Previously unrecognized, 1000 km-long Qixiang Co fault governs eastward escape of central Tibet

• We study a ∼1000 km-long sinistral fault in central Tibet: the Qixiang Co fault. • We determine a post ∼120 ka horizontal slip rate of 3.5 ± 0.2 mm/yr along the fault. • This fault connects central Tibet to the Ganzi-Xianshuihe fault in eastern Tibet. • It acts as a major tectonic boundary that governs eastward escape of central Tibet. • Including this fault is now essential in models of Tibetan Plateau deformation. A quantitative kinematic model of present-day deformation across the Tibetan Plateau is essential to understand its growth mechanism. Dominant dextral movement along the ≥2500 km-long Karakorum-Jiali fault zone, long considered the southern boundary of plateau-wide eastward extrusion, was later challenged by a locally restrained, symmetrical shortening model co-involving short (200-300 km) conjugate strike-slip faults. Here, based on meter-resolution satellite data and field measurements, we document a previously undocumented, ∼1000 km-long, ∼ENE to E-trending sinistral fault, the Qixiang Co fault (QXCF), that wholly crosses central Tibet to connect the Ganzi-Xianshuihe fault in eastern Tibet with the Gyaring Co fault and Tangra Yum Co rift in central/southern Tibet. High-resolution unmanned aerial vehicle (UAV) topographic surveys, 10 Be cosmogenic and U-series dating of a lake shoreline and several alluvial fans at 3 sites ∼240 km apart, show that up to ∼450 m of sinistral offset accrued in the last ∼120 ka, implying a horizontal slip rate of 3.5 ± 0.2 mm/yr along the fault. Four recent large paleoearthquakes ( M w 7.9–8.0) may have ruptured a > 300 km stretch of the QXCF with characteristic slips of ∼9–10 m and return times of ∼2500–2900 a. Such results demonstrate that the hitherto previously undocumented QXCF is the single most important tectonic boundary across the Qiangtang terrane, contributing predominantly to large-scale eastward escape of central Tibet and challenging the ‘V-shaped conjugate faults’ model. Including this major fault is thus now essential in models of Tibetan Plateau deformation.