云南金宝山含铂钯超镁铁质侵入体中铬铁矿的成因研究     

马言胜  陶琰  钟宏  王兴阵 《矿物学报》2007,27(3):342-350

位于扬子地台西缘的金宝山岩体赋存我国最大的独立铂族元素矿床，岩体为似层状产出的小型超镁铁岩，在时间和空间上与晚二叠纪（260Ma）峨眉山大火成岩省相关。该岩体由单辉橄榄岩、辉橄岩及橄辉岩、辉石岩异离体组成。铬铁矿以副矿物形式出现，从形态上可以分为三类：包嵌于橄榄石中的自形铬铁矿、以自形或半自形体存在于辉石中铬铁矿以及环绕结构铬铁矿。其中环绕结构铬铁矿外壁浑圆，内为棱角状，其中心为橄榄石、辉石。本文在薄片观察的基础上，结合电子探针研究，认为包嵌于橄榄石中的自形铬铁矿是在岩浆早期深部岩浆房中结晶形成的；存在于辉石中的铬铁矿则是岩浆进一步结晶演化的结果，主要为就地结晶的产物；在岩体形成的过程中，作为岩体赋存空间的堆晶相与后续岩浆持续反应，使铬铁矿不断聚集和生长，最终形成了环绕橄榄石晶体的形态。铬铁矿的生成模式进一步说明了金宝山侵入体为一岩浆通道，并且经历深部结晶分异演化。  相似文献   

The impact of boundary on the fractional advection–dispersion equation for solute transport in soil: Defining the fractional dispersive flux with the Caputo derivatives     

Xiaoxian Zhang  Mouchao Lv  John W. Crawford  Iain M. Young 《Advances in water resources》2007

The inherent heterogeneity of geological media often results in anomalous dispersion for solute transport through them, and how to model it has been an interest over the past few decades. One promising approach that has been increasingly used to simulate the anomalous transport in surface and subsurface water is the fractional advection–dispersion equation (FADE), derived as a special case of the more general continuous time random walk or the stochastic continuum model. In FADE, the dispersion is not local and the solutes have appreciable probability to move long distances, and thus reach the boundary faster than predicted by the classical advection–dispersion equation (ADE). How to deal with different boundaries associated with FADE and their consequent impact is an issue that has not been thoroughly explored. In this paper we address this by taking one-dimensional solute movement in soil columns as an example. We show that the commonly used FADE with its fractional derivatives defined by the Riemann–Liouville definition is problematic and could result in unphysical results for solute transport in bounded domains; a modified method with the fractional dispersive flux defined by the Caputo derivatives is presented to overcome this problem. A finite volume approach is given to numerically solve the modified FADE and its associated boundaries. With the numerical model, we analyse the inlet-boundary treatment in displacement experiments in soil columns, and find that, as in ADE, treating the inlet as a prescribed concentration boundary gives rise to mass-balance errors and such errors could be more significant in FADE because of its non-local dispersion. We also discuss a less-documented but important issue in hydrology: how to treat the upstream boundary in analysing the lateral movement of tracer in an aquifer when the tracer is injected as a pulse. It is shown that the use of an infinite domain, as commonly assumed in literature, leads to unphysical backward dispersion, which has a significant impact on data interpretation. To avoid this, the upstream boundary should be flux-prescribed and located at the upstream edge of the injecting point. We apply the model to simulate the movement of Cl⁻ in a tracer experiment conducted in a saturated hillslope, and analyse in details the significance of upstream-boundary treatments in parameter estimation.  相似文献   

A spectral approach to simulating intrinsic random fields with power and spline generalized covariances   总被引：4，自引：0，他引：4  

Xavier Emery  Christian Lantuéjoul 《Computational Geosciences》2008,12(1):121-132

This article presents a variant of the spectral turning bands method that allows fast and accurate simulation of intrinsic random fields with power, spline, or logarithmic generalized covariances. The method is applicable in any workspace dimension and is not restricted in the number and configuration of the locations where the random field is simulated; in particular, it does not require these locations to be regularly spaced. On the basis of the central limit and Berry–Esséen theorems, an upper bound is derived for the Kolmogorov distance between the distributions of generalized increments of the simulated random fields and the normal distribution.  相似文献   

