Qingquan Meng’s research while affiliated with Lanzhou University and other places

The uplift of the Tibet Plateau (TP) during the Miocene is crucial to understanding the evolution of Asian monsoon regimes and alpine biodiversity. However, the northern Tibet Plateau (NTP) remains poorly investigated. We use pollen records of montane conifers (Tsuga, Podocarpus, Abies, and Picea) as a new paleoaltimetry to construct two parallel midrange paleoelevation sequences in the NTP at 1332 ± 189 m and 433 ± 189 m, respectively, during the Middle Miocene [~15 million years ago (Ma)]. Both midranges increased rapidly to 3685 ± 87 m in the Late Miocene (~11 Ma) in the east, and to 3589 ± 62 m at ~7 Ma in the west. Our estimated rises in the east and west parts of the NTP during 15 to 7 Ma, together with data from other TP regions, indicate that during the Late Miocene the entire plateau may have reached a high elevation close to that of today, with consequent impacts on atmospheric precipitation and alpine biodiversity.

Cretaceous‐Miocene sedimentary rocks in the Nepalese Lesser Himalaya provide an opportunity to decipher the timing of India‐Asia collision and unroofing history of the Himalayan orogen, which are significant for understanding the growth processes of the Himalayan‐Tibetan orogen. Our new data indicate that detrital zircon ages and whole‐rock Sr‐Nd isotopes in Cretaceous‐Miocene Lesser Himalayan sedimentary rocks underwent two significant changes. First, from the Upper Cretaceous‐Paleocene Amile Formation to the Eocene Bhainskati Formation, the proportion of late Proterozoic‐early Paleozoic zircons (quantified by an index of 500‐1200 Ma/1600‐2800 Ma) increased from nearly 0 to 0.7‐1.4, and the percentage of Mesozoic zircons decreased from ~14% to 5‐12%. The whole‐rock 87Sr/86Sr and εNd(t=0) values changed markedly from 0.732139 and ‐17.2 for the Amile Formation to 0.718106 and ‐11.4 for the Bhainskati Formation. Second, from the Bhainskati Formation to the lower‐middle Miocene Dumri Formation, the index of 500‐1200 Ma/1600‐2800 Ma increased to 2.2‐3.7, and the percentage of Mesozoic zircons abruptly decreased to nearly 0. The whole‐rock 87Sr/86Sr and εNd(t=0) values changed significantly to 0.750124 and ‐15.8 for the Dumri Formation. The εHf(t) values of Early Cretaceous zircons in the Taltung Formation and Amile Formation plot in the U‐Pb‐εHf(t) field of Indian derivation, whereas εHf(t) values of Triassic‐Paleocene zircons in the Bhainskati Formation demonstrate the arrival of Asian‐derived detritus in the Himalayan foreland basin in the Eocene based on available datasets. Our data indicate that (1) the timing of terminal India‐Asia collision was no later than the early‐middle Eocene in the central Himalaya, and (2) the Greater Himalaya served as a source for the Himalayan foreland basin by the early Miocene. When coupled with previous Paleocene‐early Eocene provenance records of the Tethyan Himalaya, our new data challenge dual‐stage India‐Asia collision models, such as the Greater India Basin hypothesis and its variants and the arc‐continent collision model.

The formation of high topography on the northeastern margin of the Tibetan Plateau (the Qilian Shan) constrains the evolutionary history of the plateau. Although prominent exhumation occurred in the middle–late Miocene, the time at which deformation and relief development began in the Qilian Shan during the Cenozoic remains highly debated. Here, we use low-temperature thermochronology to reveal the histories of topographic growth in the Qilian Shan. Two transects were sampled in two primary thrust belts (Qaidam Shan and Danghenan Shan) in the southern Qilian Shan. New apatite fission track ages range from 16.6 to 113 Ma, and apatite (UTh)/He ages range from 8.4 to 63.5 Ma. Age–elevation relationships and thermal modeling show enhanced rock exhumation in the late Paleocene–early Eocene and middle–late Miocene in both transects. The results indicate two pulses of enhanced thrusting on the major thrust belts in the southern Qilian Shan in the late Paleocene–early Eocene and middle–late Miocene. Our findings imply an early Cenozoic onset of topographic growth in the northeastern Tibetan Plateau, which was quasi-synchronous with the India–Asia collision.

