the Southalpine Orobic Alps[END_REF][START_REF] Zanoni | The Variscan evolution in basement cobbles of the Permian Ponteranica formation by microstructural and petrologic analysis[END_REF]. Syn-exhumation heating is recorded in the upper Camonica valley basement prior to the late Permian [START_REF] Filippi | Cld-St-and-bearing assemblages in the central Southalpine Basement: markers of an evolving thermal regime during Variscan convergence[END_REF], and in the Dervio-Olgiasca unit in the Triassic (Fig. 1, [START_REF] Diella | Contrasting thermomechanical evolutions in the Southalpine metamorphic basement of the Orobic Alps (central Alps, Italy)[END_REF][START_REF] Di Paola | Contrasting tectonic records in pre-Alpine metabasites of the Southern Alps (Lake Como, Italy)[END_REF][START_REF] Spalla | The role of structural and metamorphic memory in the distinction of tectono-metamorphic units: the basement of the Como lake in the Southern Alps[END_REF][START_REF] Real | Carboniferous-Triassic tectonic and thermal evolution of the middle crust section of the Dervio-Olgiasca Zone (Southern Alps)[END_REF].

The Edolo diabase dykes intruded the Aprica and Passo Cavalcafiche units in the northern part of the central Southalpine, in between the Alpine Gallinera and Periadriatic lines (Fig. 1). These units mostly consist of metapelites and quartzites, in part derived from Ordovician-Silurian sediments, with minor lenses of orthogneiss [START_REF] Gosso | Note Illustrative della Carta Geologica d'Italia alla scala[END_REF].

The dominant structure in the Aprica and Passo Cavalcafiche units is the Variscan S2 foliation that developed during the tectonic coupling of these units. This foliation is supported by greenschist facies minerals (Qz + Wm + Chl + Ab + Ttn) and dips 30-80 et al., 2015). S2 developed under perturbed thermal conditions in both the units (Passo Cavalcafiche: T<400-550 • C, P<0.3-0.4 GPa; Aprica: T<300-350 • C, P<0.3 GPa), which are compatible with a late orogenic evolution [START_REF] Gosso | Note Illustrative della Carta Geologica d'Italia alla scala[END_REF][START_REF] Rebay | Superposed syn-metamorphic structures of the Alpine and pre-Alpine convergent cycles in the Southalpine basement of the Orobic Alps (Northern Italy)[END_REF][START_REF] Spalla | Influence of deformation partitioning and metamorphic re-equilibration on P-T path reconstruction in the pre-Alpine basement of central Southern Alps (Northern Italy)[END_REF][START_REF] Zanoni | Vestiges of lost tectonic units in conglomerate pebbles? A test in Permian sequences of the Southalpine Orobic Alps[END_REF].

The northern part of the central Southalpine domain displays heterogeneous deformation effects resulting from Alpine convergence. In the high strain domains, the Alpine convergence is testified by chevron folds coupled with south-verging thrusts, which also affect Permian and Mesozoic sedimentary sequences [START_REF] Carminati | Thrust kinematics and internal deformation in basement-involved fold and thrust belts: the eastern Orobic Alps case (Central Southern Alps, northern Italy)[END_REF]Rebay et al., 2015 and ref. therein). The Alpine folds are characterized by subhorizontal NE -SW trending axes and axial planes steeply dipping towards NW or SE, alongside a locally developed S3 axial plane foliation.

The Edolo diabase dykes have been extensively mapped within the Passo Cavalcafiche and Aprica units where they intersect the Variscan S2 foliation [START_REF] Filippi | Quantification of Alpine metamorphism in the Edolo diabase, Central Southern Alps[END_REF][START_REF] Rebay | Superposed syn-metamorphic structures of the Alpine and pre-Alpine convergent cycles in the Southalpine basement of the Orobic Alps (Northern Italy)[END_REF][START_REF] Schiavinato | Sulle rocce diabasiche comprese negli Scisti di Edolo in Val Camonica (Lombardia)[END_REF]. Based on the intersection relations a possible Triassic age of intrusion was suggested in the past [START_REF] Schiavinato | Sulle rocce diabasiche comprese negli Scisti di Edolo in Val Camonica (Lombardia)[END_REF]. The dykes are subvertical and W-SW striking. Locally, igneous minerals are pervasively affected by static overgrowth of lower greenschist facies minerals, which developed during late intrusive fluid circulation at temperature of 300-350 • C and pressure of 0.1-0.2 GPa [START_REF] Filippi | Quantification of Alpine metamorphism in the Edolo diabase, Central Southern Alps[END_REF]. The Alpine S3 foliation is locally developed along the margins of the dykes and is supported by greenschist facies minerals formed at a temperature of 350-420 • C and a pressure of about 0.2 GPa [START_REF] Filippi | Quantification of Alpine metamorphism in the Edolo diabase, Central Southern Alps[END_REF][START_REF] Rebay | Superposed syn-metamorphic structures of the Alpine and pre-Alpine convergent cycles in the Southalpine basement of the Orobic Alps (Northern Italy)[END_REF]. The samples for this study were carefully chosen from the central parts of the dykes to avoid greenschist facies minerals and thus ensuring the best preservation of igneous minerals and textures.

Field relations and petrography

This study is focused on the three main sites, Nembra, Corteno, and Valmoranda (Fig. 1), where swarms of meter-thick dykes intruded into the Variscan metapelites and quartzites of the Aprica and Passo Cavalcafiche units (Figs. 1,2). The dykes are composed of clinopyroxene (20-25%), amphibole (10-15%), biotite (5-10%), plagioclase (45-50%), and ilmenite (5-10%), with accessory apatite. Exceptionally rare quartz and epidote grains are found in interstitial domains in the most differentiated samples. At the core, the dykes are hypidiomorphic with variable grain size. Locally, modally heterogeneous enclaves with lobate to blurred contacts are observed (Fig. 2). At the margins, the dykes are porphyritic to aphanitic (chilled margins), with clinopyroxene, amphibole, and plagioclase phenocrysts (Fig. 2). Leucocratic veins with gently lobate to straight margins are hosted within the dykes (Fig. 2). These veins are mostly composed of plagioclase (>90% vol) with minor amphibole and biotite.

Methods

Three samples form Nembra and four from Corteno (Table 1) were analyzed for WR (whole rock) major, trace, and rare earth elements at ActLabs (Canada) by ICP-OES (Inductively Coupled Plasma -Optical Emission Spectroscopy) and ICP-MS (Inductively Coupled Plasma -Mass Spectrometry). In addition, seven auxiliary samples from Valmoranda (Supplementary File S1) have been analyzed for major and trace elements at Università degli Studi di Genova by XRF (X-Ray Fluorescence).

Minerals from Nembra, Corteno, and Valmoranda dykes were analyzed at Università degli Studi di Milano with a JEOL 8200 Super Probe at 15 kV accelerating voltage and with a current beam of 5 nA. Natural silicates were used as standards. Amphibole formulae were calculated checking the most satisfying results of 13, 15, 16 cations and 23 oxygen normalizations following the methodology of [START_REF] Locock | An Excel spreadsheet to classify chemical analyses of amphiboles following the IMA 2012 recommendations[END_REF]. Oxo-components were considered only for nomenclature.

