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1.
粤西阳江市八二花岗质岩体中广泛发育似斑状细粒闪长质暗色微粒包体，这些暗色微粒包体形态多样，与寄主岩具相似的矿物组合，对研究花岗岩成因和壳-幔相互作用具有十分重要的意义.为了探讨它们的岩石成因及构造属性，对寄主岩和暗色微粒包体开展了系统的岩相学、年代学和地球化学研究.LA-ICP-MS锆石U-Pb定年结果表明，寄主岩年龄为160.0±1.0 Ma，暗色微粒包体年龄为159.3±1.1 Ma，均为晚侏罗世的产物.全岩地球化学特征显示，寄主岩属于富钾的准铝质I型花岗岩，寄主岩和暗色微粒包体均富集轻稀土元素和大离子亲石元素，亏损重稀土元素和Nb、Ta、Ti等高场强元素.此外，两者具相似的Sr-Nd同位素组成，寄主岩的εNd（t）值为-5.73~-5.67，（87Sr/86Sr）i值为0.707 63~0.707 67；而暗色微粒包体的εNd（t）值为-5.81~-4.35，（87Sr/86Sr）i值为0.707 04~0.707 74.锆石饱和温度计和角闪石全铝压力计表明八二花岗质岩体结晶于730~754℃和19.8~20.6 km.综合寄主岩及其暗色微粒包体的岩石学、地球化学、同位素特征，晚侏罗世八二花岗质岩体可能形成于陆内伸展背景，由于软流圈物质上涌底侵，导致中下地壳变基性岩为主的源岩部分熔融，并且源区有少量幔源物质的加入，局部可能存在岩浆混合作用；暗色微粒包体是由镁铁质岩浆与长英质岩浆混合形成的. 相似文献
2.
义敦岛弧措交玛岩体岩浆混合成因:镁铁质微粒包体的证据 总被引：2，自引：0，他引：2
义敦岛弧北部的措交玛岩基岩体主要由黑云母二长花岗岩和边部的花岗闪长岩组成。在黑云母二长花岗岩中存在有少量镁铁质微粒包体,其成分为闪长质,与寄主岩石接触关系从渐变到截然。在包体周围的寄主岩石中存在黑云母、角闪石自身的包含结构,角闪石包含黑云母,斜长石发育明显的溶蚀结构,核部斜长石被溶蚀成筛状,边部环带状斜长石溶蚀不明显,是基性岩浆注入到酸性岩浆中导致岩浆混合的结果。黑云母二长花岗岩具有更高的轻重稀土分异系数,闪长质包体轻重稀土分异系数较低,黑云母二长花岗岩和暗色闪长质微粒包体具有明显相似性的微量元素特征。寄主岩黑云母二长花岗岩锆石U-Pb年龄为236±1.9Ma,闪长质包体为235±3.9Ma,二者形成年代在误差范围内基本一致,可能为甘孜-理塘洋向西俯冲过程中,俯冲洋壳部分熔融形成的玄武质岩浆上涌底侵于壳-幔边界导致地壳的部分熔融形成酸性的黑云母二长花岗岩岩基。 相似文献
3.
胶东郭家岭岩体固结冷却轨迹与隆升剥蚀 总被引：5，自引：4，他引：1
胶东郭家岭岩体位于华北克拉通东南缘,其详细的冷却固结条件缺乏系统研究,而对岩体形成与金矿之间的关系也存在争议。本文利用岩浆锆饱和温度计、角闪石全铝压力计、角闪石-斜长石温度计、角闪石-黑云母温压计、二长石温度计,结合已有的锆石U-Pb年龄和角闪石、黑云母40Ar-39Ar同位素年龄,探讨郭家岭岩体的冷却固结史及其隆升机制。花岗岩QAb-Or标准矿物共结压力图解、角闪石全铝压力计及角闪石-黑云母压力计均得到岩体就位压力约4~5kbar。锆饱和温度计、角闪石-斜长石温度计、角闪石-黑云母温度计、二长石温度计所获得温度分别为726~800℃、657~717℃、650~700℃、570~580℃,结合角闪石、黑云母的40Ar-39Ar封闭温度确定了郭家岭岩体最有可能的冷却轨迹。郭家岭岩体(130~126Ma)侵位深度约13±1.6km,侵入郭家岭岩体的艾山岩体(116±2Ma)侵位压力在1kbar左右,对应深度约2.7km,表明郭家岭岩体在约10Myr内,隆升剥蚀量达10km左右。这种快速剥蚀的机制可能与华北东部中生代岩石圈减薄导致的地壳浅部隆升有关。 相似文献
4.
