The role of pargasitic amphibole in the formation of major geophysical discontinuities in the shallow upper mantle

• Published in: Acta geodaetica et geophysica 2017-06, Vol.52 (2), p.183-204
• Main Authors: Kovács, István, Lenkey, László, Green, David. H., Fancsik, Tamás, Falus, György, Kiss, János, Orosz, László, Angyal, Jolán, Vikor, Zsuzsanna
• Format: Article
• Language: English
• Subjects: Amphiboles; Anomalies; Asthenosphere; Dehydration; Depth; Earth and Environmental Science; Earth mantle; Earth Sciences; Electrical conductivity; Electrical resistivity; Geophysical data; Geophysics; Geophysics/Geodesy; Heat; Heat flow; Heat transfer; Heat transmission; Intersections; Lithosphere; Magma; Melting; P-waves; Phanerozoic; Plate tectonics; Precambrian; Properties; Properties (attributes); Seismic velocities; Seismic waves; Silicates; Solidus; Special issue - Geothermal Energy System; Temperature; Upper mantle; Wave attenuation
• ISSN: 2213-5812; 2213-5820
• DOI: 10.1007/s40328-016-0191-3

Several explanations have been proposed for variation in geophysical properties and depths for the lithosphere–asthenosphere boundary (LAB) and mid-lithospheric discontinuities (MLD). Here, we investigate the proposal that the dehydration solidus of pargasitic amphibole-bearing upper mantle with very low bulk water (hundreds ppm) may be one of the main reasons for the observed geophysical anomalies. The dehydration solidus may be associated with a very small degree of partial melting in the upper mantle at temperatures and pressures in excess of 1050 °C (for geochemically more depleted) or 1100 °C (for geochemically less depleted upper mantle) and from 1 to 3 GPa (~30 to 90 km) respectively. This small amount of partial melt may be responsible for changes in geophysical properties (e.g. lower seismic velocity, higher attenuation of seismic waves, higher electrical conductivity) in association with the LAB and MLD. This simple petrologic model is tested on the abundant geophysical data of the Carpathian–Pannonian region (CPR), central Europe. The high resolution heat flow data available in the CPR allows us to estimate the depths to intersection of area specific depth-temperature curves with the dehydration solidus temperatures (1050 and 1100 °C isotherms). There is relatively small mismatch (