首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
《Chemical Geology》2002,182(2-4):473-482
Three lithological Groups I (medium-grained, with magmatogenic arfvedsonite), II (medium-grained, with secondary arfvedsonite) and III (fine-grained, with magmatogenic arfvedsonite) are identified in the Saertielieke alkali granite pluton, Ulungur of the northern Xinjiang, China. A weak negative correlation between the δ18O values of alkali feldspar and quartz separates from each group, and the distinctly lower δ18O values of alkali feldspar separates from Groups I and II than those from Group III are interpreted in terms of superimposed closed-system and open-system isotope exchange. A small amount of locally exsolved magmatic fluid is involved in the development of the perthitic texture in alkali feldspar at ∼400 °C that results in a volume increase and, hence, causes quartz deformation. The microtextural changes promote the closed-system oxygen isotope exchange between quartz and alkali feldspar that causes a dispersion in the quartz δ18O values. However, the distinctly lower δ18O values of alkali feldspar and secondary arfvedsonite coupled with their microtextural characteristics indicate that meteoric-derived water plays an important role in the further development of alkali feldspar exsolution texture at T<400 °C and directly causes secondary arfvedsonite formation. The estimated relative exchange rates kQuartz/kFeldspar/kArfvedsonite of ∼10/100/1 for Groups I and III, and ∼10/100/100 for Group II suggest that alkali feldspar, quartz, and secondary arfvedsonite have exchanged with meteoric-derived water mainly via dissolution–reprecipitation, whereas magmatogenic arfvedsonite has exchanged via diffusion.  相似文献   

2.
A microstructural and metamorphic study of a naturally deformed medium‐ to high‐pressure granitic orthogneiss (Orlica–?nie?nik dome, Bohemian Massif) provides evidence of behaviour of the felsic crust during progressive burial along a subduction‐type apparent thermal gradient (～10 °C km?1). The granitic orthogneisses develops three distinct microstructural types, as follows: type I – augen orthogneiss, type II – banded orthogneiss and type III – mylonitic orthogneiss, each representing an evolutionary stage of a progressively deformed granite. Type I orthogneiss is composed of partially recrystallized K‐feldspar porphyroclasts surrounded by wide fronts of myrmekite, fully recrystallized quartz aggregates and interconnected monomineralic layers of recrystallized plagioclase. Compositional layering in the type II orthogneiss is defined by plagioclase‐ and K‐feldspar‐rich layers, both of which show an increasing proportion of interstitial minerals, as well as the deformation of recrystallized myrmekite fronts. Type III orthogneiss shows relicts of quartz and K‐feldspar ribbons preserved in a fine‐grained polymineralic matrix. All three types have the same assemblage (quartz + plagioclase + K‐feldspar + muscovite + biotite + garnet + sphene ± ilmenite), but show systematic variations in the composition of muscovite and garnet from types I to III. This is consistent with the equilibration of the three types at different positions along a prograde P?T path ranging from <15 kbar and <700 °C (type I orthogneiss) to 19–20 kbar and >700 °C (types II and III orthogneisses). The deformation types thus do not represent evolutionary stages of a highly partitioned deformation at constant P?T conditions, but reflect progressive formation during the burial of the continental crust. The microstructures of the type I and type II orthogneisses result from the dislocation creep of quartz and K‐feldspar whereas a grain boundary sliding‐dominated diffusion creep regime is the characteristic of the type III orthogneiss. Strain weakening related to the transition from type I to type II microstructures was enhanced by the recrystallization of wide myrmekite fronts, and plagioclase and quartz, and further weakening and strain localization in type III orthogneiss occurred via grain boundary sliding‐enhanced diffusion creep. The potential role of incipient melting in strain localization is discussed.  相似文献   

3.
Thermoluminescence dating of potassium feldspar coarse grains from the fossiliferous Holsteinian marine formation of Herzeele, at the southern limit of the North Sea Basin, yields a minimum age of 228 £ 30 ka. A tentative correction for the long-term fading of the TL signal in potassium feldspar is proposed, assuming a lifetime (τ) of 711 ka. This correction would yield a preliminary age estimate of 271 £ 36 ka. These results support a minimum Oxygen Isotope Stage 7 age, but do not preclude, at this stage of our research, a possible correlation with late Oxygen Isotope Stage 9. These results are in agreement, within the error of the method, with independent absolute dates (U-Th and ESR) obtained on in situ marine shells, which range from 225 ka to 348 ka. This study provides evidence of the reliability of TL age estimates on potassium feldspar coarse grains from shallow-marine sediments older than the Last Interglacial.  相似文献   

