Formation of Fe-oxyhydroxides from the East Pacific Rise near latitude 13°N:Evidence from mineralogical and geochemical data     

《中国科学D辑(英文版)》2008,(2)

The mineralogical and geochemical characteristics of Fe-oxyhydroxide samples from one dredge station (long. 103°54.48'W, lat. 12°42.30'N, water depth 2655 m) on the East Pacific Rise near lat 13°N were analyzed by XRD, ICP-AES, and ICP-MS. Most Fe-oxyhydroxides are amorphous, with a few sphalerite microlites. In comparison with Fe-oxyhydroxides from other fields, the variable ranges in the chemical composition of Fe-oxyhydroxide samples are very narrow; their Fe, Si, and Mn contents were 39.90%, 8.92%, and 1.59%, respectively; they have high Cu (0.88%―1.85%) and Co (65×10?6―704×10?6) contents, and contain Co Cu Zn Ni> 1.01%. The trace-element (As, Co, Ni, Cu, Zn, Ba, Sr) and major-element (Fe, Ca, Al, Mg) contents of these samples are in the range of hydrothermal sulfide from the East Pacific Rise near 13°N, reflecting that this type of Fe-oxyhydroxide constitutes a secondary oxidation product of hydrothermal sulfide. The Fe-oxyhydroxide samples from one dredge station on the East Pacific Rise near 13°N are lower in ΣREE (5.44×10?6―17.01×10?6), with a distinct negative Ce anomaly (0.12 ― 0.28). The Fe-oxyhydroxide samples have similar chondrite-normalized rare-earth-element (REE) patterns to that of seawater, and they are very different from the REE composition characteristics of hydrothermal plume particles and hydrothermal fluids, showing that the REEs of Fe-oxyhydroxide are a major constituent of seawater and that the Fe-oxyhydroxides can become a sink of REE from seawater. The quick settling of hydrothermal plume particles resulted in the lower REE content and higher Mn content of these Fe-oxyhydroxides, which are captured in part of the V and P from seawater by adsorption. The Fe-oxyhydroxides from one dredge station on the East Pacific Rise near 13°N were formed by secondary oxidation in a low temperature, oxygenated environment. In comparison with the elemental (Zn, Cd, Pb, Fe, Co, Cu) average content of hydrothermal sulfide samples from the East Pacific Rise near 13°N, the Zn, Cd, and Pb contents of the Fe-oxyhydroxides are lower, and their Fe, Co, and Cu contents are higher.  相似文献   

Characteristics of climate change in the “significant impact zone” affected by aerosols over eastern China in warm seasons   总被引：1，自引：0，他引：1  

SHI XiaoHui  XU XiangDe  XIE LiAn State Key Laboratory of Severe Weather  Chinese Academy of Meteorological Sciences  Beijing  China 《中国科学D辑(英文版)》2008,(5)

Through analysis of the distribution pattern and changing characteristics of atmospheric aerosols over the East Asia region during warm seasons in recent 20 a and beyond as well as their possible interac- tive relationship with a variety of meteorological elements, it is found that the high-value zone of aerosol optical depth derived from the Total Ozone Mapping Spectrometer (TOMS), its significant negative correlation zones in terms of sunshine duration (SD) and surface air temperature (SAT) and its significant positive correlation zones with low-level cloud amount (LCC) are co-located in the South China region during warm periods. Based on this finding, the region is referred to as a "significant impact zone" (SI zone) affected by aerosols. Then, a comparative analysis is made on variation differ- ences of observed SAT, SD and LCC, etc. in different regions. It is also found that the LCC is increased and the SD is decreased within the "SI zone" over eastern China during the warm season. These characteristics are more evident than those beyond the zone, while the warming trend within the zone is evidently weaker than that outside it. Studies show that since recent 20 a, under the influence of aerosols, the LCC tend to increase substantially with a clear decrease of SD and an unnoticeable warming trend within the "SI zone". Comparing with the climate change beyond the zone, the difference is significant. Therefore, the effects of atmospheric aerosols on climate is possibly one of the contri- butions to the difference of climate change existed between the southern and northern parts of the Eastern China during a warm season.  相似文献   

