SYNCHRONOUS LATE MIOCENE ARC-CONTINENT COLLISION ACROSS TIMOR: FIELD CONSTRAINTS ON PLATE BOUNDARY REORGANIZATION

The Timor orogen has developed due to subduction of the Australian continental margin below the accreting Banda volcanic arc, an event commonly linked to subduction zone termination. The geologic record onshore Timor indicates this collision has been a prolonged process from the Late Miocene to the present. Previous work has inferred progressive collision from east to west across Timor, with large implications for the processes controlling plate boundary reorganization due to continental subduction. Recent work, however, reveals that the timing of collision and uplift was broadly synchronous from east to west. Foraminiferal biostratigraphy in West Timor reveals piggyback synorogenic deepwater deposition at 5.57 – 5.53 Ma, basin uplift to middle bathyal depths at 3.35 – 2.58 Ma, and basin uplift to upper bathyal depths at 2.58 – 1.30 Ma. Duplexed Australian-affinity strata produce apatite (U-Th)/He ages from 0.33 – 2.76 Ma, apatite fission track ages from 2.19 – 3.53 Ma, and partially reset zircon (U-Th)/He ages. Duplexing of Australian-affinity strata occurred in an antiformal stack pattern structurally below Banda Arc forearc, and balanced cross sections reveal 300 km of shortening with 210 km of subducted Australian continental crust. These ages of synorogenic basin deposition and uplift, exhumation rates modeled from thermochronology, and shortening amounts are all similar to results from East Timor. This implies that collision and the resulting processes leading to plate boundary reorganization were not progressive from east to west. We conclude that east-west variations in orogen morphology may instead have been controlled by along-strike changes in strain distribution due to strength heterogeneities and wedge-top sedimentation. Furthermore, synchronous collision supports the hypothesis that a continental plateau may have subducted at Timor.