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1.
Abstract Five basalt samples from the Point Sal ophiolite, California, were examined using HRTEM and AEM in order to compare observations with interpretations of XRD patterns and microprobe analyses. XRD data from ethylene-glycol-saturated samples indicate the following percentages of chlorite in mixed-layer chlorite–smectite identified for each specimen: (i) L2036 ± 50%, (ii) L2035 ± 70 and 20%, (iii) 1A-13 ± 70%, (iv) 1B-42 ± 70%, and (v) 1B-55 = 100%. Detailed electron microprobe analyses show that 'chlorite'analyses with high Si, K, Na and Ca contents are the result of interlayering with smectite-like layers. The Fe/(Fe + Mg) ratios of mixed-layer phyllosilicates from Point Sal samples are influenced by the bulk rock composition, not by the percentage of chlorite nor the structure of the phyllosilicate.
Measurements of lattice-fringe images indicate that both smectite and chlorite layers are present in the Point Sal samples in abundances similar to those predicted with XRD techniques and that regular alternation of chlorite and smectite occurs at the unit-cell scale. Both 10- and 14-Å layers were recorded with HRTEM and interpreted to be smectite and chlorite, respectively. Regular alternation of chlorite and smectite (24-Å periodicity) occurs in upper lava samples L2036 and 1A-13, and lower lava sample 1B-42 for as many as seven alternations per crystallite with local layer mistakes. Sample L2035 shows disordered alternation of chlorite and smectite, with juxtaposition of smectite-like layers, suggesting that randomly interlayered chlorite (<0.5)–smectite exists. Images of lower lava sample 1B-55 show predominantly 14-Å layers. Units of 24 Å tend to cluster in what may otherwise appear to be disordered mixtures, suggesting the existence of a corrensite end-member having thermodynamic significance. 相似文献
Measurements of lattice-fringe images indicate that both smectite and chlorite layers are present in the Point Sal samples in abundances similar to those predicted with XRD techniques and that regular alternation of chlorite and smectite occurs at the unit-cell scale. Both 10- and 14-Å layers were recorded with HRTEM and interpreted to be smectite and chlorite, respectively. Regular alternation of chlorite and smectite (24-Å periodicity) occurs in upper lava samples L2036 and 1A-13, and lower lava sample 1B-42 for as many as seven alternations per crystallite with local layer mistakes. Sample L2035 shows disordered alternation of chlorite and smectite, with juxtaposition of smectite-like layers, suggesting that randomly interlayered chlorite (<0.5)–smectite exists. Images of lower lava sample 1B-55 show predominantly 14-Å layers. Units of 24 Å tend to cluster in what may otherwise appear to be disordered mixtures, suggesting the existence of a corrensite end-member having thermodynamic significance. 相似文献
2.
粘土矿物组合和绿泥石成分常被用来讨论盆地沉积物的成岩作用和埋藏古温度。许多沉积盆地的研究结果显示,泥 岩和页岩中的粘土矿物组合和绿泥石的成分与埋藏深度/温度有关。但也见有例外的现象存在。文中主要探讨了新疆塔北隆 起泥岩中的粘土矿物组合和绿泥石成分的特征,以及与盆地古盐度的关系。研究结果表明：（1）在塔北隆起泥岩中,埋藏 深度2777.37~4604.41m,地层单位为J1-N2的粘土矿物组合为I+Chl和I+Chl+Ka; 埋藏深度5071.52~5299.37m,地层单位为 T1的粘土矿物组合为R0I/S+I+Chl和R0I/S+Chl。（2）研究区的成岩绿泥石为Ⅱb型铁镁绿泥石,其成分特征主要表现为： ①配位八面体中阳离子的占位数为11.532(总平均值);②ⅥAl含量明显大于ⅣAl含量;③（Fe+Mg）为4.016（总平均值）;④ Si/Al比值>1。（3）根据研究区盐类矿物的分布范围以及古盐度的数据,讨论了古盐度对该区粘土矿物组合和绿泥石成分的 影响,指出古盐度是影响本区粘土矿物组合和绿泥石成分变化的主要因素。用古盐度解释了<5000m深度的粘土矿物组合 中不含无序伊/蒙混层（R0I/S）矿物,而>5000m深度粘土矿物组合中含有无序伊/蒙混层（R0I/S）矿物的异常现象。揭示了 在一定的深度范围（2777.37~4405.27m）,一定的古盐度条件下（Sr/Ba比值≥0.4,并有盐类矿物出现）,绿泥石成分受到 古盐度的制约,并且随着古盐度的增高,绿泥石成分中的Al、ⅣAl、Na、Na2O、Al/Si随之增高,而Si/Al则随之降低。由 绿泥石成分温度计获得的温度值也伴随着古盐度的增高而增高。因此,由绿泥石成分温度计所计算的温度不能代表本区实 际埋藏的古温度。（4）研究区内绿泥石成分中的SiO2和FeO与母岩的对应成分之间有一定的相关性,其SiO2绿泥石与SiO2岩石、 FeO绿泥石与FeO岩石呈负相关的线性关系,并且这种关系在古盐度的干扰下也未受到影响。 相似文献
3.
