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Abstract:

This paper describes notable characteristics of feldspars in felsic rocks of the Ditrău alkaline intrusive complex, Eastern Carpathians, Romania. Microtextures and compositions of feldspars in samples of monzonite, syenite, nepheline syenite and granite belonging to four geological units of the Ditrău complex have been examined. Plagioclase grains mostly of albite compositions show intricate boundaries with microperthitic alkali feldspar grains. It is the most striking texture in alkali feldspars that large albite cores or remnants are often enclosed by low microcline with saw-tooth or lamellar boundaries, which coexist with various microperthitic textures. Microperthites consisting of low microcline (K-feldspar) with tartan twinning and low albite show diverse textural heterogeneities in the size (width), shape and distribution of constituent albite associated with cryptoperthitic~fine-microperthitic lamellae. In contrast, it is also remarkable that clear K-feldspar areas heterogenously coexist with microperthitic~meso-microperthitic areas in individual alkali feldspars. Most of the compositions of constituent albite and microcline are close to the end-members through the rocks. They are estimated to have been produced by multi-stage reactions from the higher-temperature magmatic to lower-temperature reorganization through the exsolution stage. The latest albitization and K-feldspathization ultimately overprinted or reorganized magmatic resorption and subsolidus exsolution textures and compositions.