共查询到20条相似文献，搜索用时 303 毫秒
1.
《Applied Geochemistry》1997,12(4):383-395
594 sediment samples from the Galapagos Rift System (GRS) and the crest of the East Pacific Rise (EPR) were chemically analyzed for 12 elements. Carbonate-free compositional datasets associated with each of 3 regions, the GRS, the EPR 2°N–4°S and the EPR 10°S–42°S, were separately subjected to endmember analysis. The compositions of endmember estimates were constructed for each dataset. These composition largely confirmed theidentities of endmembers that had previously been inferred from the varimax rotated loadings of a conventional factor analysis (of the correlation matrices) of the same 3 datasets.In view of the widely-reported unreliability of the correlation structure of compositional data, the confirmation by endmember analysis of the results of a factor analysis is itself quite remarkable. However, the particular advantage of endmember analysis is that the chemical compositions of extreme sources are estimated, and may readily be interpreted. The samples in the dataset can then be expressed as mixtures of these extreme sources. By contrast, the varimax rotated loadings of a factor analysis indicate only those elements that are associated together on a single factor which may or may not be an endmember, the composition of which nevertheless remains unknown. 相似文献
2.
This paper describes an estimation of endmember compositions followed by the assessment of those results by log-ratio variance analysis. As an appraisal, it deals only with the first objective of an endmember analysis namely, to identify endmembers if they exist by estimating their compositions. Following the creation of the endmember estimates, the computation of an array of log-ratio variances was a key innovation in this type of study. Log-ratio variances revealed intrinsic linear associations between the dominant elements on each of the estimated endmember compositions, largely confirming the endmember analysis. The dataset under study contained the concentrations of 16 elements in 93 samples of deep-sea manganese nodules from the Central Indian Ocean Basin. Many previous analyses of these nodules were undertaken to assess the economic potential of the deposits. This study by contrast, quantified the inter-element associations that account for the nodule compositions. Four endmembers were identified. The elements loaded on each were: (1) Mn, Zn, Ni, Cu, Mn-rich, (2) Fe, Ti, P, Co, Fe-rich, (3) Si, Al, Na, K, clay minerals, (3) Mg, ultramafic material, possibly including Mn, Cr, V, Ca, Na. These latter elements were also detected by their log-ratio variances to be associated with Mg on the 4th endmember. 相似文献
3.
Ross M. Renner 《Mathematical Geology》1995,27(4):485-497
If a geochemical compositional dataset
X (n×p)is a realization of a physical mixing process, then each of its sample (row) vectors will approximately be a convex combination (mixture) of a fixed set of (l×p)extreme compositions termed endmembers. The kpoints in p-space corresponding to a specified set of k (klinearly independent endmember estimates associated with a p-variate (n×p)compositional dataset
X,define the vertices of a (k–1)dimensional simplex
H.The nestimated mixtures
X (n×p)which together account for the systematic variation in the dataset
X,should each be convex combinations of the kfixed endmember estimates. Accordingly,the npoints in p-space which represent these mixtures should be interior points of the simplex
H.Otherwise, for each sample point which lies outside
H,at least one of the mixture coefficients (endmember contributions) will be negative. The purpose of this paper is to describe procedures for expanding
H
in the situation that its vertices are not a set of extreme points for the set which represents the mixtures. 相似文献
4.
《Applied Geochemistry》1998,13(3):313-318
Thirty one bulk (<2 mm) samples of surficial sediments from the Gulf of Gdansk and the Southern Baltic Sea off Poland were analyzed for 20 elements and the resulting compositional dataset was subjected to endmember analysis. The compositions of 4 endmember estimates were constructed and the abundances of these endmembers were calculated for each sample. Copper, Zn and Ag appear on one endmember and Cd and Pb on another. This suggests that Cu, Zn and Ag are introduced into the Gulf of Gdansk principally from the Vistula River whereas Cd and Pb are introduced as a result of atmospheric and riverine transport of these elements. The dual source of Cd and Pb into the Gulf of Gdansk may explain the complex interelement relationships displayoed by these elements in the sediments from this region. 相似文献
5.
