Incorporation rate measurements of <Superscript>10</Superscript>Be, <Superscript>230</Superscript>Th, <Superscript>231</Superscript>Pa,and <Superscript>239,240</Superscript>Pu radionuclides in manganese crust in the Pacific Ocean: A search for extraterrestrial material     

Norikazu Kinoshita  Yuko Sato  Takeyasu Yamagata  Hisao Nagai  Akihiko Yokoyama  Takashi Nakanishi 《Journal of Oceanography》2007,63(5):813-820

In order to estimate the deposition rate of extraterrestrial material onto a manganese crust in a search for supernova debris, we analyzed the contents of ¹⁰Be, ²³⁰Th, ²³¹Pa, and ^239,240Pu in a sample of manganese crust collected from the North Pacific Ocean. On the basis of the depth profile of ¹⁰Be, the growth rate of the manganese crust was determined to be 2.3 mm Myr⁻¹. The uptake rates of ¹⁰Be, ²³⁰Th, and ²³¹Pa onto the manganese crust were estimated to be 0.22–0.44%, 0.11–0.73%, and 1.4–4.5%, respectively, as compared to the deposition rates onto the deep-sea sediments near the sampling station, while that for ^239,240Pu was 0.14% as compared to the total inventory of seawater and sediment column. Assuming that sinking particles represent 0.11–4.5% of the uptake rates, the deposition rate of extraterrestrial material onto the manganese crust was estimated to be 2–800 μg cm⁻²Myr⁻¹ according to the uptake of ¹⁰Be onto the manganese crust. Further, our estimate is similar to the value of 9–90 μg cm^{− 2}Myr⁻¹ obtained using the integrated global production rate of ¹⁰Be and the deposition rate of ¹⁰Be onto the manganese crust.  相似文献   

东太平洋中部始新世末期的微锰结核研究     

尹延鸿 《海洋科学》2001,25(3):8-10

深海钻探573B孔始新世末与渐新世初地层界线处有一层含金属黏土，其底部有一微锰结核富集层。研究了这些微锰结核的形态特征、化学成分及形成,总体看来始新世末期微锰结核中锰的含量比太平洋CC区的大锰结核、微锰结核含量明显高，但铁含量则明显低，属亚氧化成岩类型。始新世末期该区丰富的金属元素和微量元素的供给、沉积间断或缓慢 的沉积速率等条件利于该时期微锰结核的形成。  相似文献   

中太平洋北部锰结核的构造及成分特点     

杨胜雄  朱而勤  陈穗田 《中国海洋大学学报(自然科学版)》1989,(1)

本文阐述了中太平洋北部锰结核的成分及结构、构造的研究结果。结核可分为粗糙型和光滑型,内部呈现具有核心的同心层状构造,壳层可分为数个粗层。各粗层之间为不整合或假整合接触,粗层内微层呈韵律性排列。通过对粗层构造以及粗层内各韵律层的元素及矿物组分分布特点的研究,作者认为粗层的生长与当地沉积物的沉积间断或沉积速率减小有关,而微层的韵律性则是结核在滚动过程中生长造成的。文中并对结核的生长过程作了一般性讨论。  相似文献   

云南大箐锰矿床成矿地质条件综合分析     

杜发永  杨泽刚 《矿产与地质》2006,20(1):19-22

通过对该矿区含矿地层特征、矿石物质组分、有关元素含量的综合分析,以及中三叠世该区岩相古地理的研究,说明在中三叠世法郎期,随着海平面的快速上升,来自越北古陆和上地幔的含锰热液中的锰质,在海平面进入相对静止状态时,在半封闭的五凤海湾而聚集成矿。  相似文献   

Spessartine Garnets in a Manganiferous Carbonate Formation from Nsuta, Ghana     

Frank K. Nyame  Katsuo Kase  Masahiro Yamamoto 《Resource Geology》1998,48(1):13-22

