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1.
Engineering properties of unfired clay masonry bricks   总被引：2，自引：1，他引：1  
The shortage of low cost and affordable housing in the UK has led to many investigations into new building masonry materials. Fired clay masonry bricks are conventionally used for mainstream masonry wall construction but suffer from the rising price of energy plus other related environmental problems such as high energy usage and carbon dioxide emission. The use of stabilised unfired clay bricks for masonry construction may solve these problems.This paper reports on the engineering properties of unfired clay bricks produced during the first industrial trial of unfired clay material development carried out at Hanson Brick Company, in Stewartby, Bedfordshire, under the Knowledge Exploitation Fund (KEF) Collaborative Industrial Research Project (CIRP) programme. The mixes were formulated using a locally available industrial by-product (Ground Granulated Blastfurnace Slag — GGBS) which is activated with an alkaline (lime or Portland cement) combined with clay soil. Portland cement was not used in the formulation of the unfired stabilised masonry bricks, except as a control, which is a significant scientific breakthrough for the building industry. Another breakthrough is the fact that only about 1.5% lime was used for GGBS activation. This level of lime is not sufficient for most road construction applications where less strength values are needed and where 3–8% lime is required for effective soil stabilisation. Hence, the final pricing of the unfired clay bricks is expected to be relatively low.The laboratory results demonstrate that the compressive strength, moisture content, rate of water absorption, percentage of void, density and durability assessment (repeated 24-hour freezing/thawing cycles) were all within the acceptable engineering standards for clay masonry units. The paper also discusses on the environmental performance of the unfired clay in comparison to the bricks, used in mainstream construction of today. The bricks produced using this technology can be used for low-medium cost housing and energy efficient masonry wall construction.  相似文献   

2.
Flooding has a significant impact on road infrastructural development and maintenance. This study was aimed at mitigating the effects of flooding of low-bearing capacity soils, a solution that could alleviate the effects of flooding on road structural layers, especially, those constructed on flood susceptible soils and/or regions. The achievement of such an improvement would foster the growth of road infrastructural development, particularly for low income economies where critical savings accruing from this mitigation effect could be invested in further development projects.Laboratory simulation of flooding was carried out on stabilized soil test specimens. The production of the test specimens involved the use of Lower Oxford Clay (LOC) as a typical low-bearing capacity soil, stabilized using varying proportions of a latently hydraulic industrial by-product material – Ground Granulated Blastfurnace Slag (GGBS) – blended with quicklime (CaO) as an activator. Reducing the use of lime by incorporating GGBS enhances sustainability of the proposed process. Cylindrical test specimens of 50 mm in diameter and 100 mm in height were statically compacted to achieve maximum dry density (MDD), prior to moist curing for varying time periods before simulating prolonged flooding. Water absorption was monitored during the flooding process, and the specimens then tested for compressive strength. The results suggest potential of these lime–GGBS–LOC mixtures in overcoming the deleterious effect of flooding, by reduced water absorption and maintenance of a rigid cementing matrix structure after prolonged flooding. This is believed to offer savings from the improved robustness of road structural layers upon flooding, through resource conservation and material durability enhancement.  相似文献   

3.
A geological survey carried out in the Yaoundé (Cameroon) region has revealed the presence of homogeneous clayey laterite in the upper part of a laterite cover on interfluves, thickest on hills (780–800 m altitude) where ferricrete is absent, and clayey heterogeneous hydromorphic material in valleys. We present in this paper the physical, mineralogical and geochemical properties of these occurrences and discuss their potential as raw material for pottery, manufacture of bricks and tiles. These clayey raw materials are mostly made up of fine particles (ranging from 55 to 60% clay + silt in the clayey laterite, more than 70% clay + silt in the clayey hydromorphic material). Their chemical composition is characterized by silica (<60% SiO2), alumina (<35% Al2O3) and iron (ranging from 3 to 14% Fe2O3). Their main clay minerals are disorganized and poorly crystallized kaolinites. The average limits of liquidity (44.56% versus 91.58%) and limits of plasticity (22.4 versus 45.93) revealed that clayey hydromorphic material has the greatest plasticity. The studied raw materials are suitable for making pottery as well as the manufacture of bricks and tiles. However, the high iron content in the clayey laterite (between 11 and 12% Fe2O3) prevents their efficient use in the manufacture of ceramics.  相似文献   

