共查询到20条相似文献，搜索用时 78 毫秒
1.
扎河坝蛇绿岩位于准噶尔北缘,是扎河坝—阿尔曼太蛇绿混杂岩带的一部分。通过对蛇绿混杂岩中堆晶辉长岩和凝灰岩夹层的锆石U-Pb年龄及Hf-O同位素进行研究,获得堆晶辉长岩的结晶年龄为485±4Ma,凝灰岩的喷发年龄为401±2.5Ma。辉长岩极度亏损Hf同位素,εHf(t)为13~20,δ~(18)O峰值为+5.37‰,显示其具有地幔特征。凝灰岩锆石的Hf同位素亏损程度低于堆晶辉长岩,εHf(t)为1.4~9.2。扎河坝蛇绿岩具有典型的SSZ型蛇绿岩特征,是通过俯冲增生到洋内弧弧前的蛇绿岩。 相似文献
2.
3.
赣东北蛇绿岩和张村岩群的锆石SHRIMP U-Pb年龄及对江南造山带构造演化的讨论 总被引：1，自引：0，他引：1
本文对赣东北樟树墩蛇绿混杂岩中基性—超基性岩的地球化学分析表明,其中辉长岩具有MORB的地球化学特征,蛇纹岩强烈亏损各微量元素。辉长岩的锆石SHRIMP O同位素分析结果给出了非常均一的O同位素组成(5.12‰±0.62‰,2σ),与地幔锆石的O同位素组成(5.3‰±0.3‰)接近。这些地球化学特征和其形成于大洋环境吻合。锆石SHRIMP U-Pb定年给出了辉长岩的形成年龄为1009±5 Ma(MSWD=1.15)。在作为赣东北蛇绿岩的围岩张村岩群中,选取凝灰岩样品进行的锆石SHRIMP U-Pb定年给出了833±10 Ma(MSWD=1.5)的形成年龄,表明蛇绿岩就位时代晚于833 Ma。结合前人的研究,本文指出赣东北蛇绿岩形成于中元古代末—新元古代初的大洋中脊环境,不同于皖南伏川蛇绿岩所代表的弧后小洋盆环境。这些新资料为华南区域大地构造演化研究提供了新的约束。 相似文献
4.
齐齐加纳克蛇绿混杂岩位于中国新疆西南天山阔克萨彦岭地区,主要由辉石橄榄岩,橄榄辉石岩,橄榄玄武岩,辉长岩,辉绿岩,基性熔岩等组成。它们以一系列构造碎片近东西向产出,断续沿长约5km,宽约500m。本文应用SHRIMP方法对该蛇绿混杂岩中玄武岩中的锆石进行SHRIMP锆石U-Pb测年,获得了399±4Ma的加权平均年龄,说明该蛇绿混杂岩形成于早泥盆世。结合前人的研究成果,我们推测齐齐加纳克蛇绿混杂岩与吉根蛇绿岩残片均为中亚造山带南天山蛇绿岩带的延伸,可能代表了一个多岛窄洋盆演化的产物,为南天山洋北向俯冲及其后的塔里木微板块与哈萨克斯坦-准噶尔板块陆陆碰撞形成的最后缝合带。 相似文献
5.
6.
蛇绿岩及蛇绿岩中浅色岩的SHRIMP U-Pb测年 总被引：101，自引：2，他引：101
文中简要评述了蛇绿岩的层状辉长岩,斜长岩和斜长花岗岩,以橄榄岩为主岩的花岗岩和蛇绿岩中的埃达克岩的锆石SHRIMP U-Pb年龄的地质意义。层状辉长岩(或堆晶层状辉长岩)通常起源于洋脊下的岩浆房,因而它的形成年龄代表洋壳形成的时代。斜长岩与层状辉长岩的时代相近或略晚。斜长花岗岩年龄的解释极其依赖锆石组成和地球化学证据。橄榄岩为主岩的花岗岩,可能记录蛇绿岩的侵位时代。蛇绿岩中的埃达克岩是消减洋壳在深部的部分熔融的产物。文中发表了新疆扎河坝蛇绿岩SHRIMP定年的中间成果,并简略地介绍了滇川西部金沙江和内蒙古图林凯等地的研究实例。根据层状辉长岩的测定结果,扎河坝蛇绿岩形成于(489±4)Ma,金沙江蛇绿岩形成于(328±8)Ma。内蒙古图林凯蛇绿岩中埃达克岩形成于(467±13)Ma～(429±7)Ma。块状辉长岩、斜长花岗岩和橄榄岩为主岩的花岗质岩石记录了蛇绿岩的复杂演化。新疆扎河坝蛇绿岩中的块状辉长岩中存在多组锆石年龄值。较老的一组为468～511 Ma,与层状辉长岩和斜长岩相似,记录了蛇绿岩或洋壳的形成时代,但是,岩石中的大部分锆石年龄为396～419 Ma,加权平均年龄为(406±4)Ma,可能反映了一次部分熔融事件。滇川西部金沙江蛇绿岩中的斜长花岗岩的形成年龄为约300～285Ma,晚于层状辉长岩和? 相似文献
7.
