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1.
Although “barkinite” has long been studied by many geologists, its geochemical characteristics and environment of deposition are still not known in detail. In order to study the petrography and geochemical characteristics of “barkinite”, coal samples from two Permian coal seams were taken from the Dahe mine, Guizhou Province. The samples were separated into maceral fractions, and then analyzed by microscopical, isotopic, Rock-Eval, and geochemical methods. The microscopical results indicate that “barkinite” occurs as four main types. According to their relationship to other maceral groups, “barkinite” is ostensibly formed under variably dry–wet or oxidizing–reducing conditions. The extract yield, isotope data and Rock-Eval values of “barkinite” are different from other macerals. Microscopical and geochemical results indicate that “barkinite” forms part of the liptinite group.  相似文献   

2.
The offsets on the ocean floor, usually called “transform-faults” are not shear faults common in solid Hookian rocks, but reflect the viscous Newtonian properties of laminar flow at the time when the upwelling magma along the spreading center was still in a liquid state. During spreading this liquid is carried away with the walls of the spreading center. This movement creates a pattern of stream lines in the liquid which run parallel to the direction of spreading. “Transform faults” are initiated along zones where a larger rate of shear disturbs the process of solidification. Consequently the strength of the basalt after solidification will be impaired along these zones. These weak zones will fracture under the thermo-elastic stresses during the final stage of cooling.The history of the term “transform fault” is discussed and the name “spreading offset” is proposed.  相似文献   

3.
The shallow level pluton of Bressanone is a Late Hercynian multiple intrusion into the South Alpine basement of the Eastern Alps. Most of this complex is composed of anatectic granodiorites and granites intruded in separate stocks 282 ± 14 Ma ago; gabbros and leucogranites occur in smaller quantities. The chronological intrusion sequence is: layered gabbro, granodiorites and granites, two-mica cordierite leucogranite and fayalite leucogranites.

The granodiorites and granites may contain hornblende or garnet. The hornblende and garnet rocks differ both in chemistry and (87Sr/86Sr)i ratio, and may be identified as “I-type” and “S-type”, respectively, according to the Chappell-White classification.

Textural and chemical patterns show that the granites may be linked to the granodiorites by cumulate-like processes. The granodiorite → granite transition, attributed to filter pressing, expresses an increase in the liquid/xenolith ratio in a magma where the liquid fraction was a minimum melt and the solid fraction was restitic material.  相似文献   


4.
George J. Simandl   《Lithos》2004,77(1-4):749-764
The tectonic setting of British Columbia (BC) differs from classic diamond-bearing intracratonic regions such as the Northwest Territories and South Africa. Nevertheless, several diamond occurrences have been reported in BC. It is also known that parts of the province are underlain by Proterozoic and possibly Archean basement. Because the continents of today are composites of fragments of ancient continents, it is possible that some of the regions underlain by old crystalline basement in eastern British Columbia were associated with a deep crustal keel. The keel may have predated the break-up of the early Neoproterozoic supercontinent called Rodinia and was preserved possibly until the Triassic. Some of these old continental fragments may have been displaced relative to their position of origin and dissociated from their keel, or the keel may have since been destroyed. Such fragments represent favourable exploration grounds in terms of the “Diamondiferous Mantle Root” model (DMR model) if they were intersected by kimberlites or lamproites prior to displacement or destruction of their underlying deep keel. Therefore, extrapolation of fragments of the diamond-bearing Precambrian basement from the Northwest Territories or Alberta to BC provides a sufficient reason for initiating reconnaissance indicator mineral surveys. The “Eclogite Subduction Zone” model (ES model) predicts formation of diamonds at lower pressure (i.e., depth) than required by the DMR model in convergent tectonic settings. Although not proven, this model is supported by thermal modeling of cold subduction zones and recent discoveries of diamonds in areas characterized by convergent tectonic settings. If the ES model is correct, then the parts of BC with a geological history similar to today's “cold” subduction zones, such as Honshu (Japan), or to continental collision zones, such as Kokchetav massif (Kazakhstan) and the Dabie–Sulu Terrane (east central China), may be diamondiferous. The terranes where geological evidences suggest an ultrahigh pressure (UHP) metamorphic event followed by rapid tectonic exhumation (which could have prevented complete resorption of diamonds on their journey to the surface) are worth investigating. If UHP rocks were intercepted at depth by syn- or post-subduction diamond elevators, such as kimberlites, lamproites, lamprophyres, nephelinites or other alkali volcanic rocks of deep-seated origin, the diamond potential of the area would be even higher.  相似文献   

