Upper mantle xenoliths as sources of geophysical information: the Perşani Mts. area as a case study
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The aim is to give an overview on how geochemical and petrological data, obtained from upper mantle xenoliths, could be utilized to provide information on the geophysical properties of the upper mantle at their origin. First we demonstrate how a tentative lithospheric column may be constructed based on the equilibrium temperature of upper mantle xenoliths and the area specific depth-temperature curves. Then it is described how the speed of seismic waves at the given pressure and temperature conditions could be calculated from the modal composition and geochemistry of major rock forming minerals of upper mantle xenoliths (e.g. olivine and orthopyroxene). It is also discussed how the lattice preferred orientation of minerals in upper mantle xenoliths provides information on the seismic anisotropy of the upper mantle, and how this information could be used to calculate the orientation and thickness of the anisotropic layer in the upper mantle if one anisotropic layer is assumed. Structural hydroxyl (or most commonly referred to as ‘water’) incorporated in nominally anhydrous minerals plays a critical role in determining the electrical conductivity and rheology of the upper mantle. Finally, it is presented how electrical conductivity and effective viscosity of the upper mantle could be approximated based on the structural hydroxyl content in olivine, the most abundant mineral constituent of the upper mantle. Our study area, the Perşani Mountains is situated in the Carpathian Bend area (Romania) which is geologically one of the most active areas in Europe. Abundant upper mantle xenoliths from the Perşani Mountains (Eastern Carpathians) will serve as examples how meaningful geophysical information can be obtained for the upper mantle. Furthermore, it is shown how these pieces of information may be utilized in interpreting geophysical and geodynamic challenges of this area.
KeywordsUpper mantle Xenoliths Geophysics Rheology Perşani Mts
We thank the Topo-Transylvania community for the motivation overs the past years, especially Viktor Wesztergom, Eszter Szűcs and Sierd Cloetingh for their continuous support and motivation. We are grateful to Anna Maria Fioretti and Raúl Carampin for their help with EMPA analyses in Padua, Italy, and also to Bernardo Cesare for facilitation. Luca Fedele is thanked for helping with geochemical analyses at Virginia Tech. We also owe thanks to Robert J. Bodnar, who facilitated the measurements at Virginia Tech. This study was financially supported by a Bolyai Postdoctoral Fellowship program to IK, and a Lendület Research Grant to the Pannon LitH2Oscope Research group and an NKFIH K128122 grant of the Innovation, Research and Development Office. This work was completed in the ELTE Excellence Program (783-3/2018/FEKUTSRAT) supported by the Hungarian Ministry of Human Capacities. This research was supported by the Hungarian Science Foundation (OTKA, 78425) to Cs. Szabó. This is the 93d publication of the Lithosphere Fluid Research Lab (Eötvös University, Hungary).
Conflict of interest
All authors declare that there is no conflict of interest regarding the present manuscript.
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