Postorogenic rigid behavior of the eastern Songpan-Ganze terrane: Insights from low-temperature thermochronology and implications for intracontinental deformation in central Asia

The Songpan-Ganze terrane (SGT), formed by Early Mesozoic closure of the Paleo-Tethys Ocean, occupies a large area of the central-eastern Tibetan Plateau. Late Mesozoic and Cenozoic strike-slip deformation has been identified in the surrounding terranes and faults (e.g., western Qinling, Altyn Tagh, and Kunlun faults); however, the coeval evolution of the SGT has not been well explored. We report apatite fission track and apatite and zircon (U-Th)/He data from a >7 km deep borehole and outcrop samples covering an area of >150 x 150 km in the eastern SGT. Thermal history modeling suggests a distinct phase of Late Jurassic-Early Cretaceous (approximate to 150-100 Ma) cooling, followed by a prolonged stage of slow cooling, for all samples despite of their differences in depositional age (Mid-Late Triassic time) and locality within a large area. The ubiquitous Late Jurassic-Early Cretaceous cooling implies little differential deformation in the eastern SGT and is best explained by regional rock uplift resulting from the transpressional strain field created by the contemporaneous Lhasa-Qiangtang collision to the south. Projecting the contemporaneous deformation surrounding the SGT onto an Early Cretaceous paleogeographic terrane reconstruction results in a new tectonic model. The model relates the Lhasa-Qiangtang collision to tens to hundreds of kilometers of shearing along the Altyn Tagh and Kunlun faults, which transferred strain into central Asia (e.g., Qinling-Dabie orogen). Results of this study suggest a rigid behavior for the eastern SGT and highlight the important role of crustal strength discontinuities in accommodating and transferring crustal deformation.