A new approach to the Nd residence time in the ocean: the role of atmospheric inputs     

K. Tachikawa  C. Jeandel  M. Roy-Barman 《Earth and Planetary Science Letters》1999,170(4):94-446

Concentrations of rare earth elements (REE) and Nd isotopic ratios were analyzed for seawater, filtered suspension and sediment trap samples collected in the tropical Atlantic Ocean (EUMELI program, EUtrophic, MEsotrophic and oLIgotrophic sites, 20°N, 18°–21°W). This is the first REE/Nd dataset on solution and different-sized particles collected at the same site. We present direct evidence of the Nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer. This exchange is probably one of the main factors that simultaneously constrains the Nd concentration and isotopic ratio budget. We propose a new approach to estimate the residence time of Nd in the ocean (τ_Nd) based on isotopic exchange: 200 yr < τ_Nd< 1000 yr. The exchange requires a partial dissolution of lithogenic Nd. We estimate that the fraction of soluble Nd proportion in atmospheric dust is of the order of 20% based on the isotopic ratios. We suggest that the partial dissolution of atmospheric fallout is probably one of the main REE sources of the ocean.  相似文献   

八卦庙超大型金矿地球化学特征及物源   总被引：6，自引：0，他引：6       下载免费PDF全文

吴烈善  韦龙明 《地质找矿论丛》1999,14(4):62-68

文章论述了八卦庙矿床围岩和含金石英脉的稀土元素及硫、硅、氢、氧、碳的同位素地球化学特征,结合合金矿床与深大断裂的时空分布特点,以及与秦只铅锌矿床和双王喷流沉积金床的对比研究,论证了八卦庙金矿的主要成矿物质来源于地壳深部,甚至上地幔。  相似文献   

长北地区生油岩干酪根的特征     

商出岫  丁桂蓉 《吉林地质》1999,18(2):42-45

本文应用元素、碳同位素和红外光谱分析,研究了长北地区生油岩干酪根的地球化学特征,结果表明该地区生油岩为陆相淡水湖相沉积,干酪根类型主要为腐殖型。随着埋深增加,同类型干酪根的成熟度增大。  相似文献   

铜厂铜矿稳定同位素研究     

叶霖  刘铁庚 《矿物岩石》1999,19(4):74-77

本文通过对铜厂铜矿的Ｓ,Ｈ,Ｏ和Ｃ同位素地球化学研究,认为本矿床属于与闪长岩有关的中低温硫化物矿床,在成矿阶段的实始热液为岩浆水,含矿流体是一种岩屑水与天水混合而Ｋ＾＋混合流体,矿床中Ｓ主要来源于细碧岩,部分来源于闪长岩,推测成矿物质来源物质也来源于细碧岩。  相似文献   

孟加拉湾MD77190柱状样第3期的韵律沉积记录及快速气候变化   总被引：9，自引：0，他引：9       下载免费PDF全文

方念乔  丁旋  陈学方  聂浩刚  张世红 《第四纪研究》1999,19(6):511-517

北印度洋孟加拉扇远源区的半远洋沉积记录在氧同位素第２期早期及第３期包含大量高频气候波动信号。该区ＭＤ７７１９０柱状样自第３期起由以富钙质生物壳体和贫钙质生物壳体为主要特色的两类沉积物构成韵律互层,它们的分布状态、互换频率及在生物和化学组分方面的细微变化反映出５９０００～２１０００ａＢ．Ｐ．期间研究区可与Ｈｅｉｎｒｉｃｈ和Ｄａｎｓｇａａｒｄ／Ｏｅｓｃｈｇｅｒ事件遥相对比的气候演化特征。有关的全球热传输机制有待深入探讨。  相似文献   

树轮纤维素中氧同位素温度意义     

陈拓  秦大河  任贾文 《冰川冻土》1999,(3)

树轮作为自然档案中的一种, 其同位素研究是较为新颖的领域文章比较系统地从树轮纤维素的提取、氧的来源、植物体内氧的分馏、与温度变化的关系等４ 个方面评述了树轮纤维素氧同位素组成的气候学意义已有的研究结果表明, 树轮纤维素氧同位素组成的变化是温度变化的良好载体, 但在定量恢复古温度变化时遇到了不少限制, 有待于进一步完善分馏模型  相似文献   

