How young mountains can be formed and preserved in foreland basins

Typical anticline mountains in the northern foothills of the Tianshan Mountains interact with rivers Photographed by Lü Honghua

A typical anticline mountainous and river-river interaction 3D terrain rendering of the northern foothills of the Tianshan Mountains courtesy of ArcGIS Online

The team of Pan Baotian, a professor at Lanzhou University, estimated the critical uplift rate of young mountain formation and conservation in the northern foothills of the Tianshan Mountains through numerical simulations, and the study began with the question “How can young mountains form and conserve in the foreland basin?” Recently published online in Science Bulletin.

The growth process of active orogenic belts is an important basis for in-depth understanding of regional geomorphological evolution and environmental evolution. The foreland basins of the orogenic belt are richly developed and continuous sedimentary records, and the geomorphological sequences are well preserved, which is a natural laboratory for exploring the relationship between tectonic deformation and mountain growth. Previous studies have revealed geological records (e.g., cryogenic thermochronology and sedimentology) about tens of millions of years of tectonic evolution, while geomorphological evidence has documented relatively young mountain topographic evolution. In the northern foothills of the Tianshan Mountains in China, there is a problem of “non-co-evolution” of “old structures” and “young landforms”. Studies have shown that the growth deformation of the inverse fracture-fold structure in the northern foothills of the Tianshan Mountains mostly began in the Neogene period, but the anticline mountains in front of the mountains only began to appear in the Late Quaternary Period. A more reasonable explanation is that the geological structure needs to face the sweeping and erosion of the pre-mountain pre-formation river in the early stage of growth, so only when the structural uplift rate exceeds the erosion capacity of the pre-formed river, the terrain can be preserved and continue to grow.

The two rows of inverse fault-anticline structure on the northernmost side of the Tianshan Mountains are currently in a continuous growth process, and the dorsal terrain of Belt II is in a typical juvenile stage, indicating that its uplift rate overcomes the river erosion capacity and has exceeded the critical uplift rate of juvenile terrain survival. Constraining the age and rate of these anticline strong uplifts is of great reference value for understanding the “non-co-evolution” mechanism of tectonic deformation and mountain growth in foreland basins. However, due to the spatial-temporal dispersion of geomorphological evidence and the limitations of chronological methods, it is difficult for traditional methods to directly obtain the critical ebb rate required to form an anticline terrain and be preserved. (Source: China Science Daily Wen Caifei Faisa)

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