Structural Evolution of Ore-Controlling Trans-Crustal Faults of the Olchan-Nera Zone: Constraints from the Khangalas Ore Cluster, Yana-Kolyma Metallogenic Belt, NE Russia

The article studies the structural evolution of ore-controlling trans-crustal faults of orogenic deposits and occurrences of the Khangalas ore cluster located in the southeastern part of the Olchan–Nera metallogenic zone, in the Upper Indigirka sector of the Yana–Kolyma metallogenic belt, North–East of Russia. Studies have shown that the formation of tectonic structures occurred during four Mesozoic deformation stages. Accretionary thrust stage D1 resulted in formation of the main pattern of the Mesozoic tectonic structures of the region. Further tectonic evolution occurred in a strike–slip setting of the accretionary D2 and post-accretionary D3–D4 stages. Post-ore strike-slip faults activate and complicate the earlier formed structures of the reverse and thrust paragenesis. Mineralization associated with the strike-slip faults has not been established, whereas formation of the gold-antimony mineralization is associated with sinistral strike–slip faults in the Adycha–Taryn metallogenic zone located to the southwest. The new data obtained are consistent with the previously proposed model of the evolution of the deformation structures of the Khangalas deposit.

Black Agates from Paleoproterozoic Pillow Lavas (Onega Basin, Karelian Craton, NE Russia): Mineralogy and Proposed Origin

The present study provides the first detailed investigation of black agates occurring in volcanic rocks of the Zaonega Formation within the Onega Basin (Karelian Craton, Fennoscandian Shield). Three characteristic texture types of black agates were identified: monocentric concentrically zoning agates, polycentric spherulitic agates, and moss agates. The silica matrix of black agates is only composed of length-fast and zebraic chalcedony, micro- and macro-crystalline quartz, and quartzine. In addition to silica minerals, calcite, chlorite, feldspar, sulphides, and carbonaceous matter were also recognised. The black colour of agates is related to the presence of disseminated carbonaceous matter (CM) with a bulk content of less than 1 wt.%. Raman spectroscopy revealed that CM from black agates might be attributed to poorly ordered CM. The metamorphic temperature for CM from moss and spherulitic agates was determined to be close to 330 °C, whereas CM from concentrically zoning agates is characterised by a lower temperature, 264 °C. The potential source of CM in moss and spherulitic agates is associated with the hydrothermal fluids enriched in CM incorporated from underlaying carbon-bearing shungite rocks. The concentrically zoning agates contained heterogeneous CM originated both from the inter-pillow matrix and/or hydrothermal fluids.

Negative assortative mating and maintenance of shell colour polymorphism in Littorina (Neritrema) species

Colour polymorphism is a widespread phenomenon in natural populations of several species. In particular, it is especially common on marine gastropod species from the genus Littorina. Recently, it has been argued that intrapopulation shell colour polymorphism in Littorina fabalis could be caused by negative frequency-dependent sexual selection via a mechanism of mate choice (indirectly estimated via negative assortative mating). Here we try to determine the existence of negative assortative mating in three species of the subgenus Neritrema (L. fabalis, L. obtusata, L. saxatilis) that share a similar shell colour polymorphism, in order to ascertain if this mechanism could represent an ancestral character in this subgenus that could be contributing to the maintenance of the colour polymorphism in each species. Here, we collected or reanalysed from previous studies a sample of mating pairs of the three species from seven locations from NW Spain and NE Russia and estimated assortative mating using the IPSI index. Our results show that all species and populations show a systematic tendency towards negative assortative mating when shell colour is grouped in the broad categories: ‘light’ and ‘dark’. Although, a more detailed analysis of each colour individually suggests that shell colour may not be the main target of assortative mating, but perhaps physically linked to another trait or through pleiotropic effects. This hypothesis opens interesting new lines of research in Littorina snails.

Cretaceous paleomagnetic directions in different volcanics in Chukotka (NE Russia)

<p>The Cretaceous Okhotsk-Chukotka volcanic belt (OChVB) is one of the largest provinces of continental marginal magmatism with length more than 3000 km along the Pacific edge of Asia. In the field studies of 2019 and 2020 we sampled 21 sections in the northern part of the OChVB and 3 sections from basement of OChVB. These sections are represented by basalts and andesites; their tuffs, ignibrites and other volcanic rocks are much less common. The age of these volcanics is estimated based on U-Pb and Ar-Ar published data and our new Ar-Ar dates.</p><p>Based on the obtained data, a new paleomagnetic pole for the Chukotka part of the OChVB was calculated. The latitude of this paleomagnetic pole differs from the expected one when compared with that calculated for Chukotka from published data from Besse and Courtillot, 2003; Torsvik et al., 2012. These results are inconsistent with most of the existing geological data. Only a few works admit younger displacements in the southern part of the Verkhoyansk fold belt or in modern diffuse boundary of the Eurasian and North American plates. Moreover, we compare our OChVB pole with results from basaltic complexes from the basement, which has been likely remagnetized when OChVB was formed.</p><p>Acknowledgements: study of cretaceous volcanics is supported by RSF grant № 19-47-04110 and jurassic by RSF grant №18-77-10073.</p>

Permafrost vulnerability to contemporary climate changes in Eastern Chukotka coastal plains (NE Russia)

<p>Recent permafrost degradation is detected in many cold regions of the world. This process is due to surface lowering caused by ice-rich sediments thaw and massive ice beds melt. Eastern Chukotka coastal plains polygon is one of the key sites for studying climate change's impact on permafrost conditions and human activity. This region is the habitat of indigenous people, concentrated in the coastal villages. The study site is approximately 400 km<sup>2</sup> in area and characterized by a variety of landscape, geomorphological, and permafrost conditions. Using remote sensing data, field observations, and shallow drilling results, we ranked and delineated the areas on their susceptibility to thermokarst, thermal erosion, and solifluction activation due to the further air temperature increasing and potential human disturbances. Spatial analysis on current thaw settlement rates combined with drilling data allowed us to map the areas with a high concentration of surficial massive ice beds. These studies provide a better understanding of permafrost conditions in Eastern Chukotka and its response to human impact and climate change.</p>

New insights into the thermal regime and hydrodynamics of the early Late Cretaceous Arctic

The Arctic is warming faster than anywhere else of comparable size on Earth, impacting global climate feedbacks and the Arctic biota. However, a warm Arctic is not novel. The Late Cretaceous fossil record of the region enables a detailed reconstruction of polar environmental conditions, and a thriving extinct ecosystem, during a previous 'hothouse’ global climate. Using leaf form (physiognomy) and tree ring characteristics we reconstruct Cenomanian to Coniacian polar thermal and hydrological regimes over an average annual cycle at eight locations in NE Russia and northern Alaska. A new high spatial resolution (∼1 km) WorldClim2 calibration of the Climate Leaf Analysis Multivariate Program (CLAMP) yields results similar to, but often slightly warmer than, previous analyses, but also provides more detailed insights into the hydrological regime through the return of annual and seasonal vapour pressure deficit (VPD), potential evapotranspiration (PET) estimates and soil moisture, as well as new thermal overviews through measures of thermicity and growing degree days. The new results confirm the overall warmth of the region, particularly close to the Arctic Ocean, but reveal strong local differences that may be related to palaeoelevation in the Okhotsk–Chukotka Volcanogenic Belt in NE Russia. While rainfall estimates have large uncertainties due to year-round wet soils in most locations, new measures of VPD and PET show persistent high humidity, but with notably drier summers at all the Arctic sites.