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1.
The chemical compositions of and the contents of CaCO3, free Fe2O3 and REE in the sediments of the Salawusu section have been analyzed to investigate the geochemical features of different sedimentary facies and explore their sedimentary enironmetnts during the Late Pleistocene.The con-tents of CaCO3, free Fe2O3 and ∑REE in lacustrine deposits of the middle part of the section are higher than those in the other parts ,except SiO2 which shows an opposite trend.According to the distribution characteristics of the components mentioned above, the section may be divided into four parts which are equivalent to those divided in terms of lithologic characters and sedimentary facies.More remarkable characteristics were observed with respect to the distribution of CaCO3, free Fe2O3,∑REE and SiO2/Al2O3 and FeO/Fe2O3 ratios, which can be adopted as the geochemical indices for paleoclimate division.From the above, four paleoclimate stages have been distinguished for the deposition process.The first stage ,dated at 0.20-0.15Ma, is characterized by a dry and cold climate,the second stage, ranging from 0.15 to 0.07 Ma ,by a warm and slightly dry climate,the third stage ,about 0.07-0.01Ma ,by a cold and humid climate;and prevailing in the last ten thorsand years is the fourth stage,with the climate changing graduall from warm-humid to warm-dry. 相似文献
2.
作者通过对陕西洛川黄土剖面中碳酸盐总量、氧化物比值和元素演化周期性的分析，讨论了黄土高原地区２．４Ｍａ以来古气候的演化模式。对渭南黄土剖面高密度连续采集的样品，着重分析了ＣａＣＯ３、Ｆｅ2Ｏ３／ＦｅＯ值和有机碳的高分辨记录。指出它们的变化彼此同步(但趋势不尽相同)，与黄土一古土壤系列变化一致，井与深海沉积物氧同位素可进行良好的对比。它们综合反映了该区１３４５００年来有五次万年级的暖湿(或凉湿)一冷干的气候波动，其中各期又有若干次级的小颤动。它们的变化与季风影响强弱程度明显有关。 相似文献
3.
Mobility Sequence of Chemical Elements During Loess Weathering—Pedogenesis,Weinan,Shaanxi Province,China 总被引：1，自引：1，他引：0
The distribution of chemical elements in the Weinan loess section shows that: (1) carbonate is the critical constituent affecting
loess chemistry. The leaching of carbonates may cause “apparent” enrichment of some other constituents. (2) CaCO3, SiO2, FeO, MgO, K2O and Na2O are mobile while Al2O3, Fe2O3 and TiO2 are inert components. The mobility sequence may follow the order of CaCO3>FeO>MgO>Na2O>K2O>SiO2>Al2O3>TiO2>Fe2O3. (3) No obvious migration is noticed of iron, except changes in valence and forms, during the pedogenic process. Little iron
has been supplied to paleosol from precipitation. (4) Carbonates and, to a lesser extent, iron are most sensitive to, and
can be therefore used as good indicators of, environmental changes.
This research project was financially supported by the National Natural Science Foundation of China (Grant No. 49672137). 相似文献
4.
Yong–Joo JWA 《Resource Geology》1998,48(4):273-284
Abstract: Five groups of the Phanerozoic granitoids in South Korea can be deduced from their temporal and spatial distributions: (1) Jurassic granitoids in the Gyeonggi massif, (2) Permo-Jurassic granitoids in the Ogcheon belt, (3) Permo-Jurassic granitoids in the Yeongnam massif, (4) Cretaceous granitoids in the Ogcheon belt, and (5) Cretaceous granitoids in the Gyeongsang basin. Though the granitoids of each group generally show calc-alkaline and orogenic natures, the petrological, geochemical and genetical features are different with each other. The Permo-Jurassic granitoids in the Ogcheon belt have lower contents