Spectral unmixing estimates the abundance of each endmember at every pixel of a hyperspectral image. Each material in traditional unmixing algorithms is represented through a constant spectral signature. However, endmember variability always exists due to environmental, atmospheric, and temporal conditions, which leads to poor accuracy of the estimated abundances. This paper proposes a new unmixing algorithm based on a new linear transformation called endmember orthonormal mapping (EOM) to overcome the aforementioned problem. The EOM transformation maps original spectral space to a new EOM space to reduce endmember variability. In the original spectral space, each material is represented by a set of spectra (endmember set) which is extracted using the automated endmember bundles (AEB) method. The EOM transforms each endmember set to a vector in the EOM space so that these vectors are orthonormal. On account of orthonormalized endmembers, the condition number of the mixing matrix in the EOM space reduces. Furthermore, we consider the noise term as an additional virtual endmember set mapped to a vector that is orthogonal to other endmembers. As a result, a promising unmixing accuracy is obtained through applying the least squares abundance estimation in the subspace orthogonal to noise. Experimental results of both synthetic and real hyperspectral images demonstrate that the proposed algorithms provide much enhanced performance compared with the state-of-the-art algorithms. 相似文献
6.
Thek points inp-space corresponding to a specified set ofk (k<p) linearly independent endmember estimates associated with ap-variate (n×p) compositional datasetX, define the vertices of a (k?1) dimensional simplexH. Then estimated mixtures which together account for the systematic variation in the datasetX, are each convex combinations of thek fixed endmember estimates. Accordingly, then-points inp-space which represent these mixtures must be interior points of the simplexH. The purpose of this paper is to describe a simple graphical procedure for examining the positions of the estimated mixtures relative tok=3 or 4 putative endmembers, and for assessing their compliance or otherwise with the convexity constraints. Since the mixture coefficients must be estimated first in order to obtain the mixture estimates, the paper begins with a review of the least-squares partitioning procedure. 相似文献
7.
Thek points inp-space corresponding to a specified set ofk (k<p) linearly independent endmember estimates associated with ap-variate (n×p) compositional datasetX, define the vertices of a (k–1) dimensional simplexH. Then estimated mixtures which together account for the systematic variation in the datasetX, are each convex combinations of thek fixed endmember estimates. Accordingly, then-points inp-space which represent these mixtures must be interior points of the simplexH. The purpose of this paper is to describe a simple graphical procedure for examining the positions of the estimated mixtures relative tok=3 or 4 putative endmembers, and for assessing their compliance or otherwise with the convexity constraints. Since the mixture coefficients must be estimated first in order to obtain the mixture estimates, the paper begins with a review of the least-squares partitioning procedure. 相似文献
8.
The Cold Bay Volcanic Center,Aleutian Volcanic Arc 总被引：1，自引：0，他引：1
James G. Brophy 《Contributions to Mineralogy and Petrology》1987,97(3):378-388
The Cold Bay Volcanic Center has experienced two major stages of eruptive activity. Early (M-Series) acitivity produced bimodal Hi-Alumina basalt and calc-alkaline andesite lavas while later (FPK-Series) activity produced only calc-alkaline andesite. The spectrum of basalt compositions is believed to be due to high pressure (8 kb) fractionation at or near the base of the crust. Abundant mineralogical and geochemical evidence support a lower pressure mixing origin for all andesites. Inspection of the mineralogical data has shown that the earliest (M-Series) andesites were produced by mixing of basalt (<53 wt% SiO2) and silicic andesite (60.5 to 62.5 wt%) while later (FPK-Series) andesites resulted from the mixing of basaltic-andesite (53 to 56 wt%) and less silicic andesite (58.5 to 60.0 wt%). The major element and trace element geochemical data are consistent with a low pressure fractionation origin for the silicic endmember magmas and support the temporal variations in both mafic and silicic endmember compositions. The complete lack of crustal inclusions in all lavas is taken as evidence for a minimal crustal melting and/or assimilation role in the origin of the silicic endmembers. Many of the features of all andesites, including the important long term convergence of endmember magma compositions, are consistent with the process of liquid fractionation, accompanied by large scale magma mixing. A deduced upper limit of 62.5 wt% SiO2 for the silicic endmember magmas suggests that liquid fractionation, in the absence of major crustal melting, cannot produce more silicic magmas. A possible explanation is the presence of a rheological barrier, based on the concept of critical crystallinity (Marsh 1981), which prohibits more silicic liquids from being extracted from a crystal-liquid suspension. 相似文献
9.