5.
A simple and efficient numerical approach is presented for the cyclic axial loading analysis of vertical single piles embedded in a layered soil profile. The soil medium along the embedded pile is represented by simple “t–z” curves which define the shear stres-vertical displacement response of the soil at each particular depth. A hyperbolic “t-z” representation of the soil medium presented by Chin and Poulos, which caters for the case of a two-layered and “Gibson” soil profiles, is utilised. Under cyclic loading conditions, the well-known Masing's criteria governing the unloading and reloading responses are incorporated into the “t-z” curves. The cyclic loading effects of pile capacity degradation and accumulation of pile displacement are catered for in an approximate manner. Some numerical results are presented to show the important parameters affecting the cyclic response of single piles embedded in a layered soil. Finally, a comparison with field measurements of a cyclic pile load test shows general agreement between numerical and field results.  相似文献   

6.
Three progressive metamorphic suites are developed in pelitic rocks of the northern Wopmay Orogen. Two suites are related to the Hepburn Batholith and one to the Wentzel Batholith. All three suites are cut by post-metamorphic wrench faults, some of which have significant vertical displacement. The structural relief so provided reveals that medium-and high-grade isograds associated with the Hepburn Batholith dip inward towards the batholith and are thus “hot-side-up”. Isograds associated with the Wentzel Batholith dip away from the batholith and are thus “hot-side-down”. It is concluded that Hepburn Batholith has the form of the flattened funnel fed from depth, and that Wentzel Batholith is the arched roof of an intrusive complex of unknown shape at depth.  相似文献   

7.
The western side of the Paranà Basin of Brazil extends to central Paraguay, where repeated and widespread magmatic activity developed from Lower Cretaceous to Oligocene, associated with late Mesozoic crustal extension trending NE-SW. In central Paraguay this trend is characterized by a zone of NW-SE normal faults which formed the Asunciòn-Sapucai graben, up to 45 km wide and 200 km long, where alkaline rocks occur as volcanic domes, complexes, lava-flows and dykes. These rocks, 128 Ma aged, are dominantly potassic and ne-normative.

A swarm of at least 200, mainley NW-SE trending, dykes occurs in the Sapucai region and seems to be formed by two main lineages: tephrite to phonolite (and peralkaline phonolite) and alkali basalt to trachyphonolite. They are characterized by ubiquitous diopside to ferrosalite, consistently yielding Al enrichment trends; common olivine, Fo81-69 in tephrites and alkaline basalts, and up to Fo65 in phonolites; zoned megacrysts of hastingsitic hornblende (core) to kaersutite (rim), associated with accessory groundmass pargasite in tephrites and phonotephrites; K-rich hastingsite and K-rich ferroan pargasite in the phonolites. Accessory groundmass mica falls in the annite-phlogopite range, and consistently yields insufficient (Si + Al) to satisfy the expected T site occupancy of 8.00 a.f.u. Fe---Ti oxides are Ti-magnetite, rarely ilmenite or haematite. Phenocrystal, i.e. xenocrystal plagioclase is An70-20, and An74-42 in the tephrites and phonolites, respectively; coexisting groundmass microlites are An22-14, associated with sodasanidine and sanidine. Feldspathoids include analcimized leucite and nepheline; accessories Ti-andradite and sphene.

The two main lineages, recognized by distinctive mineralogical variations, are consistent with the petrochemical variations. Complex interaction of discrete and independently evolving magma batches are indicated by intra- and/or interphase chemical variations, suggesting multiple equilibrations of the crystallizing phases under shallow level, volcanic pressure regime. The observed geochemical trends are quite similar to those of “Roman Region type magma” with the same negative anomalies of Ta, Nb, Zr and Ti. The most likely mantle source is a garnet-peridotite characterized by different enrichment in incompatible elements and which suffered low degree of partial melting (3–7%), which has geochemical and isotopic features distinct from those of the adjoining tholeiitic basalts (130 Ma) and nephelinites (61-39 Ma).

