Sequence and petrogenesis of the volcanic rocks from the middle Sanjiang Tethys Orogen, SW China: Implications for the Sanjiang Paleo‐Tethyan evolution

Abstract

The volcano‐sedimentary sequences from the Weixi belt provide significance for the Sanjiang Paleo‐Tethys evolution. This manuscript constrains the ages of volcano‐sedimentary sequences by LA‐ICPMS U–Pb, including bimodal volcanics (245.0–244.0 Ma) from Pantiange Formation, trachyandesite–basaltic andesite (234 ± 2.0 Ma) from Cuiyibi Formation, high silica subalkaline rhyolite (221 ± 1.4 Ma) from Waigucun Formation and Early Jurassic high silica subalkaline rhyolite (184 ± 2.2 Ma). The volcanics show various Hf isotopic composition, which includes Middle Triassic dacite (ε Hf[t] = −15.7 to −8.5, TDM2 = 2,006–1,613 Ma), Late Triassic rhyolite (ε Hf(t) = −9.8 to +1.9, TDM2 = 1,667–1,021 Ma), Late Triassic trachyandesite (ε Hf(t) = +2.6 to +5.7, TDM2 = 990–816 Ma) and Early Jurassic rhyolite (ε Hf(t) = −2.7 to +1.1, TDM2 = 1,250–1,145 Ma). The Middle–Late Triassic volcanics exhibit similar characteristics, the content of SiO2 exerts positive correlation with K2O and negative correlation with oxide of Ti, Fe, Al, Mg, Ca, Mn and P. The Hf isotopic and geochemical features indicate that the Middle Triassic basalt and rhyolite derived from mantle and crust by crystal fractionation, respectively. The absence of Lower Jurassic strata and existence of Triassic bimodal volcanic sequences suggest that the middle Sanjiang Tethys Orogen experienced collision during the Middle Triassic with local extension resulting from oblique convergence. Late Triassic–Early Jurassic rhyolite exhibit high SiO2 (77.12–77.81 wt%), K2O (4.35–6.10 wt%), Na2O (1.91–3.15 wt%) content, and a negative Eu anomaly. Together with the sedimentary sequence, the middle Sanjiang Tethys Orogen evolved into post‐collision phase during Late Triassic – Early Jurassic.

Decoupling of morphological disparity and taxonomic diversity during the end-Permian mass extinction

“…and Griesbachian postextinction interval (Post-E.). Conodont stratigraphy has been undertaken at all the investigated sections where Hindeodus parvus , whose first appearance datum (FAD) defines the base of the Triassic (Yin et al 2001), typically occurs near the base of the microbialites facies, and the Isarcicella staeschei biozone occurs above the microbialite interval (Yang et al 1999; Richoz 2006; Sudar et al 2008; Jiang et al 2014; Forel et al 2015). Furthermore, in most Permian/Triassic boundary successions, the microbialites also have irregular contact with the underlying skeletal packstone, which marks the end-Permian mass extinction horizon (Payne et al 2007; Chen et al 2009; Jiang et al 2014).…”

The Weixi High‐silica Granitoids in the Central Sanjiang Orogenic Belt, Southwest China: Implications for Growth of the Continental Crust

“…There were two Paleo-Tethyan oceanic basins in the Weixi region during the Paleozoic (i.e., the Jinshajiang and Changning-Menglian Paleo-Tethyan oceanic basins). The Jinshajiang basin closed during the Early-Middle Triassic (Peng et al, 2008(Peng et al, , 2013Zi et al, 2012a;Yan et al, 2021), whereas the Changning-Menglian basin did not completely close until the Late Triassic (Yang et al, 2014a(Yang et al, , 2019Xin et al, 2018;Wang Q Y et al, 2023;Yin et al, 2023).…”

“…Studies have suggested that the igneous rocks of the central Sanjiang orogenic belt were formed in association with the Jinshajiang Paleo-Tethys; i.e., the Early Triassic volcanic rocks were a response to the closure of the Paleo-Tethys, whereas the Middle Triassic volcanic rocks were formed by continent collision along the Jinshajiang suture zone (Zi et al, 2012a, b, c;Wang et al, 2014). The collision model is based mainly on the presence of Middle Triassic bimodal volcanic rocks (Zi et al, 2012a;Yan et al, 2021). However, a suite of andesitic rocks has been identified in the Weixi area, which provides robust evidence that the Middle Triassic volcanic rocks comprise andesite, basalt, dacite, and rhyolite (Yin et al, 2023).…”