Heat and mass transfer from the mantle: heat flow and He-isotope constraints

B. G. Polyak


Terrestrial heat flow density, q, is inversely correlated with the age, t, of tectono-magmatic activity in the Earth's
crust (Polyak and Smirnov, 1966; etc.). «Heat flow-age dependence» indicates unknown temporal heat sources in
the interior considered a priori as the mantle-derived diapirs. The validity of this hypothesis is demonstrated by
studying the helium isotope ratio, 3He/4He = R, in subsurface fluids. This study discovered the positive correlation
between the regionally averaged (background) estimations of R- and q-values (Polyak et al., 1979a). Such a correlation
manifests itself in both pan-regional scales (Norhtern Eurasia) and separate regions, e.g., Japan (Sano et al.,
1982), Eger Graben (Polyak et al., 1985) Eastern China rifts (Du, 1992), Southern Italy (Italiano et al., 2000), and
elsewhere. The R-q relation indicates a coupled heat and mass transfer from the mantle into the crust. From considerations
of heat-mass budget this transfer can be provided by the flux consisting of silicate matter rather than He
or other volatiles. This conclusion is confirmed by the correlation between 3He/ 4He and 87Sr/86Sr ratios in the products
of the volcanic and hydrothermal activity in Italy (Polyak et al., 1979b; Parello et al., 2000) and other places.
Migration of any substance through geotemperature field transports thermal energy accumulated within this substance,
i.e. represents heat and mass transfer. Therefore, only the coupled analysis of both material and energy
aspects of this transfer makes it possible to characterise the process adequately and to decipher an origin of terrestrial
heat flow observed in upper parts of the earth crust. An attempt of such kind is made in this paper.


heat flow;helium isotope ratio;geothermal energy;mass transfer

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DOI: https://doi.org/10.4401/ag-3176
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X