Geoscience professor Matthew Kohn and colleagues published an article titled “Himalayan ‘S-type’ granite generated from I-type sources” on May 30, 2025 in Proceedings of the National Academy of Sciences of the United States of America.
The significance of this research is as follows: “Classically, granites are separated into two broad categories—’I-type’ vs. ‘S-type’—representing different igneous vs. (meta)sedimentary rock sources for melting. Their geochemistry differs for diverse geochemical systems. Himalayan granites with S-type geochemistry are often considered as metasedimentary melt endmembers, while I-type granites are often considered as primary (new) additions to the crust. Here, we show the S- and I-type classification fails in the eastern Himalaya: Geochemically S-type granites were derived through partial melting of prior igneous intrusions, not metasedimentary rocks. A survey of peraluminous Himalayan leucogranite geochemistry suggests that I-type bodies may represent ~20% of leucogranites. Rather than representing new additions, rare-metal poor, igneous rock-sourced, peraluminous granites represent reworking of older crust, a likely process in large hot mountain belts.”