Early Cretaceous K-rich rhyolites from the Duolong Cu–Au deposit,southern Qiangtang,China: evidence for crustal growth     

Wei Wang  Cai Li  Jian-Jun Fan  Wei Xu  Yu-Chao Dong 《International Geology Review》2018,60(9):1098-1115

We report new zircon U–Pb age, Hf isotopic, and major and trace element data for rhyolites from the Duolong Ore Concentration Area of the Southern Qiangtang Terrane. Building on previous studies, we constrain the tectonic setting and propose a model to explain the geodynamics and crustal growth during regional magmatism in the Early Cretaceous. The analysed rhyolites yield laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb ages of 115 and 118 Ma. The rocks are K-rich (K₂O = 6.66–9.93 wt.%; K₂O/Na₂O = 8.2–19.7 wt.%), alkaline and peraluminous (A/CNK = 1.02–1.46), and are characterized by high SiO₂ contents (72.8–78.8 wt.%) similar to highly fractionated I-type granites. Fractionation of Fe–Ti oxides, plagioclase, hornblende, Ti-bearing phases, apatite, monazite, allanite and zircon contributed to the variations in major and trace element chemistry. High K₂O contents are likely due to partial melting of the continental crust. The samples have positive zircon εHf(t) values ranging from +7.1 to +11.2. These features, together with young zircon Hf crustal model ages of 489–721 Ma, indicate that the K-rich rhyolites were derived from juvenile lower crust with an input of a mantle-derived component. We suggest that the Early Cretaceous K-rich rhyolites formed in a continental arc setting during northward subduction of Bangong Co–Nujiang oceanic lithosphere. Basaltic magma underplating was responsible for vertical crustal growth, triggered by slab roll-back in the Duolong Ore Concentration Area in the Early Cretaceous.  相似文献   

Geology of the Yap Trench: new observations from a transect near 10°N from manned submersible Jiaolong     

Yaomin Yang  Jinwei Gao  Liyan Tian  Jichao Yang  Yue Xu 《International Geology Review》2018,60(16):1941-1953

This paper describes the petrology and geochemistry of rocks from the Yap Trench acquired by three dives of the Jiaolong research submarine. Combining the geophysical data and submersible observations, this paper describes the geomorphology, shallow structures, and sedimentology of the Yap Trench and further discusses the tectonics and activities of this region. Two obvious slope breaks are found on the landward slope, and horsts and grabens with small fault offsets are observed in the ocean-ward slope of the trench. Peridotites sampled from the Yap Trench inner wall are highly depleted subduction-related mantle residues. Volcanic rocks in the northern segment of the trench have subduction-related characteristics that Yap fore-arc rocks underwent metasomatism during Cenozoic subduction. The rocks with remarkable lithologic difference from lithospheric mantle and upper crust sampled in the break slopes suggest that the slope break area may represent a lithologic boundary or transition zone. The landward slope of the Yap Trench was removed by subduction erosion as a result of collision with the Caroline Ridge. The bending of the down-going plate caused normal faults, horsts, and grabens with little or no sediments indicating that the Caroline Ridge is subducting beneath the Yap arc along the trench even though the convergence rate is very slow.  相似文献   

Petrophysical characterisation of tight sandstone gas reservoirs using nuclear magnetic resonance: a case study of the upper Paleozoic strata in the Kangning area,eastern margin of the Ordos Basin,China     