Clinopyroxene is recalculated at 4 cations and 6 O, feldspar at 4 O, and biotite at 11 O. The apatite formula is recalculated according to [START_REF] Ketcham | Technical note: calculation of stoichiometry from EMP data for apatite and other phases with mixing on monovalent anion sites[END_REF]. Results of mineral-chemical analyses are shown in Tables 2 and3. The dataset is attached as Supplementary File S2.

Crystallization temperature (± 45 • C) and pressure (± 0.5 GPa) for igneous clinopyroxene was estimated by using the single-phase thermobarometer of [START_REF] Putirka | Thermometers and barometers for volcanic systems[END_REF]. Crystallization temperature (± 30 • C) for igneous amphibole was estimated applying the single-phase thermometer of [START_REF] Putirka | Amphibole thermometers and barometers for igneous systems and some implications for eruption mechanisms of felsic magmas at arc volcanoes[END_REF]. Estimates on igneous amphibole crystallization pressure were avoided since amphibole barometers are less accurate than clinopyroxene barometers (see Putirka, 2016 for a discussion).

Crystallization temperature for magmatic biotite (± 65 • C) is estimated by the single-phase thermometer of [START_REF] Li | Machine learning thermobarometry for biotite-bearing magmas[END_REF].

The concentrations of trace and REE elements in igneous clinopyroxene, amphibole, biotite, and ilmenite from Nembra and Corteno were determined at Università degli Studi di Milano by a Laser Ablation ICP-MS instrument consisting of a 193 nm ArF excimer laser equipped with a HelEx 2 volume sample chamber (Analyte Excite -Teledyne -Photon Machines) and a quadrupole ICP-MS (iCAP-Q Thermo Fisher Scientific).

Ablation was performed with a spot diameter of 40 μm, a frequency of 10 Hz, and a fluence of 2 J/cm 2 . Each analysis included 40 s of background and 60 s of ablation signal acquisition. NIST612 glass was used as external standard in the analysis. Ca was used as internal standard for clinopyroxene and amphibole, Si for biotite, and Ti for ilmenite. BCR-2G glass was included in the analytical run as a quality control sample. The raw data was processed using GLITTER software [START_REF] Van Achterbergh | Data reduction software for LA-ICP-MS: appendix[END_REF]. The results are in Supplementary File S3.

Biotite 40 Ar/ 39 Ar geochronology was performed at Géoazur, Université Cote d'Azur with an ARGUS VI mass spectrometer from Thermo-Fischer. A sample from Nembra was crushed and a 300-500 μm size fraction was cleaned in ultrasonic bath. Igneous biotite grains without evidence of alteration and inclusions were handpicked under a binocular microscope and packaged in aluminum foils and irradiated for 97 h in the McMaster Nuclear Reactor together with Fish Canyon sanidine grains as flux monitor (28.030 ± 0.056 Ma, [START_REF] Jourdan | Age calibration of the Fish Canyon sanidine 40Ar/39Ar dating standard using primary K-Ar standards[END_REF]. Raw data from each step and blank were processed, and ages were calculated using Ar -Ar CALC software [START_REF] Koppers | ArArCALC-software for 40Ar/39Ar age calculations[END_REF]. The analytical procedure and raw data are in Supplementary File S4.

Results

WR geochemistry

The mafic dykes (Table 1, Supplementary Files S1) are alkaline basalts with SiO 2 at 44.5-52.5 wt%, Na 2 O at 2.0-5.3 wt% and K 2 O at 0.8-1.9 wt% (Fig. 3). The Mg# is between 0.4 and 0.6, with low LOI values at 1.0-3.3 wt%. MgO (3.7-10.7 wt%) shows a negative correlation with Cr (50-320 ppm, Fig. 3). The Ni content remains relatively stable at around 140 ppm for MgO ranging from 5.1 to 10.7 wt%, and then decreases to 6-50 ppm in samples with the lowest MgO content (Fig. 3).

The chondrite-normalized incompatible element diagram (Fig. 3) reveals significant compositional variations among the localities. In Nembra, the profiles align closely with the reference OIB, but stand out for slightly higher Nb (45-58 ppm) and Ti contents, as well as Nb/Ta ratios. In contrast, the trace element concentrations in Corteno are significantly lower than in OIB (ocean island basalt). In addition, the mafic dykes in Corteno exhibit lower Nb contents (18-26 ppm) compared to those in Nembra, although their Ti contents and Nb/Ta ratios are similar. In comparison to the Triassic lamprophyres of the eastern Southalpine domain, the mafic dykes from Nembra and Corteno exhibit lower concentrations of Rb, Ba, and Sr, along with significantly higher Ti contents (Fig. 3).

The chondrite-normalized REE patterns show LREE enrichment over HREE, which are at about 10-20 times the CI chondrite without significant Eu anomalies (Fig. 3). Samples from Nembra display a higher LREE/HREE fractionation compared to those from Corteno, with (La/ Yb) N at 7.5-7.9 and 3.2-4.5, respectively. However, these values are lower than those of both OIB (11.6) and eastern Southalpine lamprophyres (5.6-10.4, Fig. 3).

Microstructure and mineral chemistry 4.2.1. Mafic dykes

Igneous clinopyroxene is pink at core and colorless at rim, with compositions grading from titanian diopside to diopside (Mg# = 0.6-0.7, Table 2). The clinopyroxene shows highly irregular grain boundaries and is locally rimmed by igneous amphibole and biotite (Fig. 4). The clinopyroxene cores are Na-poor and exhibit the highest Al and Ti contents (Fig. 5). In some cases, clinopyroxene is statically replaced by a late generation of green hornblende (Fig. 4).

Igneous amphibole is brown at core and pale brown to dark green at rim (Fig. 4). The core composition grades from ferri-kaersutite to Ti-rich pargasite (Mg# = 0.4-0.6, K = 0.2-0.3 apfu). The rim is ferro-pargasite (Mg# = 0.1-0.3), Ti-poorer and slightly K-richer than the core (Table 2, Fig. 5). Discontinuous and thin outer rims of blue-green amphibole are locally developed around the igneous amphibole (Fig. 4). The blue-green amphibole is ferro-ferri-hornblende (Mg# = 0.3-0.4, Table 3), characterized by the lowest Ti and K contents (Fig. 5).

Igneous biotite (annite, Mg# = 0.3-0.5) is dark brown and Ti-rich (Fig. 5), locally showing a pale brown to green rim (Fig. 4). Biotite rims clinopyroxene and fills interstitial domains between plagioclase grains (Fig. 4). Igneous plagioclase is euhedral to subhedral at cores (An 48-63 ) and displays simple and polysynthetic twins (Fig. 4). At rims, plagioclase (An 6-24 ) is untwinned and with lobate boundaries.

Ilmenite and apatite are commonly included in igneous clinopyroxene, biotite and amphibole (Fig. 4), together with very rare magnetite, rutile, and titanite in clinopyroxene. Apatite has intermediate composition between fluoroapatite and hydroxylapatite, according to significant F (0.83-1.25 apfu) and OH (0.72-1.11 apfu) and negligible Cl contents.