The similarities of the Sapucai dyke suite with Barton's “Roman Region type magma” supports the view that this magma type may not be formed as a result of orogenic and/or subduction-driven activity in this region. Therefore, a causal relationship of the latter activity with “Roman Region type magma” is not supported and remains questionable.  相似文献   


8.
In this paper we consider localization and paleogeographic conditions of palygorskite deposition in the Moscow Syneclise, which is regarded as a palygorskite province. The geology and mineralogy of the Borshchevka deposit are also characterized. Mineralogical and chemical analyses of rocks from the Steshevo Horizon (C1st), which is the most promising for palygorskite and associated smectite, have been carried out. The morphology and crystal structure of palygorskite varieties differing in origin are characterized, as well as possible use of palygorskite from the Borshchevka deposit as a drilling mud, foundry sand, and sorbent.  相似文献   

9.
Clinoptilolite, a zeolite of the heulandite group, occurs commonly in sediments as an authigenic mineral. In the Middle Eocene of southern Israel, it constitutes from a few per cent up to 80 per cent of the insoluble residue of the chalks and limestones. It is associated with opal C-T, montmorillonite and palygorskite. These chalks and limestones overlie the Danian-Palaeocene Taqiya marls which also contain a well-established clay mineral sequence consisting of opal C-T, montmorillonite, palygorskite, sepiolite, and clinoptilolite. This paragenesis of minerals is shown to be typical of the Upper Cretaceous to Eocene times. It is world-wide, occurs in deep-sea sediments as well as in shallow water sediments, and results from the abundance of silica which probably reflects a warmer climate during this time period. The concentration of magnesium in the sea-water and its ratio to the other cations seem to determine which authigenic silicate will be formed.  相似文献   

10.
ABSTRACT A cave in granitic rocks was studied in Mezesse, South Cameroon. Coralloid speleothems, draperies and dissolution traces on the cave walls attest to its truly karstic nature. The speleothems consist of microlayers of opal and taranakite (K,NH4)Al3(PO4)3(OH).9H2O. They indicate a significant mobilization of silica, Al and K from granite during the formation of the cave. Identification of silicified bacteria in the speleothems layers suggests a possible role of these micro-organisms in silica deposition. The presence of taranakite and of silicified organic remains within the speleothems lead to a better understanding of the genesis of the cave.  相似文献   

11.
This paper reports the integrated application of petrographic and Sm–Nd isotopic analyses for studying the provenance of the Neoproterozoic Maricá Formation, southern Brazil. This unit encompasses sedimentary rocks of fluvial and marine affiliations. In the lower fluvial succession, sandstones plot in the “craton interior” and “transitional continental” fields of the QFL diagram. Chemical weathering probably caused the decrease of the 147Sm/144Nd ratios to 0.0826 and 0.0960, consequently lowering originally > 2.0 Ga TDM ages to 1.76 and 1.81 Ga. 143Nd/144Nd ratios are also low (0.511521 to 0.511633), corresponding to negative εNd present-day values (− 21.8 and − 19.6). In the intermediate marine succession, sandstones plot in the “dissected arc” field, reflecting the input of andesitic clasts. Siltstones and shales reveal low 143Nd/144Nd ratios (0.511429 to 0.511710), εNd values of − 18.1 and − 23.6, and TDM ages of 2.16 and 2.37 Ga. Sandstones of the upper fluvial succession have “dissected arc” and “recycled orogen” provenance. 143Nd/144Nd isotopic ratios are also relatively low, from 0.511487 to 0.511560, corresponding to εNd values of − 22.4 and − 21.0 and TDM of 2.07 Ga. A uniform granite–gneissic basement block of Paleoproterozoic age, with subordinate volcanic rocks, is suggested as the main sediment source of the Maricá Formation.  相似文献   

12.
In this paper, I analyze the connections made between women and water in a Rajasthani drinking water supply project as a significant part of drinking water’s commodification. For development policy makers, water progressing from something free to something valued by price is inevitable when moving economies toward modernity and development. My findings indicate that water is not commodified simply by charging money for it, but through a series of discourses and acts that link it to other “modern” objects and give it value. One of these objects is “women”. I argue that through women’s participation activities that link gender and modernity to new responsibilities and increased mobility for village women involving the clean water supply, a “traditional” Rajasthani woman becomes “modern”. Water, in parallel, becomes “new”, “improved” and worth paying for. Women and water resources are further connected through project staff’s efforts to promote latrines by targeting women as their primary users. The research shows that villagers applied their own meanings to latrines, some of which precluded women using them. This paper fills a gap in feminist political ecology, which often overlooks how gender is created through natural resource interventions, by concerning itself with how new meanings of “water” and “women” are mutually constructed through struggles over water use and its commodification. It contributes to critical development geography literatures by demonstrating that women’s participation approaches to natural resource development act as both constraints and opportunities for village constituents. It examines an under-explored area of gender and water research by tracing village-level struggles over meanings of latrines.  相似文献   

