Geodynamic Setting of the Tertiary Hocheifel Volcanism (Germany), Part II: Geochemistry and Sr, Nd and Pb Isotopic Compositions

Abstract

Major and trace element as well as isotopic compositions on 26 volcanic rocks from the Tertiary Hocheifel volcanic field and for comparison from Upper Rhine Graben occurrences (western Central European Volcanic Province) were measured in order to provide geochemical evidence for the geodynamic setting of the Tertiary Eifel volcanism. Except for a few differentiated lavas there are mainly basanitic compositions. These rocks were produced by low degree partial melting of a previously metasomatized garnet peridotite source at pressures and temperatures corresponding to depths of about 75 to 90 km. In contrast to the differentiated lavas, most of the basanites are not significantly affected by crustal contamination. In the Hocheifel, the crustally contaminated basanites and the differentiated lavas form an older age group (ca. 44-39 Ma). In contrast, the basanites not affected by crustal contamination belong to a younger age group (ca. 37-35 Ma) indicating a change in the petrogenetic style of evolution with time. Low-radiogenic Sr together with high-radiogenic Nd and Pb of the Hocheifel lavas show isotope characteristics similar to LVC (Low Velocity Composition) or FOZO (Focal Zone) mantle sources. Since FOZO is con-208 Fekiacova Z, Mertz DF, Hofmann AW sidered to be a common component in the entire mantle, a contribution from the deep mantle can be neither confirmed nor excluded. Plate reconstruction modelling indicates that the Hocheifel volcanic field at its time of activity ca. 40 m.y. ago was located ~1000 km southwest relative to its recent position, and therefore a relation to a mantle-stationary Quaternary Eifel plume is not plausible. Integrating evidence from geochronology, geochemistry, isotopic compositions and plate reconstruction, we conclude that the Tertiary Hocheifel volcanism is not genetically related to a mantle plume but is caused by Middle to Upper Eocene pre-rift extensional decompression related to the Rhine Graben taphrogenetic evolution.

Temporal–spatial evolution of low-SiO2 volcanism in the Pleistocene West Eifel volcanic field (West Germany) and relationship to upwelling asthenosphere

“…Instead, motion rate and direction of the Eurasian plate during the Tertiary suggests that, for example, in case of Eocene volcanism, a possible stationary mantle plume would be located ca. 1000 km to the south relative to the recent position of the CEVP (Fekiacova et al, 2007a). Thus, results derived from the specific Pleistocene Eifel setting are likely relevant to analogous low-SiO 2 intraplate volcanism in orogenic foreland environments elsewhere, in cases where plate dynamics have severed a hypothetic physical connection between volcanism and seismologically anomalous mantle.…”

“…of Hocheifel (Jung et al, 2006;Fekiacova et al, 2007aFekiacova et al, , 2007b, Siebengebirge (Todt and Lippolt, 1980;Kolb et al, 2012), Vogelsberg (Jung and Masberg, 1998;Bogaard et al, 2001;Bogaard and Wörner, 2003;Haase et al, 2004), Westerwald (Haase et al, 2004) and Rhön (Jung and Hoernes, 2000;Jung et al, 2005;Abratis et al, 2007) (Fig. 1, inset).…”

The role of magma mixing in the petrogenesis of mafic alkaline lavas, Rockeskyllerkopf Volcanic Complex, West Eifel, Germany

“…1a) have compositions consistent with derivation from such a source (e.g. Fekiacova et al 2007;Fig. 2).…”

“…The RVC lavas have lower Al 2 O 3 , Na 2 O and Y contents and higher TiO 2 , CaO, K 2 O, Sc, V, Co, Rb and Ba than the Tertiary lavas in the nearby Hocheifel volcanic field (Fekiacova et al 2007). REE contents of the SEL and RKK Centers are similar to those of the Hocheifel lavas, whereas the Mäuseberg lavas are enriched in LREE.…”

“…The West Eifel lavas (green field) have significantly higher 87 Sr/ 86 Sr and lower 143 Nd/ 144 Nd than the CMR and show similarities with the variably metasomatised peridotite mantle xenoliths outlined in the grey field (data from Stosch et al 1980;Stosch and Lugmair 1986;Witt-Eickschen et al 2003;Witt-Eickschen et al 1993;Wörner et al 1986). Small open circles show the composition of Tertiary volcanic rocks in the Hocheifel field (data from Fekiacova et al 2007). Fields depleted MORB mantle (DMM)a and DMMb and enriched mantle (EM) 1 are from Zindler and Hart (1986) nature of the mantle source and the processes involved in generating these magmas.…”