No abstract

The Tibetan Plateau is characterized by high elevation and complex fault systems. High‐precision vertical movement data can provide important constraints for understanding the growth and expansion of the Tibetan Plateau. We collected approximately 116,000 km of leveling data, 21 continuous GNSS data sets, and their connecting surveying data; we jointly processed these data using a Helmert joint adjustment method to acquire the high‐precision vertical velocity field of the Tibetan Plateau and its surrounding areas. The primary results are as follows: (a) Vertical uplift is dominant on the southern, northeastern, and southeastern margins of the plateau, with uplift rate ranges of 2.0–3.0, 1.0–3.8, and 1.0–2.0 mm/yr, respectively; (b) Conspicuous subsidence is located along the southern portion of the Ganzi fault, with vertical rates ranging from −3.3 to −0.5 mm/yr; (c) Velocity profiles show that vertical deformation varies in different parts of the Tibetan Plateau, which is mostly accommodated by large strike‐slip and thrust faults, such as the Kunlun, Ganzi, and Longmenshan faults. Most of the surface uplift is accommodated by crustal shortening in the interior of the Tibetan Plateau; abrupt changes in vertical rates in eastern Tibet and the widely distributed surface subsidence of southeastern Tibet are consequences of crustal flow and gravitational collapse. Overall, the Tibetan Plateau is characterized by continuous deformation, with large spatial variations accommodated by complicated tectonic processes.

Understanding the tectonic nature of the Alxa area is significant in tectonic reconstruction of the Central Asian Orogenic Belt, but their tectonic correlation, affinity, and implications have not been well defined. The late Palaeozoic sediments in the northern Alxa area can help to understand this question. The sedimentary sequence of the late Palaeozoic strata (Benbatu Formation) indicates that the sedimentary environment of the study area gradually changed from a stable carbonate platform to a bathyal‐abyssal environment with relatively active tectonic setting. The results of the grain size analysis of the sandstone debris show the typical characteristics of a turbidity current. The composition of clastic particles is mainly feldspar, which is characterized by short transport distance and rapid deposition of sediments. Combined with the geochemical characteristics of sandstone, the northern Alxa Block is considered to be an active continental margin in the late Palaeozoic. Through summarizing the zircon data of the Alxa Block, Tarim Craton, and North China Craton, it is concluded that the Palaeozoic clastic zircons in the study area come from the Alxa Block and the surrounding magmatic arc, the Neoproterozoic‐Middle Proterozoic zircons come from the Alxa Block, the Archean zircons come from the North China Craton. According to the age distribution of clastic zircons, the magmatic activity may exist in the early Palaeozoic, which suggests it may not be a stable passive continental margin in the margin of northern Alxa Block in the early Palaeozoic. Based on the provenance analyses, the sources block shows no tectonic affinity to the Tarim Craton, but the Hanwula area in the north of the study area might have been accreted to the Tarim Craton, which means the size of the Paleo‐Asian Ocean between the study area and the Hangwula area is large. The earliest Palaeozoic clastic zircon ages in sedimentary rocks are recorded in the late Cambrian, whereas the earliest Palaeozoic detrital zircons in the Hangwula area are recorded in the Ordovician, which means that the magmatic activity recorded in the study area is earlier than the Hangwula area and indicates that the subduction of the south side of the Paleo‐Asian Ocean began earlier than the north side. The evidence of magmatic rocks discovered so far confirms this view.