Periodical mixing of MORB magmas near East Pacific Rise 13°N: Evidence from modeling and zoned plagioclase phenocrysts     

GuoLiang Zhang  ZhiGang Zeng  XueBo Yin  DaiGeng Chen  XiaoYuan Wang  XiaoMei Wang 《中国科学D辑(英文版)》2008,51(12):1786-1801

Thirty-six basalt samples from near East Pacific Rise 13°N are analyzed for major and trace elements. Different types of zoned plagioclase phenocrysts in basalts are also backscatter imaged, and major element profiles scanned and analyzed for microprobe. Basalts dredged from a restricted area have evolved to different extents (MgO=9.38wt%—6.76wt%). High MgO basalts are modeled for crystalliza-tion to MgO of about 7wt%, and resulted in the Ni contents (≈28 ppm) that are generally lower than that in observed basalts (>60 ppm). It suggests that low MgO basalts may have experienced more intensive magma mixing. High MgO (9.38wt%) basalt is modeled for self-"mixing-crystallization", and the high Ni contents in low MgO basalts can be generated in small scale and periodical self-mixing of new magma (high MgO). "Mixing-crystallization" processes that low MgO magmas experienced accord with recent 226Ra/230Th disequilibria studies for magma residence time, in which low MgO magmas have experi-enced more circles of "mixing-crystallization" in relatively longer residence time. Magma mixing is not homogeneous in magma chamber, however, low MgO magmas are closer to stable composition pro-duced by periodical "mixing-crystallization", which is also an important reason for magma diversity in East Pacific Rise. Zoned plagioclase phenocrysts can be divided into two types: with and without high An# cores, both of which have multiple reversed An# zones, suggesting periodical mixing of their host magmas. Cores of zoned plagioclase in low MgO (7.45wt%) basalt differ significantly with their mantle in An#, but are similar in An# with microlite cores (products of equilibrium crystallization) in high MgO (9.38wt%) basalt, which further shows that plagioclase phenocryst cores in low MgO basalts may have formed in their parental magmas before entering into the magma chamber.  相似文献   

Mesozoic paleogeography and tectonic evolution of South China Sea and adjacent areas in the context of Tethyan and Paleo-Pacific interconnections   总被引：4，自引：0，他引：4  

Di  Zhou  Zhen  Sun  Han-zong  Chen  He-hua  Xu  Wan-yin  Wang  Xiong  Pang  Dong-sheng  Cai  Deng-ke  Hu 《Island Arc》2008,17(2):186-207

Abstract   During the Mesozoic era, the South China Sea and its environs were located at the south-eastern margin of the Eurasian continent. There has been hot debate on the influences of Tethyan and Paleo-Pacific tectonics to the Mesozoic evolution of the area. This paper compiles lithofacies maps of six time slices and discusses the paleogeographic and tectonic evolution of the area based on this compilation and other data on structural deformation and magmatism. In the Early Triassic, the Paleotethys Ocean extended eastward to the study area through the Song Da passage. Then a significant east–west differential evolution began. In the Late Triassic, the western area uplifted as a result of the collision between the Indosinian and South China blocks during the Indosinian orogeny, and the Song Da passage has closed since then. Meanwhile, a transgression of Paleo-Pacific waters occurred in the eastern and south-eastern portions of the area, forming the 'East Guangdong–North-west Borneo Sea'. In the Early Jurassic, seawater transgression was even more pronounced, resulting into the connection of this sea with the Mesotethys Ocean to the west. Large quantities of Tethyan water carrying Tethyan organisms entered the area. In the Middle Jurassic, a short-lived transgression occurred in the eastern Mesotethys and resulted in the formation of the 'Yunnan–Burma Sea'. The Late Jurassic to Early Cretaceous was the climax of the subduction of both the Mesotethys and Paleo-Pacific towards the Eurasian continent. This led to the formation of the great 'Circum South-east Asia Subduction–Accretion Zone' in the Middle or Late Cretaceous. This paper also presents various lines of evidence for a newly recognized segment of this Mesozoic subduction–accretion zone buried under Cenozoic sediments in the north-eastern South China Sea.  相似文献   