Plagioclase-rich veins

Igneous amphibole in plagioclase-rich veins is pale brown at the core to dark green at rim (Fig. 4). Amphibole is Ti-rich ferro-pargasite and shows a decreasing Mg# from core (0.3-0.4) to rim (0.1-0.2). K is 0.2-0.4 apfu (Table 3, Fig. 5). Outer rims of blue-green amphibole are well developed around igneous amphibole in the plagioclase-rich veins (Fig. 4). The compositions of blue-green amphibole vary from hastingsite to ferro-pargasite (Mg# = 0.2, Table 3), with 0.1-0.2 apfu of K (Fig. 5). Remarkably, this amphibole contains up to 0.2 apfu of Cl (Table 3) suggesting late-intrusive circulation of chlorine-rich fluids along the plagioclase-rich veins.

Igneous biotite (Mg# = 0.3) is dark brown at core and dark green at rim, and often interstitial between plagioclase grains. Plagioclase (An 5-10 ) exhibits simple or polysynthetic twinning and rare intergrowths with quartz.

Thermobarometry

Crystallization temperature and pressure are consistent in the three localities. Clinopyroxene cores crystallized at 1130 ± 45 • C for a pressure comprised between 0.1 and 0.6 GPa, which are compatible with a shallow depth crystallization. Conversely, amphibole cores crystallized at a markedly lower temperature both in the lamprophyres (960 ± 30 • C) and plagioclase-rich veins (900 ± 30 • C). Amphibole rims retain the lowest crystallization temperature down to 870 ± 30 • C. A temperature of 730 ± 30 • C is determined for the amphibole outer rims, which formed at near-solidus conditions. Lastly, crystallization temperature for igneous biotite was estimated at 860 ± 65 • C in the mafic dykes and 790 ± 65 • C in the plagioclase-rich veins.

Trace elements composition of igneous minerals 4.3.1. Clinopyroxene

Clinopyroxene cores were analyzed in Nembra, Corteno, and Valmoranda (Fig. 1), where they exhibit significant variations based on locality. In Nembra, clinopyroxene is characterized by relatively high Cr (950-1450 ppm) and moderately high Ni (63-69 ppm) contents. The concentrations of incompatible elements are low, with Zr ranging from 38 to 50 ppm, Hf at 2 ppm, and Y from 17 to 21 ppm. Notably, the contents of Nb (0.1-0.3 ppm) and Ta (<0.1 ppm) are markedly low, with sub-chondritic Nb/Ta ratios.

In Corteno, clinopyroxene is characterized by relatively low Cr (12-153 ppm) and Ni (34-56 ppm) contents and moderate concentrations of incompatible elements (Zr = 40-91 ppm, Hf: = 2-4 ppm, Y = 29-39 ppm). Nb and Ta contents are in the range of 0.1-0.5 ppm and <0.1 ppm, respectively, with sub-chondritic Nb/Ta ratios.

In Valmoranda, clinopyroxene is characterized by very low Cr (8-13 ppm) and Ni (10-14 ppm) contents. Conversely, the concentrations of Zr, Hf, and Y are relatively high, with Zr ranging from 143 to 160 ppm, Hf from 6 to 7 ppm, and Y from 41 to 51 ppm. Nb (1.2-2.0 ppm) and Ta (0.3-0.4 ppm) contents are higher in comparison with the other localities, but with similar sub-chondritic Nb/Ta ratios.

In the chondrite-normalized incompatible trace element diagram (Fig. 6), clinopyroxene cores show almost chondritic values for Th, U, Nb, and Ta, with a negative anomaly in Sr, which is less pronounced in Nembra compared to Corteno and Valmoranda. In these latter localities, clinopyroxenes also display slightly higher overall concentrations of incompatible trace elements. Consistently, the clinopyroxene in Nembra exhibits lower overall REE contents compared to Corteno and Valmoranda. In the chondrite-normalized REE diagram (Fig. 6), the REE profiles are characterized by similar (La/Sm) N at 0.3-0.4. On the contrary, (Gd/Yb) N is higher in Nembra (2.7-3.0), than Corteno (2.1-2.4), and Valmoranda (2.4-2.8). Finally, clinopyroxene from Nembra exhibits a weak to absent Eu anomaly (Eu/Eu* = 0.9-1.0), while clinopyroxene from the other localities displays a more consistent Eu anomaly (Eu/Eu* = 0.8-0.9).

Amphibole

Amphibole cores and rims were analyzed in the mafic dykes from Nembra. The cores are characterized by relatively high Ni (24-31 ppm), Ba (80-262 ppm) and Sr (134-211 ppm) contents, with low Zr (456-569 ppm), . Cr is up to 17 ppm. Remarkably, amphibole cores show high Nb (215.3-285.0 ppm) and Ta (8.3-11.0 ppm) contents, with super-chondritic Nb/Ta ratios (25-29). Conversely, the amphibole rims show higher Zr (1064-1497

Mg # = 0.8 0 M g# = 0. 66 M g # = 0 .5 0 M g# = 0 .3 3 Mg # = 0.2 0
Fe (apfu) (32-86 ppm). High Nb (296-307 ppm) and Ta (13-14 ppm) contents in amphibole rims result in super-chondritic Nb/Ta ratios (21-23).

In Corteno, amphibole cores were analyzed in the mafic dykes and plagioclase-rich veins. In mafic dykes, the concentration of Ni in the amphibole cores ranges from 4 to 6 ppm, Ba from 17 to 97 ppm, and Sr from 13 to 97 ppm, which are relatively low. The Cr content is negligible. In contrast, Zr (469-751 ppm), Hf (17-25 ppm), and Y (152-220 ppm) are notably high. Remarkably, there are high and Ta (5.9-7.8 ppm) contents that result in super-chondritic Nb/ Ta ratios (26-30). In the plagioclase-rich veins, amphibole cores exhibit high contents of Zr (577-689 ppm) and Y (182-217 ppm, moderately high Ni (14-28 ppm), and low Cr (2-5 ppm), Ba (21-120 ppm) and Sr (13-35 ppm).

The chondrite-normalized incompatible trace element diagram (Fig. 6) reveals significant positive Nb anomalies in amphibole cores from both Nembra and Corteno. Notably, the amphibole cores from Nembra exhibit considerably lower Th, U, and Sr when compared to those from Corteno. In addition, the chondrite normalized REE patterns (Fig. 6) show lower overall REE contents in Nembra. The REE profiles demonstrate similar (La/Sm) N ratios, ranging from 0.8 to 1.0, in both localities. However, there is a noticeable difference in HREE fractionation, with Nembra displaying higher (Gd/Yb) N ratios from 2.4 to 2.8, whereas Corteno shows ratios from 2.0 to 2.2. All the amphibole core profiles exhibit Eu anomalies, but the anomaly is significantly more pronounced in Corteno (Eu/Eu* = 0.2-0.4) than in Nembra (Eu/Eu* = 0.6-0.7).

In the chondrite-normalized incompatible trace element diagram (Fig. 6), amphibole rims in Nembra exhibit the highest Nb, Ta, Zr, and Hf, but also the lowest Sr contents. These values are associated with a significant negative anomaly in Eu (Eu/Eu* = 0.2-0.4), a relative enrichment in LREE, and the lowest (Gd/Yb) N ratios of 1.9-2.1 in the REE profiles, similarly to the patterns observed in the amphibole cores in Corteno and plagioclase-rich veins (Fig. 6).

