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The pressure–temperature (P‐T) path of blueschist is usually applied to understanding the evolution of the subducted oceanic crust. Garnet plays a key role in calculating the metamorphic conditions, but sometimes it is absent in the blueschists. Nevertheless, the high‐P experimental simulation may serve as a useful tool to constrain the P‐T conditions. In the middle of the Longmu Co‐Shuanghu Suture, North Tibet, blueschist blocks embedded in the marble were discovered, where garnet is abundant in the core but absent in the marble‐contacting margin. These two kinds of blueschist contain similar mineral assemblage (glaucophane, epidote, and phengite) and show comparable basaltic character. Pseudosection modelling was applied to the garnet‐bearing blueschist that calculated the peak metamorphic condition of ca. 1.9 GPa and 530°C. As for the garnet‐absent blueschist, experiments (1.2–2.3 GPa and 500–800°C) were performed on the designed mixture of 93 wt% basalt and 7 wt% calcite. The results show that the total Fe content in the glaucophane and barroisite is positively correlated with the pressure but not with temperature, which could be regarded as a geobarometer. Accordingly, the peak condition was constrained at 2.3 GPa and 500–600°C. Therefore, the equivalent metamorphic conditions of the blueschists indicate that the Palaeo‐Tethys oceanic crust subducted into at least 70 km. Furthermore, both the experiments and the T‐X (CaCO3) pseudosection, constructed based on basaltic lithology, support that the absence of garnet in the blueschist is predominantly caused by the mixing of calcite. In summary, this study provides a valid attempt in exploring metamorphic conditions by experiment simulation, and evaluates the profound influence of the interaction between the basaltic crust and overlying carbonate‐bearing sediments in the subduction zone. [ABSTRACT FROM AUTHOR]

The identification of a microcontinent in Bangong–Nujiang suture zone (BNSZ) is important to understanding the tectonic evolution of Bangong–Nujiang Tethys Ocean (BNTO). Subduction‐related ophiolite is one of the keys to discriminate a microcontinent in suture zones, which can be generated during the oceanic subduction beneath the microcontinent. Generally, ophiolites in the adjacent area of a microcontinent would show characteristics of a volcanic arc, while ophiolites in adjacent area of an ocean show characteristics of a fore‐arc. North Pengco ophiolites (NPOs) and South Pengco ophiolites (SPOs) were collected in the central section of BNSZ, and dated at 115.0–111.5 Ma by SHRIMP II. According to their trace element characteristics, NPOs were determined to have formed at a setting of subduction‐related volcanic arc and affected by slab‐derived fluids or melts. The diagram based on the Ce versus Ce/Y shows that NPOs originated from the partial melting of spinel peridotites. On the other hand, SPOs were generated from the partial melting of ultra‐depleted mantle at a setting of subduction‐related fore‐arc on the basis of extraordinarily low REEs summation and HFSEs (e.g., Zr, Ti, Nb and Ta), relatively high concentrations of compatible elements (e.g., Cr, Ni), large ratios of CaO/TiO2 (37.67–437.50) and Al2O3/TiO2 (20.78–424.50), which were also affected by slab‐derived fluids. Based on the relative location of NPOs and SPOs, it reasonably proposed that a northward subduction of a minor oceanic basin had occurred at the Early Cretaceous, trigged by the Dongkaco microcontinent (DMC). In reverse, these ophiolites provide evidence for the existence of DMC in BNTO. Combining with other subduction‐related ophiolites developed in BNSZ, BNTO might have comprised of several minor oceanic basins separated by some blocks like DMC in the central and west sections, rather than a unified ocean basin. [ABSTRACT FROM AUTHOR]

