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121.
在模糊集理论与分形理论的基础上,引进了模糊分维的概念;给出了模湖容量维D0与模糊关联维D2的定义与确定方法;讨论了模糊分维与常用的分维(清晰分维)的关系.给出了模糊分维在地震研究中的应用结果: 1.根据模糊容量维D0随时间的上升趋势变化,可以划分出大地震活动的高潮期;由模糊容量维D0与模糊关联维D2随时间变化的曲线,可以分析识别大地震前的中长期前兆异常. 2.根据模糊容量维D0随空间和时间的变化,可以划分出未来大震所在的地区,并可发现大震前数年D0呈现增大或减小的趋势. 3.根据前兆数据的模糊时间分维D0随时间的变化,可以发现大地震的短期前兆异常. 相似文献
122.
Alexei V. Ivanov Elena I. Demonterova Sergei V. Rasskazov Tatyana A. Yasnygina 《Journal of Earth System Science》2008,117(1):1-21
Siberian Traps Large Igneous Province (STLIP) is one of the most voluminous volcanic provinces on Earth. The dominant erupted
rocks are low-Ti basalts, which make up 80% by volume of the classical Noril’sk lava sequence. In the west Siberian basin
and Maymecha-Kotuy area, the low-Ti basalts make up about 99% and 50% by volume, respectively. Dolerite sills in the Angara-Taseevskaya
Syncline at the southeastern STLIP exhibit trace element patterns and Sr isotope ratios typical of the low-Ti basalts of the
Noril’sk sequence. The most Mg-rich (MgO 9.5–11 wt%) and hence least differentiated dolerites are characterized by trace element
patterns with Ta-Nb depletion, low Ce/Pb and high Sr/Pr. These trace element features are similar to water-saturated, mantle
wedge-derived island arc basalts. These imply an important role of subduction fluid-derived trace elements in the source of
melting beneath the Angara-Taseevskaya Syncline and other regions of the STLIP. Less magnesium rocks (MgO 3.8–6.1 wt%) with
less prominent Ta-Nb depletion, higher Ce/Pb and lower Sr/Pr could be produced via olivine-plagioclase fractionation of primary
high-magnesium melts. 相似文献
123.
Two magma series and associated ore deposit types in the Permian Emeishan large igneous province, SW China 总被引:29,自引:0,他引:29
Mei-Fu Zhou Nicolas T. Arndt John Malpas Christina Yan Wang Allen K. Kennedy 《Lithos》2008,103(3-4):352-368
The Late Middle Permian ( 260 Ma) Emeishan large igneous province in SW China contains two magmatic series, one comprising high-Ti basalts and Fe-rich gabbroic and syenitic intrusions, the other low-Ti basalts and mafic–ultramafic intrusions. The Fe-rich gabbros are spatially and temporally associated with syenites. Each series is associated with a distinctive type of mineralization, the first with giant Fe–Ti–V oxide ore deposits such as Panzhihua and Baima, the second with Ni–Cu–(PGE) sulfide deposits such as Jinbaoshan, Limahe and Zhubu. New SHRIMP zircon U–Pb isotopic data yielded 263 ± 3 Ma for the Limahe intrusion, 261 ± 2 Ma for the Zhubu intrusion and 262 ± 2 Ma for a syenitic intrusion. These new age dates, together with previously reported SHRIMP zircon U–Pb ages, suggest that all these intrusions are contemporaneous with the Emeishan flood basalts and formed during a major igneous event at ca. 260 Ma.The oxide-bearing intrusions have higher Al2O3, FeO (as total iron) and total alkalis (Na2O + K2O) but lower MgO than the sulfide-bearing intrusions. All intrusions are variably enriched in LREE relative to HREE. The oxide-bearing intrusions display positive Nb- and Ti-anomalies and in certain cases negative Zr–Hf anomalies, whereas the sulfide-bearing intrusions have obvious negative Nb- and Ti-anomalies, a feature of crustal contamination. Individual intrusions have relatively small ranges of Nd(t) values. All the intrusions, however, have Nd(t) values ranging from − 3.9 to + 4.6, and initial 87Sr/86Sr ratios from 0.7039 to 0.7105. The syenites have very low MgO (< 2 wt.%) but highly variable Fe2O3 (2.5 to 13 wt.%) with initial 87Sr/86Sr ratios ranging from 0.7039 to 0.7089. Magmas from both series could have derived by melting of a heterogeneous mantle plume: the high-Ti series from a Fe-rich, more fertile source and the low-Ti series from a Fe-poor, more refractory source. In addition, the low-Ti series underwent significant crustal contamination. The two magma series evolved along different paths that led to distinct mineralization styles. 相似文献
124.