Phyllosilicates occurring as replacements of olivine, clinopyroxene and interstitial materials and as veins or fracture-fillings in hydrothermally altered basalts from DSDP Hole 504B, Leg 83 have been studied using transmission and analytical electron microscopy. The parageneses of phyllosilicates generally change systematically with depth and with the degree of alteration, which in turn is related to permeability of basalts. Saponite and some mixed-layer chlorite/smectite are the dominant phyllosilicates at the top of the transition zone. Chlorite, corrensite, and mixed-layer chlorite/corrensite occur mainly in the lower transition zone and upper levels of the sheeted dike zone. Chlorite, talc, and mixed-layer talc/chlorite are the major phyllosilicates in the sheeted dike zone, although replacement of talc or ohvine by saponite is observed. The phyllosilicates consist of parallel or subparallel discrete packets of coherent layers with packet thicknesses generally ranging from< 100 Å to a few hundred Å. The packets of saponite layers are much smaller or less well defined than those of chlorite, corrensite and talc, indicating poorer crystal-linity of saponite. by contrast, chlorite and talc from the lower transition zone and the sheeted dike zone occur in packets up to thousands of Å thick. The Si/(Si+Al) ratio of these trioctahedral phyllosilicates increases and Fe/(Fe+Mg) decreases in the order chlorite, corrensite, saponite, and talc. These relations reflect optimal solid solution consistent with minimum misfit of articulated octahedral and tetrahedral sheets. Variations in composition of hydrothermal fluids and precursor minerals, especially in Si/(Si+Al) and Fe/(Fe+Mg) ratios, are thus important factors in controlling the parageneses of phyllosilicates. The phyllosilicates are generally well crystallized discrete phases, rather than mixed-layered phases, where they have been affected by relatively high fluid/rock ratios as in high-permeability basalts, in veins, or areas adjacent to veins. Intense alteration in basalts with high permeability (indicating high fluid/rock ratios) is characterized by pervasive albitization and zeolitization. Minimal alteration in the basalts without significant albitization and zeolitization is characterized by the occurrence of saponite±mixed-layer chlorite/smectite in the low-temperature alteration zone, and mixed-layer chlorite/corrensite or mixed-layer talc/chlorite in the high-temperature alteration zone. Textural non-equilibrium for phyllosilicates is represented by mixed layering and poorly defined packets of partially incoherent layers. The approach to textural equilibrium was controlled largely by the availability of fluid or permeability.Contribution No. 488 from the Mineralogical Laboratory, Department of Geological Sciences, The University of Michigan 相似文献
4.
The Portage Lake Lava Series of the Keweenaw Peninsula, northernMichigan, is composed of over 5000 m of tholeiitic lava flows.Chemical and petrologic study of thin undifferentiated flowsfrom this sequence shows that the bulk of the flows are olivinetholeiites; highly ironenriched tholeiites comprise up to 10per cent of the volume. In addition, a few small rhyolitic intrusives,exceedingly rich in alkalis, are exposed in the region. Duringburial the amygdular tops of each flow acted as channelwaysfor migrating fluids during a regional metamorphic event thatproduced a progressive sequence of secondary phases within theflow tops. In the upper part of the stratigraphic section, laumontite,analcime, albite, and chlorite dominate assemblages characteristicof the zeolite facies. Stratigraphically deeper. flow tops arecharacterized by metamorphic assemblages of the prehnite-pumpellyitefacies. Within the higher rank facies, rocks along fractureshave been transformed to calcium-rich monomineralic domains(metadomains) of epidote or pumpellyite. These metadomains gradeoutward through incompletely reconstituted rocks containingalbitized feldspars, and finally, in flow centers, to basaltdisplaying few signs of mineralogical readjustment. Extremechemical disparity exists within the altered flow tops, particularlywith respect to calcium and sodium content. Calculations revealthat bulk compositions of metamorphically adjusted flow topsare similar to unaltered basalts. Thus, the chemical variationdisplayed by the metamorphic rock types resulted from localizedmetamorphic differentiation. The Keweenawan sequence displays progressive dehydration fromthe top to the base of the stratigraphic section. At the topchlorite (H2O = 12 per cent) and pumpellyite (H2O = 6 per cent)metadomains formed by dehydration. The fact that most of theserocks were hydrated strongly suggests that fluid pressures wereless than total pressures during the metamorphic event. In rocksundergoing hydration in the uper part of the stratigraphic section,therefore, water pressures decreased away from channelways.As a result, the most hydrous rock types formed in these regions.Conversely, in rock undergoing dehydration water pressures increasedaway from channelwasys, so that the most dehydrated rocks formedin such regions. Water content of an individual rock is dependenton both position in the stratigraphic pile and position withrespect to fluid channelways. 相似文献
5.