新疆东部尾亚矿区的钾长花岗岩及其包体岩相学、矿物化学和岩石地球化学特征及野外地质特征显示其为岩浆混合作用的结果。本文获得钾长花岗岩及其中暗色微粒包体闪长岩锆石U-Pb年龄为(247.5±5.3)Ma和(244.8±1.8)Ma,与该区石英二长闪长岩体的锆石U-Pb年龄(244.7±3.3)Ma在误差范围内一致,这一结果从年代学角度为钾长花岗岩及其中暗色微粒包体的岩浆混合作用成因提供证据。 相似文献
5.
《地质科技情报》2017,(6)
对湖南中生代的五峰仙岩体进行了锆石SHRIMP U-Pb定年和岩石学、岩石地球化学分析。该岩体主要由印支期的中粒斑状黑云母二长花岗岩、细粒二云母二长花岗岩组成。本次获得黑云母二长花岗岩的锆石U-Pb年龄(233.5±2.5)Ma,表明形成于晚三叠世;结合已发表的岩体年龄资料,五峰仙岩体侵位于236~233.5 Ma和221.6 Ma,具有多阶段岩浆活动特点。五峰仙花岗岩具有高的w(SiO2)、w(P2O5),含过铝质的白云母,表现为弱铝质、强铝质岩石;微量元素方面,大离子元素Rb、Th、U富集,Nb、Ba、Sr、Ti亏损明显,稀土元素配分模式右倾,轻稀土元素富集,Eu亏损相对明显以及高的Rb/Sr比值,为高成熟度陆壳物质重熔的S型花岗岩。黑云母花岗岩中发育暗色微粒包体,具淬冷结构、含长石捕获晶及呈塑形变等特征的包体为岩浆混合成因,该类花岗岩中锆石Hf同位素εHf(t)值较高,为-4.4~0.7,Hf同位素的两阶段模式年龄TDM2值为1 534~1 216Ma,变化范围较大,可能是受幔源岩浆作用所致。五峰仙岩体是在印支板块向华南板块俯冲碰撞期后(变质基底年龄258~243Ma)及华南板块与华北板块的碰撞期间(超高压变质峰期在238~218Ma)华南内陆由挤压向伸展转换的背景下形成的。 相似文献
6.
内蒙古敖仑花斑岩钼铜矿含矿斑岩的岩浆混合特征及其地质意义 总被引：2，自引：0，他引：2
敖仑花斑岩钼铜矿床的含矿斑岩中发现大量的暗色包体,包体成分主要为闪长质,具有细粒岩浆结构,形态以椭圆状为主。显微镜下包体中针状磷灰石和具有暗色镶边的眼球状石英十分发育,包体捕获了寄主岩石斑晶,如石英、斜长石、黑云母等,并具有熔蚀和再结晶的现象,反映出暗色包体具有显著的岩浆混合作用特征。元素地球化学方面,包体比寄主岩石明显偏基性,两者的主量元素具有很好的线性关系,稀土配分曲线及微量元素蛛网图比较相似,结合Sr、Nd同位素的特征显示,寄主岩石和包体之间应发生过物质交换。锆石U-Pb年龄结果表明,寄主岩石和包体年龄在误差范围内是一致的,分别为(134.1±1.4)Ma和(133.6±1.0)Ma,也进一步证实了暗色包体的岩浆混合成因。Sr、Nd同位素结果显示,敖仑花岩体的源区具有新生地壳物质的性质;暗色包体原始岩浆应该比现在更偏基性,可能起源于亏损地幔的玄武质岩浆。具有岩浆混合特征的暗色包体的发现可能是该区域幔源岩浆底侵作用的直接证据。 相似文献
7.