Domestic consumption of biomass fuels has been found as a leading source of polycyclic aromatic hydrocarbons (PAHs) in pristine regions. The biomass ashes would serve as both source and vector for PAHs, which may threaten residents' health. However, research focusing on the behaviors of waste biomass ashes acting as emission resources of PAHs is still lacking. In present study, occurrence and fate of PAHs released from disposal biomass ashes in the Tibetan Plateau were investigated by evaluating their patterns and levels in soils at different distances from the Lhasa landfill. Concentrations of 16 PAHs averaged at 1009 ng/g dry weight and 103 ng/g dry weight in landfill cover soils and surrounding soils, respectively. The spatial distributions of PAHs evidenced the local source of biomass ashes in landfill, while the fractionations of PAHs in soils profiles emphasized the post-deposal leaching. Since PAH compositions altered significantly during their transport and sequestration, the rectification factors were suggested to adjust the source diagnostic ratios. In study area, the emission flux of PAHs from waste biomass ashes to soils was 0.93 ton/year; extended to the Tibetan Plateau, the flux was estimated to be 13.1–32.5 ton/year. This study confirmed that waste biomass ashes would represent significant contributions of PAH emissions in this pristine region, which might remarkably exacerbate the total emissions of PAHs in Tibet by more than 25%. Image 1 • Biomass ashes disposed in Tibetan urban landfill served as a local PAH source. • Leaching process of PAHs was affected by their congener hydrophobicity and SOC contents. • Calibration factors were proposed for source diagnostic ratios. • PAH emission inventory of biomass ashes may reach 13.1–32.5 tons/year in Tibet. Biomass ashes acted as a local source of PAHs in the Tibetan Plateau, which remarkably exacerbated the total emissions of PAHs in this region by more than 25%. [ABSTRACT FROM AUTHOR]

• Rapid desorption, slow desorption and bound residue fractions were detected in sediment cores. • PAH history in different areas of Tibet addressed coherent response in Anthropocene. • Aging-weathered PAH profile in sediments revealed past information of energy use. • Molecular docking simulations well predicted the fraction transformation tendencies. Polycyclic aromatic hydrocarbons (PAHs) were supposed to serve as combustion marker reflecting the past energy use, but it was unclear whether their sediment records in the Anthropocene were "weathered" due to aging-induced formation of bound residues. In this study, the total concentration of PAHs (the sum of rapid desorption, slow desorption, and bound residue fractions) were determined in four dated sediment cores from eastern to central Tibet using multi-step sequential extraction method. The total 16 PAH concentrations were 11.8, 13.5, 18.9, and 29.4 ng/g dw (in average) in the Co Ngoin, Pung Co, Ahung Co, and Putok lakes, respectively. The stratigraphic records and estimated source contributions of PAHs in different areas of Tibet exhibited a coherent change in the mid-20th century in response to the Holocene-Anthropocene transition. The sediment PAHs also displayed a comparable pattern when the bound residue fraction was not accounted for, suggesting their effective retainability under natural aging conditions. This may be elucidated by the enduring forward and back conversions between slow desorption and bound residue fractions, which manifested similar time-dependent variations across PAH congeners. The distinct conversion tendencies of different congeners were predicted by the binding affinity of congeners to surface/inner regions of organic matter using molecular docking simulations. Our findings demonstrate the persistence of sediment PAH records under natural aging and validate the use of PAH documentary evidence for investigating the Anthropocene. [Display omitted] [ABSTRACT FROM AUTHOR]

Dichlorodiphenyltrichloroethane (DDT) compounds are still circulating the global environment even though the technical DDT has been restricted in agriculture since the last century. The persistent presence of DDTs worldwide remains uncertain, as it is unclear whether their existence is primarily due to ongoing use or the prolonged persistence in soils and sediments that result in continuous reemission into the atmosphere. The present study applied a sequential extraction procedure to determine the DDT concentrations in rapid desorption, slow desorption, and bound residue fractions in the dated sediment cores from distinct regions of Tibet. The temporal variation of total DDTs (sum of three fractions) in sediments from southern and eastern Tibet respectively revealed the different DDT usage histories in India and China mainland. Nevertheless, the current application volumes of DDT-containing products in these regions were found to decrease significantly. The reversible transformations among three fractions of DDTs with aging time was observed along sediment profile, including the back conversion from bound residue. This process may be the key driver to prolong the half-life of sediment p , p '-DDT, resulting in the persistence of secondary sources of this persistent organic pollutant in the global environment for a longer duration than previously expected. [Display omitted] • Tibetan sediment revealed diverse technical DDT/dicofol use histories across Eurasia. • The transformation among three fractions of DDTs proceeded in the past eight decades. • The planar conformation may contribute to the aging differences of DDT compounds. • The half-life of sediment p,p' -DDT was prolonged due to aging effect. [ABSTRACT FROM AUTHOR]