Biotite and ilmenite

Igneous biotite and ilmenite were analyzed in mafic dykes from Nembra and both minerals are characterized by high Nb and Ta contents. Specifically, Nb ranges from 93.6 to 96.4 ppm in biotite, while Ta varies from 3.2 to 3.3 ppm. In ilmenite, Nb is in the range of 176.6 to 356.0 ppm, and Ta in the range of 13.0 to 15.4 ppm. The Nb/Ta ratios are super-chondritic in biotite (26) and from chondritic to superchondritic in ilmenite (14-26).

40 Ar / 39 Ar geochronology

A single igneous biotite grain from Nembra (sample Ge15) yielded a weighted age of 204 ± 7 Ma, which corresponds to 87.5% of 39 Ar released and to 8 steps (Fig. 7). The inverse isochron for the plateau steps provides an age at 229 ± 14 Ma. A duplicate of biotite grain yielded a weighted age of 210 ± 12 Ma, which corresponds to 99.5% of 39 Ar released and to 7 steps (Fig. 7). The inverse isochron for the plateau steps provides an age at 243 ± 18 Ma. Both ages are concordant in the error bar. However, the incremental heating experiments yielded disturbed spectrum ages and the integrated age must be taken cautiously. The biotite grains analyzed provided saddle-shaped 40 Ar/ 39 Ar ages spectra, which are generally ascribed to an argon excess [START_REF] Harrison | Excess 40 Ar in metamorphic rocks from Broken Hill, New South Wales: implications for 40 Ar/ 39 Ar age spectra and the thermal history of the region[END_REF][START_REF] Lanphere | Identification of excess 40 Ar by the 40 Ar/ 39 Ar age spectrum technique[END_REF]. The low-temperature and high-temperature steps yield higher apparent 40 Ar/ 39 Ar ages than the middle-temperature steps. Therefore, the mean-temperature steps in the middle of the spectrum would correspond to a maximum estimate of the age of the grain analyzed [START_REF] Schaen | Interpreting and reporting 40Ar/39Ar geochronologic data[END_REF]. In this case we consider the biotite crystallization earlier than190-200 Ma.

Discussion

Evidence of disequilibrium between igneous minerals

The clinopyroxene grains exhibit highly irregular grain boundaries and are locally rimmed by magmatic amphibole and biotite (Fig. 4). This suggests that clinopyroxene was partially dissolved in the melt from which amphibole and biotite crystallized. In terms of composition, the lack of equilibrium between clinopyroxene and amphibole is confirmed by the higher Mg# of clinopyroxene cores (0.7-0.8) in comparison to that of amphibole (0.4-0.6) and by the exceptionally high Amp/Cpx D REE ratio, which, under equilibrium conditions, should be close to unity (e.g. Tiepolo et al., 2000a). Moreover, the disequilibrium textures and compositions are consistent with the different crystallization temperature estimated for igneous clinopyroxene (1130 ± 45 • C), amphibole (960 ± 30 • C), and biotite (860 ± 65 • C).

Insights on the composition of the clinopyroxene parental melt

In Nembra, clinopyroxene displays the highest concentrations of compatible elements such as Cr and Ni, along with the lowest overall concentrations of incompatible elements (Fig. 6). These characteristics suggest that mafic dykes from Nembra crystallized from a more primitive melt compared to those from other localities (Fig. 6). Furthermore, the clinopyroxene exhibits the highest Sr content and a weak to absent Eu anomaly since it crystallized, in most cases, before plagioclase. However, it is important to note that the clinopyroxene Mg# at 0.7 to 0.8 is not sufficient to rule out the possibility that a minor degree of differentiation may have characterized the early evolution of this melt.

The composition of the clinopyroxene parental melt was determined in Nembra using solid/liquid partition coefficients ( S/L D) that are suitable for the composition and crystallization temperature of the studied rocks [START_REF] Adam | The influence of pressure, mineral composition and water on trace element partitioning between clinopyroxene, amphibole and basanitic melts[END_REF]. As a result, the chondrite-normalized incompatible element concentrations in the clinopyroxene parental melt are overall lower than in the WR compositions (Fig. 8). Notably, the profiles reveal low concentrations of Nb and Ta, with chondritic to slightly super-chondritic Nb/Ta ratios (15-27).

Insights on the composition of the amphibole parental melt

The igneous amphibole cores crystallized from an evolved melt, as indicated by Mg# between 0.4 and 0.6. Furthermore, the amphibole compositions display depletion in Rb and Sr, along with a negative Eu anomaly in the REE profiles (Fig. 6). These observations indicate that amphibole crystallization occurred concurrently with biotite and plagioclase, as evidenced by microstructural analysis.

The amphibole cores in Nembra crystallized from a less evolved melt when compared to those in Corteno. The amphibole in Nembra is indeed richer in Cr and Ni and generally shows depletion in incompatible elements. Furthermore, it exhibits less pronounced Sr and Eu anomalies and more fractionated HREEs than in Corteno. The similarity between the amphibole rims in Nembra and amphibole cores in Corteno confirms that, in the latter locality, amphibole crystallized from a more evolved melt.

The composition of the amphibole parental melt was determined in Nembra using partition coefficients from [START_REF] Adam | The influence of pressure, mineral composition and water on trace element partitioning between clinopyroxene, amphibole and basanitic melts[END_REF].

Biotite

Remarkably, the amphibole parental melt is characterized by significantly high concentrations of Nb (828-1096 ppm), Ta (25-33 ppm), and LREE, with markedly super-chondritic Nb/Ta ratios (32-37).

Genetic relationships between parental melts

A genetic connection between the parental melts of clinopyroxene and amphibole is investigated as both these minerals coexist in the same dykes. To test this hypotesis, the evolution from clinopyroxene to amphibole parental melts was modeled through fractional crystallization. The effectiveness of clinopyroxene fractionation in the evolution of the Edolo diabase dykes is supported by the correlation between MgO and Cr (Fig. 3). In addition, weak Eu anomalies in the composition of some clinopyroxene grains may suggest minor fractionation of plagioclase (Fig. 6). Fractionation of Ti-rich phases is unlikely due to the overall high Ti contents in WR compositions and in most of the minerals that crystallized at different temperatures.

As a result, achieving LREE concentrations similar to those in the amphibole parental melt through fractional crystallization is improbable, unless extremely low residual melt fractions are taken into account. Furthermore, even with extreme fractional crystallization of clinopyroxene and plagioclase, it was not possible to achieve enrichment in Nb and Ta, as seen in the amphibole parental melt. Hence, the distinction between the parental melts of amphibole and clinopyroxene is unlikely to be solely due to fractional crystallization.

It is worth noting that a higher concentration of Nb in amphibole compared to clinopyroxene is common in mafic systems. For example, [START_REF] Coogan | Near-solidus evolution of oceanic gabbros: insights from amphibole geochemistry[END_REF] showed that intercumulus amphibole can exhibit Nb concentrations 100-1000 times greater than those of early formed cumulus clinopyroxene in a Mid-Atlantic Ridge gabbro. However, this intercumulus amphibole is fluorine-rich and crystallized in interstitial spaces from a highly evolved melt at a temperature near the solidus (T = 860 ± 30 • C). Instead, this study focuses on the cores of Ti-rich amphiboles that are mostly subhedral and crystallized at 960 ± 30 • C under markedly supersolidus conditions.

