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The Lhunze region of southeast Tibet uniquely juxtaposes Cenozoic granitic plutons with subvolcanic rocks in the Tethyan Himalayan Sequence. In this study, the potential petrogenetic connection between two-mica granite and subvolcanic rhyolite porphyry from the Lhunze area is investigated using petrology, geochronology, and geochemistry. Monazite Th Pb ages imply the two-mica granite crystallized during the mid-Eocene at c. 43.5–43.1 Ma, consistent with previous zircon U Pb isotope data. Monazite in the porphyry also records Th Pb ages of c. 44.5–42.9 Ma , suggesting contemporaneous emplacement with the two-mica granite. Porphyritic structure, feldspar aggregates and comb alignment demonstrate that the two-mica granite resulted from transient melt flow associated with melt extraction. Some plagioclase phenocrysts from the porphyry have consistent An contents with the two-mica granite, indicating that both the two-mica granite and the porphyry probably originated from a similar melt. However, the porphyry has a higher SiO 2 concentration (72.2–75.9 wt%) than the two-mica granite (69.0–73.0 wt%). In addition, the porphyry is characterized by lower TiO 2 , MgO, CaO, Ba, Sr, and Zr contents as well as Zr/Hf, Sr/Y, Nb/Ta ratios than the two-mica granite. Moreover, strontium and REE contents of monazite in both the two-mica granite and porphyry also imply that crystal fractionation dominated melt evolution. Whole-rock Sr Nd and in situ monazite Nd isotope compositions indicate that the porphyry is slightly more radiogenic than the two-mica granite, implying that the porphyry likely assimilated more ancient country rocks during its evolution. We interpret the two-mica granite and porphyry as comagmatic intrusives linked by fractional crystallization of a cognate magma mush, in which the crystals accumulated to form the two-mica granite, and the complementary high silicic melt segregated to form the porphyry. Plagioclase accumulation is responsible for the generation of the high Sr /Y adakitic geochemical feather within two-mica granite. The scenario of complementary melt extraction and crystal fractionation might also have been an important process in forming the Himalayan leucogranites. Regionally, Neo-Tethyan slab breakoff during the Eocene could have increased mantle heat flow and triggered the generation and extraction of large volumes of silicic melt. • Two-mica granite and subvolcanic rhyolite porphyry have a coeval crystallization age at 44–43 Ma. • Two-mica granite represents cumulate and the porphyry as its complementary highly fractionated melt. • Magma differentiation via melt extraction from crystal mush is an effective mechanism to produce Himalayan leucogranites. [ABSTRACT FROM AUTHOR]

Determining the geochronological framework and geochemical nature of magmatism associated with orogenic processes is crucial to decipher the evolution of orogenic belts. The Himalayan orogen has recorded considerable information regarding deformation, metamorphism, and magmatism related to orogenic processes. Here, we identify four stages of granitic magmatism on the basis of monazite U–Th–Pb dating of rocks from the Lhagoi Kangri dome, north Himalayan antiform, southern Tibet: middle Eocene (42–40 Ma), late Eocene (ca. 36 Ma), Oligocene (ca. 26 Ma), and Miocene (16–13 Ma). The middle Eocene tourmaline-bearing leucogranite is characterized by (1) relatively high SiO 2 (78.7 wt%), Al 2 O 3 (12.6 wt%), and Na 2 O (6.3 wt%) contents; (2) enrichment in light rare earth elements (LREEs), depletion in heavy REEs, high abundances of REEs, and pronounced negative Eu anomalies; and (3) relatively low values of whole-rock Sr Nd isotope compositions (87Sr/86Sr(t) = 0.72101 and εNd(t) = −9.8). And the coeval garnet–bearing two–mica granite has a pronounced negative Eu anomaly (Eu/Eu* = 0.07) and a significate lanthanide tetrad effect (TE 1,3 = 1.46). These geochemical data suggest that these leucogranites underwent fractional crystallization. They provide a robust evidence for that anatexis of the lower crust of Indian plate began at 42–40 Ma in the central Himalayan orogen. The Oligocene and Miocene two–mica granites share broadly similar geochemical characteristics, such as moderate REE contents and weak negative Eu anomalies, and are distinct from the garnet-bearing muscovite leucogranite. Whole-rock Sr Nd isotope compositions of the Oligocene and Miocene leucogranites differ from those of the middle Eocene leucogranites, with higher 87Sr/86Sr(t) ratios (0.73524–0.74188) and lower εNd(t) values (−14.7 to −13.7). These geochemical data indicate that the Oligocene and Miocene leucogranites are products of muscovite-dehydration melting of metasedimentary rocks. The garnet-bearing muscovite leucogranite shows the REE tetrad effect, which suggests that it is more evolved than the coeval two–mica granite. We therefore infer that the variations in age and isotopic characteristics of the studied leucogranites were caused by a change in melt source resulting from the compression–extension evolution of the Himalayan collisional orogenic system. • Four-stage emplacement of leucogranites were identified in the Lhagoi Kangri dome. • The age and isotopic variations of leucogranites result from a change in melt source. • Middle Eocene leucogranites reveal a long-lived anatexis in the Himalayan orogen. [ABSTRACT FROM AUTHOR]