陆相咸化湖泊沉积硫酸盐岩硫同位素组成及其地质意义   总被引：1，自引：0，他引：1  

彭立才  杨平  濮人龙 《矿物岩石地球化学通报》1999,(2)

现代海洋中的硫酸盐矿物和海水硫酸盐本身常有相似的硫同位素组成,因而可根据现代蒸发岩的硫酸盐同位素来判断古环境。据李任伟［１］引用Ｈｏｌｓｅｒ和Ｋａｐｌａｎ及格里年科的资料报道,海相蒸发岩及其所反映的古海洋硫酸盐的硫同位素组成只在较狭窄的范围内变化,现...  相似文献   

湘西钨锑金矿床成矿系列及其稳定同位素研究   总被引：2，自引：0，他引：2  

鲍振襄  万容江 《城市地质》1999,11(1):11-17

湘西钨锑金矿床成矿系列泛指湖南沉陵-益阳-带、受雪峰弧形构造及其延伸部位控制的金矿成矿带,是湖南省重要的金矿成矿系列之一。系列中不同矿种的共（伴）生组合的矿床同属变质热液成因,其形成在很大程度上取决于赋矿围岩中成矿元素的丰度及其分布形式。对该成矿系列的研究和总结将会有助于开展进一步的地质找矿和成矿预测。  相似文献   

沉积地层中成矿作用的碳同位素特征和含矿缺氧盆地成因新观点   总被引：2，自引：0，他引：2  

杨振强  陈开旭  黄惠兰 《沉积与特提斯地质》1999,19(6):21-28

沉积盆地内地层中碳的来源 ,根据其碳、氧同位素特征可归纳为 :海洋沉积碳酸盐碳、生物碳、热解非生物成因碳、大气淡水方解石碳和热卤水系统中的无机碳。热水成因的金矿及喷气 沉积矿床中的碳都具有深源成因的无机碳。深部含无机碳的热流体喷溢到海洋底部可以解释为扩张盆地底部形成的缺氧环境和含矿黑色页岩的主导原因  相似文献   

Plutonism in the Variscan Odenwald (Germany): from subduction to collision     

R. Altherr  U. Henes-Klaiber  E. Hegner  M. Satir  C. Langer 《International Journal of Earth Sciences》1999,88(3):422-443

 Latest Devonian to early Carboniferous plutonic rocks from the Odenwald accretionary complex reflect the transition from a subduction to a collisional setting. For ∼362 Ma old gabbroic rocks from the northern tectonometamorphic unit I, initial isotopic compositions (ε_Nd=+3.4 to +3.8;⁸⁷Sr/⁸⁶Sr =0.7035–0.7053;δ¹⁸O=6.8–8.0‰) and chemical signatures (e.g., low Nb/Th, Nb/U, Ce/Pb, Th/U, Rb/Cs) indicate a subduction-related origin by partial melting of a shallow depleted mantle source metasomatized by water-rich, large ion lithophile element-loaded fluids. In the central (unit II) and southern (unit III) Odenwald, syncollisional mafic to felsic granitoids were emplaced in a transtensional setting at approximately 340–335 Ma B.P. Unit II comprises a mafic and a felsic suite that are genetically unrelated. Both suites are intermediate between the medium-K and high-K series and have similar initial Nd and Sr signatures (ε_Nd=0.0 to –2.5;⁸⁷Sr/⁸⁶Sr=0.7044–0.7056) but different oxygen isotopic compositions (δ¹⁸O=7.3–8.7‰ in mafic vs 9.3–9.5‰ in felsic rocks). These characteristics, in conjunction with the chemical signatures, suggest an enriched mantle source for the mafic magmas and a shallow metaluminous crustal source for the felsic magmas. Younger intrusives of unit II have higher Sr/Y, Zr/Y, and Tb/Yb ratios suggesting magma segregation at greater depths. Mafic high-K to shoshonitic intrusives of the southern unit III have initial isotopic compositions (ε_Nd=–1.1 to –1.8;⁸⁷Sr/⁸⁶Sr =0.7054–0.7062;δ¹⁸O=7.2–7.6‰) and chemical characteristics (e.g., high Sr/Y, Zr/Y, Tb/Yb) that are strongly indicative of a deep-seated enriched mantle source. Spatially associated felsic high-K to shoshonitic rocks of unit III may be derived by dehydration melting of garnet-rich metaluminous crustal source rocks or may represent hybrid magmas. Received: 7 December 1998 / Accepted: 27 April 1999  相似文献