Multiphase flow modeling with general boundary conditions and automatic phase-configuration changes using a fractional-flow approach     

Heejun Suk  Gour-Tsyh Yeh 《Computational Geosciences》2008,12(4):541-571

The multiphase flow simulator moving particle semi-implicit (MPS) method is developed based on the fractional-flow approach, originated in the petroleum engineering literature, considering the fully three-phase flow with general boundary conditions. The fractional flow approach employs water saturation, total liquid saturation, and total pressure as primary variables. Most existing models based upon fractional flow are limited to two-phase flow and specific boundary conditions. Although there appear a number of three-phase flow models, they were mostly developed using pressure-based approaches, which require variable-switch techniques to deal with phase appearance and disappearance. The use of fractional flow-based approaches in MPS makes it unnecessary to use variable-switching to handle the change of phase configurations because the water saturation, total liquid saturation, and total pressure exist throughout the solution domain regardless of whether certain phases are present or not. Furthermore, most existing fractional flow-based models consider only specific boundary conditions, usually Dirichlet-type pressure for water phase and flux-type boundary for nonaqueous phase liquid or particular combinations for individual phase. However, the present model considers general boundary conditions of ten most possible and plausible cases. The first eight cases are the combinations of the phase pressure or the phase flux of each of the three individual phases. The other two cases are the variable boundary conditions: one for water-medium interface and the other for the air-medium interface when the directions of fluxes are not known a priori. Thus, the model’s capabilities of handling general boundary conditions extend the simulators’ usefulness in the field system.  相似文献   

Role of Syn-eruptive Cooling and Degassing on Textures of Lavas from the AD 1783-1784 Laki Eruption, South Iceland     

Guilbaud  M.-N.; Blake  S.; Thordarson  T.; Self  S. 《Journal of Petrology》2007,48(7):1265-1294

The Laki eruption involved 10 fissure-opening episodes thatproduced 15·1 km³ of homogeneous quartz-tholeiite magma.This study focuses on the texture and chemistry of samples fromthe first five episodes, the most productive period of the eruption.The samples comprise pumiceous tephra clasts from early falloutdeposits and lava surface samples from fire-fountaining andcone-building activity. The fluid lava core was periodicallyexposed at the surface upon lobe breakout, and its characteristicsare preserved in glassy selvages from the lava surface. In allsamples, plagioclase is the dominant mineral phase, followedby clinopyroxene and then olivine. Samples contain <7 vol.% of euhedral phenocrysts (>100 µm) with primitivecores [An* = 100 x Ca/(Ca + Na) >70; Fo > 75; En* = 100x Mg/(Mg + Fe) >78] and more evolved rims, and >10 vol.% of skeletal, densely distributed groundmass crystals (<100µm), which are similar in composition to phenocryst rims(tephra: An*_58–67, Fo_72–78, En*_72–81; lava:An*_49–70, Fo_63–78, En_57–78). Tephra and lavahave distinct vesicularity (tephra: >40 vol. %; lava: <40vol. %), groundmass crystal content (tephra: <10 vol. %;lava: 20–30 vol. %), and matrix glass composition (tephra:5·4–5·6 wt % MgO; lava: 4·3–5·0wt % MgO). Whole-rock and matrix glass compositions define atrend consistent with liquid evolution during in situ crystallizationof groundmass phases. Plagioclase–glass and olivine–glassthermometers place the formation of phenocryst cores at 10 kmdepth in a melt with 1 wt % H₂O, at near-liquidus temperatures(1150°C). Phenocryst rims and groundmass crystals formedclose to the surface, at 10–40°C melt undercoolingand in an 10–20°C cooler drier magma (0–0·1wt % H₂O), causing an 10 mol % drop in An content in plagioclase.The shape, internal zoning and number density of groundmasscrystals indicate that they formed under supersaturated conditions.Based on this information, we propose that degassing duringascent had a major role in rapidly undercooling the melt, promptingintensive shallow groundmass crystallization that affected themagma and lava rheology. Petrological and textural differencesbetween tephra and lava reflect variations in the rates of magmaascent and the timing of surface quenching during each eruptiveepisode. That in turn affected the time available for crystallizationand subsequent re-equilibration of the melt to surface (degassed)conditions. During the explosive phases, the rates of magmaascent were high enough to inhibit crystallization, yieldingcrystal-poor tephra. In contrast, pervasive groundmass crystallizationoccurred in the lava, increasing its yield strength and causinga thick rubbly layer to form during flow emplacement. Lava selvagescollected across the flow-field have strikingly homogeneousglass compositions, demonstrating the high thermal efficiencyof fluid lava transport. Cooling is estimated as 0·3°C/km,showing that rubbly surfaced flows can be as thermally efficientas tube-fed phoehoe lavas. KEY WORDS: lava; crystallization; basalt; cooling rate; pressure; geobarometry; P–T conditions; plagioclase; degassing; Laki, Iceland  相似文献   

