Reconciliation of the Early Slip History of the Altyn Tagh Fault, Northern Tibetan ()
1. Introduction
Large scale displacement and associated crustal thickening along the Altyn Tagh fault (ATF) have exerted a crucial influence on the geology and geography of Tibetan plateau. Although the modern ATF terminates near the Jiuxi Basin, its eastward extension in early slip history is the debate focus [1] [2] , which is a key to understanding the timing and mechanisms of crustal deformation in the northern Tibetan plateau.
Furthermore, sedimentary basins adjacent to the ATF have been subjected to Early Cretaceous widespread extension and early Late Cretaceous significant inversion, and Late Cretaceous sequence is missing. Similarly, rift basins experienced analogical inversion in East Asia affected by Paleo-Pacific tectonism during the early Late Cretaceous, such as Yin-Er Basin, East Gobi Basin, Erlian Basin and Songliao Basin, etc. Yang [3] proposed a dextral strike-slip fault system in North China due to the collision of the Okhotomorsk Block with East Asia. In addition, right-lateral movement has been recognized after tectonic inversion in East Gobi Fault Zone [4] . If ATF could extend beyond the Tibetan Plateau and link with strike-slip faults in East Asia, its nature in late Cretaceous will be redefined.
2. Approach and Result
In this study, we investigated sediment source variation in western Jiuxi Basin before and after tectonic inversion. Paleocurrent directions towards the SE-SW in the field, indicating evince sediment main derivation from the opposing side of the ATF. So considering possible strike-slip displacement, potential sediment sources are mountains on the north side of ATF, including Beishan, Dunhuang and Altyn Blocks. Besides, Qilian shan is usually regarded as one of the most important provenance of the Jiuxi Basin.
In terms of Early Cretaceous Samples from the Hongliuxia area, detrital garnet and rutile composition both indicate middle and high grade metamorphic rocks exposed in the provenance. Moreover, a single U-Pb peak age of detrital monazite is at ca. 375 - 440 Ma and 20 - 40 Ma younger than the early Paleozoic peaks of detrital zircon, matching with the timing of metamorphic events in the Dunhuang Block [5] .
Late Eocene detrital zircon separated from Hongliuxia and Huoshaogou area are characterized by the absence of Paleozoic and Mesozoic ages, these materials are mainly derived from the Neoproterozoic basement in southern margin uplift of the Xorkol Basin and eastern tectonic melange zone of North Altyn Area [6] [7] .
3. Tectonic Implications
1) The results of provenance analysis show Late Cretaceous dextral movement and >450 km sinistral offset since Late Eocene along the eastern ATF near Jiuxi Basin. Relatively, larger sinistral offset along the middle part of ATF means that currently available estimates of offset based on displaced Paleozoic and Jurassic rocks could not represent maximum offset which weakened by late Cretaceous dextral offset.
2) Early Late Cretaceous basins inversion and Late Cretaceous dextral movement along ATF are dominated by the far-field effects of Okhotomorsk Block-East Asia collision during ca 100 - 80 Ma.
Acknowledgements
This work was funded by the National Natural Science Foundation of China (No. 41102064). This is a contribution to UNESCO-IUGS IGCP Project 679.