Pleistocene Accelerated Exhumation Within the Sumatran Fault: Implications for Late Cenozoic Evolution of Sumatra (Indonesia)

Abstract The 1,900‐km‐long Sumatran fault plays an important role in accommodating oblique plate motion between the Indo‐Australian and Sunda plates. Although fault geometry, kinematics, and seismic activity are well‐studied, the onset of dextral motion on the Sumatran fault and uplift of adjacent Barisan Mountains is unclear; this hinders an understanding of the late Cenozoic evolution of Sumatra and the forearc region. In this study, we use low‐temperature thermochronology to measure cooling histories of rocks within and outside of the Sumatran fault. An accelerated exhumation within the fault zone began at ∼2 Ma. The Barisan Mountains may have experienced uplift and associated river incision in the late Miocene to Pliocene. The fault systems in the forearc region were inferred to be kinematically linked to the Andaman Sea and Sunda Strait and accommodated early relative plate convergence, then relocated the strike‐slip component of deformation to the Sumatran fault at ∼2 Ma. Plain Language Summary The 1,900‐km‐long trench‐parallel Sumatran fault plays an important role in accommodating the oblique plate motion between the Indian Ocean lithosphere and Sunda continental crust. Although fault geometry, kinematics, and seismic activity are well‐studied, the onset of motion on the Sumatran fault and uplift of adjacent Barisan Mountains is unclear, hindering an understanding of the late Cenozoic evolution of Sumatra and forearc region. Fault movement with dip‐slip components affects bedrock exhumation rates of the fault zone, which should be recorded by low‐temperature thermochronologic data. We present new apatite and zircon (U‐Th)/He data collected from the Sumatran fault zone and adjacent Barisan Mountains to examine their exhumation histories, which has previously been unconstrained. We then discuss the driving mechanism based on structural, sedimentary and chronologic observations. Our AHe and ZHe data help to provide timing constraints on the late Cenozoic tectonic and landscape evolution of the Sumatran fault and Barisan Mountains, which in turn can be related to broader plate tectonic setting. Key Points A Pleistocene accelerated exhumation is identified within the Sumatran fault zone The Barisan Mountains may have experienced uplift and rapid exhumation in the late Miocene to Pliocene Forearc faults likely accommodated early oblique plate motion and deformation relocated to the Sumatran fault around 2 Ma