Bartoy火山地帯(ロシア・バイカル地方)のアルカリ玄武岩に由来する捕獲岩とメガクリストについての新データ

概要

論文の詳細を見る
Anhydrous and amphibole-phlogopite-bearing peridotite and pyroxenite xenoliths were found in basanites of the Bartoy volcanic field about 100km south from the southern coast of the Baikal Lake. Major groups of xenoliths have been analyzed for major and trace elements in order to characterize the upper mantle structure in the peripheral part of the Baikal Rift. Spinel lherzolites, including amphibole-bearing varieties, are most abundant. Several types of metasomatic modification were detected in peridotite group using trace element characteristics of clinopyroxene and amphibole: 1) disseminated amphibole in modally depleted lherzolites; 2) disseminated amphibole and/or phlogopite in Iherzolites and Cr-diopside pyroxenites; 3) amphibole-phlogopite and amphibole-phlogopite-pyroxene vein-rocks often crosscutting the lherzolites. Pyroxenite series includes those of type I: Cr-diopside websterites, transitional Cr-diopside pyroxenites related to amphibole-phlogopite metasomatism, rare Al-rich clinopyroxenites and type II: Al-augite spinel websterites, various Alaugite and amphibole-phlogopite-bearing cumulates. Megacryst assemblages include clinopyroxene and related pyroxenites, garnet, amphibole, Ti-biotite, Ilmenite/Ti-magnetite, alkali feldspar. P-T estimations for some Cr-diopside pyroxenite xenoliths show mineral equilibration up to 20-22 kbar at 1100-1200℃, however garnet lherzolites are absent. Alaugite garnet pyroxenites correspond to 10-14 kbar and 900-1000℃. Phlogopite-bearing Iherzolites have higher two-pyroxene temperatures (1050-1100℃) than other lherzolites (900-1070℃). Clear similarities were observed for xenolith types, mineral compositions, and xenoliths' metasomatic modification between xenoliths from the Bartoy Pliocene basanites and from the Vitim Miocene picrobasalts, in spite of Vitim nodules correspond to the deeper level of garnet peridotite facies. Isotopic study of Bartoy xenoliths by Ionov et al. (1992) suggested their MORB to OIB-type source, which is different from depleted mantle sources for the Vitim and Tariat (Mongolia) xenoliths. We also show the evidences for the presence of primarily heterogeneous mantle preserved in rare harzburgite and depleted lherzolite xenoliths of the Bartoy.論文Article
東北大学の論文

Bartoy火山地帯(ロシア・バイカル地方)のアルカリ玄武岩に由来する捕獲岩とメガクリストについての新データ

スポンサーリンク

概要

著者

関連論文

スポンサーリンク