of Al2O3, Fe2O3, CaO, P2O5, but higher of FeO, FeOT, MgO, K2O than those in the Yeongnam massif. From higher feature of K2O, Na2O+K2O and K2O/Na2O, the Ogcheon belt seems to have been located at closer continent side relative to the Yeongnam massif during Permo-Jurassic time. From lower values of Fe2O3/FeO and magnetic susceptibility the granitoids of the Ogcheon belt had been solidified under more reducing environment than those of the Yeongnam massif. The Cretaceous granitoids in the Ogcheon belt have lower contents of TiO2, Fe2O3, FeO, FeOT, CaO and P2O5, but higher of MgO, K2O, Na2O+K2O and K2O/Na2O than those in the Gyeongsang basin. This feature indicates that the Ogcheon belt would correspond to the continental environment of magma genesis during Cretaceous time. Higher values of Fe2O3/FeO and magnetic susceptibility in the Cretaceous granitoids in the Gyeongsang basin suggest that the granitoids had been solidified under highly oxidizing environment. From the particular chemical features of K2O, Na2O+K2O and K2O/Na2O, the Permo-Jurassic granitoids in the Ogcheon belt, the Yeongnam massif as well as the Cretaceous ones in the Gyeongsang basin can be categorized to the continental margin type granite. The Jurassic granitoids in the Gyeonggi massif are possibly of collision type, and the Cretaceous granitoids in the Ogcheon belt of post–orogenic, intra–conti–nent type. The Jurassic granitoids in the Gyeonggi massif had been possibly generated by crustal melting during the collision of Gyeonggi massif to the northern Pyeongnam basin block. The Cretaceous granitoids in the Ogcheon belt had been emplaced at the hinterland of the continental margin during post-orogenic stage of the Honam Shear Zone. The Cretaceous granitoids in the Gyeongsang basin are often compared with Japanese Cretaceous?Paleogene granitoids in their geochemical and genetical natures. For the granitoid composition, the granitoids in the Gyeongsang basin are higher in Fe2O3, Fe2O3/FeO, Na2O, K2O, Na2O+K2O and K2O/Na2O, but lower in Al2O3, FeO, MnO, CaO and P2O5 than the Japanese granitoids. The contents of TiO2, FeOT and MgO are similar in both granitoids. This geochemical contrast would imply that the Cretaceous granitoid magmas in the Gyeongsang basin had been originated at closer place to the continent side under more tensional field, and solidified under more oxidizing environment than the coeval Japanese granitoid magmas. 相似文献
5.
周口店地区的古环境变化研究多数研究集中在中更新世时期,而缺乏对早更新世时期环境变化的研究。这主要是由于缺少保存完好的早更新世沉积记录造成的。随着对20世纪80年代在周口地区发现的东洞剖面,发现这是一个保存完好的早更新世剖面,为研究早更新世时期的古环境变化特征提供了良好的研究材料。为了重建早更新世时期的古环境变化特征,利用XRF对东洞洞穴沉积物的主要元素（SiO2,Al2O3,Fe2O3和CaO）的化学组成进行了高分辨率分析,同时对沉积物中的FeO含量进行了测试。结果显示东洞剖面沉积物的主要化学组成为SiO2,占41.6%～58.9%,其次是Al2O3和Fe2O3,其含量的变化范围分别为13.69%～29.63%和5.00%～9.81%。Al2O3和Fe2O3在剖面上与SiO2含量成明显的镜像变化关系,显示出Al2O3和Fe2O3对沉积物中SiO2含量的稀释作用。另外,Fe2O3与Al2O3在剖面上具有很好的相关性,表明Fe2O3主要富集在富铝的矿物中。从元素含量在剖面的上分布看,东洞剖面的化学组成发生3次大的波动,主要表现为SiO2和FeO含量增高,而Fe2O3与Al2O3含量的减少。这3次波动分别出现在剖面的15.3～14.6m,11.0～9.9m和8.40～7.84m深度处。在3次化学组成的波动出现的同时,指示沉积物风化程度和温度变化的Si/Al（SiO2/Al2O3）和FeO/Fe2O3比值也发生了明显变化,比值增高,指示了3次大的干冷事件。另外,在剖面上部（10.00～7.84m,即第2次事件以后）SiO2/Al2O3和FeO/Fe2O3比值变高且波动频繁,表明自第2次干冷事件后沉积区的环境变得不稳定,逐渐向冷干气候转变。东洞剖面的地球化学记录（SiO2/Al2O3和FeO/Fe2O3）与泾川黄土剖面的粒度曲线具有较好的对比性,支持了东洞剖面记录的环境信息与黄土沉积记录的环境变化具有一致性。通过与泾川粒度曲线的对比发现,东洞剖面记录的3次干冷事件在时段上分别对应于黄土-古土壤序列中的L26,L15和L13。 相似文献
6.