Decompression-induced growth of albite porphyroblasts, Fleur de Lys Supergroup, western Newfoundland 总被引：2，自引：0，他引：2
Abstract Albite porphyroblasts are widely distributed in pelitic and semi-pelitic schists of the Fleur de Lys Supergroup, western Newfoundland. Textures and mineral assemblages indicate that albite grew during nearly isothermal decompression from P-T conditions of about 500° C, 9 kbar, to conditions of 550° C, 6.5 kbar. Three compositional varieties of albite-bearing schists, here termed PMAQ (paragonite-muscovite-albite-quartz), MMAQ (microcline-muscovite-albite-quartz), and PMMQ (paragonite-muscovite-margarite-quartz), can be distinguished on the basis of pre-porphyroblast mineral assemblages. Analysis of these assemblages in terms of the composition of the coexisting fluid [log a (Na+ /H+ ) versus log a (K+ /H+ )] suggests that, as pressure and temperature changed, the stability field of albite expanded at the expense of coexisting matrix phyllosilicates. This promoted growth of albite on pre-existing or newly formed nuclei. Late oligoclase in PMAQ and PMMQ samples is associated with replacement of matrix garnet by plagioclase + mica ° Chlorite, particularly in strongly sheared samples. 相似文献
6.
Drits V. A. Ivanovskaya T. A. Sakharov B. A. Gor'kova N. V. Karpova G. V. Pokrovskaya E. V. 《Lithology and Mineral Resources》2001,36(4):337-352
Globular, platy, and fine-dispersed phyllosilicates of chloritic composition were studied in the outer contact of dike with glauconite-bearing rocks. It is shown that the globular Al-glauconite is replaced by pseudomorphs of mixed-layer Mg- and Fe-bearing chlorite–berthierine containing 5% berthierine layers in this zone. The crystallochemical characteristics and microstructure are reported for the globular, platy, and fine-dispersed chlorites. The possible models of chlorite–berthierine formation are discussed. 相似文献
7.
Compositional studies on different forms of magnetite, ulvospinel, ilmenite and hematite mineral phases occurring in 37 lava flows and 6 dykes of the Mandla lobe are presented in this paper. Ilmenite (0001) in equilibrium with titanomanetite show high values of temperature of equilibration, ranging from 1172–974°C, for high alumina quartz normative tholeiitic lava flows of Chemical Type - A; 1129–1229°C for low alumina quartz normative tholeiitic lava flows of Chemical Type - B; 1283–1124°C for tholeiitic lava flows of Chemical Type - F and 1243°C and 99O°C for two diopside olivine normative tholeiite flows of Chemical Type D. High olivine normative flows of Chemical Type - G and H show 1095°C and 1092°C respectively. Whereas, high hypersthene normative tholeiite flow of Chemical me C shows temperature of 1187°C. Data plots disposition over iron-titanium oxide equilibration temperature vs – logfo2, diagram for Mandla lava flows and other parts of the Deccan (Igatpuri, Mahabaleshwer, Nagpur and Sagar areas) revealed that tholeiitic (evolved) basalt of the eastern Deccan volcanic province formed at high temperatures whereas, picritic (primitive) lavas of Igatpuri and tholeiitic basalt of Mahabaleshwar areas were formed at low temperatures. Mahabaleshwer basalts follow FMQ (fayalite-magnetite-quartz) buffer curve but, plots of the Mandla basalts lie above this curve indicating higher temperatures of crystallisation of ilmenite-titanomagnetite than that of the lava flows from other parts of Deccan 'Raps. The eastern Deccan Traps are most evolved types of lava as characterised by its low Mg-number and Ni content whereas, Igatpuri lava flows are picritic (primitive), having high Mg-number and Ni contents. Temperature vs FeO + Fe2O3 / FeO + Fe2O3 + MgO ratio data plots for Mandla and other Deccan lava flows and liquidus data for Hawaiian tholeiites, indicated that Igatpuri basalts lie parallel to the liquidus line of Hawaiian tholeiite but at lower temperatures. Large data plots of Mandla lava flows lie along the liquidus line of the Hawaiian lava. The highly vesicular nature of compound lava flows having large amount of volatile is responsible for low temperature values whereas, lava flows represented by high temperatures show high modal values of glass and opaque minerals. 相似文献
8.