4.
In the current study, an integration of Enhanced Thematic Mapper Plus (ETM+), field, and laboratory data have been used for lithological mapping of different granitic phases in the Kadabora area, Eastern Desert, Egypt. Application of enhancement techniques, including a new proposed band ratio combination (ratio 5/3, 3/1, 7/5 in RGB, respectively) and supervised classification images are used in discriminating different granitic phases in the Kadabora pluton from each other and from their environs. The data have been proved with the help of field and geochemical investigations. The results revealed that: (1) the Kadabora granitic pluton could be distinguished into three phases that recognized by field and laboratory investigation including granodiorite (phase I), monzogranite (phase II), and syeno-alkali feldspar granite (phase III). These phases are arranged according to their relative ages while the country rocks include ophiolitic mélange and metagabbro–diorite complex. It is also confirmed that the granitic pluton is invaded by dyke swarms which is trending in N–S direction. Geochemically, results show that the granodiorite is calc-alkaline, I-type and formed under subduction tectonic regime. Monzogranite falls within the alkaline and highly fractionated calc-alkaline granites, whereas syeno-alkali feldspar granite extends into proper alkaline granitoids field. Monzogranite and syeno-alkali feldspar granite belong to the A2-subtype granite. This A2-subtype granite was probably formed in an extensional regime, subsequent to subduction which can lead to tensional break-up of the crust (i.e., post-collisional, post-orogenic granites). The monzogranite and the syeno-alkali feldspar granite were probably formed by partial melting of relatively anhydrous lower crust source and/or tonalite to granodiorite is viable alternative to the granulite source.  相似文献   

5.
X-ray diffraction (XRD), X-ray Fluorescence (XRF), optical microscopy, Scanning Electron Microscopy coupled with Energy Dispersive Spectrometry (SEM-EDS) and Electron Probe micro-analyser (EPMA) and Wavelength-Dispersive Spectroscopy (WDS) were conducted on charnockite from the Caparaó Suite and its alteration cortex to determine the mineralogical, micromorphological and geochemical transformations resulting from the weathering process. The hydrolysis of the charnockite occurred in different stages, in accordance with the order of stability of the minerals with respect to weathering: andesine/orthopyroxene, pargasite and alkali feldspar. The rock modifications had begun with the formation of a layer of incipient alteration due to the percolation of weathering solutions first in the pressure relief fractures and then in cleavage and mineral edges. The iron exuded from ferromagnesian minerals precipitated in the intermineral and intramineral discontinuities. The layer of incipient alteration evolves into an inner cortex where the plagioclase changes into gibbsite by direct alitisation, the ferromagnesian minerals initiate the formation of goethitic boxworks with kaolinitic cores, and the alkali feldspar initiates indirect transformation into gibbsite, forming an intermediate phase of illite and kaolinite. In the outer cortex, mostly traces of alkali feldspar remain, and they are surrounded by goethite and gibbsite as alteromorphics, characterising the formation of the isalteritic horizon that occurs along the slope and explains the bauxitization process at the Caparaó Range, SE Brazil.  相似文献   

