[S-MP41] [EE] Oceanic and Continental Subduction Processes

[SMP41-P08] 大陸と海洋のリソスフェリックマントルの岩石学的比較研究：Helmstaedtモデルの検証

*新堀 希望¹、辻森 樹⁴、平野 直人⁴、木村 純一²、マリコベッツ ウラジミール³ (1.国立大学法人東北大学、2.海洋研究開発機構、3.ソボレフ地質鉱物学研究所、シベリア支部、ロシア科学アカデミー、4.東北大学東北アジア研究センター)

キーワード：lithospheric mantle, mantle xenolith, lithosphere stacking, trace element, garnet

Understanding nature of subcontinental lithospheric mantle (SCLM) is of considerable importance as underscored by the abundance of studies in different Solid Earth Sciences, including petrology, geochemistry, volcanology, seismology, and geodynamics. So far many researchers have endeavored to accurately visualize heterogeneity of SCLM and its evolution. One possible model to form lithologic heterogeneity is the lithosphere stacking model proposed by Helmstaedt and Schulze (1989). In order to evaluate the model, two contrasting mantle peridotites from cratonic (continental) and oceanic lithospheres were investigated. Deformed garnet peridotite xenoliths from the Udachnaya kimberlite pipe, as a representative material of SCLM, record multiple mantle processes beneath a craton. In-situ trace elements analyses of garnet and clinopyroxene of the garnet peridotite, confirmed at least two times of mantle–melt interaction and possible fluid infiltration at the latest process. Comparing petrological features of Siberian SCLM xenolith together with an oceanic lithospheric mantle xenolith (spinel peridotite) from the Miyagi offshore petit spot volcano, the lithosphere stacking model was revisited. No matter whether the model is realistic or not, this study confirmed that deep SCLM materials contain geochemical and mineralogical evidences of the presence of “water”, likely supplied from deeply subducted oceanic lithosphere.