ZHANG Xuetong ZHANG Ronghu HU Shumin YU WenbinOpen Research Laboratory of Geochemical Kinetics Chinese Academy of GeologicalSciences Baiwanzhuang Ro Beijing 《《地质学报》英文版》2000,74(2):406-411
This work presents new experimental results on surface chemistry of reacting minerals and interface kinetics between mineral and aqueous solutions. These experiments were carried out using a flow reactor (packed bed reactor) of an open system as well as a continuous stirred tank reactor, CSTR. The authors measured reaction rates of such minerals as zeolite, albite and carbonate (rhodochrosite, dolomite) in various solutions, and tested corresponding mineral surface by using SEM, XPS, SIMS, etc. This paper mainly presents the experimental results of zeolite dissolution in water and in low pH solutions at room temperature, and dolomite dissolution at elevated temperatures. The results show that the release rates of Si, Al and Na of zeolite are different in most cases. The incongruent dissolution of zeolite is related to surface chemical modifications. The Na, Al and Si release rates for dissolution of albite and zeolite in water and various solutions were measured as a function of temperature, flow veloci 相似文献
9.
内蒙锡林浩特鸽子山火山地质研究 总被引：4，自引：3，他引：1
鸽子山火山位于内蒙古自治区锡林浩特市东南,处于大兴安岭-大同新生代火山喷发带中段,是锡林浩特-阿巴嘎火山群中保存最为完好的一座玄武质火山。火山喷发物的分布面积约55km2,主要为降落火山渣、溅落熔结火山碎屑岩和熔岩流,成分主要为碧玄岩,晚期有少量的橄榄拉斑玄武岩,碧玄岩中含有较多二辉橄榄岩包体和辉石及歪长石巨晶。火山由锥体、熔岩流和火山碎屑席组成,锥体由早期的降落锥和晚期溅落锥复合而成。火山口经历多次塌陷而成为破火口。锥体西侧及北东侧出露两个仍保留了原始形态的熔岩溢出口,熔岩流类型为结壳熔岩,由多个岩流单元组成,局部地区的熔岩流中发育较多保存完好的喷气锥、喷气碟或喷气塔。火山碎屑席主要分布在锥体的东侧,厚度由锥体向外逐渐减薄。火山活动可分为早、晚两个阶段,早期为爆破式喷发,形成火山渣锥和碎屑席,属亚布里尼型喷发,晚期主要为溢流式喷发,形成溅落锥和大规模熔岩流,其活动时代为晚更新世末-全新世。 相似文献
10.