在大量查阅分析和研究前人资料基础上,提出阿勒吞昆多蛇绿混杂岩是卡拉麦里蛇绿岩带的向东延伸部分。卡拉麦里蛇绿岩带西起卡拉麦里—塔克扎勒—大黑山至伊吾县阿勒吞昆多一带,向东可能延伸至蒙古境内。该蛇绿混杂岩中斜长花岗岩产于辉长岩顶部,二者呈突变或渐变接触关系。应用SHRIMP方法对斜长花岗岩进行了锆石U-Pb定年,获得了(351±6Ma)的年龄,这一年龄反映阿勒吞昆多蛇绿岩形成于早石炭世。同时,该蛇绿混杂岩上覆岩系的时代为晚石炭世,表明阿勒吞昆多蛇绿混杂岩侵位时代不晚于晚石炭世。 相似文献
8.
东准噶尔玛因鄂博蛇绿混杂岩形成时代确定 总被引：1，自引：0，他引：1
玛因鄂博蛇绿混杂岩位于额尔齐斯-玛因鄂博板块缝合带内,由枕状基性熔岩、辉长质杂岩、深海沉积物等组成,与基质岩石构成蛇绿混杂增生岩楔.对层状辉长岩、枕状玄武岩进行锆石SHRIMP U-Pb测年,谐和年龄分别为403 Ma和397 Ma,证实玛因鄂博蛇绿混杂岩为北天山洋盆(古亚洲洋中支)在晚志留—早泥盆世的残余. 相似文献
9.
本文应用SHRIMP方法精确测定了金沙江蛇绿岩带中蛇绿岩的辉长岩和斜长岩、呈脉状产于辉长岩和变质橄橄岩中的斜长花岗岩、以及呈岩株状侵入蛇绿岩中的花岗闪长岩的锆石U-Pb年龄,提供了古特提斯洋壳演化的年代学制约。滇西之用层状角闪辉长岩的年龄为328±8Ma,书松斜长岩为329±7Ma,白马雪山辉长岩为282～285Ma,它们可能反映了海底扩张不同阶段的时代。研究还表明,在这些辉长岩和斜长岩中,部分锆石记录了375～352Ma的略老的年龄,暗示蛇绿岩浆活动可能始于晚泥盆世。在金沙江蛇绿岩中,滇西娘九丁斜长花岗岩和川西雪堆斜长花岗岩,具有高硅低钾的成分特征。但是,这些岩石的REE总量高,LREE富集;Sr初始值高,达0.7058～0.7070;在其锆石组成中,存在继承锆石。这些证据表明斜长花岗岩中存在陆壳物质的混染,可能与洋壳俯冲消减有关。娘九丁斜长花岗岩的年龄为285±6Ma,雪堆斜长花岗岩为300±5Ma,记录了古特提斯洋壳俯冲消减事件。滇西吉义独花岗闪长岩,呈岩株状侵入蛇绿岩中,年龄为263±6Ma,限定了蛇绿混杂岩的年代上限。 相似文献
10.
莫钦乌拉山尤尔敦蛇绿混杂岩位于天山山脉东北部莫钦乌拉山,该区构造上为东准噶尔卡拉麦里构造带的向东延伸。通过野外地质调查、地球化学和年代学研究,初步查明尤尔敦蛇绿混杂岩基质与外来岩块的主要特征。基岩岩石化学特征表明,洋岩石圈残片形成于弧相关盆地,获得洋壳辉长岩锆石U-Pb年龄为（411.5±2.7）Ma。结合前人资料和区域地质特征,认为尤尔敦蛇绿混杂岩所代表的洋盆是卡拉麦里有限洋盆的向东延伸,形成于早—中泥盆世,晚泥盆世开始俯冲消减,于石炭世晚期闭合。 相似文献
11.
Police, politics, and the right to the city 总被引：1，自引：0，他引：1
Mustafa Dikeç 《GeoJournal》2002,58(2-3):91-98
Space and spatiality have recently been at the core of debates concerning the political possibilities of the city. The arguments advanced in this paper might be seen as an attempt to contribute to these debates through a reflection on the spatiality of (in) justice, politics, and the right to the city. The case of French urban policy, with its focus on distressed urban areas, and the `suburban problem' in France are used as examples to make arguments more concrete. 相似文献
12.
