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International audienceMarking the northern boundary of the Tibetan plateau, the Altyn Tagh fault plays a crucial role in accommodatingthe Cenozoic crustal deformation affecting the plateau. However, its initiation time and amount of offset are stillcontroversial despite being key information for the understanding of Tibet evolution. In this study, we present1122 single LA-ICP-MS detrital zircon U–Pb ages obtained from 11 Mesozoic to Cenozoic sandstone samples, collectedalong two sections in the northwestern Qaidam basin (Eboliang and Huatugou). These data are combinedwith new3D seismic reflection profiles to demonstrate that: (1) fromthe Paleocene to early Eocene, the Eboliangsection was approximately located near the present position of Anxi, 360 ± 40 km southwest from its currentlocation along the Altyn Tagh fault, and sediments were mainly derived from the Altyn Tagh Range. At thesame period, the Huatugou section was approximately located near the present position of Tula, ca. 360 kmsouthwest from its current location along the Altyn Tagh fault, and the Eastern Kunlun Range represented a significantsediment source. (2) Left-lateral strike-slip movement along the Altyn Tagh fault initiated during theearly-middle Eocene, resulting in northeastward displacement of the two sections. (3) By early Miocene, the intensivedeformation within the Altyn Tagh Range and northwestern Qaidam basin strongly modified the drainagesystem, preventing the materials derived fromthe Altyn Tagh Range to reach the Eboliang and the Huatugousections. The post-Oligocene clastic material in the western Qaidam basin is generally derived fromlocal sourcesand recycling of the deformed Paleocene to Oligocene strata. From these data, we suggest enhanced tectonic activitywithin the Altyn Tagh Range and northwestern Qaidam basin since Miocene time, and propose an earlymiddleEocene initiation of left-lateral strike-slip faulting leading to a 360 ± 40 km offset along the Altyn Taghfaul