It is known that that the D Nb , D Ta , and D Nb/Ta ratios for dehydrogenated amphibole can vary by order of magnitude, mostly depending on the content of Fe, Mg, and Ti in the melt Tiepolo et al. (2000b). Nevertheless, high concentrations of Nb and Ta and high Nb/Ta ratios are also observed in biotite and ilmenite that crystallized concurrently with amphibole in the Edolo diabase dykes. For this reason, the compositional gap between clinopyroxene and amphibole parental melts is unlikely to be explained by a not appropriate choice of the S/L D values. Instead, the high Nb and Ta contents and ratios reflect the composition of the melt from which amphibole, biotite, and ilmenite crystallized.

The compositional difference between the clinopyroxene and amphibole parental melts can be attributed to crustal assimilation. In this view, assimilation likely occurred after clinopyroxene but before amphibole crystallization. Crustal assimilation can account for the increased concentrations of LREEs in the amphibole parental melt. However, it is challenging to achieve high Nb and Ta contents and ratios by assimilating conventional crustal rocks with low Nb and Ta contents and subchondritic ratios [START_REF] Rudnick | Nature and composition of the continental crust: a lower crustal perspective[END_REF]. Therefore, if crustal assimilation is considered, the distinctive compositions of assimilated rocks are crucial in shaping the composition of the amphibole parental melt.

Alternatively, clinopyroxene and amphibole may have crystallized from magmas with contrasting compositions. The formation of these magmas might have occurred either concomitantly due to heterogeneities in the source rocks, fluids, and evolutionary pathways, or diachronously. In the latter case, clinopyroxene could have crystallized from a less differentiated melt with low Nb and Ta contents and was subsequently assimilated by a second, more evolved, Nb-and Ta-rich alkaline melt. Despite the differences between these hypotheses, rocks with high Nb and Ta contents and ratios are considered here as potential sources for the amphibole parental melt. [START_REF] Taylor | Planetary Crusts: Their Composition, Origin and Evolution[END_REF]. WR (whole rock) compositions of the Edolo diabase dykes from Nembra are included for comparison. The reference values for OIB (ocean island basalt) are from [START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF], for CC (continental crust) are from [START_REF] Rudnick | Nature and composition of the continental crust: a lower crustal perspective[END_REF].

Geodynamic implications

The compositional difference between clinopyroxene and amphibole parental melts could lead to contrasting interpretations in terms of tectonic environment. The relatively primitive composition of the clinopyroxene parental melt resembles what is expected in arc settings (e. g. [START_REF] Foley | Growth of early continental crust controlled by melting of amphibolite in subduction zones[END_REF]. Unfortunately, the crystal chemical filter does not permit clinopyroxene to incorporate LIL elements that could serve as a proxy for a more effective tectonic interpretation. Contrastingly, the amphibole seems to have crystallized from an alkaline melt (Figs. 5 and8), a feature reflected by the WR compositions of the Edolo diabase dykes (Fig. 3) and commonly associated with continental rifting (e.g., [START_REF] Galli | Jurassic carbonatite and alkaline magmatism in the Ivrea zone (European Alps) related to the breakup of Pangea[END_REF].

In the Triassic framework of the Adria passive margin, the high-K shoshonitic Predazzo complex in the eastern Southalpine domain is the nearest intrusive complex to the Edolo diabase dykes. This complex is of middle Triassic age and exhibits arc affinity (Casetta et al., 2018a;[START_REF] Sloman | Triassic shoshonites from the dolomites, northern Italy: alkaline arc rocks in a strike-slip setting[END_REF] broadly comparable to that of the clinopyroxene parental melt. Middle Triassic igneous and volcaniclastic rocks with arc affinity are also found in the southeasternmost Southalpine domain, Dinarides [START_REF] Storck | Timing and evolution of Middle Triassic magmatism in the Southern Alps (northern Italy)[END_REF]Lustrino et al., 2019 and ref. therein), and the eastern Austroalpine domain (Eisenkappel / Karawanken, Miller et al., 2011 and ref. therein). Conversely, in the western Southalpine domain, middle Triassic diorites in the outer gabbro of Finero display a more transitional character with a MORB imprint, suggesting a back-arc setting. A possible link to a subduction zone is here highlighted by the high-H 2 O content of these rocks [START_REF] Zanetti | SHRIMP U-Pb zircon Triassic intrusion age of the Finero mafic complex (Ivrea-Verbano Zone, Western Alps) and its geodynamic implications[END_REF]. Transitional to tholeiitic igneous products are also found in the extensive extrusive and subvolcanic rocks within the middle Triassic sedimentary sequences of the central Southalpine domain, along with minor intermediate dykes [START_REF] Cassinis | Permian to Triassic geodynamic and magmatic evolution of the Brescian Prealps (eastern Lombardy, Italy)[END_REF][START_REF] Lustrino | Origin of Triassic magmatism of the Southern Alps (Italy): constraints from geochemistry and Sr-Nd-Pb isotopic ratios[END_REF]. In this framework, the parental melt of clinopyroxene in the Edolo diabase dykes shares more similarities with the rocks of the eastern Southalpine domain.

Previous authors have often suggested a genetic link between middle Triassic magmatism and Paleotethys subduction to the east. However, establishing a direct link between these processes is challenging, primarily due to the inferred distance between the Southalpine domain and this subduction zone [START_REF] Edel | Late Palaeozoic palaeomagnetic and tectonic constraints for amalgamation of Pangea supercontinent in the European Variscan belt[END_REF][START_REF] Van Hinsbergen | Orogenic architecture of the Mediterranean region and kinematic reconstruction of its tectonic evolution since the Triassic[END_REF]. On the contrary, the disputed arc affinity observed in the Middle Triassic magmatism of the central to eastern Southalpine domain is more recently interpreted as a consequence of the melting of the subcontinental mantle, along with Variscan to Permian igneous cumulates (Storck et al., 2019 and ref. therein). This process would have involved amphibole-peritectic melting acting as a water source, while Ti, Nb, and Ta being retained in restitic rutile and ilmenite. A second given hypothesis to explain the arc affinity of middle Triassic magmatism is the reactivation after about 100 million years of the metasomatized mantle wedge of the Variscan subduction, whose features were not fully erased by the Permian magmatism [START_REF] Beltrán-Triviño | Triassic magmatism on the transition from Variscan to Alpine cycles: evidence from U-Pb, Hf, and geochemistry of detrital minerals[END_REF][START_REF] De Min | Triassic magmatism in the European Southern Alps as an early phase of Pangea break-up[END_REF][START_REF] Lustrino | Origin of Triassic magmatism of the Southern Alps (Italy): constraints from geochemistry and Sr-Nd-Pb isotopic ratios[END_REF][START_REF] Sloman | Triassic shoshonites from the dolomites, northern Italy: alkaline arc rocks in a strike-slip setting[END_REF]. Regardless of the chosen scenario, both hypotheses require an uprising thermal state in the subcontinental mantle after the Permian event, which aligns well with the Permian-Triassic asthenospheric upwelling.