龙木错与结则茶卡盐湖卤水兑卤及蒸发析盐规律研究   总被引：1，自引：0，他引：1  

崔玉虎  袁建军  杨美洁  沙作良 《海洋与湖沼》2014,45(2):239-243

本文以西藏龙木错与结则茶卡为对象,研究了两盐湖卤水在不同兑卤比情况下,混合卤各组分的变化,并对兑卤后的混合卤水进行了15°C蒸发过程的研究。实验分别对两种原料卤水和兑卤后卤水蒸发所得的9个卤水样品进行了常量化学组分分析,研究了兑卤后卤水蒸发过程中盐类的富集行为和析出规律。混合卤蒸发析盐规律结果基本符合Na+、K+、Mg2+//Cl–、24SO?-H2O(15°C)五元水盐体系相图。  相似文献   

On quantifying post-classification subpixel landcover changes     

《ISPRS Journal of Photogrammetry and Remote Sensing》2014

The post-classifications change matrix is well defined for hard classifications. However, for soft classifications, where partial membership of pixels to landcover classes is allowed, there is no single definition for such a matrix. In this paper, we argue that a natural definition of the post-classification change matrix for subpixel classifications can be done in terms of a constrained optimization problem, according to which the change matrix should allow an optimal prediction of the subpixel landcover fractions at the latest date from those of the earliest date. We first show that the traditional change matrix for crisp classification corresponds to the optimal solution of the unconstrained problem. Then, the formulation is generalized for subpixel classifications by incorporating certain constraints pertaining to desirable properties of a change matrix, thus resulting in a constrained least square (CLS) change matrix. In addition, based on intuitive criteria, a generalized product (GPROD) was parameterized in terms of an exponent parameter and used to derive another change matrix. It was shown that when the exponent parameter of the GPROD operator tends to infinity, one of the most commonly used methods for map comparison from subpixel fractions, namely the MINPROD composite operator, results. The three matrices (CLS, GPROD and MINPROD) were tested on both simulated and real subpixel changes derived from QuickBird and Landsat TM images. Results indicated that, for small exponent values (0–0.5), the GPROD matrix yielded the lowest errors of estimated landcover changes, whereas the MINPROD generally yielded the highest errors for the same estimations.  相似文献   

