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Maximum plant height (Hmax), stem tissue mass density (SD), leaf mass per area (LMA), and relative growth rate (RGR) have all been linked to flowering phenology. However, it is still unknown whether these functional traits varying with flowering phenology are related to other floral traits associated with pollinator preference and reproductive success. We investigated the relationship between vegetative and floral traits, as well as the rates of insect visitation and seed set of five Gentiana species in eastern Tibetan meadows. Our results showed that flowering onset and flowering offset time were all found to be positively correlated with the Hmax, SD, and LMA, but negatively correlated with the RGR. Flowering onset time was positively correlated with corolla diameter and pollen grain number, whereas was negatively correlated with flower number and flower longevity. The rates of insect visitation were positively related to flowering onset time, pollen grain number, corolla diameter, and seed set, but negatively related to flower number and longevity. Early flowering species have higher RGR but lower SD, LMA and Hmax, as well as smaller flowers, fewer pollen grains, longer flower longevity, and lower insect visitation rates than late-flowering plant species. Our findings indicate that floral traits are related to vegetative traits in Gentiana species. Also these plant trait relationships were associated with pollinator preference, and plant reproductive success of eastern Tibetan meadows. We speculate that these traits relationships are likely adaptive in unpredictable and often pollinator-limited environments in the Tibet alpine meadows. [ABSTRACT FROM AUTHOR]

Southernmost Tibet exhibits an anomalously twice the normal thickness of average continental crust. There is no available theory to explain and the driving mechanism remains uncertain. Here, we interpret a north-striking, 180 km-long deep seismic reflection profile traversing the southern Lhasa terrane (SLT) to the central Lhasa terrane (CLT). In addition to reflections showing subducting Indian crust, our results reveal lateral heterogeneity between the SLT and CLT, where north-dipping reflections beneath the CLT outline a tilted crystalline basement, while the non-reflective domain beneath the SLT represents homogeneous juvenile crust. Our integrated analysis leads to models calling upon episodic magmatism onto the southern margin of the basement to result in progressive construction of the SLT. We hypothesize that this crustal thickening via crustal-scale magma accretion contributed to surface uplift of the southern margin of the Tibetan plateau and leading to the development of the vast internal drainage system of Tibet. Mechanism driving continental growth on modern Earth has long been debated. By interpreting the long deep seismic reflection data across the ongoing India-Eurasia collision zone, the authors report crustal-scale magma accretion onto the south of central Lhasa terrane produced net continental growth. [ABSTRACT FROM AUTHOR]

There has been considerable debate concerning the petrogenesis of Cenozoic highly felsic, strongly peraluminous, leucogranites within the Himalayan–Tibetan orogen, with two contrasting viewpoints regarding their origin, either as primary melts from parting melting or magmatic differentiation. This debate hampers our understanding of the tectono‐magmatic evolution and associated uplift and exhumation processes during Himalayan orogenesis. This study attempts to resolve this debate by means of an integrated petrographic, geochronological, and geochemical study on the Cenozoic Cuonadong leucogranites (including two‐mica granites, garnet‐bearing granites, and tourmaline‐bearing granites) in the eastern part of the south Himalayan–Tibetan orogen. One SHIRIMP zircon U–Pb dating of two‐mica granites and four LA–ICP–MS monazite U–Th–Pb dating of all three types of granites yield ages of ca. 21.9–19.7 Ma. Combined with previous published continuous U–Th–Pb zircon/monazite ages varying from 16.5 to 21.8 Ma, indicating that Cuonadong leucogranites have experienced continuously multiple episodes of intrusion and long‐term crystallization from ca.16 to 22 Ma, and lasted for ca. 6 Myrs. Major and trace element geochemistry combined with whole‐rock Sr–Nd isotope data suggest that the Cuonadong's three types of leucogranites are highly fractionated and garnet‐ and tourmaline‐bearing granites are more evolved. The Cuonadong leucogranite melts are mainly derived from metapelites within the High Himalayan Crystalline Sequence, and underwent fractional crystallization of biotite, monazite, and plagioclase during melt migration. This study indicates Cuonadong leucogranites are Cenozoic highly fractionated strongly peraluminous leucogranites, which, combined with previous intermittent documentations of fractionated leucogranites, point to an increasing maturation of the continental crust composition during continental orogenesis. [ABSTRACT FROM AUTHOR]

