Determination of the Lithosphere-Asthenosphere Boundary (LAB) beneath the Nógrád-Gömör Volcanic Field by combined geophysical (magnetotellurics) and geochemical methods

摘要

Understanding the fundamental role of LAB is substantial for the investigation of the geodynamic evolution ofudthe Earth. The LAB depths can be estimated by different geophysical methods (seismology, magnetotellurics),udhowever these depths are controversial. It has been emphasized in the literature that combined geophysical andudgeochemical approach may lead to better understanding of these depths.udThe magnetotellurics (MT) is very powerful method because it indicates the sudden increase in conductivity atudthe LAB. The mantle xenoliths (small fragments of the lithospheric mantle) provide the information to reconstructudtheir P-T paths.udIn the Carpathian-Pannon region (CPR) five, well-studied occurrences of mantle xenoliths-bearing Plio-Pleistoceneudalkali basalts are known, which makes the CPR a very promising area for investigating the inconsistency in theudLAB estimates. As a test area Nógrád-Gömör Volcanic Field (NGVF) has been chosen.udThe host basalt erupted at the NGVF collected mantle xenoliths from a small volume of the upper mantle in auddepth of about 40-50 km. The major element geochemistry of the studied xenoliths indicates that most of themudrepresent common lherzolitic mantle, whereas others show strong wehrlitisation process. This metasomatismudis supposed to be caused by a migrating mafic melt agent, resulting in the transformation of a large portion ofudlherzolite to wehrlite beneath the NGVF, possibly just below the crust mantle boundary.udIn aim to detect the LAB at the research area and find the correlation with petrologic and geochemical resultsudwe carried out MT deep soundings. The campaign contained 12 long period MT stations with 3-5 km averageudspacing along 60 km long profile SSE to NNW direction. This presentation summarizes the preliminary results ofudthe combined geophysical and geochemical approaches to determine the LAB depths.