Application of Chlorite Geothermometry to Hydrothermal Alteration in Toyoha Geothermal System, Southwestern Hokkaido, Japan 总被引：1，自引：0，他引：1
In this study, we applied chemical geothermometers to the estimation of formation temperatures of chlorites from various types of hydrothermally altered rocks in the Toyoha geothermal field, using core samples from six drill holes (TH-2 to TH-7) together with wasted ore samples from Toyoha vein-type ore deposit. Based on the preliminary examination of mineral assemblages by X-ray powder diffraction and optical microscopy, hydrothermal alteration observed through the drill holes was classified into four types of alteration zones: propylitic, mixed-layer minerals, kaolin minerals, and ore mineralized zones. The mineral assemblage of the ore mineralized zone observed through TH-2, TH-4, and TH-6 is similar to those of Toyoha ore veins reported previously. The Fe3+/ΣFe ratios of chlorites were determined by X-ray photoelectron spectroscopy (XPS), in addition to the usual microprobe analyses. The ratios ranged from 0.20–0.26 for chlorites from the propylitic alteration zone and from 0.13 to 0.17 for those from the ore mineralized zone associated with sulfide minerals. After correcting the Fe3+ contents in the octahedral sites of chlorite structures, we obtained acceptable temperatures of the chlorite formation by application of geothermometers, for instance, a similar range of 150–300°C for chlorites from either the propylitic zone or the ore mineralized zone developed through TH-2, TH-4, and TH-6. Chlorites from the ore mineralized zone proximal to the Toyoha deposit are characterized by high Fe and Mn contents compared to the propylitic chlorites, which is similar to the Toyoha vein-filling chlorites; the formation temperatures were close to both the homogenization temperatures of fluid inclusions and the present subsurface temperatures measured through drill holes. Chlorites from the Toyoha ore veins, however, gave slightly higher formation temperatures (180–350°C) than those of chlorites from the ore mineralized zone in the drill cores. This suggests that several types of hydrothermal alteration occurred at different stages in the Toyoha geothermal field and the composition of product chlorite was controlled not only by the temperature but also the composition of fluid related to the formation. Reliable estimation of temperature for the chlorite formation provides basic information on evaluating correctly other physicochemical conditions prevalent at the formation. 相似文献
11.
Niranjan D. Chatterjee 《Contributions to Mineralogy and Petrology》1973,42(3):259-271
The reaction 3 Na-montmorillonite + 2 albite 3 paragonite + 8 quartz has been studied experimentally using starting materials composed of natural low albite, kaolinite and quartz. Rate studies at 2, 4 and 7 kb demonstrate that the reaction takes place at 335–315° C from lower to higher pressures. Attempts to reverse this reaction with runs lasting several months were without success. Comparison with pertinent data from natural mineral assemblages indicate that despite non-reversal, the data presented here may be very near to the true lower thermal compatibility limit of the assemblage quartz-paragonite.The above reaction becomes metastable beyond the upper pressure stability limit of the phase Na-montmorillonite; it is replaced here by another reaction 1 albite + 1 kaolinite 1 paragonite + 2 quartz + 1 H2O, as suggested originally by Zen (1960). A P-T-grid showing possible compatibility relations of the assemblage quartz-paragonite is provided (Fig. 4). Perusal of natural assemblages belonging to the subsystem Na2O-Al2O3-SiO2-H2O lends credence to this grid.In course of the rate studies reported here, various regular paragonite-sodium montmorillonite mixed-layer phases were encountered (Fig. 2); the 11 regular mixed-layer phase represents the synthetic analogue of the mineral rectorite (sometimes called allevardite), widely recorded from deep diagenetic and anchimetamorphic environments. Results of rate-studies (Fig. 3) suggest that the mixed-layer phases are all transient, metastable products obtained during the transformation of the albite-Na-montmorillonite assemblage to paragonite-quartz. As such, rectorite and related mixed-layer phases on the join montmorillonite-paragonite, are always less stable relative to the assemblage Na-montmorillonite-paragonite. 相似文献
12.
Yen-Hong Shau Donald R. Peacor Eric J. Essene 《Contributions to Mineralogy and Petrology》1990,105(2):123-142
Many chloritic minerals in low-grade metamorphic or hydrothermally altered mafic rocks exhibit abnormal optical properties, expand slightly upon glycolation (expandable chlorite) and/or have excess AlVI relative to AlIV, as well as significant Ca, K and Na contents. Chloritic minerals with these properties fill vesicles and interstitial void space in low-grade metabasalt from northern Taiwan and have been studied with a combination of TEM/AEM, EMPA, XRD, and optical microscopy. The chloritic minerals include corrensite, which is an ordered 1:1 mixed-layer chlorite/smectite, and expandable chlorite, which is shown to be a mixed-layer chlorite/corrensite. Corrensite and some mixed-layer chlorite/corrensite occur as rims of vesicles and other cavities, while later-formed mixed-layer chlorite/corrensite occupies the vesicle cores. The TEM observations show that the mixed-layer chlorite/corrensite has ca. 20%, and the corrensite has ca. 50% expandable smectite-like layers, consistent with XRD observations and with their abnormal optical properties. The AEM analyses show that high Si and Ca contents, high AlVI/AlIV and low FeVI/(Fe+Mg)VI ratios of chlorites are correlated with interstratification of corrensite (or smectite-like) layers in chlorite. The AEM analyses obtained from 200–500 Å thick packets of nearly pure corrensite or chlorite layers always show that corrensite has low AlIV/SiIV and low FeVI/(Fe+Mg)VI, while chlorite has high AlIV/SiIV and high FeVI/(Fe+Mg)VI. This implies that the trioctahedral smectite-like component of corrensite has significantly lower AlIV/SiIV and FeVI/(Fe+Mg)VI. The ratios of FeVI/(Fe+Mg)VI and AlIV/SiIV thus decrease in the order chlorite, corrensite, smectite. The proportions of corrensite (or smectite-like) layers relative to chlorite layers in low-grade rocks are inferred to be controlled principally by Fe/Mg ratio in the fluid or the bulk rock and by temperature. Compositional variations of chlorites in low-grade rocks, which appear to correlate with temperature or metamorphic grade, more likely reflect variable proportions of mixed-layered components. The assemblages of trioctahedral phyllosilicates tend to occur as intergrown discrete phases, such as chlorite-corrensite, corrensite-smectite, or chlorite-corrensite-smectite. A model for the corrensite crystal structure suggests that corrensite should be treated as a unique phase rather than as a 1:1 ordered mixed-layer chlorite/smectite. 相似文献
13.
