New Constraints on the Late Oligocene‐Miocene Thermo‐Tectonic Evolution of the Southeastern Tibetan Plateau From Low‐Temperature Thermochronology

Abstract

The southeastern (SE) Tibetan Plateau (Yunnan) is characterized by low‐relief uplands that were deeply incised by large rivers. The thermal history of basement rocks in this region remains poorly investigated, while this data is needed to elucidate the complex relationship between tectonics and climate in shaping the surface. To better understand its thermo‐tectonic evolution, we carried out apatite fission track thermochronology on 31 samples collected from a large area that covers different tectonic units, including a vertical profile in the middle Mekong River valley; additional zircon LA‐ICP‐MS U‐Pb dating was performed on four basement rocks. Our results confirm that a large portion of Mesozoic crystalline rocks constitute the basement of the SE Tibetan Plateau. Inverse thermal history modeling of fission track data reveal extensive late Oligocene to Miocene rapid basement cooling and exhumation episodes from both inside and outside the active zones (i.e., ductile shear zone and river valley). These thermal events were coincident with the activities of large‐scale strike‐slip faults that dominate the structural framework. Combined with the published data, we propose that widespread crustal shortening and thickening took place in the SE Tibetan Plateau during the Oligocene‐Miocene in the context of a compressive tectonic regime. Low‐temperature thermochronological data reveal that both tectonic forcing and climate‐driven erosion have played important roles in exhuming the basement rocks in the region. It is also deduced that the present‐day relatively low‐elevation landscape of the Yunnan area resulted from complex interaction between regional tectonic activity and surficial erosion since the late Oligocene.

Formation of the Great Bend and Enhanced Quaternary Incision of the Upper Yangtze River: New Insights from Low-Temperature Thermochronology and Tributary Morphology

“…Approximately 80 km northwest of the Great Bend (Figure 1 In fact, this Middle-Late Miocene rapid cooling has been widely identified from rocks obtained from most of the major river valleys of southeastern Tibet: from Early Miocene until at least ca. 11 Ma in the Salween River valley [12,39,55], starting during the Middle-Late Miocene in the Mekong River valley [41,48,56], 11-8 Ma for the Yangtze River valley (this study), 14-10 Ma in the Red River valley [15,49], 13-9 Ma in the Dadu River valley [9,57], and starting at ca. 20-14 Ma in the Yalong River valley [57,58].…”

“…The emplacements of these plutons are regarded as indicative of lithospheric delamination or continental subduction during the Eocene [27]. Therefore, recent studies of the Jianchuan Basin have suggested that fluvial incision associated with the generation of topographic relief in SETP occurred during the late Eocene-Early Miocene [5,[10][11][12], implying that the formation of the Great Bend and regional drainage rearrangement took place during the same period.…”

“…35 Ma [10,45], corresponding to widespread rapid exhumation in the SETP since the late Paleogene [10,30,[46][47][48][49][50]. An increasing number of studies have suggested an early stage of Tibetan Plateau uplift since the late Paleogene based on paleo-altimetric, low-temperature thermochronological, and sedimentological data [12,13,19,51,52], accompanied by the widespread intrusion of plutons [5,13,14]. The Oligocene or earlier uplift is also recorded by the boundary faulting of the metamorphic rocks in the Great Bend area, which was characterized by the development of a large-scale décollement at ca.…”

“…Based on provenance studies of sediments from the present-day upper and middle sections of the Yangtze River, which are considered as residues left by the paleo-Yangtze River, the reconfiguration of the modern Yangtze River has been constrained to Early Pliocene-Middle Pleistocene (e.g., [2,3,[6][7][8]). In contrast, low-temperature thermochronological data from the area to the southwest of the Great Bend have provided evidence for widespread rapid river-valley incision during the Oligocene-Early Miocene (e.g., [9][10][11][12]), corresponding to exhumation/basement cooling of the Tibetan Plateau, but no late Cenozoic incision has been documented. In addition, studies of the stratigraphy of basins along the paleo-southward river course have suggested that the eastward flow of the Yangtze River was most likely initiated before the Miocene (e.g., [4,5,13,14]).…”

Fluvial geomorphic parameters of the Shuiluo River Catchment and their tectonic implications, SE Tibetan Plateau

“…Since the Cenozoic, along with the collision of the Indian and Eurasian plates, and resulting compression, the highest in the world has been formed-Tibetan Plateau (Molnar and Tapponnier 1975;England 1997;Chen et al 2017;He et al 2023;Ma et al 2023a, b). The Tibetan Plateau has a profound impact on atmospheric circulation and thus global climate, and is an ideal place for scientific research (Tapponnier 2001).…”