Limited underthrusting of India below Tibet: ³ He/ ⁴ He analysis of thermal springs locates the mantle suture in continental collision

Abstract

Significance Our regional-scale geochemical dataset ( 3 He/ 4 He) resolves the geometry of the continental collision between India and Asia. Geophysical images have led to contradictory interpretations that India directly underthrusts Tibet as a horizontal plate or India subducts steeply into the mantle. Helium transits from mantle depths to the surface within a few millennia, such that the ratio of mantle-derived 3 He to dominantly crust-derived 4 He provides a snapshot of the subsurface. 3 He/ 4 He data from 225 geothermal springs across a >1,000-km-wide region of southern Tibet define a sharp boundary subparallel to the surface suture between India and Asia, just north of the Himalaya, delineating the northern limit of India at ∼80-km depth. The India–Asia collision resembles oceanic subduction with an asthenospheric mantle wedge.

Subducting Indian Lithosphere Controls the Deep Carbon Emission in Lhasa Terrane, Southern Tibet

“…These volatiles are more likely the degassing products of mantle partial melting, ascending along deeply seated faults throughout the crust, as suggested by Klemperer et al. (2022).…”

“…As an example, the R / R A of magmas in Yaqian (DXR, Figure 6) following this model would be 0.24 (±0.10), which are lower than that of the nearby Biela samples (0.69; Figure 1b). Furthermore, the ultrapotassic magmatism is mainly distributed west of 87°E in Lhasa terrane (Figure 1b; Guo et al., 2015), inconsistent with the widely distributed MHD samples in GYR of eastern Lhasa (Figure 1b; Klemperer et al., 2022). Considering the lack of Quaternary volcanism in Lhasa terrane, previous studies proposed that the 3 He anomaly may indicate fresh mantle melts (Hoke et al., 2000; Zhang, Guo, Zhang et al., 2017).…”

“…During the incipient remelting of the carbonated‐enriched mantle (CEM) and the subsequent degassing, mantle‐derived volatiles, such as CO 2 and helium, are released to the overlying crust and migrate upward through the deep‐seated faults (Kapp & Guynn, 2004; Klemperer et al., 2013, 2022; Zhang, Guo, Zhang et al., 2017). Amounts of radiogenic 4 He are added into the ascending volatiles by fluid‐rock interactions in the hydrothermal systems (Figure S3 in Supporting Information S1).…”

“…Several studies have been carried out on the sources, budget, and tectonic implications of CO 2 ‐rich fluids in southern Tibet and its adjacent regions (e.g., Hoke et al., 2000; Klemperer et al., 2013, 2022; Zhang, Guo, Sano et al., 2017; Zhang, Guo, Zhang et al., 2017; Zhang, Guo et al., 2021; Zhang, Zhang et al., 2021). However, these data sets are limited to the carbon degassing caused by regional metamorphism in the Himalayas (e.g., Becker et al., 2008; Newell et al., 2008) and focused on relatively limited regions of Lhasa terrane, for example, the geothermal fields in the Gulu‐Yadong rift (GYR, Figure 1b; Yokoyama et al., 1999; Zhang, Guo, Sano et al., 2017).…”

Recognition of Geothermal Surface Manifestations: A Comparison of Machine Learning and Deep Learning

“…A recent study indicates that 3 He/ 4 He analysis of thermal springs locates the mantle suture in a continental collision [52]. State-of-the-art methods like GIS and remote sensing, ML and DL (e.g., ANN, CNN, and transformer), and other photographic technology could improve geothermal data analysis and analytical model building methods.…”