Y. Y. Huyan  T. S. Liu  F. J. Jiang  X. Z. Chen  X. Q. Ma 《Australian Journal of Earth Sciences》2018,65(6):863-875

Residual and movable porosity are significant parameters for characterising petrophysical properties, especially in tight reservoirs. Eight tight sandstone samples from the upper Paleozoic gas-bearing strata in the Kangning area, from the eastern margin of the Ordos Basin, were analysed using nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), petrography, and porosity and permeability tests. The lithology and pore types were identified and classified using petrography and SEM. The residual and movable porosity were obtained with NMR. In addition, NMR was used to visualise pore structure and pore size distribution. The results suggest that the upper Paleozoic sandstones in the study area mainly comprise feldspathic litharenite and litharenite. The sandstone porosity and permeability are low, with means of 5.9% and 0.549 mD, respectively. Four pore types exist in the tight sandstones: residual primary pores, grain dissolution pores, micropores (clay-dominated) and microfractures. The T₂ spectra under water-saturated conditions correlate with pore size and can be used to distinguish small and large pores based on the transverse relaxation time cutoff value of 10 ms, which corresponds to a pore diameter of 0.232 μm. Small pores account for 72% of the pores in the tight sandstones. The continuous bimodal T₂ spectra suggest good connectivity between small and large pores, despite the low porosity and permeability. In this study, the movable porosity of the major tight sandstone gas reservoirs is higher than the residual porosity, which confirms the effective evaluation of movable porosity to tight sandstone reservoirs, based on NMR experiments.  相似文献   

N and C Isotopic Compositions of the Lower Triassic of Southern Primorye and Reconstruction of the Habitat Conditions of Marine Organisms     

Y. D. Zakharov  M. Horacek  Y. Shigeta  A. M. Popov  L. G. Bondarenko 《Stratigraphy and Geological Correlation》2018,26(5):534-551

N and C isotopic data are recorded and presented for the first time for the Lower Triassic claystones of Southern Primorye (Abrek Section). Five N isotope intervals and 11 more or less pronounced negative C isotope excursions, likely to reflect instability of the temperature regime and the oceanographic situation in the Early Triassic, are recognized in the section. The most favorable conditions for ammonoid recovery and other marine organisms in the Early Triassic (after the end- Permian ecological crisis) were associated with the late Induan—early Olenekian transgression and probable cooling.  相似文献   

Characterisation of primary and secondary carbonates in hypabyssal kimberlites: an integrated compositional and Sr-isotopic approach     

Castillo-Oliver  Montgarri  Giuliani  Andrea  Griffin  William L.  O&#;Reilly  Suzanne Y. 《Mineralogy and Petrology》2018,112(2):555-567

Carbonates in fresh hypabyssal kimberlites worldwide have been studied to understand their origin [i.e. primary magmatic (high T) versus deuteric (‘low T’) versus hydrothermal/alteration (‘low T’)] and identify optimal strategies for petrogenetic studies of kimberlitic carbonates. The approach presented here integrates detailed textural characterisation, cathodoluminescence (CL) imaging, in situ major- and trace-element analysis, as well as in situ Sr-isotope analysis. The results reveal a wide textural diversity. Calcite occurs as fine-grained groundmass, larger laths, segregations, veins or as a late crystallising phase, replacing olivine or early carbonates. Different generations of carbonates commonly coexist in the same kimberlite, each one defined by a characteristic texture, CL response and composition (e.g., variable Sr and Ba concentrations). In situ Sr isotope analysis revealed a magmatic signature for most of the carbonates, based on comparable ⁸⁷Sr/⁸⁶Sr values between these carbonates and the coexisting perovskite, a robust magmatic phase. However, this study also shows that in situ Sr isotope analysis not always allow distinction between primary (i.e., magmatic) and texturally secondary carbonates within the same sample. Carbonates with a clear secondary origin (e.g., late-stage veins) occasionally show the same moderately depleted ⁸⁷Sr/⁸⁶Sr ratios of primary carbonates and coexisting perovskite (e.g., calcite laths-shaped crystals with ⁸⁷Sr/⁸⁶Sr values identical within uncertainty to those of vein calcite in the De Beers kimberlite). This complexity emphasises the necessity of integrating detailed petrography, geochemical and in situ Sr isotopic analyses for an accurate interpretation of carbonate petrogenesis in kimberlites. Therefore, the complex petrogenesis of carbonates demonstrated here not only highlights the compositional variability of kimberlites, but also raises concerns about the use of bulk-carbonate C-O isotope studies to characterise the parental melt compositions. Conversely, our integrated textural and in situ study successfully identifies the most appropriate (i.e. primary) carbonates for providing constraints on the isotopic parameters of parental kimberlite magmas.

