Seafloor Magnetism Under Hydrothermal Alteration: Insights From Magnetomineralogy and Magnetic Properties of the Southwest Indian Ridge Basalts

Shishun Wang, Liao Chang, Chunhui Tao, Dario Bilardello, Long Liu, Tao Wu

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Titanomagnetites in mid-ocean ridge basalt (MORB) experience variable post crystallization alterations associated with seafloor tectonic and environmental processes. Compared to low-temperature oxidation, seafloor hydrothermal alteration is thought to be more destructive but its magnetic aftermaths are insufficiently documented. Here we present comprehensive rock magnetic and electron microscopic analyses of fresh and hydrothermally-altered MORBs dredged from the Longqi and Yuhuang hydrothermal fields, Southwest Indian Ridge. We observe large variations in magnetic properties of fresh MORBs, originated from relative proportions of nano-scale single-domain to vortex state and micron-scale vortex to multi-domain state dendritic titanomagnetites. Progressive hydrothermal alteration produces secondary magnetite through recrystallization of exsolved and dissolved Fe from primary titanomagnetite. Exsolution is evident by a dual Verwey transition signature and coexisting Ti-poor titanomagnetites and sphenes in partially chloritized basalts. A schematic model is proposed to explain the variations in magnetomineralogy and magnetic properties with progressive hydrothermal alteration. Intermediate hydrothermal alteration products retain a secondary chemical remanent magnetization (CRM) which is related to the long-term magnetization variations in oceanic basalts. The established framework allows characterizing MORB hydrothermal alteration and ultimately contributes to resolving the complexity of seafloor magnetism.

Original languageEnglish (US)
Article numbere2021JB022646
JournalJournal of Geophysical Research: Solid Earth
Volume126
Issue number12
DOIs
StatePublished - Dec 2021

Bibliographical note

Funding Information:
We thank Pengfei Xue and Hoabin Hong for assistance in magnetic measurements and Thomas Berndt for helpful discussions. Constructive reviews by Marco Maffione and one anonymous reviewer have improved this manuscript. We also thank editor Mark Dekkers and associate editor Bjarne Almqvist for editorial handling. This study was supported by the National Key R & D Program of China under contract No. 2018YFC0309901, the National Natural Science Foundation of China (grants 42061130214, 41722402), and COMRA Major Project under contract No. DY135‐S1‐01‐06. Liao Chang acknowledges additional support from a Royal Society‐Newton Advanced Fellowship (NAF\R1\201096). Shishun Wang acknowledges a Visiting Research Fellowship from the Institute for Rock Magnetism (IRM), University of Minnesota. The IRM is a US National Multi‐user Facility supported through the Instrumentation and Facilities Program of the National Science Foundation, Earth Sciences Division, and by funding from the University of Minnesota. This is IRM publication #2105.

Funding Information:
We thank Pengfei Xue and Hoabin Hong for assistance in magnetic measurements and Thomas Berndt for helpful discussions. Constructive reviews by Marco Maffione and one anonymous reviewer have improved this manuscript. We also thank editor Mark Dekkers and associate editor Bjarne Almqvist for editorial handling. This study was supported by the National Key R & D Program of China under contract No. 2018YFC0309901, the National Natural Science Foundation of China (grants 42061130214, 41722402), and COMRA Major Project under contract No. DY135-S1-01-06. Liao Chang acknowledges additional support from a Royal Society-Newton Advanced Fellowship (NAF\R1\201096). Shishun Wang acknowledges a Visiting Research Fellowship from the Institute for Rock Magnetism (IRM), University of Minnesota. The IRM is a US National Multi-user Facility supported through the Instrumentation and Facilities Program of the National Science Foundation, Earth Sciences Division, and by funding from the University of Minnesota. This is IRM publication #2105.

Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.

Keywords

  • Verwey transition
  • hydrothermal alteration
  • magnetic anomaly
  • magnetic properties
  • mid-ocean ridge basalt
  • titanomagnetite

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