Drilled petit-spot basalts reveal asthenospheric mantle heterogeneity before subduction
Abstract
Submarine petit-spot volcanoes form where oceanic plates bend and flex before sinking into subduction zones, providing a rare opportunity to sample mantle-derived melts before subduction. Here we report results from the first scientific drilling of a sediment-buried petit-spot volcano during International Ocean Drilling Programme Expedition 502, recovering basalts from a previously inaccessible interior of a petit-spot magmatic system. The recovered basalts exhibit a distinctive geochemical signature among oceanic intraplate magmas, combining Ni-rich olivine phenocrysts with unusually low Mg/(Mg + Fe2+), SiO2-rich bulk compositions, pronounced Ba enrichment and Th–U–Nb–Ta depletion, and the most enriched mantle 1 (EM1)-like Sr–Nd isotopic compositions yet recognized in petit-spot basalts. Thermodynamic modelling rules out fractional crystallization of dry or carbonated peridotite-derived parent melts and requires a contribution from enriched SiO2-excess pyroxenite. Fresh glasses further record CO2 depletion and low vesicularity relative to exposed petit-spot basalts. These findings reveal the petrological complexity of known EM1-type mantle heterogeneity, with isotopic signatures that can mask diverse mantle lithologies and melting processes that remain hidden from conventional seafloor sampling.
Related
- Cadmium isotope compositions of basalts from the East Pacific Rise and Southwest Indian Ridge: Implications for magma differentiation and mantle heterogeneity
- Heavy boron isotopes reveal deep carbon recycling in hot subduction zones
- A 400 Myr subduction memory in the mid-ocean ridge source
- When and why does CO2 mineralization in basalts stall? A critical review of microscale passivation, pore-clogging mechanisms and the multiscale imaging needed to resolve them
- Archean subduction-derived noble gases in the lithospheric mantle beneath the São Francisco Craton
BibTeX
@misc{akizawa2026drilled,
title = {{Drilled petit-spot basalts reveal asthenospheric mantle heterogeneity before subduction}},
author = {Norikatsu Akizawa and Kazuto Mikuni and Jennifer M. Lington and Christopher Yen and Takashi Miyazaki and Francesco Narduzzi and Takanori Kagoshima and Katie Preece and Hayato Ueda and Paola Vannucchi and Lottie Atton and Hirano Naoto and Shiki Machida and Takeshi Hanyu and Tomoki Sato and Bogdan S. Vaglarov and Qing Chang and Yuto Sato and Kenji Shimizu and Takayuki Ushikubo and Asuka Yamaguchi and Hiroko Kitajima and Natsumi Okutsu and Yuya Akamatsu and Olivier Fabbri and Matt J. Ikari and Taro Kido and Rachel Lauer and Kenji M. Matsuzaki and Ayumu Miyakawa and Yasuyuki Nakamura and Hanaya Okuda and Andrew P. Roberts and Louisa H. Stokes and Fuka Takuwa and Taizo Uchida and Edoardo Barbero and Chin-Yeh Chen and Jose-Abel Flores and Mila Huebsch and Yuji Kato and Eun Young Lee and Jason P. Morgan and Sebastien Pilet},
howpublished = {EarthArXiv},
year = {2026},
month = oct,
doi = {10.31223/x5db90},
url = {https://eartharxiv.org/repository/view/15421/},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - UNPB
TI - Drilled petit-spot basalts reveal asthenospheric mantle heterogeneity before subduction
AU - Norikatsu Akizawa
AU - Kazuto Mikuni
AU - Jennifer M. Lington
AU - Christopher Yen
AU - Takashi Miyazaki
AU - Francesco Narduzzi
AU - Takanori Kagoshima
AU - Katie Preece
AU - Hayato Ueda
AU - Paola Vannucchi
AU - Lottie Atton
AU - Hirano Naoto
AU - Shiki Machida
AU - Takeshi Hanyu
AU - Tomoki Sato
AU - Bogdan S. Vaglarov
AU - Qing Chang
AU - Yuto Sato
AU - Kenji Shimizu
AU - Takayuki Ushikubo
AU - Asuka Yamaguchi
AU - Hiroko Kitajima
AU - Natsumi Okutsu
AU - Yuya Akamatsu
AU - Olivier Fabbri
AU - Matt J. Ikari
AU - Taro Kido
AU - Rachel Lauer
AU - Kenji M. Matsuzaki
AU - Ayumu Miyakawa
AU - Yasuyuki Nakamura
AU - Hanaya Okuda
AU - Andrew P. Roberts
AU - Louisa H. Stokes
AU - Fuka Takuwa
AU - Taizo Uchida
AU - Edoardo Barbero
AU - Chin-Yeh Chen
AU - Jose-Abel Flores
AU - Mila Huebsch
AU - Yuji Kato
AU - Eun Young Lee
AU - Jason P. Morgan
AU - Sebastien Pilet
PY - 2026
DA - 2026/10/09
PB - EarthArXiv
DO - 10.31223/x5db90
UR - https://eartharxiv.org/repository/view/15421/
AB - Submarine petit-spot volcanoes form where oceanic plates bend and flex before sinking into subduction zones, providing a rare opportunity to sample mantle-derived melts before subduction. Here we report results from the first scientific drilling of a sediment-buried petit-spot volcano during International Ocean Drilling Programme Expedition 502, recovering basalts from a previously inaccessible interior of a petit-spot magmatic system. The recovered basalts exhibit a distinctive geochemical signature among oceanic intraplate magmas, combining Ni-rich olivine phenocrysts with unusually low Mg/(Mg + Fe2+), SiO2-rich bulk compositions, pronounced Ba enrichment and Th–U–Nb–Ta depletion, and the most enriched mantle 1 (EM1)-like Sr–Nd isotopic compositions yet recognized in petit-spot basalts. Thermodynamic modelling rules out fractional crystallization of dry or carbonated peridotite-derived parent melts and requires a contribution from enriched SiO2-excess pyroxenite. Fresh glasses further record CO2 depletion and low vesicularity relative to exposed petit-spot basalts. These findings reveal the petrological complexity of known EM1-type mantle heterogeneity, with isotopic signatures that can mask diverse mantle lithologies and melting processes that remain hidden from conventional seafloor sampling.
ER -