Geochemical Evaluation of the Permian Ecca Shale in Eastern Cape Province,South Africa: Implications for Shale Gas Potential

Shale gas has been the exploration focus for future energy supply in South Africa in recent time. Specifically, the Permian black shales of the Prince Albert, Whitehill, Collingham, Ripon and Fort Brown Formations are considered to be most prospective rocks for shale gas exploration. In this study,outcrop and core samples from the Ecca Group were analyzed to assess their total organic carbon(TOC), organic matter type, thermal maturity and hydrocarbon generation potential. These rocks have TOC ranging from 0.11 to 7.35 wt%. The genetic potential values vary from 0.09 to 0.53 mg HC/g,suggesting poor hydrocarbon generative potential. Most of the samples have Hydrogen Index(HI) values of less than 50 mg HC/g TOC, thus suggesting Type-Ⅳ kerogen. Tmax values range from 318℃ to601℃, perhaps indicating immature to over-maturity of the samples. The vitrinite reflectance values range from 2.22% to 3.93%, indicating over-maturity of samples. Binary plots of HI against Oxygen Index(OI), and HI versus Tmax show that the shales are of Type II and mixed Type Ⅱ-Ⅲ kerogen.Based on the geochemical data, the potential source rocks are inferred as immature to over-matured and having present-day potential to produce gas.     

Stenian A-type granitoids in the Namaqua-Natal Belt,southern Africa,Maud Belt,Antarctica and Nampula Terrane,Mozambique:Rodinia and Gondwana amalgamation implications

We carried out SHRIMP zircon U-Pb dating on A-type granitic intrusions from the Namaqua-Natal Province,South Africa,Sverdrupfjella,western Dronning Maud Land,Antarctica and the Nampula Province of northern Mozambique.Zircon grains in these granitic rocks are typically elongated and oscillatory zoned,suggesting magmatic origins.Zircons from the granitoid intrusions analyzed in this study suggest~1025-1100 Ma ages,which confirm widespread Mesoproterozoic A-type granitic magmatism in the Namaqua-Natal(South Africa),Maud(Antarctica) and Mozambique metamorphic terrains.No older inherited(e.g.,~2500 Ma Achean basement or~1200 Ma island are magmatism in northern Natal)zircon grains were seen.Four plutons from the Natal Belt(Mvoti Pluton,Glendale Pluton,Kwalembe Pluton,Ntimbankulu Pluton) display 1050-1040 Ma ages,whereas the Nthlimbitwa Pluton in northern Natal indicates older 1090-1080 Ma ages.A sample from Sverdrupfjella,Antarctica has~1091 Ma old zircons along with~530 Ma metamorphic rims.Similarly,four samples analysed from the Nampula Province of Mozambique suggest crystallization ages of~1060-1090 Ma but also show significant discordance with two samples showing younger~550 Ma overgrowths.None of the Natal samples show any younger overgrowths.A single sample from southwestern Namaqualand yielded an age of~1033 Ma.Currently available chronological data suggest magmatism took place in the Namaqua-Natal-MaudMozambique(NNMM) belt between~1025 Ma and~1100 Ma with two broad phases between~1060-1020 Ma and 1100-1070 Ma respectively,with peaks at between~1030-1040 Ma and~1070-1090 Ma.The age data from the granitic intrusions from Namaqualand.combined with those from Natal,Antarctica and Mozambique suggest a crude spatial-age relationship with the older1070 Ma ages being largely restricted close to the eastern and western margins of the Kalahari Craton in northern Natal,Mozambique.Namaqualand and WDML Antarctica whereas the younger 1060 Ma ages dominate in southern Natal and western Namaqualand and are largely restricted to the southern and possibly the western margins of the Kalahari Craton.The older ages of magmatism partially overlap with or are marginally younger than the intracratonic Mkondo Large lgneous Provinee intruded into or extruded onto the Kalahari Craton,suggesting a tectonic relationship with the Maud Belt.Similar ages from granitic augen gneisses in Sri Lanka suggest a continuous belt stretching from Namaqualand to Sri Lanka in a reconstituted Gondwana,formed during the terminal stages of amalgamation of Rodinia and predating the East African Orogen.This contiguity contributes to defining the extent of Rodinia-age crustal blocks,subsequently fragmented by the dispersal of Rodinia and Gondwana.     