Abstract: Manganese carbonate ore beds and host rock manganiferous phyllites at the Nsuta mine, western Ghana, contain well developed garnet crystals. Individual crystals are idioblastic, sometimes porphyroblastic, and homogeneous, and are associated with rhodochrosite (with or without kutnahorite), quartz and muscovite. The conspicuous absence of chlorite in garnet-rich assemblages, and of garnet in chlorite-rich rocks, suggest chemical constraints may have been important in the formation of the two minerals. Gondite bands within carbonate ores are interpreted to have resulted from localised processes in which manganese carbonates, in environments rich in alumino-silicate minerals, may have been completely exhausted during metamorphic reactions.  相似文献   

Kinetics of the Abiotic Reduction of Polymeric Manganese Dioxide by Nitrite: An Anaerobic Nitrification Reaction     

George W. Luther III  Jeannette I. Popp 《Aquatic Geochemistry》2002,8(1):15-36

Manganese oxides are strong environmental oxidants recently found to be involvedin the nitrogen cycle. Of the several possible reactions with reduced nitrogen species,the reduction of MnO₂ by nitrite has only received marginal attention. Yet, this reaction might explain why nitrification can occur in the absence of O₂, observed in both sediments and water columns. We have determined the stoichiometry of this reaction, as well as the chemical kinetics and the activation parameters, using a soluble polymeric form of MnO₂. The reaction rate decreases with increasing pH and decreasing temperature. The reaction is first order in each reactant with a second order rate constant (k) = 493 M^-1 min^-1 at 21.5 °C and pH = 5.00. The energy of activation (Ea = 9.370 kJ/mole) and the entropy of activation ( S = -169.5 J/mole) show the reaction to be associative and diffusion controlled, occurring via an inner-sphere mechanism, likely with O atom transfer from MnO₂ to HNO₂. The reaction is proton assisted and slowsdown at pH 5.5 where NO₂ ^- and MnO₂ (unprotonated and negatively charged) become the dominant species. In natural waters and sediments where anaerobic nitrification has been observed the pH is higher than this. Thus, the thermodynamically favorable reaction will likely proceed by microbial mediation.  相似文献   

湘中地区奥陶系和震旦系含锰层中稳定同位素组成的沉积学新解释          下载免费PDF全文

杨振强  蒋德和  赵时久 《沉积与特提斯地质》1993,(2):25-36

湘中地区有中奥陶世和早震旦世两个重要的锰碳酸盐层。安化县附近的湘锰组含锰泥灰岩和锰白云岩的碳和氧同位素值分别为—2.69～—4.00‰PDB和—6.87～—14.04‰PDB。湘锰组MnCO_3有δ~(12)C值—7.44～—13‰PDB和δ~(18)O值—2.65～—13.03‰。磨刀溪组黑色页岩(中奥陶世)中的Mn-泥灰岩显示负的δ~(13)C值(—1.7～—6.56‰PDB)和δ~(18)O值(—11.67～—14‰PDB)。但结晶锰矿石有更高的负δ~(13)C(—4.70％～—17.79‰PDB)和δ~(18)O(—11.67～17.27‰)。本区存在三种锰碳酸盐岩C和O同位素演化趋势:(1)安化地区的锰灰岩为稳定的δ~(13)C趋势;(2)湘锰组黑色页岩中的MnCO_3具有同步趋势:(3)中奥陶世黑色页岩中的锰矿石具有强烈反向趋势。碳成岩作用对锰碳酸盐形成过程中C和O同位素组成影响很大。湘锰组碳酸盐来源为非生物成因的海洋CO_2和SR至Me带的有机碳加入有关。磨刀溪组结晶锰碳酸盐的主要来源是热解脱羧基带(D)。δ~(34)S也为生物来源(—8～—27.49‰CDT)。Mn(％)品位与δ~(13)C呈负相关关系。证据表明锰碳酸盐成因与海盆地缺氧事件和海底热水(喷气)沉积有关。  相似文献   

