High magnesian andesitic/dioritic rocks (HMA) and magnesian andesitic/dioritic rocks (MA)： two igneous rock types related to oceanic subduction

Abstract：This paper discusses two igneous rock types (HMA and MA) related to oceanic subduction based on a brief review of the experimental petrological data. On such a basis, some suggestions are put forward as follows： (1) The utilization of both the MgO % and FeO/MgO (% ratio) at given SiO2 as the diagnostic parameters is emphasized in recognition of HMA and MAl. (2) On the basis of the LF-CA (Low-Fe calc-alkaline) characteristics, HMA and MA may be distinguished from each other by using the SiO2%-MgO % parameter system. (3) Either of the two methods, i.e., the diagram approach (Fig.2&3) or the numeric approach (Table 1,2&3), may be used for the nomenclature of HMA and MA.