Fluid Phases in the System K sub 2 O-MgO-SiO sub 2 -H sub 2 O and Their Possible Significance for the Genesis of Ultrabasic Rocks

摘要

Experimental investigations at a pressure of 1000 atm and temperatures of 500 to 900 deg C yielded extensive fields of molten silicate liquids in the system K sub 2 O-MgO-SiO sub 2 -H sub 2 O. Since the compositions of these melts approximate the limiting system MgO-SiO sub 2 -H sub 2 O that is important for ultrabasic rocks, even relatively small potassium contents can convert ultrabasics into so-called ''crystal mushes'' (coexistence of crystals and molten liquid), which remain capable of migration and thus of intrusion down to ca. 700 deg C. At lower temperatures, a K-rich gas replaces the liquid, and can escape from the now completely solidified ultrabasic to cause alkalization in the neighboring rock. 20 refs., 5 figs. (ERA citation 11:007885)