Magmatic flare-ups are well recognized as a fundamental feature of continental arc magmatism, but its driven mechanism still remains unresolved. Exploring this behavior is of significance in unraveling the deep dynamic processes related to plate subduction and crustal growth. In central Tibet, arc magmatism within the South Qiangtang terrane (SQT) caused by the northward subduction of the Bangong-Nujiang Ocean (BNO) is featured by a prominent high-flux event during Jurassic, but its details and corresponding geodynamic background are not determined. This paper reports geochronological and geochemical data of the granodiorites near the Rigen Co area in the middle part of SQT. These rocks were generated at ca. 150 Ma and display typical adakitic characters. Their low MgO (1.41–2.39 wt%), initial 87Sr/86Sr ratios (0.7055–0.7059) and slightly low ε Nd (t) values (−1.9 to −1.2), and high zircon ε Hf (t) (+1.9 to +8.4) and δ18O values (+6.6 to +9.2 ‰) suggest the adakitic granodiorites were derived from partial melting of subducted crust involving 10–20% inputs of overlying sediment. Our sample, together with previous reports delineates a distinct slab-window association (adakite and oceanic island basalt (OIB)-type diabase) along the southmost of SQT, which coincided with the magmatic flare-up at ca. 155 Ma as revealed by the age spectra of magmatic rocks and complementary detrital zircons. Furthermore, a trench-ward migration is recognized for the arc magmatism from ca. 170 Ma to 155 Ma, implying a slab-roll back process. Accordingly, this high-flux event with the slab-window formation is best explained by the trigger of ensuing slab break-off. These results, combined with other geological evidence, contribute new constraints on elucidating the Jurassic geodynamic evolution of the BNO subduction. • The Rigen Co granodiorites were generated by oceanic crust melting at ca. 150 Ma. • Jurassic arc magmatism in the South Qiangtang terrane shows a trench-ward migration. • The Late Jurassic magmatic flare-up was triggered by slab break-off. • A oceanic plateau-continent collision was proposed to explain these processes. [ABSTRACT FROM AUTHOR]

Background contamination levels of contemporary persistent organic pollutants (POPs) may be elevated due to local discharges, and hence it is of high importance to assess and monitor them in alpine and Polar Regions. This study investigated the role of waste disposal in the Tibetan plateau as the local source of short-chain chlorinated paraffins (SCCPs). SCCPs were determined in soils from the urban landfill and rural dumpsites, with a concentration range of 56.8–1348 ng/g dw. The gradient descent of SCCP levels from Lhasa landfill to the surrounding soils with increasing distances suggested a significant SCCP release from waste disposal. The transport pattern was well fitted by the Boltzmann equation after normalization in terms of soil organic carbon contents. Compared to the landfill cells closed in early years, the recently closed cells contained higher concentrations but lower proportions of the short-chain congener groups, likely reflecting the SCCP use history in Tibet. In open-burning dumpsites, higher SCCP levels and dominance of lighter congener groups indicates that such crude waste treatment process might cause an extra release of volatile SCCPs. This study elucidates local SCCP inputs to the background environment, and demonstrates that both urbanization and badly-managed landfill have been contributing to the presence of contemporary POPs in the Tibetan Plateau. Image 1 • Tibetan urban landfill was evidenced as a local source for SCCPs. • Boltzmann equation well described the transport of SCCPs. • Temporal shifts of SCCP profiles in landfill soils may reflect use history. • Open-burning in Tibetan rural dumpsites caused an extra release of SCCPs. [ABSTRACT FROM AUTHOR]