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The formation of magma reservoir and resultant construction of large batholith are increasingly recognized as long-term incremental processes. Here we employed back-scattered electron and cathodoluminescence images, in-situ major and trace elements, and Sr isotopes of plagioclase for five lithological groups from the Quxu complex batholith (south Tibet), which shed new light on the nature and incremental construction processes of batholith. Our results show that plagioclases display diverse textures and show systematic differences in geochemistry and Sr isotopes for different lithologies, indicating that their host rocks originated from multiple magma sources and/or underwent distinct magmatic processes. Plagioclases in Group I granodiorites and Group III mafic dykes and mafic magmatic enclaves exhibit comparable textural features (e.g., resorption and sieved textures) and share similar Sr (< 1500 ppm) and Ba (< 200 ppm) contents, and 87Sr/86Sr ratios (I Sr) (0.7035–0.7050) at given lower An (20–50) values, suggesting that they were evolved from similar mafic magma sources. The significant variations in An (20–90), Sr and Ba contents of plagioclase in Group III indicate both fractional crystallization and magma mixing. Plagioclases in Group II monzogranites have a similar An ranges to Group I but higher Sr (900–2200 ppm) contents and I Sr (mostly 0.7045 to 0.7066) values, suggesting that they formed from partial melting of juvenile mafic crust without significant mantle contribution. Plagioclases in Group IV granodiorites and Group V monzogranites exhibit higher Sr (500–3000 ppm) contents than other groups at given An values. Their I Sr values fall within the range of Group II, indicating a similar magma source. Abundant plagioclases displaying normal and oscillatory zonings in them implies that fractional crystallization occurred, while the presence of typical glomerocrysts in Group V indicates mush disaggregation. The simulation results of the trace elements indicate that the different lithologies of the Quxu batholith represent different states of magma reservoirs, corresponding to crystal mushes with varying degrees of extracted melts. The incremental growth processes of lager batholith operate as an open system, in which magma convection, mixing and recharge, crystal accumulation, recycling and reaction with melts, and mush disaggregation commonly occur. • Plagioclase can be an invaluable tool for investigating the detailed assembly and evolution processes of the batholith. • The Quxu batholith was constructed through long-term accumulation of repeated magma pulses in an open system. • The Quxu batholith is a crystal mush that has experienced different degrees of extraction of silicic melts. [ABSTRACT FROM AUTHOR]

• The 65–40 Ma exposed Gangdese batholiths mainly intruded into the middle to upper crust. • They are solidified crystal mushes that lost some interstitial liquids. • Most of them were mantle-derived and evolved through polybaric crystallization. • Polybaric differentiation processes play a key role in crustal differentiation. The understanding of storage conditions and evolution processes of igneous rocks is pivotal in unraveling the architecture and dynamics of trans-crustal magmatic systems. Here we combine amphibole major and trace elements compositions, geothermobarometers and chemometry and published whole-rock compositions of the Paleocene-Eocene (65–40 Ma) Gangdese batholith from longitude 85° E to 95° E to discuss the nature and formation processes of the batholith, explore the across sectional structure of the large-scale paleo-continental magmatic arc batholith, and reveal the resultant implications for crustal formation and evolution. The pressure results suggest that most of the exposed 65–40 Ma Gangdese batholith was emplaced at 1–8 kbar, corresponding to the middle to upper crust. Specifically, these exposed intrusions were predominantly emplaced at 2–4 kbar, with deeper denudation observed toward the eastern part of the Gangdese arc. The calculated melts in equilibrium with amphiboles are more silicic (mainly rhyolitic) than their host rocks (dioritic to granodioritic), yet share similar geochemical features with those of the coeval Gangdese high-Si granites and Linzizong high-Si rhyolites. This feature suggests that the granitoid batholiths represent crystal mushes that experienced varying degrees of partial melt loss prior to solidification, and high-Si magmas are residual silicic melts extracted from the batholitic magma mushes. The geochemical evolutionary trend of the 65–40 Ma Gangdese batholith parallels the 1–8 kbar isobaric and polybaric experimental liquid lines of descent of hydrous basaltic magmas. The whole-rock geochemical data suggest that most mafic samples of the Gangdese batholith are not primitive basaltic magmas, but rather underwent fractional crystallization at depth prior to emplacement. Some samples even contain minor amphiboles cores derived from magma reservoirs in the deep crust. These observations indicate that most of magmas were mainly mantle-derived and evolved through polybaric crystallization processes. The shallower granitoid batholiths could represent frozen fossilized magma mushes, intricately linked with shallow volcanic eruptions, magmatic processes in the deep crust, or even melting in the mantle source. Despite crustal rock remelting and magma mixing can occur during batholith formation, polybaric differentiation processes in trans-crustal magmatic columns, saturating with distinct mineral assemblages at different depths, crucially shapes the chemically stratified continental crust. [ABSTRACT FROM AUTHOR]

The origin of the K-feldspar megacrysts is still controversial and how magmas move in crystal-rich reservoir and the mechanism of the reactivation of crystal mushes after rheological locking are still elusive. K-feldspar megacryst in granitoids is a good candidate to constrain these issues. We carried out an integrated study of field geology, crystal size distribution (CSD), LA-ICP-MS zircon U Pb geochronology, whole-rock geochemistry, and in-situ major and trace elements and Pb isotopic compositions of K-feldspar megacrysts from the monzogranites and mafic microgranular enclaves (MMEs) of the Quxu batholith in the Gangdese belt, southern Tibet. The Quxu monzogranites have a magma crystallization age of ∼50 Ma. Some elements (e.g., Al, Sr, Cr and Ni) of the Quxu monzogranite and MMEs show scatter and no linear variations with increasing SiO 2 , indicating that simple magma mixing between mafic and felsic endmembers is unconspicuous for the formation of the Quxu monzogranites. The K-feldspar megacrysts from the Quxu monzogranites and MMEs can be divided into three types: normal zoning, reverse zoning and oscillatory zoning or no zoning. In-situ major and trace element of the K-feldspar megacrysts, combined with their variation in-situ Pb isotopic composition (206Pb/204Pb = 18.41–18.80, 207Pb/204Pb = 15.42–15.75 and 208Pb/204Pb = 38.29–39.06), indicate that the Quxu monzogranites were formed by the assembly of multiple heterogeneous magma pulses. The CSD results suggest that K-feldspar megacrysts have a longer residence time of 0.14–0.33 k.yr to 4.1–52 k.yr. We suggest that K-feldspar megacrysts could grow prolongedly via crystals transfer or magma injection of different batches in melt-present environments, and magma mush in cold-stored could be rejuvenated by the repeatedly recharging of hot magma pulses. • The Quxu monzogranites were formed by assembly of many heterogeneous magma pulses. • The K-feldspar megacrysts is the results of prolonged growth via crystal transfer or injection into different magma batches. • Rejuvenation of cold-stored mush is caused by repeatedly injection of multiple hot magma pulses. [ABSTRACT FROM AUTHOR]