Late Cretaceous (~81Ma) high-temperature metamorphism in the southeastern Lhasa terrane: Implication for the Neo-Tethys ocean ridge subduction

Abstract

An integrated study of U\Pb zircon dating, geochemical and Sr\Nd\Hf isotopic compositions of garnet-bearing granulite and marble from the granulite-facies domain of the Nyingchi Complex (eastern Himalayan syntaxis) has provided insights into the tectonic evolution of the southern Lhasa terrane. The peak metamorphism of the garnet-bearing granulite is marked by a mineral assemblage of garnet + orthopyroxene + high-Ti amphibole + plagioclase + quartz + rutile. Abundant exsolved rutile needles are observed within amphibole, garnet and quartz. The peak metamorphic temperatures are estimated at 803-924°C. Geochemical data from the garnet-bearing granulites provide evidence for a basaltic protolith that formed in a continental-margin arc setting. Sr\Nd\Hf isotopic compositions indicate that this protolith was sourced from partial melting of a depleted mantle. LA-ICP MS U\Pb zircon dating shows that the protolith age and metamorphic age of the garnet-bearing granulites are 89.3 ± 0.6 Ma and 81.1 ± 0.8 Ma, respectively. The detrital magmatic zircons from the marble yield ages from 86.3 to 167 Ma. The age distribution and Hf isotopic composition (ε Hf (t) = +5.9 to +17.5) of the detrital magmatic zircon in the marble are consistent with the isotopic data of zircons from the Jurassic-Cretaceous Gangdese batholiths, suggesting that the clastic sediments were partially derived from these intrusives or associated volcanic rocks, and deposited in the fore-arc basin of the Gangdese arc. The metamorphic zircons in the marble yield a metamorphic age of 81.4 ± 0.5 Ma. These results show that both the arc magmatic rocks and forearc sedimentary rocks underwent high-temperature (HT) granulite-facies metamorphism at~81 Ma, indicating anomalously high heat input in the forearc region. A range of tectonic observations, including a coeval hiatus in arc magmatism and a period of regional uplift, indicate that HT metamorphism resulted from the subduction of the Neo-Tethys ocean ridge beneath the southern Lhasa terrane during the Late Cretaceous.

Metamorphic imprint of accretion and ridge subduction in the Pan‐African Damara Belt, Namibia

“…Considering that ridge subduction is an inescapable consequence of plate tectonics and an inevitable process associated with suturing and supercontinent assembly, it is perhaps surprising that it has not been more readily recognized in the geological record. Tethyan ridge subduction prior to Himalayan collision is proposed to account for the metamorphism and adakite‐like magmatism preserved in the Lhasa terrane of southeastern Tibet (Zhang et al ., ; Guo et al ., ), but to the best of our knowledge, this is the first instance where the imprint of ridge subduction is recognized from a suture zone associated with supercontinent assembly. An obvious explanation for its apparent scarcity in the geological record is that the accretionary history is typically pervasively overprinted and reworked during the subsequent collisional stage.…”

“…This heating results in the occurrence of localized high‐ T metamorphism in the otherwise low‐ T –high‐ P domain, and has been recognized in some modern accretionary margins associated with circum‐Pacific subduction, including British Columbia (Fairchild & Cowan, ; Rusmore & Cowan, ), Alaska (Pavlis & Sisson, ) and Japan (Hibbard & Karig, ; Underwood et al ., ; Brown, ). However, the metamorphic imprint of ridge subduction and heating by the slab window is only rarely recognized in older accretionary complexes (Zhang et al ., ; Guo et al ., ), and has not been described for suture zones associated with supercontinent assembly. This could be because in these areas accretionary metamorphism is typically overprinted by collisional orogenesis, causing the accretionary assemblages to be pervasively re‐equilibrated to higher temperature conditions (e.g.…”

Identification of a new source for the Triassic Langjiexue Group: Evidence from a gabbro-diorite complex in the Gangdese magmatic belt and zircon microstructures from sandstones in the Tethyan Himalaya, southern Tibet

“…These voluminous magmatic rocks belong to four major flareups at 237-160 Ma, The first flareup has been suggested to have subduction-related calc-alkaline affinity, owing to the subduction of the Neotethyan oceanic lithosphere (Lang et al, 2017;Meng et al, 2016a). Two different models have been proposed for the 100-80 Ma magmatic flareup: one is ridge subduction (Guo et al, 2013a;Zhang et al, 2010), and the other is extension due to slab rollback (Ma et al, 2015). The 65-40 Ma magmatic flareup, represented by the Linzizong volcanic rocks and Quxu batholith, resulted from slab rollback and breakoff associated with the Indo-Asian collision (Ding et al, 2003;Mo et al, 2003Mo et al, , 2005bLee et al, 2009b).…”

Tectonic erosion and crustal relamination during the India-Asian continental collision: Insights from Eocene magmatism in the southeastern Gangdese belt

“…1B) mainly consists of the high-grade metamorphic Nyingchi Complex and Mesozoic−Cenozoic (165−22 Ma) granitoids (Booth et al, 2004;Dong et al, 2012;Guo et al, 2011Guo et al, , 2012Guo et al, , 2013Ji et al, 2017;Zhang et al, 2008Zhang et al, , 2010aZhang et al, , 2010bZhang et al, , 2013Zhang et al, , 2014Zhang et al, , 2015. The Nyingchi Complex represents the exposed middle-lower crust of the Gangdese arc and is composed of mafic and felsic granulites, amphibolites, migmatites, orthogneisses, paragneisses and marble (Guo et al, 2012(Guo et al, , 2013Zhang et al, 2010bZhang et al, , 2013Zhang et al, , 2014Zhang et al, , 2015. The mafic granulites from the Nyingchi Complex have protolith ages of 82-95 Ma and metamorphic ages of 90-68 Ma (Guo et al, 2013;Zhang et al, 2010bZhang et al, , 2014.…”

“…The Nyingchi Complex represents the exposed middle-lower crust of the Gangdese arc and is composed of mafic and felsic granulites, amphibolites, migmatites, orthogneisses, paragneisses and marble (Guo et al, 2012(Guo et al, , 2013Zhang et al, 2010bZhang et al, , 2013Zhang et al, , 2014Zhang et al, , 2015. The mafic granulites from the Nyingchi Complex have protolith ages of 82-95 Ma and metamorphic ages of 90-68 Ma (Guo et al, 2013;Zhang et al, 2010bZhang et al, , 2014. Their protoliths have depleted Sr-Nd-Hf isotopic compositions that are typical of arc magmatic rocks (Guo et al, 2013;Zhang et al, 2014).…”