Continental-scale shear zones play an important role in accommodating block extrusion and rotation as shown by deformation on the Ailaoshan-Red River shear zone (ASRRSZ) in the SE Tibetan Plateau. This study presents 13 apatite (U-Th)/He, 11 zircon (U-Th)/He, and three apatite fission track dates, together with thermal modeling in the Ailaoshan and Xuelongshan segments (ALSZ and XLSZ) of the shear zone to investigate its Cenozoic exhumation history and mechanism, which are critical for understanding its tectonic and landscape evolution. Our results, combined with published chronologic data, reveal that shear zone rocks along the ALSZ experienced prominent and rapid cooling from high temperature (>500°C) to 120-60°C at a rate of 75-100°C/Myr during 29-17 Ma with northwestward younging onset. A second, lower magnitude accelerated cooling occurred at 14-10 Ma along the ALSZ at a rate of 20-30°C/Myr, with a later initiation on the XLSZ at~5 Ma and continuing to present with a cooling rate of~20°C/Myr. Thermal modeling reveals a single rapid cooling phase with a rate of 17-14°C/Myr in the Eocene to early Oligocene for samples outside the shear zones. These three fast cooling episodes are directly related to deformation stages including crustal shortening across the SE plateau, sinistral ductile shearing along the ASRRSZ, and dextral faulting with a dip-slip component on the Red River and Weixi-Qiaohou faults along the shear zone flanks. Furthermore, the northward migration of kinematic reversal and associated cooling along strike since the mid-late Miocene likely reflects the northward advance of the eastern Himalayan syntaxis.

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Supplemental file 1 Geology of the Babu ultramafic-mafic complex and sample DescriptionsThe Babu ultramafic-mafic complex in the Malipo county, southeastern Yunnan, outcrops in a tectonic nappe between the NW-striking Wenshan-Malipo and Funing strike-slip faults (Fig. 2a; YunnanBGMR 1990). The autochthonous strata are Devonian and Triassic argillaceous and sandy turbidites. The exotic Permian-Carboniferous limestones overlying structurally onto the turbidites may have been deposited originally in seamounts or oceanic islands (Xu et al. 2008a; Zhang et al. 2013a). The Babu ultramafic-mafic complex is distributed in a belt of about 20 km-long and 4 -8 km-wide, and in fault contact with the Triassic Lanmu Formation (T3l; Fig. 2; Xu et al. 2008a; Zhang et al. 2013). The Babu ultramafic-mafic complex is composed of three major units from the base upward: meta-peridotite, diabase-gabbro and mafic lava. No layered gabbro or sheeted dikes have been recognized (Wu et al. 1999; Xu et al. 2008a; Zhang et al. 2013). The meta-peridotite is overlain tectonically by a diabase-gabbro assemblage. The basalt is in fault contact with the meta-peridotite, and the relationship between the basalt and the diabase-gabbro assemblage is not clear.Although strongly serpentinized, the meta-ultramafic rocks are identified as mostly harzburgites with minor pyroxenites and lherzolites (Supplemental file 2).Serpentinized harzburgites show a gray to black to dark green color and strong mylonitic foliations. Major original minerals include pyroxene (50%-55%), olivine (30%-35%), plagioclase (3%-5%), and magnetite (1%-2%). Altered minerals are mainly talc and serpentine (Supplemental file 2b). Fresh olivine is scarce. Most olivine grains have been altered to serpentine, chlorite and talc, whereas pyroxene is altered to bastite. Plagioclase blebs, altered to clay, were noted in some samples.Pyroxenite is composed of subhedral to euhedral clinopyroxene with varying amounts of olivine and extremely rare orthopyroxene.Metagabbro and metadiabase crop out as massive isotropic gabbro and dikes (Fig. 2). They show dark green color and massive structure (Supplemental file 3). Major minerals include augite, plagioclase, hornblende, and magnetite, and olivine in some samples. Most of the augite grains have been altered into amphibole, epidote or chlorite. Plagioclase is more euhedral and has been altered to clay. Amphibole show mainly hypidiomorphic and granular structure and is mainly from the alteration of pyroxene. The amphibole surrounds the euhedral-subeuhedral plagioclase. The metadiabases have ophitic textures, and consist of plagioclase, pyroxene, hornblende and ilmenite (Supplemental file 3). Sparse plagioclase phenocrysts are altered to clay and calcite. Pyroxene is altered to amphibole or chlorite.The mafic lavas consist of massive basalt, amygdaloidal basalt and porphyritic basalt (Supplemental file 3). Pillow basalt also crops out in the Tongchang village being inter-bedded with cherts and limestones (Fig. 2). They show mainly greenschist facie...