The Himalayan Collisional Orogeny: A Metamorphic Perspective

Abstract

This paper introduces how crustal thickening controls the growth of the Himalaya by summarizing the P‐T‐t evolution of the Himalayan metamorphic core. The Himalayan orogeny was divided into three stages. Stage 60–40 Ma: The Himalayan crust thickened to ∼40 km through Barrovian‐type metamorphism (15–25 °C/km), and the Himalaya rose from <0 to ∼1000 m. Stage 40–16 Ma: The crust gradually thickened to 60–70 km, resulting in abundant high‐grade metamorphism and anatexis (peak‐P, 15–25 °C/km; peak‐T, >30 °C/km). The three sub‐sheets in the Himalayan metamorphic core extruded southward sequentially through imbricate thrusts of the Eo‐Himalayan thrust, High Himalayan thrust, and Main Central thrust, and the Himalaya rose to ≥5,000 m. Stage 16–0 Ma: the mountain roots underwent localized delamination, causing asthenospheric upwelling and overprinting of the lower crust by ultra‐high‐temperature metamorphism (30–50 °C/km), and the Himalaya reached the present elevation of ∼6,000 m. Underplating and imbricate thrusting dominated the Himalaya' growth and topographic rise, conforming to the critical taper wedge model. Localized delamination of mountain roots facilitated further topographic rise. Future Himalayan metamorphic studies should focus on extreme metamorphism and major collisional events, contact metamorphism and rare metal mineralization, metamorphic decarbonation and the carbon cycle in collisional belts.

A timeline of the Cenozoic tectonic–magmatic–metamorphic evolution and development of ore resources in the Himalayas

“…The HHT divides the GHC into upper and lower parts (Wang et al, 2015). The U–Pb ages of monazite record the prograde, peak and retrograde stages of the upper GHC at 35–33 Ma, 30–26 Ma and 20–16 Ma, respectively, while the stages of the lower GHC are 33–27 Ma, 26–20 Ma and 15–14 Ma, respectively (Goscombe et al, 2018; Wang, Wu, et al, 2022). This indicates that the subduction and exhumation of the two rock slices above and below the HHT occurred in sequence (Figure 5c, d).…”

“…However, in general, the pressure (6 kbar) and temperature (550°C) of the LHS during the peak period of metamorphism are much lower than those of the GHC and its metamorphism time is also later than that of the GHC (Figure 5e). The metamorphic facies of the LHS consist of greenschist and amphibole and the prograde, peak and retrograde metamorphism times recorded by monazite U–Pb ages are approximately 16–15 Ma, 10–7 Ma and 6–3 Ma, respectively (Figure 3) (Goscombe et al, 2018; Wang, Wu, et al, 2022). It should be noted that along the strike in the Himalayas, not only does the P–T–t–H 2 O of the GHC and NHGD differ greatly in different places but also the metamorphism process of the LHS is very different in different places (Kohn, 2014; Searle, 2015).…”

“…The most complex and controversial process involves the exhumation mechanism, denudation process and metamorphism time of the GHC. This is especially reflected in the debate surrounding the two end‐member models of channel flow and critical wedge (Wang, Wu, et al, 2022; Webb et al, 2017). Among them, research on the upper and lower boundary faults (STDS and MCT) of the GHC and the properties and activity time of the HHT in the GHC are critical (Cottle et al, 2015).…”

“…For example, (1) in terms of tectonic evolution, palaeomagnetic evidence suggests that there was a “Great India Basin” on the northern margin of the Indian continent during the Cretaceous period, which led to two collisions between the India and Lhasa blocks (van Hinsbergen et al, 2012) circa 58 Ma and 25–15 Ma (van Hinsbergen et al, 2019). (2) In terms of the metamorphism and denudation of the middle–upper crust, new geological evidence indicates that the Greater Himalayan Crystalline complex (GHC) is not a complete ductile metamorphic zone but is divided into upper and lower tectonic regions by the High Himalayan Thrust (HHT) (Carosi et al, 2018), which challenges the perspective that the metamorphism and exhumation of the GHC were driven by the classical channel flow model (Wang, Wu, et al, 2022). (3) The latest magmatic rock research found that in addition to leucogranites derived from the low‐degree partial melting of the GHC (Cao, Pei, et al, 2022), a large number of Cenozoic intermediate‐basic magmatic rocks, such as lamprophyre (Liu et al, 2021), gabbro (Ma et al, 2023) and silicocarbonatite (Hu et al, 2022), developed during the Cenozoic in the Himalaya.…”

Latest Neogene Paleoclimate Variation in Yunnan, Southwest China, Revealed by Fossil Leaf Physiognomy

“…Recently some researchers argued that the Tibetan Plateau was not a coherent rise as one unit but rather a high low-relief surface (a plateau) developed as a result of tectonic processes spanning at least 200 million years (Spicer et al, 2020(Spicer et al, , 2021a. The interactions between the topography, climate, and biodiversity in the Tibetan region are complex because of the development of the Tibet (Xiong et al, 2020;Li et al, 2021;Wang et al, 2022). On the other hand, the transition from a -greenhouse‖ to an -icehouse‖ Earth occurred during the Neogene.…”