40Ar/39Ar AGE OF ALKALINE ROCKS OF VERHNEAMGINSKIY MASSIF (ALDAN SHIELD, SOUTH YAKUTIA)

Abstract

The relevance of the research is caused by the need to expand mineral resources base, including gold-bearing ores. Large alkaline provinces, like Aldan-Stanovoy shield, are of interest because gold-bearing ores usually related to alkaline rock. They may form large and even giant deposits. Verkhneamginskiy massif is located in Verkhneamginskiy ore field in Aldan-Stanovoy shield. Verkhneamginskiy ore field is the part of large Charo-Aldan metallogenic zone, its length is more than 700 km from west to east. A characteristic feature of the Verkhneamginskiy ore region is its association with the Amginsky submeridional structural zone of the tectonic melange separating the Central Aldan compound terrain in the East from the West Aldan and Tynda composite terrains in the West and South, respectively. The main aim of the research is to detect the main rock types of Verkhneamginskiy massif, to study the features of structure and composition and to identify the age of massif crystallization as well as to compare the results with the available geochronological data on Mesozoic magmatism of the Aldan shield. Methods: petrographic study and 40Ar/39Ar dating by the step heating method by phlogopite monofractions. Results. The main phases of Mesozoic alkaline magmatism are leucocratic syenites and mesocratic lamprophyres. Using the 40Ar/39Ar dating of phlogopite monofraction the authors have determined two discrete impulses: (1) 129,1.5±2,5 Ma emplacement of syenites; (2) 117,7±3,4 Ma emplacement of lamprophyre dikes. Mesozoic magmatism, manifested in Verkhneamginskiy area, demonstrates similar age boundaries with magmatic processes shown in the Aldan shield in the Mesozoic era.

Keywords

• aldan-stanovoy shield
• aldan shield
• verhneamginskiy massif
• verhneamginskiy ore field
• petrography
• mesozoic
• alkaline rock
• 40ar/39ar dating