Tholeiitic and Alkaline Basaltic Lavas of Wang-Tian’e and Changbaishan Volcanoes (Northeastern China): Timing and Genetic Relationship

Doklady Earth Sciences - Changbaishan and Wang-Tian’e volcanoes of Changbaishan area (Northeast China) were formed with a slight time gap in the last four million years. Wang-Tian’e...     

Geochronology and evolution of quaternary volcanism at the Keli Highland,Greater Caucasus

The paper reports newly obtained stratigraphic, petrographic, and isotope-geochronological data on modern moderately acid lavas from the Keli Highland at the Greater Caucasus and presents a geological map of the territory, in which 35 volcanoes active in Late Quaternary time were documented by the authors. The total duration of volcanic activity at the highland was estimated at 250 ka. The volcanic activity was discrete and occurred in three phases: Middle Neopleistocene (245−170 ka), Late Neopleistocene (135−70 ka), and Late Neopleistocene-Holocene (<30 ka). Newly obtained lines of evidence indicate that certain volcanoes erupted in the latest Neopleistocene-Holocene. The first phase of volcanic activity was connected mainly with lava volcanoes, and eruptions during the later phases of volcanic activity in this part of the Greater Caucasus produced mainly lavas. The most significant eruptions are demonstrated to occur in the territory during the second phase. The major evolutionary trends of volcanic processes during the final phase in the Keli Highland are determined. It was also determined that the overwhelming majority of volcanoes that were active less than 30 ka B.P. are spatially restricted to long-liven local magmatic zones, which were active during either all three or only the final two phases of activity. These parts of the territory are, perhaps, the most hazardous in terms of volcanic activity.     

Monzonitoid association of the Kavalerovo ore district (Primorye): geochronology and some genetic problems

This paper is dedicated to the isotope-geochronological study of the rocks that compose two large intrusions and a separate group of minor intrusions in the western part of the Kavalerovo ore district. In most publications, these rocks are considered as monzonitic or trachyandesite-monzonitic association. On the basis of the amphibole and biotite K-Ar ages and the Rb-Sr whole-rock and mineral datings, the studied association was formed within the interval of 113–98 Ma. A wider interval of 115–95 Ma was obtained with allowance for other isotope data, including those on the rocks of the volcanic facies. This is consistent with the concepts that the studied association belongs to a single magmatic complex. No significant and systematic age differences have been established between the compositionally similar rocks from the different massifs. In compliance with the scheme of the geodynamic evolution of the region, the chambers of latitic melts of the volcanic and most intrusive rocks of the complex were formed prior to the initiation of the Sikhote-Alin subduction volcanic belt. The initial stage of the formation of the latter is presumably constrained by the data on the biotite from the quartz diorites from the Uglovaya VTS (90 Ma), which is located in the central part of the region, and on the late amphibole from the monzonitoids of its western part (91–92 Ma). The geochemical differences between rocks from the different intrusive bodies could be caused by the specifics of the melt evolution in the intermediate or crystallization chambers.     

Physical characteristics of the Gulf Stream as an indicator of the quality of large-scale circulation modeling

The general idea of this work is to show that the efficiency of modeling boundary currents (compared to the results of observations) can serve as an indicator of correctness for the modeling of the entire large-scale ocean circulation. The results of calculation of the mean surface currents in the Gulf Stream area based on direct measurements from drifters are presented together with the results of numerical modeling of variability of the Gulf Stream transport at 33°N over the period 2005–2014 based on data from Argo profiling buoys.