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)

Integrating whole-rock and mineral-scale geochemical data can help provide insight into the compositional variability of igneous systems and the mechanisms that drive their evolution.The exhumed magma storage system of the Ditrău Alkaline Massif (Eastern Carpathians, Romania) is an excellent natural laboratory for studying the igneous processes in trans-crustal magmatic systems.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 micro-scale. Petrographic observations were implemented by bulk-rock and mineral-scale geochemical data to further support this hypothesis.Whole-rock major and trace element composition of the studied felsic rocks validates the presence of two, compositionally different felsic cumulate piles in the massif. Mineral chemical data (amphibole, clinopyroxene and plagioclase) were acquired from crystals of different textural positions (clot-forming and isolated). The composition of clinopyroxene overlaps with the formerly published data. Nevertheless, a new, cumulus-phase occurrence of the intermediate clinopyroxenes was identified. Three different magma batches were discriminated by the amphiboles. The amphibole and plagioclase compositions, together with the bulk-rock data point to the hybrid nature of most of the studied felsic rocks.This study provides valuable information about the compositional and textural variability of felsic magmatism. Our recent geochemical data support the previous, mostly 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.The integration of high-resolution analytical techniques, such as LA-ICP-MS, with traditional petrographic and geochemical methods offers an excellent opportunity to improve our understanding of magmatic systems and the processes that drive magmatic differentiation and evolution.