通过调研近年来国内外学者对于花岗岩类中暗色微粒包体的研究成果,总结了其野外地质、岩相学、地球化学和同位素等特征以及成因研究中的主要问题。暗色微粒包体(MME)广泛分布于I型花岗岩中,一般呈随机分布,形态多样,但以塑性特征为主;一般认为是岩浆混合成因,其原始物源是玄武质岩浆,具典型的火成岩结构,发育针状磷灰石、环带结构和筛状结构的斜长石;相对于寄主岩石,暗色微粒包体富Fe,Mg,贫Si,Na,其锆石U-Pb年龄在误差范围内与寄主岩石年龄一致等,反映了壳幔源岩浆的混合事件。暗色微粒包体与岩浆动力学行为、矿化关系及区域地质演化等方面值得进一步研究、探索。 相似文献
8.
南岭中段的锡田岩体燕山期岩石以斑状黑云母二长花岗岩为主,岩体中广泛发育暗色微粒包体。暗色微粒包体为岩浆结构,大多数具有塑性外形,发育淬冷边、反向脉,存在多种不平衡结构和矿物组合,如钾长石环斑、石英眼斑、针状磷灰石等,显示岩浆混合特征。岩石地球化学方面,暗色微粒包体具有比寄主岩贫硅、贫碱,富K、Fe、Mg、Ca、Ti特征;暗色微粒包体及寄主岩富集轻稀土元素(LREE/HREE=2.6~8.8),具有中-强的铕负异常(δEu=0.09~0.74)以及具有相似的稀土元素配分曲线和微量元素蛛网图;在主要氧化物含量Harker图解中投点多呈直线变异趋势,反映了两者具有密切的亲缘关系,利用共分母和不共分母图解进行判别,暗色微粒包体与寄主岩具岩浆混合特征,在MgO-TFeO判别图解中也指示包体为岩浆混合成因。上述岩相学和元素地球化学特征表明暗色微粒包体是基性岩浆侵入到酸性岩浆中淬冷形成的,指示锡田岩体存在两种岩浆的混合作用。通过LA-ICP-MS锆石U-Pb定年,得到寄主岩形成年龄(150.04±0.52)Ma,暗色包体形成年龄(145.09±0.63)Ma,二者年龄在测试误差范围内一致,显示岩浆混合作用发生的时间大致为晚侏罗世。 相似文献
9.
内蒙古中部土牧尔台地区位于华北克拉通北缘,区内广泛发育黑云母二长花岗岩及暗色闪长岩包体,绝大多数包体与寄主岩石呈渐变过渡的接触关系。锆石LA-ICP-MS U-Pb定年结果显示,寄主岩石年龄为273～271Ma,包体年龄为268±2Ma,两者均形成于早-中二叠世。其中,寄主岩石具有高钾钙碱性、弱过铝质、高分异I型花岗岩的地球化学特点,且富集K、Rb、Th等大离子亲石元素和LREEs,亏损Nb、P、Ti等高场强元素和HREEs,具有典型的大陆弧岩浆特征。花岗岩中锆石ε_(Hf)(t)值为-13.0～-6.1,二阶段Hf模式年龄(t_(DM2))为2.12～1.68Ga,ε_(Nd)(t)值为-11.3～-10.7,亏损地幔模式年龄(t_(DM))为2.44～1.73Ga,指示岩浆源自华北克拉通下地壳的部分熔融。暗色包体多呈塑性形态,镁铁质矿物含量明显高于寄主岩石,且发育大量针状磷灰石,同位素(ε_(Nd)(t)值为-11.1～-10.2,tDM为2.13～1.85Ga)特点与寄主岩石相近。本文对黑云母二长花岗岩及其暗色包体的研究表明,区域上这些具有弧岩浆性质的早-中二叠世岩浆岩,很可能源自古亚洲洋俯冲洋壳及下地壳的部分熔融,幔源基性岩浆与下地壳长英质岩浆的混合形成寄主岩石及暗色包体,揭示了早-中二叠世时期区域上岩浆具有壳-幔相互作用的特点,且印证了该时期古亚洲洋洋壳尚未完全消失,中亚造山带的造山作用为区域岩浆岩及包体的形成提供地球动力学条件。 相似文献
10.
