Multiple metasomatism beneath the Nógrád-Gömör Volcanic Field (northern Pannonian Basin) revealed by upper mantle peridotite xenoliths

Liptai, Nóra and Patkó, Levente and Kovács, István János and Hidas, Károly and Pintér, Zsanett and Jeffries, Teresa and Zajacz, Zoltán and O'Reilly, S.Y. and Griffin, W.L. and Pearson, N.J. and Szabó, Csaba (2016) Multiple metasomatism beneath the Nógrád-Gömör Volcanic Field (northern Pannonian Basin) revealed by upper mantle peridotite xenoliths. Journal of Petrology. ISSN 0022-3530, ESSN: 1460-2415 (Submitted)

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Peridotite xenoliths from the Nógrád-Gömör Volcanic Field (NGVF) record the geochemical and structural evolution of the subcontinental lithospheric mantle beneath the northern margin of the Pannonian Basin. The xenoliths are divided into a lherzolitic and a wehrlitic series based on their modal composition and textural features. This paper focuses on the lherzolite series and presents petrography and major- and trace-element geochemistry for xenoliths 51 selected from all xenolith-bearing localities of the NGVF. The xenoliths consist of olivine, orthopyroxene, clinopyroxene, spinel ± amphibole. Protogranular textures are most frequently found in the northern part, while to porphyroclastic and equigranular textures are more dominant in the central and southern parts. The xenoliths have undergone varying degrees (<5-30 %) of partial melting with overprinting by different metasomatic processes. Based on heir Mg#, the spinel lherzolite xenoliths can be subdivided into two major groups. Group I has olivine Mg# between 89 and 92, whereas Group II has Mg# <89, and significant enrichment of Fe and Mn in olivine and pyroxenes, and of Ti in spinel. Trace-element contents of the xenoliths vary widely, allowing a further division based on LREE enrichment or depletion in pyroxenes. REE patterns of amphiboles match those of clinopyroxenes in each xenolith where they appear, and depict different origins based on their Nb (and other HFSE) content. It is inferred that Nb-poor amphiboles record the oldest metasomatic event, caused by volatile-bearing silicate melts, followed by at least two further metasomatic processes: one that resulted in U-Th-(Nb-Ta)- LREE-enrichment and crystallization of Nb-rich amphibole, affecting selective domains under the entire NGVF, and another evidenced by Fe-Mn-Ti-enrichment which overprinted previous geochemical signatures. We suggest that the metasomatic agents in both cases were basaltic silicate melts, compositionally similar to the host basalts. These melts were generated during the Miocene extension of the Pannonian Basin. The effects of heating and subsequent cooling are evident in significantly different equilibration temperatures.

Item Type: Article
Subjects: Q Science / természettudomány > QD Chemistry / kémia > QD05 Crystallography / kristálytan
Q Science / természettudomány > QE Geology / földtudományok > QE02 Geochemistry / geokémia
Q Science / természettudomány > QE Geology / földtudományok > QE03 Geodynamics / geodinamika
Q Science / természettudomány > QE Geology / földtudományok > QE06 Petrology. Petrography / kőzettan, petrográfia
Depositing User: Dr. István János Kovács
Date Deposited: 04 Oct 2016 17:07
Last Modified: 04 Oct 2016 17:07

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