Provenance and tectonic setting of the Palaeozoic sediments in the northern Alxa area: Implications for the Central Asian Orogenic Belt

Abstract

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.

Accretionary tectonics, deep structures and metallogeny of southern Altaids

“…The late Palaeozoic sediments in the northern Alxa area can help to understand critical questions such as tectonic correlation, affinity, and implications of the Alxa area. Provenance analyses performed by Yin et al (, this issue) indicate that the Palaeozoic sediments in the northern Alxa were deposited in an active continental margin in the late Palaeozoic, with 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. Detrital zircon data also reveal that the subduction of the south side of the PAO began earlier than the north side.…”

Kinematics, strain patterns, rheology, and geochronology of Woka ductile shear zone: Product of uplift of Gangdese batholith and Great Counter Thrust activity

“…The LA–ICP–MS U–Pb method was applied to zircon grains obtained from the granitic mylonite zone in the south of the Woka ductile shear zone (1 sample, B–TW1, sampling location shown in Figure 2). Zircon selection, mounting, photography, and CL imaging were performed at the laboratory of Hebei Regional Geological Survey Institute (for the specific sample processing method, see Yin et al, 2020). The LA–ICP–MS U–Pb zircon analysis was performed at the Tianjin Institute of Geology and Mineral Resources, China.…”

“…From north to south, the Tibetan Plateau is divided into the Songpanganzi Terrane, the Qiangtang Terrane, the Lhasa Terrane, and the Indian Terrane (Yin et al, 2020). Among these, the Lhasa Terrane includes the Bangong-Nujiang Suture Zone (BNSZ), the Shiquan River-Nam Tso Mélange Zone (SNMZ), the Luobadui-Milashan Fault (LMF), and the Indus-Yarlung Zangbo Suture Zone (IYTSZ).…”

“…The Tibetan Plateau is bounded by the three structural suture zones of the Jinshajiang Suture Zone (JSSZ), the Bangong–Nujiang Suture Zone (BNSZ), and the Indus–Yarlung Zangbo Suture Zone (IYTSZ). From north to south, the Tibetan Plateau is divided into the Songpanganzi Terrane, the Qiangtang Terrane, the Lhasa Terrane, and the Indian Terrane (Yin et al, 2020). Among these, the Lhasa Terrane includes the Bangong–Nujiang Suture Zone (BNSZ), the Shiquan River–Nam Tso Mélange Zone (SNMZ), the Luobadui–Milashan Fault (LMF), and the Indus–Yarlung Zangbo Suture Zone (IYTSZ).…”