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• Development trend of collaborative security in middle reaches is considerable. • Collaborative security levels of Sichuan, Hunan and Jiangxi are lowest in 2020. • Bellman optimal equation is used to calculate expected benefits of measures. • Quantitative assessment is conducive to the collaborative security of the nexus. • Optimal implementation sequences of indictors with poor performance are proposed. Water, energy, and food are essential for human survival, and the production and consumption of these three resources are closely related. In the backdrop of limited resources and constantly expanding demand, the collaborative security of the water-energy-food nexus (WEF-nexus) is under serious threat. It is of great practical significance to study the adaptive management countermeasures of the collaborative security of the WEF-nexus in the Yangtze River Economic Belt (YREB) and to quantitatively evaluate the implementation sequence of relevant management countermeasures to improve the collaborative security and promote the sustainable development of the WEF-nexus. This study first establishes an evaluation indicator system for the collaborative security of the WEF-nexus in the YREB by utilizing the pressure-state-response (PSR) model. Then, the CRITIC and TOPSIS methods are used to determine the weight of indicators and the collaborative security level of the WEF-nexus in each province and city. The state transition matrix is determined based on the transition at the collaborative security level. Finally, based on the barrel theory to make up for shortcomings, the adaptive management countermeasures of provinces and cities with low collaborative safety levels are studied by combining the Bellman optimal equation. By comparing the expected returns of the same countermeasure in different implementation sequences and conducting quantitative research on the implementation sequence of adaptive management countermeasures, targeted policy suggestions are proposed based on regional characteristics, providing a reference for strategic decision-making of relevant resources in the YREB and improving regional WEF-nexus collaborative security. The results show that: (1) For Jiangxi, improving the water conservancy engineering regulation and storage capacity and other ways in a particular order can effectively improve the collaborative security level of nexus. (2) For Hunan, increasing the investment proportion of agriculture, forestry and water conservancy and resource exploration intensity and other means in a particular order can effectively improve the collaborative security level of the nexus. (3)For Sichuan, increasing the water-saving irrigation rate according to a particular order and other ways can effectively improve the collaborative security level of nexus. [ABSTRACT FROM AUTHOR]

Continental scaled extension is the major Late Mesozoic (Jurassic and Cretaceous) tectonic event in East Asia, characterized by faulting, magmatic intrusions and half-grabens in an area with a length of > 5000 km and a width of > 1000 km. Numerous studies have been conducted on this topic in the South China Block (SCB), However, the space and time ranges of the compressional or extensional regimes of the SCB during the Jurassic are still unclear, partly due to the lack of structural data. The emplacement fabrics of granitic plutons can help determine the regional tectonic background. In this study, a multidisciplinary approach, including Anisotropy of Magnetic Susceptibility (AMS), macro and microstructural analyses, quartz c-axis preferred orientation, gravity modeling and monazite EPMA dating, was conducted on the Hengshan composite granitic massif in SCB that consists of the Triassic Nanyue biotite granitic pluton and the Late Jurassic Baishifeng two-mica granitic pluton. The magnetic fabrics are characterized by a consistent NW–SE oriented lineation and weakly inclined foliation. A dominant high temperature deformation with a top-to-the-NW shear sense is identified for both plutons. The deformation increasing from the center of the Baishifeng pluton to its western border is associated to the development of the West Hengshan Boundary Fault (WHBF). The gravity modeling shows a “saw tooth-shaped” NE–SW oriented structure of the Baishifeng pluton, which may be considered as NE–SW oriented tension-gashes formed due to the NW–SE extension. All results show that the Triassic Nanyue pluton was deformed under post-solidus conditions by the WHBF coeval with the emplacement of the Late Jurassic Baishifeng pluton. All these observations comply with the NW–SE extensional tectonics coeval with the emplacement of the Baishifeng pluton, which argues that the NW–SE crustal stretching started since the Late Jurassic, at least in this part of the SCB. [ABSTRACT FROM AUTHOR]

The Late Mesozoic granitic belt in the northeastern Hunan province (situated in the south of the middle Yangtze region) represents the western front of the large magmatic province of SE China. In order to determine their ages and petrogenesis, we carried out zircon U–Pb dating, Hf isotope and whole-rock geochemical analyses for four granitic plutons, namely Taohuashan, Dayunshan-Mufushan, Wangxiang and Lianyunshan. Our SIMS zircon U–Pb ages, together with previously published data, reveal that the magmatic activities in this area can be roughly subdivided into three phases at 151–146 Ma, 132–127 Ma and ca. 117 Ma, and the Dayunshan-Mufushan batholith therein is a composite pluton. These four plutons are mainly composed of weakly to strongly peraluminous biotite or two-mica monzogranites, with a minor amount of biotite granodiorites. Their geochemical features are similar to S-type as well as fractionated S-type granites, with enrichment in LREEs and negative Ba, Sr, Nb, P and Ti anomalies. All samples show negative zircon εHf(t) values ranging from −12.5 to −3.6, corresponding to crustal Hf model (T DM C ) ages of 1.4–2.0 Ga. It is inferred that these granitoids were derived from partial melting of metasedimentary rocks analogous to the Neoproterozoic Lengjiaxi Group, predominantly with psammitic component. Fractional crystallization probably played an important role in the magma evolution, while input of mantle-derived magma was insignificant. Combined with other geological evidence, our new data allow us to propose that the Cretaceous (132–127 Ma and ca. 117 Ma) magmatism might be response to episodic slab rollback of the Paleo-Pacific plate, while the early-stage (151–146 Ma) magmatism that overlapped the epilogue of Jurassic magmatic flare-up and subsequent magmatic quiescence probably foreshadowed the transformation from foundering of a subducted flat-slab to slab rollback. Alternatively, slab foundering after a SE-directed intracontinental subduction in the central SCB cannot be ruled out for geodynamic interpretation of the Jurassic magmatism in SE China. [ABSTRACT FROM AUTHOR]