The 1.78 Ga Xiong'er Volcanic Province (XVP) and coeval North China giant mafic Dyke Swarm (NCDS) are the most important magmatic events occurring after the amalgamation of the North China craton (NCC). The XVP consists of 3–7 km of extrusive volcanics and some feeder dykes/sills located along the southern margin of the NCC and extending over an area > 0.06 M km2. Compositions vary from basalt to rhyolite, but are predominantly intermediate in terms of silica content. There are also minor sedimentary intercalations and pyroclastic units. The sedimentary interlayers indicate an environment changing from continental-facies to oceanic-facies up-section. The XVP is characterized by fractional crystallization from an EM I type mantle source, and both continental arc (Andean-type) and rift environments have been proposed. The NCDS is widespread in the central NCC with an outcrop area > 0.1 M km2, and are exposed at variable depths up to 20 km (deepest in the north). Dyke compositions vary from basalt to andesite and dacite, but are dominantly mafic, and comprise two series of magmatism. Previous studies revealed that the NCDS recorded assimilation and fractional crystallization of an EM I type magma source, with a minor DM contribution in the younger magmas. Both syn-collisional and intra-continental anorogenic environments have been proposed. Spatial and petrogenic correlations suggest a cogenetic relationship between the NCDS and XVP, and considered together, they define a Large Igneous Province (LIP) of > 0.1 M km2 in area and > 0.1 M km3 in volume, which is also notable for its continuous compositional range from mafic to felsic (with no gap at intermediate compositions). The petrology is explained by a common magma source that undergoes a silica-poor and iron-enriched fractionation trend at depth followed by a silica-rich and iron-poor fractionation trend in shallow-level magma conduits (dykes) and surface lavas. A mantle plume is favored as the cause of this 1.78 Ga North China LIP. 相似文献
125.
Christina Yan Wang Hazel M. Prichard Mei-Fu Zhou Peter C. Fisher 《Mineralium Deposita》2008,43(7):791-803
The Jinbaoshan Pt–Pd deposit in Yunnan, SW China, is hosted in a wehrlite body, which is a member of the Permian (∼260 Ma)
Emeishan Large Igneous Province (ELIP). The deposit is reported to contain one million tonnes of Pt–Pd ore grading 0.21% Ni
and 0.16% Cu with 3.0 g/t (Pd + Pt). Platinum-group minerals (PGM) mostly are ∼10 μm in diameter, and are commonly Te-, Sn-
and As-bearing, including moncheite (PtTe2), atokite (Pd3Sn), kotulskite (PdTe), sperrylite (PtAs2), irarsite (IrAsS), cooperite (PtS), sudburyite (PdSb), and Pt–Fe alloy. Primary rock-forming minerals are olivine and clinopyroxene,
with clinopyroxene forming anhedral poikilitic crystals surrounding olivine. Primary chromite occurs either as euhedral grains
enclosed within olivine or as an interstitial phase to the olivine. However, the intrusion has undergone extensive hydrothermal
alteration. Most olivine grains have been altered to serpentine, and interstitial clinopyroxene is often altered to actinolite/tremolite
and locally biotite. Interstitial chromite grains are either partially or totally replaced by secondary magnetite. Base-metal
sulfides (BMS), such as pentlandite and chalcopyrite, are usually interstitial to the altered olivine. PGM are located with
the BMS and are therefore also interstitial to the serpentinized olivine grains, occurring within altered interstitial clinopyroxene
and chromite, or along the edges of these minerals, which predominantly altered to actinolite/tremolite, serpentine and magnetite.
Hydrothermal fluids were responsible for the release of the platinum-group elements (PGE) from the BMS to precipitate the
PGM at low temperature during pervasive alteration. A sequence of alteration of the PGM has been recognized. Initially moncheite
and atokite have been corroded and recrystallized during the formation of actinolite/tremolite, and then, cooperite and moncheite
were altered to Pt–Fe alloy where they are in contact with serpentine. Sudburyite occurs in veins indicating late Pd mobility.
However, textural evidence shows that the PGM are still in close proximity to the BMS. They occur in PGE-rich layers located
at specific igneous horizons in the intrusion, suggesting that PGE were originally magmatic concentrations that, within a
PGE-rich horizon, crystallized with BMS late in the olivine/clinopyroxene crystallization sequence and have not been significantly
transported during serpentinization and alteration. 相似文献
126.
