湖北宜昌樟村坪埃迪卡拉系陡山沱组硅磷质结核中的微体化石     

陈寿铭  尹崇玉  刘鹏举  高林志  唐烽  王自强 《地质学报》2010,84(1):70-77

本文报道的微体化石产于湖北宜昌樟村坪万家沟剖面埃迪卡拉纪陡山沱组第10层的硅磷质结核中,化石组合包括疑源类Appendisphaera grandis、Ericiasphaera spjeldnaesii、Knollisphaeridium maxi mum、Leiosphaeridia tenuissi ma、Meghystrichosphaeridium perfectum、Tianzhushania polysiphonia、T.spinosa、T.ornata;丝状蓝藻Oscillatoriopsis obtusa、Polytrichoides induviatus、P.lineatus、Salome hubeiensis、Siphonophycustypicum;多细胞藻类Sarcinophycus palilloformis、Wengania minuta。该微体化石组合面貌与黄陵背斜东、南翼陡山沱组二段硅质结核中以大型具刺疑源类Tianzhushania为特征的组合相同,与贵州瓮安地区陡山沱组上磷块岩下部保存的微体化石组合面貌基本一致。  相似文献   

河南窑场铁矿床成因矿物学研究及其地质意义     

张东阳  苏慧敏  田磊  康健丽  高阳 《矿物岩石》2010,30(1)

窑场铁矿床位于河南鲁山地区,大地构造位置属于华北陆块南缘,控矿地层为太华群铁山岭组,主要矿体共有两个,主要有辉石铁英岩和角闪石铁英岩组成,夹有少量的黑云角闪片岩、大理岩和花岗质混合岩,主要的矿石矿物为磁铁矿(30%～35%),少量赤铁矿(5%)和镜铁矿(3%)。脉石矿物有石英、角闪石、辉石、石榴子石等。围岩的组成包括黑云辉石岩、黑云角闪岩、黑云角闪片岩、黑云片岩、角闪黑云变粒岩、大理岩及少量的花岗质混合岩。矿石中的角闪石均属于镁角闪石,辉石有富铁透辉石、斜铁辉石,磁铁矿以纯磁铁矿为特征;围岩中的角闪石属于镁角闪石和纯镁闪石,辉石主要为透辉石,黑云母为镁质黑云母,伴有少量金云母,石榴子石以铁铝榴石为主,含有镁铝榴石、钙铝榴石分子。化学成分分析显示本区的变质相达角闪岩相,估算其变质的压力范围为0.36GPa～0.74GPa。与典型华北陆块前寒武纪铁矿床对比,窑场铁矿床的矿物组合、变质等级以及沉积相类型均与新太古代的条带状铁建造相似。磁铁矿高Ni、低Co的特点表明其成矿来源与深部物质有关。  相似文献   

210Pb and 7Be as Tracers for Aerosol Transfers at Center Guizhou，China：Ⅰ．The Explanation by Weekly Interval     

Wan Guojiang  Zheng Xiangdong  Lee H N  Bai Z G  Wan Enyuan  Wang Shilu  Yang Wei 《地球科学进展》2010,25(5):492-504