13.
14.
Humboldt, Arago, and the temperature of groundwater 总被引：1，自引：0，他引：1
Stanley N. Davis 《Hydrogeology Journal》1999,7(5):501-503
15.
Average concentrations of Pb, Zn, Cu, and other metals, as well as S and As, were calculated for the Aue granitic cupola,
the contact aureole of which hosts the large vein-type uranium deposit of Schlema-Alberoda and the Schneeberg uranium-base
metal deposit (Erzgebirge, Germany). The cupola was exposed by mine workings and boreholes, which provided an opportunity
to evaluate variations in the abundances of metals in the granites over a vertical interval of more than 2.5 km and estimate
their losses in the upper oxidized part of the investigated volume of the cupola (coefficient of iron oxidation, KO
Fe, increases in the granites from bottom to top from 7 to 70%) compared with the lower unaltered and unoxidized part (with
a KO
Fe plateau at about 5%). The average concentrations of metals in the upper part of the cupola are lower than those in the lower
part by a factor of 2.5 for Pb, 1.56 for Zn, 1.45 for Cu, 1.3 for Co, etc. A similar decrease in the abundances of ore elements
along the vertical section associating with the relative epigenetic alteration and oxidation of the granite was previously
described by us for U and Th and for the components of high-temperature ores, W, Sn, and Mo. The removal of ore elements from
the granite was accompanied by a decrease in the bulk contents of sulfur and arsenic by a factor of 1.35 and 1.65, respectively.
The leaching of trace metals from the granites of the upper part of the Aue cupola was followed by their partial redeposition
above the cupola in the ore veins of the Schlema and Schneeberg deposits.
Original Russian Text ? Vikt. L. Barsukov, N.T. Sokolova, O.M. Ivanitskii, 2006, published in Geokhimiya, 2006, No. 9, pp.
967–982. 相似文献
16.
Text, talk, things, and the subpolitics of performing place 总被引：1，自引：0，他引：1
This article tells the story of how a group of Dutch and Belgian citizens organized themselves to promote an area that they valued, to put it on the map, to raise awareness about its qualities, and to protect it from urban and industrial development. Our theoretical perspective focuses on the performative and political aspects of this place-making process and the discursive and material practices involved. We connect this to Beck’s concept of subpolitics.Our findings show how the group performed this place not only through text and talk - giving the area a name, using their knowledge and expertise to raise awareness about its values, lobbying and cooperating with decision-makers -, but also through things - installing art objects and information signs that articulate certain characteristics and values of the area. Our findings demonstrate the struggles involved in these performances. The group involved multiple perspectives on what the important values and characteristics of the area are and on what strategies would work best in trying to influence decision-making and protect the area. However, the use of expertise as the main strategy to gain influence excluded the more critical and activist strategies and privileging archaeological and historical values and characteristics came at the expense of attention on agricultural and natural values.Our findings make clear that performing place cannot be taken to be homogeneous and that it inevitably involves multiple perspectives and demands. The struggles, power relations and dynamics of inclusion and exclusion that this multiplicity implicates reveal a form of sub-politics that involves both politicization and depoliticization. Also, it is a form of subpolitics that is more diverse and ambiguous than Beck’s conceptualization presupposes by its emphasis on the role of outsiders as a homogeneous group. 相似文献
17.
Shaofeng Wang Yongfeng Jia Shuying Wang Xin Wang He Wang Zhixi Zhao Bingzhu Liu 《Applied Geochemistry》2009,24(9):1702-1711
Mercury contamination in aquatic environments is of worldwide concern because of its high biomagnification factor in food chains and long-range transport. The rivers, estuary and the bay along the northwestern Bohai Sea coast, northeastern China have been heavily contaminated by Hg due to long-term Zn smelting and chlor-alkali production. This work investigated the distributions of total Hg (THg) and monomethylmercury (MMHg) in the water, sediment and hydrophytes from this area. Concentrations of THg in sediment (0.5–64 mg kg−1) and water (39–2700 ng L−1) were elevated by 1–3 orders of magnitude compared to background concentrations, which induced high concentrations of MMHg in these media. The highest concentration of MMHg in sediment reached 35 μg kg−1, which was comparable to that in the Hg mining area, Wanshan, China, and the highest MMHg concentration of 3.0 ng L−1 in the water sample exceeded the MMHg Chinese drinking water guideline of 1.0 ng L−1. Concentrations of THg in a sediment profile from Jinzhou Bay were found to be consistent with annual Hg emission flux from a local Zn smelter (r = 0.74, p < 0.01), indicating that Hg contamination was mainly caused by Zn smelting locally. For some freshwater hydrophytes, concentrations of THg and MMHg ranged from 5.2 to 100 μg kg−1 and 0.15 to 12 μg kg−1, respectively. Compared to sediment, concentrations of THg in hydrophytes were 2–3 orders of magnitude lower but MMHg was comparable or higher, indicating that the bioaccumulation in plants was distinct for the two Hg species studied. The data suggest that a significant load of Hg has been released into the northwestern coastal region of the Bohai Sea. 相似文献
18.