  相似文献   

Club convergence and spatial distribution dynamics of carbon intensity in China’s construction industry     

Qiang Du  Min Wu  Yadan Xu  Xinran Lu  Libiao Bai  Ming Yu 《Natural Hazards》2018,94(2):519-536

Climate change caused by carbon emissions continuously threatens sustainable development. Due to China’s immense territory, there are remarkable regional differences in carbon emissions. The construction industry, which has strong internal industrial differences, further leads to carbon emission disparity in China. Policymakers should consider spatial effects and attempt to eliminate carbon emission inequality to promote the sustainable development of the construction industry and realize emission reduction targets. Based on the classic Markov chain and spatial Markov chain, this paper investigates the club convergence and spatial distribution dynamics of China’s carbon intensity in the construction industry from 2005 to 2014. The results show that the provincial carbon intensity in the construction industry is characterized by “convergence clubs” during the research period, and very low-level and very high-level convergence clubs have strong stability. Moreover, the carbon intensity class transitions of provinces tend to be consistent with that of their neighbors. Furthermore, the transition of carbon intensity types is highly influenced by their regional backgrounds. The provinces with high carbon emissions have a negative influence on their neighbors, whereas the provinces with low carbon emissions have a positive influence. These analyses provide a spatial interpretation to the “club convergence” of carbon intensity.  相似文献   

Influence of the sediment delivery ratio index on the analysis of silting and break risk in the Plasencia reservoir (Central System,Spain)     

Sánchez  Y.  Martínez-Graña  A.  Santos-Francés  F.  Yenes  M. 《Natural Hazards》2018,90(3):1407-1426

The random forest method was used to generate susceptibility maps for debris flows, rock slides, and active layer detachment slides in the Donjek River area within the Yukon Alaska Highway Corridor, based on an inventory of landslides compiled by the Geological Survey of Canada in collaboration with the Yukon Geological Survey. The aim of this study is to develop data-driven landslide susceptibility models which can provide information on risk assessment to existing and planned infrastructure. The factors contributing to slope failure used in the models include slope angle, slope aspect, plan and profile curvatures, bedrock geology, surficial geology, proximity to faults, permafrost distribution, vegetation distribution, wetness index, and proximity to drainage system. A total of 83 debris flow deposits, 181 active layer detachment slides, and 104 rock slides were compiled in the landslide inventory. The samples representing the landslide free zones were randomly selected. The ratio of landslide/landslide free zones was set to 1:1 and 1:2 to examine the results of different sample ratios on the classification. Two-thirds of the samples for each landslide type were used in the classification, and the remaining 1/3 were used to evaluate the results. In addition to the classification maps, probability maps were also created, which served as the susceptibility maps for debris flows, rock slides, and active layer detachment slides. Success and prediction rate curves created to evaluate the performance of the resulting models indicate a high performance of the random forest in landslide susceptibility modelling.  相似文献   

Volume estimation and stage division of the Mahu landslide in Sichuan Province,China     

Yulong Cui  Jianhui Deng  Chong Xu 《Natural Hazards》2018,93(2):941-955

The Mahu lake, the third deepest lake in China, is located on the west bank of the Jinsha River in Leibo county, Sichuan Province. It is a dammed lake created by an old landslide on the ancient Huanglang river, a tributary on the west bank of the Jinsha River. Previous studies (Wang and Lu in J Mt Res S1:44–47, 2000) suggested that this landslide was caused by an earthquake approximately 372 ka (Middle Pleistocene), during which a few hundreds of million cubic meters of debris were deposited between 1177 and 900 m a.s.l. (above sea level), covering an area of around 15 km². Our further investigations, including geodetic survey, borehole drilling, and field reconnaissance, combining with five chronological data, have made some new discoveries at this site. First, the toe of the landslide extends from 900 m a.s.l. down to 320 m a.s.l., i.e., the local bed elevation of the contemporary Jinsha River. Second, the area of the landslide deposits is 17.3 km² with a volume of 2.38 km³, much larger than the previous estimation. Thus, it should be one of the largest known landslides in China. And the lower elevation of the landslide’s toe also rules out the possibility that it is a hanging valley on the ancient Huanglang river. Our work suggests that this landslide was created by five events according to the overlapping characteristics of the deposits and five chronological data, which are old than 52,600 years, old than 16,000 years, old than 15,500 years, 5800 years, and old than 4200 years, respectively.  相似文献   