6.
徐海军  张超  武云  陶明 《地球科学》2016,41(9):1511-1525
文象花岗岩具有特殊文象结构,研究其三维拓扑结构和形成过程有助于了解花岗质岩石的结晶作用.以北京周口店房山岩体和湖北罗田蕙兰山的文象花岗岩为研究对象,综合利用光学显微镜、扫描电镜、电子探针和电子背散射衍射等技术方法,对岩石矿物组成、结晶学取向和拓扑结构进行了系统研究.结果表明:(1) 文象花岗岩的矿物组成与其形成地质环境有关,石英和长石的含量变化范围很大,其中石英含量通常在20%~45%,但是相同地区同期形成的文象花岗岩具有相对稳定的矿物组成;(2) 长石作为寄主矿物通常呈半自形－自形粗大晶体,可以是碱性长石或斜长石,其端元组分以钾长石和钠长石为主,低温下常分解为条纹长石;(3) 石英在长石寄主矿物中规则穿插生长,在三维空间通常呈近似平行板状、长条状/柱状或非连通枝杈状,并只在特定岩石断面形似象形文字;(4) 正交偏光显微镜下,石英可以具有多种消光位,但是通常在一定范围内同时消光;(5) 石英普遍发育道芬双晶,偶见日本双晶;(6) 条纹长石中钾长石与钠长石对应(100)、(010)、(001) 面和[001]轴近似平行;(7) 多数石英颗粒与寄主长石之间具有密切结晶学取向关系,即石英[1123]轴近似平行长石c[001]轴.该研究证实文象花岗岩是石英和长石同时生长的结果,而长石作为寄主矿物影响并控制着石英的成核与生长方向.   相似文献   

7.
Polymict cristalline breccias are typical impact products of the Ries crater. They occur within the Ries crater (Appetshofen, Lierheim, Leopold Meyers Keller), on its rim (Maihingen-Klostermühle) and within the immediate vicinity of the crater (Itzing). Apart from very rare admixtures of sedimentary rock fragments the polymict cristalline breccias consist almost exclusively of fragments of various cristalline rocks, namely granites, gneisses and amphibolites. The petrographical and statistical investigations have shown that breccias from different localities have different composition. This reflects a possible difference in local compositions of the cristalline basement. The rocks in the breccias have been affected to various degress by shock metamorphism. The amphibolites could thus be shown to belong predominantly to stage I (diaplectic quartz and feldspar, 100–300 kb) and stage II (diaplectic quartz and feldspar glasses, 350–500 kb) whereas the granites and geisses can be attributed mostly to stage 0 (fractured quartz and feldspar, <100 kb) and stage I. This is in part the result of the bulk shock wave impedance of the rocks in question.Deformation structures resulting from shock metamorphism have been observed for the first time in sphene as well as in various planes of apatite.A large part of breccia rocks, which contain diaplectic quartz and feldspar glasses were altered into montmorillonite at a later date. The authigenic minerals were examined by x-rays and chemically by microprobe analysis.

Herrn Prof. Dr. W. von Engelhardt danke ich für Diskussion und Beratung. Dem Bundesministerium für Bildung und Wissenschaft sei für die finanzielle Unterstützung dieser Arbeit gedankt.  相似文献   

8.
A polycrystalline grain of granitic composition with compound feldspar and quartz overgrowths is described from the continental Helsby Sandstone Formation (Triassic; Sherwood Sandstone Group) of the Cheshire Basin, northwest England. Overgrown phases, as seen by thin section and scanning electron microscopy, are in crystallographic continuity with respective components of the host grain and have mutual relationships which indicate the quartz to be the later diagenetic phase. Energy dispersive spectrometry (EDS) of the grain surface and of the earlier formed overgrowths indicates the feldspar to have a potassium aluminosilicate composition which is in accordance with the adularia-habit crystal form of the authigenic phase.  相似文献   

9.
赞比亚东北部伊鲁米德带是一个北东向延伸的中元古代构造活动带,起自赞比亚中部,向北东一直延伸至赞比亚-坦桑尼亚边境,并进入马拉维北部;其东北部以古元古代乌本迪构造带为界;西北部以班韦乌卢地块为界;西部和西南部受新元古代的达马拉-卢菲利安弧-赞比西构造事件的影响.Kachinga长石砂岩位于伊鲁米德带的东北部伊索卡南部.本文获得Kachinga长石砂岩的416颗碎屑锆石U-Pb年龄多集中在1749±25～1920±23Ma之间,Kachinga长石砂岩的形成时代可能晚于1331±26Ma,属于中元古代.Kachinga长石砂岩碎屑锆石CL图像表明,大部分锆石为岩浆结晶锆石,少部分锆石颗粒为增生-混合型锆石,表明其经历了多期构造-热事件的改造.锆石中存在有一部分磨圆度较好的颗粒,表明其经历了多次搬运和沉积过程,从而指示了古老沉积岩为Kachinga长石砂岩提供了物源.主量元素、微量元素和稀土元素构造环境判别及物源分析表明了Kachinga长石砂岩物源主要为上地壳大陆长英质源区,并且可能混有古老沉积物成分,物源区构造背景为大陆岛弧环境.  相似文献   

