Thermochronology constraints on the Cretaceous-Cenozoic thermo-tectonic evolution in the Gaize region, central-western Tibetan Plateau: Implications for the westward extension of the proto-Tibetan Plateau

Abstract

• The Gaize region has experienced three exhumation events of ∼100-70 Ma, ∼50-38 Ma and since early Miocene. • The central Tibetan Plateau has undergone five-stage thermo-tectonic evolution since the late Jurassic. • Late Cretaceous exhumation associated with surface uplift and topography growth in the Gaize region represented the westward extending of proto-Plateau. • Low-relief high-elevation topography of the central Tibetan Plateau has established by the early Oligocene. The temporal and spatial variations of exhumation in the central Tibetan Plateau (TP) contain information about timing of the initial rise and growth of the TP. Here, we present multiple system thermochronology data (zircon U-Pb, biotite 40 Ar/ 39 Ar, zircon and apatite fission track, and apatite (U-Th)/He ages) from the Gaize region, central-western TP, to reveal its exhumation and thermo-tectonic history since the Cretaceous. Zircon and apatite fission track and apatite (U-Th)/He analyses in combination with thermal history modeling depicted a three-phase of rapid exhumation scenario in the study area: a phase of Late Cretaceous rapid exhumation (∼10 °C/Ma) followed by an accelerated Eocene-early Oligocene exhumation event (∼ 12 °C/Ma) and a limitedly rapid exhumation episode (∼3 °C/Ma) since the early Miocene. Our study reveals that the Gaize region initially underwent a Late Cretaceous intense exhumation event associated with surface uplift and topography growth which represented the westward extending of proto-Plateau. Our results integrated with previous tectonic, sedimentology, magmatism and low-temperature thermochronology studies throughout the central TP enable us to reappraise a five-phase thermo-tectonic evolution since the Late Jurassic. The Central-Southern Qiangtang terrane experienced the earliest exhumation related to the initial Lhasa-Qiangtang collision during the late Jurassic-Cretaceous (∼150-125 Ma). This process propagated southwards to the southernmost Qiangtang and central Lhasa terranes by the late Early Cretaceous (∼125-100 Ma). Subsequently, most central TP underwent significant cooling and exhumation event during the Late Cretaceous (∼100-70 Ma) in response to the crustal thickening and subsequently lithospheric foundering beneath the Central-Northern Lhasa and southernmost Qiangtang terranes. A phase of rapid exhumation event was also extended to the central TP during ∼55 Ma to ∼30 Ma which was likely triggered by the combination of India-Asia hard collision and southward intracontinental subduction of Jinsha suture zone. Finally, the central TP experienced a limited exhumation with a slow erosion rate since the early Oligocene, suggestive of the establishment of low-relief, high-elevation topography of the proto-TP. Such five-stage thermo-tectonic evolution of the central TP supports an outward growth process of the TP that nucleated in the central Qiangtang core since the Late Jurassic.