New Provisions for Volcanogenic Rocks in the Petrographic Code

摘要

Results are reported from recent developments relating to volcanic rocks; these were necessary inconnection with an analysis of remarks and proposals for the 1995 Petrographic Code, as well as resulting froman analysis of practical applications of this document. The new materials are concerned with three directions:(1) further specification of the "total alkali–silica" diagram (TAS) for acidic rocks and trachytes; (2) improvingthe classification of clastic volcanogenic rocks and regulating the volcaniclastic terminology; and (3) substan-tiating the principles for subdividing sedimentary-and-volcanogenic rocks into subunits of different hierarchi-cal levels and specifying the associated criteria. The insertion of results of these developments into a second,revised and supplemented edition of the Petrographic Code and their application to geological studies willenhance the quality of the latter.