Cambrian magmatism in the Tethys Himalaya and implications for the evolution of the Proto‐Tethys along the northern Gondwana margin: A case study and overview

Abstract

The Cuonadong Dome in southern Tibet is a newly discovered gneiss dome in the Tethys Himalaya. Here, we investigate the Late Cambrian augen gneiss (orthogneiss) within the core of this dome to address the controversy surrounding early Palaeozoic tectonic evolution of the northern margin of eastern Gondwana. We report new zircon laser ablation multicollector inductively coupled plasma mass spectrometry (LA‐(MC‐)ICP‐MS) U‐Pb ages, Lu‐Hf isotopes, whole‐rock major and trace element geochemistry, and Sr‐Nd‐Pb data on representative samples from the granitic gneiss. The weighted mean of 116 analyses of zircon grains yields an age of 498.2 ± 1.5 Ma (mean square weighted deviation [MSWD] = 1.2). Forty‐one spots analyses on these grains show consistent εHf (t) values of −2 to +4 (average = +1.1), corresponding to Hf crustal model age (TDM2) of 1.3 to 1.6 Ga (average = 1.39 Ga). The orthogneiss (metagranite) is characterized by high Si and K contents, with low Al, Mg, and Ti, and A/CNK values ranging from 0.87 to 0.98 with an average of 0.92, indicating a metaluminous composition and I‐type granitoid affinity. The granitoid displays significant enrichment in light rare earth elements (LREEs) and relatively flat high rare earth element (HREE) patterns, with strong negative Eu anomalies (Eu/Eu* = 0.26–0.31). The primitive mantle‐normalized trace elements show a relative enrichment in large‐ion lithophile elements, such as Rb, and high‐field strength elements, such as Th, U, Zr, and Hf, with depletion in Ba, Nb, Ta, Sr, P, and Ti. The rocks show high initial 87Sr/86Sr ratios (0.7221–0.7248) and low εNd (t) values (−8.9 to −7.3) with Nd model ages (TDM) of 1.79–1.91 Ga. Their radiogenic Pb isotopic compositions show (206Pb/204Pb)t = 18.804–19.110, (207Pb/204Pb)t = 15.730–15.768, and (208Pb/204Pb)t = 38.409–39.054, indicating an ancient upper middle continental crustal origin. Our study shows that the protolith of the metagranite was most likely derived from the partial melting of upper continental crust with a minor contribution of depleted mantle materials. Through integration of the regional information on early Palaeozoic magmatism and metamorphic events, we contend that the protolith of the Cuonadong granitic gneiss formed in an accretionary setting associated with the early Palaeozoic Proto‐Tethys Oceanic plate subduction beneath the Gondwana continent.

Crustal thickening prior to 43 Ma in the Himalaya: Evidence from lower crust‐derived adakitic magmatism in Dala, eastern Tethyan Himalaya, Tibet

“…Tectonic map of the Himalaya–Tibetan Plateau region: (a) geotectonic sketch of southeastern Asia (Cao et al, ; Yin & Harrison, ); (b) simplified geological map of Himalaya, showing the distribution of leucogranites (modified after Cao et al, ; Guillot et al, ; Zhang et al, ). Age of Dajia granites is from Wang et al (); age of the Langshan gabbros is from Ji et al (); age of the Napuri adakitic rocks is from Ma et al () [Colour figure can be viewed at wileyonlinelibrary.com]…”

Phanerozoic flooding of North America and the Great Unconformity

“…The southern margin of Gondwana, spanning approximately 15,000 km, had initiated subduction by 530 Ma, which progressed into the Terra Australis Orogen that peaked around 515 to 500 Ma ( 78 – 82 ). The margin of northeastern Gondwana was also convergent within this time window, with subduction along the entire margin from Australia to Turkey from 530 to 490 Ma ( 82 – 85 ). This subduction extended west as part of the Avalonian-Cadomian orogenic arc, essentially along the entire northern margin of Gondwana ( 86 – 89 ).…”

Deep structure and prospecting significance of the Cuonadong dome, Tethys Himalaya, China: Geophysical constraints

“…These domes, between the ITSZ and the STDS, all belong to the North Himalayan Gneiss Domes (NHGD; Fu et al, 2020; Langille, Jessup, Cottle, & Ahmad, 2014; Lee, Hacker, & Wang, 2004). Lalong, Qialong, and Cuonadong were newly discovered dome structures in recent years (Huang et al, 2017; Huang, Fu, Li, Zhang, & Liu, 2019; Zhang et al, 2018, 2019). These domes exhibit a similar geologic framework with leucogranites, gneisses, migmatites, and unmetamorphosed sedimentary rocks (Langille et al, 2014; Lee et al, 2004).…”

“…As one of the regions with the strong metallogenic potential for Cu–Pb–Zn–Au deposits in the Qinghai‐Tibet Plateau, the Tethys Himalaya metallogenic belt is thus considered to be a critical mineral resource enrichment zone. In recent years, Be‐W‐Sn deposits were found in the Cuonadong dome (Fu et al, 2017, 2018a; Li et al, 2017; Zhang et al, 2019). Moreover, mineral exploration further confirmed that this type deposit has a very high exploration potential (Cao et al, 2020; Sun et al, 2018; Xie et al, 2017; Zhang et al, 2018).…”

“…In recent years, much research has been conducted into the surface geological features and the lithologic‐tectonic units (Fu et al, 2017; Li et al, 2017; Zhang et al, 2019). However, the deep structure of the Cuonadong dome is unclear, which severely constrains getting a better understanding of the prospecting models and dynamic mechanisms of the dome in the Tethys Himalaya.…”