Provenance and thermal history of the Bayan Har Group in the western‐central Songpan–Ganzi–Bayan Har terrane: Implications for tectonic evolution of the northern Tibetan Plateau

Abstract

Triassic turbidites dominate the Songpan-Ganzi-Bayan Har (SGBH) terrane of the northern Tibetan Plateau. U-Pb dating on single detrital zircon grains from the Triassic Bayan Har Group turbidites yield peaks at 400-500 m.y., 900-1000 m.y., 1800-1900 m.y., and 2400-2500 m.y., These results are consistent with recently published U-Pb zircon ages of pre-Triassic bedrock in the East Kunlun, Altyn, Qaidam, Qilian and Alaxa areas to the north, suggesting that provenance of the Bayan Har Group may include these rocks. The similarities in the compositions of the lithic arkosic sandstones of the Bayan Har Group with the sandstones of the Lower-Middle Triassic formations in the East Kunlun terrane to the north also suggests a common northern provenance for both. A well exposed angular unconformity between the Carboniferous-Middle Permian mélange sequences and the overlying Upper Permian or Triassic strata indicates that regional deformation occurred between the Middle and Late Permian. This deformation may have been the result of a soft collision between the Qiangtang terrane and the North China Plate and the closure of the Paleo-Tethyan oceanic basin. The Bayan Har Group turbidites were then deposited in a re-opened marine basin on a shelf environment. Fission-track dating of detrital zircons from the Bayan Har Group sandstones revealed pre-and post-depositional age components, suggesting that the temperatures did not reach the temperatures necessary to anneal retentive zircon fission tracks (250-300°C). A 282-292 m.y. peak age defined by low U concentration, retentive zircons likely reflects a northern granitic source. Euhedral zircons from two lithic arkoses with abundant volcanic fragments in the southern area yielded a~237 m.y. zircon fission track (ZFT) peak age, likely recording the maximum age of deposition. A dominant postdepositional 170-185 m.y. ZFT peak age suggests peak temperatures were reached in the Early Jurassic. Some samples appear to record a younger thermal event at~140 m.y., a short lived event that apparently affected only the least retentive zircons.i ar_666 444..466

Detrital zircon geochronology of pre‐Tertiary strata in the Tibetan‐Himalayan orogen

“…Detrital zircon ages from the Songpan Ganzi complex have previously been reported by Bruguier et al [1997], Weislogel et al [2006, 2010], and Wang et al [2009]. Sampled strata are mainly Middle–Late Triassic in age, and were collected from a broad region of the eastern portion of the terrane (Figure 1).…”

“…However, provenance of the central and western Songpan–Ganzi remains unstudied and could have had other origins. The Songpan–Ganzi basin subsequently collapsed and inverted during Jurassic accretion of the Qiangtang terrane and formation of the Jinsa suture [ Zhou and Graham , 1996; Yin and Nie , 1996; Yin and Harrison , 2000; Weislogel et al , 2006, 2010; Wang et al , 2009] (Figures 13g and 13h).…”

“…This assemblage consists primarily of Upper Triassic marine strata and, in southern portions of the terrane, arc‐type volcanic rocks [ Yin and Harrison , 2000; Roger et al , 2004; Weislogel et al , 2006; Weislogel , 2008]. Provenance studies and mass balance calculations suggest that most of the strata were shed from the Qinling–Dabie orogen to the east (which closed during Triassic collision between the North China and South China cratons), as well as from the Kunlun arc (to the north), the North China craton, and the South China craton [ Nie et al , 1994; Zhou and Graham , 1996; Bruguier et al , 1997; Weislogel et al , 2006; Enkelmann et al , 2007; Wang et al , 2009].…”

Detrital zircon multi‐chronology, provenance, and low‐grade metamorphism of the Cretaceous Shimanto accretionary complex, eastern Shikoku, Southwest Japan: Tectonic evolution in response to igneous activity within a subduction zone

“…Detrital zircon U–Pb dating over the past two decades has been used to determine maximum (oldest) depositional ages using the youngest or peak age, enabling the reconstruction of the tectonic evolution of sediment provenance (e.g. Aoki et al, , ; Beranek & Mortensen, ; Cawood, Hawkesworth, & Dhuime, ; Dickinson & Gehrels, ; Ernst, Martens, & Valencia, ; Fedo, Sircombe, & Rainbird, ; Fujisaki et al, ; Hampton, Ridgway, & Gehrels, ; Han et al, ; Tsutsumi, Miyashita, Horie, & Shiraishi, ; G. G. Wang et al, ). In addition, combining detrital zircon U–Pb ages and provenance analysis provides not only maximum depositional ages but also information on the tectonic setting, and temporal and spatial variations in sediment provenance (Chen et al, ; Hu, Cawood, Du, Yang, & Jiao, ; Long et al, ).…”

“…Detrital zircon U-Pb dating over the past two decades has been used to determine maximum (oldest) depositional ages using the youngest or peak age, enabling the reconstruction of the tectonic evolution of sediment provenance (e.g. Aoki et al, 2012Aoki et al, , 2014Beranek & Mortensen, 2011;Cawood, Hawkesworth, & Dhuime, 2012;Dickinson & Gehrels, 2009;Ernst, Martens, & Valencia, 2009;Fedo, Sircombe, & Rainbird, 2003;Fujisaki et al, 2014;Hampton, Ridgway, & Gehrels, 2010;Han et al, 2015;Tsutsumi, Miyashita, Horie, & Shiraishi, 2012;G. G. Wang et al, 2009).…”