A new K-Ar illite dating application to constrain the timing of subduction in West Sarawak, Borneo

The timing of subduction is a fundamental tectonic problem for tectonic models, yet there are few direct geological proxies for constraining it. However, the matrix of a tectonic melange formed in a subduction-accretion setting archives the physical/chemical attributes at the time of deformation during the subduction-accretion process. Thus, the deformation age of the matrix offers the possibility to directly constrain the period of the subduction-accretion process. Here we date the Lubok Antu tectonic melange and the overlying Lupar Formation in West Sarawak, Borneo by K-Ar analysis of illite. The ages of authigenic illite cluster around 60 Ma and 36 Ma. The maximum temperatures calculated by vitrinite reflectance values suggest that our dating results were not affected by external heating. Thus, the ages of authigenic illite represent the deformation age of the melange matrix and the timing of the Rajang Unconformity, indicating that the subduction in Sarawak could have continued until ca. 60 Ma and the thermal and/or fluid flow events triggered by a major uplift of the Rajang Group occurred at ca. 36 Ma. Furthermore, this study highlights the potential of using the tectonic melange to extract the tion INTRODUCTION by forearc-backarc metamorphic melt unknown tion in phic subduction in times, such from (Figs. related exact (2012) in directed block margin Breitfeld argued timeframe of subduction zone episodic evolution directly.

Automated summary

Dating the tectonic melange in West Sarawak, Borneo using K-Ar analysis of illite provides constraints on the deformation age and duration of subduction activity. The results suggest that subduction in Sarawak may have continued until approximately 60 Ma, with major uplift events occurring at around 36 Ma. This study also highlights the potential of using tectonic melange to extract information about unknown periods of metamorphic melt generation during subduction.