Mesozoic (125–135 Ma) cratonic low-Ti lamproites from the northern part of the Aldan Shield do not conform to typical classification schemes of ultrapotassic anorogenic rocks. Here we investigate their origins by analyzing olivine and olivine-hosted inclusions from the Ryabinoviy pipe, a well preserved lamproite intrusion within the Aldan Shield. Four types of olivine are identified: (1) zoned phenocrysts, (2) high-Mg, high-Ni homogeneous macrocrysts, (3) high-Ca and low-Ni olivine and (4) mantle xenocrysts. Olivine compositions are comparable to those from the Mediterranean Belt lamproites (Olivine-1 and -2), kamafugites (Olivine-3) and leucitites. Homogenized melt inclusions (MIs) within olivine-1 phenocrysts have lamproitic compositions and are similar to the host rocks, whereas kamafugite-like compositions are obtained for melt inclusions within olivine-3. Estimates of redox conditions indicate that “lamproitic” olivine crystallized from anomalously oxidized magma (∆NNO +3 to +4 log units.). Crystallization of “kamafugitic” olivine occurred under even more oxidized conditions, supported by low V/Sc ratios. We consider high-Ca olivine (3) to be a fingerprint of kamafugite-like magmatism, which also occurred during the Mesozoic and slightly preceded lamproitic magmatism. Our preliminary genetic model suggests that low-temperature, extension-triggered melting of mica- and carbonate-rich veined subcontitental lithospheric mantle (SCLM) generated the kamafugite-like melts. This process exhausted carbonate and affected the silicate assemblage of the veins. Subsequent and more extensive melting of the modified SCLM produced volumetrically larger lamproitic magmas. This newly recognized kamafugitic “fingerprint” further highlights similarities between the Aldan Shield potassic province and the Mediterranean Belt, and provides evidence of an overlap between “orogenic” and “anorogenic” varieties of low-Ti potassic magmatism. Moreover, our study also demonstrates that recycled subduction components are not an essential factor in the petrogenesis of low-Ti lamproites, kamafugites and leucitites.

<p>Crystalline continental crust of the northern East European platform, particularly within the Arkhangelsk diamondiferous province (ADP), is covered by sedimentary rocks, and no direct samples are available. Scarce data on the age and evolution of continental crust of the province is based upon the studies of lower-crustal xenoliths (Koreshkova et al., 2014; Shchukina et al., 2018). In order to obtain more information on the age and evolution of continental crust of the ADP we study a set of 135 zircon xenocrysts selected from heavy minerals fraction of the V. Grib kimberlite. Zircons are between 100 and 250 micron in size and mostly rounded with some remnants of crystallographic shapes. CL images show a variety of types of zoning, dark or oscillatory zoned cores often have hexagonal shapes surrounded by bright rims. Other zircons have blocked irregular structure and some grains are homogeneous.  Zircons show a wide range of <sup>207</sup>/<sup>206</sup> Pb ages from 3.12 to 1.12 Ga with the two major peaks on the relative probability plot. The first corresponds to the Archean age of 2.5-2.6 Ga and the second to Paleoproterozoic of 1.9 Ga. If we consider core age only the two major peaks remain but Proterozoic peaks are less sharp and the proportion of Archean to Proterozoic ages is increased. Over half of the grains analyzed have discordant ages mostly within 10 % and plots below the Concordia line indicating Pb loss. Zircon also have a wide variation in their Hf isotope composition. The range of ɛHf (t) values calculated with corresponding U-Pb ages are vary from 4.5 to – 36. The vast majority of zircons have negative ɛHf (t) values that suggest re-setting U-Pb ages of older zircons by later tectono-thermal events. The calculated Hf T<sub>DM</sub> model ages are mostly Archean being of 2.9-3.4 Ga with the oldest of 3.8 Ga.  From the synthesis of zircons U-Pb and Lu-Hf isotope data the several steps of formation and evolution of continental crust of ADP can be proposed. The first fragment of continental crust of ADP was formed in the Eoarchean time app at 3.6-3.8 Ga as evidenced from the Hf T<sub>DM</sub> model ages of two zircons. The major event of continental crust growth occurred at 3.4-3.1 Ga. However, all of this crust has been reworked later by collision with the other Archean terrane at app 2.8-2.7 Ga. At that time, some magmatic activation in the area was occur as three of this age zircons have juvenile Hf isotope composition with positive ɛHf (t) values. The next tectono-magmatic episode at 1.8-2.0 Ga significantly affected all the crust in the area, both Archean and newly formed Paleoproterozoic. This event corresponds to final amalgamation and stabilization of Kola-Karelian craton. After that, continental crust of ADP remains stable with some magmatic activation in Meso-Proterozoic time. The rocks of this age not experienced metamorphism as their zircons U-Pb ages are concordant and keep positive ɛHf (t) values. </p> <p>This work was supported by the Russian Science Foundation, grant No. 20-77-10018</p>

The chemical composition of 42 samples of raw glass from the Komarov settlement on the Middle Dniester was studied by means of SEM-EDS, EPMA and LA-ICP-MS analyses. We singled out groups of colourless glass of Levantine and Egyptian origin, the chronology of which indicates that the workshop could be dated to the 4th – early 5th century. The data on the chemical composition of the raw glass do not confirm that glassmaking industry existed here in an earlier period, as was previously believed. The manufacturing in Komarov combines the use of high-quality perfectly decolourized raw glass with intensive use of cullet, which might point out either different levels of the glassware manufactured here, or selective recycling. The characteristic features of the workshop's raw glass supply are the absence of the HIMT glass and late spread of antimony-decolourized glass.

No abstract

The aim of this work is to determine the provenance for the Upper Visean Solnechnay formation (The Southern Urals) using the U-Pb dating of detrital zircons. 138 zircon grains with discordance range of ± 10% were selected for the analysis. The vast majority of the zircons yielded the Ordovician and Cambrian ages. The main peak corresponds to the beginning of the Ordovician period (circa 480 Ma), and the secondary peaks correspond to the beginning of the Late Ordovician, the middle Cambrian, and the early Cambrian. The clastic material was derived from the East Ural megazone exclusively.