Sedimentary characteristics and the implications of cobalt-rich crusts resources at Caiwei Guyot in the Western Pacific Ocean

Abstract

Cobalt-rich crust has attracted increased attention due to their economic value. Studies have indicated that seamounts in the Western Pacific Ocean are rich in cobalt-rich crust resources. The Caiwei Guyot in Western Pacific Ocean is one of the cobalt-rich crust exploration areas contracted between China and the International Seabed Authority. A large volume of research has been conducted to elucidate the tectonic evolution, basement type, sediment type, gravity and magnetic anomaly characteristics, and geochemical characteristics of shallow surface sediments at Caiwei Guyot. However, a research gap exists on the sedimentary strata below the pelagic deposits and above the volcanic basement of the Caiwei Guyot. This paper summarizes that two main types of sediments existing on the top of Caiwei Guyot. The deposition thickness on the top of Caiwei Guyot is characterized by three sedimentary centers and exposed periphery. Pelagic sediments are difficult to form at the northeastern portion and edge area of Caiwei Guyot due to the strong bottom current environment, which makes these areas suitable for crust growth. This paper delineated three cobalt-rich crust prospective areas at the Caiwei Guyot with of significant implications for exploration and mining-lease-block selections at Caiwei Guyot.     

维嘉海山沉积过程及其对西太平洋海山演化的意义

海山沉积过程与全球气候变化和古海洋演化有着紧密联系,维嘉海山保留了西太平洋晚中生代以来的完整沉积记录,是探索西太平洋海山构造演化的理想场所.基于浅地层剖面、大洋钻探和最新相关研究成果,通过研究海山的沉积特征、火山活动和沉降速率等,探索西太平洋维嘉海山晚中生代以来的沉积过程.结果显示维嘉海山顶部发育3个沉积单元,并发现了...     

Magnetic minerals in Mid-Pleistocene sediments on the Caiwei Guyot,Northwest Pacific and their response to the Mid-Brunhes climate event

Seamounts are ubiquitous topographic units in global oceans, and their influences on local oceanic circulation have attracted great attention in physical oceanography; however, previous efforts were less made in paleoclimatology and paleoceanography. The Caiwei Guyot in the Magellan Seamounts of the western Pacific is a typical seamount, and in this study, we investigate a well-dated sediment core by magnetic properties to reveal the relationship between deep-sea sedimentary processes and global climate changes. The principal results are as follows: (1) the dominant magnetic minerals in the sediments are low-coercivity magnetite in pseudo-single domain range, probably including a biogenic contribution; (2) the variabilities of magnetic parameters can be clustered into two sections at ～500 ka, and the differences between the two units are evident in amplitudes and means; (3) changes in the grainsize-dependent magnetic parameters can be well correlated to records of global ice volume and atmospheric CO2 in the middle Pleistocene. Based on these results, a close linkage was proposed between deep-sea sedimentary processes in the Caiwei Guyot and global climate changes. This linkage likely involves different roles of biogenic magnetite in the sediments between interglacial and glacial intervals, responding to changes in marine productivity and deep-sea circulation and displaying a major change in the Mid-Brunhes climate event. Therefore, we proposed that the sedimentary archives at the bottom of the Caiwei Guyot record some key signals of global climate changes, providing a unique window to observe interactions between various environmental systems on glacial-interglacial timescales.     

桩基础在大型泥石流拦砂坝中的应用

"5.12"震后,震区泥石流处于高发期。拦砂坝是目前泥石流治理工程中主要的工程措施,新近泥石流堆积体上修建重力式拦砂坝对地基和基础要求较高。以魏家沟泥石流治理工程1#拦砂坝实例,分析桩基承台基础在泥石流治理工程中的应用,并为类似工程的治理提供参考。     

Fine-scale compositional variations in a Co-rich Mn crust from the Marcus-Wake Seamount cluster in the western Pacific based on electron microprobe analysis (EMPA)

The internal structure and composition of a 37-mm-thick Co-rich Mn crust from the Lamont Guyot in the Marcus-Wake Seamount cluster have been studied in detail by means of electron-probe microanalysis (EPMA). 184 point analyses for 16 elements were carried out at an average spacing of 0.20 mm and each point was dated using the Co-geochronometer method. Two types of variation in composition were observed in the crust: long-term trends and short-term erratic variations. The long-term trends were identified using the fifth order polynomial. Mn and Ni were shown to increase in concentration from 23.3 Ma to a maximum at about 20 Ma and then decline steadily to the Present, whereas Fe, P and Si showed the opposite trend. By contrast, Co displayed a double humped pattern with maxima at about 19 Ma and 3.5 Ma and minima at 23.3 Ma, about 11 Ma and at Present. The long-term trends in element concentrations in the crust lead us to suggest that much of the Fe in western Pacific Ocean ferromanganese crusts is aeolian in origin and derived from the deserts of central Asia. Cooling of the Asian mainland at about 20 Ma led to an increase in the flux of Fe to the oceans. This was supplemented by an additional input of Fe into the crusts as a consequence of the dissolution of biogenic CaCO₃ tests at 4.5−10.5 Ma. For the short-term erratic variations, three periods of 0.61, 0.96 and 1.65 m.y. were identified by spectral analysis. The second harmonics of these periods are 1.22, 1.92 and 3.30 m.y., which may correspond to the highest-order periods for eccentricity of 1.31, 2.04 and 3.47 m.y. This suggests the possibility that the high-frequency oscillations of the time series data are linked to climatic changes controlled by the highest-order periods of the Milankovitch cycles.     

