Over the almost 190 years-long research of the Ditrău Alkaline Massif (Eastern Carpathians, Romania), felsic rocks have been regarded as homogeneous, uniform units of the igneous complex. Nevertheless, our detailed textural study revealed that the felsic suite (diorite–alkaline feldspar syenite and nepheline-bearing syenite–granite series) cropping out north of the Jolotca Creek valley is more heterogenous at micro-scale than previously thought. This heterogeneity partly derives from abundant mafic mineral-rich clusters; nevertheless, felsic minerals also exhibit various, remarkable textural features. Outcrop to micro-scale traits of felsic crystal settling, mafic mineral aggregates and flow fabrics along with metamorphic country rock xenoliths suggest that the studied rocks crystallized under dynamic magmatic conditions. Cumulate formation, shear flow, convection currents as well as various open-system magmatic processes (e.g., magma recharge, magma mixing and mingling, crystal or mush transfer and recycling, country rock assimilation) played a significant role in the petrogenesis of the examined felsic suite.
Based on field observations as well as on the microtextural relationship of the minerals, two major groups of felsic rocks were distinguished: (1) felsic rocks (lacking or containing sparse mafic minerals) spatially associated with mafic rocks and (2) felsic rocks (with mafic minerals and clots) spatially unassociated with mafic rocks. Rocks of the former group are dominated by plagioclase, accompanied by minor alkaline feldspar, biotite and accessory titanite. Distinct structural and textural features suggest the physical accumulation of the rock-forming phases. Such textural properties can also be observed in some rocks of the second group. Isolated mafic minerals are rather scarce in the latter; nevertheless, different types of aggregates made up of either identical or various mafic phases are more common. Clustered minerals are either intact or show different stages of alteration.
A detailed petrographic study of the above-mentioned peculiarities has been implemented in order to define their potential origin(s) and petrogenetic significance.
The timing of Triassic magmatism of the Ditrău Alkaline Massif (Eastern Carpathians, Romania) is important for constraining the tectonic framework and emplacement context of this igneous suite during the closure of Paleotethys and coeval continental rifting, as well as formation of back-arc basins.
Our latest geochronological data refine the previously reported ages ranging between 237.4 ± 9.1 and 81.3 ± 3.1 Ma. New K/Ar and U–Pb age data combined with all recently (post-1990) published ages indicate a relatively short magmatic span (between 238.6 ± 8.9 Ma and 225.3 ± 2.7 Ma; adding that the most relevant U–Pb ages scatter around ∼230 Ma) of the Ditrău Alkaline Massif. The age data complemented by corresponding palinspastic reconstructions shed light on the paleogeographic environment wherein the investigated igneous suite was formed.
The magmatism of the Ditrău Alkaline Massif could be associated with an intra-plate, rift-related extensional tectonic setting at the southwestern margin of the East European Craton during the Middle–Late Triassic (Ladinian–Norian) period.