Clinopyroxene phenocrysts from the Księginki nephelinite (SW Poland)

Abstract

RecordChemical composition and textures of clinopyroxene phenocrysts from Księginki nephelinite record complex history of melt reacting with mantle rocks and "in situ" crystallisation of the melt. AbstractThe Eocene nephelinite from Księginki quarry (SW Poland) contains five types of clinopyroxene phenocrysts varying by texture and chemical composition. Type I phenocrysts are formed of Mg-rich (mg# = 0.93-0.88) homogenous cores, patchy mantle and zoned rims. Abundant type II is less magnesian (mg# = 0.65-0.88) and consists of spongy or spongy-patchy core surrounded by zoned rims, whilst in type III (mg# = 0.69-0.84), the cores are massive but patchy. The mg# of cores of type IV phenocrysts is slightly lower than that of type I (0.79-0.89), but its cores are either massive or patchy. Type V is very scarce and consist of relatively Mg-poor (mg# = 0.75-0.77) core enveloped by nonpatchy, sometimes zoned mantle and zoned outer rim. Chemical composition of type I and type IV cores suggests that they are xenocrysts introduced into the nephelinite from disintegrated peridotite and clinopyroxenitic xenoliths, respectively. Type V is also of xenocrystic nature, but its source rock was significantly more evolved than mantlederived ones. Types II and III are possibly cognates from the host nephelinite or a melt related to the nephelinite. All the types of phenocrysts suffered from disequilibrium with the nephelinitic (or proto-nephelinitic) melt or dissolution during adiabatic uplift. Linear variation in chemical composition of phenocrysts of Księginki nephelinite suggests its evolution because of fractional crystallisation, without significant influence of other differentiation processes.

Provenance studies of basaltic tools from the Polish Lowlands in the light of geochemical and mineralogical studies

“…The presented result and the literature data point that the basaltic material used for artefact production is characterized by aphiritic, very fine‐grained to aphanitic texture and scarce porphyrocrysts of Ca‐Na feldspar. Such characteristic resembles that of the reference basaltic from Volyn and dolerites from Scania (Kuzmenkova et al, 2011; Obst et al, 2004; Shumlyanskyy et al, 2007) and differs from that of the typical basaltoids from Scania (Tappe, 2004) and Lower Silesia (Goleń et al, 2015) (Figure 5e,f) where olivine and clinopyroxene porphyrocrysts are abundant and the rock has porphyritic texture. It should be pointed that olivine is occasionally present in rocks from Volyn, but it is usually altered to bowlinigitic and iddinsitic pheudomorphoses, scarcely with remnants of olivine preserved in cores.…”