龙新岩体和夏郢岩体位于扬子地块与华夏地块拼合带的西南端,岩体中的Ⅰ型花岗岩成因研究对揭示桂东南地区早古生代的地球动力学背景及其构造演化具有重要的地质意义.对龙新岩体的寄主岩和其暗色微粒包体,以及夏郢岩体岩石进行了LA-ICP-MS锆石U-Pb定年、Lu-Hf同位素和全岩地球化学研究.锆石U-Pb定年结果显示,龙新岩体的寄主岩（花岗闪长岩）的年龄为440±2 Ma;龙新岩体的暗色包体（闪长岩）的年龄为441±1 Ma,寄主岩与暗色包体为同期岩浆作用的产物.夏郢岩体花岗闪长岩和二长花岗岩年龄分别为447±3 Ma和436±3 Ma,说明夏郢岩体至少发生了2期岩浆侵入事件.Hf同位素研究表明,龙新岩体寄主岩和暗色微粒包体的锆石εHf（t）值分别为-3.32~-5.83和-17.89~-1.82,二阶段模式年龄（TDM2）分别为1.62~1.76 Ga和1.57~2.54 Ga;夏郢岩体早期花岗岩闪长岩和晚期二长花岗岩的锆石εHf（t）值分别为-15.43~3.03和-4.79~6.82,TDM2分别为1.59~1.99 Ga和0.97~1.70 Ga,指示物源主要来自古-中元古代的地壳物质.地球化学特征表明龙新岩体寄主岩为准铝质高钾钙碱性Ⅰ型花岗岩,寄主岩和暗色微粒包体均富集轻稀土元素和大离子亲石元素,亏损重稀土元素及高场强元素;夏郢岩体早期的花岗闪长岩为弱过铝质高钾钙碱性Ⅰ型花岗岩,晚期的二长花岗岩则为强过铝质高钾钙碱性Ⅰ型花岗岩,主微量元素特征均与龙新岩体寄主岩相似.根据研究区花岗岩和镁铁质包体的岩相学、年代学、地球化学及Hf同位素组成特征,表明龙新岩体的暗色包体（闪长岩）为岩浆混合成因,而龙新岩体寄主岩（花岗闪长岩）和夏郢岩体（早期花岗岩闪长岩和晚期二长花岗岩）具有一致的岩石源区和岩石成因,但在后期的成岩过程中存在岩浆混合和结晶分异程度的差异.综合以往对华南地区构造背景的研究,认为龙新和夏郢岩体是在扬子地块和华夏地块陆内造山期后,岩石圈伸展减薄,热的幔源岩浆上涌底侵,中-下地壳受到地幔热影响发生部分熔融,形成的酸性岩浆在源区和基性岩浆经历了不均一且不强烈的壳-幔混合作用形成的. 相似文献
11.