13.
The Reguibat Shield comprises a western “Archaean terrane” and eastern “Eburnean terrane” juxtaposed during the early Palaeoproterozoic Eburnean Orogeny. Metasedimentary rocks of probable Palaeoproterozoic age are preserved as flat-lying klippen (Kediat Ijil and Guelb Zednes) and steep imbricate zones (El Mahaoudat range and Sfariat Belt). These are interpreted to record a phase of thrust tectonics that emplaced a continental margin succession onto a composite Archaean foreland prior to ca. 2.06 Ga sinistral transcurrent deformation. Together, these events reflect partitioned Eburnean transpression.  相似文献   

14.
In the Witwatersrand approximately 40% of the gold is intimately associated with so-called “carbon” in “carbon seam reefs”, which occur in over a dozen paleoplacers, many of them concentrated at two stratigraphic levels in the 7000-m-thick succession of Archean siliciclastic sedimentary rocks. This is reduced carbon, present as kerogen admixed in various proportions with derivative (now solid) bitumen(s). Oil generation and migration were active geological processes during Early Earth history. Numerous possible source rocks for oil generation, including the carbon seams themselves, occur within the Witwatersrand basin. In the Witwatersrand ore, oil-bearing fluid inclusions are also present, derived like the bitumen, by thermal maturation of the kerogen. The presence of kerogen and bitumen in the Witwatersrand sedimentary rocks, together with a wealth of observations on the spatial distribution of the carbon seams confirm that the carbon originated in situ from living organisms in microbial mat cover, as opposed to flowing in from elsewhere as liquid hydrocarbons as some researchers have suggested. Paleochannels, which truncated auriferous carbon seams early in the depositional history, are of widespread occurrence, and micro-synsedimentary faults offset carbon seams. The carbon seams are thus indigenous biogenic markers that grew contemporaneously with placer development. The various features highlighting the nature and spatial distribution of Witwatersrand carbon seams provide a classic case where field evidence trumps laboratory data in the reconstruction of geological processes.  相似文献   

15.
Leping coal is known for its high content of “barkinite”, which is a unique liptinite maceral apparently found only in the Late Permian coals of South China. “Barkinite” has previously identified as suberinite, but on the basis of further investigations, most coal petrologists conclude that “barkinite” is not suberinite, but a distinct maceral. The term “barkinite” was introduced by (State Bureau of Technical Supervision of the People's Republic of China, 1991, GB 12937-91 (in Chinese)), but it has not been recognized by ICCP and has not been accepted internationally.In this paper, elemental analyses (EA), pyrolysis-gas chromatography, Rock-Eval pyrolysis and optical techniques were used to study the optical features and the hydrocarbon-generating model of “barkinite”. The results show that “barkinite” with imbricate structure usually occurs in single or multiple layers or in a circular form, and no definite border exists between the cell walls and fillings, but there exist clear aperture among the cells.“Barkinite” is characterized by fluorescing in relatively high rank coals. At low maturity of 0.60–0.80%Ro, “barkinite” shows strong bright orange–yellow fluorescence, and the fluorescent colors of different cells are inhomogeneous in one sample. As vitrinite reflectance increases up to 0.90%Ro, “barkinite” also displays strong yellow or yellow–brown fluorescence; and most of “barkinite” lose fluorescence at the maturity of 1.20–1.30%Ro. However, most of suberinite types lose fluorescence at a vitrinite reflectance of 0.50% Ro, or at the stage of high volatile C bituminous coal. In particular, the cell walls of “barkinite” usually show red color, whereas the cell fillings show yellow color under transmitted light. This character is contrary to suberinite.“Barkinite” is also characterized by late generation of large amounts of liquid oil, which is different from the early generation of large amounts of liquid hydrocarbon. In addition, “barkinite” with high hydrocarbon generation potential, high elemental hydrogen, and low carbon content. The pyrolysis products of “barkinite” are dominated by aliphatic compounds, followed by low molecular-weight aromatic compounds (benzene, toluene, xylene and naphthalene), and a few isoprenoids. The pyrolysis hydrocarbons of “barkinite” are mostly composed of light oil (C6–C14) and wet gas (C2–C5), and that heavy oil (C15+) and methane (C1) are the minor hydrocarbon.In addition, suberinite is defined only as suberinized cell walls—it does not include the cell fillings, and the cell lumens were empty or filled by corpocollinites, which do not show any fluorescence. Whereas, “barkinite” not only includes the cell walls, but also includes the cell fillings, and the cell fillings show bright yellow fluorescence.Since the optical features and the hydrocarbon-generating model of “barkinite” are quite different from suberinite. We suggest that “barkinite” is a new type of maceral.  相似文献   

