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The paper presents the results of isotope-geochronological and petrological-geochemical study of young volcanic rocks in the Geghama highland (Central Armenia), which were formed at the Pliocene–Early Quaternary stage of the Late Cenozoic post-collisional magmatism of the Lesser Caucasus. The boundaries of the area of volcanic activity manifested during this stage were established. The total duration (3.5–1.9 Ma) of the Pliocene–Early Quaternary stage, the time range of its main phases, and the scale and nature of eruptions were determined. Petrological and geochemical data indicate that the studied young volcanic rocks from Central Armenia belong to the mildly alkaline series and are represented by a continuous association of (trachy-)basalt–mugearite–latite–trachyte–rhyolite. The geochemical evolution of parental basaltic melts was mainly controlled by the fractional crystallization with Cpx as the main cumulus phase. Crustal assimilation and mixing of magmas were of limited importance: their possible contribution was recorded only in the most silicic rocks. The deep source responsible for magma generation under the studied part of the Lesser Caucasus at the Pliocene–Pleistocene boundary was represented by the asthenospheric mantle that was enriched during previous long-term (tens of millions of years) subduction of the Neotethys slab. Melting occurred in the Grt-peridotite stability zone; the composition of derived melts was geochemically similar to E-MORB basalts. An important feature of the regional mantle source was the notable admixture of subduction component. The generalization of the obtained petrological–geochemical and isotope–geochemical data on the young igneous rocks formed at different stages of Late Cenozoic magmatism at the Geghama highland allowed us to trace the evolution of the main parameters (mineral, chemical, and isotopic composition, depth of location, degree of melting) of mantle reservoirs responsible for magma generation beneath Central Armenia at the post-collisional stage (from the Late Miocene to the Holocene). [ABSTRACT FROM AUTHOR]

Tristan da Cunha is a volcanic island group situated in the central South Atlantic. The oldest of these islands, Nightingale Island, has an age of about 18 Ma. In the interior of the island, there are several wetlands situated in topographic depressions. The ages of these basins have been unknown, and their genesis has been debated. Aiming towards the reconstruction of the geomorphological history of these basins, we conducted geoelectrical resistivity measurements to map the subsurface topography, extracted peat and sediment cores and dated the onset of sedimentation applying the radiocarbon method. The irregular shapes of the basins and the lack of clear erosional features indicate that they are not eruption craters and were not formed by erosion. Instead, we regard them as morphological depressions formed between ridges of trachytic lava flows and domes at a late stage of the formation of the volcanic edifice. The onset of sedimentation within these basins appears to have occurred between 24 and 37 ka with the highest situated wetland yielding the highest ages. These ages are very young compared to the timing of the main phase of the formation of the island, implying volcanic activity on the island during the Late Pleistocene. [ABSTRACT FROM PUBLISHER]