Geochemical Characteristics of Metasediment—Rich Lower Continental Crust: Insights From the Ivrea‐Verbano Zone (DIVE Drilling Project, ICDP Expedition 5071, Val d’Ossola, Italy)

Abstract

Whole‐rock geochemical data from two drill cores obtained through the ICDP (International Continental Scientific Drilling Program) funded Drilling the Ivrea‐Verbano Zone (IVZ) (DIVE) project: 5071_1_B (Ornavasso) and 5071_1_A (Megolo), provide new insights into the composition of the lower continental crust (LCC) in the IVZ. Borehole 5071_1_B (578.5 m) consists of upper amphibolite facies rocks equilibrated at ∼750°C and 0.75 GPa, whereas 5071_1_A (909.5 m) consists of (meta‐)gabbroic rocks with intercalations of granulite facies felsic gneisses equilibrated at ∼950°C and 1 GPa. Systematic downhole sampling of the drill cores in 10 m intervals, along with whole‐rock geochemical analyses (X‐ray fluorescence, LA‐ICP‐MS), yields a statistically robust data set capturing lithological variability. Bulk silica content ranges from 32 to 99 wt.% SiO ₂ , reflecting the association of various metasedimentary rocks from quartzite, psammites, metapelites and calcsilicate rocks, with minor amphibolites within the Ornavasso lower‐crustal section. The geochemical variations generally reflect original depositional conditions, and thus their protoliths. Comparison with literature data highlights the potential for compositional bias in studies based solely on surface outcrops. The recovered lithologies likely derive from near‐surface Paleozoic protoliths. Subduction and accretion processes may explain the dominance of metasediments in this archetypal crustal section. Modeled seismic velocities ( V _P  ≈ 6.0–7.2 km/s), are consistent with values reported for the lower range of global LCC. The average bulk composition of the 5071_1_B section overlaps with upper crustal estimates and reaches the upper range of published LCC compositions, underscoring the significant contribution of metasedimentary rocks to the most felsic estimates of global LCC.