Deep-seated inclusions from the in Zun-Murin basanites (Tunka rift valley,Prebaikalia)

A basanitic lava flow bearing deep-seated inclusions erupted about 10 Ma ag o south of the Tunka basin in the Zun-Murin River valley on the northern sl ope of the Khamar-Daban ridge. The inclusions involve uppermost mantle rock s, namely Cr-diopside-bearing spinel lherzolites ("green" series) and clino pyroxenites, wehrlites, and gabbros with augite-salite-fassaite pyroxenes ( "black" series), Clinopyroxenes and spinels show broadly varying ferric-fer rous ratios. Spinel lherzolites underwent metasomatism, which resulted In o xidation of Iron In Cr-diopsides accompanied by an increase in Na and a dec rease in Cr contents and partial melting manifested in reduction of iron an d lower concentrations of Na. The deep inclusions in the Tunka alkali basalts formed in the transitive a crust-mantle zone at the suture between the Riphean Tuva-Mongolian and Cale donian Dzhida terranes. The depth of uptake of crustal xenoliths by the asc ending alkali-basaltic melts may have been controlled by the major fault th at bounds the northern steep side of the rift valley and reaches the crust- mantle boundary just beneath the Zun-Murin site. North of the major fault, inclusions from alkali basalts are olivine-clinopyroxene to plagioclase-amp hibole cumulates crystallized From basaltic melts trapped at crustal depths .