Bulk-rock and mineral-scale geochemical evidence of open-system magmatic processes in the felsic rocks of the northern part of the Ditrău Alkaline Massif (Eastern Carpathians, Romania)

Luca Kiri (1) , Máté Szemerédi (1) , Saskia Erdmann (2, 3) , Elemér Pál-Molnár (1) , Anikó Batki (1)

1 University of Szeged [Szeged]
2 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
3 Magma - UMR7327

The felsic suite in the northern part of the Ditrău Alkaline Massif has previously been considered as a homogeneous, uniform unit of the igneous complex. However, these felsic rocks exhibit remarkable diversity on the microscale. Petrographic observations were complemented by bulk-rock and mineral-scale geochemical data to further support this hypothesis. Whole-rock composition of the studied rocks validates the presence of two, compositionally-different felsic cumulate piles in the massif (characterised by Eu/Eu * = 2.5-6.7, ΣREE = 125-206 ppm and Eu/Eu * = 1.0-1.1, ΣREE = 358-688 ppm, respectively). Mineral chemical data (amphibole, clinopyroxene, and plagioclase) were acquired from crystals of different textural positions (clot-forming and isolated) to understand which of the ferromagnesian minerals and plagioclase have the highest potential for recognising distinct magmatic environments and open-system magmatic processes. The composition of clinopyroxenes (diopside with mg# = 0.77 and 0.85, respectively) overlaps with the formerly published data. Moreover, a new, cumulus-phase occurrence of the clinopyroxenes with a convex REE pattern has been identified. Abrupt changes of Ba, Sr, TiO 2 and ΣREE concentrations in different domains of the zoned amphibole crystals and variations in the MgO, FeO, TiO 2 , Sr, Ba, La, Ce, and anorthite content in plagioclase crystals, together with the bulk-rock data point to the hybrid nature of the majority of the investigated rocks. Our recent geochemical data support the previous, predominantly petrography-based assumptions that the felsic suite in the northern area of the massif was formed in a dynamic, open-system magmatic environment, wherein crystal settling, magma mixing, crystal/mush transfer, and recycling as well as country rock assimilation, prevailed.

Mots clés: Eastern Carpathians Ditrău Alkaline Massif felsic cumulate hybridisation magma mixing mineral chemistry; Eastern Carpathians; Ditrău Alkaline Massif; felsic cumulate; hybridisation; magma mixing; mineral chemistry

Domaines: Planète et Univers [physics]

Luca Kiri, Máté Szemerédi, Saskia Erdmann, Elemér Pál-Molnár, Anikó Batki. Bulk-rock and mineral-scale geochemical evidence of open-system magmatic processes in the felsic rocks of the northern part of the Ditrău Alkaline Massif (Eastern Carpathians, Romania). Geologica carpathica, 2023, 74 (4), ⟨10.31577/GeolCarp.2023.20⟩. ⟨insu-04454286⟩