西太平洋Lamont海山中新世以来富钴结壳成矿环境的演化

分析了西太平洋Lamont海山12个站位33个富钴结壳样品的主元素和稀土元素,结果表明,该海山富钴结壳成因类型属于水成成因,并且在形成过程中基本未受到磷酸盐化作用的影响。Lamont海山的一个富钴结壳样品剖面的电子探针数据显示,该海山富钴结壳的成矿环境在新第三纪以来至少存在2个演化阶段:第1阶段,23~15 Ma,富钴结壳中Mn相对富集,成矿环境以富氧贫硅为特征;第2阶段,15~0 Ma,富钴结壳中Fe相对富集,成矿环境以贫氧富硅为特征。成矿环境的氧化能力总体上呈现下降的趋势。联系新生代世界大洋,尤其是西太平洋的地质演化背景,认为引起成矿环境演变的原因主要是西太平洋大洋板块的WNW向漂移和新第三纪以来全球水道开合,造成了Lamont海山所处海区最低含氧带逐渐减薄。     

湘南魏家钨矿区祥林铺岩体锆石LA-MC-ICP-MSU-Pb测年——对南岭西端晚侏罗世钨矿成岩成矿作用的指示

魏家钨矿床位于湘南西部铜山岭地区,是近年来在南岭成矿带西端新发现的一超大型矽卡岩型钨矿床。矿体主要产于祥林铺花岗岩与其围岩的接触带内,其形成与祥林铺花岗岩密切相关。为厘清其成岩成矿时代,本文对魏家钨矿区的花岗斑岩和石英斑岩进行了锆石LA-MC-ICP-MS U-Pb测年。结果显示,矿区花岗斑岩侵位时间为(157.8±0.9)Ma(MSWD=1.06),石英斑岩侵位时间为(158.3±1.4)Ma(MSWD=0.2)。矿区内花岗斑岩与石英斑岩侵位时间在误差范围内一致,表明两者可能是同一岩浆演化至不同阶段的产物,矿区内花岗质岩浆活动与钨多金属成矿作用时限约为158 Ma,为南岭地区中生代"大规模成矿"作用(160~150 Ma)的组成部分。另外,花岗斑岩中捕获有少量加里东期的岩浆锆石(435 Ma),指示该区曾发生加里东期岩浆活动,这与华南地区广泛存在的加里东期构造岩浆活动事件吻合。魏家钨矿成岩成矿时代的厘定对于在南岭成矿带西端寻找晚侏罗世钨矿具有重要的指示意义。     

南岭魏家钨矿床地质特征及找矿前景分析

魏家钨矿是近年来进行新一轮矿产远景调查时,在南岭成矿带北缘发现的又一大型钨矿。本文在讨论成矿地质背景基础上,对矿床地质特征进行了研究。矿体的空间展布受矿区内基底构造、岩性、祥林铺背斜、祥林铺花岗斑岩体以及铜山岭花岗闪长岩体往北东侵入的隐伏岩体控制。由于岩浆的二次侵位,形成二次成矿。矿床成因为斑岩-矽卡岩型钨矿床。同时指出了找矿标志,分析了找矿远景及今后工作方向,对以后的找矿工作有一定的指导意义。     

Seedbed of Reform: Arnold Guyot and School Geography in Massachusetts, 1849–1855

Abstract

Swiss-born Arnold Henri Guyot (1807–1884) was the first professionally trained geographer to hold an academic position in the United States. After his migration to this country in 1848 he lived for several years in Massachusetts. During this period he introduced contemporary German-Swiss ideas of geography to key opinion leaders in an important series of lectures (published as Earth and Man), established a system of weather stations, and lectured on methods of teaching geography in Massachusetts teachers' institutes and normal schools. This article discusses Guyot's work in the reform of school geography in Massachusetts as the seedbed for his later, better-known work as the author of innovative textbooks and other teaching aids.     

维嘉平顶海山富钴铁锰结壳空间分布特征:基于“蛟龙号”载人潜水器近海底观测资料的分析

基于对具有高精度水下定位功能的载人潜水器“蛟龙号”近海底观测视像资料数据的分析研究,本文首次报道了维嘉平顶海山山顶平台凸起区域、顶坡过渡带以及斜坡上部地形单元内的富钴结壳分布特征,对我国富钴结壳资源勘查评价具有重要意义。研究表明:(1)不同地形单元发育的富钴结壳具有明显不同的分布特征;(2)山顶平台凸起区发育有连续分布的富钴结壳,可作为我国富钴结壳资源勘查工作的关注区;(3)顶坡过渡带—斜坡上部区域发育有连续分布的富钴结壳,然而往往被白色波纹状沉积物隔成数段;(4)顶坡过渡带钴结核发育较少,与马尔库斯—威克海山群平顶海山存在明显的不同。