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Accommodation of India-Asia convergence via strike-slip faulting and block rotation in the Qilian Shan fold-thrust belt, northern margin of the Tibetan Plateau
No full textExisting models of intracontinental deformation have focused on plate-like rigid body motion v. viscous-flow-like distributed deformation. To elucidate how plate convergence is accommodated by intracontinental strike-slip faulting and block rotation within a fold-thrust belt, we examine the Cenozoic structural framework of the central Qilian Shan of northeastern Tibet, where the NW-striking, right-slip Elashan and Riyueshan faults terminate at the WNW-striking, left-slip Haiyuan and Kunlun faults. Field- and satellite-based observations of discrete right-slip fault segments, releasing bends, horsetail termination splays and off-fault normal faulting suggest that the right-slip faults accommodate block rotation and distributed west-east crustal stretching between the Haiyuan and Kunlun faults. Luminescence dating of offset terrace risers along the Riyueshan fault yields a Quaternary slip rate of c. 1.1 mm a(-1), which is similar to previous estimates. By integrating our results with regional deformation constraints, we propose that the pattern of Cenozoic deformation in northeastern Tibet is compatible with west-east crustal stretching/lateral displacement, non-rigid off-fault deformation and broad clockwise rotation and bookshelf faulting, which together accommodate NE-SW India-Asia convergence. In this model, the faults represent strain localization that approximates continuum deformation during regional clockwise lithospheric flow against the rigid Eurasian continent. Supplementary material: Luminescence dating procedures and protocols is available at Thematic collection: This article is part of the Fold-and-thrust belts and associated basins collection available at
Dust storms in northern China during the last 500 years
No full textThe history and mechanisms of dust storms in northern China remain unclear owing to the paucity of reliable long-term, high-resolution geological records. In this study, we reconstructed the dust storm history of the last similar to 500 years in northern China, based on sedimentary coarse fraction (>63 mu m) of a well-dated core from Lake Daihai, Inner Mongolia. The high-resolution data reveal three intervals of frequent dust storms: AD 1520-1580, AD 1610-1720, and AD 1870-2000. The dust storm events in the Lake Daihai area were broadly synchronous with those inferred from other historical or geological records and generally occurred during cold intervals. Changes in the intensity of Siberian High and the westerlies modulated by temperature variations are the likely major factors controlling dust storm dynamics. An interesting feature is that although the intensities of dust storms have been systematically increased during the recent warming period, a clear decreasing trend within this period is evident. The recent increase in average dust storm intensity may be ascribed to an increase in particle supply resulting from a rapid increase in human activity, whereas the weakening trend was likely caused by decreases in average wind speed resulting from the recent global warming
Distinct effects of winter monsoon and westerly circulation on dust aerosol transport over East Asia
No full textThe transport of dust aerosol in East Asia is affected by the East Asian winter monsoon (EAWM) and westerly circulation both for modern and geological periods. There are obvious seasonal changes in the intensity and range of EAWM and westerly jet; however, their impacts and relative contributions to East Asian dust transmission are still unclear. In this study, we use Regional Climate Model 4 (RegCM4) to simulate the changes in the East Asian dust cycle under present conditions, assessing the effects of EAWM and westerly jet on dust transport. The results show that the dust at the upper level is mainly transported by the westerly circulation, while that of the lower layer is mainly transported by the EAWM. In March, the westerly jet is located on the south side of the Tibet Plateau, and the high-level dust aerosol is transmitted eastward to the northern Pacific. Low-level dust is transmitted to the southeastern China with the influence of EAWM. With the northward shift of the westerly jet, the control range of the westerly winds increases in May and their correlations are weakened. In contrary, the impact of EAWM on the lower layer dust is enhanced. Due to the strengthened interaction between the westerly winds and the EAWM, they can both affect the middle-level dust transmission. The effect of EAWM is sensitive to the dust particle sizes. Under the action of EAWM, fine-grained dust is transmitted far away, while coarse-grained dust is limited to the vicinity of the source area. Once the dust is carried to the westerly layer, the influence of westerly winds on the transmission of different particle sizes dust is similar
Spatiotemporal variation, sources, and secondary transformation potential of volatile organic compounds in Xi'an, China
