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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

The Altyn Tagh fault, located in the northern Tibetan Plateau, is a large left-lateral strike-slip fault heavily responsible for the growth and formation of the plateau during Cenozoic time. Despite its significance, the initial timing and kinematic patterns of movement along the Altyn Tagh fault remain highly debated. Here, we present a detailed analysis of the stratigraphy and geochronology of three key lithologic sections (Tula, Anxi, and Caishiling) along the Altyn Tagh fault to better understand this kinematic history. By correlating stratigraphic contacts and lithology with the U-Pb age spectra of Mesozoic samples within the western Qaidam Basin, we find the Altyn Tagh fault has experienced a total of ~360 km of displacement during the Cenozoic. By combining seismic profile data with geologic observations, we divide the activity along this fault into two distinct stages of motion:(1) an initial stage, which occurred between early Eocene (ca. 49 Ma) and mid-Miocene time (ca. 15 Ma) and resulted in ~170 km of offset, and (2) an early stage, which began in the late Miocene Epoch and continues into the present, resulting in ~190 km of offset along the fault. We identify the Tula and Anxi sections as piercing points along the western segment of the Altyn Tagh fault and define these regions as residual parts of the original Qaidam Basin. These estimates suggest that motion along the Altyn Tagh fault has accelerated from an average left-lateral strike-slip rate of ~5.0 mm/yr during initial stage faulting to a rate of ~12.6 mm/yr between the late Miocene Epoch and present day.

Northward growth of the Qimen Tagh Range: A new model accounting for the Late Neogene strike-slip deformation of the SW Qaidam Basin. Tectonophysics, Elsevier, 2014, 632, pp.32-47. 10.1016/j.tecto.2014 A C C E P T E D M A N U S C R I P T initially a left-lateral strike-slip fault system rather than a thrusting system. Growth strata indicate an Early Miocene onset age for this strike-slip deformation. However, earthquakes focal mechanisms show that the present-day tectonic pattern of this fault system is dominated by NE-SW transpression. As for the Qimen Tagh fault system, numerous linear geomorphic features and fault scarps indicate that it was again a strike-slip fault system. Deformed sediments within the Adatan Valley prove that strike-slip motion prevailed during the Pleistocene, yet the present day deformation is marked by NE-SW transpression. Collectively, the Kunbei and Qimen Tagh fault systems were initially left-lateral strike-slip fault systems that formed during Early Miocene and Pleistocene respectively. Colligating with these southward younging left-lateral strike-slip faulting ages and the fact that these convex-northward structures converge to the center segment of active Kunlun Fault in the east, we thus considered the Kunbei and Qimen Tagh fault systems as former western segments of the Kunlun Fault once located further south in the present-day location of that fault. These faults gradually migrated northward since the Early Miocene while their kinematics changed from left-lateral strike-slip motion to NE-SW transpression. ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT

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