南海北部西沙海槽沉积物管状黄铁矿特征及其形成机理^*          下载免费PDF全文

石思思  吴朝东  梁金强  王熠哲  叶云涛  方允鑫  马健  翟俪娜 《古地理学报》2020,22(1):175-192

南海北部西沙海槽S1站位的岩心柱沉积物中广泛发育自生矿物黄铁矿,其形态以管状为主,且具有内部中空的圈层结构。使用扫描电镜、电子探针、LA-ICP-MS、SIMS等测试方法研究了管状黄铁矿的形态及圈层结构,结果显示: (1)管状黄铁矿发育内部中空的圈层结构,其中内圈层(I_py)由莓球状黄铁矿呈五角十二面体紧密堆积组成,外圈层(O_py)由晶形较好晶粒较大的八面体黄铁矿组成,并混有沉积碎屑及钙质生物壳体;(2)内圈层和外圈层分别呈现出贫S富Fe和富S贫Fe的特征,其成因是甲烷渗漏造成的局部还原环境使得As进入黄铁矿中导致晶格空缺或被扭曲,从而促进Ni、Co、Cu、Zn、Pb等微量元素的掺入;(3)内圈层、外圈层发生了明显的硫同位素分馏现象,内圈层中 δ³⁴S 平均为-37.8‰,外圈层中 δ³⁴S 平均为-29.3‰。研究认为,管状黄铁矿作为曾经甲烷渗漏的通道,其生长机制可分为3个阶段: (1)气水通道形成阶段: 向上运移的甲烷流体在沉积物孔隙中逐渐形成气水通道;(2)外圈层形成阶段: 当向上运移的甲烷与硫酸盐发生甲烷厌氧氧化时,逐渐形成晶体较大、晶形较好的八面体黄铁矿外圈层;(3)内圈层形成阶段: 随着甲烷浓度逐渐降低,在气水通道中的微生物作用下,剩余甲烷与向下运移的硫酸盐继续反应形成莓球状黄铁矿内圈层。因此,南海北部的泥岩中大量发育的管状黄铁矿常常与地层中甲烷水合物的存在有关。  相似文献   

2007-2017年中国沙尘气溶胶的三维分布特征及输送过程     

贾瑞  刘玉芝  吴楚樵  祝清哲  汪兵 《中国沙漠》2019,39(6):108-117

利用最新发布的CALIPSO产品，构建了2007-2017年中国沙尘气溶胶的三维分布，并结合HYSPLIT-4模式和再分析数据，探讨了沙尘的三维输送过程。结果表明：中国的沙尘排放源区主要是塔克拉玛干沙漠和巴丹吉林沙漠，沙尘气溶胶出现频率分别为60%和35%。塔克拉玛干沙漠排放的沙尘主要（50%~70%）停留在源地0~6 000 m高度，少部分向东输送至甘肃和内蒙古；巴丹吉林沙漠排放的沙尘则主要向东输送。中国沙尘排放量在春季最大，向东输送最强；夏季，东亚夏季风限制了沙尘向东输送；秋季，沙尘排放减弱，输送强度和夏季相当；沙尘排放量在冬季最小，输送最弱。夏季，沙尘在输送过程中可被抬升至高度5 000 m以上，春季次之，秋、冬季的沙尘主要在低层大气输送。沙尘在向东输送的过程中被抬升并和当地人为污染物混合变为污染性沙尘，华北地区污染性沙尘出现频率高达30%；输送到海洋的沙尘也会与洋面上（0~3 000 m高度）的海盐气溶胶混合，出现频率约为10%。  相似文献   

琼东南盆地华光凹陷天然气水合物稳定带厚度的影响因素     

刘杰  杨睿  邬黛黛  金光荣  张辉 《海洋学报》2019,41(8):13-25

为了探讨琼东南盆地华光凹陷海底天然气水合物稳定带的分布规律，定量研究了静水压力、底水温度、地温梯度和气源组分对水合物稳定带的影响程度。在此基础上，分析了华光凹陷现今甲烷水合物稳定带的厚度分布。最后，综合各因素的历史演化过程，初步探讨了华光凹陷1.05 Ma BP以来天然气水合物稳定带的演化。结果表明:(1)气源组分和海底温度的变化对研究区内水合物稳定带的影响较大；水合物稳定带厚度与海底温度呈良好的线性负相关性。(2)水深超过600 m的海域具备形成天然气水合物的温压条件；超过600 m水深的海域水合物稳定带厚度大部分超过 100 m，其中西北部稳定带的最大厚度超过300 m，是有利的水合物勘探区。(3)华光凹陷1.05 Ma BP以来天然气水合物稳定带厚度经历了快速增厚–窄幅变化–快速减薄和恢复的过程。麻坑群与水合物稳定变化敏感区在空间上具有较好的叠合关系。结合前人的研究成果，推测其形成与天然气水合物的分解释放有关。  相似文献   

