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From 24 January 2020 to 18 May 2020, Chaoshan took measures to limit the spread of coronavirus disease 2019 (COVID-19), such as restricting public gatherings, wearing masks and suspending classes. We explored the effects of these measures on the pathogen spectrum of paediatric respiratory tract infections in Chaoshan. Pharyngeal swab samples were collected from 4075 children hospitalised for respiratory tract infection before (May–December 2019) and after (January–August 2020) the COVID-19 outbreak. We used liquid chip technology to analyse 14 respiratory pathogens. The data were used to explore between-group differences, age-related differences and seasonal variations in respiratory pathogens. The number of cases in the outbreak group (1222) was 42.8% of that in the pre-outbreak group (2853). Virus-detection rates were similar in the outbreak (48.3%, 590/1222) and pre-outbreak groups (51.5%, 1468/2853; χ2 = 3.446, P = 0.065), while the bacteria-detection rate was significantly lower in the outbreak group (26.2%, 320/1222) than in the pre-outbreak group (44.1%, 1258/2853; χ2 = 115.621, P < 0.05). With increasing age, the proportions of respiratory syncytial virus (RSV) and cytomegalovirus (CMV) infections decreased, while those of Mycoplasma pneumoniae and adenovirus infections increased. Streptococcus pneumoniae, CMV and rhinovirus infections peaked in autumn and winter, while RSV infections peaked in summer and winter. We found that the proportion of virus-only detection decreased with age, while the proportion of bacteria-only detection increased with age (Table 2). Anti-COVID-19 measures significantly reduced the number of paediatric hospitalisations for respiratory tract infections, significantly altered the pathogen spectrum of such infections and decreased the overall detection rates of 14 common respiratory pathogens. The proportion of bacterial, but not viral, infections decreased.
The South Qinling block, a segment of the Yangtze craton involved in the Qinling–Dabie orogen, is critical for understanding the tectonic evolution of eastern China. However, the tectonic setting of the South Qinling block and the northern margin of the Yangtze block during middle Neoproterozoic time has long been the subject of debate, with two distinctly different models (continental rift or volcanic arc) proposed. Here, a comprehensive study of zircon U–Pb geochronology and geochemistry has been carried out on the Chengwan granitic pluton from the Suizao terrane in the South Qinling block. The granites are monzogranite and syenogranite in lithology, and are mainly composed of potash feldspar, quartz, plagioclase and biotite. This suite has long been regarded as a Palaeozoic magmatic pluton, but zircon U–Pb ages of 809 ± 9 Ma and 816 ± 4 Ma are obtained in this study. The granites are metaluminous to strongly peraluminous with high alkali contents, and exhibit highly fractionated features, including high SiO2, low Zr/Hf ratios, rare earth element tetrad effects and enrichment of K and Rb. They show Hf–Nd isotopic decoupling, which may be genetically related to their petrogenetic process. Based on the geochemical features and the positive εHf(t) values of the zircons, it is indicated that the granites may have been derived from partial melting of juvenile tonalitic rocks by biotite breakdown under fluid-absent conditions. The Chengwan granite geochemically belongs to the A2-subtype granites, suggesting that it might have formed in a post-orogenic tectonic setting. The highly fractionated A-type granite in this study may represent extensional collapse shortly after the collisional events in the South Qinling block, and thus indicate a tectonic regime switch, from compression to extension, as early as middle Neoproterozoic time. Integrating our new data with documented magmatic, metamorphic and sedimentary events during middle Neoproterozoic time in the region may support a continental rift model, and argues against arc models.
A comprehensive geochronological and geochemical study was carried out on the gneissic monzogranites, porphyritic granodiorites and charnockites in the Gaozhou complex of the Yunkai massif in the southern part of the South China block to better understand the Early Palaeozoic tectonic regime of the South China block. Laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) U–Pb dating of zircons indicates an age of 453.2 ± 5.1 Ma to the formation of the gneissic monzogranites, whereas the porphyritic granodiorites and charnockites were generated at 437.0 ± 1.5 Ma and 435.2 ± 2.2 Ma, respectively. The gneissic monzogranites show geochemical features consistent with the high-K, calc-alkaline rock series and are strongly peraluminous. They have SiO2 contents ranging from 67.75 to 69.65 wt. % and relatively low CaO contents (1.66–1.94 wt. %). Their REE patterns are fractionated with enriched LREEs and negative Eu anomalies. The samples also show enrichment in LILEs (e.g. Rb and K) and Pb, and depletion in Sr, Ba and HFSEs (e.g. Nb, Ta, Ti and P). They have εNd(t) values of −8.2 to −7.7. Conversely, the porphyritic granodiorites and charnockites are characterized as medium-K, calc-alkaline rock series and weakly to strongly peraluminous. They exhibit pronounced depletions in HFSEs and positive Pb anomalies. Compared to the earlier gneissic monzogranites, these rocks have relatively lower SiO2 (65.50–69.36 wt. %), but higher CaO contents (3.34–4.05 wt. %), and have slightly lower εNd(t) values (−9.1 to −8.4). Petrography and geochemical compositions of the gneissic monzogranites indicate that they are S-type granite and likely formed by partial melting of Neoproterozoic to Early Palaeozoic immature metagreywackes; whereas The porphyritic granodiorites and charnockites are A-type granite and likely derived from low degrees of partial melting of the dry, granulitic residue depleted by prior extraction of granitic melt. The new data for the Caledonian granitoids in the Yunkai massif suggest that they were formed in a post-collisional tectonic setting. They represent the earliest post-collisional alkaline magmatism reported so far in the Yunkai massif, and thus indicate a tectonic regime switch, from compression to extension, as early as the Late Ordovician to Early Silurian (~450–435 Ma).
Palaeoproterozic metasedimentary rocks, also referred to as khondalites, characterized by Al-rich minerals, are extensively exposed in the nucleus of the Yangtze craton, South China block. Samples of garnet–sillimanite gneiss in the khondalite suite were collected from the Kongling complex for Nd isotopic and elemental geochemical study. These rocks are characterized by variable SiO2 contents ranging from 35.71 to 58.07 wt%, and have low CaO (0.45–0.84 wt%) but high Al2O3 (18.56–29.04 wt%), Cr (174–334 ppm) and Ni (42.5–153 ppm) contents. They have high CIW (Chemical Index of Weathering) values (90.4–94.7), indicating intense chemical weathering of the source material. The samples display light rare earth elements (LREE) enrichment with negative Eu anomalies (Eu/Eu*=0.40–0.68), and have flat heavy rare earth elements (HREE) patterns. The high contents of transition elements (e.g. Cr, Ni, Sc, V) and moderately radiogenic Nd isotopic compositions suggest that the paragneisses might be those of first-cycle erosion products of predominantly mafic rocks mixing with small amounts of felsic moderately evolved Archaean crustal source. Geochemical and Nd isotopic compositions reveal that at least some of the protoliths of Kongling khondalite were sourced from local pre-existing mafic igneous rocks in a continental arc tectonic setting. Combined with documented zircon U–Pb geochronological data, we propose that the Palaeoproterozoic high-pressure granulite-facies metamorphism, rapid weathering, erosion and deposition of the khondalites in the interior of the Yangtze craton might be related to a Palaeoproterozoic collisional orogenic event during 2.1–1.9 Ga, consistent with the worldwide contemporary orogeny, implying that the Yangtze craton may have been an important component of the Palaeoprotorozoic Columbia supercontinent.
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