It′s essential to measure air concentrations and depositional fluxes of environmental radionuclides in different regions for modeling global contamination transfer and validation, tracing deposition process and dating, referencing watershed erosion trace and assessing natural radiation of ecosystem. This study introduces the research background and methods and explains weekly variations of ²¹⁰Pb and ⁷Be concentrations in surface air and precipitation at Mt. Guanfeng/Guiyang since 2001. The results indicate that ²¹⁰Pb and ⁷Be concentrations in surface air fluctuate periodically at 2~6 week interval because of the meteorological condition changes. The annual trend in ²¹⁰Pb air concentration is overall influenced by air temperature variation and periodical rainfall. ⁷Be air concentration varies up and down regualarly. The synchronization of low concentrations for both ²¹⁰Pb and ⁷Be in surface air and high ratio (²¹⁰Pb/⁷Be ≥ 0.8) indicate oceanic poor ²¹⁰Pb-⁷Be air mass invasion. The synchronization of high concentrations of ²¹⁰Pb and ⁷Be in surface air and low ratio (²¹⁰Pb/⁷Be ≤ 0.7) implies rich ⁷Be air mass invasion from altostratus atmosphere. Weekly concentrations of ²¹⁰Pb and ⁷Be in precipitation and the K_d coefficients are high in late Autumn to Spring, and low in late Spring to Autumn. Although ²¹⁰Pb and ⁷Be concentrations vary seasonally, their weekly concentrations in precipitation increase with that of air concentration. The ²¹⁰Pb and ⁷Be weekly concentrations for seasonal division is about 0.2 Bq/L and 1 Bq/L, respectively. However, the K_d coefficient decreases when ²¹⁰Pb and ⁷Be air concentrations increase. Deposition of ²¹⁰Pb and ⁷Be with precipitation mainly take place in Spring and Summer; The weekly fallout of ²¹⁰Pb and ⁷Be increases with increasing precipitation; the increase of ⁷Be is triple of that of ²¹⁰Pb and 2.5 when precipitation nears to zero. The weekly-high fallout of ²¹⁰Pb and ⁷Be with precipitation corresponds with the dramatic decrease of their air concentrations within or vicinal weeks. The ratio of ²¹⁰Pb to ⁷Be in rainfall is overall ≤ 0.5 and varies synchronously with the ratio in surface air, indicating that the two radionuclides are cleaned by precipitation from air at close speed. In the extreme freezing disaster in 2008, both ²¹⁰Pb and ⁷Be air concentrations were low and coupling with coexist of low concentration of aerosol and high nuclides activities. Weekly concentration of ⁷Be in surface air at Mt. Guanfeng demonstrates the anticipated concentration level in the low-latitude and high-elevation region; the short-term fluctuations of ⁷Be concentration indicated the hysteresis was influcenced by the strong air current submersion and the low-elevation air mass rising differently at Mt. Guanfeng and Mt. Waliguan.   相似文献   

汶川地震地表破裂面形貌特征   总被引：1，自引：0，他引：1  

魏占玉  石峰  高翔  徐长鹏  何宏林 《地学前缘》2010,17(5):53

准确描述破裂面形貌对于我们理解地震断层作用是非常重要的,破裂面的形貌特征包含许多关于地震和断层机制的有用信息。在Mw7.9 2008汶川地震中断层活动产生了两个新鲜的破裂面,八角庙破裂面和沙坝破裂面。我们使用3D便携式激光扫描仪(Tri mble GX)对两个破裂表面进行测量,在野外微观尺度上研究了破裂面形貌特征。通过能谱密度和均方值两个方法分析破裂面形貌,新鲜的破裂面表现为自相仿性,能谱密度和均方值均与剖面长度存在幂律关系。在能谱密度与空间频率的对数图中,能谱密度曲线存在明显的拐点,该拐点所对应的波长称为"特征波长",表明单一分形不能准确描述破裂面形貌。八角庙破裂面在平行滑动方向上的特征波长为7 mm,在垂直方向上特征波长略大一些(区域Ⅰ为10 mm,区域Ⅱ为9 mm);沙坝破裂面在平行滑动方向上的特征波长为8 mm,但垂直方向上特征波长略小(6 mm)。均方值曲线的最小二乘拟合直线的斜率为Hurst指数,该指数依赖于剖面线方向并描述破裂面形貌的各向异性,H指数的最小值和最大值分别与平行擦痕和垂直擦痕方向对应,这与野外断层面擦痕测量结果一致。沙坝破裂面的H指数极坐标图中存在次级H指数峰值(对应剖面线方向为85°和160°),这揭示破裂面上存在一组隐匿擦痕。该组隐匿擦痕为汶川地震之前断层活动中形成的,但这还不足以推测上一次断层活动的时间和规模。另外,通过比较新鲜节理面和破裂面表明H指数是否大于0.8反映了断层类型。在整个空间频率域上,能谱密度曲线斜率(-α)和均方值曲线斜率(H)的线性拟合关系为α=1.22+1.72H,并不严格满足两者之间理论关系式,α=1+2H。这个差异是由于测量信号噪音、破裂面的多分形性和分析方法的差异造成的。  相似文献   

