(Ultra)high‐Pressure Metamorphism in Sedimentary Versus Basaltic Rocks: Insights From a Variscan Mélange in the South Carpathians

Reconstructing the pressure–temperature–time ( P–T–t ) evolution of (ultra)high‐pressure rocks is essential for constraining subduction and collisional dynamics. Subduction zones are often investigated using basic eclogites, whereas nonbasic high‐pressure rocks remain comparatively understudied, potentially hindering a comprehensive understanding of complex subduction systems. The Bughea Complex is a modern‐style mélange within the pre‐Alpine basement of the South Carpathians (Romania) that hosts a wide variety of eclogitic rocks, providing an opportunity to investigate their response to subduction processes. Here, we integrate phase equilibrium modelling, rutile thermometry, zircon and apatite U–Pb dating coupled with trace element analysis and garnet Lu‐Hf dating to reconstruct the P–T–t evolution of three different eclogitic rocks from the Bughea Complex: a kyanite eclogite, a basic eclogite and an eclogitic schist. The kyanite eclogite is interpreted to derive from a continental sedimentary protolith based on its continental crust‐like trace‐element patterns and detrital‐like zircon U–Pb age spectrum (ranging from Archean to Cambrian). It records the highest peak pressure conditions (~3.2–3.6 GPa at 700°C–820°C), consistent with ultrahigh‐pressure metamorphism, followed by decompression and cooling to < 1.6 GPa and < 675°C. In contrast, the basic eclogite, interpreted to derive from altered oceanic crust based on its MORB‐like trace‐element patterns, and the eclogitic schist, which exhibits trace‐element signatures similar to trench sediments in volcanic‐arc settings, record lower peak pressures (~2.0–2.3 GPa at 580°C –610°C and ~1.9–2.4 GPa at 530°C–600°C, respectively). The former records near‐isothermal decompression (~1.3 GPa at 585°C–615°C), whereas the latter records decompression and minimal heating (~1.0–1.2 GPa at 600°C–615°C). Distinct garnet Lu–Hf ages (469 ± 96 to 345 ± 21 Ma) suggest diachronous metamorphism during a prolonged Variscan subduction, whereas apatite U–Pb age (ca. 340 Ma) likely records late‐stage cooling and exhumation. Differences in P–T–t records may reflect mélange rheology and variations in subduction dynamics, whereas limited heating during retrogression and compositional buoyancy appear critical for preserving peak conditions, particularly in nonbasic rocks. Overall, these findings demonstrate that continental‐derived metasedimentary rocks can preserve evidence of extreme pressure conditions not always recorded by associated basic eclogites, highlighting the importance of integrating nonbasic high‐pressure rocks into P – T – t reconstructions of subduction‐related mélanges to achieve a more complete understanding of complex collisional systems.