Geochemistry and geochronology of the Jawornik granitoids, Orlica-Śnieżnik Dome, Sudetes, Poland

The Jawornik granitoids intrude, in vein-like form, a sequence of a polymetamorphic metavolcanic and metapelitic rocks of the Orlica-Śnieżnik Dome, Sudetes, Poland. This paper provides whole-rock geochemical data, sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon geochronological data as well as 40Ar-39Ar age determinations to constrain the genetic and temporal relationships of the different rock types forming these veins. Based on macroscopically visible features of the granitoids and their relationship with tectonic structures visible in the country rocks, four varieties of the Jawornik granitoids have been distinguished: amphibole- and biotite-bearing granites (HBG), biotite-bearing granites (BG), biotite- and muscovite-bearing granites (BMG) and muscovite-bearing granites (MG). The Jawornik granitoids as a whole show a limited but significant variation in major element chemical composition, with SiO2 ranging from 65 to 76 wt.% (average 69.16 wt.%, n = 24). They are subalkalic, peraluminous and calc-alkaline [average A/CNK = 1.07, average (Na2O + K2O) = 7.75, average (Fe2O3t/(Fe2O3t + MgO) = 0.59]. Close inspection of their geochemical parameters showed that the samples investigated can be subdivided into two groups. The first group, the HBG, BG, and BMG varieties, comprising most of the granitoids in the Złoty Stok-Skrzynka Tectonic Zone, were formed by melting of greywackes or/and amphibolites. The MG, belonging to the second group, were formed by partial melting of a more felsic source. The HBG yielded a zircon U-Pb age of 351 ±1.3 Ma and well-defined 40Ar-39Ar plateau ages for hornblende (351.1 ±3.9 Ma) and coexisting biotite (349.6 ±3.8 Ma), indicating probably the oldest magmatic event in this region. Zircons from the MG, the youngest rock variety on the basis of their relationship with the tectonic structures in the host rocks, yielded a U-Pb age of 336.3 ±2.4 Ma, though based on three points only. The biotites and muscovites from the BMG have 40Ar-39Ar plateau ages of 344.1 ±4.7 Ma and 344.6 ±3.8 Ma, respectively. These data, in combination with already published isotopic ages, suggest that the Jawornik granitoids intruded host rocks of the Orlica-Śnieżnik Dome in three stages, at ~350, ~344 and ~335 Ma.

Millet pollen quality depending on the growing conditions and varietal characteristics

The aim of the study is to find out the features of forming the quality of pollen grains, namely their size and viability, depending on the growing conditions and varietal characteristics of switchgrass. The research deals with the peculiarities of millet pollen grains formation, depending on the conditions of vegetation and varietal composition, as the pollen quality – its size and viability – affects the seeds germination. It was established that the pollen quality depended both on the conditions of the growing season and varietal composition. Thus, in the 2018 growing season the weather conditions in the flowering phase (July) were favorable for the viable pollen formation, and high temperatures in August, exceeding 35 oC after 11:00 am at the absence of precipitation affected the viability of the pollen. In all the varieties, the viability of pollen was low. The most viable pollen was in the Morozko variety and the least viable – in the Cave-in-Rock variety, which negatively affected the seed germination. Pollen grains are spherical in form and colorless. They were not uniform in size both depending on the genotype and the growing conditions. In 2018 the pollen grains size ranged from 29 to 60 microns, in 2019 – from 5.2 to 57.2 microns. In 2019, the smaller pollen formed compared to 2018 due to high average daily air temperatures that exceeded average daily long-term values and due to significant moisture deficiency. Millet pollen is not homogeneous, depending on the both genotype and vegetation conditions. In 2018, which was favorable for pollen formation, the size varied from 29 to 60 microns, and in the less favorable 2019, it was smaller and ranged from 5.2 to 57.2 microns. The largest size of pollen grains formed in the Sunburst variety compared to other varieties. The most uniform – 85.3 % of the total amount – was the pollen in the Cave-in-Rock variety. Key words: pollen grains, quality, pollen size, viability, pollen form, variability, uniform.