青藏高原昆仑—汶川地震系列与巴颜喀喇断块的最新活动   总被引：23，自引：1，他引：22  

邓起东  高翔  陈桂华  杨虎 《地学前缘》2010,17(5):163

青藏高原是中国最主要的地震活动区之一。最近十多年来,在青藏高原中部连续发生了1997年西藏玛尼Ms7.5级地震、2001年青海昆仑山Ms8.1级地震、2008年3月新疆于田Ms7.3级地震和5月四川汶川Ms8.0级地震及2010年青海玉树Ms7.1级地震,它们相继发生于青藏断块区巴颜喀喇断块四周边界活动断裂带上,是该断块最新活动的结果。发生于断块南北边界断裂上的3次地震都是走滑断裂错动的结果,发生在断块东南端的汶川地震则是挤压逆冲断裂的产物,而西北端的于田地震则呈现出张性特征,它们共同反映青藏断块区巴颜喀喇条状断块向东南方向滑动的最新活动。自1900年以来,青藏断块区和巴颜喀喇断块的强震活动表现出多期活动和区域性转移的特征,20世纪早期Ms7.0级以上强地震活动的主体地区在青藏断块区北部边界构造带,中期转移到高原南部喜马拉雅板块边界构造带和断块区南部断块,最近十多年来则在巴颜喀喇断块及周缘边界断裂上活动。青藏高原这种块体活动和地震活动与澳大利亚-印度板块对亚洲大陆的推挤作用相关,因而,青藏高原和巴颜喀喇断块的强震活动与澳-印板块边界苏门答腊强震活动相对应。目前苏门答腊地区强震活动仍在继续,因此,近期对巴颜喀喇断块及青藏高原南部地区的强震活动和强震危险性仍需加以注意。  相似文献   

Cracking mechanisms during galena mineralization in a sandstone-hosted lead–zinc ore deposit: case study of the Jinding giant sulfide deposit, Yunnan, SW China     

Junlai Liu  Anjian Wang  Haoran Xia  Yunfeng Zhai  Lan Gao  Qunye Xiu  Zhaochong Zhang  Zhidan Zhao  Dianhua Cao 《Mineralium Deposita》2010,45(6):567-582

There are two types of lead–zinc ore bodies, i.e., sandstone-hosted ores (SHO) and limestone-hosted ores (LHO), in the Jinding giant sulfide deposit, Yunnan, SW China. Structural analysis suggests that thrust faults and dome structures are the major structural elements controlling lead–zinc mineralization. The two types of ore bodies are preserved in two thrust sheets in a three-layered structural profile in the framework of the Jinding dome structure. The SHO forms the cap of the dome and LHO bodies are concentrated beneath the SHO cap in the central part of the dome. Quartz, feldspar and calcite, and sphalerite, pyrite, and galena are the dominant mineral components in the sandstone-hosted lead–zinc ores. Quartz and feldspar occur as detrital clasts and are cemented by diagenetic calcite and epigenetic sulfides. The sulfide paragenetic sequence during SHO mineralization is from early pyrite to galena and late sphalerite. Galena occurs mostly in two types of cracks, i.e., crescent-style grain boundary cracks along quartz–pyrite, or rarely along pyrite–pyrite boundaries, and intragranular radial cracks in early pyrite grains surrounding quartz clasts. The radial cracks are more or less perpendicular to the quartz–pyrite grain boundaries and do not show any overall (whole rock) orientation pattern. Their distribution, morphological characteristics, and geometrical relationships with quartz and pyrite grains suggest the predominant role of grain-scale cracking. Thermal expansion cracking is one of the most important mechanisms for the generation of open spaces during galena mineralization. Cracking due to heating or cooling by infiltrating fluids resulted from upwelling fluid phases through fluid passes connecting the SHO and LHO bodies, provided significant spaces for crystallization of galena. The differences in coefficients of thermal expansion between pyrite and quartz led to a difference in volume changes between quartz grains and pyrite grains surrounding them and contributed to cracking of the pyrite grains when temperature changed. Combined thermal expansion and elastic mismatch due to heating and subsequent cooling resulted in the radial and crescent cracking in the pyrite grains and along the quartz–pyrite grain boundaries.  相似文献   

Chromium spinels in North Chinese kimberlites,Huabei platform     

Gao Xiaoying  T. V. Posukhova 《Moscow University Geology Bulletin》2010,65(4):234-243

Samples from diamondiferous pipes in the Mengyin and Fuxian regions were investigated. The chemical compositions of Cr spinels in kimberlites of China were found to be similar to those in kimberlites of the Arkhangelsk province in Russia. A long and complex evolution that was individual for each pipe was demonstrated. The kimberlites of the Shandong Province proved to be rich in high-Cr chromites. This means that the kimberlites formed at large depths in the field of diamond thermodynamic stability. Variations in the redox conditions were noted. They manifested themselves as a wide range of fluctuations of the chemical composition of microcrystalline spinels, up to formation to Ti-magnetite and magnetite.  相似文献   