The ongoing India‐Asia collision has led to the formation of the northern Himalayan gneiss domes belt in southern Tibet. The domes are the result of the ongoing convergence and were formed by geological processes that may include crustal thickening, metamorphism, partial melting, and exhumation of middle crustal rocks to the surface. A combination of compressional, extensional, and diapiric processes has been invoked to explain the formation and evolution of these domes. Differentiating among these competing hypotheses requires well‐defined geophysical images of the internal structure of the domes. The Mabja dome is the largest dome within the northern Himalayan gneiss domes belt. A 70‐km long deep seismic reflection profile across Mabja dome was acquired in 2016. The seismic data could provide new information about the structural elements beneath the domes to the depth of 25 Km. We address the structure of the Mabja dome by conducting an integrated analysis of shallow crustal velocity structure and a normal‐incidence seismic reflection image of deeper crust. Our work suggests that the Mabja dome is underlain by shear zones at depths of 10–15 km and two high‐velocity bodies at depths of 3 km possibly representing the eclogitic‐facies rocks or mafic intrusions. We propose that the dome formation may have been controlled by collision‐induced north‐south shortening expressed by thrust stacking of middle crustal rocks, which led to the doming of the upper‐crustal rocks. The proposed mechanism inferred for Mabja dome can be applied to interpret the widespread domes throughout the southern Tibet and other related structures in orogenic mountain belts. Key Points: Two high‐velocity bodies, with an average velocity as high as 6.6 and 7.2 km/s, are constrained at a depth of 3 km from the surfaceA series of sub‐horizontal reflections are observed at depths of 11–20 km which are interpreted to represent a thrust systemThe thrust stacking in the middle crust is the main mechanism that controls the formation of the Mabja dome formation [ABSTRACT FROM AUTHOR]

The Xiaojiang Fault Zone (XJF) is an important boundary fault on the southeast border of the Tibetan Plateau, with a complex subterranean structure and strong tectonic activity. In the present study, 252 seismograph stations were deployed in the northern section of the XJF to collect ambient noise data in a span of 35 days. The minimum resolution attained was 2 km × 2 km to develop a high-precision underground velocity structure model. The velocity model helped in revealing that the low-velocity distribution originated below the XJF. It was also found that the fault, which is the primary channel for magma to rise, might be the cause of the upper crustal deformation of the XJF. The Dongchuan mining area is located to the west of the XJF, which has a low-velocity structure. However, the high-velocity structure appeared on both sides of the ore body. It is speculated that the ore was formed by magma intrusion. The intrusion serves as a heat source for the mining area and promotes deposit formation. [Display omitted] • A short-period dense array based ambient noise tomography for Xiaojiang fault. • High and low velocity 3D structure under Xiaojiang fault. • Deep ore metallogenesis constraints beneath the Dongchuan ore field. [ABSTRACT FROM AUTHOR]

• Integrated broadband and dense-nodal seismic-array investigation in northern Tibet. • Revealing significant Moho offsets indicative of deep thrust shear zones. • Imaging stark contrasts across the Haiyuan Fault indicative of strain partitioning. • Northern Tibetan plateau margin was constructed by a lithospheric-scale thrust-wedge. • Our results favor an overall oblique continental subduction model. The Tibetan plateau is one of the best field laboratories to investigate mechanisms of continental-lithosphere deformation, which contrasts sharply with the typical rigid-plate behavior of the oceanic lithosphere. Several end-member processes have been proposed for the plateau formation involving vertically coherent pure-shear shortening, decoupled upper- and lower-crustal shortening, oblique continental subduction, and crustal channelized flow. In order to test the above models, we conducted an integrated broadband and dense-nodal seismic-array investigation along two traverses across the northern Tibetan plateau margin in the Qilian Shan and its foreland region. The integrated observation provides the first coherent structural image of the lithosphere in general and shallow crust correlative to surface geology in particular in northern Tibet with an updated resolution. Our seismic imaging shows that the surface-exposed south-dipping Qilian Shan frontal thrust zone is closely associated with a low-velocity zone with concentrated seismicity in the upper crust, and along an inclined convertor can be extended downward into the middle-lower crust near a >10-km Moho offset beneath the Haiyuan Fault zone. This dipping feature and an inferred lithospheric detachment zone with oriented anisotropic fabrics constitute a lithospheric-scale thrust zone that bounds crustal-scale thick-skinned thrusts above, coupled with the development of distributed thrust shear zones that cut across the lowermost crust and uppermost mantle. We interpret the bounding lithospheric-scale thrust zone as the basal thrust of a thrust-wedge system across the northern Tibetan plateau margin. A minimum ∼26% bulk shortening strain is accommodated in the thrust-wedge system, which is compatible with the surface-geology constraints. Together with magnetotelluric data, our seismic imaging reveals stark contrasts in the crustal structure and rheology across the left-slip Haiyuan Fault. The involvement of strain partitioning across this regional structure in the thrust wedge supports the earlier proposed transpressional continental underthrusting of North China beneath the Tibetan plateau. [ABSTRACT FROM AUTHOR]

