Hot Archean orogens suppressed voluminous S-type granite formation

S-type granites are far less abundant during much of the Archean than in the Phanerozoic, and this paucity remains puzzling. We propose that the suppression of S-type granite formation at scale may have been an inherent consequence of the hotter Archean crust. A key insight from fossil P-T-t paths in representative orogens is that the onset of melting can trigger exhumation and thereby limit the maximum burial depth of sediments.​ In a hot crust, this maximum burial depth is relatively shallow, because hot geotherms initiate melting at shallow depths due to the pressure dependence of dehydration melting. By contrast, colder geotherms in Phanerozoic orogens effectively suppress melting until higher pressures and temperatures. As a result, Archean sedimentary packages were exhumed too early to undergo extensive decompression and dehydration melting attainable in modern cycles. Phase equilibria modeling shows that the exhuming metasediments in the Archean may only generate melt fractions 1/3 to 1/2 of those in the Phanerozoic. Such low melt productivity in the Archean may have inhibited the formation of large S-type plutons and batholiths. More broadly, these processes may have impeded deep recycling of sediments and, by limiting upward distillation of heat-producing elements, slowed the cooling of the Archean continental crust.