4.
The main objective of this research was to investigate the effect of mellowing on the swelling properties of stabilized Lower Oxford Clay (LOC), a sulfate-bearing clay soil that has caused concern in the past due to expansion upon stabilization. Two stabilizers were used, quicklime and a more sustainable stabilizer — wastepaper sludge ash (WSA), an industrial by-product used on its own and in combination with either quicklime (CaO) or ground granulated blastfurnace slag (GGBS). Quicklime was used on its own as a control. Compacted cylinders of LOC stabilized with the various stabilizers were made either mellowed (compacted 3 days after mixing with stabilizer) or unmellowed (compacted immediately after mixing with stabilizer). The linear expansion of the stabilized cylinders during moist curing and subsequent soaking was monitored for a total of 100 days. The results obtained showed that the linear expansion of unmellowed stabilized LOC was significantly reduced, and thus in terms of swelling potential, mellowing was not beneficial in the LOC system investigated. The results observed also suggest that there are technological, economic as well as environmental advantages of utilizing WSA and similar industrial by-products, in the stabilization of sulfate-bearing and other clay soils, as an alternative to the traditional stabilizers of lime and/or Portland Cement.  相似文献   

5.
Lateritic soils which have been described as highly weathered tropical or subtropical residual soils were studied with an attempt to establish its suitability or otherwise as sustainable material in building bricks and housing development that will meet the present challenge of sustaining the environment without costing too much and maintaining a high standard of strength, durability and aesthetics. Index properties of the tested lateritic soils revealed them as mostly well graded, comprising both cohesive (silt and clay) and cohesionless (sand and gravel) soil fraction. The geotechnical analyses on the studied lateritic soil revealed a strong compressive strength with a relatively sound dry density which could guarantee a good durability in resulting bricks made from these soil materials. Further test on the strength and durability of the compressed earth bricks (CEBs) made from these lateritic soils revealed a brick with compressive strength ranging between 6.33 and 15.57 MPa which is considered to be of good strength coupled with its sound durability strength established over a period of more than one year under a complete cycle of weather and seasonal conditions. In conclusion, lateritic soils from the study area were found to be suitable as materials for bricks (CEB) with good compressive and durability strength which qualifies them as sustainable and cost-effective materials for low-cost housing development.  相似文献   

6.
The increasing demand for building materials has led to indiscriminate exploitation of clay-rich topsoil from wetlands including the paddy lands of Central Kerala in the southwestern coast of India. The problem is critical in areas adjoining the major developmental centers having low per capita land and natural resource availability. Loss of fertile topsoil, shrinkage of agricultural lands and consequent food security issues, erosion of naturally evolved nutrients, lowering of water table in wells adjacent to the mining sites, etc., are some of the major environmental issues arising from indiscriminate brick and tile clay mining. Although, brick and tile clay mining brings short-term economic benefits and employment opportunities to a section of people, the process in the long run creates severe damages to the environmental settings of the area. The present paper deals with a few aspects of brick and tile clay mining in the paddy lands of Central Kerala, especially around Kochi City, a fast developing urban-cum-industrial center in South India, which demands large quantities of building materials including bricks and tiles for construction of infrastructural facilities. It is estimated that 729,695 tons/year (ty?1) of brick and tile clays are extracted from the coastal lowlands of Central Kerala, spreading to the Chalakudy (135,975 ty?1), Periyar (483,820 ty?1) and Muvattupuzha (109,900 ty?1) river basins. The N, P and K loss through extraction of brick and tile clays amounts to 210 ty?1, 96 ty?1 and 9,352 ty?1, respectively. As nutrient loss is an irreversible process in human time scale, its implications on agricultural productivity is a matter of serious concern. The study warrants the need for a comprehensive policy with an aim to regulate the mining activities on an environment- friendly basis in the densely populated coasts of the world, in general, and the study area in particular.  相似文献   

