Episodic slab rollback and back-arc extension in the Yunnan-Burma region: Insights from Cretaceous Nb-enriched and oceanic-island basalt–like mafic rocks

First Identification of Late Permian Nb‐Enriched Basalts in Ailaoshan Region (SW Yunnan, China): Contribution From Emeishan Plume to Subduction of Eastern Paleotethys

“…Therefore, minor contamination of these sedimentary rocks could give rise to the xenocrystic zircons but with insignificant effect on the geochemical compositions of the NEB magmas. Generally, significant crustal contamination would have caused Nb‐Ta depletion (H. Liu et al, ; C. Y. Wang et al, ; Q. Wang et al, ), rather than Nb‐Ta enrichments in the Ailaoshan NEBs (Figure b). In addition, magmas from a relatively depleted mantle source have high ε Nd( t ), but low Th/Nb and La/Sm ratios, whereas magmas from the continental crust have low ε Nd( t ), but high Th/Nb and La/Sm values (e.g., Condie, ; DePaolo, ).…”

“…Therefore, minor contamination of these sedimentary rocks could give rise to the xenocrystic zircons but with insignificant effect on the geochemical compositions of the NEB magmas. Generally, significant crustal contamination would have caused Nb-Ta depletion (H. Liu et al, 2017;C. Y. Wang et al, 2012;Q.…”

Geochemistry of high‐Nb basalt‐andesite in the Erguna Massif (NE China) and implications for the early Cretaceous back‐arc extension

“…Thirty Meiletu volcanic samples display a wide range of SiO 2 contents (50.4–58.2 wt.%) and variable Mg # (100 × [atomic MgO/(MgO + FeOT)]) values of 19–62 (Supplemental File 1). Unlike the typical Nb‐enriched basalts (i.e., the Cretaceous NEBs in the Ailaoshan area; Liu, Wang, Cawood, & Guo, ), they show high Na 2 O + K 2 O (5.5–7.5 wt.%), TiO 2 (1.7–3.2 wt.%), P 2 O 5 (0.7–1.7 wt.%), and Zr (314–600 ppm) contents, and low Zr/P 2 O 5 and Na 2 O/K 2 O (0.97–1.81) ratios, and were classified as alkali basalt (Figures a–e and Supplemental File 2). The Meiletu samples are characterized by unusually high Nb (14.6–34.0 ppm) contents and high Nb/U (8.3–24.8) and (Nb/Th) PM (0.26–0.91) ratios.…”

Early Cretaceous (∼138–134 Ma) Forearc Ophiolite and Tectonomagmatic Patterns in Central Tibet: Subduction Termination and Re‐initiation of Meso‐Tethys Ocean Caused by Collision of an Oceanic Plateau at the Continental Margin?

“…(2011), high‐Nb basalts (Nb > 20 ppm) are signals of subduction zone environments and are formed by the partial melting of mantle wedge metasomatized by slab‐derived melt; that is, adakites. The high Sr/Y and La/Yb ratios and highly radiogenic ε Hf values of these high‐Nb basalts (Liang et al., 2017; Xu et al., 2017) give particular support to such a petrological hypothesis (Liu H. et al., 2017). Second, the Jurassic‐Early Cretaceous arc‐type igneous rocks in the Qiangtang Terrane can be divided into northern and southern parts (Figure S1; X. K. Li et al., 2018), with the southern part containing only Early Cretaceous rocks that show clearly more juvenile isotope values compared with the Jurassic‐dominant igneous rocks of the northern part (Figure 6).…”