No full textAs critical precursors of ozone (O-3) and secondary organic aerosols, volatile organic compounds (VOCs) play a vital role in air quality, human health, and climate change. In this study, a campaign of comprehensive field observations and VOC grid sampling was conducted in Xi'an, China, from 20 June to 20 July 2019 to identify the spatiotemporal concentration levels, sources, and secondary transformation potential of VOCs. During the observation period, the average VOC concentrations at the Chanba (CB), Di Huan Suo (DHS), Qinling (QL), and gridded sampling sites were 27.8 +/- 8.9, 33.8 +/- 10.5, 15.5 +/- 5.8, and 29.1 +/- 8.4 ppb, respectively. Vehicle exhaust was the primary source of VOC emissions in Xi'an, and the contributions of vehicle exhaust to VOCs at the CB, DHS, and QL sites were 41.3 %, 30.6 %, and 23.6 %-41.4 %, respectively. While industrial emissions were the second-largest source of VOCs in urban areas, contributions from aging sources were high in rural areas. High potential source contribution function values primarily appeared in eastern and southern Xi'an near the sampling site, which indicates that Xi'an exhibits a strong local VOC source. Moreover, alkenes, aromatics, and oxygenated VOCs played a dominant role in secondary transformation, which is a major concern in reducing O-3 pollution in Xi'an
Constraining Paleoearthquakes by Combining Faulted Stratigraphy and Microgeomorphology: A Case Study on the Haiyuan Fault, Northwestern China
No full textSurface-rupturing strong earthquakes will leave evidence distributed along fault zones. The combination of paleoearthquake trench excavation and faulted microgeomorphic analysis at the same site provides more comprehensive knowledge of paleoearth-quakes than either method could accomplish alone. In this article, we report on our use of trench excavation and dating, together with a 5-cm resolution digital elevation model obtained from an unmanned aerial vehicle based on the structure from motion photogrammetry technology, to investigate the timing and size of strong paleoearth-quake events in the Dashagou site near the west end of the Haiyuan fault, which rup-tured in the 1920 Haiyuan earthquake. The result reveals that at least four strong paleoearthquake events with the same or even higher magnitude (including the 1920 Haiyuan earthquake) have occurred along the west end of the Haiyuan fault since the mid-Holocene. Event IV occurred shortly before 6.0 ka with a horizontal displace-ment of 4.27 +/- 1.50 m and a vertical displacement of 0.70 +/- 0.39 m. Event III occurred at approximately 4.65 +/- 0.45 ka with a horizontal displacement of 5.45 +/- 1.25 m and a vertical displacement of 0.38 +/- 0.23 m. Event II occurred at approximately 1.0 ka with a horizontal displacement of 3.86 +/- 0.90 m and a vertical displacement of 0.55 +/- 0.27 m. The most recent event was the 1920 Haiyuan earthquake, with a horizontal displace-ment of 2.15 +/- 0.82 m and a vertical displacement of 0.26 +/- 0.12 m. From the results of these four events, we can certainly conclude that the fault has mainly maintained the strike-slip kinematic pattern over the past 6 ka. These observations highlight the benefits of combining trench excavation and faulted microgeomorphology to gain a more complete understanding of paleoearthquakes
Improved Oxygen Activation over a Carbon/Co3O4 Nanocomposite for Efficient Catalytic Oxidation of Formaldehyde at Room Temperature
No full textOxygen activation is a key step in the catalytic oxidation of formaldehyde (HCHO) at room temperature. In this study, we synthesized a carbon/Co3O4 nanocomposite (C-Co3O4) as a solution to the insufficient capability of pristine Co3O4 (PCo3O4) to activate oxygen for the first time. Oxygen activation was improved via carbon preventing the agglomeration of Co3O4 nanoparticles, resulting in small particles (approximately 7.7 nm) and more exposed active sites (oxygen vacancies and Co3+). The removal efficiency of C-Co3O4 for 1 ppm of HCHO remained above 90%, whereas P-Co3O4 was rapidly deactivated. In static tests, the CO2 selectivity of C-Co3O4 was close to 100%, far exceeding that of P-Co3O4 (42%). Various microscopic analyses indicated the formation and interaction of a composite structure between the C and Co3O4 interface. The carbon composite caused a disorder on the surface lattice of Co3O4, constructing more oxygen vacancies than P-Co3O4. Consequently, the surface reducibility of C-Co3O4 was improved, as was its ability to continuously activate oxygen and H2O into reactive oxygen species (ROS). We speculate that accelerated production of ROS helped rapidly degrade intermediates such as dioxymethylene, formate, and carbonate into CO2. In contrast, carbonate accumulation on P-Co3O4 surfaces containing less ROS may have caused P-Co3O4 inactivation. Compared with noble nanoparticles, this study provides a transition metal-based nanocomposite for HCHO oxidation with high efficiency, high selectivity, and low cost, which is meaningful for indoor air purification
Time-Spatial Features of Mix El Nino
No full textThe diversity of El Nino is a critical field of the climate research. The eastern Pacific (EP) and central Pacific (CP) types of El Nino have been identified in the previous studies. However, the extreme El Nino event that occurred in 2015-2016 is quite different from both the EP and CP El Nino events. The sea surface temperatures anomalies (SSTA) for this event widely spread in both the central and eastern Pacific and have a small zonal gradient in the central-eastern Pacific. Many researchers regarded this event as a mixed type of El Nino. Using the regression-EOF method, the Mix El Nino pattern is extracted from the tropical Pacific SSTA field during the period from 1900 to 2019. Here, we reveal that the Mix El Nino is a very usual rather than a new type of El Nino, it is just that the EP and CP El Nino events are more frequent since the 1980s, while the Mix El Nino events frequently appear before the 1980s. The time-spatial features of the Mix El Nino are further investigated. The results demonstrate a unique westward propagation of the maximum SSTA for the Mix El Nino from the far eastern Pacific to the central