Classification and Source Materials of Continental Crust Transformation Series Granitoids in South China 总被引：7，自引：2，他引：7
The granitoids of the continental crust transformation series in South China may be divided into threetypes: (1) synorogenic migmatic and magmatic type. (2) anorogenic continental crust anatexis type, and (3)syncollision type. Based on the results of Sr and Nd isotopic determinations, the source material compositionof the three types of granitoids is calculated with crust-mantle binary mixing simulation. The calculations indi-cate that the granitoids of the first type consist of 78.6-89.7% upper crust endmember materials and15.0-10.3% depleted mantle endmember materials, the granitoids of the second type are composed of 63.7%upper crust endmember materials and 36.3% depleted mantle endmember materials, and those of the third type100% upper crust endmember materials. Hence. the source material composition of the granitoids of all thethree types is dominated by upper crust endmembers. 相似文献
10.
During the late Paleozoic Oslo rifting event, the SW part of the Baltic Shield was penetrated by mantle-derived magmas from a depleted lithospheric or sublithospheric source. Along the way to their final emplacement, these magmas may have interacted with a heterogeneous continental crust, consisting of a mosaic of continental terranes, each with its unique composition and internal crustal history. Information on radiogenic isotope ratios and trace element distributions in the Precambrian terranes surrounding the rift can be used to define characteristic crustal components. These components may be used as endmembers in petrogenetic modelling of the Oslo Rift magmatic system. Based on available data, six endmember components can be identified, and (semi) quantitatively characterized in terms of Sr, Nd and Pb isotopes and selected trace elements. Data on the distribution of rock-types along the rift flanks allow estimates to be made of the relative importance of the components in different parts of the rift. Combining these data with petrological information may allow a realistic understanding of crust–magma interaction in the Oslo Rift magmatic system. 相似文献
11.
Geochemical fluxes from watersheds are typically defined using mass-balance methods that essentially lump all weathering processes operative in a watershed into a single flux of solute mass measured in streamflow at the watershed outlet. However, it is important that we understand how weathering processes in different hydrological zones of a watershed (i.e., surface, unsaturated, and saturated zones) contribute to the total geochemical flux from the watershed. This capability will improve understanding of how geochemical fluxes from these different zones may change in response to climate change. Here, the geochemical flux from weathering processes occurring solely in the saturated zone is investigated. This task, however, remains exceedingly difficult due to the sparsity of subsurface sampling points, especially in large, remote, and/or undeveloped watersheds. In such cases, springflow is often assumed to be a proxy for groundwater (defined as water residing in fully saturated geologic formations). However, springflow generation may integrate different sources of water including, but not limited to, groundwater. The authors’ hypothesis is that long-term estimates of geochemical fluxes from groundwater using springflow proxies will be too large due to the integrative nature of springflow generation. Two conceptual models of springflow generation are tested using endmember mixing analyses (EMMA) on observations of spring chemistries and stable isotopic compositions in a large alpine watershed in the San Juan Mountains of southwestern Colorado. In the “total springflow” conceptual model, springflow is assumed to be 100% groundwater. In the “fractional springflow” conceptual model, springflow is assumed to be an integration of different sources of water (e.g., groundwater, unsaturated flow, preferential flow in the soil, etc.) and groundwater is only a fractional component. The results indicate that groundwater contributions in springflow range from 2% to 100% overall and no springs are consistently composed of 100% groundwater; providing support for the fractional springflow conceptual model. Groundwater contributions are not strongly correlated with elevation, spring contributing area, spring discharge, or seasonality. This variability has a profound effect on long-term geochemical fluxes. The geochemical fluxes for total springflow overestimate long-term solute release by 22–48% as compared to fractional springflow. These findings illustrate that springflow generation, like streamflow generation, integrates many different sources of water reflecting solute concentrations obtained along many different geochemical weathering pathways. These data suggest that springs are not always ideal proxies for groundwater. Springs may be integrating very distinct portions of the groundwater flow field and these groundwater contributions may become mixed at the spring emergence with much younger sources of water that have never resided in the groundwater system. 相似文献
12.
