EGU25-16604, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-16604
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
From the lower crust towards the crust–mantle transition zone: Initial results from the ICDP DIVE project
Othmar Müntener1, Hetényi György1, Greenwood Andrew2, Ziberna Luca3, Zanetti Alberto4, Pistone Mattia5, Giovanelli Donato6, Venier Marco7, and the DIVE Drilling Project Science team*
Othmar Müntener et al.
  • 1University of Lausanne, Institute of Earth Sciences, Lausanne, Switzerland (othmar.muntener@unil.ch)
  • 2Montanuniversität Leoben, Austria
  • 3Dipartimento di Matematica e Geoscienze, Università di Trieste, Italy
  • 4CNR Pavia, Italy
  • 5Department of Geology, University of Georgia, US
  • 6Università di Napoli, Italy
  • 7Johannes-Gutenberg-Universität Mainz, Geowissenschaften, Mainz, Germany
  • *A full list of authors appears at the end of the abstract

We report initial results from the first phase of the ICDP-funded ‘Drilling the Ivrea-Verbano zonE‘ (DIVE) project in Val d’Ossola (northern Italy). Characterized by pronounced geophysical anomalies, the exposed Ivrea-Verbano Zone offers unique opportunities to test geophysical and petrologic models about the lower continental crust (LCC) and its transition to the upper mantle. From October 2022 to April 2024 two boreholes of respectively 578.5 and 909.5 m depth were drilled using continuous diamond double tube wireline coring. Core recovery was ~100% for both boreholes. During and after drilling, geophysical logs were acquired, providing natural and spectral gamma ray, magnetic susceptibility, electrical resistivity (SPR and DLL), spontaneous potential, sonic, acoustic and optic televiewer data. Retrieved rock cores were described and classified by the DIVE drilling project science team and later shipped to the BGR Rock Core Repository in Spandau-Berlin, where core density and magnetic susceptibility were measured with a multi-sensor core logger followed by XRF scans.

Here we summarize core descriptions, initial geochemical results, geophysical logging data, drill hole fluid chemistry and gas compositions, and preliminary microbiological investigations. The two boreholes sampled two fundamentally different compositions of the lower continental crust: one (5071_1_B) mostly consists of metasedimentary rocks and a few amphibolites, and the second hole (5071_1_A) mostly captures a variety of gabbroic rocks with intercalations of granulite facies metasediments, pyroxenite, and intrusive gabbronorite. This is in agreement with the expected structural positions but allow to study the continental lower crust across numerous spatial scales.

In borehole 5071_1_A, several zones of ultramylonites, cataclasites, fault gauges and pseudotachylites were recovered documenting important episodes of semi-brittle behaviour of the LCC after assembly in the Lower Permian. Along the entire drillholes fractures and open cracks were observed and sampled, some of them filled with precipitates of quartz, carbonates, sulfides, graphite, and oxides.

Continuous monitoring of borehole fluids and gases provide evidence of varying gas mixtures including H2, CH4, and CO2, indicating diverse fluid sources and microbial activities in the deep crust. At the current stage, we are evaluating the biotic and abiotic contributions. Some of these open fractures are potentially promising hosts for microbial communities and are currently under investigation. Additional samples for microbiological studies were taken every 20 m from the drillcores and are currently cultivated for further investigations and also analyzed for bulk rock major and trace elements.

The two drillholes of DIVE provide unprecedented details of the variability of lower continental crust. Metasedimentary sections of the drilled LCC are important reservoirs for volatile and radiogenic heat producing elements, while dominantly mafic sections of the lower continental crust are depleted in these elements. Measured seismic velocities and densities are affected by numerous fractures but metasedimentary rocks are uniformly lower in density (2.5-2.8 g/cm3) compared to the mafic section (2.8-3.4 g/cm3) indicating that the lowermost part of the drilled section enters the continental crust–mantle transition zone.

DIVE Drilling Project Science team:

Bjarne Almqvist, Ludovic Baron, Marco Beltrame, Florian Bleibinhaus, Mattia Bonazzi, Eva Caspari, Ana Cernok, Sarah Degen, Matteo Del Rio, Hugo Dutoit, Donato Giovannelli, Andrew Greenwood, Friedrich Hawemann, Katja Heeschen, Jörg Hermann, György Hetényi, Klaus Holliger, Jochem Kück, Kim Lemke, Junjian Li, Zheng Luo, Hadis Mansouri, Davide Mariani, Othmar Müntener, Francesco Narduzzi, Luca Pacchiega, Benoît Petri, Simona Pierdominici, Mattia Pistone, Silvia Pondrelli, Daniela Rubatto, Alexia Secrétan, Gaia Siravo, Sören Tholen, Virginia Toy, Bernd Trabi, Laurent Truche, Marco Venier, Marie Violay, Thomas Wiersberg, Alberto Zanetti, Luca Ziberna

How to cite: Müntener, O., György, H., Andrew, G., Luca, Z., Alberto, Z., Mattia, P., Donato, G., and Marco, V. and the DIVE Drilling Project Science team: From the lower crust towards the crust–mantle transition zone: Initial results from the ICDP DIVE project, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16604, https://doi.org/10.5194/egusphere-egu25-16604, 2025.