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931.
吉塘变质核杂岩是研究北澜沧江缝合带构造演化过程的重要窗口。本文通过对吉塘变质核杂岩进行构造岩性填图、构造解析及锆石U-Pb测年,将变质核杂岩自上而下解析为沉积盖层、韧性流变层及核部变质杂岩的“三元结构”,核部变质杂岩与韧性流变层之间以韧性拆离带相连,拆离带具有上盘向南东方向剪切的运动学特征。吉塘变质核杂岩中同剪切花岗质糜棱岩的锆石U-Pb年龄为(33.0±1.2) Ma～(28.4±0.6) Ma,剪切后脉体的锆石U-Pb年龄为(18.35±1.2) Ma。综合以上研究结果,推测吉塘变质核杂岩新生代的隆升过程为：强烈的走滑断层活动形成了拉分盆地,其伸展环境使地壳减薄,大量岩浆上涌,最终导致了吉塘变质核杂岩于渐新世—中新世的隆升。吉塘变质核杂岩为渐新世—中新世大型走滑断层作用导致的区域性造山后伸展及大规模南东向逃逸构造事件的产物。
相似文献932.
Fan Wei Mei Han Guangxuan Han Min Wang Lixin Tian Jiqian Zhu Xianglun Kong 《海洋学报(英文版)》2022,41(9):192-204
Coastal wetlands are located in the ecotone of interaction between the land surface and sea, and anthropogenic activities extensively interfere with these wetlands through the reclamation of large tidal wetlands and destruction of the function of the ecosystems. In this study, we investigated the dynamic evolutionary characteristics of the Bohai Rim coastal area over the past 40 years using the Modified Normalized Difference Water Index, the fractal dimension, object-oriented classification, the land-use transfer trajectory, and regression analysis. Additionally, we quantified and monitored the evolution of reclamation and analyzed the correlation between reclamation and coastal wetlands based on 99 Landsat-2, -5, and -8 images (at 60 m and 30 m spatial resolution) over the period 1980–2019. The results are as follows. (1) The coastline of the Bohai Rim increased by 1 631.2 km from 1980 to 2019 with a zigzag variation. The artificial coastline increased by 2 946.1 km, whereas the natural coastline decreased by 90%. (2) The area of man-made wetlands increased by 3 736.9 km2, the area of construction land increased by 1 008.4 km2, and the natural wetland area decreased by 66%. The decrease of tidal flats is the main contributor to the decrease of natural wetland area (takes account for 91.1%). Coastal areas are affected by intense human disturbance, which was taken place across a large area of tidal flats and caused the landscape to fragment and be more heterogeneous. The coastal zone development activities were primarily concentrated in the southern Laizhou Bay, the Yellow River Delta, the Bohai Bay, the northern Liaodong Bay, and the Pulandian Bay. The solidified shorelines and increase in sea level have resulted in intertidal wetlands decreasing and impaired wetland ecology. (3) There is a good agreement between reclamation and the size of the coastal wetlands. Both land reclamation and the reduction in coastal wetland areas are significantly related to the population size, fishery output value, and urbanization rate. In summary, human activities, such as the construction of aquaculture ponds and salt pans, industrialization, and urbanization, are the primary forces that influence the environmental changes in the coastal region. This study is beneficial for establishing and improving the systems for the rational development and utilization of natural resources, and provides theoretical references for restoring wetland ecology and managing future reclamation activities in other coastal zone-related areas. 相似文献
933.
为准确建立海底地声模型,本文探讨地声模型的基本组成和基本结构。通过样品实验室测量,分析南海海底表层沉积物的密度、孔隙度与声速随着埋深变化的关系,得出海底实际存在的低声速表面–声速缓慢变化类型、低声速表面–声速增大类型、高声速表面–声速缓慢变化类型和高声速表面–声速增大类型4种典型地声结构;对比钻探测量,分析黄海海底沉积物的密度、孔隙度与声速随埋深变化关系,得出海底地声模型分层特征与地声结构组合特征。研究表明,地声模型可以归结为4种基本地声结构的组合,通过与底层海水声速、同层内声速剖面以及与上层海底沉积物下表面声速的比较,可以建立各种海底地声模型;基于实验室测量法建立的地声模型可以作为参考地声模型,但需要考虑实际海底温度和压力梯度以及海底沉积物的频散特性等,借助于声速比校正法和频散性理论模型进行计算及修正。 相似文献
934.