Although the Lhasa terrane of southern Tibet is an integral part of the Tibetan plateau, how the area has achieved its current high altitude of ~5000 m remains poorly understood. This is largely due to the fact that little is known about deep (>15 km) crustal structures and the depth and geometry of the Moho below the terrane. In this study, we address this question by acquiring and analyzing high-resolution seismic reflection data gathered from four high-energy dynamite shots along a 137-km north-south traverse spanning the southern Lhasa terrane. Our new seismic data reveal the presence of north-dipping reflectors in the crust, a seismically weak-reflection layer at the lowermost crust, and a sub-horizontal and locally discontinuous Moho at depth of 69–72 km with a crustal velocity of 6.30 km/s. The discordant relationship between the crustal dipping reflectors, the subhorizontal lower crustal layer, and the flat Moho suggests that the ~12-km basal section of the Lhasa terrane crust is a decoupling zone accommodating different styles of lithospheric-scale deformation. Because the north-dipping reflectors can be projected and/or connected with the reflectors in the Cenozoic Himalayan thrust system and the southernmost Lhasa terrane, we propose that the dipping crustal reflectors are parts of a south-directed crustal-scale thrust duplex created by the Cenozoic India-Asia collision. The relatively discontinuous and horizontal geometry at the base of the crust indicates that the Moho was reconstituted through ductile deformation in the lowermost crust caused by abnormally high temperature. Unlabelled Image • Moho geometry is observed on a 137-km, deep seismic profile in the Lhasa terrane. • North-dipping intra-crustal reflections are observed. • The Moho depth remains constant at ~69–72 km beneath the Pumqu-Xianza rift. • The flat Moho geometry contrasts with the north-dipping intra-crustal reflections. • A comprehensive model is proposed to document this varied tectonic response. [ABSTRACT FROM AUTHOR]

The uplift mechanism and geodynamic model of the northeastern (NE) Tibetan Plateau remain controversial. Two competing models have been proposed for the uplift of the NE Tibetan Plateau, including crustal shortening through folding or thrust faulting and the middle-lower crustal flow model. Here, we applied the joint inversion of surface wave dispersions and receiver functions with P-wave velocity constraints on a dense linear broadband seismic array to obtain the Vs and Vp/Vs profiles of the crust and uppermost mantle across northeastern Tibet. The inversion yields robust structural images that show stark Vs and Vp/Vs jumps across the West Qinling fault from the Songpan-Ganzi and Kunlun-West Qinling terranes (south) to the Qilian and North China terranes (north). The results reveal that regional low-Vs/high-Vp/Vs anomalies present in the middle-to-lower crust, which may be the signature of viscous flow, are distinctly limited south of the West Qinling fault. In contrast, the imaged physical properties of the crust and mantle lithosphere north of this fault manifest a rigid pattern, which is inferred to be originated from the North China craton underthrust below the northern margin of the Tibetan plateau. Our seismic imaging indicates that the NE corner of the Tibetan Plateau does not currently serve as the flow channel of the ductile material from the central and northern Tibet. • Joint inversion produces crustal Vs and Vp/Vs structures across NE Tibet. • Revealing a distinct lithospheric property contrast across the West Qinling fault. • North of the West Qinling fault is manifested as a rigid pattern. • Inferred crustal flow is limited south of the West Qinling fault. [ABSTRACT FROM AUTHOR]

The geodynamic setting of Late Triassic magmatic activity along the Longmu Co–Shuanghu suture zone (LSSZ) in central Qiangtang, Tibet is a matter of debate. This paper presents zircon LA–ICP–MS U–Pb ages, zircon Hf isotopic compositions, and whole-rock geochemical data for the Sangehu (SGH) granitic intrusion in central Qiangtang, and addresses the petrogenesis of Late Triassic magmatism, and the history of collision between the northern and southern Qiangtang terranes. The SGH pluton consists mainly of biotite adamellite with mafic microgranular enclaves (MMEs), and small amounts of K-feldspar granite. The biotite adamellite, MMEs, and K-feldspar granite give ages of 207.8 ± 3.0 Ma, 212.4 ± 31 Ma, and 211.6 ± 3.8 Ma, respectively. The MMEs show magmatic textures and acicular apatite, and are coeval with the host biotite adamellite, suggesting they were produced by magma mixing. All samples from the SGH pluton show high Sr and low Y contents, and positive Eu anomalies, similar to adakitic rocks. The high K 2 O contents and low Mg#, Cr, and Ni contents, and enriched Hf isotopic characteristics of the zircons indicate that these magmas were derived from the partial melting of thickened crust. However, the whole-rock geochemical data and zircon Hf isotopic compositions also reveal heterogeneity at the source. The combined magmatic and metamorphic records suggest that Triassic magmatic activity in central Qiangtang was closely related to the collision of the northern and southern Qiangtang terranes. The large-scale Late Triassic (225–200 Ma) magmatic event in central Qiangtang may have resulted from the breakoff of the Longmu Co–Shuanghu Tethys Ocean lithospheric slab in the early Late Triassic (236–230 Ma). The Late Triassic magmatic rocks, including adakitic rocks, are coeval with retrograde high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks in central Qiangtang, and show characteristics of syn-exhumation magmatism. The early adakitic rocks (>220 Ma) were generated by melting of the edge of the slab, which was heated by upwelling asthenospheric mantle after subduction slab breakoff, and the late adakitic rocks (<220 Ma) were generated by partial melting of the thickened crust. [ABSTRACT FROM AUTHOR]