7.
As the two important components of shale, organic matter(OM) and clay minerals are usually thought to strongly influence the hydrocarbon generation, enrichment and exploitation. The evolution process of OM and clay minerals as well as their interrelationship over a wide range of thermal maturities are not completely clear. Taking Yanchang(T_3y), Longmaxi(S_1l) and Niutitang(?_1n) shales as examples, we have studied the microstructure characteristics of OM and clay minerals in shales with different thermal maturities. The effects of clay minerals and OM on pores were reinforced through sedimentation experiments. Using a combination of field emission scanning electron microscopy(FESEM) and low-pressure N_2 adsorption, we investigated the microstructure differences among the three shales. The results showed that both OM and clay minerals have strong effects on pores, and small mesopore(2–20 nm) is the dominant pore component for all three samples. However, the differences between the three samples are embodied in the distribution of pore size and the location. For the T_3y shale, clay minerals are loosely arranged and develop large amounts of pores, and fine OM grains often fill in intergranular minerals or fractures. Widespread OM pores distribute irregularly in S_1l shale, and most of the pores are elliptical and nondirectional. The ?_1n shale is characterized by the preferred orientational OM-clay aggregates, and lots of pores in the composites are in the mesopore range, suggesting that over maturity lead to the collapse and compaction of pores under huge pressure of strata. The results of the current research imply that with increasing thermal maturity, OM pores are absent at low maturity(T_3y), are maximized at high maturity(S_1l) and are destroyed or compacted at over-mature stage(?_1n). Meanwhile, clay minerals have gone through mineral transformation and orientational evolution. The interaction of the two processes makes a significant difference to the microstructure evolution of OM and clay minerals in shale, and the findings provide scientific foundation in better understanding diagenetic evolution and hydrocarbon generation of shale.  相似文献   

8.
Tertiary volcanism in the İkizce region at the western edge of the eastern Pontides paleo-magmatic arc is represented by basaltic and andesitic rocks associated with sediments deposited in a shallow basin environment. The basaltic rocks contain plagioclase (An58–80), olivine (Fo82–84), clinopyroxene (Wo44–48En35–42Fs7–17), hornblende (Mg# = 0.68–0.76) phenocrysts, and magnetite microcrysts, whereas the andesitic rocks include plagioclase (An25–61), clinopyroxene (Wo46–49En38–43Fs11–13), hornblende (Mg# = 0.48–0.81), biotite (Mg# = 0.48–0.60) phenocrysts, titanomagnetite, apatite, and zircon microcrysts.Geochemical data indicate magmatic evolution from tholeiitic-alkaline transitional to calc-alkaline characteristics with medium-K contents. The geochemical variation in the rocks can be explained by fractionation of common mineral phases such as clinopyroxene, olivine, hornblende, plagioclase, magnetite, and apatite. The trace elements’ distributions of the volcanic rocks show similarities to those of E-Type MORB, have a shape that is typical of rocks from subduction-related tectonic setting with enrichment in LILE and to a lesser extent in LREE, but depletion in HFSE. The rocks evolved from a parental magma derived from an enriched source formed by subduction induced metasomatism of basaltic rocks, the latter formed through clinopyroxene ± olivine controlled fractionation in a high level magma chamber. The andesitic rocks developed through hornblende ± plagioclase controlled fractionation in shallow level magma chamber(s).  相似文献   