Food security is the primary prerequisite for achieving other Millennium Development Goals(MDGs).Given that the MDG of“halving the proportion of hungers by 2015”was not realized as scheduled,it will be more pressing and challenging to reach the goal of zero hunger by 2030.So there is high urgency to find the pattern and mechanism of global food security from the perspective of spatio-temporal evolution.In this paper,based on the analysis of database by using a multi-index evaluation method and radar map area model,the global food security level for 172 countries from 2000 to 2014 were assessed;and then spatial autocorrelation analysis was conducted to depict the spatial patterns and changing characteristics of global food security;then,multi-nonlinear regression methods were employed to identify the factors affecting the food security patterns.The results show:1)The global food security pattern can be summarized as“high-high aggregation,low-low aggregation”.The most secure countries are mainly distributed in Western Europe,North America,Oceania and parts of East Asia.The least secure countries are mainly distributed in sub-Saharan Africa,South Asia and West Asia,and parts of Southeast Asia.2)Europe and sub-Saharan Africa are hot and cold spots of the global food security pattern respectively,while in non-aggregation areas,Haiti,North Korea,Tajikistan and Afghanistan have long-historical food insecurity problems.3)The pattern of global food security is generally stable,but the internal fluctuations in the extremely insecure groups were significant.The countries with the highest food insecurity are also the countries with the most fluctuated levels of food security.4)The annual average temperature,per capita GDP,proportion of people accessible to clean water,political stability and non-violence levels are the main factors influencing the global food security pattern.Research shows that the status of global food security has improved since the year 2000,yet there are still many challenges such as unstable global food security and acute regional food security issues.It will be difficult to understand these differences from a single factor,especially the annual average temperature and annual precipitation.The abnormal performance of the above factors indicates that appropriate natural conditions alone do not absolutely guarantee food security,while the levels of agricultural development,the purchasing power of residents,regional accessibility,as well as political and economic stability have more direct influence. 相似文献
935.
海水中的颗粒有机碳(POC)与生物的生命过程、初级生产力关系密切,是海洋食物链中重要的物质基础和能量来源,因此POC的分布特征可以有效反映其生物地球化学环境。利用中国第33次南极考察期间(2016年12月至2017年1月)在南极半岛邻近海域采集的海水颗粒物样品,研究POC的空间分布特征及其影响因素。结果表明,斯科舍海0—200 m的POC浓度范围为7.44—193.52μg·L~(-1),平均浓度为(48.84±35.09)μg·L~(-1);南斯科舍海岭0—200 m的POC浓度范围为9.13—62.17μg·L~(-1),平均浓度为(29.76±14.12)μg·L~(-1);鲍威尔海盆0—200 m的POC浓度范围为5.87—270.72μg·L~(-1),平均浓度为(48.57±38.92)μg·L~(-1)。表层POC高值出现在斯科舍海区和鲍威尔海盆区,而低值出现在海岭区,与叶绿素a(Chla)的变化趋势一致,与营养盐的变化趋势相反。垂向分布上,各个区域POC平均浓度随深度的增加而减少,鲍威尔海盆和斯科舍海POC最高值都出现在25 m层。分析结果表明光合浮游植物是研究海域POC的主要来源, POC的主要影响因素为温度、水团混合以及海冰环境。斯科舍海与鲍威尔海盆整体非生命POC占比高,可能是由于高磷虾生物量、海冰碎屑以及陆源输入的干扰;南斯科舍海岭整体非生命POC占比低。 相似文献
936.
