Detrital zircon geochronology and geochemistry of Jurassic sandstones in the Xiongcun district, southern Lhasa subterrane, Tibet, China: implications for provenance and tectonic setting

Abstract

Jurassic sandstones in the Xiongcun porphyry copper–gold district, southern Lhasa subterrane, Tibet, China were analysed for petrography, major oxides and trace elements, as well as detrital zircon U–Pb and Hf isotopes, to infer their depositional age, provenance, intensity of source-rock palaeo-weathering and depositional tectonic setting. This new information provides important evidence to constrain the tectonic evolution of the southern Lhasa subterrane during the Late Triassic – Jurassic period. The sandstones are exposed in the lower and upper sections of the Xiongcun Formation. Their average modal abundance (Q21F11L68) classifies them as lithic arenite, which is also supported by geochemical studies. The high chemical index of alteration values (77.19–85.36, mean 79.96) and chemical index of weathering values (86.19–95.59, mean 89.98) of the sandstones imply moderate to intensive weathering of the source rock. Discrimination diagrams based on modal abundance, geochemistry and certain elemental ratios indicate that felsic and intermediate igneous rocks constitute the source rocks, probably with a magmatic arc provenance. The detrital zircon ages (161–243 Ma) and εHf(t) values (+10.5 to +16.2) further constrain the sandstone provenance as subduction-related Triassic–Jurassic felsic and intermediate igneous rocks from the southern Lhasa subterrane. A tectonic discrimination method based on geochemical data of the sandstones, as well as detrital zircon ages from sandstones, reveals that the sandstones were most likely deposited in an oceanic island-arc setting. These results support the hypothesis that the tectonic background of the southern Lhasa subterrane was an oceanic island-arc setting, rather than a continental island-arc setting, during the Late Triassic – Jurassic period.

Geochemistry, detrital zircon geochronology and Hf isotope of the clastic rocks in southern Tibet: Implications for the Jurassic-Cretaceous tectonic evolution of the Lhasa terrane

“…In the southern Lhasa terrane, the subduction-related Xiongcun porphyry Cu deposit with ore-bearing country rocks of the Early-Middle Jurassic Xiongcun Formation volcano-sedimentary sequence was developed to the west of the Yeba Formation (Lang et al, 2014(Lang et al, , 2018Tafti et al, 2009;Tang et al, 2015). Sillitoe (1998) favored the compressional regime for the formation of subduction-related porphyry Cu deposits in terms of the statistic study on global Cu deposits; however, no Cu deposits have been found in the Yeba Formation, which was previously considered to be formed in continental arc setting (Zhu et al, 2008 suggests a tropical climate (Lang et al, 2018). The Yeba sandstones, however, are predominated by recycled quartz and underwent high chemical weathering, indicating that they were gradually deposited in the basin with relatively subdued uplift and low elevations (Fig.…”

“…The Q-F-L ternary plot (Dickinson, 1985) showing clastic composition of samples from the Yeba, Xiongcun, Chumulong and Shexing Formations. The Xiongcun Formation data are from Lang et al, (2018). Q, quartz; F, feldspars; L, lithic fragments; RO, recycled orogen; UMA, undissected magmatic arc; TMA, transitional magmatic arc; DMA, dissected magmatic arc; BU, basement uplift; TC, transitional continental; CI, craton interior.…”

“…Ternary plots of (A) A-CN-K and (B) A-CNK-FM showing sandstones and mudstones from the Jurassic-Cretaceous strata in the southern Lhasa terrane (afterNesbitt and Young, 1989;McLennan et al, 1993). The Xiongcun Formation data are fromLang et al, (2018). A = Al 2 O 3 , C = CaO*, N = Na 2 O, K = K 2 O, F = total Fe as FeO, M = MgO.…”

Early Carboniferous Back‐Arc Rifting‐Related Magmatism in Southern Tibet: Implications for the History of the Lhasa Terrane Separation From Gondwana

“…245 Ma in the SL (X. X. Ma et al, 2020, and references therein;, and a middle Triassic-early Jurassic island arc system is within the Neo-Tethys (Lang, Liu, et al, 2019;X. X. Ma, Meert, et al, 2019;X.…”

“…The central Lhasa subterrane retains the most complete sedimentary record in the region and consists of Carboniferous‐Permian and late Jurassic‐early Cretaceous volcano‐sedimentary sequences, with minor Ordovician, Silurian, and Triassic limestones and rare Precambrian strata (Figure 2; e.g., Kapp et al, 2007; Zhu et al, 2013; Zhu, Zhao, Niu, Mo, et al, 2011, and references therein), which signal the presence of a Precambrian basement in the central subterrane. The southern Lhasa subterrane is dominated by the voluminous Cretaceous‐Eocene Gangdese batholith and the Paleogene Linzizong volcanic succession, with minor middle Triassic‐middle Jurassic volcano‐sedimentary sequences and intrusions (Figure 2; Lang et al, 2020; Lang, Liu, et al, 2019; Lang, Wang, et al, 2019; X. H. Wang, Lang, et al, 2019; Zhu et al, 2013; Zhu, Zhao, Niu, Mo, et al, 2011). However, some Paleozoic and Paleo‐ and Meso‐Proterozoic magmatic rocks have recently been found in this subterrane (Figure 2; Ji et al, 2012; Dong, Zhang, Geng, et al, 2010; Dong et al, 2014; Dong, Zhang, & Santosh, 2010; Lin et al, 2013; L. Ma, Kerr, et al, 2019), which suggests that the southern Lhasa subterrane is an ancient microcontinent that underwent extensive Phanerozoic crustal reworking and growth rather than a Mesozoic‐Paleogene juvenile accretionary arc terrane (L. Ma, Kerr, et al, 2019).…”