by Othmar Müntener, Mattia Pistone, Luca Ziberna, György Hetényi, Andrew Greenwood, Alberto Zanetti

The Ivrea-Verbano Zone (IVZ) in the Italian Alps is one of the most complete and best studied archetype of a continental crust– upper mantle section on Earth. Recent evidence illustrates that the IVZ is an exceptional archive of trans-crustal continental magmatism documenting lower crustal processes of magma emplacement, crystallisation and crustal assimilation, and of the development of near-surface magmatism, including evidence for protracted super-eruptions during the Permian period. A defining feature of the IVZ is that the available geophysical evidence points to the surficial, indeed as shallow as 3 km or even less, presence of mantle-type high-velocity, high-density rocks. This structure is referred to as the Ivrea Geophysical Body (IGB), which, based on its classical interpretation, gained worldwide notoriety as the enigmatic “Bird’s Head”. As such, the IVZ provides a truly unique natural laboratory to fundamentally advance our understanding of the continental lower crust and the crust–mantle transition zone by a combination of geoscientific approaches and scientific drilling, complementing offshore attempts to drill through the Moho. A successful workshop in May 2017 has built great momentum toward this objective and an international team of thirty-three investigators thus proposes a comprehensive drilling program in the IVZ. Drilling two 1 km deep holes into the IVZ at strategic locations will provide an unrivalled opportunity to link geophysical and geological data via core observations, downhole logging, microbiological sampling, hydrological studies, and various geophysical-geological surveys. This will address long-standing fundamental questions on the nature of the continental lower crust, resolve potential connections to the IGB, allow for a comprehensive characterisation of the physical and chemical rock properties and fabrics, explore the relation of permeability to fracturing, weathering, alteration, and unravel the nature and origin of the prevailing fluids. Together with studies on the extent and diversity of the subsurface biosphere and its relation to the volatile element budget of exhumed lower continental crust, these studies will contribute to advance our understanding of metabolic energy sources for microbial ecosystems in various crystalline bedrocks. Important societal benefits of the project notably comprise the development of educational platforms for schools and university students as well as the formation of the next generation of leading researchers in Earth Science. Finally, the interests of the larger public are enticed through active collaborations with the Val Grande National Park, the Sesia Val Grande UNESCO Global Geopark and local institutions including a new visitor centre.

• 1) Bridging geophysical and geological scales using physical and chemical data systematically collected along drill cores, downhole logging data and local/regional field surveys to develop combined petrological and geophysical models on the nature and evolution of the continental lower crust and Moho transition zone,
• 2) Investigating chemical variability and ductile and brittle structures using lattice preferred orientation and crystal shape data in continental plutonic and metasedimentary lower crust and Moho transition zone to determine the mechanism of melt transport, partial melting, assimilation, crystallisation and deformation,
• 3) Quantifying the volatile- and heat-producing element budget in the continental lower crust during non-magmatic stages, magmatic additions, and fluid percolation along fractures and shear zones,
• 4) Quantifying the thermal and temporal records of construction and modification of lower crust using mineral compositions, diffusion profiles, radiogenic and stable isotopes to determine the evolution of lower continental crust,
• 5) Unravelling the origin and genesis of fluids and gases and of altered minerals and rocks including characterisation of fracture and vein spacing, initial hydration, oxidation and resulting mass transfer in the lower crust and continental Moho transition zone,
• 6) Studying subsurface alteration and microbiological communities in exhumed continental lower crust and upper mantle rocks, transitions of the microbial communities from bacteria to archaea, and availability of organic carbon, graphite and carbon dioxide for the deep biosphere,
• 7) Exploiting the potential of hydrogen, methane and abiotic hydrocarbons as a source of metabolic energy for subsurface microbial communities and as potentially extractable energy resources in geological environments.

Continental Crust, Moho Transition Zone, Rock Physics, Seismic Structure

Latitude: 45.98928, Longitude: 8.399