Reassessing the intrusive tempo and magma genesis of the late Variscan Aar batholith: U–Pb geochronology, trace element and initial Hf isotope composition of zircon

Abstract The Variscan orogeny was responsible for the formation of a significant volume igneous basement throughout present-day Europe. Detailed understanding these rocks has, however, been obfuscated by overprinting during younger geologic events. In order to better understand this basement, we present U–Pb dates, trace element concentrations and Hf isotope compositions zircon from 17 intrusions Aar batholith, located in Massif, Central Alps, Switzerland. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) used generate large set on untreated zircon, as well pretreated chemical abrasion. Furthermore, subset samples also analyzed high-precision geochronology using abrasion, dilution, thermal ionization (CA-ID-TIMS). dates both dating techniques are significantly dispersed, indicating that they influenced multiple forms complexity, including inheritance, domains secondary alteration likely related Alpine overprint or growth, decay damage Pb-loss, potentially protracted magmatic growth. Decay-damage Pb-loss is subordinate source age scatter within data, therefore abrasion pretreatment not capable completely mitigating observed analytical scatter. After rejection outliers, remaining data still exhibit excess several percent among 206 Pb/ 238 U individual samples, however it possible interpret reasonable ages data. These new interpretations indicate batholith grew incrementally through four major pulses, which occurred at approximately 348, 333, 309 298 Ma. Based geochemistry, melt source(s) evolved duration transitioning (i) melting depleted mantle 348 Ma stage active continental arc magmatism (?Hf = + 12 10), (ii) metasomatically enriched lithospheric mantle, possibly contaminated crust 333 pulse ? 10 3), followed (iii) an increasing incorporation juvenile components pulses 3 6). Finally, yield more detailed integrating mapping Massif Geological Atlas Switzerland, allowing accurate characterization categorization variably deformed heterogeneous intrusive bodies.