ISOTOPIC AGE AND PALEOGEODYNAMIC POSITION OF ULTRAPOTASSIC MAGMATISM OF CENTRAL CHUKOTKA
The <sup>40</sup>Ar/<sup>39</sup>Ar dating of ultrapotassic rocks from Central Chukotka shows that these rocks are Early Cretaceous, and yields a narrow range of age variations (109 to 107 Ma), which correlates fairly well with the range of age variations of granitoids typical of the study area (117-105 Ma). There are thus grounds to suggest that the ultrapotassic magmas and granitoids resulted from the same geological process that can be identified from the material characteristics of the ultrapotassic magmas. In the modern concepts of the regional geological development, the formation of the granitoid and ultrapotassic magmas can be related to the continental lithosphere extension due to the collision of Eurasian plate and the Chukotka -Arctic Alaska continental block. Using modern genetic models based on the interpretations of the material characteristics of ultrapotassic magmas, it is possible to limit the number of genetic hypotheses and to relate the continental lithosphere extension to the processes that took place in the upper mantle of the study area.