9.
To further our knowledge of the coupling between the hydraulic and mechanical behaviours of the swelling soils, this paper presents an experimental study on a bentonite/silt mixture using an osmotic odometer. A loading/unloading cycle was applied to samples with different initial dry densities (1.27, 1.48, and 1.55 Mg m− 3) at different constant suctions (0, 2, and 8 MPa). We noted that the initial state of the soils after compaction significantly influenced the values of the apparent preconsolidation stress p0(s), the virgin compression index λ(s), and the elastic compression index κ.These experimental results provided a sufficient database to interpret the mechanical behaviour of the swelling soil and define three yielding surfaces:
– the suction limit between micro- and macrostructure (sm/M) and the suction limit between nano- and microstructure (sn/m), which depend completely on the soil fabrics and the diameter separating the nano-, micro-, and macrostructure,
– the Loading Collapse (LC) curve, representing the preconsolidation stress variation as a function of suction,
– the Saturation Curve (SC), representing the variation of the saturation stress (Psat) as a function of suction.
In general, we can state that the increase of compaction pressure unified the LC and SC surfaces and decreased the (sm/M) value without modifying the (sn/m) value.  相似文献   

10.
Two kimberlite pipes in Elliott County contain rare ultramafic xenoliths and abundant megacrysts of olivine (Fo85–93), garnet (0.21–9.07% Cr2O3), picroilmenite, phlogopite, Cr-poor clinopyroxene (0.56–0.88% Cr2O3), and Cr-poor orthopyroxene (<0.03–0.34% Cr2O3) in a matrix of olivine (Fo88–92), picroilmenite, Cr-spinel, magnetite, perovskite, pyrrhotite, calcite, and hydrous silicates. Rare clinopyroxene-ilmenite intergrowths also occur. Garnets show correlation of mg (0.79–0.86) and CaO (4.54–7.10%) with Cr2O3 content; the more Mg-rich garnets have more uvarovite in solution. Clinopyroxene megacrysts show a general decrease in Cr2O3 and increase in TiO2 (0.38–0.56%) with decreasing mg (0.87–0.91). Clinopyroxene megacrysts are more Cr-rich than clinopyroxene in clinopyroxene-ilmenite intergrowths (0.06–0.38% Cr2O3) and less Cr-rich than peridotite clinopyroxenes (1.39–1.46% Cr2O3). Orthopyroxene megacrysts and orthopyroxene inclusions in olivine megacrysts form two populations: high-Ca, high-Al (1.09–1.16% CaO and 1.16–1.18% Al2O3) and low-Ca, low-Al (0.35–0.46% CaO and 0.67–0.74% Al2O3). Three orthopyroxenes belonging to a low-Ca subgroup of the high-Ca, high-Al group were also identified (0.86–0.98% CaO and 0.95–1.01% Al2O3). The high-Ca, high-Al group (Group I) has lower mg (0.88–0.90) than low-Ca, low-Al group (Group II) with mg=0.92–0.93; low mg orthopyroxenes (Group Ia) have lower Cr2O3 and higher TiO2 than high mg orthopyroxenes (Group II). The orthopyroxene megacrysts have lower Cr2O3 than peridotite orthopyroxenes (0.46–0.57% Cr2O3). Diopside solvus temperatures indicate equilibration of clinopyroxene megacrysts at 1,165°–1,390° C and 1,295°–1,335° C for clinopyroxene in clinopyroxene-ilmenite intergrowths. P-T estimates for orthopyroxene megacrysts are bimodal: high-Ca, high-Al (Group I) orthopyroxenes equilibrated at 1,165°–1,255° C and 51–53 kb (± 5kb) and the low-Ca, low-Al (Group II) orthopyroxenes equilibrated at 970°–1,020°C and 46–56 kb (± 5kb). Garnet peridotites equilibrated at 1,240°–1,360° C and 47–49 kb. Spinel peridotites have discordant temperatures of 720°–835° C (using spinel-olivine Fe/Mg) and 865°–1,125° C (Al in orthopyroxene).Megacrysts probably precipitated from a fractionating liquid at >150 km depth. They are not disaggregated peridotite because: (1) of large crystal size (up to 1.5 cm), (2) compositions are distinctly different from peridotite phases, and (3) they display fractionation trends. The high mg, low T orthopyroxenes and the clustering of olivine rims near Fo89–90 reflect liquid changes to higher MgO contents due to (1) assimilation of wall-rock and/or (2) an increase in Fe3+/Fe2+ and subsequently MgO/FeO as a result of an increase in f o.  相似文献   