The behavior of trace elements under conditions of partial melting of granitoid rocks has been studied. The element’s partition coefficients between minerals and the melt Dimin/melt depends, in the first place, on the composition of the primary melt. In biotite the HREE Di are a little below 1, while those of LREE, especially Di for Ce, are 1–3 orders of magnitude less. This leads to an efficient differentiation of REEs in anatexic melts especially when biotite is the main mineral phase of restite. On the contrary, there are feldspars, the Di of which cannot provide such a magnitude of differentiation. Unlike garnets and pyroxenes, whose stability in restite permits enrichment of anatexic melts produced in migmatization zones with Nb, Ti, and Cr, the presence of biotite in restite causes depletion of melts with those elements as well as with Rb. Feldspars, under conditions of their fractional crystallization or during differentiation of an anatexic melt, deplete the latter with Sr, Ba, and Rb, but enrich it with Nb, Ti, Cr, Y, Zr, and V. 相似文献
19.
The dielectric constants and dielectric loss values of 4 Ca-containing minerals were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: vesuvianitel κ′ a=9.93 tan δ=0.006 κ′ c=9.79 tan δ=0.005 vesuvianitel κ′ a=10.02 tan δ=0.002 κ′ c=9.85 tan δ=0.003 zoisite1 κ′ a =10.49 tan δ=0.0006 κ′ b =15.31 tan δ=0.0008 κ′ c=9.51 tan δ=0.0008 zoisite2 κ′ a =10.55 tan δ=0.0011 κ′ b =15.45 tan δ=0.0013 κ′ c=9.39 tan δ=0.0008 epidote κ′ 11= 9.52 tan δ=0.0008 κ′ 22=17.1 tan δ=0.0009 κ′ 33= 9.37 tan δ=0.0006 fluorapatite1 κ′ a =10.48 tan δ=0.0008 κ′ c = 8.72 tan δ=0.0114 fluorapatite2 κ′ a =10.40 tan δ=0.0010 κ′ c=8.26 tan δ=0.0178 The deviation (δ) between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to α D (mineral)=∑ α D (oxides) for vesuvianite is ～ 0.5%. The large deviations of epidote and zoisite from the additivity rule with Δ=+ 10.1 and + 11.7%, respectively, are attributed to “rattling” Ca ions. The combined effects of both a large F thermal parameter and possible F-ion conductivity in fluorapatite are believed to be responsible for Δ=+2–3%. Although variation of oxygen polarizability with oxygen molar volume (Vo) is believed to affect the total polarizabilities, the variation of Vo in these Ca minerals is too small to observe the effect. 相似文献
20.
Over the past decade researchers working on the rocks of the Beaufort Group in the main Karoo Basin of South Africa have vastly increased our understanding of this important Permo-Triassic sequence. Many new fossil forms have been discovered, allowing for breakthroughs into the biodiversity, biogeography and biostratigraphy of the group. Taxonomic and phylogenetic advances are many and varied, and cover most of the vertebrate taxa, but with emphasis placed on the temnospondyl amphibians, archosauriforms and non-mammalian synapsids, in particular the anomodontia. Biostratigraphic breakthroughs have centered on the Middle Permian Eodicynodon and Tapinocephalus assemblage zones, the Late Permian Dicynodon Assemblage Zone, and the Triassic Lystrosaurus and Cynognathus assemblage zones. Correlation of these biozones with better dated sequences in Europe, Russia and China has allowed for many chronostratigraphic refinements, which are in turn vital for sequence stratigraphical analysis of the basin fill. Based on fossil data, both the lower (Ecca–Beaufort) and upper (Beaufort–Molteno) contacts of the group have been proved to be highly diachronous. The refined chronostratigraphic framework has also allowed for a better analysis of the basin evolution through time, particularly in terms of the correlation of external stimuli that affect basin sedimentation patterns. 相似文献