EVOLUTION OF GRANITE-PEGMATITES IN THE GEOLOGIC HISTORY OF FOLD SYSTEMS, AS ILLUSTRATED BY THE PAMIRS AND THE HINDU KUSH

Abstract

Our work has shown that the evolution of granite pegmatites in different tectonomagmatic and metamorphic cycles of development of the Alpine-Himalayan fold belt is expressed in a systematic change from some pegmatite associations to others. The established sequence of formation of these pegmatite associations in the geologic history of the fold system under consideration, i.e., deep-seated pegmatite with gemstones → deep mica-bearing → medium-depth rare-metal' shallow with rock crystal, reflects the systematic variation of thermodynamic conditions, which also controlled their metallogenetic and genetic specificity. In this sequence of pegmatite associations from deep-seated to mica-bearing, rare-metal and rock-crystal-bearing in the region studied, the spatial and genetic relationship between granite and pegmatite becomes much stronger, the scale of the pegmatite process increases, and the effect of the host rocks on pegmatite compositions decreases, while the role of direct crystallization in forming the pegmatite bodies becomes stronger.