11.
The Zagros fold-and-thrust belt of SW-Iran is among the youngest continental collision zones on Earth. Collision is thought to have occurred in the late Oligocene–early Miocene, followed by continental shortening. The High Zagros Belt (HZB) presents a Neogene imbricate structure that has affected the thick sedimentary cover of the former Arabian continental passive margin. The HZB of interior Fars marks the innermost part of SE-Zagros, trending NW–SE, that is characterised by higher elevation, lack of seismicity, and no evident active crustal shortening with respect to the outer (SW) parts. This study examines the brittle structures that developed during the mountain building process to decipher the history of polyphase deformation and variations in compressive tectonic fields since the onset of collision. Analytic inversion techniques enabled us to determine and separate different brittle tectonic regimes in terms of stress tensors. Various strike–slip, compressional, and tensional stress regimes are thus identified with different stress fields. Brittle tectonic analyses were carried out to reconstruct possible geometrical relationships between different structures and to establish relative chronologies of corresponding stress fields, considering the folding process. Results indicate that in the studied area, the main fold and thrust structure developed in a general compressional stress regime with an average N032° direction of σ1 stress axis during the Miocene. Strike–slip structures were generated under three successive strike–slip stress regimes with different σ1 directions in the early Miocene (N053°), late Miocene–early Pliocene (N026°), and post-Pliocene (N002°), evolving from pre-fold to post-fold faulting. Tensional structures also developed as a function of the evolving stress regimes. Our reconstruction of stress fields suggests an anticlockwise reorientation of the horizontal σ1 axis since the onset of collision and a significant change in vertical stress from σ3 to σ2 since the late stage of folding and thrusting. A late right-lateral reactivation was also observed on some pre-existing belt-parallel brittle structures, especially along the reverse fault systems, consistent with the recent N–S plate convergence. However, this feature was not reflected by large structures in the HZB of interior Fars. The results should not be extrapolated to the entire Zagros belt, where the deformation front has propagated from inner to outer zones during the younger events.  相似文献   

12.
Some of the rocks and soil-originated materials used in building construction are the serious natural radiation sources. Soil-originated bricks and roof-tiles and their raw material in the Salihli-Turgutlu area were tested in situ for natural radiation levels using a gamma-ray spectrometer. The concentrations of the radioelements 40K, 238U and 232Th and air-absorbed radiation rates were measured for soil, raw material heaps, brick and roof-tile stacks and waste brick heaps. The radium-equivalent activity Raeq of the raw material varied between 187.9 and 216.4 Bq kg?1. The external radiation hazard index Hex values ranged between 0.51 and 0.58. For building material and its products, recommended Raeq and Hex levels are 370 Bq kg-1 and 1.0, respectively. On the other hand, both Raeq and Hex values for waste brick heaps, containing broken brick pieces, coal pieces and ash, were higher than the recommended levels, i.e. Raeq values varied from 473.8 to 651.0 Bq kg-1 and Hex values were within the range 1.15–1.76. The annual dose rate and radium-equivalent activity values of the brick and roof-tiles were below the level of criteria. Annual dose rate ranged between 0.42 and 0.62 mSv y?1 and radium equivalent activity was in the range 172.9–245.2 Bq kg?1. The external and internal radiation hazard indices were all below the value of 1.0 for the Salihli-Turgutlu area bricks and roof-tiles. Results of this study were compared with results of previous studies. Natural radiation levels of construction raw material of study area are generally higher than of those of previous studies.  相似文献   

