Insight into the Evolution of Lithosphere beneath Pannonian Basin Through Studying H2O Content in NAMs from Füzes-Tó Upper Mantle Xenoliths (Hungary)

Pintér, Zsanett and Kovács, István János and Szabó, Csaba (2015) Insight into the Evolution of Lithosphere beneath Pannonian Basin Through Studying H2O Content in NAMs from Füzes-Tó Upper Mantle Xenoliths (Hungary). In: Goldschmidt 2015, 16–21 Aug 2015., Prague.

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Abstract

The youngest xenolith-bearing alkali basaltic outcrop (Füzes-tó) in Bakony-Balaton Highland Volcanic Field (BBHVF) in the central Carpathian-Pannonian region (CPR) includes peridotite xenoliths with the highest diverse textures from the BBHVF. Based on prior studies [1], a two-layered continental lithospheric mantle is present beneath the region: 1) shallow lithospheric mantle portion with fine-grained texture from the MOHO to 40 km depth, and 2) deeper, coarse-grained layer between 40 km depth and the present LAB boundary. The deeper layer could represent a juvenile lithosphere which was transformed form asthenosphere following the Miocene extension event. It was also proposed that tabular equigranular textures xenoliths may form a thin horizon which may separate these two layers [2]. Six representative and well characterized spinel peridotite xenoliths were selected for detailed FTIR study, covering the two mantle domains and, in addition, three tabular equigranular textured xenoliths from Füzes-tó are also inlcuded. H2O content of the nominally anhydrous minerals (NAMs) were calculated from avaraged unpolarized FTIR spectra of each NAM [3]. Xenoliths from shallow layer show generally low bulk H2O content (6-13 ppm), wheares the xenoliths from juvenile deep mantle have higher bulk H2O contents (~20 ppm). The tabular equigranular textured xenoliths from the horizon that separate the two main domains show the most elevated H2O concentrations in bulk NAM (~25 ppm). The higher water content of the deeper layer may be explained by its asthenospheric origin due to higher water activity presumably induced by the instability of pargasitic amphibole.

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