C. E. JACOBSON 《Journal of Metamorphic Geology》1995,13(1):79-92
Abstract The Rand and Pelona Schists consist of eugeoclinal rock types overlain by continental basement along the Vincent-Chocolate Mountains (VCM) faults. Both schists display inverted metamorphic zonation, defined in part by a systematic variation in composition of calcic to sodic-calcic amphibole in mafic schist structurally upward. The compositional progressions include increase of total A1, A1IV and Ti, but decrease in the ratios of Na/(Na + Ca) to A1/(A1 + Si), and NaM4 to (A1VI + Fe3+ + Ti). These variations imply that structurally high rocks belong to a lower-pressure metamorphic fades series than those at depth. This result is consistent with previous views that the inverted metamorphic zonations represent intact structural sequences.
Amphibole composition is dependent not only on structural position (i.e. P-T ), but also upon bulk-rock composition. The important controls are whole-rock Mg/(Mg + Fe2+ + Mn) and Fe3+ /Fe2+ . The greatest impact of these factors, however, is on the absolute values of Na and Al, rather than their ratio. Thus, interpretation of facies series is not seriously hindered by compositional variability.
Sodic amphibole in epidote blueschists from the Rand Schist is extensively replaced by sodic-calcic amphibole. Sodic-calcic amphibole in the Rand Schist and Pelona Schist is, itself, rimmed by actinolitic amphibole. Similar blueschist to greenschist transitions in other metamorphic terranes are typically attributed to exhumation. In the Rand and Pelona Schists, the sequence probably formed during burial. 相似文献
Amphibole composition is dependent not only on structural position (i.e. P-T ), but also upon bulk-rock composition. The important controls are whole-rock Mg/(Mg + Fe
Sodic amphibole in epidote blueschists from the Rand Schist is extensively replaced by sodic-calcic amphibole. Sodic-calcic amphibole in the Rand Schist and Pelona Schist is, itself, rimmed by actinolitic amphibole. Similar blueschist to greenschist transitions in other metamorphic terranes are typically attributed to exhumation. In the Rand and Pelona Schists, the sequence probably formed during burial. 相似文献
14.
Twenty-three basalts from northwestern Formosa were analyzed for Si, Ti, Al, Fe, Mg, Ca, Na, K, Rb, Sr, Hf, Co, Sc, Cr, Th, and 7 REE. Formosan alkalic basalts are generally similar to most alkalic basalts, and Formosan tholeiites are somewhat similar to island arc and continental tholeiites in terms of trends in K/Rb, Rb/Sr, K/Sr, and Ca/Sr ratios. Compared to most submarine tholeiites, Formosan tholeiites are enriched in Rb relative to K and Sr, and enriched in Sr relative to K and Ca. Both types of Formosan basalts show, relative to chondritic proportions, enrichments in light REE which smoothly decrease through the heavy REE. Their REE patterns are similar to those observed in Dogo-Oki alkalic basalts, Hawaiian basalts, and Deccan Plateau basalt, but differ strikingly from those of Japanese tholeiites and oceanic ridge basalts. These relationships and contrasts suggest that Formosan basalts originated in a plagioclase-free portion of the upper mantle and at greater depths that did Japanese tholeiites and oceanic ridge basalts. 相似文献
15.