10.
花岗岩是陶瓷工业中所需长石原料的重要来源之一.由于花岗岩中云母和氧化铁的存在,其最终产品的质量受到影响（强度、硬度、密度降低）.本研究对浙江花岗岩采用两阶段分离方法,以提高花岗岩中长石的质量.第一阶段为重力分离,去除重矿物杂质;第二阶段为磁性分离,进一步减少铁含量.用机械方法对不同加工阶段的3种样品进行了成分测试：1）原料花岗岩;2）第一阶段处理的花岗岩;3）第二阶段处理的花岗岩.结果显示,最终处理后的样品较之原始花岗岩在显微硬度、强度、密度及裂隙坚韧性方面都有明显提高.  相似文献   

11.
The weight-percent values of four mineralogic variables (quartz, K feldspar, color index, and muscovite) for 10 sets of granitic rocks (20–50 samples in each set) from magmatic units of the Singhbhum granite were used for (1) computation of the Mahalanobis' generalized distance functions (D 2) between all pairs of the 10 sets, (2) testing significance of the difference between the multivariate means, and (3) computation of the linear discriminant functions between all possible pairs of the sets. The 10 data sets are for six magmatic units which belong to three successive but closely related phases of emplacement. The multivariate means for all sets are significantly different except for those between two of the sets of phase I. Cluster analysis on the basis of theD 2 values enables the 10 sets to be placed into four distinct groups. Group A includes two subgroups, one of which consists of two sets representing typical members of phase I; the other subgroup includes two sets which are typical of phase II. Group B includes two sets which are typical of phase III. The other four sets do not group with the typical representatives of the three phases, probably because of certain special conditions of their emplacement. A separate series ofD 2 computation from the same data, but excluding the color index, was unsuccessful in making the four aberrant sets group with the typical members of the respective phases. Efficient LDF's could be determined for discrimination between most pairs of the 10 sets of granite rocks.  相似文献   

12.
Batch reactor experiments were conducted to assess perthitic alkali-feldspar dissolution and secondary mineral formation in an initially acidic fluid (pH = 3.1) at 200 °C and 300 bars. Temporal evolution of fluid chemistry was monitored by major element analysis of in situ fluid samples. Solid reaction products were retrieved from two identical experiments terminated after 5 and 78 days. Scanning electron microscopy revealed dissolution features and significant secondary mineral coverage on feldspar surfaces. Boehmite and kaolinite were identified as secondary minerals by X-ray diffraction and transmission electron microscopy. X-ray photoelectron spectroscopy analysis of alkali-feldspar surfaces before and after reaction showed a trend of increasing Al/Si ratios and decreasing K/Al ratios with reaction progress, consistent with the formation of boehmite and kaolinite.Saturation indices of feldspars and secondary minerals suggest that albite dissolution occurred throughout the experiments, while K-feldspar exceeded saturation after 216 h of reaction. Reactions proceeded slowly and full equilibrium was not achieved, the relatively high temperature of the experiments notwithstanding. Thus, time series observations indicate continuous supersaturation with respect to boehmite and kaolinite, although the extent of this decreased with reaction progress as the driving force for albite dissolution decreased. The first experimental evidence of metastable co-existence of boehmite, kaolinite and alkali feldspar in the feldspar hydrolysis system is consistent with theoretical models of mineral dissolution/precipitation kinetics where the ratio of the secondary mineral precipitation rate constant to the rate constant of feldspar dissolution is well below unity. This has important implications for modeling the time-dependent evolution of feldspar dissolution and secondary mineral formation in natural systems.  相似文献   

