Корневые структуры Даригангского и Витимского вулканических полей Японско-Байкальского геодинамического коридора: Соотношения источников позднекайнозойских магматических расплавов и современных локальных низкоскоростных аномалий в верхней мантии

Abstract

In the Dariganga volcanic field of southeastern Mongolia, mainly basalt and tephrite melts with a MgO content of 5–11 wt. % and La/Yb ratio 7–40, derived from the mantle region of transition from the asthenosphere to the lithosphere, erupted in the last 14 million years. Basanite melts with a high MgO content (11–15.8 wt. %) and phonotephrite melts with a high La/Yb ratio (40–54) played a special role. Some basanites erupted after melting of the material of a residual slab source with a high potential temperature (Tp = 1489 °C) in the time interval of 10–5 million years ago, others due to melting of an OIB-like source at Tp up to 1423 °C about 4–3 million years ago. Phonotephrites resulted from low-temperature degassing of mantle fluids during the Quaternary. For the sources of basanites and phonotephrites, Pb-isotope age estimates yield age estimates for the protomantle (4.47 and 4.45 Ga, respectively) and age-modified mantle (3.11 and 2.74 Ga, respectively). We suggest that Quaternary degassing of mantle fluids with phonotephrite eruptions in the Dariganga volcanic field is reflected in the generation of the local East Mongolian anomaly of low S-wave velocities in the upper mantle on the SSW flank of the Japan-Baikal geodynamic corridor and that similar mechanism of Quaternary degassing of mantle fluids is responsible for the formation of the local North Baikal low-velocity root structure of the Vitim volcanic field at the axial part of the geodynamic corridor. High-Mg rocks (basanites and picrobasalts) of the latter volcanic field has been shifted relative to the root structure by 300 km in the last 16 million years.