Miocene high-temperature leucogranite magmatism in the Himalayan orogen

Abstract

Himalayan leucogranites of Cenozoic age are generally attributed to partial melting of metasedimentary rocks at low temperatures of <770 °C. It is unknown what the spatial distribution and characteristics of high-temperature (>800 °C) leucogranites are in the Himalayan orogen. The present study reports the occurrence of such leucogranites in the collisional orogen. We use the Ti-in-zircon thermometry in combination with the thermodynamically calibrated relationships of T-aSiO2-aTiO2 to retrieve crystallization temperatures of Miocene (ca. 17 Ma) two-mica granites from Yalaxiangbo, in the eastern Himalaya, SE Tibet. The results give the maximum temperature as high as ∼850 °C for granite crystallization, providing a significant constraint on the nature of thermal sources. Phase equilibrium modeling using metasedimentary rocks as the source rocks indicates that felsic melts produced at ∼850 °C and 6−10 kbar can best match the target leucogranites in lithochemistry. In this regard, the anatectic temperatures previously obtained for the production of Himalayan leucogranites would probably be underestimated to some extent. Such high temperatures are difficult to explain purely by the internal heating of the thickened orogenic crust. Instead, they require an extra heat source, which would probably be provided by upwelling of asthenospheric mantle subsequent to thinning of the orogenic lithospheric mantle by foundering along the convergent plate boundary. Therefore, the Himalayan leucogranites of Miocene age would be derived from partial melting of the metasedimentary rocks in the post-collisional stage.

Fluid circulation in the South Tibetan Detachment System: Evidence from fluid inclusions and oxygen isotope data of quartz veins in the Ramba Dome, North Himalayan Gneiss Domes

“…The equilibrium fractionation between quartz and water was used to estimate δ 18 O fluid values for the leucogranites (Fekete et al, 2016). Given that the crystallization temperature is about 800 C for granites in the NHGD (Gao, Zheng, Mayne, & Zhao, 2020), the calculated δ 18 O fluid is 12.51-13.40‰. Bodnar, 1980).…”

Copper-rich tin deposits

“…However, where mafic magma and associated fluid recharge of the silicic chambers does not take place, Cu-poor Sn deposits are the likely outcome. As a corollary, Sn deposits associated with ilmenite-series, S-type magmas generated in thickened crust without direct mafic magma input should be Cu-poor, with the Miocene Himalayan leucogranites being the type example (Cao et al 2021;Gao et al 2021). In contrast, where appreciable metasedimentary crust is not involved in transcrustal magma systems, Cu deposits, particularly those of porphyry type, are the norm.…”

Origin of the Miocene Adakitic Rocks and Implication for Tectonic Transition in the Himalayan Orogen: Constraints from Kuday Granitoid Porphyry in Southern Tibet

“…A number of discontinuous North Himalayan Gneiss Domes (NHGD) are distributed in the THS [58]. These NHGD exposed the high-grade metamorphic rocks that form a natural window of insight into the structure of the Himalayan Orogen [11,14,[59][60][61][62][63][64]. Sakya Dome, one of the NHGD, is located in the central part of the Himalayan Orogen and has been studied well [10,38,[60][61][62].…”

“…Himalayan Orogen [85]. The contribution of the mantle to the formation of the leucogranite includes (1) upwelling of asthenosphere providing an additional heat source to the continued partial melting of the GHC [64,86] and (2) causing significant N-S extension and the extrusion of the GHC, which induced or enhanced decompression melting of the GHC [87]. However, the discussions about the deep dynamic processes and mantle-derived heat promote the formation of the leucogranites are scarce in the Himalayan Orogen [13,19].…”

“…The presence of three magmatic events concentrated in the Miocene may be a result of a uniform tectonic setting, asthenospheric upwelling, which led to the partial melting at different depths [64]. The leucogranite represented partial melting of mid-lower crustal metasedimentary rocks [9-14, 81, 82], and the adakitic rocks represented partial melting of lower crustal mafic rocks [26][27][28][29], and potassic/ ultrapotassic rocks represented partial melting of the lithospheric mantle [46].…”