The Limahe Ni–Cu sulfide deposit is hosted by a small mafic–ultramafic intrusion (800 × 200 × 300 m) that is temporally associated
with the voluminous Permian flood basalts in SW China. The objective of this study is to better understand the origin of the
deposit in the context of regional magmatism which is important for the ongoing mineral exploration in the region. The Limahe
intrusion is a multiphase intrusion with an ultramafic unit at the base and a mafic unit at the top. The two rock units have
intrusive contacts and exhibit similar mantle-normalized trace element patterns and Sr–Nd isotopic compositions but significantly
different cumulus mineralogy and major element compositions. The similarities suggest that they are related to a common parental
liquid, whereas the differences point to magma differentiation by olivine crystallization at depth. Sulfide mineralization
is restricted to the ultramafic unit. The abundances of sulfides in the ultramafic unit generally increase towards the basal
contacts with sedimentary footwall. The δ
34S values of sulfide minerals from the Limahe deposit are elevated, ranging from +2.4 to +5.4‰. These values suggest the involvement
of external S with elevated δ
34S values. The mantle-normalized platinum-group element (PGE) patterns of bulk sulfide ores are similar to those of picrites
associated with flood basalts in the region. The abundances of PGE in the sulfide ores, however, are significantly lower than
that of sulfide liquid expected to segregate from undepleted picrite magma. Cr-spinel and olivine are present in the Limahe
ultramafic rocks as well as in the picrites. Mantle-normalized trace element patterns of the Limahe intrusion generally resemble
those of the picrites. However, negative Nb–Ta anomalies, common features of contamination with the lower or middle crust,
are present in the intrusion but absent in the picrites. Sr–Nd isotopes suggest that the Limahe intrusion experienced higher
degrees of contamination with the upper crust than did the picrites. The results of this study permit us to suggest that the
parental magma of the Limahe intrusion was derived from picritic magma by olivine fractionation and contamination in a staging
chamber at mid-crustal levels. Depletion of PGE in the sulfide ores in the Limahe intrusion is likely due to previous sulfide
segregation of the parental magmas in the staging chamber. Sulfide mineralization in the Limahe intrusion is related to second-stage
sulfide segregation after the fractionated magmas acquired external S from pyrite-bearing country rocks during magma ascent
to the Limahe chamber. The abrupt change in mineralogical and chemical compositions between the ultramafic unit and the overlying
unit suggests that at least two separate pulses of magma were involved in the development of the Limahe intrusion. We propose
that the Limahe intrusion was once a wider part of a dynamic conduit that fed magma to the overlying subvolcanic dykes/sills
or lavas. The ultramafic unit formed by the first, relatively more primitive magma, and the mafic unit formed by the second,
relatively more fractionated magma. Immiscible sulfide droplets that segregated from the first magma settled down with olivine
crystals to form the sulfide-bearing, olivine-rich rocks in the base of the intrusion. The overlying residual liquids were
then pushed out of the chamber by the second magma. Critical factors for the formation of an economic Ni–Cu sulfide deposit
in such a small intrusion include the dynamic petrologic processes involved and the availability of external sulfur. The Limahe
deposit reminds us that small, multiphase, mafic–ultramafic intrusions in the region should not be overlooked for the potential
of economic Ni–Cu sulfide deposits. 相似文献
127.
早中侏罗世大鄂尔多斯古地理重建与内陆拗陷的发育演化 总被引:17,自引:2,他引:17
通过沉积构成、古流体系和相带分布等沉积的成因联系及沉积学比较分析,论证了现今鄂尔多斯与其以东山西宁武、大同等地下中侏罗统同期地层原始沉积充填的统一性,证实了它们属于同一个大鄂尔多斯沉积盆地。并按照四个时期重建和阐明了早中侏罗世盆地沉积古地理,从而揭示了大鄂尔多斯拗陷-隆升-再拗陷的形成演化的构造阶段性及其充填动力学背景的迁移性。关于内陆拗陷构造背景的探讨,从更小尺度上揭示了华北陆内印支-燕山构造的变格运动及其发生的时间. 相似文献
128.
在模糊集理论与分形理论的基础上,引进了模糊分维的概念;给出了模湖容量维D0与模糊关联维D2的定义与确定方法;讨论了模糊分维与常用的分维(清晰分维)的关系.给出了模糊分维在地震研究中的应用结果: 1.根据模糊容量维D0随时间的上升趋势变化,可以划分出大地震活动的高潮期;由模糊容量维D0与模糊关联维D2随时间变化的曲线,可以分析识别大地震前的中长期前兆异常. 2.根据模糊容量维D0随空间和时间的变化,可以划分出未来大震所在的地区,并可发现大震前数年D0呈现增大或减小的趋势. 3.根据前兆数据的模糊时间分维D0随时间的变化,可以发现大地震的短期前兆异常. 相似文献
129.
Sediment deposition and its accumulation in a large resorvoir depends on the inflow and reservoir storage content, respectively. Because of this fact it is possible to model the cumulative deposition of sediment as an additive process defined on a bivariate Markov chain. Using the bivariate Markov chain model the mean and variance of the cumulative deposition of John Martin Reservoir, Colorado, U.S.A. are estimated and compared with observed sedimentation data. 相似文献
130.
This paper presents numerical simulations of Cone Penetration Test (CPT) in water-saturated soft soils taking into account pore pressure dissipation during installation. Besides modelling interaction between soil skeleton and pore fluid, the problem involves large soil deformations in the vicinity of the penetrometer, soil–structure interaction, and complex non-linear response of soil. This makes such simulations challenging. Depending on the soil’s permeability and compressibility, undrained, partially drained or drained conditions might occur. Partially drained conditions are commonly encountered in soils such as silts and sand–clay mixtures. However, this is often neglected in CPT interpretation, which may lead to inaccurate estimates of soil properties. This paper aims at improving the understanding of the penetration process in different drainage conditions through advanced numerical analyses. A two-phase Material Point Method is applied to simulate large soil deformations and generation and dissipation of excess pore pressures during penetration. The constitutive behaviour of soil is modelled with the Modified Cam Clay model. Numerical results are compared with experimental data showing good agreement. 相似文献