Scientific publications

This article presents the results of a mineralogical and geochemical study of magmatic enclaves in Rapakivi granites (wiborgite). These granites belong to the Salmi anorthositerapakivi granite complex aged 1.55–1.53 Ga (southern Karelia, Russia). Samples of the enclaves were studied in detail using optical and electron microscopy, X-ray fluorescence analysis, ICP-MS, and quantitative chemical analysis. The enclaves proved to be quartz diorites, low-alkali quartz diorites, and granodiorites. Petrochemically, they are characterized by an increased content of Fe2O3 total (10.8–15.2 % w/w), TiO2 (1.12–1.59 % w/w), Zr (1370–2240 ppm), and P (1160–1721 ppm) in comparison with granitoids. In this sense, they are more similar to FTP rocks (with high concentrations of Fe, Ti, and P), which are considered as residual melts after crystallization of anorthosite associated with rapakivi granites. The mineralogical features (high-iron olivine and pyroxene, low-calcium plagioclase) indicate the probable crystallization of the enclaves from the magma produced through the fractional crystallization of basaltic melt, accompanied by significant iron accumulation in the melt. A comparative study of the geochemical features of the enclaves against similar Fe, Ti, and P-enriched rocks from various anorthosite provinces of the world (Ukraine, Brazil, and North America) has shown that, despite the similarity of the trace element composition, the silica and alkali content of the enclaves places them outside of the fields of typical anorthosite-associated rocks. Combined with geological and petrographic evidence of active interaction between mafic and felsic magmas, these facts point to a hybrid nature of the enclaves. The question of whether these enclaves are the product of residual magma capture by the acidic melt after anorthosite crystallization remains open.