History of subduction erosion and accretion recorded in the Yarlung Suture Zone, southern Tibet

Abstract

The history of pre-Cretaceous subduction accretion and erosion along the Yarlung Suture Zone remains poorly constrained. We present new geological mapping along c. 200 km of the suture zone, 4881 detrital zircon U–Pb ages, and sandstone petrography for the subduction complex and Tethyan Himalayan strata. We provide the first documentation of the c. 158 Ma marine Xiazha Formation, which contains volcanic clasts of intermediate to felsic volcanic rocks and ooids with both calcareous and volcanic cores. Based on our new data and synthesis of published data, we present a model in which the Zedong arc represents the southwards migration of the Gangdese arc onto a forearc ophiolite that was generated proximal to the southern Asian margin during Neotethyan slab rollback at 160–150 Ma. This contrasts with previous suggestions that the Zedong arc, Yarlung ophiolites and subduction complex rocks developed above an intra-oceanic subduction zone thousands of kilometres south of Asia. Although Gangdese arc magmatism began in the Middle Triassic, the only forearc units preserved are 160 Ma until collision between the Xigaze forearc basin and Tethyan Himalaya at c. 59 Ma. This suggests that almost all pre-Cretaceous forearc assemblages have been removed by subduction erosion at the trench.

The Ancestral Lhasa River: A Late Cretaceous trans-arc river that drained the proto–Tibetan Plateau

“…Prior to India-Asia collision, the southern Lhasa terrane was Andean-style (Murphy et al, 1997), comprising a Cretaceous to Paleocene subduction-accretion complex (e.g., Cai et al, 2012;Metcalf and Kapp, 2019) structurally overlying Jurassic and Cretaceous ophiolites (Göpel et al, 1984;McDermid et al, 2002;Hébert et al, 2012;Chan et al, 2015) and unconformably overlying Cretaceous to Paleocene Xigaze forearc basin strata (Einsele et al, 1994;Ding et al, 2005;Orme et al, 2015). These marginal assemblages are bounded to the north by the Late Triassic or Early Jurassic to Eocene Gangdese magmatic arc (Schärer et al, 1984;Lee et al, 2009;Zhu et al, 2011;Wang et al, 2016).…”

“…110 and 51 Ma (An et al, 2014;Orme et al, 2015;Orme and Laskowski, 2016) and sedimentation in trench basins prior to ca. 85-70 Ma incorporation into the subduction-accretion complex (Cai et al, 2012;An et al, 2018;Wang et al, 2018;Metcalf and Kapp, 2019). Given that Lhasa terrane crystallization ages and isotopic compositions of igneous rocks (Zhu et al, 2011;Wang et al, 2016;Chapman and Kapp, 2017) and characteristic age spectra of sedimentary rocks (Gehrels et al, 2011) are well known, detrital zircon (DZ) geochronology is appropriate for determining sediment provenance.…”

Discovery of Vestige Sedimentary Archives of the India‐Asia Collision in the Eastern Yarlung Zangbo Suture Zone

“…N is the number of igneous samples from Lhasa Terrane instead of analyzed zircon number. Data sources: Triassic sandstone of Lhasa Terrane compilation from Li et al (2014), Li et al (2016); the Rongmawa Fm within trench from Cai et al (2012), Wang et al (2018), Metcalf and Kapp (2019), Laskowski et al (2019); igneous rocks of Lhasa Terrane compilation from Wen et al (2008), Ji et al (2009), Zhu et al (2011), Zhu et al (2017), Zhu et al (2018), Zhang et al (2014), Wang, Wu, et al (2016), Zhao et al (2016), Li et al (2018), Zhou et al (2018), Zhang et al (2019); Triassic sandstone of NE Tethys Himalaya (Langjiexue Group, Shannan Terrane) from Aikman et al (2008), Aitchison et al (2011), Li et al (2010), Li et al (2016), and Webb et al (2013); Jiachala Fm of NE Tethys Himalaya from Wu et al (2014); Cretaceous sandstones of NE Tethys Himalaya from Hu et al (2010) and Hu et al (2012).…”

“…Thick‐bedded marbles indicate that protoliths of the Langxian unit could have been deposited in a shallow sea environment rather than in trench or trench‐slope basin. This is because trench or trench‐slope basin in the central YZSZ often comprises deep‐water deposits such as chert and turbiditic sandstone (An et al, 2018; Cai et al, 2012; Metcalf & Kapp, 2019; Wang et al, 2018) and receives detritus only sourced from magmatic arc, recycled accretionary wedge, or forearc sequences in the north (An et al, 2018; Cai et al, 2012).…”

“…The latter two formations are considered as the syncollisional sedimentary records (e.g., Ding et al, 2005; Hu, Wang et al, 2016; Jia et al, 2005; Orme et al, 2015; Wan et al, 2001). The sandy‐muddy mélange subzone of the YZSZ outcrops east to Zedong and contains abundant syncollisional sedimentary records (e.g., An et al, 2017; Burg & Chen, 1984; Ding et al, 2005; Metcalf & Kapp, 2017, 2019). Within the subzone, the syncollisional sediments are characterized by the Paleocene radiolarian cherts and sandstones in Saga area (e.g., DeCelles et al, 2014; Ding et al, 2005; Hu et al, 2015) and by the Zongzhuo mélange dominated by olistoliths in Gyangze area (e.g., Cai et al, 2011; Li et al, 2005; Wu et al, 1977; Wu et al, 2014).…”