Shoshonite latite series of the Eastern Transbaikalia: 40Ar/39Ar age, geochemistry, and Sr Nd isotope composition of rocks from the Akatui volcano plutonic association of the Aleksandrovskii Zavod depression
Abstract The paper presents new data on age, geochemistry, and Sr and Nd isotope composition of rocks from the Akatui massif and comagmatic rocks from the lower unit of the Kailas Formation (Akatui volcano plutonic association) localized within the Aleksandrovskii Zavod depression. The amphibole 40 Ar/ 39 Ar age date the monzogabbro of the early phase of the Akatui massif at 154.8 4.4 Ma; the monzonite of the main phase yields a 40 Ar/ 39 Ar age of 160.7 3.9 Ma, and the shoshonite basalt of the lower unit of the Kailas Formation yields a 40 Ar/ 39 Ar age of 161.5 1.7 Ma. The leading petrogenetic mechanism for the Akatui volcano plutonic association is crystal fractional differentiation of melts with minor crustal contamination, which can be suggested from the mineralogical and petrographic features and geochemical and isotope characteristics of rocks. The geochemical data for the Akatui volcano plutonic association show LILE, LREE, U, Th, and Pb enrichment with a characteristic depletion in high field strength elements (HFSE) such as Nb and Ti. They are also depleted in P. Sr Nd isotope data 87 Sr/ 86 Sr( 1 6 0 Ma 0.70642 0.70688 and PSNd(160 Ma 0.6 to 2.2) suggest an EMII type mantle source and could also indicate a negligible degree of crustal contamination in the evolved melts.