Phytoliths infer locally dense and heterogeneous paleovegetation at FLK North and surrounding localities during upper Bed I time, Olduvai Gorge, Tanzania     

Doris Barboni  Gail M. Ashley  Manuel Dominguez-Rodrigo  Henry T. Bunn  Audax Z.P. Mabulla  Enrique Baquedano   《Quaternary Research》2010,74(3):344-354

The phytolith content of 10 samples collected immediately under Tuff IF (~ 1.785 Ma) at FLK N and other surrounding localities (~ 2 km²) provides a direct botanical evidence for woody vegetation in the eastern margin of Olduvai Gorge during uppermost Bed I time. Observation and counting of 143 phytolith types (5 to >150 μ) reveal dense but heterogeneous woody cover (~ 40–90%) of unidentified trees and/or shrubs and palms associated to the freshwater springs surrounding FLK N, and more open formation (presumably ~ 25–70% woody cover) in the southeast at localities VEK, HWK W and HWK E. The paleovegetation is best described as groundwater palm forest/woodland or bushland, which current analogue may be found near Lake Manyara in similar hydrogeological context (freshwater springs near saline/alkaline lake). Re-evaluating the published pollen data based on this analogy shows that 70% of the pollen signal at FLK N may be attributed to thicket-woodland, Acacia groundwater woodland, gallery and groundwater forests; while < 30% is attributed to swamp herbage and grasslands. Micro-botanical, isotopic, and taphonomical studies of faunal remains converge on the same conclusion that the area surrounding FLK N, which attracted both carnivores and hominins in the early Pleistocene, was densely wooded during uppermost Bed I time.  相似文献   

Comparative analysis of marine paleogene sections and biota from West Siberia and the Arctic Region     

M. A. Akhmet’ev  N. I. Zaporozhets  A. I. Iakovleva  G. N. Aleksandrova  V. N. Beniamovsky  T. V. Oreshkina  Z. N. Gnibidenko  Zh. A. Dolya 《Stratigraphy and Geological Correlation》2010,18(6):635-659

The analysis of the main biospheric events that took place in West Siberia and the Arctic region during the Early Paleogene revealed the paleogeographic and paleobiogeographic unity of marine sedimentation basins and close biogeographic relations between their separate parts. Most biotic and abiotic events of the first half of the Paleogene in the Arctic region and West Siberia were synchronous, unidirectional, and interrelated. Shelf settings, sedimentation breaks, and microfaunal assemblages characteristic of these basins during the Paleogene are compared. The comparative analysis primarily concerned events of the Paleocene-Eocene thermal maximum (PETM) and beds with Azolla (aquatic fern). The formation of the Eocene Azolla Beds in the Arctic region and West Siberia was asynchronous, although it proceeded in line with a common scenario related to the development of a system of estuarine-type currents in a sea basin partly isolated from the World Ocean.  相似文献   

豫西嵩县前范岭石英脉型钼矿床地质特征及辉钼矿Re-Os同位素年龄   总被引：14，自引：2，他引：12  

高阳  李永峰  郭保健  程国祥  刘彦伟 《岩石学报》2010,26(3):757-767

位于熊耳山-外方山地区的前范岭钼矿是东秦岭地区新近发现的石英脉型钼矿床之一。赋矿围岩为古元古界熊耳群安山质火山岩类。矿体主要以含辉钼矿石英脉产出,矿石类型以石英脉型为主。金属矿物以辉钼矿和黄铁矿为主,脉石矿物以石英为主,其次为方解石、萤石等。围岩蚀变类型有硅化、钾长石化、青磐岩化等。对6件辉钼矿样品进行Re-Os同位素测年所获得的模式年龄为233.3±3.3～248.2±3.5Ma,等时线年龄为239±13Ma,表明矿床形成于中三叠世。矿床的成矿作用发生于华北与扬子两个板块碰撞对接的晚期阶段。区域上整体的挤压造成了局部的剪切和伸展环境,这种环境为控矿断裂的形成和成矿流体的运移提供了有利条件。嵩县境内现已发现的多处脉型钼矿床很可能形成于同一时期(三叠纪),它们构成了熊耳山与外方山之间的嵩县脉型钼矿田。  相似文献