真光层的颗粒动力学──Ⅵ.南海东北部海域上层水体颗粒动力学的示踪研究     

陈敏  黄奕普  陈飞舟  邱雨生  徐茂泉  姜德盛 《热带海洋学报》1997,(2)

利用234Th－238U不平衡研究南海东北部海域3个站位上层水体中的颗粒动力学性质，测定了水往中溶解态及颗粒态234Th的比活度，具体讨论各相中234Th／238U）AR（放射性活度比）比值的垂直分布情况及其与水化学要素间的关系。运用稿态箱式模型计算出各站位不同水层中溶解态234Th相对于清除至颗粒物的平均停留时间和颗粒态234Th相对于迁出作用的停留时间。由模型得出的参数表明3个站位的真光层具有两种不同的层化图像，这一情形与我们在南沙群岛海域得到的结果相一致。结合POC／PTh比值，估算出3个站位从真光层输出的颗粒有机碳（POC）通量分别为4.025.0和5．4mmolC·m－3－d-1。文中进一步讨论了234Th与POC两者停留时间的关系。  相似文献   

Zircon M257 ‐ a Homogeneous Natural Reference Material for the Ion Microprobe U‐Pb Analysis of Zircon     

Lutz Nasdala  Wolfgang Hofmeister  Nicholas Norberg  James M. Martinson  Fernando Corfu  Wolfgang Dörr  Sandra L. Kamo  Allen K. Kennedy  Andreas Kronz  Peter W. Reiners  Dirk Frei  Jan Kosler  Yusheng Wan  Jens Götze  Tobias Häger  Alfred Kröner  John W. Valley 《Geostandards and Geoanalytical Research》2008,32(3):247-265

We introduce and propose zircon M257 as a future reference material for the determination of zircon U‐Pb ages by means of secondary ion mass spectrometry. This light brownish, flawless, cut gemstone specimen from Sri Lanka weighed 5.14 g (25.7 carats). Zircon M257 has TIMS‐determined, mean isotopic ratios (2s uncertainties) of 0.09100 ± 0.00003 for ²⁰⁶pb/²³⁸U and 0.7392 ± 0.0003 for ²⁰⁷pb/²³⁵U. Its ²⁰⁶pb/²³⁸U age is 561.3 ± 0.3 Ma (unweighted mean, uncertainty quoted at the 95% confidence level); the U‐Pb system is concordant within uncertainty of decay constants. Zircon M257 contains ～ 840 μg g^?1 U (Th/U ～ 0.27). The material exhibits remarkably low heterogeneity, with a virtual absence of any internal textures even in cathodoluminescence images. The uniform, moderate degree of radiation damage (estimated from the expansion of unit‐cell parameters, broadening of Raman spectral parameters and density) corresponds well, within the “Sri Lankan trends”, with actinide concentrations, U‐Pb age, and the calculated alpha fluence of 1.66 × 10¹⁸ g^?1. This, and a (U+Th)/He age of 419 ± 9 Ma (2s), enables us to exclude any unusual thermal history or heat treatment, which could potentially have affected the retention of radiogenic Pb. The oxygen isotope ratio of this zircon is 13.9%o VSMOW suggesting a metamorphic genesis in a marble or calc‐silicate skarn.  相似文献   

Geochronology and geochemistry of eclogites from the Mariánské Lázně Complex,Czech Republic: Implications for Variscan orogenesis     

Brian L. Beard  L. Gordon Medaris Jr  Clark M. Johnson  Emil Jelínek  J. Tonika  Lee R. Riciputi 《International Journal of Earth Sciences》1995,84(3):552-567

The Mariánské Lázn complex (MLC) is located in the Bohemian Massif along the north-western margin of the Teplá-Barrandian microplate and consists of metagabbro, amphibolite and eclogite, with subordinate amounts of serpentinite, felsic gneiss and calcsilicate rocks. The MLC is interpreted as a metaophiolite complex that marks the suture zone between the Saxothuringian rocks to the north-west and the Teplá-Barrandian microplate to the south-east. Sm-Nd geochronology of garnet-omphacite pairs from two eclogite samples yields ages of 377±7, and 367±4 Ma. Samples of eclogite and amphibolite do not define a whole rock Sm-Nd isochron, even though there is a large range in Sm/Nd ratio, implying that the suite of samples may not be cogenetic. Eclogites do not have correlated _Nd values and initial ⁸⁷Sr/⁸⁶Sr ratios. Five of the eight eclogite samples have high _Nd values (+10.2 to +7.1) consistent with derivation from a MORB-like source, but variable ⁸⁷Sr/⁸⁶Sr ratios (0.7033 to 0.7059) which probably reflect hydrothermal seawater alteration. Three other eclogite samples have lower _Nd values (+ 5.4 to –0.8) and widely variable ⁸⁷Sr/⁸⁶Sr ratios (0.7033 to 0.7096). Such low _Nd values are inconsistent with derivation from a MORB, source and may reflect a subduction or oceanic island basalt component in their source. The MLC is an important petrotectonic element in the Bohemian Massif, providing evidence for Cambro-Ordovician formation of oceanic crust and interaction with seawater, Late Devonian (Frasnian-Famennian) high- and medium-pressure metamorphism related to closure of a Saxothuringian ocean basin, Early Carboniferous (Viséan) thrusting of the Teplá terrane over Saxothuringian rocks and Late Viséan extension.  相似文献   

Interferometric observations of HCN and CN towards carbon stars     

M. Lindqvist  R. Lucas  H. Olofsson  A. Omont  K. Eriksson  B. Gustafsson 《Astrophysics and Space Science》1995,224(1-2):501-502