13.
This paper describes the distribution of Fe and Ni between the octahedral and tetrahedral sites in pentlandite (Fe,Ni)9S8. The dependence of the distribution on pressure and temperature and the activation energy of the cation exchange reaction were determined through annealing experiments. Synthetic crystals were annealed at 433–723 K and pressures up to 4 GPa, and natural crystals were annealed at 423, 448 and 473 K in evacuated silica capillary tubes for various durations. The cation distributions in the synthetic crystals were determined with an X-ray powder method employing the anomalous dispersion effect of CuK. and FeK radiations, while those of natural crystals were calculated from the cell dimensions. The values of U, S and V for the Fe/Ni exchange reaction are –6818 J mol–1, 20.52 J K–1 mol–1, and 6.99 × 10–6 m3 mol–1, respectively. The dependence of the Fe/Ni distribution on pressure (Pa) and temperature (Kelvin) was determined as lnK = 2.47+8.20 × 102 T –1+8.41 x 10–7 T –1 P, where K = (Fe/Ni)octahedral /(Fe/Ni)tetrahedral. The activation energy of the cation exchange reaction was 185 kJ mol–1.  相似文献   

14.
The overexploitation of groundwater in some parts of the country induces water quality degradation. The untreated industrial effluents discharged on the surface causes severe groundwater pollution in the industrial belt of the country. This poses a problem of supply of hazard free drinking water in the rural parts of the country. There are about 80 tanneries operating in and around Dindigul town in upper Kodaganar river basin, Tamilnadu, India. The untreated effluents from the tanneries have considerably affected the quality of groundwater in this area. To assess the extent of groundwater deterioration, a detailed analysis of groundwater quality data has been carried out. The concentration of cations such as Calcium (Ca2+), Magnesium (Mg2+), Sodium (Na+) and Potassium (K+), and anions such as Bicarbonate (HCO3–), Sulphate (SO42–), Chloride (Cl–) and Nitrate (NO3–) in the groundwater have been studied. Apart from these constituents, pH, electrical conductivity (EC), total dissolved solid and total hardness (TH as CaCO3) were also studied. The correlation of these constituents with the EC has been carried out. The highest correlation is observed between EC and chloride with a correlation coefficient of 0.99. Progressive reduction in correlation coefficients for Mg2+, (Na+ + K+), Ca2+ and SO42– are observed as 0.91, 0.87, 0.86 and 0.56, respectively. It is found that the quality of groundwater in the area under investigation is deteriorated mainly due to extensive use of salt in the leather industries.  相似文献   

15.
Alkaline lavas were erupted as phonolites and trachytes around Karaburhan (Sivrihisar–Eskisehir, NW Anatolia) within the Izmir–Ankara–Erzincan suture zone. These volcanic rocks were emplaced as domes, close and parallel to the ophiolite thrust line. According to 40Ar/39Ar geochronological analyses of sanidine crystals from the phonolites, the age of the alkaline volcanics is 25 Ma (Late Oligocene–Early Miocene).The flow-textured phonolites are porphyritic and consist mainly of sanidine, clinopyroxene, and feldspathoid crystals. The clinopyroxenes show compositional zoning, with aegirine (Na0.82–0.96Fe+30.68–0.83) rims and aegirine–augite cores (containing calcium, magnesium, and Fe+2). Some aegirine–augites are replaced with sodium-, calcium-, and magnesium-rich amphibole (hastingsite). Feldspathoid (hauyne) crystals enriched with elemental Na and Ca have been almost completely altered to zeolite and carbonate minerals. The fine-grained trachytes with a trachytic texture consist of feldspar (oligoclase and sanidine) phenocrystals and clinopyroxene microphenocrystals within a groundmass made up largely of alkali feldspar microlites.Although there are some differences in their element patterns, the phonolites and trachytes exhibit enrichment in LILEs (Sr, K, Rb, Ba, Th) and LREEs (La, Ce, Pr, Nd) and negative anomalies in Nb and Ta. These geochemical characteristics indicate a lithospheric mantle enriched by fluids extracted from the subduction component. In addition, the high 87Sr/86Sr (0.706358–0.708052) and low 143Nd/144Nd (0.512546–0.512646) isotope concentrations of the alkaline lavas reflect a mantle source that has undergone metasomatism by subduction-derived fluids. Petrogenetic modeling indicates that the alkaline lavas generated from the subduction-modified lithospheric mantle have undergone assimilation, fractional crystallization, and crustal contamination, acquiring high Pb, Ba, Rb, and Sr contents and Pb isotopic compositions during their ascent through the thickened crust in an extensional setting.  相似文献   