13.
Authigenic minerals and the diagenetic sequence of the dawsonite-bearing sandstones from the Binnan Region of the Dongying Sag, Bohai Bay Basin, China were studied to understand the formation of dawsonite, as a possible mechanism for mineral trapping of CO2 in carbon capture and storage (CCS) programmes. Authigenic minerals include quartz overgrowth, dawsonite (5–15 vol%), calcite, ferrocalcite and ankerite. The major rock types are medium- to fine-grained arkose, feldspathic litharenite and lithic arkose. Quantitative analysis suggests that the burial depth and feldspar content are the two dominant controlling factors of the growth of dawsonite. The dawsonite content increases initially before decreasing with burial depth, with the peak dawsonite content occurring at approximately 1500 m depth. This trend is probably due to increases in temperature and pCO2 with the burial depth and contributes to the formation of dawsonite. However, the pCO2 content and stability of dawsonite decrease with increasing distance from the centre of the gas reservoir. When the formation temperature exceeds the upper limit of the preservation temperature of dawsonite, the dawsonite is suppressed, while the dissolution of dawsonite is promoted. Overall, the dawsonite content exhibits a positive correlation with the feldspar content. The dissolution of feldspar makes both Na+ and Al3+ available and creates the accommodation space necessary for dawsonite growth. In addition, feldspar dissolution also neutralises the acidity of the thermal fluid present, which again facilitates the growth and preservation of the dawsonite.  相似文献   

14.
Ute Mann  Michael Marks  Gregor Markl   《Lithos》2006,91(1-4):262-285
The igneous rocks of the Katzenbuckel, Southwest Germany, represent a unique and unusual alkaline to peralkaline association within the European Volcanic Province. The magmatic activity can be subdivided into two main phases. Phase I comprises the main rock bodies of phonolite and nepheline syenite, which were later intruded by different peralkaline dyke rocks (tinguaites and alkali feldspar syenite dykes) of phase II. The dyke assemblage was accompanied by magnetite and apatite veins and was followed by a late-stage pneumatolytic activity causing autometasomatic alterations.

As is typical for alkaline to peralkaline igneous rocks, early mafic minerals of phase I rocks comprise olivine, augite and Fe–Ti oxides, which are substituted in the course of fractionation by Na-amphibole and Na-pyroxene. For the early magmatic stage, calculated temperatures range between 880 and 780 °C with low silica activities (0.4 to 0.6) but high relative oxygen fugacities between 0.5 and 1.9 log units above the FMQ buffer. Even higher oxygen fugacities (above the HM buffer) are indicated for the autometasomatic alteration, which occurred at temperatures between 585 and 780 °C and resulted in the formation of pseudobrookite and hematite.

The unusually high oxygen fugacities (even during the early magmatic stage) are recorded by the major element compositions of the mafic minerals (forsterite content in olivine between 68 and 78 mol%, up to 6.2 wt.% ZrO2 and 8.5 wt.% TiO2 in clinopyroxene), the unusual mineral assemblages (pseudobrookite, freudenbergite) and by the enrichment of Fe3+ in the felsic minerals (up to 2.8 wt.% Fe2O3 in alkali feldspar and up to 2.6 wt.% Fe2O3 in nepheline). These observations point to a metasomatically enriched and highly oxidized lithospheric mantle as a major source for the Katzenbuckel melts.  相似文献   


15.
The Pongkor gold–silver mine is situated at the northeastern flank of the Bayah dome, which is a product of volcanism in the Sunda–Banda Arc. The hydrothermal alteration minerals in the Ciurug–Cikoret area are typical of those formed from acid to near‐neutral pH thermal waters. On the surface, illite/smectite mixed layer mineral (I/Sm), smectite and kaolinite, and spotting illite, I/Sm and K‐feldspar alteration occur at the top of the mineralized zone. Silicification, K‐feldspar and I/Sm zones are commonly formed in the wall rock, and gradually grade outwards into a propylitic zone. The mineralization of precious metal ore zone is constrained by fluid temperatures between 180 and 220°C, and with low salinity (<0.2 wt% NaCl equivalent) and boiling condition. The minimum depth of vein formation below the paleo‐water table is approximately 90–130 m for the hydrostatic column. Hydrogen and oxygen isotope data for quartz and calcite show relatively homogeneous fluid composition (?53 to ?68‰δD and ?5.7 to +0.3‰δ18O H2O). There is no specific trend in the data with respect to the mineralization stages and elevation, which suggests that the ore‐forming fluids did not significantly change spatially during the vein formation. The stable isotope data indicate mixing between the hydrothermal fluids and meteoric water and interaction between the hydrothermal fluids and the host rock.  相似文献   

