Meso-Cenozoic thermo-tectonic evolution of the Yili block within the Central Asian Orogenic Belt (NW China): Insights from apatite fission track thermochronology

The Yili block in the Central Asian Orogenic Belt (CAOB), forms the easternmost part of the Kazakhstan collage system. Exploring its thermo-tectonic history is important to reconstruct the intra-continental evolution of the Tianshan belt. In this contribution, we report new apatite fission track (AFT) data from the basement rocks from the northern (i.e. the Wenquan complex) and southern (i.e. the Dahalajunshan - Nalati range) margins of the Yili block. Thermal history modeling reveals that the Wenquan complex underwent moderate basement cooling in the Cretaceous, possibly due to far-field effects of the Tethys-deformation and the following Lhasa-Qiangtang collision. These events at the southern Eurasian margin propagated tectonic stress to the northern Yili and triggered localized deformation. Early Triassic-middle Jurassic moderate cooling is also identified in the Dahalajunshan - Nalati range, and is interpreted to be related to the post-orogenic strike-slip motion along the major shear zones and the effects of the Qiangtang and Kunlun-Qaidam collision. Combined with the published thermochronological data, it is suggested that the northern and southern parts of the Yili block experienced different Mesozoic thermo-tectonic evolution. Basement cooling of the northern Yili block generally took place before the Cretaceous, exhuming shallower crustal levels as compared with the southern one. The intermontane Yili basin may have accommodated substantial propagated contraction induced by the Cretaceous collisional events. Based on our new results and the previously published thermochronological data, it is suggested that the intra-continental reactivation of the North Tianshan and Nalati faults probably did not invoke significant regional exhumation during the Meso-Cenozoic. Instead, small-scale brittle faults controlled localized enhanced denudation.