Lateral and Vertical Heterogeneity in the Lithospheric Mantle at the Northern Margin of the Pannonian Basin Reconstructed From Peridotite Xenolith Microstructures

This study analyzes the microstructures and deformational characteristics of spinel peridotite xenoliths from the Nógrád-Gömör Volcanic Field (NGVF), located on the northern margin of a young extensional basin presently affected by compression. The xenoliths show a wide range of microstructures, bearing the imprints of heterogeneous deformation and variable degrees of subsequent annealing. Olivine crystal preferred orientations (CPOs) have dominantly [010]-fiber and orthorhombic patterns. Orthopyroxene CPOs indicate coeval deformation with olivine. Olivine J indices correlate positively with equilibration temperatures, suggesting that the CPO strength increases with depth. In contrast, the intensity of intragranular deformation in olivine varies as a function of the sampling locality. We interpret the microstructures and CPO patterns as recording deformation by dislocation creep in a transpressional regime, which is consistent with recent tectonic evolution in the Carpathian-Pannonian region due to the convergence between the Adria microplate and the European platform. Postkinematic annealing is probably linked to percolation of metasomatism by mafic melts through the upper mantle of the NGVF prior to the eruption of the host alkali basalt. Elevated equilibration temperatures in xenoliths from the central part of the volcanic field are interpreted to be associated with the last metasomatic event, which only shortly preceded the ascent of the host magma. Despite well-developed olivine CPOs in the xenoliths, which imply a strong seismic anisotropy, the lithospheric mantle alone cannot account for the shear wave splitting delay times measured in the NGVF, indicating that deformation in both the lithosphere and the asthenosphere contributes to the observed shear wave splitting.
The authors would like to thank the people who contributed to this work. We owe thanks to Fabrice Barou and David Adams for their help with EBSD-SEM analyses at Geosciences Montpellier and at CCFS Macquarie University, respectively. L?szl? Aradi is acknowledged for his help with field work, petrography and MTEX application. We are grateful for the constructive criticism of Sandra Piazolo and Jacques Pr?cigout and two anonymous reviewers, as well as for the editorial handling of Stephen Parman. Our research received financial support from a Marie Curie International Reintegration Grant (grant NAMS-230937), a postdoctoral grant (grant PD101683) of the Hungarian Scientific Research Fund (OTKA), and a Bolyai J?nos Postdoctoral Research Fellowship of the Hungarian Academy of Sciences to I. J. K., as well as from the Lend?let Pannon LitH2Oscope Research Group (Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences). N. L. received support from Macquarie University international PhD scholarship and project and travel funding from ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS). K. H. acknowledges funding from Ministry of Economy, Industry and Competitiveness (MINECO, Spain) and the State Research Agency (AEI, Spain; grants FPDI-2013-16253 and CGL2016-81085-R). Instruments used at Macquarie University are funded by DEST Systemic Infrastructure Grants, ARC LIEF, NCRIS/AuScope, industry partners, and Macquarie University. The data used in this paper are listed in the references, tables, and supporting information. The raw EBSD data are available from the corresponding author upon request. This is the 92nd publication of the Lithosphere Fluid Research Lab (LRG), contribution 1361 from the ARC Centre of Excellence for Core to Crust Fluid Systems (www.ccfs.mq.edu.au) and 1320 from the GEMOC Key Centre (www.gemoc.mq.edu.au).