| Growth, evolution, and destruction of continental crust at convergent margins profoundly alters the structure and composition of Earth's crust and mantle. Metamorphic rocks from continental collision zones and retro-arc fold-and-thrust belts directly record these processes in their textures, parageneses, chemistry, and isotopic signatures. Three separate studies document these relationships with petrology and SHRIMP-RG geochronology + geochemistry.; Gneiss-hosted eclogites of the Sulu ultra-high pressure (UHP) terrane, eastern China, contain unusually abundant (15--40 vol%) hydrous phases, and record prograde, peak (30--35 kbar, 600--700°C), and retrograde metamorphism during Late Triassic subduction of the South China craton. Garnet-epidote oxygen barometry on the peak assemblage indicates oxygen fugacities above the hematite-magnetite buffer stabilized the epidote-talc assemblage without an unusually Mg-rich bulk composition, and precluded microdiamond formation in this area.; The Funeral Mountains metamorphic core complex, Death Valley, California, records mid-crustal processes of retro-arc crustal thickening during the Cretaceous Sevier orogeny. Garnet amphibolites record 7--9 kbar, 620--680°C peak conditions, and 91.5 +/- 1.4 Ma monazite from garnet-kyanite-staurolite schist records lower plate prograde metamorphism. A deformed 85.8 +/- 1.4 Ma pegmatite dike reflects syn-metamorphic anatexis, and predates core complex-related extensional deformation. Deep-level granite dikes reflect younger melting (∼62 Ma), possibly related to shallow subduction. Similarity of metamorphic, leucosome, and pegmatite ages to periods of Sevier belt thrusting and voluminous Sierran arc magmatism suggests that both thrust burial and regional magmatic heating contributed to metamorphism and subsequent partial melting.; Gneiss-hosted eclogite layers, North Qaidam terrane, western China, record the age and duration of UHP metamorphism during collision of the Qilian and Qaidam micro continents. Eclogite zircon cores record prograde metamorphism as old as 475 Ma; clinozoisite pseudomorphs of lawsonite in garnet cores suggest low-temperature prograde metamorphism. Zircon rims with eclogite-facies inclusions and REE patterns yield 422--449 Ma ages which suggest ∼25 m.y. of eclogite-facies growth. Two host orthogneisses yield ∼925 Ma protolith crystallization ages. The age similarity of Proterozoic orthogneiss, Archean-Proterozoic zircon cores in paragneiss, and Paleozoic HP/UHP eclogite in three North Qaidam localities over 350 km, and in South Altyn terrane localities NW of the Altyn Tagh fault supports their proposed correlation in a HP/UHP belt. |