Two Holocene sediment cores were retrieved respectively from the enclosed Lake Daihai in the monsoon/arid transition zone
of North China and the Taihu Lake coast in the monsoonal area of the Yangtze delta, Eastern China. Distribution of major geochemical
elements and their ratios were employed to reveal the characteristics of Holocene climate and associated environmental implications
in the two regions. It is suggested that the temporal distribution of major elements serve as a useful indicator to denote
the variations of monsoon effective precipitation for the enclosed lake area. High values of resistant elements such as Al2O3, SiO2, TiO2, (FeO + Fe2O3), MnO in the lake sediments correspond to the depressed chemical weathering and weakened mon-soon effective precipitation,
while the highs of mobile and easy soluble elements such as MgO, CaO, Na2O reflect the enhanced chemical weathering and increased monsoon effective precipitation in the lake basin. In comparison,
the behaviors of the major elements in sediments of the Taihu Lake coast were largely controlled by the changes both in sea
transgression in the different Holocene time periods and the monsoon precipitation. The relatively highs of Al2O3, TiO2, (FeO + Fe2O3), in marine-influenced sediments suggest relatively strong coastal hydrodynamics and chemical weathering, and vice versa.
Meanwhile, the lows of SiO2, Na2O and CaO in the non-marine-influenced sediments also denote relatively strong hydrodynamics and chemical weathering due to
enhanced monsoon precipitation, and vice versa. Sedimentary environment should be taken into account when achieving a full
understanding of their climate implications. 相似文献
7.
吐鲁番盆地是天山山脉中的一个山间盆地,古近系保存完好,是研究中国西北地区古近纪气候变迁的良好地区。通过对吐鲁番盆地连木沁剖面古近系多种气候代用指标（Fe2O3、FeO、CaCO3、有机碳、有机碳同位素）的研究,探讨了吐鲁番盆地古近纪的气候变迁和重要气候事件。利用Fe3+/Fe2+值,恢复了吐鲁番盆地古近纪的气温：古新世的年均气温为22.35℃,始新世为21.82℃,渐新世为15.69℃,并且在渐新世的早期和晚期发生较大幅度的降温事件。对地层中CaCO3（碳酸钙）含量的研究表明,古新统和始新统碳酸钙平均含量分别为468％和666％,指示该沉积时期气候相对比较湿润,而渐新统达15.01％,指示渐新世气候明显干旱化,并且渐新世的早期和晚期气候更为干旱。有机碳同位素（δ13Corg）值分布于C3植物的范围内,表明其受C3植物的影响。对地层中的δ13Corg值研究显示,该值与地层中碳酸钙含量呈负相关,与气温呈正相关,即该值偏负时,地层中碳酸钙含量增加,气温降低。各种气候指标指示吐鲁番盆地古新世和始新世气候比较温暖湿润,而渐新世气候干旱温凉。 相似文献
8.
In this paper, the evolutional characteristics of palaeoclimate and oxidation-reduction conditions as well asacidity-alkalinity environment are discussed by means of the step-regression, cluster, optimal partitioning andcorrelation analyses of CaCO_3, C / P_2O_5, Fe~(2+) / Fe~(3+), pH and Eh values, taking the Xiaodukou section in theNihewan basin as an example. The CaCO_3, C / P_2O_5 and pH were calculated respectively using the optimalpartitioning method. Thus five cold zones and six warm zones as well as five reduction and six oxidation zoneswere distinguished. Then the inductive method was used to produce four numerical groups: 8.10, 8.3-8.4,8.6-8.7 and 8.9-8,97. The above-mentioned results are respectively based on CaCO_3 content, C/P_2O_5 andpH values. From Fig. 3, Tables 1 and 2 it can be seen that the Nihewan Beds were formed mainly under a re-duction and slightly alkaline environment of cold climate, with pH values of 8.3-8.4. Fig. 3 shows that bed 35is approximately near the boundary between the Brunhes and Matuyama polarity epochs, 0.73 Ma in age; bed26 is roughly near the Jaramillo event (base), 0.97 Ma in age; bed 18 coincides roughly with themagnetostratigraphic boundary of 2.00 Ma (?). Bed 13 may be the Pleistocene-Pliocene boundary, 2.48 Ma inage. Thus geochemical zones Ⅰ, Ⅱ, Ⅲ and Ⅳ include respectively cold zones 1; 2 and 3; 4; and 5. 相似文献
9.