16.
The most evolved rocks of the Pilansberg alkaline complex are aegirine lujavrites in which three varieties of eudialyte are recognized on the basis of textural relationships and composition. Manganoan eudialyte-I is a relict orthomagmatic phase occurring as poikilitic plates or as relict grains in pseudomorphed euhedral phenocrysts. Late eudialyte-II ranges in composition from manganoan eudialyte through kentbrooksite to taseqite-like varieties and is considered to be formed by cation exchange with eudialyte-I and alkaline fluids. Eudialyte-III is a hydrothermal phase replacing eudialyte-II, and has either taseqite-like (5–7.3 wt.% SrO, < 2.0 wt.% REE2O3) or kentbrooksite (< 1.5 wt.% SrO,  8.5 wt.% REE2O3) compositions. Three styles of replacement of eudialyte-I and -II are recognizable. Type 1 involves replacement by complex aggregates of zircon, fergusonite-(Ce), allanite-(Ce), britholite-(Ce), titanite, pyrochlore, albite and potassium feldspar, i.e. a “miaskitic” paragenesis. Type 2 alteration consists of complex aggregates dominated by deuteric Na–Zr-silicates (?catapleiite), stronalsite, strontium-apatite and lamprophyllite replacing eudialyte-I and -II and relicts of the “miaskitic paragenesis”, i.e. a highly sodic “agpaitic-to-hyperagpaitic” paragenesis. Type 3 replacement involves mantling of any residual eudialyte-II and zircon, and replacement of deuteric Na–Zr-silicates by eudialyte-III together with barytolamprophyllite as late hydrothermal phases. Further alteration and replacement resulted in the superposition of natrolite, britholite, pyrochlore, allanite and diverse Ba- and Mn-based minerals onto the types 2 and 3 assemblages, and ultimately to the deposition of allanite-(La), La-dominant REE carbonates and rarely a silica phase. All of the alteration styles are considered to have occurred in situ under subsolidus conditions (< 450 °C) by interaction of pre-existing eudialyte and other minerals with deuteric, sodium- and chlorine-bearing aqueous fluids. The evolution of the replacement products is from a miaskitic through an agpaitic to a hyperagpaitic paragenesis and ultimately back to a low agpaitic-to-miaskitic assemblage, reflecting changes in the a(Na+)/a(Cl−) ratio and alkalinity of the deuteric/hydrothermal fluids.  相似文献   

17.
The Tiámaro deposit in Michoacán state has been dated as Lower Cretaceous (Valanginian), though most of the porphyry deposits in central Mexico were dated or have an attributed Eocene–Oligocene age. The host rocks belong to a volcanoplutonic complex overlain by red conglomerates. These rocks were intruded by pre-Valanginian plutonic and hypabissal rocks. Propylitic, phyllic, and argillic alteration assemblages developed, and their superimposition draws the evolution of the deposit. Stage I is represented by propylitic assemblages, stage II contains the main ore forming stockworks and both phyllic and argillic assemblages, and stage III contains late carbonatization assemblages. The obtained temperatures and salinities from inclusion fluids are low for a porphyry-type deposit, but we interpret that the known part of the deposit represents the shallow portion of a bigger deposit. The evolution of mineralizing fluids draws a dilution trend of brines from “porphyry-like” to “epithermal-like” stages. The richest ore zone is roughly located between the 300 and 350 °C isotherms, though unnoticed resources may occur at depth.  相似文献   