16.
In order to evaluate the complex interplay between dissolution and precipitation reaction kinetics, we examined the hypothesis of partial equilibria between secondary mineral products and aqueous solutions in feldspar-water systems. Speciation and solubility geochemical modeling was used to compute the saturation indices (SI) for product minerals in batch feldspar dissolution experiments at elevated temperatures and pressures and to trace the reaction paths on activity-activity diagrams. The modeling results demonstrated: (1) the experimental aqueous solutions were supersaturated with respect to product minerals for almost the entire duration of the experiments; (2) the aqueous solution chemistry did not evolve along the phase boundaries but crossed the phase boundaries at oblique angles; and (3) the earlier precipitated product minerals did not dissolve but continued to precipitate even after the solution chemistry had evolved into the stability fields of minerals lower in the paragenesis sequence. These three lines of evidence signify that product mineral precipitation is a slow kinetic process and partial equilibria between aqueous solution and product minerals were not held. In contrast, the experimental evidences are consistent with the hypothesis of strong coupling of mineral dissolution/precipitation kinetics [e.g., Zhu C., Blum A. E. and Veblen D. R. (2004a) Feldspar dissolution rates and clay precipitation in the Navajo aquifer at Black Mesa, Arizona, USA. In Water-Rock Interaction (eds. R. B. Wanty and R. R. I. Seal). A.A. Balkema, Saratoga Springs, New York. pp. 895-899]. In all batch experiments examined, the time of congruent feldspar dissolution was short and supersaturation with respect to the product minerals was reached within a short period of time. The experimental system progressed from a dissolution driven regime to a precipitation limited regime in a short order. The results of this study suggest a complex feedback between dissolution and precipitation reaction kinetics, which needs to be considered in the interpretation of field based dissolution rates.  相似文献   

17.
Shallowly plunging and branching pipe systems in Lease and Bobbejaankop Granite at the Zaaiplaats mine are host to major tin mineralization. Detailed textural study of Maggs Pipe indicates that dissolution of the granite was a major process in the formation of open space which provided permeability for the passage of hydrothermal fluids, and sites for the precipitation of ore and gangue minerals. The pipe formation process initiates with the dissolution of granite quartz and subsequently extends to feldspar dissolution, particularly in the central portion of Maggs Pipe. Spaces created by mineral dissolution are filled by hydrothermal phases and the relict feldspar matrix becomes progressively more altered toward the centre of the pipe. The distribution of alteration and infill minerals defines a zoning pattern which, from the outer margin to the central core, includes calcite-quartz, chlorite (± cassiterite, albite, fluorite) and synchisite-calcite zones. It is postulated that quartz and feldspar dissolution resulted from interaction between the granite and hydrothermal fluids containing alkali-chloride, -fluoride or -carbonate complexes which had separated from the granite magma during crystallization. Preliminary observations on several other pipes at Zaaiplaats indicate that quartz and feldspar dissolution was a major procress in forming the pipe systems.  相似文献   

18.
对大兴安岭伊勒呼里山早白垩世碱长花岗岩进行了岩相学、地球化学、LA-ICP-MS锆石U-Pb定年研究。伊勒呼里山地区碱长花岗岩主量元素具有富Si、富碱,贫Mg、Ca的特征;微量元素亏损Sr、P、Eu、Ti,富集K、Rb、Th等不相容元素,元素地球化学特征表明,岩体为铝质A型花岗岩(A/CNK=0.88~1.21,A/NK=0.94~1.49)。测年结果显示,粗中粒碱长花岗岩的锆石年龄为140.3±1.0Ma,细中粒碱长花岗岩锆石年龄为137.9±0.8Ma,均形成于早白垩世。结合区域研究资料,伊勒呼里山地区碱长花岗岩岩体的形成与蒙古-鄂霍茨克洋闭合后的岩石圈伸展密切相关,其岩浆源区可能为地壳物质的部分熔融。  相似文献   