16.
Ultramafic-mafic rocks from Makrirrakhi, Central Greece exhibit features of an original ophiolite sequence which contains depleted mantle material, ultramafic containing partial melt textures and possibly the mafic pluton which resulted from the coalescing of these partial melt segregations. Considerable mineralogical variation exists: unzoned olivine crystals range in composition from Fo78–84 (mafics) to Fo88–92 (ultramafics), plagioclases An64–79 (mafics) to An80–90 (ultramafics) and spinel varies from a chromian spinel (ultramafics) to a more aluminous-titaniferous spinel (mafics). Pyroxenes from the ultramafics display a limited range: En89–92 Fs9–8 Wo0–2 (orthopyroxene) and En48–54 Fs1–10 Wo38–50 (clinopyroxene). Mafic rocks display a greater range being richer in ferrosilite En36–65 Fs3–20 Wo33–51. Pyroxenes from within the partial melt segregations have chemical affinities with those from the gabbrotroctolite series. A model of partial melt within the upper mantle, and, a set of criteria to distinguish partial melt textures from cumulate textures, are developed from analytical data and textural evidence.  相似文献   

17.
Magnetic properties, free and active Fe oxides, grain size distribution and mineral assemblage of a Quaternary loess–Tertiary red clay (TRC) section in Lingtai County in the Chinese Loess Plateau were studied. The results suggest that the TRC of the Lingtai section shares similar aeolian characteristics with the overlying Quaternary loess-paleosol sequence (QLPS), but the former is generally more intensively weathered than the latter, as indicated by its higher citrate–bicarbonate–dithionite (CBD) extractable Fe (Fed), finer grain size and lower content of easily weathered primary minerals. However, magnetic susceptibility (χlf) and magnetic remanence (χarm, SIRM and SOFT etc.) of the main part of the TRC are significantly lower, implying the decline of ferrimagnetic minerals (FM). In contrast, hematite and goethite in the TRC is significantly enhanced, as indicated by its higher HIRM. The acid ammonium oxalate (AAO) extractable Fe (Feo) of the whole section sharply decreases with increasing age. Feo and Feo/Fed values of the section are significantly correlated with χlf. Especially in the TRC, the low values of Feo and Feo/Fed correspond to weak χlf. This suggests a significant influence of the age-related transformation of Fe oxides on the decline of FM in the TRC. Lower FM and higher hematite and/or goethite in the TRC further suggest the transformation of FM into hematite with the aging of Fe oxides during post-depositional processes, though more evidence is needed to understand the processes involved. χlf of the TRC in the Chinese Loess Plateau mostly cannot be regarded as a promising paleoclimatic proxy because its weak magnetism does not correlate to its strong pedogenesis.  相似文献   

