Late Paleoproterozoic Basic Dikes in the Ulkan-Uchur District, Eastern Aldan-Stanovoi Shield: Structural Position, Composition, and Paleogeodynamic Setting

摘要

Lale Paleoproterozoic dikes of the Maimakan Complex were studied in the Ulkan-Uchur district at the eastern margin of the Aldan-Stanovoi Shield. The dikes are parallel or arranged en echelon in the Uchur-Uyan, South Uchur, and Ukikan fields of dike swarms. The spatial distribution of the dike swarms pertaining to the Maimakan Complex in the Ulkan Trough and its framework shows that the area of their intersection is located in the center of the Ulkan granitoid batholith. The basic dikes, which are distinguished by elevated contents of alkali metals, Fe, Ti, and P in combination with a low Mg content, are defined as moderately alkaline rocks transitional from tholeiitic to alkaline series similar in composition to within-plate basalts and E-MORB. The REE pattern is comparable to that of tholeiitic and subalkaline series in extensional settings. Along with the geological data, this indicates that the complex was formed under conditions of intraconti-nental extension. As follows from geological relationships, the age of dikes is estimated as 1670-1715 Ma.