Lithospheric boundaries and upper mantle heterogeneity beneath Russian Eurasia: evidence from the DSS profile QUARTZ

摘要

A combined interpretation of seismic data from the 3850-km-long Russian seismic profile QUARTZ using chemical and nuclear explosions reveals complex structure of the lithosphere related to the regional tectonics. Our analysis is focused on the structure of the uppermost mantle and based on 2D ray-tracing and inversion of the data from all 51 shots along the profile, on 2D attenuation measurements, and on the results of an analysis of the long-range P-n phase. Three groups of reflectors within the lithosphere are associated with regional- to global boundaries previously recognized in stable continental environments. One almost continuous upper mantle boundary occurs at 65 to 80-km depth and another with an approximately 40-km-thick low-velocity zone (LVZ) occurs at 120-140 km depth. The shallow upper mantle blocks and the extensive interfaces indicate strong upper mantle heterogeneity imaged by this unique profile. The thickness of the lithosphere varies from 220 km under the Baltic Shield to about 120-130 km under the tectonically active Himalayan Altay-Sayan fold belt. Within the lower part of the lithosphere, a zone of lower velocity, increased attenuation, and varying thickness might be related to hydration and partial melting, Large structural differences related to tectonic ages and histories are characteristic for the entire lithosphere and extend 200-400 km into the asthenosphere. Analysis of QUARTZ data gives confident indication of seismic heterogeneity from crustal to regional mantle scales indicating strong involvement of the mantle in tectonic processes. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 36]