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

Abstract

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.

Seismic anisotropy in the mantle of a tectonically inverted extensional basin: A shear-wave splitting and mantle xenolith study on the western Carpathian-Pannonian region

“…This is in agreement with the fact that the xenoliths of the Nógrád-Gömör volcanic field do not show evidence of depth-related layering in terms of their petrography or LPO. In contrast, the variability in their texture and composition was attributed to the different ages and spatial distribution (Liptai et al, 2017(Liptai et al, , 2019. However, in the central and southern regions of the western CPR, including basin areas and the transition zone towards the Eastern Alps, more stations indicate multi-layered anisotropy, especially in the vicinity of Lake Balaton (Fig.…”

“…In the Styrian Basin and the Nógrád-Gömör volcanic fields, the texture and deformation patterns of the xenoliths did not show evidence for multiple layers in the mantle with different orientation (Aradi et al, 2017;Liptai et al, 2019). Therefore, these authors assumed a single anisotropic layer and concluded that the most realistic scenario is a vertical foliation and horizontal lineation, with a NW-SE orientation.…”

“…However, since the Carpathian-Pannonian region is characterized by a thin crust in general (<30 km; Horváth, 1993;Kalmár et al, 2021), the crustal contribution to surface delay times was usually ignored in SWS splitting analyses in the area (e. g., Qorbani et al, 2016;Petrescu et al, 2020). In a previous study of the Nógrád-Gömör xenoliths (Liptai et al, 2019), the authors attributed a ~ 0.25 s of the delay time to the crust; however, this is well below the delay time of the A336A station closest to the xenolith locality. Furthermore, without the examination of potentially complex crustal structures, it appears appropriate to assume that our delay time values mainly refer to a mantle source.…”

“…1): the Styrian Basin, Little Hungarian Plain, Bakony -Balaton Highland, and Nógrád-Gömör (e.g., Szabó et al, 2004). Seismic properties calculated from the LPO were reported by several studies for these locations (Falus, 2004;Hidas et al, 2007;Kovács et al, 2012;Klébesz et al, 2015;Aradi et al, 2017;Liptai et al, 2019), which were used to estimate the thickness of a single anisotropic layer. However, these studies were mainly focusing on local mantle deformation state and history, and while some of them mentioned links to shear-wave splitting results in relation with the studied area, a thorough and detailed comparative study of the greater region is still missing.…”

Interplay between melt infiltration and deformation in the deep lithospheric mantle (External Liguride ophiolite, North Italy)

“…Postkinematic percolation of the pyroxenite-producing melts can be excluded, because it implies near solidus conditions associated with the presence of reactive interstitial melts, which would result in fast annealing of the plastic deformation structures through recovery and static recrystallization processes in the peridotites (e.g., Aradi et al, 2017;Hidas et al, 2016;Liptai et al, 2019;Rampone et al, 2010;Tommasi et al, 2008). Moreover, although melt percolation controlled by the preexisting structure of the peridotites has been proposed to explain small-scale features, for instance, the orientation of mm-scale websterite lenses within harzburgite in the Lherz massif (Le Roux et al, 2008), such anisotropic percolation cannot play a major role when large melt/rock ratios are at play.…”