The Role of Deep Fluids in Crustal Subsidence of the Cratonic Interior: The Moscow Sedimentary Basin during the Late Devonian

Abstract Slow crustal subsidence nonuniform in time and space occurred in the sedimentary basin of the Moscow Syneclise during 20 Ma in the Late Devonian. On the cool Precambrian lithosphere of the East European Craton, subsidence of this kind could have occurred only due to rock contraction in the lower crust resulting from prograde metamorphism. Crustal subsidence in the Middle and Late Devonian occurred after a long period of stability. This required the influx of mantle fluids into the lithosphere and then into the crust, which catalyzed the metamorphic reaction. The distribution of crustal subsidence was very heterogeneous, and its pattern repeatedly and radically changed over time. This indicates that the influx of deep fluids into the lithosphere was also highly variable, both in time and in space. There is no evidence of any connection between large basement faults and the pattern of the Late Devonian crustal subsidence. Together with a high variability of the subsidence, this suggests that, over the course of several million years, fluids have penetrated into the crust through an undisturbed mantle lithosphere 150 km thick. This indicates that the fluids had specific properties: they were surface-active and wetted grains of crystalline rocks, spreading as thin films into the inter-grain space. Rapid and frequent changes in the influx of deep fluids into the lithosphere rules out their connection with slow large-scale convective currents in the mantle. The slow, but long-term, extended over tens of millions of years, influx of surface-active mantle fluids into the lithosphere is also quite different from the powerful short-term outbursts of fluids from large mantle plumes approaching the lithospheric layer. The occurrence of crustal subsidence and kimberlite magmatism in a number of cratonic areas remote from each other suggests a widespread influx of deep fluids into the lithospheric layer on the continents.