Magmatism, Metasomatism and recycling above a subduction zone. Insights from mantle xenoliths from the andesitic volcano Avachinsky (Kamchatka, Russia)

• Main Author: Bénard, Antoine
• Other Authors: Université Jean Monnet - Saint-Étienne (UJM), Université Jean Monnet, Dmitri Ionov
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2011
• Subjects: subduction; mantle xenoliths; veins; boninites; lithophile trace elements; platinum group elements; volatile elements; xénolithes mantelliques; veines; éléments en trace lithophiles; éléments du groupe du platine; éléments volatils; [SDU]Sciences of the Universe [physics]; Pacific; Kamchatka
• Online Access: https://theses.hal.science/tel-03499517; https://theses.hal.science/tel-03499517/document; https://theses.hal.science/tel-03499517/file/The%CC%80se_Kamchatka_Antoine_Be%CC%81nard.pdf

We have studied spinel harzburgites sampled at the andesitic volcano Avachinsky (South of Kamchatka, Russia). These rocks contain spinel-hosted glassy inclusions and are crosscut by pyroxenitic veins. The study of glassy inclusions in spinels reveals two types of liquids: (1) one formed at high temperature (>1200°C) in the asthenosphere and (2) one formed at lower temperature (>900°C) in the lithospheric sub-arc mantle. This work allows to measure directly the composition in major and trace elements of liquids produced by partial melting in the sub-arc mantle. Websteritic veins crosscutting the xenoliths are formed by Ca-rich boninites. These liquids can be produced by partial melting of an harzburgite, hybridized by alumino-silicated fluids deriving from the sinking Pacific plate. Ca-rich boninites can be produced in a mature arc, may not be reliable geodynamic indicators and rather precursors of some eruptive products of the andesitic volcanism. The study of orthopyroxenitic veins crosscutting the xenoliths reveals the processes of modification of liquids produced and percolating in the sub-arc mantle. These processes are characterized by a combination of fractionnation and partial re-equilibration of the percolating liquid with the host peridotite. The overall process affects liquids with various geochemical signatures and is characterized by the formation of U-shaped rare-earth elements spectra coexisting with Zr-Hf spykes. The trace element signature of Ca-poor boninites can result from this process. The methodological development of three-dimensional imaging by multiphoton microscopy applied to disseminated sulfides in xenoliths shows that this technique allows to obtain a sub-micronic resolution with a minimum of implementation. The study of the platinum group elements signature of sulphides in orthopyroxenitic veins reveals that this signature is also strongly modified during the interaction of the percolating liquid with an interstitial sulfide liquid located in the host harzburgite. The study of ...