Gangdese magmatism in southern Tibet and India–Asia convergence since 120 Ma

Abstract

A compilation of 290 zircon U–Pb ages of intrusive rocks indicates that the Gangdese Batholith in southern Tibet was emplaced from c. 210 Ma to c. 10 Ma. Two intense magmatic pulses within the batholith occur at: (1) 90 ± 5 Ma, which is restricted to 89–94° E in the eastern segment of the southern Lhasa subterrane; and (2) 50 ± 3 Ma, which is widespread across the entire southern Lhasa subterrane. The latter pulse was followed by a phase of widespread but volumetrically small, dominantly felsic adakitic intrusive rocks at 16 ± 2 Ma. The Linzizong volcanism in the Linzhou Basin was active from 60.2 to 52.3 Ma, rather than 69–44 Ma as previously estimated. During 120–75 Ma, Gangdese Batholith magmatism migrated from south to north, arguing against rollback of the downgoing, north-dipping Neo-Tethyan oceanic lithosphere for the generation of the 90 ± 5 Ma magmatic pulse. Petrological, geochemical and metamorphic data indicate that this pulse was likely to have been generated through subduction of the Neo-Tethyan oceanic ridge lithosphere. Subsequent Gangdese Batholith magmatism propagated both south and north during 70–45 Ma, and finally concentrated at the southern margin of the Lhasa Terrane at 45–30 Ma. The enhanced mafic magmatism since c. 70 Ma, magmatic flare-up with compositional diversity at c. 51 Ma and increased magmatic temperature at 52–50 Ma are interpreted as the consequences of slab rollback from c. 70 Ma and slab breakoff of the Neo-Tethyan oceanic lithosphere that began at c. 53 Ma. The India–Asia convergence was driven by Neo-Tethyan subduction with a normal rate of convergence at 120–95 Ma, ridge subduction at 95–85 Ma, then subduction of a young and buoyant oceanic lithosphere after ridge subduction with rate deceleration at 84–67 Ma, Deccan plume activity and slab rollback with rate acceleration at 67–51 Ma, slab breakoff for sudden drop of the convergence rate at c. 51 Ma, and finally the descent of the high-density Indian continental lithosphere beneath Asia since c. 50 Ma.

Reconciling Orogenic Drivers for the Evolution of the Bangong‐Nujiang Tethys During Middle‐Late Jurassic

“…Collisional orogenic belts involve an initial accretionary episode of oceanic slab subduction and subsequent continental collision (Cawood et al, 2009;Dewey & Spall, 1975;Murphy & Nance, 1991;Zhu et al, 2019). The magmatic systems that develop on the upper plate during subduction and initial collision record the processes of convergence and orogenesis (Cawood et al, 2009;Stern, 2002;Zhu et al, 2019).…”

Discovery of Vestige Sedimentary Archives of the India‐Asia Collision in the Eastern Yarlung Zangbo Suture Zone

“…N is the number of igneous samples from Lhasa Terrane instead of analyzed zircon number. Data sources: Triassic sandstone of Lhasa Terrane compilation from Li et al (2014), Li et al (2016); the Rongmawa Fm within trench from Cai et al (2012), Wang et al (2018), Metcalf and Kapp (2019), Laskowski et al (2019); igneous rocks of Lhasa Terrane compilation from Wen et al (2008), Ji et al (2009), Zhu et al (2011), Zhu et al (2017), Zhu et al (2018), Zhang et al (2014), Wang, Wu, et al (2016), Zhao et al (2016), Li et al (2018), Zhou et al (2018), Zhang et al (2019); Triassic sandstone of NE Tethys Himalaya (Langjiexue Group, Shannan Terrane) from Aikman et al (2008), Aitchison et al (2011), Li et al (2010), Li et al (2016), and Webb et al (2013); Jiachala Fm of NE Tethys Himalaya from Wu et al (2014); Cretaceous sandstones of NE Tethys Himalaya from Hu et al (2010) and Hu et al (2012).…”

Aeromagnetic Anomalies in Central Yarlung‐Zangbo Suture Zone (Southern Tibet) and Their Geological Origins

“…The rock types include gabbro, diorite, granodiorite, monzogranite, and syenogranite. U‐Pb dating of the Gangdese granitoids suggests that there were four major stages of magmatism: 205–152 Ma (Jurassic), 109–80 Ma (late Cretaceous), 65–41 Ma (Paleocene‐Eocene), and 33–13 Ma (Oligocene‐Miocene), with the 65–41 Ma range being the most prominent stage (Ji et al, ; Zhu et al, ).…”

“…Dong et al () linked these mafic rocks to the north magnetic lineament, with no further discussion, but the scale of these gabbroic rocks in the Gangdese batholith is relatively small compared to the north magnetic lineament (Figure d). In fact, the granitoids in the Gangdese batholith always contain abundant mafic enclaves and dykes (Ji et al, ; Zhu et al, ), indicating that the formation of the Gangdese granitoids may have been related to mafic magma. Therefore, we consider that the Gangdese batholith containing massive mafic constituents is the most likely explanation for the source of the north magnetic lineament in the YZS zone.…”