Mesozoic–Cenozoic multistage tectonic evolution of the Pamir: Detrital fission‐track constraints from the Tajik Basin

Abstract

Knowledge of the tectonic history of the Pamir contributes to our understanding of both the evolution of collisional orogenic belts as well as factors controlling Central Asian aridification. It is, however, not easy to decipher the Mesozoic-Cenozoic tectonics of the Pamir due to extensive Neogene deformation in an orogen that remains largely understudied. This study reports detrital apatite and zircon fission-track (FT) ages from both the eastern Tajik Basin sedimentary rocks and Pamir modern river sands. These FT data, supported by vitrinite reflectance and zircon and apatite U-Pb double dating, suggest that the majority of the FT ages are unreset and record exhumation stages of the Pamir, which has served as the source terrane of the Tajik Basin since the Cretaceous. Furthermore, we combine the new data with a compilation of published detrital apatite and zircon FT data from both the Tajik Basin sedimentary rocks and Pamir modern river sands, to explore the Mesozoic-Cenozoic tectonic history of Pamir. Deconvolved FT Peak Ages document two major Mesozoic exhumation events associated with the Late Triassic-Early Jurassic Cimmerian orogeny that reflects accretion of the Pamir terranes, as well as the Early-early Late Cretaceous deformation associated with the northward subduction of the Neo-Tethys Ocean beneath Pamir.The compiled data also show significant Late Eocene-Neogene exhumation associated with the ongoing formation of the Pamir, which peaks at ca. 36, 25, 14 and 7 Ma.

Meso–Cenozoic Exhumation in the South Qinling Shan (Central China) Recorded by Detrital Apatite Fission-Track Dating of Modern River Sediments

“…You et al [28] reported that the concentration of peak age fluoclastic apatite fission tracks in the Daba Shan during the early Cenozoic occurred predominantly at 37 Ma (Figure 7(26)). The zircon and apatite fission-track ages near the source of the Hanjiang River constrain the timing of exhumation to 40 Ma [17] (Figure 7 (27)). The bedrock apatite fission-track and (U-Th)/He age confirm the exhumation of the western South Qinling Shan at (Figure 7 (28)).…”

“…The low-temperature thermochronological age of clastic sediments from rivers that flow in linear orogenic belts can provide more detailed information about the exhumation history of the orogenic belt [18][19][20][21]. This method has been extensively employed in the investigation of exhumation processes in linear orogenic belts, particularly the Alps in Europe [22][23][24], the Andes in South America [25], and the Tian Shan in Asia [26,27]. While conducting a modern fluvial apatite fission-track analysis on the tributaries of the Hanjiang River, You et al [28] primarily focused their study on the exhumation history of the Daba Shan, which is a branch of the Qinling Shan (Figure 2b).…”