Effect of spatially variable saturated hydraulic conductivity with non-stationary characteristics on the stability of reservoir landslides     

Xue  Yang  Wu  Yiping  Miao  Fasheng  Li  Linwei  Liao  Kang  Ou  Guangzhao 《Stochastic Environmental Research and Risk Assessment (SERRA)》2020,34(2):311-329

Stochastic Environmental Research and Risk Assessment - Conventional landslide analyses, based on deterministic methods or simple random variable methods, cannot consider the spatial variability...  相似文献   

2012-2018年巢湖水质变化趋势分析和蓝藻防控建议   总被引：4，自引：3，他引：1  

张民  史小丽  阳振  陈开宁 《湖泊科学》2020,32(1):11-20

巢湖自1990s中期至2012年间水质明显改善,但是近年来水质改善效果变缓,2018年蓝藻水华面积显著增加,为有效评估巢湖水体环境的变化,通过对20122018年巢湖17个点位的逐月调查数据分析阐述了近年来巢湖水质和藻情的变化特征,并在流域空间尺度上分析了巢湖流域水污染治理的进展和不足,为后续治理方向的调整和确定提供支撑.20122018年湖区调查数据显示:巢湖湖体总磷和总氮浓度显著升高,铵态氮浓度显著下降,水华蓝藻总量显著升高.在空间上,各污染指标水平呈现由西向东呈逐渐降低的趋势,但是各指标在不同湖区随时间的变化趋势差异明显,西部湖区的总磷、总氮和水华蓝藻指标近年来略有下降或持平,中部和东部湖区则显著升高,所以巢湖湖体总氮和总磷浓度的升高主要源于中、东部湖区的升高,这也是这两个湖区水华蓝藻变动的主要驱动因素.主要入湖河口数据显示:西部4条主要入湖污染河流(南淝河、十五里河、塘西河和派河)水质明显改善,但仍处于较高污染水平,中东部入湖河流(兆河、双桥河和柘皋河)总磷浓度明显升高,是中东部湖区水体营养盐升高的主要原因.中东部河流入湖污染的增加加剧了该区域湖体的富营养化水平,尤其是总磷浓度明显提升,导致中东部湖区夏季水华蓝藻的优势种从鱼腥藻种类演替为微囊藻种类.夏季微囊藻的大量繁殖,使得2018年巢湖中东部湖区部分月份水华面积异常增高.因此,巢湖流域的治理应该在持续强化流域西部合肥市污染治理的同时,增加对流域中部和东部治理的关注和投入.  相似文献   

Mantle transition zone structure beneath the Central Asian Orogenic Belt     

Jing HE  Qingju WU 《中国科学:地球科学(英文版)》2020,63(4):548-560

Over the past decades, there have been hot debates in the geodynamic community regarding to the deep evolution mechanisms of Cenozoic volcanism in the Central Asian Orogenic Belt(CAOB). Of all the constraints available, high resolution structure of upper mantle discontinuities, especially the discontinuities at depths of 410 km(D410) and 660 km(D660), is of the most important, which may provide reliable clues on the magma channel as well as its evolution. In this work, we adopt the common conversion point stacking technique with teleseismic radial P-wave receiver functions to examine the D410 and D660 discontinuities. The primary results exhibit that the major characteristics of the mantle transition zone(MTZ) obtained by different velocity models are largely consistent. Obviously elevated D410 and slightly depressed D660 are observed beneath the Hannuoba Volcano, suggesting possible delamination of the local lithosphere deposited at the D410. This process may induce upwelling of the asthenospheric materials filling the space left by the delaminated lithosphere, and subsequently trigger volcanic eruptions. Strong depressions are observed at both D410 and D660 depths beneath west of the Dariganga Volcano, and the depression of D660 is more pronounced. It leads to the apparently thickened MTZ, indicating the presence of cold material at the D660. This cold material is speculated as a stagnant slab from the subducted Pacific Plate or the remains of a detached island arc system from the collision and formation of the CAOB. Slightly thinner MTZ is found beneath the Hentey Mountains and the Middle Gobi Volcano. Apparently, this thinner MTZ is not significant enough to support the existence of high thermal anomalies,which may rule out the possibility of large-scale hot material upwelling from either the local MTZ or even the lower mantle.  相似文献   

Metallogenesis and major challenges of porphyry copper systems above subduction zones   总被引：1，自引：0，他引：1  