Remote sensing-based assessment of vegetation damage by a strong typhoon (Meranti) in Xiamen Island,China     

Meiya Wang  Hanqiu Xu 《Natural Hazards》2018,93(3):1231-1249

Remote sensing is a cost-effective tool for assessing vegetation damage by typhoon events at various scales. Taking Xiamen Island, southeastern China, as a study case, this paper aimed to assess and analyze the vegetation damage caused by Typhoon Meranti landfalling on September 15, 2016, using two high spatial resolution remote sensing images before and after the typhoon event. Seven severely damaged vegetation regions were selected based on the classification of vegetation types and visual interpretation of the images. Regression analysis was used to correct seasonal variation of the two high-solution images before and after typhoon. The vegetation area of the whole of Xiamen Island and the selected seven regions before and after typhoon were then calculated, respectively. Two spectral vegetation indicators, normalized difference vegetation index (NDVI) and fractional vegetation coverage (FVC), were also retrieved for the whole island and the seven regions. By comparing the difference in NDVI values before and after the typhoon of the two high spatial resolution images, we analyzed the most affected vegetation areas, as well as the most seriously damaged vegetation species. The typhoon has caused a decrease in vegetation area by 95.1 ha across the whole Xiamen Island. The mean NDVI and FVC decreased by 0.209 and 13 percentage points, respectively. While, in the seven selected severely damaged areas, the mean NDVI decreased by 0.356–0.444 and FVC decreased by 27–42 percentage points. The visual inspection showed that the tone of typhoon-damaged vegetation became darker, the patches of damaged vegetation became smaller and more fragmented, and the gap between vegetation canopies became larger. The most affected vegetation areas occurred in the southeastern hilly area, Jinshang and Hubin South Roads, as well as the Wuyuan Bay area. The most seriously damaged vegetation type is broad-leaved trees, especially the species, Acacia confusa, Delonix regia, Bauhinia variegata, Chorisia speciosa, Ficus benjamina and F. Concinna.  相似文献   

Evaluating climate change adaptation efforts on the US 50 states’ hazard mitigation plans     

Qiao Hu  Zhenghong Tang  Lei Zhang  Yuanyuan Xu  Xiaolin Wu  Ligang Zhang 《Natural Hazards》2018,92(2):783-804

Climate change brings uncertain risks of climate-related natural hazards. The US Federal Emergency Management Agency (FEMA in Climate change: long-term trends and their implications for emergency management, 2011. https://www.fema.gov/pdf/about/programs/oppa/climate_change_paper.pdf) has issued a policy directive to integrate climate change adaptation actions into hazard mitigation programs, policies, and plans. However, to date there has been no comprehensive empirical study to examine the extent to which climate change issues are integrated into state hazard mitigation plans (SHMPs). This study develops 18 indicators to examine the extent of climate change considerations in the 50 SHMPs. The results demonstrate that these SHMPs treat climate change issues in an uneven fashion, with large variations present among the 50 states. The overall plan quality for climate change considerations was sustained at an intermediate level with regard to climate change-related awareness, analysis, and actions. The findings confirm that climate change concepts and historic extreme events have been well recognized by the majority of SHMPs. Even though they are not specific to climate change, mitigation and adaptation strategies that can help reduce climate change risks have been adopted in these plans. However, the plans still lack a detailed assessment of climate change and more incentives for collaboration strategies beyond working with emergency management agencies.  相似文献