The smectite to chlorite transition in a fossil seamount hydrothermal system: the Basement Complex of La Palma, Canary Islands 总被引：3，自引：0，他引：3
Abstract The hydrothermal metamorphism of a sequence of Pliocene-aged seamount extrusive and volcanoclastic rocks on La Palma includes a relatively complete low-P-T facies series encompassing the zeolite, prehnite-pumpellyite, and greenschist facies. The observed mineral zonations imply metamorphic gradients of 200–300° C km-1. The transition from smectite to chlorite in the La Palma seamount series is characterized by discontinuous steps between discrete smectite, corrensite and chlorite, which occur ubiquitously as vesicles and, to a much lesser extent, vein in-fillings. Trioctahedral smectites [(Mg/(Fe + Mg) = 0.4–0.75] occur with palagonite and Na-Ca zeolites such as analcime and a thompsonite/natrolite solid solution. Corrensite [(Mg/(Fe + Mg) = 0.5–0.65] first appears at stratigraphic depths closely corresponding to the disappearance of analcime and first appearance of pumpellyite. Discrete chlorite [(Mg/(Fe + Mg) = 0.4–0.6] becomes the dominant layer silicate mineral coincident with the appearance of epidote and andraditic garnet. Within the stratigraphic section there is some overlap in the distribution of the three discrete layer silicate phases, although random interstratifications of these phases have not been observed. Although smectite occurs as both low- and high-charge forms, the La Palma corrensite is a compositionally restricted, 1:1 mixture of low-charge, trioctahedral smectite and chlorite. Electron microprobe analyses of coarse-grained corrensite yield structural formulae close to ideal values based on 50 negative charge recalculations. Calcium (average 0.20 cations/formula unit) is the dominant interlayer cation, with lesser Mg, K and Na. The absence of randomly interlayered chlorite/smectite in the La Palma seamount series may reflect high, time-integrated fluid fluxes through the seamount sequence. This is consistent with the ubiquity of high-variance metamorphic mineral assemblages and the general absence of relict igneous minerals in these samples. 相似文献
16.
Kinetics of Hydrothermal Reactions of Minerals in Near-critical and Supercritical Water 总被引：9，自引：1，他引：8
ZHANG Ronghu HU Shumin ZHANG XuetongOpen Research Laboratory of Geochemical Kinetics Chinese Academyof Geological Sciences Baiwanzhuang Ro Beijing 《《地质学报》英文版》2000,74(2):400-405
This work presents new experimental results on the kinetics of mineral dissolution in near-critical and supercritical water in a temperature range (T) from 25 to 400℃ and a constant pressure of 23 MPa. Kinetic experiments were carried out by using a flow reactor (packed bed reactor) of an open system. The dissolution rates of albite and magnetite were measured under these experimental conditions. Na, Al and Si release rates for albite dissolution in water were measured as a function of the temperature and flow velocity in the reaction system. The maximum release rates of Na, AI and Si of albite dissolution in the hydrothermal flow systems under different flow velocities were always obtained at 300℃, that is to say, the maximum albite dissolution rates in the flow systems, regardless of different flow rates, were repeatedly measured at 300℃. Results indicate a wide fluctuation in albite dissolution rates occurring close to the critical point of water. The dissolution rates increased when the temperatu 相似文献
17.
长白山天池火山气象站期晚期碱流质熔岩的岩石学研究 总被引：3，自引：0，他引：3
通过野外火山堆积物的相分析、岩石显微鉴定和造岩矿物化学分析,可以确认气象站期晚期碱流质熔岩是典型的溢流熔浆冷却固结形成的,不是碎成熔岩。熔岩流的顶部和底部是黑曜质碱流岩的表壳相,中部是致密厚层与薄层相间产出的、具有塑性变形的碱流岩的内部相。组成熔岩流的岩石具有斑状和聚斑结构,从表壳相向内部相基质依次发育玻璃质结构、（微）球粒结构和霏细结构。斑晶矿物钠透长石、钙铁辉石、铁橄榄石和少量石英出现在熔岩流的所有岩相中,而钠铁闪石、铁钠透闪石和钛铁矿则作为内部相基质中的显微斑晶出现。气象站期晚期碱流质熔岩是过铝质、过碱性的钠闪碱流质熔岩,属于碱性系列,与意大利潘泰莱里亚岛碱流岩相比,富Si、Al、K、Mg、Ca和P而贫Fe、Na、Mn和Ti。 相似文献
18.
