Mesozoic and Cenozoic Cooling History of the Qiangtang Block, Northern Tibet, China: New Constraints from Apatite and Zircon Fission Track Data

Abstract

This study used a new set of zircon and apatite fission track ages to quantitatively document the tectonic evolution and cooling histories of the Qiangtang block of the central Tibetan Plateau. The results indicate that the Qiangtang block underwent three cooling stages at ~148 -73, ~50 -20, and ~20 -0 Ma. The three-stage cooling history and tectonic exhumation were controlled by the closure of the Bangong-Nujiang Suture during the Late Jurassic-Late Cretaceous, the India-Asia collision in the Paleogene, and the underthrusting of the India Plate during the Late Cenozoic. In addition to revealing the Late JurassicLate Cretaceous cooling events, the annealing patterns of the zircon fission track samples indicate different burial depths, which may help identify the Jurassic basin characteristics of the Qiangtang block. The apatite fission track (AFT) ages range from 60 ± 5 Ma to 26 ± 3 Ma, with a mean age of 44 Ma. These ages indicate that the Cenozoic exhumation of the Qiangtang block may have started in the Eocene. Inverse modeling of the AFT data shows that the Qiangtang block had a relatively slow cooling rate of approximately 0.5 -1°C Myr -1 from 50 to 20 Ma. After ~20 Ma, most of the samples show evidence for a rapid cooling stage with a cooling rate of 4 -6°C Myr -1 .

Sedimentary and tectonic evolution of the southern Qiangtang basin: Implications for the Lhasa‐Qiangtang collision timing

“…On the other hand, zircon Hf isotope ratios with ε Hf (t) as high as +12 in the Sewa and Gaaco formations have never been reported yet from zircon crystals contained in 183–170 Ma igneous rocks of the Qiangtang block. This might be explained by the still pioneering stage of geological research in the vast and rough Qiangtang block, or by complete erosion of igneous rocks that sourced the southern Qiangtang basin during the several subsequent exhumation event suggested by low‐temperature thermochronology [ Song et al , ], or even by burial of the continental‐arc source beneath younger Mesozoic strata [ Guynn et al , ; Guynn et al , ]. Further work is needed to address this problem adequately.…”

Apatite and zircon (U–Th)/He thermochronological evidence for Mesozoic exhumation of the Central Tibetan Mountain Range

“…(a) Tectonic map of central TP, showing the main terrane and sutures, together with available thermochronological data locations (Dai, Wang, Hourigan, & Santosh, 2013; Song et al, 2013; Wang et al, 2008; Wang & Wei, 2013; Zhang et al, 2019; Zhao et al, 2017, 2020), the yellow dotted line is the CTMR, the red box is this study area. Distribution of major thrust belts and timing of initiation and/or duration of deformation in Qiangtang Terrane, after Kapp et al (2005) and Li, Wang, Zhao, Yin, & Ma (2012).…”

“…Compared to the Lhasa Terrane, the exhumation history of the Qiangtang Terrane (QT) receives much less attention and remains ambiguous. Previous studies basically employed the detrital apatite fission track (AFT) ages in both the northern (NQT) and southern Qiangtang Terrane (SQT; Ren et al, 2015; Song, Wang, Fu, & Hei, 2013; Wang et al, 2008; Wang & Wei, 2013; Zhang et al, 2019), which reveal at least two stages of rapid exhumation: Late Cretaceous and Early Cenozoic, respectively. Four granite samples have been conducted only for zircon (U–Th)/He (ZHe) analyses in the Central Tibetan Mountain Range (CTMR) that separated the NQT and the SQT (Zhao, Bons, Stübner, Wang, & Ehlers, 2017).…”

New apatite fission track evidence from the northern Qiangtang terrane reveal two‐phase evolution of central Tibet

“…Published thermochronological ages, including apatite fission track (AFT), apatite (U‐Th)/He (AHe) and zircon (U‐Th)/He (ZHe) (Dai, Wang, Hourigan, & Santosh, 2013; Ren et al., 2015; Rohrmann et al., 2012; Song, Wang, Fu, & Hei, 2013; Wang, Zhao, et al, 2008; Wang & Wei, 2013; Zhang et al., 2019; Zhao et al., 2020; Zhao, Bons, Stübner, Wang, & Ehlers, 2017), in the western part are older than those in the eastern part of the QT (Figure 1b). Although AFT data are widely distributed, many existing studies only show apparent ages without track length information and the northern QT north of the Shuanghu County is not covered (Figure 1b).…”

“…(a) Tectonics of Tibetan Plateau showing major terranes and suture zones. (b) Topography of central Tibet showing the location of study area and low‐temperature thermochronological (AHe, AFT and ZHe) ages from the literature (Dai et al., 2013; Ren et al., 2015; Rohrmann et al., 2012; Song et al., 2013; Wang, Zhao, et al, 2008; Wang & Wei, 2013; Zhang et al., 2019; Zhao et al., 2017, 2020). Thermochronological ages from the literature are provided in Table S1.…”