Most sulfide-rich magmatic Ni-Cu-(PGE) deposits form in dynamic magmatic systems by partial melting S-bearing wall rocks with variable degrees of assimilation of miscible silicate and volatile components, and generation of barren to weakly-mineralized immiscible Fe sulfide xenomelts into which Ni-Cu-Co-PGE partition from the magma. Some exceptionally-thick magmatic Cr deposits may form by partial melting oxide-bearing wall rocks with variable degrees of assimilation of the miscible silicate and volatile components, and generation of barren Fe ± Ti oxide xenocrysts into which Cr-Mg-V ± Ti partition from the magma. The products of these processes are variably preserved as skarns, residues, xenoliths, xenocrysts, xenomelts, and xenovolatiles, which play important to critical roles in ore genesis, transport, localization, and/or modification. Incorporation of barren xenoliths/autoliths may induce small amounts of sulfide/chromite to segregate, but incorporation of sulfide xenomelts or oxide xenocrysts with dynamic upgrading of metal tenors (PGE > Cu > Ni > Co and Cr > V > Ti, respectively) is required to make significant ore deposits. Silicate xenomelts are only rarely preserved, but will be variably depleted in chalcophile and ferrous metals. Less dense felsic xenoliths may aid upward sulfide transport by increasing the effective viscosity and decreasing the bulk density of the magma. Denser mafic or metamorphosed xenoliths may also increase the effective viscosity of the magma, but may aid downward sulfide transport by increasing the bulk density of the magma. Sulfide wets olivine, so olivine xenocrysts may act as filter beds to collect advected finely dispersed sulfide droplets, but other silicates and xenoliths may not be wetted by sulfides. Xenovolatiles may retard settling of – or in some cases float – dense sulfide droplets. Reactions of sulfide melts with felsic country rocks may generate Fe-rich skarns that may allow sulfide melts to fractionate to more extreme Cu-Ni-rich compositions. Xenoliths, xenocrysts, xenomelts, and xenovolatiles are more likely to be preserved in cooler basaltic magmas than in hotter komatiitic magmas, and are more likely to be preserved in less dynamic (less turbulent) systems/domain/phases than in more dynamic (more turbulent) systems/domains/phases. Massive to semi-massive Ni-Cu-PGE and Cr mineralization and xenoliths are often localized within footwall embayments, dilations/jogs in dikes, throats of magma conduits, and the horizontal segments of dike-chonolith and dike-sill complexes, which represent fluid dynamic traps for both ascending and descending sulfides/oxides. If skarns, residues, xenoliths, xenocrysts, xenomelts, and/or xenovolatiles are present, they provide important constraints on ore genesis and they are valuable exploration indicators, but they must be included in elemental and isotopic mass balance calculations. 相似文献
12.
Between 1985 and 1991, two new mountain protected areas (MTNPA) covering more than 35,000 km2 and based on participatory management models — the Makalu-Barun National Park and Conservation Area, Nepal, and Qomolangma Nature Preserve, Tibet Autonomous Region — were successfully established through the collaborative efforts of Woodlands Mountain Institute and conservationists in China and Nepal. Characteristics common to both projects include the importance of establishing (1) effective rationales, (2) local support constituencies, (3) a senior advisory group, (4) a task force, (5) linkages between conservation and development, and (6) fund raising mechanisms. The lessons derived from the experiences of Woodlands Mountain Institute are of significant value to others in preserving MTNPA. Increased collaboration and communication between all interested in conservation, however, will remain a critical component for expanding mountain protected area coverage to throughout the world. 相似文献
13.
《Geoforum》2017
This article advances critical geographies of youth through examining the spatiality implicit in the imagined futures of young women in rural India. Geographers and other scholars of youth have begun to pay more attention to the interplay between young people’s past, present, and imagined futures. Within this emerging body of scholarship the role of the family and peer group in influencing young people’s orientations toward the future remain underexamined. Drawing on eleven months of ethnographic fieldwork, my research focuses on a first generation of college-going young women from socioeconomically marginalized backgrounds in India’s westernmost state of Gujarat. I draw on the “possible selves” theoretical construct in order to deploy a flexible conceptual framework that links imagined post-educational trajectories with motivation to act in the present. In tracing the physical movement of these young women as they navigate and complete college, my analysis highlights the ways in which particular kinds of spaces and spatial arrangements facilitate and limit intra- and inter-generational contact, and the extent to which this affects young women’s conceptions of the future. I conclude by considering the wider implications of my research for ongoing debates surrounding youth transitions, relational geographies of age, and education in the Global South. 相似文献
14.
15.