18.
Barite occurrences related to the Cenozoic (Late Alpine) low-temperature hydrothermal activity are present in the continental Ohře (Eger) Rift area. A specific, Ra-bearing type of barite has been known under the name “radiobarite” from this area since 1904. Revision of 12 localities revealed the presence of alleged radiobarite only in the Teplice (Lahošť–Jeníkov) and Karlovy Vary areas. Barite from other localities is radium-poor. Barite crystals showing concentric oscillation colour zoning totally prevail. Isomorphous substitution of Sr (X×10−1 to X×wt%), Ca (X×10−2 wt%) and Fe (X×10−1 wt%) for Ba was proved. Average SrO contents of 0.4 wt% are markedly exceeded in some samples from Lahošť–Jeníkov (max. 3.2 wt%) and Karlovy Vary (max. 4.9 wt%). Besides inclusions of stoichiometric iron disulphide, the same samples also contain iron disulphides with unusual high contents of Co (max. 12.2 wt%) and Ni (max. to 8.4 wt%). Specific activity of 238U in the studied barites is very low while that of 226Ra reaches 8 Bq/g in several samples. Therefore, 226Ra is not in equilibrium with its parent uranium. These “radiobarites” or their parts must be therefore relatively young, not older than 10–15 ka. Very low uranium contents (<0.4 ppm) were also confirmed by neutron activation analyses of barite samples.

Unit-cell dimensions refined from X-ray powder diffraction data do not show any systematic variation with the measured chemical composition. Their values agree with the data given in the literature. Reflection half-widths, however, seem to correlate with chemistry. Peaks are wider in samples from Lahošť–Jeníkov and Karlovy Vary.

Sulphur and oxygen stable isotope compositions of the Cenozoic barite mineralization of Teplice area are very uniform (δ34S values between 3.9‰ and 7.1‰ CDT, and δ18O values between 6.1‰ and 7.7‰ SMOW), while the barites of Děc˘ín area show more variable sulphur sources. Sulphate derived from sediments of the Tertiary Most Basin seems to dominate for the Teplice area, while Cretaceous sediments are a more probable sulphur source in the Děc˘ín area. Calculation of oxygen isotope composition of hydrothermal fluids based on fluid inclusion homogenization temperatures and barite δ18O data shows δ18Ofluid values in the range of meteoric waters or δ18O – shifted deep circulating meteoric or basinal waters.  相似文献   


19.
Dolomite is a common mineral in the rock record but rare in recent superficial environments. Where it does occur, it is related to anoxic, sulfate-rich environments and microbial activity. The occurrence of some dolomite deposits in caves, however, indicates that dolomite formation is also possible in oxic, non-sulfate settings. Dolomite is forming at 17 °C and in oxic-vadose conditions on the host rocks and aragonite speleothems of the Castañar Cave, Cáceres, Spain. It appears as spheroids and dumbbells 50–300 μm in diameter that internally consist of micron-sized rhombic to rounded crystals. Initially this dolomite is Ca-rich, non-stoichiometric and poorly ordered. Mg-rich solutions allow the precipitation of metastable Mg-rich carbonates, such as huntite. This soon transforms into this Ca-rich dolomite, which later “ages” to form a more stoichiometric dolomite. These dolomites show similarities to those grown under anoxic, sulfate-rich conditions and their presence in caves provides a different setting that may contribute to the understanding of the “dolomite problem”, including their initial formation and later recrystallization processes.  相似文献   

20.
In the Mt. Franks area of the Willyama Complex, microfabric evidence suggests that the alteration of andalusite to sillimanite has taken place by a process similar to that suggested by Carmichael (1969). Andalusite is pre- to syn-S2 in age. Alteration to “sericite” has resulted in the formation of “sericite” laths, some of which are crenulated about S2, and some which are syn- and post-S2. “Fibrolite” occurs in these andalusite—“sericite” aggregates within the sillimanite zone and is wholly embedded in “sericite”. “Fibrolite” is pre- to syn-S2 in age. This evidence is interpreted as suggesting that the formation of sillimanite from andalusite took place via a “sericite” phase.Further microfabric observations are interpreted to imply constant volume for the reaction aluminosilicate → “sericite”. This suggests a situation in which Al3+ is relatively mobile but Al4+ is relatively immobile. This suggestion differs from Carmichael's (1969) idea of Al3+ immobility.  相似文献   

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