北秦岭灰池子花岗岩基成岩物质来源探讨 总被引：3，自引：0，他引：3
本文主要通过Ｎｄ，Ｓｒ和Ｏ同位素示踪研究，分析了灰池子花岗岩基的成岩物质来源，初步查明该岩体的岩浆源区由６９％的地幔物质和３１％的陆壳物质混合而成，属壳幔型花岗岩。 相似文献
13.
特提斯喜马拉雅成矿带产出数十个规模不等的金矿、锑金矿、锑矿和铅锌多金属矿,近期的矿产勘查在片麻岩穹窿发现了铍稀有多金属矿床.该成矿带内发育两期金锑铅锌矿化,其一为以邦布金矿和马攸木金矿为代表的造山型金矿,形成于59~45 Ma,属于青藏高原造山主碰撞阶段的产物;其二为以姐纳各普金矿、车穷卓布锑矿、扎西康铅锌矿的晚期矿化和吉松铅锌矿等为代表的热液型矿化,集中形成于21~12 Ma的后碰撞造山阶段.大量的流体包裹体研究表明喜马拉雅金锑铅锌成矿带的成矿流体主要为中低温(小于300℃)、中低盐度流体(< 10% NaCleqv).本文统计了已发表的和新获得的带内不同类型矿床共169个石英、绢云母、菱锰矿等热液矿物氢氧同位素数据,发现在δ18OH2O-δDV-SMOW相图中,这些同位素组成构成了3个端元:A端元以车穷卓布锑矿为代表,显示出极低的δ18OH2O值(低于-13‰)和低的δDV-SMOW值(< -111‰),靠近现代雨水线,完全落入西藏地热水H-O同位素范围;B端元以沙拉岗锑矿为代表,显示出具有最低的δDV-SMOW值(最低至-172‰)和较高的δ18OH2O值(高达12‰),落入建造水的H-O同位素范围内;端元C以邦布金矿和浪卡子金矿为代表,显示出具有极高的δDV-SMOW值(高达-43‰)和中等的δ18OH2O值,与造山型金矿氧同位素6‰~13‰的范围相同,包括了原始岩浆水的范围和部分变质水的范围.带内主要金属矿床成矿流体氢氧同位素均介于这3个流体端元之间,显示出绝大部分矿床的流体均非单一流体来源,而具有多源流体混合的特征. 相似文献
14.
Many data sets can be viewed as a collection of samples representing mixtures of a relatively small number of end members. When end members are present in the sample set, the algorithm QMODEL by Klovan and Miesch can efficiently determine proportionate contributions. EXTENDED QMODEL by Full, Ehrlich, and Klovan was designed to deduce the composition of realistic end members when the end members are not represented by samples. However, in the presence of high levels of random variation or outliers not belonging to the system of interest, EXTENDED QMODEL may not be reliable inasmuch as it is largely dependent on extreme values for definition of an initial mixing polyhedron. FUZZY QMODEL utilizes the fuzzy c-means algorithm of Bezdek to provide an alternative initial mixing polyhedron. This algorithm utilizes the collective property of all the data rather than outliers and so can produce suitable solutions in the presence of noisy or “messy” data points. 相似文献
15.
H.-J. Frster 《Lithos》2006,88(1-4):35-55
A comprehensive survey of the accessory-mineral assemblages in Variscan granites of the German Erzgebirge and Pan-African granites from Jordan revealed the occurrence of intermediate solid solutions of the tetragonal thorite–xenotime–zircon–coffinite mineral group with partially novel compositions. These solid solutions preferentially formed in evolved and metasomatically altered, P-poor leucogranites of either I- or A-type affinity. Thorite from the Erzgebirge contained up to 18.8 wt.% Y2O3, 16.1 wt.% ZrO2, and 23.3 wt.% UO2. Xenotime and zircon have incorporated Th in abundances up to 36.3 wt.% and 41.8 wt.% ThO2, respectively. Extended compositional gradation with only minor gaps is confined to hydrated members of this mineral group, and is observed to exist between thorite and xenotime, thorite and coffinite, and Y–HREE-bearing thorite and zircon. Complex, hydrous solid solutions containing elevated abundances of three or more of the endmembers are subordinate. Previously reported intermediate solid solutions between anhydrous zircon and xenotime, and anhydrous zircon and thorite, are not observed and are in conflict with experimental work demonstrating very limited miscibility between anhydrous species of endmember composition. The majority of hydrous intermediate solid solutions in the Th–Y–Zr–U system are likely thermodynamically unstable. Instead, they are probably metastable responses to unusual physico-chemical conditions involving various parameters and conditions, the relative importance of which is incompletely known. Leaching and dissolution of preexisting accessory phases during interaction with F-bearing hydrous fluids enriched in Th, Y(HREE), Zr, and/or U, and common deposition of the various elements at disequilibrium (supersaturation) seems to play a key role, but other processes may be of similar importance. Experimental work involving hydrous conditions and complex systems composed of more than two endmembers are needed to shed light into the stability relations of the chemically uncommon compositions treated in this study. 相似文献
16.