Chen  Huayong  Wu  Chao 《中国科学:地球科学(英文版)》2020,63(7):899-918

Porphyry copper±molybdenum±gold deposits(PCDs) are the most representative magmatic-hydrothermal metallogenic system above subduction zones with important economic value. Previous studies revealed that large PCDs are generally formed from initial arc magmas(from subduction-induced partial melting of the mantle wedge), which eventually ascend to the shallow crust(3–5 km) for mineralization after a series of complex evolution processes. These processes include(1) the dehydration or partial melting of subducting slab, which induces partial melting of the metasomatized mantle wedge;(2)the ascent of mantle-derived magma to the bottom of the lower crust, which subsequently undergoes crustal processes such as assimilation plus fractional crystallization(AFC) or melting, assimilation, storage and homogenization(MASH);(3) the magma chamber formation at the bottom of the lower, middle and upper crust;(4) the final emplacement and volatilization of porphyry stocks; and(5) the accumulation of ore-forming fluids and metal precipitation. Despite the many decades of research, many issues involving the PCD metallogenic mechanism still remain to resolve, such as(1) the tectonic control on the geochemical characteristics of ore-forming magma;(2) the reason for the different lifespans of the long-term magmatic arc evolution and geologically "instantaneous" mineralization processes;(3) the source of ore-forming materials;(4) the relative contributions of metal pre-enrichment to mineralization by the magma source and by magmatic evolution; and(5) the decoupling behaviors of Cu and Au during the pre-enrichment. These issues point out the direction for future PCD metallogenic research, and the resolution to them will deepen our understanding of the metallogenesis at convergent plate boundaries.  相似文献   

四川地区震后应急会商资料快速产出系统的设计与实现     

祁玉萍  汪小厉  林圣杰  肖本夫  何畅  廖晓峰 《震灾防御技术》2020,15(1):176-183

地震预报意见以大量资料为基础，依靠专家经验和多学科知识并通过会商讨论形成。显著地震发生后，快速、准确、有效地研判震情可为后期应急指挥和地震现场工作奠定基础。本文以Datist软件为平台，基于四川及邻区的基础资料，设计研发符合四川震情的震后会商资料快速产出系统，当四川及邻区发生中强地震时，通过该系统可在收到地震短信5分钟内以请求触发的方式快速产出应急会商资料，并以微信、PowerPoint和Word的形式将基础资料发送给分析预报人员，为后期趋势分析奠定基础。  相似文献   

Cyclical one-way continental rupture-drift in the Tethyan evolution: Subduction-driven plate tectonics     

Wan  Bo  Wu  Fuyuan  Chen  Ling  Zhao  Liang  Liang  Xiaofeng  Xiao  Wenjiao  Zhu  Rixiang 《中国科学:地球科学(英文版)》2019,62(12):2005-2016

Numerous continents have rifted and drifted away from Gondwana to repeatedly open ocean basins over the past-500 millionyears.These Gondwana-derived continents drifted towards and collided with components of the Eurasian continent to successively close the preexisting oceans between the two.Plate tectonics satisfactorily describes the continental drift from Gondwana to Eurasia but does not define the geodynamic mechanism of continuously rifting to collisions of continents in the Tethy an Realm.After reappraisal of geological records of the rift,collision and subduction initiation from the surface and various geophysical observations from depth,we propose that Eurasia-directed subducting oceanic slabs would have driven Tethyan system in the Phanerozoic.The Eurasia-directed subduction would have dragged the passive Gondwana margin to rift and drift northwards,giving birth to new oceans since the Paleozoic.The closure of preexisting oceans between the Gondwana-derived continents and Eurasia led to continental collisions,which would have induced the initiation of oceanic subduction in the Tethyan Realm.Multiple episodic switches between collision-subduction-rift repeatedly led to the separation of continental fragments from Gondwana and dragged them to drift towards Eurasia.The final disappearance of Neo-Tethy s would have induced collision of the Gondwana-derived continents with the Eurasian continent,giving rise to the Cenozoic Alpine-Zagros-Himalayan collisional system.Therefore,the Eurasia-directed oceanic subduction would have acted as a 'one-way train' that successively transferred the ruptured Gondwana continental fragments in the south,into the terminal in the north.In this regard,the engine of this "Tethyan one-way train" is the negative buoyancy of subducting oceanic slabs.  相似文献   

湍流度随高度的变化及其对城市宏观地形的依赖     

李大全  孙武  欧阳睿康  黄盛  高梦媛  李庆祥  黄启明 《热带地理》2019,39(3):365-376

分别构建广州主建成区垂直比例尺为1﹕2 000、1﹕1 000和1﹕500的3个建筑物模型，利用大型边界层风洞，在西北和东南两风向下，基于中性流模拟分析了复杂城市地形下湍流度随高度的变化及其对宏观地形的依赖。结果表明：风廓线指数α与不同高度的湍流度之间的关系密切，利用现有模型，根据4类粗糙度边界层和不同垂直比例尺，可确定相应的湍流度随高度变化模型的主要系数，预测精度高。城市地形下最大湍流度面发育在0~0.2 h之间狭窄的范围内。用湍流度形态指数β来表征湍流度随高度的变化，无论城市屋脊还是平坦地形，随着风程区的延伸，廓线的指数α升高，湍流度形态指数β降低。表明同一高度湍流度值具有由迎风区、丘顶区向背风区增高，沿风程逐渐增大的规律，对地形部位和风程的依赖性强，与来流翻越简单地形时的特征一致。  相似文献