This paper reports a geochemical study on the major and trace elements and Pb–Sr isotopes of a weathering profile developed in the Lower Cambrian black shales in central Hunan (China). Six weathering horizons were identified and sampled vertically throughout the profile. The chemical composition of the profile consists of variable concentrations of the major elements Fe2O3, FeO, MnO, MgO, CaO, Na2O, and P2O5 and of less variable concentrations of SiO2, TiO2, Al2O3, and K2O. The chemical change caused by weathering is estimated by mass-balance calculations, and the results show that the element mobility is characterised by substantial loss of SiO2, FeO, CaO, K2O, Na2O, LOI, Cr, V, Ba, Cs, Rb, Sr, U, and Th, and moderate loss of Al2O3, MgO, Fe2O3, Ni, Cu, Pb, Tl, Sn, Sc, Ge and REE (Y). The high field strength elements TiO2, Sn, Sc, U, Ga, Ge, Zr, Hf, Nb, and Ta were immobile during weathering. The chemical changes and the Pb–Sr isotopic data suggest that four types of chemical reactions occurred: the oxidation of sulphide minerals (e.g., pyrite) and organic carbon (OS), the dissolution of less resistant clinochlore-Ia, calcite, and P-bearing minerals (DL), the dissolution of detrital albite and microcline (DA), and the transformation of clay (TC) minerals (e.g., muscovite and illite–smectite). These chemical reactions then led to two stages of geochemical processes, an early stage of chemical differentiation and a later stage of chemical homogenisation. The chemical differentiation dominated by the OS, DL, and DA reactions, led to the leaching of mobile elements (e.g., MgO, Na2O, K2O, P2O5, Sr, and REE) and the redistribution of some less mobile elements (e.g., SiO2 and Al2O3). In contrast, the chemical homogenisation, which was caused by TC reactions, led to the leaching of both mobile and less mobile elements from the system and ultimately transformed the weathered black shales into soil. Soils derived from black shales in South China might result from the above two geochemical processes. 相似文献
10.
11.
A study was made on samples from one core collected immediately after the December 2004 Asian tsunami to know the geochemical
nature of the offshore tsunami sediments. The core sample was analyzed for sediment grain size, CaCO3, organic carbon (OC) and major elements (SiO2, TiO2, Al2O3, Fe2O3, CaO, MgO, Na2O, K2O, P2O5, MnO). The results indicate that the core sample can be divided into two parts: (1) upper 0–25 cm, interpreted to be deposited
after tsunami (AT), and (2) lower 25–45 cm, interpreted as before tsunami (BT) as evidenced by the sandy nature AT with fluctuating
CaCO3 contents. The AT part is devoid of OC suggesting that the sediment could have been transported to deeper regions along with
the finer particles. Major elements such as SiO2, TiO2, CaO indicate high values than the other elements in AT part than in the BT part. The BT part contains Al rich alluvium mud
associated with finer mud and organic particles. An analysis of the correlation matrix indicates the possible source of elements
and transport of heavy minerals in the AT part than the BT part. The overall results suggest that the sediments could possibly
have two different origins. 相似文献
12.
Kamal Abou Elmagd Ashraf Emam Mohamed Wahbi Ali-Bik Muhammad Hazem 《Arabian Journal of Geosciences》2018,11(13):355
The present work assesses the potential industrial uses of Paleocene limestone deposits, Garra Formation in Sinn El-Kaddab Plateau, South Western Desert of Egypt, based on their mineralogy and geochemical characteristics. Eighty-six limestone samples collected from ten stratigraphic columnar sections were analyzed using X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques. Petrographically, Garra limestone deposits consist dominantly of benthic foraminiferal wackestone and packstone microfacies. The XRD data revealed dominance of low-Mg calcite as essential carbonate mineral in the studied limestone. The bulk rock XRF results revealed CaO (29.28–55.75%) with an average of 52.74%. The CaO exhibits a strong negative correlation with MgO, SiO2, TiO2, Al2O3, and moderate negative correlation with Fe2O3 which indicates that the contribution of these elements is mainly due to detrital input. On the other hand, Al2O3 and Na2O contents exhibit significant negative correlation with loss of ignition (LOI) wt% indicating their incorporation within terrigenous matrix. The average Sr content attains 1297 ppm indicating deposition in temperate marine environment. The average molar CaCO3% values of bulk samples have been computed for individual columnar sections to determine the purity status of Garra limestone deposits. They range from impure (CaCO3%?=?79.92%) to high-pure (CaCO3%?=?97.76%) limestone. Therefore, Garra limestone deposits have extremely valuable uses in a wide spectrum of industrial applications including Portland cement, steel, ceramics, whiting, chemical uses, paper, and feed stuff. 相似文献
13.
