منشاء آنكلاوهاي ميكروگرانولار در توده گرانيتوئيدي كوه دم، شمال شرق اردستان

Origin of Microgranular Enclaves in Kuh-e Dom Granodiorite Body, NE Ardestan

Kuh-e Dom granodiorite intrusion, located at the Northeastern of Ardestan, includes abundant of rounded and rarely ellipsoid microgranular enclaves composed of quartz diorite, monzodiorite and quartz monzodiorite. The diameters of the enclaves range from a few millimeters to 30 centimeters. These enclaves are very fine-grained and show chilled margin so that the size of their crystal gradually decreases from center to the margin. The chilled margin is an evidence of rapid magma cooling once the enclaves were surrounded by host felsic magma. The occurrence of mafic microgranular enclaves within the felsic rocks accompany with the disequilibrium textures including: 1) poikilitic and Antirapakivi texture at K-feldspar megacrysts, 2) ocelli quartz rimmed by a zone of fine-grained aggregates of early formed minerals, 3) rounded and corroded plagioclase, 4) mafic clots, 5) acicular apatite, 6) small lath-shaped plagioclase in large plagioclase, and 7)crenated and cuspate contact in enclave-host rock which all indicate the mingling of two magmas. Based on microprobe data, the plagioclase crystals show a variable composition from oligoclase to andesine in granodiorite and from andesine to labradorite in enclaves. They have essentially normal zoning and occasionally indicate oscillatory zoning. The enclaves and their host rocks, geochemically, are different from each other and based on the fact that the first one is Na-rich whilst the other is K-rich. In addition, the enclaves display LREE and LILE depletion accompany with the HREE and Ti enrichment compared to their host granodiorites. Therefore, it seems that the enclaves and granodiorites might have been originated from two various magmas which were located adjacent to each other by magma mingling process.