RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, NO. 1, PAGES 35–50, doi:10.2205/2005ES000170, 2005

The composition, genesis, and mantle xenoliths of the Late Miocene fergusite-carbonatite-syenite series of the Pamir: The problem of superthick crust formation in mobile belts

Institute of Geology of the Tajik Academy of Science, Dushanbe, Tajikistan

Abstract

[1]  The aim of this paper is to offer the geostructural and petrochemical characteristics of the diatremes and dykes of the Late Miocene fergusite-carbonatite-syenite series and of the mantle xenoliths. The evidence obtained in this study for the petrogeochemistry of the subvolcanic bodies and for the composition and thermobarometry of their mantle and crustal inclusions allowed us to clarify the conditions of magma intrusion and differentiation, as well as the depths and types of the potential sources of the ultrapotassic alkali-basic magmas. Models are offered for the formation of a superthick crust and a newly formed pyroxenite-eclogite upper mantle under the Pamir region. The tectonic positions of the Late Miocene rock bodies and their formation analysis proved their association with the post-collision conditions. A view is advanced that the horizontal displacement of the Pamir (at least of its eastern block), as well as the formation of its modern structural style, associated with the India-Asia collision, was completed in the Late Miocene.

Received 18 February 2005; published 12 March 2005.

Keywords: Late Miocene, composition, genesis, mantle xenoliths, fergusite-carbonatite-syenite series, mobile belts, Pamir}

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