19.
根据我国鄂尔多斯盆地上古生界和四川盆地三叠系须家河组砂岩成岩作用和次生孔隙形成机制的研究,总结了碎屑岩成岩过程中长石、高岭石、伊利石之间的物质交换及其对次生孔隙形成的影响。研究表明：（1）砂岩埋藏前组成中长石的类型及相对含量、含膨胀层的粘土矿物（如同期火山物质）的数量、系统的开放性与封闭性以及流体中额外钾离子的存在与否直接控制了长石的溶解方式和次生孔隙的形成机制;（2）在热力学上最不稳定且低温条件下更易溶解的偏基性斜长石在同生到埋藏成岩作用初期已大量溶解,并伴随高岭石的沉淀,在热力学上相对稳定的钾长石是保存时间最长的长石类型,也是以后埋藏成岩过程中对次生孔隙贡献最多的长石类型;（3）在埋藏成岩作用初期到120—140℃古地温以前的成岩阶段中,蒙皂石．伊利石的转化反应是克服埋藏成岩过程中钾长石溶解动力学屏障的重要机制,如果骨架颗粒中存在较多的钾长石和较多的含膨胀层的粘土矿物,则次生孔隙主要由钾长石溶解提供,并有斜长石的钠长石化或自生钠长石沉淀,这是鄂尔多斯盆地上古生界石盒子组和三叠系延长组次生孔隙的主要形成机制;（4）在120～140℃古地温以后的深埋藏成岩阶段中,高岭石的伊利石化是克服埋藏成岩过程中钾长石溶解动力学屏障的另一重要机制,而钾长石的溶解又是封闭条件下高岭石的伊利石化的必要伴随反应,地层中钾长石和高岭石的相对数量控制了长石的溶解以及溶解产物中钾长石、高岭石、伊利石三种矿物间的数量关系,只要地层中钾长石（或高岭石）没有消耗完,钾长石的溶解和高岭石伊利石化反应就会持续发生并在深埋藏条件下形成次生孔隙,这是鄂尔多斯盆地东部太原组和四川盆地三叠系须家河组二段砂岩?  相似文献   

20.
 Lherzolite xenoliths in Miocene to Pleistocene basalts from five sites in the Hamar-Daban range in southern Siberia provide sampling of the mantle close to the axis of the Baikal rift. These anhydrous spinel lherzolites commonly have foliated fabrics and spongy rims around clinopyroxene, and many contain accessory feldspar. The feldspar occurs in reaction zones adjacent to spinel and orthopyroxene (where it appears to have been formed by the reaction: spl+opx+cpx+fluid →fs+ol) and less commonly as thin, irregular veins. The feldspars have variable compositions but are generally alkali-rich; their K2O content ranges from 0.3 to 11.2% and is much higher than in plagioclase from orogenic lherzolites (usually <0.1% K2O). The temperature range for the Hamar-Daban xenolith suite (950–1010° C) is more restricted than for spinel peridotite xenoliths from other occurrences in the Baikal area. The feldspar-bearing lherzolites yield equilibration temperatures similar to or slightly lower than feldspar-free ones. The majority of the Hamar-Daban lherzolites are fertile and clinopyroxene-rich, as for most other occurrences in the Baikal region. Trace element compositions of selected xenoliths and their clinopyroxenes were determined by ICP-MS, INAA and proton microprobe. Feldspar-bearing xenoliths are enriched in alkalies indicating that feldspar formation is associated with addition of material and is not simply due to isochemical phase changes. Most xenoliths and their clinopyroxenes studied are depleted in light REE and have contents of Sr, Zr and Y common for fertile or moderately depleted mantle peridotites. Few are moderately enriched in LREE, Sr, Th and U. Sr-Nd isotope compositions of clinopyroxenes indicate long-term depletion in incompatible elements similar to unmetasomatised xenoliths from other occurrences south and east of Lake Baikal. The formation of feldspar and of spongy aggregates after clinopyroxene, and the enrichment in alkalies appear to be recent phenomena related to infiltration of an alkali-rich, H2O-poor fluid into spinel peridotites. Received: 20 March 1995 / Accepted: 26 June 1995  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号