《Chemical Geology》2007,236(1-2):13-26
We examined the coprecipitation behavior of Ti, Mo, Sn and Sb in Ca–Al–Mg fluorides under two different fluoride forming conditions: at < 70 °C in an ultrasonic bath (denoted as the ultrasonic method) and at 245 °C using a Teflon bomb (denoted as the bomb method). In the ultrasonic method, small amounts of Ti, Mo and Sn coprecipitation were observed with 100% Ca and 100% Mg fluorides. No coprecipitation of Ti, Mo, Sn and Sb in Ca–Al–Mg fluorides occurred when the sample was decomposed by the bomb method except for 100% Ca fluoride. Based on our coprecipitation observations, we have developed a simultaneous determination method for B, Ti, Zr, Nb, Mo, Sn, Sb, Hf and Ta by Q-pole type ICP-MS (ICP-QMS) and sector field type ICP-MS (ICP-SFMS). 9–50 mg of samples with Zr–Mo–Sn–Sb–Hf spikes were decomposed by HF using the bomb method and the ultrasonic method with B spike. The sample was then evaporated and re-dissolved into 0.5 mol l− 1 HF, followed by the removal of fluorides by centrifuging. B, Zr, Mo, Sn, Sb and Hf were measured by ID method. Nb and Ta were measured by the ID-internal standardization method, based on Nb/Mo and Ta/Mo ratios using ICP-QMS, for which pseudo-FI was developed and applied. When 100% recovery yields of Zr and Hf are expected, Nb/Zr and Ta/Hf ratios may also be used. Ti was determined by the ID-internal standardization method, based on the Ti/Nb ratio from ICP-SFMS. Only 0.053 ml sample solution was required for measurement of all 9 elements. Dilution factors of ≤ 340 were aspirated without matrix effects. To demonstrate the applicability of our method, 4 carbonaceous chondrites (Ivuna, Orgueil, Cold Bokkeveld and Allende) as well as GSJ and USGS silicate reference materials of basalts, andesites and peridotites were analyzed. Our analytical results are consistent with previous studies, and the mean reproducibility of each element is 1.0–4.6% for basalts and andesites, and 6.7–11% for peridotites except for TiO2. 相似文献
16.
Models have become so fashionable that many scientists and engineers cannot imagine working without them. The predominant use of computer codes to execute model calculations has blurred the distinction between code and model. The recent controversy regarding model validation has brought into question what we mean by a ‘model’ and by ‘validation.’ It has become apparent that the usual meaning of validation may be common in engineering practice and seems useful in legal practice but it is contrary to scientific practice and brings into question our understanding of science and how it can best be applied to such problems as hazardous waste characterization, remediation, and aqueous geochemistry in general. This review summarizes arguments against using the phrase model validation and examines efforts to validate models for high-level radioactive waste management and for permitting and monitoring open-pit mines. Part of the controversy comes from a misunderstanding of ‘prediction’ and the need to distinguish logical from temporal prediction. Another problem stems from the difference in the engineering approach contrasted with the scientific approach. The reductionist influence on the way we approach environmental investigations also limits our ability to model the interconnected nature of reality. Guidelines are proposed to improve our perceptions and proper utilization of models. Use of the word ‘validation’ is strongly discouraged when discussing model reliability. 相似文献
17.
I. Bejarano-Ramirez Jose M. Jurado R. Muñiz-Valencia Á. Alcázar Silvia G. Ceballos-Magaña A. Olivos-Ortiz O. Rangel 《International Journal of Environmental Science and Technology》2017,14(6):1333-1342
The contents of As, Cd, Cu, Cr, Mg, Mn, Ni, Pb and Zn have been determined in sediment and water samples from Valle de las Garzas estuary and Port Manzanillo (Colima, Mexico) using ICP-AES. The concentrations of these elements were used for a comparative study to determine the distribution of heavy metals and to evaluate which elements reflect natural or anthropogenic backgrounds. For this purpose, seven sampling points were selected: Four of them correspond to the lagoon, and three were situated in the port. Statistical analysis of the mineral content was assessed. Initially, data comparison was assessed by statistical tests for each variable. Principal component analysis was then applied considering the influence of all variables at the same time by obtaining the distribution of samples according to their scores in the principal component space. In this way, four studies were carried out: (1) study of sediments collected during the dry season; (2) study of sediments collected during the rainy season; (3) comparative study between sediments from rainy and dry season; and (4) study of water composition collected during rainy season. From the results of the performed analyses, it can be concluded that metals distribution pattern reflected natural and anthropogenic backgrounds (e.g., sediments from the lagoon, situated at the beginning of the rain channel, presented high contents of Zn and Cu, perhaps related to anthropogenic activities or the influence of igneous sediments). 相似文献
18.