18.
The Tin Zebane gabbro–anorthosite layered mafic intrusion represented by plagioclase-rich cumulates forms a set of small lenticular to round-shaped mainly undeformed bodies intruding the Pan-African high-pressure metamorphic rocks from western Hoggar (Tuareg shield, southwest Algeria). The coarse-grained anorthosites are mainly made of slightly zoned bytownite (An86–74) with the higher anorthite content at the cores. Anorthosites are interlayered with leucogabbros and gabbros that show preserved magmatic structures and with olivine gabbros characterised by coronitic textures. The primary assemblage in gabbros includes plagioclase (An93–70), olivine (Fo77–70), zoned clinopyroxene (En43–48Fs05–13Wo41–49 with Al2O3 up to 4.3 wt.%) and rare orthopyroxene (En73–78). Pyroxenes and olivine are commonly surrounded by Ca-amphibole. The olivine–plagioclase contact is usually marked by a fine orthopyroxene–Cr-spinel–amphibole symplectite. A magnesian pigeonite (En70–75Fs19–20Wo6–10) is also involved in corona. The coronitic minerals have equilibrated with the primary mineral rims at P–T–aH2O conditions of 797 ± 42 °C for aH2O=0.5 and 808 ± 44 °C for aH2O=0.6 at 6.2 ± 1.4 kbar. The Tin Zebane gabbroic rocks are depleted in REE with a positive Eu anomaly, high Sr (>10 * chondrite) and Al2O3 concentrations (17–33%) that support plagioclase accumulation with the extreme case represented by the anorthosites. The REE patterns can be modelised using plagioclase, clinopyroxene and orthopyroxene REE signature, without any role played by accessory minerals. High MgO content points to olivine as a major cumulate phase. Anorthositic gabbros Sr and Nd isotopic initial ratios are typical of a depleted mantle source (Sri=0.70257–0.70278; Nd=+5.9 to +7.8). This isotopic signature is identical to that of the 10-km wide 592 Ma old dyke complex composed of alkaline to peralkaline granites and tholeiitic gabbros and one single bimodal complex can be inferred. The source of the Tin Zebane basic rocks corresponds to the prevalent mantle (PREMA). The Tin Zebane complex was emplaced along the mega-shear zone bounding to the west the Archaean In Ouzzal metacraton. The model proposed suggests a linear lithospheric delamination along this rigid and cold terrane due to post-collisional transtensional movements. This allowed the asthenosphere to rise rapidly and to melt by adiabatic pressure release. Transtension along a rigid body allowed these mantle melts to reach the surface rapidly without any crustal contamination.  相似文献   

19.
The Francisco I. Madero deposit, central Mexico, occurs in the Mesozoic Guerrero Terrane, which hosts many ore deposits, both Cretaceous (volcanogenic massive sulfides) and Tertiary (epithermal and skarn deposits). It is hosted by a 600 m-thick calcareous-pelitic unit, of Lower Cretaceous age, crosscut by porphyritic dikes that strike NW–SE. A thick felsic volcanic Tertiary sequence, consisting of andesites and rhyolitic ignimbrites, unconformably overlies the Cretaceous series. At the base, the mineralization consists of several mantos developed within calcareous beds. They are dominantly composed of sphalerite, pyrrhotite and pyrite with minor chalcopyrite, arsenopyrite and galena. At the top of the orebody, there are calcic skarns formed through prograde and retrograde stages. The resulting mineral assemblages are rich in manganoan hedenbergite (Hd75–28Di40–4Jh40–20), andraditic garnets (Adr100–62Grs38–0), epidote (Ep95–36Czo60–5Pie8–0), chamosite, calcite and quartz. The temperature of ore deposition, estimated by chlorite and arsenopyrite geothermometry, ranges from 243° to 277 °C and from 300° to 340 °C, respectively. The pressure estimated from sphalerite geobarometry averages 2.1 kbar. This value corresponds to a moderately deep skarn and agrees with the high Cu content of the deposit. Paragenesis, P–T conditions and geological characteristics are compatible with a distal, dike-related, Zn skarn deposit. Its style of mineralization is similar to that of many high-temperature carbonate replacement skarn deposits in the Southern Cordillera.  相似文献   

20.
Multi-equilibrium thermobarometry shows that low-grade metapelites (Cubito-Moura schists) from the Ossa–Morena Zone underwent HP–LT metamorphism from 340–370 °C at 1.0–0.9 GPa to 400–450 °C at 0.8–0.7 GPa. These HP–LT equilibriums were reached by parageneses including white K mica, chlorite and chloritoid, which define the earliest schistosity (S1) in these rocks. The main foliation in the schists is a crenulation cleavage (S2), which developed during decompression from 0.8–0.7 to 0.4–0.3 GPa at increasing temperatures from 400–450 °C to 440–465 °C. Fe3+ in chlorite decreased greatly during prograde metamorphism from molar fractions of 0.4 determined in syn-S1 chlorites down to 0.1 in syn-S2 chlorites. These new data add to previous findings of eclogites in the Moura schists indicating that a pile of allochtonous rocks situated next to the Beja-Acebuches oceanic amphibolites underwent HP–LT metamorphism during the Variscan orogeny. To cite this article: G. Booth-Rea et al., C. R. Geoscience 338 (2006).  相似文献   

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