With the decrease of gloal temperature,glacial epoch came over the earth and global climate fluctuated over a great range since the beginning of Quatenary .Paleoclimotologists of various countries have focussed attention to the periodic characteristics and dynamics of climation flucturation in the past many years(Berger,1977;Imbrie and Hays,1984:ding zhongli et al.,1990;Yu zhiwei et al.,1992:Liu Youmei et al.,1996),Although some of the workers have paid their attention to the nonlinear characteristics of the global Quaternary environmental evolution(Nicolis and Nicolis,1984,Lu Houyuan et al.,1993)_,it is worth while to do this kind of work in some special areas in the world,for example the Qinghai-Tibet Plateau.Using R/S analysis,the authors calculated the Hurst indexes H of some geochemical proxies,including organic carbon,FeO,Fe2O3 and FeO/Fe2O3,from the Tianshuihai Lake core in West Kunlun Mountain of the Qinghai-Tibet Plateau,The proxies satisfy the Hurst law with Honrg.carbon=0.735,HFe2O3=0.757,HFeO=0.848and HFeO/Fe2O3=0./646,All the indexs are greater than 0.5,meaning that from 240 to 15ka B.P.,there were some long-run dependencies-persistence in the climatic and environmental evolution around the Tianshuihai Lake area.This is in accordance with the climate there from 240 to 15ka B.P.(Yu Suhua et al.,1996),The paleo-climate and paleo-environment evolution around the Tianshuihai Lake area is of persistence as well as of fluctuation and is a combination of these two components,There are some differences between the four Hurst indexes,Which Probably resulted from the differnet intensitites of Persistence of the four proxies,organic carbon.FeO,Fe2O3 and FeO/Fe2O3,or from the change of drainage system around the Tianshuihai Lake area from opemness to closeness(Li Bingyuan et al.,1991;Sun Honglie,1996:Shi Yafeng et al.1998_).The Qinghai-Tibet plateau was the starter and sensor of the climatic and environmental variation of the surrounding areas(Yao Tandong et al.,1991;Feng Song et al., 1998) and some other scientists even regarded it as the driver and amplifier of global climatic variations (Pan Baotian and Li Jijun,1996).The persistence in which the climate and environment around the Tianshuihai Lake area evolved from 240 to 15ka B.P.is probably a function of the continuous uplift of the palteau in the same period of time. 相似文献
14.
Environmental conditions inferred from multi-element concentrations in sediments off Cauvery delta,Southeast India 总被引：1，自引：1，他引：0
Judith D. Silva S. Srinivasalu P. D. Roy M. P. Jonathan 《Environmental Earth Sciences》2014,71(5):2043-2058
We present multi-element concentrations in the surface sediments from the offshore of Cauvery delta of southeast India to evaluate the impact of coastal pollution on the geochemical behaviour of surface deposits. For this study, 16 surface sediment samples were collected from the offshore of Cauvery delta of southeast India and were analysed using traditional XRF for various major (SiO2, Al2O3, MgO, Fe2O3, MnO, Na2O, K2O, CaO, P2O5, TiO2) and trace elements (Rb, Sr, Ba, Y, Zr, Nb, V, Cr, Co, Ni, Cu, Zn, Th, Pb) after powdering it to ASTM 230 (<63 μm). The main objectives of this study were to understand the geochemical behaviour of the coastal surface sediments and its performance and relation with the pollution indices and statistical analysis. To meet out the objective, pollution indices such as enrichment factor (EF), contamination factor (CF) and Geoaccumulation Index (I geo) were calculated and statistical analyses were performed to understand the relationship between the geochemical parameters. Both EF and I geo show the enrichment of Cu, Cr and Zr, whereas CF shows enrichment of Cu and Cr. Statistical analyses exhibit poor correlation between these elements and fine fraction indicating the insignificant role played by both grain size and organic matter. Strong positive association between Cu and Zn with CaCO3 exhibits the role of carbonates in precipitating these metals from the overlying water column possibly related to agricultural pollution. Distribution and association of other elements suggest the influence of mineralogy in geochemical composition of surface sediments. Based on this study, we suggest that environmental indices alone should not be considered for evaluating environmental conditions and a prior geogenic characterisation of the sediments is necessary. 相似文献
15.
