Continental Crustal Growth Processes Recorded in the Gangdese Batholith, Southern Tibet

Abstract

The continental crust in the overriding plate of the India-Asia collision zone in southern Tibet is characterized by an overthickened layer of felsic composition with an underlying granulite-eclogite layer. A large data set indicates that this crust experienced magmatism from 245 to 10 Ma, as recorded by the Gangdese Batholith. Magmatism was punctuated by flare-ups at 185−170, 90−75, and 55−45 Ma caused by a combination of external and internal factors. The growth of this crust starts with a period dominated by fractional crystallization and the formation of voluminous (ultra)mafic arc cumulates in the lower crust during subduction, followed by their melting during late-subduction and collision, due to changes in convergence rate. This combined accumulation-melting process resulted in the vertical stratification and density sorting of the Gangdese crust. Comparisons with other similarly thickened collision zones suggests that this is a general process that leads to the stabilization of continental crust. ▪ The Gangdese Batholith records the time-integrated development of the world's thickest crust, reaching greater than 50 km at 55–45 Ma and greater than 70 km after 32 Ma. ▪ The Gangdese Batholith records three magmatic flare-ups in response to distinct drivers; the last one at 55−45 Ma marks the arrival of India. ▪ Magmatism was first dominated by fractional crystallization (accumulation) followed by crustal melting: the accumulation-melting process. ▪ Accumulation-melting in other collision zones provides a general process for vertical stratification and stabilization of continental crust.

Intraoceanic Subduction System Within the Neo‐Tethys: Evidence From Late Cretaceous Arc Magmatic Rocks of the Eastern Himalaya

“…It is widely accepted that a long‐lived Neo‐Tethyan subduction zone operated along the southern margin of Asia during the Late Triassic to Early Paleocene, as a Mesozoic continental magmatic arc is well documented from the southern part of Lhasa and Karakoram terranes (Chapman et al., 2018; Coulon et al., 1986; Debon et al., 1986; Ravikant et al., 2009; Searle & Hacker, 2018; C. Wang, Ding, Zhang, et al., 2016; Yin & Harrison, 2000). The remnants of this magmatic arc extend for over 2,500 km from the Karakoram, through Ladakh to Gangdese (Figure 1a), and consist of the Trans‐Himalayan batholith, which contains voluminous hornblende and biotite‐bearing granites, granodiorites, and diorites of calc‐alkaline I‐type affinity (Chung et al., 2005, 2009; L. Ding et al., 2003; Harris et al., 1988; Mo et al., 2005, 2007, 2008; Rolland, 2002; C. Wang, Ding, Zhang, et al., 2016; Wen et al., 2008; Zhu et al., 2011, 2019, 2023). This batholith and associated volcanic rocks mostly were generated during the Mesozoic to Early Paleocene, and therefore provides undisputed evidence for prolonged northwards subduction of Neo‐Tethyan oceanic lithosphere beneath the southern margin of the Asian plate (Chu et al., 2006; L. Ding et al., 2003; Guo et al., 2011; Ji et al., 2009; Wu et al., 2014; Yin & Harrison, 2000; Z. M. Zhang, Ding, Dong, et al., 2022; Zhu et al., 2011, 2019).…”

“…The remnants of this magmatic arc extend for over 2,500 km from the Karakoram, through Ladakh to Gangdese (Figure 1a), and consist of the Trans-Himalayan batholith, which contains voluminous hornblende and biotite-bearing granites, granodiorites, and diorites of calc-alkaline I-type affinity (Chung et al, 2005(Chung et al, , 2009L. Ding et al, 2003;Harris et al, 1988; Rolland, 2002;Wen et al, 2008;Zhu et al, 2011Zhu et al, , 2019Zhu et al, , 2023. This batholith and associated volcanic rocks mostly were generated during the Mesozoic to Early Paleocene, and therefore provides undisputed evidence for prolonged northwards subduction of Neo-Tethyan oceanic lithosphere beneath the southern margin of the Asian plate (Chu et al, 2006;L.…”

Fe–Mg Isotopes Trace the Mechanism of Crustal Recycling and Arc Magmatic Processes in the Neo‐Tethys Subduction Zone

“…The Gangdese arc is located at the central part of the >8,000‐km‐long Neo‐Tethyan arc system from Kohistan to Sumatra (Searle et al., 1987; X. Zhang et al., 2019), a product of the northward subduction of the Neo‐Tethyan oceanic slab under the Lhasa terrane in the southernmost part of the Asian continent, from at least the Middle Triassic to the end of the Mesozoic (e.g., Guo et al., 2020; Ji et al., 2009; Wen et al., 2008; Z. M. Zhang et al., 2010, 2014, Zhu et al., 2019, 2023; Figure 1a). The Lhasa terrane is classified into the northern, central, and southern subterranes, which are separated by the Shiquan River‐Nam Tso Mélange Zone and Luobadui Milashan Fault, respectively (e.g., Zhu et al., 2011; Figure 1b).…”

“…200-160 and ca. 105-85 Ma (Zhu et al (2023) and references therein). The existing arc rocks are composed of a large number of plutons with a small number of volcanic successions (Figure 1b).…”

“…The existing arc rocks are composed of a large number of plutons with a small number of volcanic successions (Figure 1b). The main products of the Cretaceous arc magmatism are gabbros/norites, diorites, granodiorites, with small amounts of ultramafic cumulates, including hornblendite, wehrlite, and dunite (Zhu et al (2023) and references therein). These plutons occur along a ∼50-km-wide, eastwest striking narrow belt, that is sub-parallel to the Indus Yarlung Zangbo Suture Zone (IYZSZ), from Xigaze in the central Gangdese arc (CGA; ∼88°-92°E) to Nyingchi in the eastern Gangdese arc (EGA; ∼92°-95°E) (Figure 1b; L. Chen et al, 2022;W.…”