什么是 Granite typology？

An I-type granite is a granite whose source was dominantly an older igneous rock, an S-type granite one whose source was dominantly a sedimentary (metasedimentary) rock, and an M-type granite one derived from the mantle. An A-type granite is defined by its chemistry and setting rather than its source: ferroan and potassic, strongly enriched in incompatible elements, and emplaced in stable intra-plate, back-arc or post-collisional settings.