On the other hand, the amphibole parental melt in the Edolo diabases exhibits a high-Nb alkaline signature. In the late Triassic, alkaline to carbonatitic magmatism affected the western and eastern Southalpine domain [START_REF] Casetta | The alkaline lamprophyres of the Dolomitic Area (Southern Alps, Italy): markers of the late Triassic change from orogenic-like to anorogenic magmatism[END_REF][START_REF] Galli | Jurassic carbonatite and alkaline magmatism in the Ivrea zone (European Alps) related to the breakup of Pangea[END_REF][START_REF] Zaccarini | Zirconolite and Zr-Th-U minerals in chromitites of the Finero complex, Western Alps, Italy: evidence for carbonatite-type metasomatism in a subcontinental mantle plume[END_REF]. Some of these rocks exhibit moderate to high Nb contents [START_REF] Cassinis | Permian to Triassic geodynamic and magmatic evolution of the Brescian Prealps (eastern Lombardy, Italy)[END_REF][START_REF] Galli | Jurassic carbonatite and alkaline magmatism in the Ivrea zone (European Alps) related to the breakup of Pangea[END_REF][START_REF] Schaltegger | Megacrystic zircon with planar fractures in miaskite-type nepheline pegmatites formed at high pressures in the lower crust (Ivrea Zone, southern Alps, Switzerland)[END_REF][START_REF] Stähle | Permian metabasalt and Triassic alkaline dykes in the northern Ivrea zone: clues to the post-Variscan geodynamic evolution of the Southern Alps[END_REF], or, at least, an absence of Ti, Nb, and Ta negative anomalies [START_REF] Casetta | The alkaline lamprophyres of the Dolomitic Area (Southern Alps, Italy): markers of the late Triassic change from orogenic-like to anorogenic magmatism[END_REF], characteristics that were present in the middle Triassic magmatism. The high concentrations of Ti, Nb, and Ta in the Edolo diabase dykes may be tentatively explained by melting of Nb-and Ta-rich sources during progressive asthenosphere upwelling, similarly to what has been suggested in the western Southalpine domain, where the late Triassic alkaline magmatism is interpreted as due to melting of amphibole-rich mantle domains [START_REF] Galli | Jurassic carbonatite and alkaline magmatism in the Ivrea zone (European Alps) related to the breakup of Pangea[END_REF].

The late Triassic alkaline to carbonatitic magmatism anticipated the opening of the Alpine Tethys of some 25-35 Myr (cfr. Rebay et al., 2018;[START_REF] Gleißner | Contemporaneous opening of the Alpine Tethys in the Eastern and Western Alps: constraints from a late Jurassic gabbro intrusion age in the Glockner Nappe, Tauern Window, Austria[END_REF]Nicollet et al., 2022 and references therein). To the west, the coeval emplacement of mafic complexes and alkaline lamprophyres of the CAMP announces the opening of the Atlantic Ocean [START_REF] Najih | Initial Pangean rifting north of the West African Craton: insights from late Permian U-Pb and 40Ar/39Ar dating of alkaline magmatism from the Eastern Anti-Atlas (Morocco)[END_REF]. A correlation between these magmatic provinces has been suggested by similar ages and geochemical characters (Denyszyn et al., 2018 and ref. therein), as well as by paleogeographic reconstructions that show the Alpine Tethys as a branch of the Atlantic Ocean [START_REF] Doré | Similarities and differences in the tectonics of two passive margins: the Northeast Atlantic Margin and the Australian North West Shelf[END_REF][START_REF] Van Hinsbergen | Orogenic architecture of the Mediterranean region and kinematic reconstruction of its tectonic evolution since the Triassic[END_REF].

Conclusions

In the central Southalpine domain, the Ti-rich alkaline Edolo diabase dykes were emplaced at the end of the Triassic in the Variscan basement. The early-crystallized clinopyroxene shows low Nb and Ta contents and ratios, and contrasts with the compositions of late-crystallized amphibole, biotite, and ilmenite. Such compositional evolution is likely not solely due to fractional crystallization. The clinopyroxene parental melt may reflect the composition of the sub-continental mantle inherited from Variscan subduction or transformed during the Permian, as proposed in the eastern part of the Southalpine domain for explaining the disputed arc affinity of the middle Triassic magmatism (e.g., [START_REF] Lustrino | Origin of Triassic magmatism of the Southern Alps (Italy): constraints from geochemistry and Sr-Nd-Pb isotopic ratios[END_REF][START_REF] Storck | Timing and evolution of Middle Triassic magmatism in the Southern Alps (northern Italy)[END_REF]. On the other hand, the amphibole composition is likely influenced by successive melting or assimilation of Nb-Ta-rich phases, a process similar to that which explains the composition of the late Triassic magmatism in the western Southalpine domain [START_REF] Galli | Jurassic carbonatite and alkaline magmatism in the Ivrea zone (European Alps) related to the breakup of Pangea[END_REF]. The composition of the Triassic Edolo diabase dykes is thus influenced by the heterogeneity of the Adriatic lithosphere that underwent continuous astenospheric upwelling due to Permian-Triassic extensional tectonics.

Fig. 1 .

 1 Fig. 1. Geologic sketch of the central Southalpine domain with location of the Edolo diabase dykes (modified after Filippi et al., 2022, and refs therein). Variscan tectono-metamorphic units: AB = Aprica basement; DCZ = Domaso -Cortafò Zone; DOZ = Dervio -Olgiasca Zone; MMZ = Monte Muggio Zone; PCB = Passo Cavalcafiche Basement; TVB = Tre Valli Bresciane Basement; VCB = Upper Val Camonica Basement; VVB = Val Vedello Basement. Regional scale structures: CE = Cedegolo anticline; GT = Gallinera thrust; MF = Musso fault; OA = Orobic anticline; OT = Orobic thrust; PT = Porcile thrust; SGF = Southern Grigna fault; TC = Trabuchello-Cabianca anticline; VGF = Val Grande fault. Coordinate system: WGS84-UTM32N.

Fig. 2 .

 2 Fig. 2. Structural relationships and texture of Edolo diabase dykes. A: a metric-thick dyke intersecting the late-Variscan S2 foliation in metapelites in Nembra; hat for scale. B: detail on the chilled margin and pervasive hydrothermal alteration (yellow to brown) zone along a dyke wall in Corteno; camera cap for scale. C: plagicolase-and clinopyroxene-rich enclaves in a dyke in Nembra; camera cap for scale. D: a plagicolase-rich vein in a dyke in Nembra; compass for scale. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3 .

 3 Fig. 3. WR compositions of the Edolo diabase dykes. A: Total Alkali versus Silica diagram. B: Nb/Y versus Zr/Ti classification diagram. C: K 2 O vs Na 2 O. D: Ni vs MgO. E: Cr vs MgO. F: chondrite-normalized incompatible element diagram. G: chondrite normalized REE diagram. The reference values for OIB (ocean island basalt) are from Sun and McDonough (1989). The compositions of Triassic alkaline lamprophyres from eastern Southalpine domain are from Casetta et al. (2019) and De Min et al. (2020).

Fig. 4 .

