The paper presents a first complete description of the alkaline syenite-leucogranite series which dates back to the beginning of Late Hercynian magmatic episode in the western Transbaikalia and Northern and Central Mongolia. The radiologic Rb – Sr and K – Ar dating of the series indicates an age of about 275–285 Ma, ISr = 0.7061. Three successive rhythms have been distinguished in the series: two syenitic and one granitic. Magmatic rocks of the rhythms do not form a common homodromous succession, which can be attributed to mixing of basic and syenite magmas as well as to the partial melting of syenites which probably played an important role during their formation. Quantitative evaluations of crystallization temperature (950°C), total pressure (2–3 kbar), and lg fO2 (–12) for syenite magmas are obtained.
Zanvilevich et al. (Fri,) studied this question.
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