山东济阳拗陷第三玄武岩的Pb同位素组成变化明显：^206Pb/^204Pb值为16.864-18.361,^207Pb/^204Pb值为15.268-15.599,^208Pb/^204Pb值为36.770-39.118。在Pb-Pb和Pb-Sr图上，所有数据点形成良好的线性关系，而且都分布于DMM、EMⅠ和EMⅡ3个地幔端员组分之间。这些特征表明，同位素组成的明显变化应主要归因于玄武岩浆形成幔源区中不同端员组分之间的混合作用，地壳混染作用影响不明显。 相似文献
17.
To investigate the potential of tourmaline as a geochemical monitor, a comprehensive dataset on major, minor and trace element concentrations as well as Fe3+/ΣFe ratios of tourmaline is presented. The dataset includes samples from five plutonic complexes related to diverse magmatic to hydrothermal stages of the Cornubian Batholith (SW England). Tourmaline composition found in barren and cassiterite-bearing samples include all three primary tourmaline groups and tourmaline species with the general endmembers schorl, dravite, elbaite, uvite, feruvite, foitite and Mg-foitite.Based on textures and compositions, it is possible to distinguish not only between late-magmatic and hydrothermal tourmaline, but also between several formation stages. Hence, tourmaline monitors late-magmatic processes and the partitioning of elements during exsolution of an aqueous phase. For example, in hydrothermal tourmaline Sn is strongly enriched, while Ti, Cr, V and Sc are depleted compared to late-magmatic tourmaline of the same sample. Several tourmaline generations that precipitated from magmatic fluids can be distinguished with differing major and minor elements and REE patterns depending on the composition of the melt from which they were expelled from. Strongly zoned tourmaline allows for unraveling the hydrothermal history of a distinct location including ore precipitation. The precipitation of SnO2 in the study area was probably caused by mixing between acidic, reduced, Sn-bearing magmatic fluids and oxidized meteoric fluids, which is in agreement with London and Manning (1995) and Williamson et al. (2000). Hence, the ability of tourmaline composition to monitor changes in Sn concentration and redox conditions in hydrothermal fluids has potential as an exploration tool. 相似文献
18.
Teresa Suter Bowers Karen L. Von Damm John M. Edmond 《Geochimica et cosmochimica acta》1985,49(11):2239-2252
Chemical analyses yielding elemental concentrations of major and minor elements of four hot springs on the East Pacific Rise at 21°N and 10 hot springs from the southern trough of the Guaymas Basin, Gulf of California provide a basis for thermodynamic modeling of conductive cooling of the hydrothermal endmembers, mixing of the hydrothermal endmember with seawater, and reaction of an EPR-type fluid with sediment of bulk chemical composition corresponding to unaltered sediment from DSDP hole 477 in the Guaymas Basin. Results of the calculations indicate that conductive cooling of endmember fluids within closed chimneys and conduits accounts for the solution composition of one vent on the East Pacific Rise and several vents in Guaymas Basin. Mixing of the hydrothermal fluids with seawater yields a prediction of mineral assemblages closely approximating those observed in samples of chimneys from the East Pacific Rise and drill cores in Guaymas Basin. The hypothesis that Guaymas Basin hydrothermal fluids result from interaction of an EPR-type fluid with sediment cover in Guaymas Basin is supported by calculations which predict an increase in pH to a value similar to Guaymas Basin fluids, an order-of-magnitude decrease in metal concentrations, and an excellent agreement between predicted mineral assemblages as a function of extent of interaction with sediment, and observed mineral assemblage distribution with depth. 相似文献
19.
