Paleocene-Early Eocene uplift of the Altyn Tagh Mountain: Evidence from detrital zircon fission track analysis and seismic sections in the northwestern Qaidam basin

摘要

Most existing tectonic models suggest that the deformation and uplift of the northern Tibetan Plateau is the latest crustal response to the collision of the India Plate and Eurasian Plate. The tectonic evolution of Altyn Tagh Mountain (hereafter called simply the "Altyn Tagh"), on the northern margin of the Tibetan Plateau, has attracted considerable scientific attention. In this study, we use fission track age dates of detrital zircons from the northwestern Qaidam basin together with sedimentary observations to understand more fully the Cenozoic tectonic uplift of the Altyn Tagh. Detrital zircons from five borehole samples distributed in different folds in the northwestern Qaidam basin yielded ages mainly ranging from 88.5 to 49.2 Ma, older than their sedimentary deposition ages (43.8-22 Ma). The binomial distribution in grain age fitted peaks was generally dominated by one young peak, P-1, which varied from 73.6 to 47.2 Ma. A thinning of the Cenozoic Lulehe Formation (53.5-43.8 Ma) stretched from the inner Qaidam basin to the slopes of the Altyn Tagh in the seismic sections of the northwestern Qaidam basin. Based on magnetostratigraphic dating, there was a hiatus in sedimentation in the Qaidam basin between 65 Ma and 54 Ma; this was confirmed by seismic profiles and borehole data, which show an unconformity between the Mesozoic Quanyagou Formation and the Lulehe Formation. Combined with an analysis of provenance, the detrital zircon young peak age and the sedimentary record revealed that the most significant regional uplift of the Altyn Tagh occurred during the Paleogene-Early Eocene, almost coinciding with the collision of the Indian and Eurasian plates between 65 Ma and 44 Ma.