Comparison of supracrustal rocks and HP–UHP rocks in the South Altyn terrane: Implications for subduction zone structure and subduction-exhumation process

• Precambrian supracrustal rocks share background with SAT HP–UHP rocks’ protolith, lacking Cambrian metamorphic overprint. • The Precambrian supracrustal rocks may represent the unsubducted overlying plate (i.e., the Central Altyn). • Modern configuration of SAT HP–UHP and supracrustal rocks formed by differential exhumation and modification. Weakly to non-metamorphosed supracrustal rocks are widespread in high- to ultrahigh-pressure (HP–UHP) subduction zones yet frequently neglected in orogenic evolution. Establishing their spatiotemporal relationships with HP–UHP rocks and comparing protolith affinities are essential for deciphering subduction zone architecture and exhumation dynamics. In this study, we investigate Precambrian supracrustal rocks in the South Altyn terrane (SAT) through integrated field investigations, geochronology, and geochemical analysis, in comparison with HP–UHP rocks. Granites emplaced at 933–898 Ma exhibit crustal melting and syncollisional affinities, serving as robust markers for Rodinia convergence and consistent with the protolith of regional HP–UHP granitic gneiss. A mafic dyke emplaced at ∼ 806 Ma exhibits within-plate basalt (WPB) affinities, marking the transition from collision to extension, and is consistent with protolith of regional (retrograde) eclogites. (Meta-)sedimentary rocks deposited during 1150–940 Ma show affinities with the Taxidaban Group of the Central Altyn block (CAB). Our results reveal that these supracrustal rocks lack significant Cambrian metamorphic overprinting but share protolith ages and geochemistry characteristics with the HP–UHP units, suggesting a cogenetic origin but contrasting structural positions during subduction. The comparison implies that these supracrustal rocks may represent the non-subducted overlying plate of the SAT Early Paleozoic subduction zone. Integrating existing metamorphic records, we propose that the current spatiotemporal pattern of supracrustal rocks and HP–UHP rocks in the SAT resulted from Early Paleozoic unified continental subduction and subsequent differential exhumation. Concurrently, the final mineral assemblages and fabric characteristics of the SAT HP–UHP rocks result from peak HP–UHP metamorphism and differential retrograde modification.