《International Geology Review》2012,54(8):744-755
The Güneyocak chromite mineralization is hosted by the Upper Cretaceous Divrigi ophiolitic melange, which consists of serpentinite, serpentinized harzburgite and dunite, gabbro, diabase dikes, pyroxenite, blocks of limestone, and radiolarite. Serpentinites were intensely listwaenitized near the mineralization and in other locations in the study area. The Guneyocak chromite mineralization is of interest because of its internal structure and abundant, repeated chromitite bands, as well as for its chemistry. These features are unusual for ophiolite-hosted chromite. Major-element chemistry shows that the chromites have very high Fe2O3 and MgO and very low FeO. The Guneyocak chromites are classified as of Alpine type on the basis of host-rock lithology and Cr2O3, Al2O3, FeO(T), and Cr/Fe values. However, the very high Fe2O3 and MgO and very low FeO compositions of the chromites do not correspond to those of an Alpine-type chromite deposit. Repeated chromite banding and high Fe2O3 content of the chromite strongly suggest repeated oxygen fugacityf(O2) fluctuations and that the Guneyocak mineralization formed at relatively shallow depths. The Güneyocak chromite is characterized by a slightly boninitic character, which represents high partial melting under conditions of high oxygen fugacity. We conclude that the Guneyocak chromite mineralization formed in the uppermost part of the ultramafic rock series of the Divrigi ophiolitic melange. 相似文献
16.
Using the thermodynamic algorithm of Sugawara (Contributions to Mineralogy and Petrology 141, 2001, p. 659–686), FeO and Fe2O3 concentrations in plagioclase were computed for 420 published experiments on tholeiitic, FeTi-tholeiite, calc-alkaline, and alkaline magma compositions. Estimates of the partition coefficient between plagioclase and liquid range from 0.19 to 0.92 for Fe2O3 and from 0.008 to 0.050 for FeO, i.e. ca. twenty times greater for Fe2O3 than for FeO. Partitioning of Fe2O3 and FeO is independent of both oxygen fugacity and plagioclase composition, contradicting the common assumption that partitioning of Fe2O3 correlates positively with the amount of aluminium in plagioclase. In contrast, the SiO2-content of the magma correlates positively with the partition coefficients for Fe2O3 and FeO. This is ascribed to increasing activity of iron in polymerised SiO2-rich magma. Advances of micro-beam Fe-XANES techniques allow the determination of Fe3+/Fe in plagioclase. Using such plagioclase data and the partition coefficients for Fe2O3 and FeO, the Fe2O3/FeO and oxygen fugacity of equilibrium magma may be estimated. As petrological examples, we estimate that the oxygen fugacity of the Palisades sill ranged from the QFM buffer to 0.5 log unit below it (QFM to QFM –0.5), the Lake County basalt from QFM to QFM –2, and Upper Zone a of the Skaergaard intrusion from QFM –1 to QFM –1.5.Editorial responsibility: I. Parsons 相似文献
17.
Paul C. Ragland John J. W. Rogers Philip S. Justus 《Contributions to Mineralogy and Petrology》1968,20(1):57-80
Ten dolerite dikes intruded into Triassic fault troughs in the Piedmont area of North Carolina have been analyzed for the contents of major elements plus selected trace elements. The average composition of the initial magma, as indicated by four chill margins for major elements and three for trace elements, is: SiO2, 48.6%; Al2O3, 16.9%; TiO2, 0.57%; Fe2O3, 3.30%; FeO, 6.72%; MgO, 10.59; CaO, 10.42%; Na2O, 2.03%; K2O, 0.20%; MnO, 0.20%; Rb, 2.6 ppm; Sr, 133 ppm; Zr, 46 ppm; Th, 0.4 ppm; and U, below detection limit of approximately 0.1 ppm. One large dike (BP) exhibits a Palisades-type of differentiation by crystal settling of olivine, and the comparatively thick JY dike shows development of micropegmatite toward the center; the smaller dikes, however, are relatively homogeneous across their width. Study of the relationship between SiO2 content and the ratio FeO+Fe2O3/MgO+ FeO+Fe2O3 indicates that most dikes crystallize under conditions of decreasing oxygen pressure, but the differentiation trend of the JY, RD, and RS dikes indicates either constant or increasing oxygen pressure during their evolution.Statistical comparison of the composition of the initial dolerite magmas with a variety of basalt types around the world suggests that the North Carolina dolerites are far more similar to oceanic or oceanic margin tholeiites than to continental tholeiites. The North Carolina rocks are distinctly different from plateau basalts but are similar to the chill zones of the Precambrian Bushveld and Stillwater lopoliths. The comparatively low contents of Th, U, and Sr, plus the relatively high K/Rb ratio all support the possibility that the magmas for the North Carolina dolerites evolved in a dominantly oceanic environment. It seems distinctly possible that continental-type crust and mantle did not exist in the Appalachian Piedmont area in Triassic time, even after major orogeny and the concurrent formation of granitic intrusions. 相似文献
18.
