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This study investigates the water vapor transport to the Tibetan Plateau (TP) induced by Bay of Bengal (BOB) tropical cyclones (TCs) in May during 1979–2019. The water vapor around the BOB TCs can be transported to the south of the TP by the southerlies at the upper troposphere east of the TC center. Whether the water vapor can cross the southern boundary of the Tibetan Plateau (SBTP) may rely on the different configurations of BOB TCs and long-wave trough and ridge. We found that the water vapor may (may not) cross SBTP if the TC's wind field converges with the westerlies in front of the trough (ridge). The physical mechanism is explored according to the momentum equation. When the TC moves northward around the SBTP, its wind field could interact with the trough (Type-T TC) and ridge (Type-R TC) in the westerlies. In the area close to the trough line (ridge line), the meridional acceleration is positive (negative), hence meridional component of velocity increases (decreases). Therefore, it is more favorable for the water vapor transported northward if the Type-T TC's wind field enters the westerlies from the area close to the trough line than the ridge line. The simulation of the BOB TC cases using WRF model confirms the importance of the relative position between the Type-T TC and the SBTP to the water vapor transport over the SBTP. For the Type-T TC, the meridional moisture budget over the SBTP is positively correlated with the TC intensity and negatively correlated with the meridional distance between the TC center and the SBTP. However, for the Type-R TC, the meridional moisture budget is not related to the TC intensity and the meridional distance. The configuration of TC and long-wave trough or ridge may be predictable through the intraseasonal oscillation activity in the eastern BOB and the southern Arabian Sea. [ABSTRACT FROM AUTHOR]

The mechanisms driving crustal deformation and uplift of orogenic plateaus are fundamental to continental tectonics. Large‐scale crustal flow has been hypothesized to occur in eastern Tibet, but it remains controversial due to a lack of geologic evidence. Geochemical and isotopic data from Cenozoic igneous rocks in the eastern Tibet‐Gongga‐Zheduo intrusive massif, provide a way to test this model. Modeling results suggest that Cenozoic magmas originated at depths of ∼30–40 km, the depth that crustal flow has been postulated to occur at. Detailed isotopic analyses indicate that the igneous rocks are derived from partial melting of the local Songpan‐Ganzi crust, arguing against a long‐distance crustal flow. Episodic magmatism during the Cenozoic showing a repeated shifting of magmatic sources can be correlated with crustal uplift. The continued indentation of the Indian Block and upwelling of the asthenosphere contribute to the crustal deformation, magmatism, and uplift. Plain Language Summary: How the Tibetan Plateau grows outward and deformed remains controversial. A large‐scale crustal flow model has been favored for the expansion of the southeast Tibetan Plateau, arguing that crustal materials could flow hundreds of km resulting in crustal thickening and uplift. Detailed geochemical and isotopic investigations on the largest intrusion (Gongga‐Zheduo) in the eastern margin of the Tibetan Plateau show that their magmatic source is local crustal rocks of the Songpan‐Ganzi terrane without the input of crustal materials from central Tibet. Thermodynamic and trace element modeling results show that the Cenozoic magma is derived from ∼30 to 40 km depth, similar to the depth of postulated crustal flow. The results are inconsistent with the large‐scale eastward crustal flow model. A repeated shifting of magmatic sources during the Cenozoic is correlated with crustal uplift. Mantle‐crust interaction plays a primary role in the formation of magmatism and modifying crustal rheology. The continued collision between the Indian and Asian blocks and upwelling of the asthenosphere contribute to the crustal deformation and uplift. Key Points: Isotopic and thermodynamic modeling results indicate that Gongga‐Zheduo granitic rocks in eastern Tibet are sourced from the local crustNo crustal materials from central Tibet are observed in eastern Tibet arguing against the large‐scale crustal flow modelCenozoic episodic magmatism in eastern Tibet with a repeated vertical shifting of sources is correlated with staged crustal uplift [ABSTRACT FROM AUTHOR]

The Tethys Himalaya tectonic belt has long been a passive continental margin north of Gondwana, commonly known as the Tethys Himalaya, which Indo-Asian collision orogeny developed until the Cenozoic era. It is of great scientific significance to determine its geo-tectonic evolution over geological history. Therefore, to reveal the geodynamic background of the Late Cretaceous Tethys Himalaya and its internal connection with the subduction of the Neo-Tethys ocean, in this study, we analysed the petrology, and whole-rock geochemistryof the Zongzhuo Formation basalt, which is widely distributed in the Tethys Himalaya Rongbu area. Further, we investigated the basalt types, magma source, tectonic setting and causes that gave rise to the Zongzhuo Formation to further research on the evolution of the Tethys Himalaya tectonic domain. The Zongzhuo Formation features a basalt set of compatible elements and is characterised by low Cr (average: 86.838 ppm) and enrichment of high-field-strength elements (e.g. Nb, Ta and Hf). The characteristics of the major elements, i.e. high TFeO (average: 10.43 wt %), TiO2 (average: 3.44 wt %) and P2O5 (average: 0.47 wt %), indicate an oceanic–island–basalt (OIB) geochemical signature with obvious light REE and heavy REE fractionation. The characteristics of the trace elements confirm the alkalinity of the Zongzhuo Formation basalts. Based on these results, the Zongzhuo Formation basalt was assigned to within–plate OIB. The magma might be the metasomatism products of the oceanic lithosphere mantle with low crystal fractionation and no crustal contamination, its tectonic background includes a passive–to–active transformation in the continental margin. By analysing the Tethys Himalaya belt in the south of Tibet, we concluded that the Zongzhuo Formation basalt strata in the Rongbu area were likely formed owing to Mesozoic volcanic activity and the extension and thinning of the Tethys Himalaya in the area. [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]

Monazite is a key accessory mineral for metamorphic geochronology, but interpretation of its complex chemical and age zoning acquired during high-temperature metamorphism and anatexis remains a challenge. We investigate the petrology, pressure-temperature and timing of metamorphism in pelitic and psammitic granulites that contain monazite from the Greater Himalayan Crystalline Complex (GHC) in Dinggye, southern Tibet. These rocks underwent isothermal decompression from pressure of >10 kbar to ~5 kbar at temperatures of 750-830 °C, and recorded three metamorphic stages at kyanite (M), sillimanite (M) and cordierite-spinel grade (M). Monazite and zircon crystals were dated by microbeam techniques either as grain separates or in thin sections. U-Th-Pb ages are linked to specific conditions of mineral growth on the basis of zoning patterns, trace element signatures, index mineral inclusions (melt inclusions, sillimanite and K-feldspar) in dated domains and textural relationships with co-existing minerals. The results show that inherited domains (500-400 Ma) are preserved in monazite even at granulite-facies conditions. Few monazites or zircon yield ages related to the M-stage (~30-29 Ma), possibly corresponding to prograde melting by muscovite dehydration. During the early stage of isothermal decompression, inherited or prograde monazites in most samples were dissolved in the melt produced by biotite dehydration-melting. Most monazite grains crystallized from melt toward the end of decompression (M-stage, 21-19 Ma) and are chemically related to garnet breakdown reactions. Another peak of monazite growth occurred at final melt crystallization (~15 Ma), and these monazite grains are unzoned and are homogeneous in composition. In a regional context, our pressure-temperature-time data constrains peak high-pressure metamorphism within the GHC to ~30-29 Ma in Dinggye Himalaya. Our results are in line with a melt-assisted exhumation of the GHC rocks. [ABSTRACT FROM AUTHOR]

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]