Changqing Yang Baofu Han Chuansheng Yang Yanqiu Yang Jin Sun Fusheng Yu 《Geological Journal》2020,55(1):239-252
The East China Sea Shelf Basin (ECSSB) is located on the south-eastern edge of the Eurasian Plate. The tectono-evolution and dynamic mechanism of the ECSSB are related to the collision of the Pacific Plate with the Eurasian Plate, and the remote pushing effect of the Indo-Australian Plate remains a hot topic of debate. Based on the latest survey data, this paper mainly focuses on the evolution of the Mesozoic basin in the East China Sea Shelf by means of assessing the regional tectonic background, conducting structural physical simulation experiments, and applying balanced geological section recovery technology to discuss the processes of dynamic transition in Southeast China. Our data suggest that the ECSSB experienced an evolutionary sequence involving the pre-Late Triassic passive continental margin; the Late Triassic–Middle Jurassic active continental margin extrusion-depression; the extrusional stress from the low-angle subduction of the Izanaki Plate under the Eurasian Plate; the late Early Cretaceous to Late Cretaceous active continental marginal extension faulted basin, during which the extensional stress originated from the lithospheric thinning and palaeoenvironment resulting from the subduction of the Palaeo-Pacific Plate under the Eurasian Plate; and the Palaeogene back-arc extension faulted sags. The transition time from the E-W-trending Palaeo-Tethys tectonic system to the NE-trending Palaeo-Pacific tectonic system in Southeast China occurred at the end of the Middle Triassic. The low-angle subduction and withdrawal of subduction of the Palaeo-Pacific Plate probably represented the deep geological processes of the Mesozoic in Southeast China. 相似文献
937.
Wukeyila Wutiepu Yanchen Yang Shijiong Han Yufei Guo Shijia Nie Chao Liu Wenliang Fan 《Geological Journal》2020,55(1):501-516
The Jiapigou gold ore belt is located in the northeastern corner of the wedge-shaped North China Craton and is hosted by Neoarchean basement gneiss and amphibolite, along with late Palaeozoic and Mesozoic granitoids. In this paper, whole-rock major and trace element geochemistry together with zircon U–Pb ages and Lu–Hf isotope compositions are reported for Late Permian to Triassic igneous rocks from the gold belt. The dominant population of zircons in all these rocks shows oscillatory growth zoning in CL images, and relatively high Th/U ratios (0.10–5.23) that are indicative of a magmatic origin. Zircon U–Pb data indicate that the igneous rocks formed during two major phases: ca. 252 Ma and ca. 230–213 Ma. Geochemically, the Late Permian (ca. 252 Ma) diorites are high-K calc-alkaline in composition and low total Fe2O3, MgO, and CaO contents, and represented by enrichment in LILEs relative to HFSEs and HREEs, all of which are indicative of a postcollision high-K calc-alkaline granite affinity. In contrast, the Late Triassic (ca. 230–213 Ma) igneous rocks are mainly quartz syenite porphyries, felsites, and granodiorites, and are variable medium- to high-K calc-alkaline series and exhibit a negative Eu anomaly with A-type affinities, indicating an extensional environment. In addition, in situ Hf isotopic analyses of zircons from four dated samples reveal that they have εHf(t) values of −3.0 to +2.2, with two-stage model (TDM2) ages range from 964 to 1,210 Ma, indicating that they probably originated from the partial melting of a dominantly Mesoproterozoic to Neoproterozoic crustal source. On the basis of the geochemical data and regional geological investigations, we further propose that the Jiapigou gold ore belt in the Late Permian was formed in a postcollisional tectonic setting, whereas an extensional tectonic setting in the Late Triassic that caused lithospheric thinning during a postorogenic event. 相似文献
938.
