Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)

Origin of layered granitic rocks of the Khan Bogd peralkaline massif in southern Mongolia

 

Jindřich Kynický, Lukáš Krmíček, Cheng Xu, Jan Mašek, Michaela Krmíčková

Geoscience Research Reports 43, 2010 (GRR for 2009), pages 274–277

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Abstract

The Permian post-collisional A-type peralkaline granitic complex of Khan Bogd is located in the Gobi desert in southern Mongolia. The Khan Bogd, one of the world's largest peralkaline ring complexes, is a product of extended fractional crystallization. Layered granitic ring dykes of the Khan Bogd peralkaline massif occur near the contact with the host rocks and the roof pendants of the surrounding volcanic arc complex. Combined field and petrographic investigation of rhythmically layered ekerite-aplite-pegmatite series suggest they were emplaced during transitions from the ductile to the brittle regime. Adiabatic changes of pressure ("swinging eutectic") connected with ductile-to-brittle transitions, resulted in repeated episodes of undercooling during which crystallized the volatile-rich ekeritic layers.