Rapid evolution of the Eocene accretionary complex (Hyuga Group) of the Shimanto terrane in southeastern Kyushu, southwestern Japan     

Makoto  Saito 《Island Arc》2008,17(2):242-260

Abstract   Detailed geologic examination of the Eocene accretionary complex (Hyuga Group) of the Shimanto terrane in southeastern Kyushu revealed that the oceanic plate was composed of Paleocene to Lower Eocene mudstone and siliceous mudstone, lower Middle Eocene red mudstone, and mid-Middle Eocene trench-fill turbidite with siltstone breccia, successively overlying the pre-Eocene oceanic plate. This oceanic plate sequence was overlain by Upper Eocene siltstone. Deposition of the lower Middle Eocene red mudstone was accompanied by basalt flows and it is interbedded with continental felsic tuff, which indicates that the basalt and red mudstone were deposited near the trench just before accretion. The Hyuga Group has very similar geological structure to that of the chert–clastic complexes found in the Jurassic accretionary complexes in Japan: that is, a decollement fault formed in the middle of an oceanic plate sequence, and an imbricate structure formed only in the upper part of the sequence. Thus, it appears that the Hyuga Group was formed by the same accretionary process as the Jurassic accretionary complexes. No accretion occurred before the Middle Eocene, and the rapid accretion of the Hyuga Group was commenced by the supply of coarse terrigenous sediments in the mid-Middle Eocene, when the direction of movement of the Pacific Plate changed. The pre-Eocene oceanic basement and lower Middle Eocene volcanic activity suggest that the oceanic plate partly preserved in the Hyuga Group was very similar to the northern part of the present West Philippine Sea Plate.  相似文献   

Foreword     

George W. Housner 《地震工程与工程振动(英文版)》2008,7(2):I0001-I0001

Destructive earthquakes have caused great damage in China and the United States and collapsing buildings havecaused many deaths and injuries. The field of earthquake engineering studies earthquake hazards, the occurrence ofearthquakes of various magnitudes, the nature of the ground shaking during an earthquake, the vibration of structuresduring earthquakes, the strengthening of existing structures and the design of new structures to be earthquake resistant,and finally, how to cope with earthquake damage and restore a city to normal functioning. Such efforts are in progressin both countries, but unfortunately, the language barrier interferes with the free flow of information between China andthe Untied States. It would be mutually beneficial if some means could be developed to promote the exchangeof information across the Pacific Ocean. This new journal has been established for this purpose and its success willbe an important step in promoting earthquake engineering in China and the United States.  相似文献   

南川市三泉镇岩溶区农田生态系统植被碳库的动态变化   总被引：3，自引：0，他引：3  

罗怀良  袁道先  陈浩 《中国岩溶》2008,27(4):382-387

通过农田样方观测与实验分析获得南川市三泉镇农田生态系统主要农作物的含碳率、经济系数、果实水分系数,结合该区近26年来( 1980- 2005)主要农作物产量与耕地面积的相关数据,用农作物产量与碳储量转换模型计算法估算和分析该区农田生态系统植被碳库的总量及构成的动态变化。结果发现: 近26年来该镇农田植被碳库和碳密度略有提高,具有微弱的碳汇效应。与邻近的四川盆地非岩溶区相比,该区农田植被碳密度较低。针对农田生态系统植被碳库的构成特点和动态特征,该镇今后应进行作物结构调整,适度增加水稻等大春作物的种植和马铃薯、油菜和饲料等小春作物的种植面积,稳定小麦等作物的播种面积; 加强农田基本建设,发展生态农业,以进一步提高农田生态系统植被碳库的碳储量和碳密度。   相似文献   