河北省赤城县独石口沸石岩矿物学特征及其性能研究 总被引：2，自引：0，他引：2
独石口沸石岩共生矿物组合为斜发沸石、蒙脱石、α-方石英和少量丝光沸石。斜发沸石呈微晶产于玻璃质岩屑和火山尘中,也呈板状产于玻屑和珍珠岩溶解形成的孔洞中,沸石总量大于70％;化学成分显示高Si、高Al、富K、富Ca、贫Na的特征;阳离子交换容量高,交换性阳离子以Ca为主,其次为K,Na,Mg;阳离子选择交换顺序为NH_4~+>K~+>Ca~(2+)>Na~+>Mg~(2+);不同阳离子类型的沸石岩其热稳定性和吸附性有差异,K型和Na型沸石岩可稳定至700℃,而Ca型沸石岩在500℃时结构被破坏;Ca型沸石岩吸附性好,而K型差。 相似文献
19.
Raymond A. Duraiswami Purva Gadpallu Babaji Maskare Aishwarya Purwant Pooja Meena P. Krishnamurthy B. Mahabaleshwar 《Journal of the Geological Society of India》2017,90(6):742-747
Flow mapping and physical volcanology of 15 basaltic lavas exposed in three critical road pass sections (ghats) in the Koyna-Warna region of the western Deccan Traps is presented in this paper. Transitional lavas like rubbly pahoehoe are most common morpho-type exposed in these ghat sections. Sinking of rubbly breccia into flow interiors and formation of breccia-cored rosette are common in some lava flows. Few rubbly lavas exhibit slabby tendencies. The amount and nature of the associated rubble is variable and result from the mechanical fracturing and auto-brecciation of the upper vesicular crust in response to distinctive stages in the cooling, crystallization and emplacement history of individual lava flows. Occurrence of aa and pahoehoe morpho-types in the lava flow sequence is subordinate. Three prominent pahoehoe flows separated by red bole horizons are seen in the upper parts of the Kumbharli ghat. These are thick, P-type sheet pahoehoe. The pahoehoe lavas represent compound flow fields that grew by budding, endogenous lava transfer and inflation. Presence of pahoehoe lavas in the Koyna-Warna region hints at possible hitherto unrecorded southern extension of Bushe-like flow fields. This study reconfirms the existence of pahoehoe-slabby-rubbly-aa flow fields and transitions even in the upper echelons of the Deccan Trap stratigraphy. The study of morphology and internal structure of lava flows exposed at the ghat sections in the Koyna-Warna region could guide subsurface core-logging that is critical in deciphering the physical volcanology and emplacement dynamics of basaltic lava flows penetrated by drill holes sunk under the scientific deep drilling programme. 相似文献
20.
Richard H. April 《Sedimentary Geology》1981,29(4):283-307
The clay mineralogy of the Newark Supergroup (Upper Triassic/Lower Jurassic) in the Connecticut Valley was studied by X-ray diffraction analysis. Clay minerals identified in 126 samples are illite, chlorite, smectite, kaolinite, vermiculite, expandable chlorite, mixed-layer illite/smectite, mixed-layer chlorite/smectite, and mixed-layer chlorite/vermiculite. In general, the rocks are illitic with subordinate amounts of chlorite. However, the various lithofacies in the Newark Supergroup are characterized by distinct clay-mineral assemblages. Red beds of floodplain origin contain clays mainly of detrital nature with 2M illite most abundant. Subordinate amounts of chlorite, smectite, vermiculite, kaolinite and mixed-layer illite/smectite are also present. An interstratified chlorite/vermiculite occurs in red mudstone underlying basalt flows. Lacustrine gray beds are generally characterized by the clay-mineral assemblage 1Md illite + chlorite with minor amounts of smectite ane expandable chlorite. An interstratified chlorite/smectite predominates in gray mudstone associated with perennial lake cycles in the East Berlin Formation. Black shales of deeper lacustrine origin contain the assemblage 1Md ifillite + trioctahedral smectite and traces of chlorite. Illite and smectite also occur as mixed-layer phases.In many respects, the distribution of clay minerals in the Connecticut Valley can be likened to the general scheme proposed for the Permo-Triassic basins of Europe and Africa. These display both vertical and horizontal variations in clay-mineral assemblages that reflect the chemical and spatiotemporal evolution of intrabasin depositional and diagenetic environments. Chemical data indicate that magnesium, especially, was concentrated in the black muds of large perennial lakes that intermittently occupied the Connecticut rift valley. Pore waters derived from these sediments played an important role in the development of Mg-rich 2 : 1 and interstratified clay minerals during early diagenesis. 相似文献