Using the IRAM interferometer we have observed four carbon stars (U Cam, CIT6, Y CVn, IRC+40540) in the HCN(J=1 0) and CN(N=1 0) lines. Here we present some results for CIT6 and U Cam.  相似文献   

RACIALIZED TOPOGRAPHIES: ALTITUDE AND RACE IN SOUTHERN CITIES*     

JEFF UELAND  BARNEY WARF 《Geographical review》2006,96(1):50-78

ABSTRACT. This study examines altitudinal residential segregation by race in 146 cities in the U.S. South. It begins by embedding the topic in recent theorizations of the social construction of nature, the geography of race, and environmental justice. Second, it focuses on how housing markets, particularly in the South, tend to segregate minorities in low‐lying, flood‐prone, and amenity‐poor segments of urban areas. It tests empirically the hypothesis that blacks are disproportionately concentrated in lower‐altitude areas using gis to correlate race and elevation by digital elevation‐model block group within each city in 1990 and 2000. The statistical results confirm the suspected trend. A map of coefficients indicates strong positive associations in cities in the interior South‐where the hypothesis is confirmed‐and an inverse relationship near the coast, where whites dominate higher‐valued coastal properties. Selected city case studies demonstrate these relationships connecting the broad dynamics of racial segregation to the particularities of individual places.  相似文献   

滇西水成铀矿勘探综合测井成果   总被引：2，自引：0，他引：2  

罗志明  张世涛 《云南地质》2005,24(4):386-394

滇西龙川江盆地发现水成铀矿。本文借助地球物理综合测井技术，对龙川江盆地水成铀矿的成矿规律作有益分析和探讨。重点论述滇西水成铀成矿的成矿（沉积）环境及其成矿物征。  相似文献   

柴北缘绿梁山地区辉长岩的锆石U-Pb年龄及意义   总被引：11，自引：0，他引：11  

袁桂邦  王惠初  李惠民  郝国杰  辛后田  张宝华  王青海  田琪 《华北地质》2002,25(1):36-40

柴达木盆地北缘绿梁山地区的辉长岩侵入到古生代滩间山群及超基性岩中 ,地球化学、微量元素、稀土元素显示出源幔特征。选自其中的锆石明显具岩浆型锆石特点 ,4个单颗粒锆石U -Pb同位素年龄均为谐和年龄 ,2 0 6 Pb 2 38U表面年龄统计权重平均值为 (496 .3± 6 .2 )Ma ,代表了该岩体的结晶年龄 ,从而间接地否定了本区滩间山群的时代为晚奥陶世 -志留纪的认识。辉长岩与滩间山群是柴北缘活动大陆边缘火山岛弧的组成部分。此类岩体同位素地质年龄的确定对柴北缘榴辉岩、滩间山群时代及大地构造性质的重新认识具有重要意义  相似文献   

Book Reviews     

《The Professional geographer》2003,55(4):528-529

  相似文献   

南京直立人的U/Th和U/Pa年代   总被引：2，自引：0，他引：2  

程海  艾思本  汪永进 《高校地质学报》2003,9(4):667-677

中国直立人化石的准确定年对于研究人类演化有着极为重要的意义。1993～1994年在南京汤山葫芦洞发现的两个直立人头盖骨化石和一枚牙化石被称为“南京直立人”。其中1号头盖骨化石之上的方解石钙板的U/Th年龄为53.3_(-1.2)~(+1.5)万年;但考虑到定年的准确性,则为53.3_(-3.0)~(+3.5)万年。其~(231)Pa/~(235)U活度比值为0.998±0.006。这表明“南京直立人”的年代应该大于50万年。与”南京直立人”伴生的动物牙化石U/Th年代为18.5～29.0万年;U/Pa年代为13.7～17.2万年。此外,对于同一颗牙化石,牙釉的年龄小于牙本质的年龄。同一样品的U/Pa年龄也显著小于其U/Th年龄。因此,牙化石的U摄取过程并不符合U早期摄取模式。多数牙化石分析点在~(234)U/~(238)U-~(230)Th/~(238)U图上落在位于U早期摄取和线性摄取模式曲线之间,指示牙化石的U摄取过程很可能介于上述两种模式之间。如果这一假设成立,那么牙化石的U/Th和U/Pa线性摄取模式年龄则为其年代的上限。因为不受U摄取过程~(234)U/~(238)U变化的影响,U/Pa线性摄取模式年龄比U/Th较为可靠。最小的U/Pa线性摄取模式年龄为1Ma,这是”南京直立人”上限年龄的估计。从定年结果看,”南京直立人”可能生活在海洋同位素(MIS)16阶段,但这不是最终结论。  相似文献   

博格达山晚石炭纪造山活动的变形地质记录   总被引：13，自引：2，他引：13  

王宗秀  李涛  周高志  卢苗安  柳永清  李寅 《地学前缘》2003,10(1):63-69

主要由钙碱性火山岩、火山碎屑岩组成的博格达古岛弧是天山缝合造山带的重要组成部分 ,是一个发育较成熟的山链 ,其演化经历了晚古生代的韧性剪切收缩 ;中生代伸展调整及新生代再造山过程。晚古生代的造山活动在博格达山有很好的地质记录 ,并以显著的韧性剪切变形带的形成和发育同造山的褶皱构造为特点。剪切变形带内同构造的石英脉中的锆石U PbSHRIMP测年结果与山链中花岗岩、辉长岩年龄颇为一致 (311～ 316Ma) ,这个年龄反映在结束洋盆散聚、碰撞焊接的晚华力西期造山过程中 ,博格达古岛弧内存在一次虽不甚强烈 ,但又较为明显的构造岩浆事件 ,其成因可能与引起石炭纪大规模裂陆式喷发的深部断裂构造重新活动有关。  相似文献