Extremely rapid up-and-down motions of island arc crust during arc-continent collision

Mountain building and the rock cycle often involve large vertical crustal motions, but theirrates and timescales in unmetamorphosed rocks remain poorly understood.We utilize high-resolution magneto-biostratigraphy and backstripping analysis of marine deposits in an activearc-continent suture zone of eastern Taiwan to document short cycles of vertical crustaloscillations. A basal unconformity formed on Miocene volcanic arc crust in an upliftingforebulge starting ~6 Ma, followed by rapid foredeep subsidence at 2.3–3.2 mm yr−1(~3.4–0.5 Ma) in response to oceanward-migrating flexural wave. Since ~0.8–0.5 Ma, arccrust has undergone extremely rapid (~9.0–14.4 mm yr−1) uplift to form modern CoastalRange during transpressional strain. The northern sector may have recently entered anotherphase of subsidence related to a subduction polarity reversal. These transient vertical crustalmotions are under-detected by thermochronologic methods, but are likely to be characteristicof continental growth by arc accretion over geologic timescales.