Cretaceous intraplate volcanism of Govorov Guyot and formation models of the Magellan seamounts, Pacific Ocean

ABSTRACT

The OIB-type volcanic rocks of Govorov Guyot in Magellan Seamounts (Pacific Ocean) include basalts, trachybasalts, basaltic trachyandesites, and trachyandesites dated by the ⁴⁰Ar-³⁹Ar plateau from 121 ± 2.8 to 98.5 ± 1.4 Ma. Some rocks bear amphibole-spinel wehrlite xenoliths and clinopyroxene-amphibole (Cpx-Amp) mantle vein fragments in xenoliths and xenocrysts, which are remnants of metasomatized oceanic lithosphere. The pressure and temperature crystallization for pargasitic amphibole were the highest (1170–1130°C and 2.5–1.6 GPa, 73–53 km depth) in wehrlite peridotite and the lowest (1.6–1.1 GPa, shallower than 52 km, and 1070–980°C) in Cpx-Amp metasomatic mantle veins. Ti-bearing Amp phenocrysts and microlites crystallized from the parent melts of basaltic rocks at 1060–910°C and 1.2–0.4 GPa (40–15 km). The ascending basaltic melts lost H₂O from 8.6 ± 1.2 to 2.6 ± 0.4 wt% upon decompression. Amphibole mantle xenocrysts became replaced by Ti-magnetite- and rhönite-bearing mineral assemblages in intermediate magma chambers within oceanic crust (3–7 km). Pargasitic Amp in wehrlite and metasomatic mantle veins may have crystallized at different depths from hydrous (6–4.5 ± 0.7 wt% H₂O) mafic melts that percolated through peridotite. The sources of heat and metasomatic agents (silicate melts and/or fluids enriched in volatiles) most likely had no relation to the Pacific Plate subduction but may be associated with the Southern Pacific Superplume in the South Pacific Thermal and Isotopic Anomaly region, or may be located at the Lithosphere-Asthenosphere Boundary (LAB) level in the plume absence. Repeated events of Cretaceous intraplate volcanism in the Magellan guyots can be explained in terms of plume (hotspot) activity or decompression partial melting of enriched or metasomatized asthenosphere and/or metasomatized oceanic lithosphere caused by Pacific Plate deformation and fracturing from the LAB level.

Graphical Abstract

KEYWORDS:

• Matasomatized oceanic lithosphere
• wehrlite xenoliths
• mantle xenocrysts
• pargasitic amphibole
• Ti-amphibole
• Govorov Guyot
• Magellan Seamounts
• Pacific ocean

Highlights

• The OIB-type volcanic rocks of Govorov Guyot in Magellan Seamounts include basalts, trachybasalts, basaltic trachyandesites, and trachyandesites dated from 121 ± 2.8 to 98.5 ± 1.4 Ma.

• Some basaltic rocks bear amphibole-spinel wehrlite xenoliths, clinopyroxene-аmphibole metasomatic mantle vein fragments in xenoliths, clinopyroxene, and pargasitic amphibole xenocrysts.

• Pargasitic amphibole in wehrlite and mantle veins may have crystallized at estimated temperatures 1070–980°C and depths 73–44 km from hydrous mafic melts that percolated through peridotite.

• Repeated events of Cretaceous intraplate volcanism in the Magellan guyots can be explained in terms of plume activity or decompression partial melting of enriched or metasomatized asthenosphere and/or metasomatized oceanic lithosphere caused by Pacific Plate deformation and fracturing from the LAB level.

Acknowledgments

We wish to thank the crew of R/V Gelendzhik for support during the cruises of 2016–2017. We are grateful to all our colleagues who helped us: Pulaeva, I.A. (JSC Yuzhmorgeologiya) for aid in sampling; Khromova, L.A. (Geological Institute SB RAS, Ulan-Ude), Karmanov, N.S. (IGM SB RAS, Novosibirsk), and Cherbakov, Yu.D. (IGC SB RAS) for SEM EDS measurements; Yudin, D.S. (IGM SB RAS, Novosibirsk) for Ar-Ar dating. The manuscript profited much from constructive criticism by two anonymous reviewers.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2022.2145512

Additional information

Funding

The study was carried out as part of Basic Research Program 0284-2021-0006 of the Russian Academy of Sciences and was supported by grant 075-15-2022-1100 from the Ministry of Science and Higher Education of the Russian Federation.