The shape of sedimentary particles may carry important information on their history. Current approaches to shape classification
(e.g. the Zingg or the Sneed and Folk system) rely on shape indices derived from the measurement of the three principal axes
of the approximating tri-axial ellipsoid. While these systems have undoubtedly proved to be useful tools, their application
inevitably requires tedious and ambiguous measurements, also classification involves the introduction of arbitrarily chosen
constants. Here we propose an alternative classification system based on the (integer) number of static equilibria. The latter
are points of the surface where the pebble is at rest on a horizontal, frictionless support. As opposed to the Zingg system,
our method relies on counting rather than measuring. We show that equilibria typically exist on two well-separated (micro
and macro) scales. Equilibria can be readily counted by simple hand experiments, i.e. the new classification scheme is practically
applicable. Based on statistical results from two different locations we demonstrate that pebbles are well mixed with respect
to the new classes, i.e. the new classification is reliable and stable in that sense. We also show that the Zingg statistics
can be extracted from the new statistics; however, substantial additional information is also available. From the practical
point of view, E-classification is substantially faster than the Zingg method. 相似文献
19.
Hirokazu Fujimaki 《Contributions to Mineralogy and Petrology》1986,94(1):42-45
Concentration ratios of Hf, Zr, and REE between zircon, apatite, and liquid were determined for three igneous compositions: two andesites and a diorite. The concentration ratios of these elements between zircon and corresponding liquid can approximate the partition coefficient. Although the concentration ratios between apatite and andesite groundmass can be considered as partition coefficients, those for the apatite in the diorite may deviate from the partition coefficients. The HREE partition coefficients between zircon and liquid are very large (100 for Er to 500 for Lu), and the Hf partition coefficient is even larger. The REE partition coefficients between apatite and liquid are convex upward, and large (D=10–100), whereas the Hf and Zr partition coefficients are less than 1. The large differences between partition coefficients of Lu and Hf for zircon-liquid and for apatite-liquid are confirmed. These partition coefficients are useful for petrogenetic models involving zircon and apatite. 相似文献
20.
Pools,riffles, and channelization 总被引：2，自引：0，他引：2
Edward A. Keller 《Environmental Geology》1978,2(2):119-127
The addition of regularly spaced deeps (pools) and shallows (riffles) that provide a variety of flow conditions, areal sorting
of stream-bed material, cover for wildlife, and a positive aesthetic experience, may be desirable in many channel projects.
Such designs will reduce adverse environmental impacts of stream channel modifications.
Analysis of variance for pool-to-pool spacing data suggests that there is no significant difference with respect to channel
width between pools that form in natural streams and those in streams affected by a variety of human uses. Short of channelization,
which changes the channel width, pools and riffles, within limits, are not particularly sensitive to environmental stress.
Experiments in Gum Branch near Charlotte, North Carolina, support the hypothesis that channel form and process evolve in harmony
and that manipulation of cross-channel morphology can influence the development of desired channel processes. Planned manipulation
of its channel form induced Gum Branch to develop as desired. Morphologic stability consisting of incipient point bars, pools,
and riffles was maintained over a period of high magnitude flood events, only to be degraded later by a wave of sediment derived
from upstream construction and stream-bank failures. Thus, environmentally desirable channel morphology in urban streams cannot
remain stable if changes in the sediment load or storm-water runoff exceed the limits of the stream's ability to make internal
adjustments while maintaining morphologic stability. 相似文献