Magmatic Response to Subduction Initiation, Part II: Boninites and Related Rocks of the Izu‐Bonin Arc From IOPD Expedition 352

John W. Shervais, Mark K. Reagan, Marguerite Godard, Julie Prytulak, Jeffrey G. Ryan

Research output: Contribution to journalArticlepeer-review

Abstract

<p> International Ocean Discovery Program Expedition 352 to the Izu&hyphen;Bonin forearc cored over 800 m of basement comprising boninite and boninite&hyphen;series lavas. This is the most extensive, well&hyphen;constrained suite of boninite series lavas ever obtained from in situ oceanic crust. The boninites are characterized as high&hyphen;silica boninite (HSB), low&hyphen;silica boninite (LSB), or basaltic boninite based on their SiO <sub> 2 </sub> &hyphen;MgO&hyphen;TiO <sub> 2 </sub> relations. The principal fractionation products of all three series are high&hyphen;Mg andesites (HMA). Lavas recovered &gt;250 meters below seafloor (mbsf) erupted at a forearc spreading axis and are dominated by LSB and HMA. Lavas recovered fromoff&hyphen;axis and are dominated by HSB. The axial and off&hyphen;axis lavas are characterized by distinct chemostratigraphic trends in their major, trace, and isotopic compositions. The off&hyphen;axis lavas are chemically similar to boninite from the type locality at Chichijima, with concave&hyphen;upward rare earth elements patterns. In contrast, the more abundant axial lavas have distinctly light rare earth element&hyphen;depleted patterns and represent a new, previously unsampled precursor to the Chichijima&hyphen;type boninite lavas. Petrogenetic modeling suggests that the axial lavas formed by fluxing of refractory mantle (likely the residue from forearc basalt extraction), with amphibolite&hyphen;facies melt derived from subducting altered oceanic crust. The upper, off&hyphen;axis lavas require an additional component of sediment&hyphen;derived melt in addition. Both models are consistent with previously published isotopic data.</p>
Original languageAmerican English
JournalGeochemistry, Geophysics, Geosystems
Volume22
DOIs
StatePublished - Jan 1 2021

Keywords

  • boninite
  • IODP Expedition 352
  • Izu‐Bonin‐Mariana forearc
  • JOIDES Resolution
  • ophiolites
  • Sites U1439
  • U1442
  • subduction initiation

Disciplines

  • Earth Sciences

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