湖南桃江奥陶系磨刀溪组锰质岩的内碎屑结构和重力流沉积   总被引：2，自引：0，他引：2  

赵东旭 《岩石学报》1992,(4)

湖南桃江一带的奥陶纪锰质碳酸盐岩,具有清晰的内碎屑结构和一些粒度递变沉积构造。锰质岩或锰矿层呈薄层或条带夹在含有笔石的黑色泥页岩中,表现出它们在成因或沉积环境方面的极不协调。以砂屑和藻屑为主组成的白色、灰白色锰质碳酸盐岩是清洁、浅水、碱性环境中的产物;以细粉砂级颗粒为主并含有硅质、碳质的泥页岩则是污浊、深水、酸性环境中的沉积。这种不协调的沉积组合是由于浅水锰质碳酸盐沉积物以重力流方式进入深水盆地与黑色泥质沉积物混合、交互沉积结果。  相似文献   

火山沉积建造——最重要的含锰建造   总被引：1，自引：0，他引：1  

孟祥化  刘红军 《现代地质》1992,6(4):418-425

本文根据沉积建造分析原理,提出了一个含锰沉积建造新的系统分类,并指出火山沉积建造的形成与地壳的破裂有关,控制含锰建造矿质来源的主要因素是板块构造活动引起的深成幔源热动力场。 我国地史上发育的含锰建造具有多旋回性、分区性。每次大的区域张裂活动之后和全球海平面上升阶段均有特定的含锰建造层的产出。把火山沉积建造作为最重要的含锰建造提出来,对于开辟新的研究思路和找矿方向具有重要的理论和实际意义。  相似文献   

Genesis of the Nasirabad manganese occurrence,Fars province,Iran: Geochemical evidences     

Alireza Zarasvandi  David Lentz  Mohsen Rezaei  Houshang Pourkaseb 《Chemie der Erde / Geochemistry》2013

The Nasirabad manganese occurrence is located to the south of the Neyriz in the Fars province. Structurally and lithologically, this occurrence lies in the southwest part of the Zagros Thrust Belt and was deposited as Mn-nodules and interconnected ore-bearing interlayer's with radiolarite cherts in the vicinity of the Neyriz ophiolites. The present work deals with the geology and geochemistry of the Nasirabad manganese occurrence with a discussion of its genesis. High Mn/Fe (average 18.85) and high Ba (average 28,830 ppm) with low Pb (2.0 ppm) and LREE > HREE, La_n/Nd_n (average 4.5), Dy_n/Yb_n (average 1.2) and negative Eu anomaly suggest distal hydrothermal source. The Co/Zn (average 2.2), Ce/La ratio (average 0.67) and trace element discrimination diagrams indicate hydrothermal–hydrogenous processes. Y/Ho ratio (average 24.85) and strong positive correlation coefficient between major oxides and some high field strength elements (HFSE) like; TiO₂ vs Fe₂O₃ (r = 0.98), Al₂O₃ vs Zr (r = 0.97), Al₂O₃ vs Fe₂O₃ (r = 0.98), Zr vs K₂O (r = 0.98), Nb vs TiO₂ (r = 0.92), Th vs Fe₂O₃ (r = 0.76), Th vs MgO (r = 0.86) reveal the presence of volcaniclastics and (or) terrigenous detritals of mafic composition being deposited into the depositional basin. It seems that intermittent interlayering of mafic detrital material derived from volcanic eruption of the Neyriz island arc directly affected the physicochemical conditions of hydrothermal ore precipitation in this basin and consequently the Nasirabad manganese ores represent hydrothermal–hydrogenous geochemical characteristics. The Nasirabad is an example of non-sulphidic, oxic Mn-mineralization. Similar trend between the enrichment and depletion of some bioessential elements (e.g., Mn, As, Ba, Sr, Co, Ce) might have been resulted from selective sequestering of metal ions by microbial processes and hence hydrogenous characteristics may also be the result of biogenetic processes. Moreover the high dilution of distal hydrothermal exhalations by sea water cannot be ruled out.  相似文献