بررسي تغييرات جرم ناشي از دگرساني هيدروترمال سنگ هاي آتشفشاني تتماج، شمال غرب نطنز

Mass Changes Due to Hydrothermal Alteration of Totmaj Volcanic Rocks, NW of Natanz, Iran

The submarine volcanic rocks of Totmaj area as a small part of Sahand-Bazman volcanic belt are mainly composed of mafic and intermediate lava flow and pyroclastic rocks which locally show an alternation with Oligocene sedimentary rocks. The volcanic rocks undertaken the hydrothermal alteration during the waning stages of the explosive activity and include secondary minerals such as albite, chlorite, calcite, actinolite, epidote, hematite and quartz. Based on the chemical and mineralogical characteristics, the altered rocks have been divided into four following groups: least altered, chlorite-epidote rich, hematite rich, and epidote rich rocks. Least altered rocks, including basalt, andesite and basaltic andesite, form approximately 10 percent of the area. The chlorite-epidote alteration which is the earliest hydrothermal event, has extensively affected the rocks due to seawater circulation into the heat submarine volcanic rocks. These rocks, compared to least altered rocks, suffered some increase Ti02, Sr, CaO, and Ni in Basalt and Rb, Th, CaO and K20 in andesite. The epidote rich zones have been as a high permeable part of chlorite-epidote rich zones which during interaction with Ca rich fluid have been enriched of epidote and lost some elements such as Fe, Mg, and Na. The rocks containing hematite, subsequent to chlorite-epidote alteration, have been evolved by high-temperature Fe and Mg rich fluid which have been circulated within the chlorite-epidote rich rocks leading to CaO leaching.