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Russian Geology and Geophysics

2005 year, number 3

DYNAMICS OF MELTING OF MANTLE-DERIVED ROCKS ABOVE A HOT SPOT BENEATH OCEANIC RIDGES

V.N. Sharapov, L.N. Perepechko*, and I.F. Rakhmenkulova
Institute of Geology, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
* Institute of Thermal Physics, Siberian Branch of the RAS,
1 prosp. Akad. Lavrent'eva, Novosibirsk, 630090, Russia
Keywords: Magmatic systems, asthenosphere, hot spot, decompression melting
Pages: 278-286

Abstract

During the formation of intraplate volcanic ridges the hot upper mantle controls the decompression melting of ascending low-density upper-mantle material above hot spots. Depending on the degree to which the upper mantle is warmed up, the extent and dynamics of partial melting as well as the dimensions of the asthenosphere can considerably differ: (1) The time of existence of a zone of partial melting varies from 15 to 90 Myr; (2) the maximum degree of partial melting may differ by a factor of 5-10 (from 5-7 to 50-60 vol.%); (3) horizontal dimensions of the asthenosphere may change from 150-200 to 400-500 km.
Depending on given conditions, such parameters as melting depth, asthenosphere thickness, and position of the upper solidus boundary can considerably change with time. Our calculations show that the ultimate depths of the upper solidus boundary is about 100 km. It is unlikely that any standard (in composition of magmas and extent of melting) types of plume-related magmatic systems existed in the geological past. Given no initial conditions in the upper mantle, the dynamics of hot spots can be inferred from geochemical characteristics of magmas rather than from temperature and size of hot spots.