 4 Fig. 4. Microphotographs of the Edolo diabase dykes (optical microscope and BSE imaging). A: hypidiomorphic texture characterized by euhedral to subhedral clinopyroxene and amphibole, along with subhedral to anhedral plagioclase and interstitial biotite, cross-polarized light. B: porphyritic texture with phenocrysts of plagioclase and clinopyroxene, plane-polarized light. C: clinopyroxene with plagioclase and interstitial biotite; plane-polarized light. D: igneous dark-brown amphibole surrounding a clinopyroxene grain with irregular boundaries, plane-polarized light. E: igneous biotite surrounding a clinopyroxene grain with irregular boundaries, plane-polarized light. F: plagioclase and amphibole in a plagicolase-rich vein; cross-polarized light. G: biotite and minor blue-green amphibole surrounding clinopyroxene grains with irregular boundaries, plane-polarized light. H: clinopyroxene partially replaced by hornblende and rimmed by igneous amphibole. An additional outer rim of blue-green amphibole is developed around this grain, in contact with hornblende, clinopyroxene, and igneous amphibole, BSE image. I: blue-green amphibole and biotite filling interstices between plagioclase, plane-polarized light. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 6 .

 6 Fig. 6. Chondrite-normalized incompatible element and REE diagrams for igneous clinopyroxene and amphibole. The CI values are from Taylor and McLennan (2009).

Fig. 7 .

 7 Fig.7.40 Ar/ 39 Ar age spectra as a function of 39 Ar released. The error boxes of each step are at the 2 σ level. The error of ages is given at the 2 σ level.

Fig. 8 .

 8 Fig. 8. Chondrite-normalized incompatible element diagram for the parental melts of clinopyroxene and amphibole in Nembra. The CI values are from[START_REF] Taylor | Planetary Crusts: Their Composition, Origin and Evolution[END_REF]. WR (whole rock) compositions of the Edolo diabase dykes from Nembra are included for comparison. The reference values for OIB (ocean island basalt) are from[START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF], for CC (continental crust) are from[START_REF] Rudnick | Nature and composition of the continental crust: a lower crustal perspective[END_REF].

Table 1

 1 WR composition (major, trace, and REE elements) of the Edolo diabase dykes.

		Mafic dykes
	Locality	Corteno	Corteno	Corteno	Corteno	Nembra	Nembra	Nembra
	Sample	D34a	D34b	D32	Ge3	Ge10	Ge15	Ge16
	SiO 2 (wt%)	47.63	44.65	47.05	48.10	48.57	44.87	52.53
	TiO 2	3.41	2.75	2.11	2.33	2.61	3.08	2.06
	Al 2 O 3	13.47	12.20	14.07	13.46	13.98	14.68	16.33
	Fe 2 O 3	15.47	17.74	14.78	14.88	13.08	14.91	10.67
	MgO	5.12	9.05	8.40	8.07	7.20	5.77	3.71
	MnO	0.21	0.20	0.19	0.22	0.17	0.21	0.14
	CaO	8.41	8.61	6.70	5.28	6.97	7.94	5.34
	Na 2 O	3.89	2.00	3.10	3.16	3.77	3.44	5.33
	K 2 O	1.06	1.48	0.85	1.32	1.56	1.85	1.25
	P 2 O 5	0.62	0.22	0.33	0.34	0.56	1.13	0.73
	LOI	1.00	1.72	2.88	3.26	2.23	1.75	2.16
	Total	100.29	100.62	100.45	100.42	100.70	99.62	100.24
	Mg#	0.39	0.50	0.52	0.51	0.52	0.43	0.40
	Rb (ppm)	32	48	21	41	50	42	32
	Ba	170	101	108	189	172	221	239
	Th	3.1	1.5	2.5	2.1	3.8	3.8	5.6
	U	0.9	0.5	0.7	0.7	1.2	1.1	1.6
	Nb	25.2	17.9	23.1	25.5	44.6	50.1	57.5
	Ta	1.3	0.96	1.22	1.32	2.25	2.53	2.81
	Sr	390	222	263	264	499	579	515
	Zr	155	107	140	141	196	213	265
	Hf	4.4	3	3.7	3.8	5	4.8	6.6
	Y	42.6	26.3	27.2	34.3	30.8	37.3	38.3
	La	19	9.78	14.1	15.3	24.7	30.1	33.2
	Ce	42.5	21.8	30.1	30.9	50.7	63	68.3
	Pr	5.73	2.94	3.86	4.23	6.34	7.97	8.47
	Nd	26.6	14.3	17.9	19.3	27.9	37.3	35.1
	Sm	8.06	4.47	4.98	5.72	7.1	9.94	8.77
	Eu	2.63	1.56	1.57	1.95	2.3	3.09	2.76
	Gd	8.91	5.11	5.23	6.37	6.92	10	8.43
	Tb	1.41	0.87	0.87	1.06	1.08	1.48	1.34
	Dy	8.36	5.19	5.16	6.49	6.28	8.25	7.6
	Ho	1.56	0.96	0.95	1.24	1.14	1.43	1.37
	Er	4.13	2.56	2.62	3.38	3	3.67	3.62
	Tm	0.521	0.341	0.35	0.452	0.379	0.448	0.479
	Yb	3.1	2.07	2.1	2.75	2.22	2.61	2.84
	Lu	0.478	0.317	0.323	0.421	0.339	0.387	0.417

Table 2

 2 Compositional

	Locality	Rock	Generation	Si	Ti	Al VI	Fe 2+	Fe 3+	Mg	Mg#	Ca	Na
		type
		Mafic
	Corteno	dyke	Cpx core	1

range (bold, apfu) and average value (± s.d., apfu) for clinopyroxene in the Edolo diabase dykes.

.81-1.90 0.03-0.06 0.01-0.06 0.24-0.31 0.03-0.08 0.67-0.74 0.67-0.70 0.82-0.86 0.03-0.04

				1.85 ±	0.05 ±	0.03 ±	0.27 ±	0.06 ±	0.71 ±	0.69 ±	0.84 ±
			(5 data)	0.03	0.01	0.02	0.02	0.02	0.03	0.01	0.01	-
			Cpx rim	1.98	0.01	0.04	0.28	0.00	0.71	0.72	0.94	0.02
			(1 data)	-	-	-	-	-	-	-	-	-
		Mafic
	Valmoranda	dyke	Cpx core	1.73-1.91	0.03-0.12	0.00-0.03	0.26-0.36	0.02-0.10	0.58-0.64	0.61-0.64	0.85-0.91	0.03-0.05
				1.80 ±	0.08 ±	0.02 ±	0.31 ±	0.06 ±	0.62 ±	0.63 ±	0.87 ±	0.04 ±
			(10 data)	0.05	0.02	0.01	0.03	0.02	0.02	0.01	0.02	0.01
			Cpx rim	1.97-1.98	0.01-0.02	0.01-0.03	0.50-0.53	0.03-0.05	0.41-0.43	0.42-0.44	0.89-0.91	0.06-0.07
						0.02 ±	0.52 ±	0.04 ±	0.42 ±	0.43 ±	0.90 ±
			(3 data)	-	-	0.01	0.01	0.01	0.01	0.01	0.01	-
		Mafic
	Nembra	dyke	Cpx core	1.75-1.92	0.03-0.08	0.02-0.06	0.18-0.31	0.00-0.09	0.66-0.78	0.66-0.76	0.83-0.87	0.03-0.05
				1.85 ±	0.05 ±	0.04 ±	0.24 ±	0.05 ±	0.72 ±	0.71 ±	0.85 ±	0.04 ±
			(27 data)	0.05	0.01	0.01	0.03	0.02	0.04	0.03	0.01	0.01
			Cpx rim	1.87-1.99	0.00-0.04	0.00-0.05	0.30-0.46	0.00-0.09	0.52-0.74	0.52-0.71	0.84-0.94	0.01-0.05
				1.94 ±	0.02 ±	0.03 ±	0.36 ±	0.04 ±	0.63 ±	0.62 ±	0.88 ±	0.04 ±
			(10 data)	0.04	0.01	0.02	0.06	0.03	0.07	0.06	0.03	0.01

