Understanding the tectonic geomorphological evolution of the northeastern margin of the Tibetan Plateau (NETP) is crucial for deciphering the mechanisms of plateau uplift and lateral growth. Previous low- temperature thermochronological investigations have predominantly focused on fault- bounded domains, delineating the Cenozoic northeastward expansion of the Tibetan Plateau through episodic fault- driven exhumation. However, thermochronological data from inter- fault block areas remain limited, with pre- Cenozoic ages (e.g. , 153~92 Ma in the Xining Basin and 153~98 Ma in the Xunhua basin) suggesting minimal preservation of Neogene tectonic signals in these stable blocks. To resolve the uplift- erosion history of these relatively tectonically stable regions, this study conducted apatite fission track analyses on six granite samples collected from the Longyang Gorge and Hudan River headwaters east of Qinghai Lake. By integrating thermal history inversion modeling and regional exhumation rate quantification using Age2exhume software, we identify two key findings: ① A pronounced phase of rapid cooling initiated less than 10 Ma ago in intra- block areas, indicating ongoing northeastward plateau expansion; ② Enhanced exhumation rates (peaking at ~0. 27 mm/a) and substantial cumulative erosion (＞3 km) along the Laji Mountain- Jishi Mountain belt since the mid- Miocene, directly correlating with intensified fault activity during this period. This study bridges the gap between fault zones and stable intra- block domains, providing critical thermochronometric constraints on the spatiotemporal progression of plateau expansion. Our results demonstrate that the NETP' s northeastward growth involved both fault- driven deformation and intra- block crustal adjustment, offering new insights into the interplay between tectonic forcing and landscape evolution during orogenic plateau development.