DURATION OF YOUNG (PLIOCENE) INTRUSIVE MAGMATISM IN THE TYRNYAUZ ORE FIELD, NORTHERN CAUCASUS: NEW K-AR AND RB-SR DATA

Abstract

The isotopic-geochronological study of the young magmatic rocks of the Tyrnyauz ore field showed that magmatism in this region terminated ~1.90–1.95 Ma ago after the emplacement of vitrophyre dikes. These dikes are not related to volcanism of the Elbrus center, as previously suggested, since volcanic activity in the Elbrus area began about 900 ka ago, whereas the Elbrus Volcano originated no earlier than 250 ka ago [12]. The Eldzhurtinsky granite massif and the network of subvolcanic rhyolite bodies and vitrophyre dikes, which crosscut the rhyolite bodies, formed without significant temporal gaps within the interval of 1.9–2.5 Ma; i.e., these events lasted no more than 600 ka. All young magmatic rocks of the Tyrnyauz ore field are characterized by narrow age interval, similar chemical composition, and identical initial 87Sr/86Sr isotopic ratios, suggesting their formation from a common magmatic source and relation to a single Late Pliocene volcano-plutonic complex.