Pacific. In contrast, the SSTA center is locked in the far eastern Pacific region for the EP El Nino and the central Pacific region for the CP El Nino. The evolutions of subsurface ocean temperature anomalies and sea surface height anomalies are also examined to support this. The ocean-atmosphere interaction plays an important role in the evolution of the Mix El Nino. The anomalous atmospheric Walker circulation for the Mix El Nino is mainly in the western and central Pacific as well as very weak in the eastern Pacific. In contrast, there are significant westerlies/easterlies in the eastern Pacific for the EP/CP El Nino. The small gradient of SSTA in the central-eastern Pacific for the Mix El Nino leads to weak zonal wind anomalies, which further weaken the zonal gradient of SSTA. All this suggests that the Mix El Nino is not unusual and fundamentally different from the EP and CP El Nino with important implications for global climate effects
Time-Spatial Features of Mix El Nino
No full textThe diversity of El Nino is a critical field of the climate research. The eastern Pacific (EP) and central Pacific (CP) types of El Nino have been identified in the previous studies. However, the extreme El Nino event that occurred in 2015-2016 is quite different from both the EP and CP El Nino events. The sea surface temperatures anomalies (SSTA) for this event widely spread in both the central and eastern Pacific and have a small zonal gradient in the central-eastern Pacific. Many researchers regarded this event as a mixed type of El Nino. Using the regression-EOF method, the Mix El Nino pattern is extracted from the tropical Pacific SSTA field during the period from 1900 to 2019. Here, we reveal that the Mix El Nino is a very usual rather than a new type of El Nino, it is just that the EP and CP El Nino events are more frequent since the 1980s, while the Mix El Nino events frequently appear before the 1980s. The time-spatial features of the Mix El Nino are further investigated. The results demonstrate a unique westward propagation of the maximum SSTA for the Mix El Nino from the far eastern Pacific to the central Pacific. In contrast, the SSTA center is locked in the far eastern Pacific region for the EP El Nino and the central Pacific region for the CP El Nino. The evolutions of subsurface ocean temperature anomalies and sea surface height anomalies are also examined to support this. The ocean-atmosphere interaction plays an important role in the evolution of the Mix El Nino. The anomalous atmospheric Walker circulation for the Mix El Nino is mainly in the western and central Pacific as well as very weak in the eastern Pacific. In contrast, there are significant westerlies/easterlies in the eastern Pacific for the EP/CP El Nino. The small gradient of SSTA in the central-eastern Pacific for the Mix El Nino leads to weak zonal wind anomalies, which further weaken the zonal gradient of SSTA. All this suggests that the Mix El Nino is not unusual and fundamentally different from the EP and CP El Nino with important implications for global climate effects
Isotopic Compositions (Li-B-Si-O-Mg-Sr-Nd-Hf-Pb) and Fe2+/sigma Fe Ratios of Three Synthetic Andesite Glass Reference Materials (ARM-1, ARM-2, ARM-3)
No full textTo expand the newly developed ARM glasses as reference materials for in situ microanalysis of isotope ratios and iron oxidation state by a variety of techniques such as SIMS, LA-MC-ICP-MS and EPMA, we report Li-B-Si-O-Mg-Sr-Nd-Hf-Pb isotope data and Fe2+/sigma Fe ratios for these glasses. The data were mainly obtained by TIMS, MC-ICP-MS, IR-MS and wet-chemistry colorimetric techniques. The quality of these data was cross-checked by comparing different techniques or by comparing the results from different laboratories using the same technique. All three glasses appear to be homogeneous with respect to the investigated isotope ratios (except for B in ARM-3) and Fe2+/sigma Fe ratios at the scale of sampling volume and level of the analytical precision of each technique. The homogeneity of Li-B-O-Nd-Pb isotope ratios at the microscale (30-120 mu m) was estimated using LA-MC-ICP-MS and SIMS techniques. We also present new EPMA major element data obtained using three different instruments for the glasses. The determination of reference values for the major elements and their uncertainties at the 95% confidence level closely followed ISO guidelines and the Certification Protocol of the International Association of Geoanalysts. The ARM glasses may be particularly useful as reference materials for in situ isotope ratio analysis
Collapse of the Liangzhu and other Neolithic cultures in the lower Yangtze region in response to climate change
No full textThe Liangzhu culture in the Yangtze River Delta (YRD) was among the world's most advanced Neolithic cultures. Archeological evidence suggests that the Liangzhu ancient city was abandoned, and the culture collapsed at similar to 4300 years ago. Here, we present speleothem records from southeastern China in conjunction with other paleoclimatic and archeological data to show that the Liangzhu culture collapsed within a short and anomalously wet period between 4345 +/- 32 and 4324 +/- 30 years ago, supporting the hypothesis that the city was abandoned after large-scale flooding and inundation. We further show that the demise of Neolithic cultures in the YRD occurred within an extended period of aridity that started at similar to 4000 +/- 45 years ago. We suggest that the major hydroclimatic changes between 4300 and 3000 years ago may have resulted from an increasing frequency of the El Nino-Southern Oscillation in the context of weakened Northern Hemisphere summer insolation