Granitic intrusions enhance strain localization and rapid mantle exhumation along an oceanic detachment fault

by

Scientists drilling into the Tyrrhenian Sea seafloor as part of the International Ocean Discovery Program recovered rock cores showing granite intrusions mixed with peridotite along an ancient detachment fault. Dating and chemical analysis show the granites formed about 4 million years ago some 7 to 9 kilometres down, then were rapidly brought to the seafloor within roughly half a million years. The results suggest that weak granitic rocks can focus deformation along detachment faults, speeding up mantle exhumation during continental breakup and the birth of new ocean basins.

Abstract. Serpentinization and magmatism weaken the lithosphere and facilitate mantle exhumation during magma-poor rifting and ultraslow seafloor spreading. However, the complex interplay and timing among these competing mechanisms along detachment faults remain poorly constrained. The International Ocean Discovery Program (IODP) Expedition 402 drilled an incipient oceanic basin in the Tyrrhenian Sea offshore Italy. Recovered cores consist of one sequence of variably deformed granitic intrusions intercalated with slivers of peridotites and another of primarily serpentinized peridotites with heterogeneous deformation and local granitic intrusions. Geochronological and geochemical data reveal that the granites crystallized at 4 million years ago at a depth of ~7 to 9 kilometers and rapidly exhumed within ~0.5 million years, requiring exhumation rates of ~2 centimeters per year. Structural observations show that these granites accommodated significant postcrystallization strain and enhanced localization of detachment faulting. Stable isotopes record serpentinization temperatures of ~200°C, suggesting that serpentinization occurred after the emplacement and deformation of granites. We conclude that weak felsic rocks may enhance strain localization along detachment faults at intermediate depths and aid continental breakup and mantle exhumation.

Map of the Tyrrhenian Sea showing IODP Expedition 402 drill sites with core photos and lithology logs.
Fig. 1. Map, recovery, and core photos. (A) Map of the Tyrrhenian Sea with drilled locations during Expedition 402 and ODP 107 Leg, from (29). Bathymetry grid is from the EMODnet portal (https://emodnet.ec.europa.eu/en/). (B) Core summary at Expedition 402 Sites U1612 and U1614 with lithologies, structural fabric indicators, and locations of samples used in this study. Yellow and green stars represent locations of the granites and peridotites samples used in this study, respectively. mbsf, meters below seafloor. (C to E) Representative recovered granites and surrounding mafic and ultramafic lithologies with increasing depth for holes U1612A, U1612B, and U1614C. From Poulaki et al. (2026), Science Advances, reproduced under CC BY.

Poulaki, E.M., Bickert, M., Vannucchi, P., Shuck, B.D., Akizawa, N., Pandey, A., Morishita, T., Sanfilippo, A., Cunningham, E.H., Barnes, J.D., Garber, J.M., Nistor, C., Bernard, R., Tribuzio, R., Loocke, M., Abe, N., Di Stefano, A., Filina, I.Y., Fu, Q., Gontharet, S.B.L., Kearns, L.E., Koorapati, R.K., Lei, C., Loreto, M.F., Magri, L., Menapace, W., Pavlovics, V.L., Pezard, P.A., Rodriguez-Pilco, M.A., Zhao, X., Pérez-Gussinyé, M., Garrido, C.J., Ranero, C.R., Estes, E.R., Malinverno, A. and Zitellini, N., 2026. Granitic intrusions enhance strain localization and rapid mantle exhumation along an oceanic detachment fault. Science Advances, 12(23), p.eaec6950. https://doi.org/10.1126/sciadv.aec6950

Code and data: Zenodo: 10.5281/zenodo.18893357

Loading

Share