In this paper, we present organic carbon isotope records from continental sediments spanning the late Paleocene-middle Miocene (57.9–15.0 Ma) in the Lanzhou Basin, northeastern Tibetan Plateau to investigate terrestrial ecosystem-response to global climate change. The continuous sediment δ¹³CTOC values that we obtained range from −27.83‰ to −20.05‰. Combining these data with the sediment C/N ratios and n-alkane distribution, we infer that the major source of sediment organic matter was terrestrial C3 plants. Furthermore, we note that both sediment δ¹³CTOC and δ¹³Cn-alkanes values gradually become more positive from 57.9 to 26 Ma and then become relatively more negative from 26 to 15 Ma. These δ¹³C values vary closely with global temperature changes. We propose that global temperature controlled δ¹³C values with cooler conditions resulting in less rainfall in inland Asia, and vice versa. Therefore, mainly driven by the global temperature, the regional climate in the Lanzhou Basin gradually changed from warm-wet to cold-dry conditions during 57.9–26 Ma, and the climatic conditions became warmer and wetter again after 26 Ma. This long-sequence terrestrial ecologic environment study obtained from the northeast Tibetan Plateau powerfully demonstrates the first-order role of global climate in regulating the long-term evolution of regional environment.

Timing and patterns of the Cenozoic deformation of the Qilian Shan orogenic belt (QSOB) in the northern Tibetan Plateau are key to elucidating the mechanism(s) of plateau growth but remain matters of debate. The Oligocene-Miocene sediments in the Subei Basin, an intermontane basin situated at the junction of the central and southern QSOB, provide direct insight into the Cenozoic deformation of the QSOB. Here, a comprehensive provenance study based on detrital zircon geochronology, paleocurrents, conglomerate components and sedimentary facies in the Subei Basin demonstrates that this region experienced three stages of tectonic events during the Cenozoic. (1) Oligocene strata contain zircons of 200-300, 400-500, 700-1000, 1600-2000 and 2400-2700 Ma, indicating primary derivation from recycled Mesozoic sedimentary rocks in the QSOB and suggesting early Cenozoic deformation in this region. (2) One sample (21.5 Ma) yields similar age populations to those of Oligocene samples, except for the complete disappearance of 200-300 Ma zircons as a result of the widespread deformation of the QSOB. (3) Two samples (18.5-13.6 Ma) show a unimodal age cluster at 400-500 Ma, while one sample (9 Ma) contains zircon ages similar to those of Oligocene samples, indicating tectonic uplift of the southern QSOB in the middle-late Miocene, which is also recorded by the sedimentary transition from fluvial to alluvial fan. Based on these findings and those of previous studies, we suggest that the entire QSOB has undergone multistage tectonic events since the early Cenozoic due to far-field effects associated with the India-Eurasia plate collision and the continued convergence.

The Cenozoic tectonic evolution of the North Qaidam-Qilian Shan fold-thrust belt in the northern Tibetan Plateau is important to understanding the tectonic rejuvenation of orogeny and growth of the plateau. However, the deformation processes in this region remain controversial. This study presents new apatite fission track (AFT) data from Paleogene strata in the northern Qaidam Basin to investigate the time of deformation in this site. Thermal modeling of these partially annealed detrital AFT ages shows a thermal history with a noticeable transition from heating to cooling after ∼10 Ma. This transition is attributed to the intensified thrusting and folding of the northern Qaidam Basin since ∼10 Ma. Integrated with published tectonics and thermochronology results, we suggest the North Qaidam-Qilian Shan fold-thrust belt experienced prevailing tectonism since the late Miocene.