Journal of African Earth Sciences (and the Middle East)最新文献_第5页

Recent eruptive episodes of the Rungwe volcanic field (Tanzania) recorded in lacustrine sediments of the Northern malawi rift 在马拉维北部裂谷的湖泊沉积物中记录的Rungwe火山场(坦桑尼亚)最近的爆发事件

Journal of African Earth Sciences (and the Middle East) Pub Date : 1993-07-01 DOI: 10.1016/0899-5362(93)90020-Q

T.M. Williams , P.J. Henney , R.B. Owen

{"title":"Recent eruptive episodes of the Rungwe volcanic field (Tanzania) recorded in lacustrine sediments of the Northern malawi rift","authors":"T.M. Williams , P.J. Henney , R.B. Owen","doi":"10.1016/0899-5362(93)90020-Q","DOIUrl":"10.1016/0899-5362(93)90020-Q","url":null,"abstract":"<div>Discrete ash horizons in Holocene sediments from northern Lake Malawi provide evidence of six eruptive episodes within the nearby Rungwe Volcanic Field between c.9000-360 BP. Rare earth element (REE) analyses show the ash layers to be strongly enriched in La, Ce, Pr, Nd, Sm, Tb, Dy, Er, Tm, Yb and Lu, with low Eu/Eu∗ and high LaN/SmN values, relative to the surrounding muds. Mixing calculations suggest possible affinities between the Rungwe ash emissions and silicic volcanics from other important Quaternary centres (e.g. Naivasha) with respect to HREE geochemistry. The LREE spectra are less comparable and may indicate a less fractionated ash assemblage for Rungwe Field. In the absence of clear in situ evidence regarding the timing and frequency of Holocene eruptions at Rungwe, the Lake Malawi sediments may prove a valuable reconstructive tool. However, the direction and extent of ash dispersal is strongly controlled by wind/climatic factors and the retention of a complete record at any single location is unlikely.</div>","PeriodicalId":100750,"journal":{"name":"Journal of African Earth Sciences (and the Middle East)","volume":"17 1","pages":"Pages 33-39"},"PeriodicalIF":0.0,"publicationDate":"1993-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(93)90020-Q","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53885631","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 20

Un modèle de lagune d'âge protérozoïque supérieur: le schisto-calcaire du Congo 上元古代泻湖模型:刚果片岩-石灰石

Journal of African Earth Sciences (and the Middle East) Pub Date : 1993-07-01 DOI: 10.1016/0899-5362(93)90024-K

Ph. Alvarez

引用次数: 4

Thermal treatment for separating quartz from geethitic iron ore of Gebel Ghorabi, Bahariya oasis, Western Desert, Egypt 埃及西部沙漠Bahariya绿洲Gebel Ghorabi土质铁矿石中石英的热处理研究

Journal of African Earth Sciences (and the Middle East) Pub Date : 1993-07-01 DOI: 10.1016/0899-5362(93)90025-L

H.M.Abdel Monen, A.F. Kamel

{"title":"Thermal treatment for separating quartz from geethitic iron ore of Gebel Ghorabi, Bahariya oasis, Western Desert, Egypt","authors":"H.M.Abdel Monen, A.F. Kamel","doi":"10.1016/0899-5362(93)90025-L","DOIUrl":"10.1016/0899-5362(93)90025-L","url":null,"abstract":"<div>Gebel Ghorabi is located at the extreme northern end of Bahariya Oasis and the mineralized area covers an area of about 2 km2. Geologically, the iron ore is composed of random alternations of three main yellow, brown and dark brown colored bands. The former band is relatively thicker than the others. The iron particles range in size from a (pisolitic ⪢) fraction > 2 mm to earthy (the so-called pisolites may grade down from coarse to about 0.25 mm in size).A bulk sample corresponding more or less to the yellow iron ore band contains 54.16% Fe2O3, 26.13% SiO2 and 5.39% Al2O3 as major components.Technologically, the combined effect of a thermal reduction and of a quenching shock on the crushed iron sample (-12 mm) has been investigated. This technique has been found to sufficiently enhance the magnetic properties of the iron minerals which could be easily separated by using a low intensity magnetic separator.The maximum severance of quartz grains from the reduced iron oxides was reached for samples subjected to a slow heating at 700°C for 60 min. and to a fast cooling by quenching in water.A flow sheet for handling the yellow iron ore is here proposed to produce a magnetic iron concentrate with 87.63% Fe3O3 and 1.40% SiO2, and with a recovery of 97.21%.</div>","PeriodicalId":100750,"journal":{"name":"Journal of African Earth Sciences (and the Middle East)","volume":"17 1","pages":"Pages 89-94"},"PeriodicalIF":0.0,"publicationDate":"1993-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(93)90025-L","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53885702","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 4

Editorial: Software survey section 编辑:软件调查部分

Journal of African Earth Sciences (and the Middle East) Pub Date : 1993-07-01 DOI: 10.1016/0899-5362(93)90030-T

引用次数: 0

Redistribution and fractionation of U, Th and rare-earth elements during weathering of subalkaline granites in SW Cape Province, South Africa 南非西南开普省亚碱性花岗岩风化过程中U、Th和稀土元素的重分布与分选

Journal of African Earth Sciences (and the Middle East) Pub Date : 1993-07-01 DOI: 10.1016/0899-5362(93)90021-H