Kai Song Qing-Feng Ding Qiang Zhang Long Cheng Yu Han Fei Liu 《Geological Journal》2020,55(2):1507-1528
The Hongshuihe area of Eastern Kunlun Orogen is well-known for the BIF-type deposits. Some widespread intrusive rocks in the northern Hongshuihe area were previously thought to be emplaced in the Hercynian. This article presents LA-ICP-MS zircon U–Pb ages, with LA-MC-ICP-MS in situ Hf isotopes and major and trace element data for quartz diorites and granites of the Hongshuihe pluton. Two samples from the Hongshuihe quartz diorite and granite yielded a weighted mean zircon U–Pb age of 244 ± 2 Ma (Anisian) and 246 ± 1 Ma (Olenekian), respectively. The Hongshuihe subalkaline quartz diorite is metaluminous with the alumina saturation index values of 0.93–1.00, and high SiO2 contents of 59.67–65.51 wt.%, low Y values of 11.1–16.7 ppm, and low HREE (Yb = 1.08–1.83 ppm) that collectively suggest high-SiO2 adakite-like rocks. The Hongshuihe granites have slightly high alkali contents of 7.04–8.12 wt.%, alumina saturation index values of 1.01–1.03, low (Zr + Nb + Ce + Y) contents of 315.30–455.50 ppm, and high Fe2O3T/MgO ratios of 4.03–5.16, indicating fractionated I-type normal island arc magma. The zircon εHf(t) values from −4.0 to −1.1 for the Hongshuihe quartz diorite sample and values from −2.4 to +1.7 for the granite sample correspond to partial melting of Mesoproterozoic thickened lower crust and partial melting of juvenile mantle-derived mafic lower crust, respectively. We conclude that during the Early–Middle Triassic, the Eastern Kunlun area underwent a tectonic setting of the northward subduction of the Palaeo-Tethys oceanic slabs. 相似文献
939.
Xu Song Xiuxiang Lü Han Quan Xiaoxiao Zhou Yao Guan Xinluo Feng 《Geological Journal》2020,55(12):7872-7891
The Kuqa Depression is an important oil and gas exploration area in the Tarim Basin, and exploration practices indicate that the gas reservoirs such as Dabei, Kela, and Keshenare distributed in the Cretaceous palaeo-uplift area. However, few studies have been done on the Cretaceous palaeo-uplifts. On the basis of the logging gamma curve, the spectrum analysis of the Bashijiqike Formation shows that the sedimentation of the Lower Cretaceous stratum was controlled by the Milankovitch cycles. As the stratum exhibits the characteristic Milankovitch periodicities, 133, 124, 100, and 95 ka eccentricity, 46.5 and 36.6 ka obliquity, and 22.2 ka precession periods are identified in the residual Bashijiqike Formation. By combining the results of cyclic analysis and thermal simulation of apatite fission track (AFT), the stratum denudation amount of Dabei-Tubei palaeo-uplift and Kelasu palaeo-uplift in the Late Cretaceous was calculated, and the palaeo-uplifts were restored. The results show that the original thickness of the Cretaceous stratum in the core of the Dabei-Tubei palaeo-uplift was ~1,500 m and was more than 1,800 m in the core of the Kelasu palaeo-uplift. The AFT modelling results indicate that there were two cooling phases in provenance, that is, since the Late Triassic–Early Jurassic (ca. 200 Ma) and the Late Jurassic–Early Cretaceous (ca. 160–130 Ma). In addition, the depositional area also experienced two cooling phases, namely, since the Late Cretaceous (ca. 110–60 Ma) and the Late Palaeogene–Early Neogene (ca. 20 Ma). 相似文献
940.
西藏切穷地区早侏罗世花岗岩岩体位于西藏冈底斯构造—岩浆带之中带。其主要岩性为不等粒二长花岗岩+花岗闪长岩。LA-ICP-MS锆石U-Pb定年结果表明,研究区花岗岩岩体侵位年龄主要集中在（192.8±1.3 Ma～189.1±0.66 Ma）,属早侏罗世。花岗岩SiO2 = 65.58%～75.57%,K2O+Na2O = 7.00%～8.25%,铝饱和指数A/CNK = 0.81～1.33;轻重稀土元素分馏较明显,（La/Yb）N = 2.47～42.03,负Eu异常,δEu = 0.27～0.72;微量元素表现出Rb、Th、U、La和Ce的强烈富集,Nd、Hf、Sm、Y、Yb和Lu相对富集,K、Nb、Sr、P和Ti元素相对亏损的特点,属高钾钙碱性S型花岗岩系列。根据岩体的成因类型并结合区域构造环境演化,分析认为研究区花岗岩形成于同碰撞环境,是壳源岩石重熔作用的产物。 相似文献