In uplifting mountains, hillslopes steepen toward a threshold angle set by substrate material strength. Hillslopes beyond the threshold angle, referred to as excess topography, are mechanically unstable. The residence time scale of rock masses in excess topography (Tex) is critical for understanding time scales of surface processes and landscape evolution in steep mountains. However, Tex remains loosely constrained for varying slopes and lithologies. Here, we calculate Tex in the eastern Tibetan mountains by quantifying excess topography across lithologies, long‐term landslide erosion rates caused by seismicity and climate, and exhumation rates. Tex increases with local slope angles and is of the same order of magnitude across different lithologies but slightly longer for metamorphic rocks. Range‐scale Tex is estimated as ∼61–157 kyr, ∼3–9% of the relief‐rejuvenation timespan of threshold topography. Similar Tex regardless of lithologies and methods suggest steady‐state construction and erosion of excess topography over thousand to million years time scales in this orogen.

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Microcontinents are fragments of continental lithosphere rifted away from a continent, now surrounded by oceanic lithosphere (Abera et al., 2016;Müller et al., 2001). Various mechanisms have been proposed for the isolation and tectonic evolution of microcontinents, each governed by a different tectonic setting (Nemčok et al., 2016). Continental fragments can become isolated by wrench faulting that forms strike-slip duplexes and stepovers between shear zones (e.g., Antobreh et al., 2009) or by horsetail splays via shearing of intervening blocks (e.g., Misra et al., 2014). Rifting across relatively parallel and overlapping spreading centers can also isolate microcontinents by two zones of extension and two sub-parallel transform boundaries (Nemčok et al., 2016) that can accommodate block rotation (Molnar et al., 2018). The role of a given microcontinent formation mechanism in the evolution of a plate boundary can be evaluated by constraining the orientation, sense of slip, and age of faulting on a microcontinent. However, most microcontinents are submarine (e.g., Nemčok et al., 2016), making them difficult to study.