R. Scheepers, A. Rozendaal

{"title":"Redistribution and fractionation of U, Th and rare-earth elements during weathering of subalkaline granites in SW Cape Province, South Africa","authors":"R. Scheepers, A. Rozendaal","doi":"10.1016/0899-5362(93)90021-H","DOIUrl":"10.1016/0899-5362(93)90021-H","url":null,"abstract":"<div>Major and trace element behaviour during initial and advanced weathering stages in a weathering profile and saprolith developed on two subalkaline granites respectively indicated that Ca, Na and Sr are preferentially removed. Fe2+, K and Y are also lost, followed by P, Mg, Rb and Si. Zr and Nb remained constant relative to Ti. Mn, Fe3+, Al, Ga and Th initially increase eventually decreasing during advanced stages of weathering.U, Th and the REE behaviour could be related to the primary and secondary mineralogy of the granites. The HREE are removed in solution, while the concentrations of LREE are significantly increased relative to HREE during early weathering stages. Ce is initially slightly depleted relative to other LREE, but positive Ce animalies develop during advanced stages of weathering in the profile. Previous hydrothermal alteration of the granite is largely responsible for the behaviour of REE, U and Th during weathering. U and Th values increase with increasing oxidation. U correlates with Fe3+ adn Th with Mn and Fe3+.</div>","PeriodicalId":100750,"journal":{"name":"Journal of African Earth Sciences (and the Middle East)","volume":"17 1","pages":"Pages 41-50"},"PeriodicalIF":0.0,"publicationDate":"1993-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(93)90021-H","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53885642","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 18

Evolution tectonique récente de la zone de faille du Nékor: importance paléogéographique et structurale dans le Rif externe, Maroc nekor断层带的近期构造演化:摩洛哥Rif外部的古地理和构造意义

Journal of African Earth Sciences (and the Middle East) Pub Date : 1993-07-01 DOI: 10.1016/0899-5362(93)90023-J

L. Asebriy, J. Bourgois , T.E. Cherkaoui , A. Azdimousa

引用次数: 27

The petrology, geochemistry and petrogenesis of the Edough igneous rocks, Annaba, NE Algeria 阿尔及利亚东北部安纳巴Edough火成岩的岩石学、地球化学及成因

Journal of African Earth Sciences (and the Middle East) Pub Date : 1993-07-01 DOI: 10.1016/0899-5362(93)90027-N

Y. Ahmed-Said, B.E. Leake , G. Rogers

引用次数: 17

Geoscientific research in Northeast Africa 东北非洲的地球科学研究

Journal of African Earth Sciences (and the Middle East) Pub Date : 1993-07-01 DOI: 10.1016/0899-5362(93)90029-P

C.A. Kogbe

引用次数: 2

Pressure-temperature constraints on the evolution of an Early proterozoic plutonic suite in southern Ghana, West Africa 西非加纳南部早元古代深成套演化的压力-温度约束

Journal of African Earth Sciences (and the Middle East) Pub Date : 1993-07-01 DOI: 10.1016/0899-5362(93)90018-L

E. Opare-Addo , P. Browning , B.E. John

{"title":"Pressure-temperature constraints on the evolution of an Early proterozoic plutonic suite in southern Ghana, West Africa","authors":"E. Opare-Addo , P. Browning , B.E. John","doi":"10.1016/0899-5362(93)90018-L","DOIUrl":"10.1016/0899-5362(93)90018-L","url":null,"abstract":"<div>Contrasting structural, textural, fabric and mineralogical features between an Early Proterozoic plutonic migmatite suite and granitoids of the Dixcove-type from southern Ghana have been attributed to their contrasting geological histories, despite the fact that they are coeval, cogenetic and have similar geochemical properties. The migmatites occur as strongly foliated, banded, medium- to coarse-grained rocks and display shear and swirled structures. In contrast, the Dixcove granitoids are weakly foliated, homogeneous, fine- to medium-grained porphyritic rocks associated with volcanic rocks and show extensive hydrothermal alteration.There is no observable variation in P-T regime within the migmatite terrane exposed in southern Ghana, yet different geothermobarometers applied to constrain their conditions of formation consistently indicate that the migmatites were emplaced at relatively deep crustal levels, in excess of 5 kbars, compared to the Dixcove granitoids which crystallised under relatively shallow conditions, generally less than 5 kbars.These results suggest that the differences between the migmatites and Dixcove granitoids might have been caused by their different depths of emplacement, rather than deformational or bulk compositional differences as previously thought. These data provide significant constraints to any model for the evolution of these rocks and, indeed, the early Proterozoic terrane of the West African craton.</div>","PeriodicalId":100750,"journal":{"name":"Journal of African Earth Sciences (and the Middle East)","volume":"17 1","pages":"Pages 13-22"},"PeriodicalIF":0.0,"publicationDate":"1993-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0899-5362(93)90018-L","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"53885604","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 20

Pleistocene evolution of the reef terraces of the Red Sea coastal plain between Hurghada and Marsa Alam, Egypt 埃及Hurghada和Marsa Alam之间红海沿岸平原礁台的更新世演化

Journal of African Earth Sciences (and the Middle East) Pub Date : 1993-07-01 DOI: 10.1016/0899-5362(93)90028-O

M.E.E. El Moursi

引用次数: 6