Table 3

 3 Compositional range (bold, apfu) and average value(± s.d., apfu) for magmatic amphibole in the Edolo diabase dykes.

	Locality	Rock type	Generation	Si	Ti	Al VI	Mg#	Ca	Na	K	Cl
	Corteno	Mafic dyke	Amp core	6.13-6.33	0.43-0.53	0.17-0.19	0.46-0.55	1.75-1.78	0.82-0.90	0.20-0.22	0.00-0.01
			(3 data)	6.20 ± 0.09	0.47 ± 0.04	0.18 ± 0.01	0.50 ± 0.04	1.76 ± 0.01	0.85 ± 0.04	0.21 ± 0.01	-
			Amp rim	6.08-6.27	0.25-0.40	0.19-0.34	0.22-0.27	1.73-1.83	0.77-1.00	0.27-0.31	0.00-0.01
			(3 data)	6.15 ± 0.09	0.31 ± 0.06	0.28 ± 0.06	0.25 ± 0.02	1.79 ± 0.05	0.86 ± 0.10	0.29 ± 0.02	-
			Amp out. rim	6.57-6.89	0.01-0.08	0.23-0.49	0.26-0.40	1.73-1.82	0.42-0.58	0.02-0.05	0.02-0.04
			(4 data)	6.72 ± 0.11	0.05 ± 0.02	0.41 ± 0.10	0.35 ± 0.06	1.79 ± 0.03	0.50 ± 0.06	0.04 ± 0.01	0.03 ± 0.01
		Plagioclase-rich
		vein	Amp core	6.25-6.47	0.43-0.44	0.15-0.20	0.37	1.72-1.75	0.51-0.83	0.23	0.00-0.01
			(2 data)	-	-	-	-	-	-	-	-
			Amp rim	5.94-6.35	0.18-0.35	0.14-0.44	0.09-0.19	1.70-1.84	0.55-0.80	0.26-0.35	0.00-0.03
			(4 data)	6.18 ± 0.15	0.26 ± 0.06	0.30 ± 0.11	0.15 ± 0.04	1.75 ± 0.07	0.71 ± 0.09	0.32 ± 0.03	-
			Amp out. rim	6.06-6.66	0.04-0.12	0.16-0.66	0.16-0.29	1.80-1.90	0.39-0.87	0.05-0.22	0.10-0.24
			(8 data)	6.29 ± 0.19	0.07 ± 0.03	0.46 ± 0.16	0.20 ± 0.05	1.86 ± 0.03	0.63 ± 0.14	0.11 ± 0.06	0.13 ± 0.05
	Valmoranda	Mafic dyke	Amp core	5.95-5.99	0.47-0.50	0.00-0.02	0.52-0.54	1.82-1.84	0.77-0.83	0.22	0.00
			(2 data)	-	-	-	-	-	-	-	-
			Amp out. rim	6.80	0.03	0.31	0.40	1.91	0.31	0.22	0.08
			(1 data)	-	-	-	-	-	-	-	-
	Nembra	Mafic dyke	Amp core	6.04-6.34	0.45-0.64	0.16-0.32	0.44-0.56	1.74-1.85	0.40-0.93	0.18-0.26	0.00-0.03
			(17 data)	6.18 ± 0.08	0.53 ± 0.05	0.21 ± 0.04	0.50 ± 0.04	1.79 ± 0.02	0.76 ± 0.13	0.23 ± 0.02	0.01 ± 0.01
			Amp rim	5.83-6.42	0.01-0.46	0.07-0.83	0.12-0.35	1.74-1.97	0.55-0.95	0.12-0.37	0.01-0.07
			(13 data)	6.12 ± 0.19	0.26 ± 0.17	0.41 ± 0.23	0.24 ± 0.07	1.83 ± 0.06	0.76 ± 0.12	0.27 ± 0.07	0.02 ± 0.02

  Composition of magmatic amphibole, biotite, and clinopyroxene in the Edolo diabase dykes. Element concentrations are in apfu. Alkaline and calc-alkaline fields for amphibole classification are from[START_REF] Ridolfi | Calcic amphiboles in calc-alkaline and alkaline magmas: thermobarometric and chemometric empirical equations valid up to 1,130 • C and 2.2 GPa[END_REF].

		0.20							0.30								1.00
			Mafic dykes			clinopyroxene			clinopyroxene							Mafic dykes	Plagioclase-rich veins	biotite
			Corteno															Corteno
		0.15	Cpx core Valmoranda Cpx rim Cpx core						0.25								0.80	Nembra Bt Bt Valmoranda	Bt
			Cpx rim															Bt
			Nembra						0.20
	Na (apfu)	0.10	Cpx core Cpx rim					Al IV (apfu)	0.15							Mg#	0.40 0.60
									0.10
		0.05
									0.05								0.20
		0.00							0.00								0.00
		0.0	0.2	0.4	0.6	0.8	1.0	0.00	0.02	0.04	0.06	0.08	0.10	0.12	0.14	0.00		0.20	0.40	0.60	0.80	1.00
					Mg#							Ti (apfu)							Ti (apfu)
		1.00						1.00								5.00
			Mafic dykes	Plagioclase-rich veins		amphibole							amphibole						amphibole
			Corteno
			Amp core	Amp core
		0.80	Amp rim Amp out. rim	Amp rim Amp out. rim			0.80								4.00
			Valmoranda
			Amp core
			Amp out. rim
	K (apfu)	0.40 0.60	Amp core Nembra Amp rim					0.40 Ti (apfu) 0.60							Mg (apfu)	2.00 3.00
							alkaline
		0.20	calc-alkaline			series	0.20								1.00
			series
		0.00						0.00								0.00
		8.00	7.50	7.00	6.50	6.00	5.50	5.00	0.00		1.00	2.00		3.00		4.00	0.00	1.00	2.00	3.00	4.00	5.00
				Si (apfu)							Al (apfu)
	Fig. 5. ppm) and Hf (31-42 ppm) than the cores, comparable to slightly lower
	Ni (26-29 ppm) and Y (127-139 ppm), and lower Ba (81-96 ppm) and
	Sr

Acknowledgments

This work is part of the PhD thesis of M. Filippi. G. Sessa and A. Risplendente are acknowledged for technical assistance. The authors express their gratitude to F. Casetta and an anonymous reviewer for their constructive reviews, which have greatly contributed to enhancing the quality of the text. A special thanks is also extended to G. Shellnutt for his meticulous editorial handling. This work received support from the Italian Ministry for University and Research (MUR) through the project "Dipartimenti di Eccellenza 2023-27".

Author statement

All listed authors have contributed to the development and execution of this research. No undisclosed authors have contributed to this work. This research was conducted with the highest ethical standards, adhering to the guidelines and regulations governing scientific research.

Declaration of Competing Interest

The authors declare that there are no conflicts of interest that could affect the impartiality of the research.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi. org/10.1016/j.lithos.2023.107435.