Ray Macdonald Bogus?aw Bagiński Fiorenzo Ronga Piotr Dzier?anowski Michele Lustrino Andrea Marzoli Leone Melluso 《Mineralogy and Petrology》2012,104(3-4):163-175
Matrix glass and melt inclusions in phenocrysts from pantellerite lavas of the Boseti volcanic complex, Ethiopia, record extreme fractionation of peralkaline silicic magma, with Al2O3 contents as low as 2.3?wt.%, FeO* contents up to 17?wt.% and SiO2 contents ~65?wt.%. The new data, and published data for natural and experimental glasses, suggest that the effective minimum composition for peralkaline silicic magmas has ~5?wt.% Al2O3, 13?wt.% FeO* and 66?±?2?wt.% SiO2. The dominant fractionating assemblage is alkali feldspar?+?fayalite?+?hedenbergite?+?oxides?±?quartz. Feldspar – melt relationships indicate that the feldspar is close to the minimum on the albite-orthoclase solid solution loop through the entire crystallization history. There is petrographic, mineralogical and geochemical evidence that magma mixing may have been a common process in the Boseti rhyolites. 相似文献
19.
Major and trace element distribution in the bottom sediments from Hole 13 drilled in Lake Grand, Magadan district, was studied using the method of principal components. It was established that geochemical characteristics are correlated with environmental changes. The sediments of cold MIS2 and MIS4 are characterized by the enriched TiO2, MgO, Al2O3, Fe2O3, and Cr and low Na2O, K2O contents, which is related to the grain-size composition of sediments. Sediments of warm stages show an opposite tendency. High concentration peaks of iron, phosphorus, and manganese correspond to the accumulation levels of vivianite and ferromanganese rocks. Silica is represented by biogenic and abiogenic varieties. Maximum SiO2 contents were found in the Late Holocene sediments and mark the high biological productivity of the basin. Revealed variations of some elements are correlated with the Heinrich events. 相似文献
20.
区域化探全国扫面计划获得的海量地球化学数据在基础地质和矿产勘查研究中已发挥了重要作用。全国矿产资源潜力评价化探工作组将全国陆地国土划分为5个地球化学域(古亚洲地球化学域、秦祁昆地球化学域、特提斯地球化学域、扬子地球化学域和滨太平洋地球化学域)和25个地球化学省。在全国地球化学图中位于云南西部地区的花岗岩类侵入体具有显著富K2O、Th、U、La、Y、Zr而贫Co、Ni、V、Cr、Ti、Fe2O3的特征。基于云南西部地区区域化探数据利用因子分析确定了高场强元素组合(F2)和相容元素组合(F1)两个公因子:F2=0.87Th+0.86Y+0.77U+0.77Zr+0.67La+0.61K2O+0.58Al2O3+0.53Be,F1=0.95Fe2O3+0.93V+0.93Ti+0.92Co+0.81Cr+0.80Ni。利用二者因子得分比值(F2/F1)构建了推断花岗岩类侵入体的区域地球化学综合指标和推断模型。以F2/F1为例介绍了制作地球化学图和地球化学异常图的方法技术。在F2/F1地球化学图中的高值区或在其地球化学异常图中的异常区与云南西部地区花岗岩类侵入体的地表出露范围十分吻合,从而验证了地球化学推断花岗岩类侵入体模型的可行性。基于构建的推断模型在全国近7百万平方千米的范围内进行推演并绘制F2/F1的地球化学图和地球化学异常图。选择华南中部地区进行详细分析,结果发现模型指标异常区与实测花岗岩类侵入体在空间形态和规模上十分吻合,尤其在韶关至桂林、贺州一带花岗岩类侵入体边界与F2/F1异常区边界几乎一致。这一结果不仅证实了针对花岗岩类侵入体所建立的区域地球化学推断模型的可行性,而且该模型在基础地质研究方面具有潜在应用价值。 相似文献