印度洋Carlsberg洋脊玄武岩岩石地球化学特征及其地质意义   总被引：2，自引：0，他引：2  

淳明浩  于增慧  翟世奎 《海洋学报》2015,37(8):47-62

本文对采自印度洋Carlsberg脊14个站位的新鲜玄武岩样品进行了常量和微量元素组成分析,旨在研究岩浆源区地幔的性质以及岩浆作用过程。研究结果表明:该区玄武岩为典型的源于亏损型地幔的大洋中脊玄武岩,不同样品经历了不同程度的结晶分异作用,演化过程主要受控于橄榄石的结晶分异作用,部分样品中有单斜辉石结晶分异作用的影响,斜长石的结晶分异作用不显著;玄武岩岩浆来源于亏损型尖晶石二辉橄榄岩地幔的熔融,主微量元素组成中尚未见到富集型组分混入的证据;源区地幔不同比例的熔融作用及其后岩浆演化过程的差异是造成不同样品间地球化学性质差异的主要原因,彼此独立的局部岩浆作用过程是岩浆作用差异的主控制因素。Carlsberg脊玄武岩整体与全球标准大洋中脊玄武岩(N-MORB)平均组分相近,不同脊段间岩浆源区地幔的组成、熔融程度(比例)和熔融深度等无明显差异,这种特征向南直到CIR的北段。  相似文献   

钙碱性火成岩的角闪石全铝压力计 ——回顾、评价和应用实例   总被引：4，自引：0，他引：4  

汪洋 《地质论评》2014,60(4):839-850

定量地获得岩体结晶时的压力,对于探讨其剥蚀深度及了解造山带的构造热演化史等方面有重要意义。对于钙碱性侵入岩而言,可以应用角闪石全铝压力计对钙碱性火成岩结晶压力进行估计。对于不同角闪石压力计公式的选择,前提是满足它们各自的适用条件,否则所得结果没有意义。角闪石全铝压力计不能用于估算A型花岗岩的结晶压力,更不能用于计算变质岩的变质压力。对于结晶温度低于750℃的钙碱性中酸性岩体而言,Anderson和Smith(1995)的温度校正意义不大。Ridolfi等(2010)提出的指数关系角闪石压力计公式适用于钙碱性火山岩中角闪石斑晶的结晶压力估算。Uchida等(2007)的黑云母全铝压力计缺乏理论和实验基础,不建议使用。应用角闪石全铝压力计所得到薛家石梁—黑山寨复式岩体侵位深度的区域变化,指示了云蒙山变质核杂岩下盘的掀斜;低角度正断层(拆离断层)可以通过高角度正断层的掀斜旋转而形成。  相似文献   

攀枝花岩体钛铁矿成分特征及其成因意义   总被引：2，自引：1，他引：1  

郑文勤  邓宇峰  宋谢炎  陈列锰  于宋月  周国富  刘世荣  向建新 《岩石学报》2014,30(5):1432-1442

峨眉大火成岩省是全球最大的钒钛磁铁矿床聚集区,攀枝花岩体是其中的典型代表。根据岩性特点,攀枝花岩体主体可划分为上、中、下三个岩相带,其中中部岩相带和下部岩相带岩性旋回非常发育,每个旋回从下向上铁钛氧化物和暗色硅酸盐矿物逐渐减少,块状铁钛氧化物矿石或磁铁矿辉长岩都出现在每个旋回的底部和下部。然而,尽管钛铁矿固相线以下固溶体出溶远弱于磁铁矿,从而能更好地保留成因信息,但其成分变化的成因意义没有受到足够重视。本次研究发现作为主要金属氧化物之一的钛铁矿的成分不仅在不同岩性中有明显差异,同时,中、下部岩相带的各岩性旋回中钛铁矿成分也具有周期性变化。例如,块状矿石中钛铁矿具有最高的MgO和TiO2及最低的FeO、Fe2O3和MnO,而辉长岩中钛铁矿则具有相反的成分特征。同时,钛铁矿的MgO含量与磁铁矿的MgO含量及橄榄石的Fo牌号具有显著的正相关关系。这种规律性变化说明每个旋回可以代表一次比较明显的岩浆补充,每次新岩浆补充后,钛铁矿和磁铁矿及橄榄石都是结晶较早的矿物。与Skaergaard岩体相比,攀枝花岩体钛铁矿的MgO含量较高,表明攀枝花岩体分离结晶过程中铁钛氧化物结晶较早;与挪威Tellnes斜长岩套铁钛矿床中的钛铁矿相比,攀枝花岩体的钛铁矿不仅具有较高的MgO和FeO,还具有极高的TiO2和MnO,但Fe2O3却很低,说明地幔柱背景下形成的钛铁矿与斜长岩套中钛铁矿的成分有显著的区别。  相似文献