Late Cenozoic exhumation history of the Luoji Shan in the southeastern Tibetan Plateau: insights from apatite fission-track thermochronology

Abstract

Denudational history inferred from bedrock low-temperature thermochronological data provides significant constraint to tectonic models for explaining the growth of the Tibetan Plateau. Here, we present new apatite fission-track ages from the Luoji Shan, bounded by the Anninghe and Zemuhe faults in the southeastern Tibetan Plateau. Cooling ages vary from c. 5 to c. 13 Ma from the bottom to the top of a vertical profile. The age–elevation relationship can be interpreted as either (1) a phase of river incision at a rate of c. 0.16 km Ma −1 from c. 13 to c. 5 Ma or (2) a phase of denudation of c. 0.40 km Ma −1 between c. 13 and c. 10 Ma, followed by a phase of extremely slow denudation ( c. 0.03 km Ma −1 ). The results suggest that initiation of river incision started before c. 13 Ma in the study area. Combined with previously published data from adjacent sites, our results indicate that denudation in this region displayed substantial spatial variation. This finding does not support the existing lower crustal flow model for Tibetan Plateau growth, which predicts uniform denudation. We further speculate that the vertical component of slip along the southern extension of the Anninghe fault might have significantly declined since late Miocene time, explaining the decreased rate of erosion c. 10 Ma.