The central peaks of several craters on the flanks of syrtis major are made up of an even more silica - rich rock , granite , that may have formed by extreme crystal separation or by large - scale remelting of earlier basalts 在大三角側(cè)面,幾個火山口的中間尖點是由一種矽含量更高的巖石花崗巖所構(gòu)成,可能是經(jīng)極度晶體分化,或早期玄武巖大?圍重新熔融而形成。