东太平洋CC区多金属结核的地质学特征及形成环境     

李国胜 《地质与资源》2008,17(4):286-291

通过对东太平洋CC区洋底地质取样及实验测试分析,运用洋底照相、多频探测等多种地球物理方法手段,进一步阐明了CC区多金属结核的形态、主要类型、丰度、覆盖率、品位、化学成分及分布特征.通过对CC区区域地质背景及地形地貌的综合研究,深入探讨了多金属结核的形成环境.通过对CC区多金属结核的分布规律与形成环境的综合研究,揭示了该区多金属结核的形成与地质环境之间的内在关系,这对于分析研究该区多金属结核的形成机理,为多金属结核资源评价和开发提供科学依据,对于大力开发与利用洋底多金属矿产资源,具有重要的科学意义和经济意义.  相似文献   

太平洋海温异常对大理雨季开始期的影响   总被引：1，自引：0，他引：1  

高志伟  钟爱华  李建美  陈红玉 《云南地理环境研究》2009,21(4):87-94

采用大理州雨季开始期资料、1961年6月~2008年5月太平洋5°×5°共286个格点的逐月平均海温资料及NCEP/NCAR的SSTA资料,通过相关分析发现,太平洋海温与大理雨季开始期的关系密切,春季和上年秋季太平洋海温对大理雨季开始的影响较大。雨季开始前若发生厄尔尼诺事件,大理雨季开始期偏晚,反之,若发生拉尼娜事件,大理雨季开始期偏早。N ino3区的海温异常对大理雨季开始期的影响相当明显,当5月N ino3区的海温异常偏高时,大理雨季开始期偏晚;反之,当5月N ino3区的海温异常偏低时,大理雨季开始期偏早,N ino3区海温异常可以作为大理雨季开始期预测的一个强信号因子。  相似文献   

东亚夏季风的年际变化及其对环流和降水的影响     

于淑秋  施晓晖  林学椿 《地理学报(英文版)》2009,19(1):67-80

Using NCEP/NCAR reanalysis geopotential height (GHT) and wind at 850 hPa, GHT at 500 hPa, precipitation rate, sea level pressure (SLP) and precipitation observations from more than 600 stations nationwide in June–August from 1951 to 2006, and focusing on the East Asia-West Pacific region (10°–80°N, 70°–180°E), interannual variation of East Asian summer monsoon (EASM) and its correlations with general circulation and precipitation patterns are studied by using statistical diagnostic methods such as 9-point high pass filtering, empirical orthogonal function (EOF) analysis, composite analysis and other statistical diagnosis, etc. It is concluded as follows: (1) EOF analysis of SLP in the East Asia-West Pacific region shows the existence of the zonal dipole oscillation mode (APD) between the Mongolia depression and the West Pacific high, and APD index can be used as an intensity index of EASM. (2) EOF analysis of GHT anomalies at 500 hPa in the East Asia-West Pacific region shows that the first EOF mode is characterized with an obvious meridional East Asian pattern (EAP), and EAP index can also be used as an EASM intensity index. (3) The composite analysis of high/low APD index years reveals the close correlation of APD index with EAP at 500 hPa (or 850 hPa). The study shows an obvious opposite correlation exists between APD index and EAP index with a correlation coefficient of −0.23, which passes the confidence test at 0.10 level. (4) Both APD and EAP indexes are closely correlated with precipitation during flood-prone season in China and precipitation rate over the East Asia-West Pacific region. The significant correlation area at 5% confidence level is mainly located from the southern area of the Yangtze River valley to the ocean around southern Japan, and the former is a positive correlation and the latter is a negative one. Foundation: Cooperative Project funded by the Ministry of Science and Technology of the People’s Republic of China, No.2007DFB20210; National Natural Science Foundation of China, No.90502003; JICA China-Japan Technical Cooperative Project “China-Japanese Cooperative Research Center on Meteorological Disasters”. Author: Yu Shuqiu, Associate Professor, specialized in climate and climate change.  相似文献