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Geochemical composition, petrography and ^sup 40^Ar/^sup 39^Ar age of the Heldburg phonolite: implications on magma mixing and mingling
Ist Teil von
International journal of earth sciences : Geologische Rundschau, 2015-11, Vol.104 (8), p.2033
Ort / Verlag
Berlin: Springer Nature B.V
Erscheinungsjahr
2015
Link zum Volltext
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
Issue Title: From mantle roots to surface eruptions: Cenozoic and Mesozoic Continental Basaltic Magmatism Differentiated magmatic rocks such as trachyte and phonolite are volumetrically subordinate to mafic volcanic rocks within the Cenozoic Central European Volcanic Province (exceptions are the East Eifel and the Rhön volcanic fields). Within the volcanic field of the "Heldburg dike swarm" (Heldburger Gangschar), the phonolite of the Burgberg near Heldburg represents the only known occurrence of differentiated magmatic rocks. However, the Heldburg phonolite is famous foremost for containing mantle xenoliths (spinel lherzolite). Former studies proposing a cogenetic relationship between the phonolite and the peridotites concluded that the phonolite magma must have evolved under upper mantle conditions. Herewith, we present petrographic and geochemical evidence for magma mixing and mingling in the Heldburg phonolite melt due to the intrusion of mantle-derived basanitic magma, which is exposed today as dikes at the foot of the Heldburg Burgberg. During this process, the mantle xenoliths were introduced into the phonolite melt as they all contain rims of basanitic magma. Extensive mingling features (e.g., schlieren layers, load casts, flame structures, mafic enclaves) are developed, indicating that the basanite and the zoned phonolitic body were melts at the time of mixing. These petrographic and geochemical indications of two coeval melts of different composition are substantiated by ^sup 40^Ar/^sup 39^Ar dating, revealing identical ages of ca. 15 Ma.