AGE AND GEODYNAMIC SETTINGS OF THE FORMATION OF CRETACEOUS IGNEOUS ROCKS ALONG THE WESTERN BOUNDARY OF THE BADZHAL TERRANE (SIKHOTE-ALIN OROGENIC BELT)

The paper presents the results of the study of geochemistry and U-Pb zircon dating of Cretaceous igneous rocks of the westernmost part of the Badzhal terrane within the Badzhal and Dusse-Alin volcanic zones of the Khingan-Okhotsk magmatic belt. The granites of the Verkhneurmysky pluton and Pravourmyskaya dyke in the Badzhal zone were dated at 100±1 and 93±1 Ma, respectively. The age of diorite in the Suluk-Egono interfluve of the Dusse-Alin zone was estimated at 88±1 Ma, and the ages of three tuff zircon populations were estimated at 88±2, 97±1 and 105.5±1.3 Ma. The dating results indicate that the synorogenic reduced granites of the Verkhneurmysky ore cluster were formed under the transform continental margin regime, which gave rise to the occurrence of a large Albian-Cenomanian magmatic province of Pacific Asia. The magnetite series diorites of the Dusse-Alin zone were formed during the subsequent subduction-related Turonian-Maastrichian stage, but their geochemical characteristics are not typical of suprasubduction magmas. This may indicate a later transition to subduction at this section of the continental margin, or the existence of local extension and/or transcurrent faulting in the subduction settings. The studied igneous rocks of both stages and volcanic zones were formed with significant involvement of material from the mature continental crust, and are characterized by a similar range of ε Nd (t) values from –0.9 to –2.6 and two-stage Nd model ages from 1.22 to 1.05 Ga.