In the spring of 1995, 24 samples were collected from a widely distributed system of municipal water wells in Albuquerque, N.M., and analyzed for hydrogen (δD) and oxygen (δ18O) isotopic compositions. δD values for 15 of these samples are largely similar to those reported by Yapp in 1985, but have locally become more negative by as much as 5 per mil (ö). δD–δ18O data define two endmembers that are well aligned along the familiar meteoric water line (MWL): (1) the eastern domain (mountain precipitation runoff), having δD>–86ö (similar to the criteria of Yapp) and δ18O>–12.1ö (this work); and (2) a central basin domain, which may be in part derived from water seepage from the Rio Grande, having δD<–95ö and δ18O<–13.2ö. Only a few wells across the basin have δD values near the "baseline" value of the Rio Grande, defined by Yapp as –92ö. The proximity of these wells to the Rio Grande is consistent with recharge by seepage from the river bed under baseline conditions. Extensive pumping in the eastern domain and West Mesa areas may be partly responsible for an apparent expansion of the central-basin regime of water more depleted in δD, much as a plume migrating in response to transient perturbations in original hydraulic gradients. Vertically stacked groundwater occurrences having limited interconnection are inferred from the significant differences in isotopic compositions of samples from two wells screened at multiple depths. The central and western parts of the basin are little influenced by contributions from the eastern domain. Some groundwaters from the western part of the basin plot below the MWL and clearly cannot be mixtures solely of the eastern domain and central basin endmembers. The origins of these western groundwaters and the most depleted central basin groundwaters are as yet unknown, but we speculate they may have received recharge under climatic conditions different from the present. 相似文献
20.
Germanium/silica (Ge/Si) ratios of dolostone- and mudstone-hosted chert nodules from the Ediacaran (635–542 Ma) Doushantuo Formation in the Yangtze Gorges area, South China, are reported. These chert nodules typically have a calcite rim, a pyrite rim, and a silica core, the latter sometimes containing disseminated pyrite. The silica core was precipitated by early diagenetic replacement of carbonate and silty/muddy sediments. Two types of chert nodules are identified based on their mineralogy and geochemistry. Type-1 chert nodules are poor in disseminated pyrite in the silica core. They also have low Al, and show a strong positive correlation between Al contents and Ge/Si with a near-zero or negative intercept. In contrast, Type-2 chert nodules contain abundant disseminated pyrite in the silica core and show a weakly positive correlation between Ge/Si ratios and Al contents (with a large positive intercept on the Ge/Si axis). The Ge/Si of Doushantuo nodules are greater than those of Cretaceous deep-sea cherts, suggesting that the Ge/Si ratio of Ediacaran seawater/porewater was greater than the Cretaceous due to the more effective discrimination against Ge by inorganic opal precipitation relative to biogenic opal precipitation. The positive correlation between Ge/Si and Al can be interpreted using a mixing model with a pure chert (characterized by a low Ge/Si ratio) and an Al-rich endmember (characterized by a high Ge/Si ratio). The latter is most likely represented by a clay component, but the model-based estimate of the Ge/Si ratio inferred for the Al-rich (clay) endmember is much higher than that of Phanerozoic clay minerals. These high Ge/Si ratios for the clay endmember may be related to the generally high Ge/Si ratio of Ediacaran seawater, but could also be related to clay–organic matter interactions. Organic matter absorbed to clays could provide an additional source of Ge because certain organic molecules are known to have a high affinity for Ge due to their strong metal ion-chelating properties. The high Ge/Si ratio of the Al-rich endmember in Type-1 chert nodules suggests that Ge in porewaters from which these cherts precipitated may have been dominated by Ge–organic complexes. The low Ge/Si ratio inferred for the Al-rich endmember in Type-2 chert nodules is therefore taken to indicate that Ge was released from organic matter, perhaps due to anaerobic degradation of organic matter (accompanied by the formation of pyrite), and was redistributed between clay–organic endmembers and pure chert, resulting in a non-zero intercept in the Ge/Si vs. Al2O3 plots. These observations suggest that a strong terrestrial influence in a restricted sedimentary basin or a high content of dissolved organic carbon in Ediacaran seawater and porewater may have contributed to the dominance of Ge–organic complexes in the Doushantuo basin in the Yangtze Gorges area. 相似文献