Meso-Cenozoic collision-accretionary volcanic complexes of the Central andSouthern Pamirs (an example of active margin-plume magmatism evolution)

The paper presents results of a comparative geochemical analysis of the Bar tang, Kyzylrabat, Pshart, and Dunkel'dyk volcanic complexes in the Central and Southern Pamirs. The Bartang and Kyzylrabat complexes represent the Cre taceous-Eocene Tethys active margin, and the age of the other two correspon ds to the India-Eurasia collision. Volcanism acted upon a thick (60-75 km) crust that involved Archean sialic plates. The rock chemistry was studied on 115 representative samples by the XRF, ga mma- and atomic-absorption spectrometry, INAA, and other methods at the Ins titute of Geology, Geophysics and Mineralogy (Novosibirsk). The Bartang and Kyzylrabat complexes are assigned to the margin-continental type on the ba sis of their petrology and geochemistry, namely, high Al and low Ti content s, high LILE/HFSE ratios, and a Ta-Nb minimum. The Pshart complex evolved i n a back-are continental rift, as evidenced by elevated contents of Ti, low er LILE/HFSE ratios, and a smooth Ta-Nb minimum. The Dunkel'dyk alkali-basa ltic rocks, apparently related to hotspot activity, are rich in incompatibl e elements, especially in LREE and RAE, and differ from intraplate magmatic rocks of the same type in having deep Ti, Ta, and Nb minima. The four volc anic complexes are derived from primitive or enriched metasomatic mantle, w ith a great contribution of crustal material.