A Newly Identified “Proto-Kenting Mélange (S. Taiwan)” Represents a Missing Link for a Continuous Early Cretaceous Paleo–Pacific Subduction–Accretion System

Most mélanges in exhumed subduction-accretion complexes are polygenetic, recording significant information about the nature of geological processes during their formation. Here, we apply micro-chemical analysis and illite K-Ar dating to constrain the deformation mechanism and timing of the pervasively sheared scaly matrix in the accretionary complex rocks presently known as “Kenting Mélange” in the Hengchun Peninsula (South Taiwan). Our results reveal that parts of the matrix were formed in Cretaceous (96.7 ± 8.6 Ma and 108 ± 18.4 Ma) due to pressure solution. These new, older matrix ages suggest that the Kenting Mélange, which was considered as Cenozoic and interpreted to have been associated with the subduction of the South China Sea, preserves different primary chaotic units (e.g., mélange and/or olistostrome). Our findings imply the Kenting Mélange is actually polygenetic and allow part of Kenting Mélange that we named the “proto-Kenting Mélange” to be interpreted as a remnant of a primary mélange, which was mixed and/or juxtaposed in the Cenozoic Kenting Mélange. The block-in-matrix fabric with a pervasively sheared scaly muddy matrix, along with the preservation of slightly older oceanic crust blocks, suggests that the proto-Kenting Mélange is most likely an ocean plate stratigraphy mélange. This unit initially formed near a Paleo-Pacific subduction margin during the latest Early Cretaceous. Our results reveal a nearly 3000-km-long physical archive of latest Early Cretaceous subduction–accretion processes, which took place adjacent to the continental margin of East Asia during the consumption of Paleo–Pacific ocean floor during the latest Mesozoic.