Petrology, Origin and Metamorphic History of Proterozoic-aged Granulites of the Natal Metamorphic Province, Southeastern Africa

The geochemistry of the Leisure Bay Formation, Natal Metamorphic Province suggests that its protoliths were greywackes, pelites and arkoses that were deposited in an oceanic island arc environment. These rocks contain the mineral assemblage biotite + hypersthene + cordierite (with hercynite inclusions) + garnet + quartz + feldspar. Numerous generations of garnet genesis are evident from which a long history of metamorphism can be interpreted. M₁ involved syn-D₁ high temperature/low pressure metamorphism (4kb and >850^oC) and dehydration melting to produce essentially anhydrous assemblages particularly in the vicinity of, and probably related to the intrusion of the Munster Suite sills. The inclusions of hercynite in cordierite and the garnet + quartz symplectites after hypersthene + plagioclase (550^oC and 5kb) suggests isobaric cooling after M₁. This indicates an anticlockwise P-T loop related to the early intrusion of subduction related calc-alkaline magmatic rocks. M₂ involved syn-D₂ dehydration melting of hydrous assemblages possibly related to the emplacement of many A-type rapakivi charnockite granitoids, which provided heat and loading. The D₂ tectonism post-dated all lithologies in the region, except for syn- to late-D₂ granitoid plutons, and is interpreted as a transpressional tectonothermal reworking of pre-existing (Proterozoic) crust at 1030Ma.     

An evaporitic facies in Neoproterozoic post-glacial carbonates: The Gifberg Group, South Africa

A geological study of the hitherto poorly described Neoproterozoic Gifberg Group, with emphasis on lithogeochemistry and O, C and Sr isotopic composition of the carbonate-dominated Widouw Formation (Vredendal Outlier, westernmost South Africa) revealed that the entire group is an equivalent of the relatively well constrained Port Nolloth Group in the external, paraautochthonous part of the Pan-African Gariep Belt further north. Thus, the Vredendal Outlier can be regarded as the southern extension of the Port Nolloth Zone. Two diamictite units are recognised in the Vredendal Outlier, which can be correlated respectively with the c. 750 Ma Kaigas Formation diamictite and the 583 Ma, syn-Gaskiers Numees Formation diamictite in the Gariep Belt proper. The dominating carbonate unit in the studied area is post-glacial with respect to the older of the two diamictite units. The combined textural, structural and geochemical evidence suggests that parts of the variably dolomitised limestone succession represent former evaporite beds. Sedimentation in a restricted, very shallow and proximal basin led to a wide range in C isotope ratios (δ¹³C_PDB from − 4.2 to + 4.8‰), very high Sr concentrations (derived from original anhydrite) and initial ⁸⁷Sr/⁸⁶Sr ratios that are significantly higher (0.70785) than those of coeval seawater. As C and Sr isotopes are commonly used for chemostratigraphic correlation, and high Sr concentrations in Neoproterozic carbonates are often interpreted as evidence of former aragonite, the findings of this study should be used as warning against uncritical use of geochemical and isotopic parameters for describing ancient seawater composition. Thus C and Sr isotope ratios alone in Neoproterozoic carbonates may be less powerful proxies of ancient seawater composition, and high Sr contents are not necessarily indicative of an “aragonite sea”, as previously inferred.     

Temnospondyls from the Beaufort Group (Karoo Basin) of South Africa and Their Biostratigraphy

The Permo-Triassic Beaufort Group (Karoo Basin) of South Africa is biostratigraphically subdivided into eight, temporally successive assemblage zones based on therapsids (‘mammal-like reptiles’). The Temnospondyli, fossil tetrapods usually regarded as extinct amphibians, are second only to therapsids in terms of diversity and abundance in these strata, with nine higher-level taxa (‘families’) known. Temnospondyls are also playing an increasingly important role in biostratigraphy and correlation of the Beaufort strata. The lower Beaufort Group (Late Permian) contains six of the eight biozones, but only one temnospondyl ‘family’, the Rhinesuchidae, whose record in the Karoo is the richest in the world. However, rhinesuchid taxonomy remains in flux and the group is thus of limited biostratigraphic utility. The Early Triassic Lystrosaurus Assemblage Zone (middle Beaufort Group) contains the Rhinesuchidae, Amphibamidae, Lydekkerinidae, Tupilakosauridae, Rhytidosteidae, Mastodonsauridae and Trematosauridae, although the biostratigraphy of temnospondyls within this biozone is poorly constrained. The uppermost reaches of the Lystrosaurus biozone contain a paucity of fossils but includes ‘Kestrosaurus’ (Mastodonsauridae) and ?Trematosuchus (Trematosauridae), taxa previously thought to pertain to the lower part of the overlying Cynognathus biozone. The late Early to Middle Triassic Cynognathus Assemblage Zone (upper Beaufort Group) hosts the Mastodonsauridae, Trematosauridae, Brachyopidae, Laidleriidae and, possibly, the Rhytidosteidae. Based largely on the spatial and temporal distribution of mastodonsaurids, this biozone has been biostratigraphically subdivided into a lower A, middle B and upper C subzones, characterised by differing ages and faunas.     

Rb-Sr and Sm-Nd Mineral Isochron Ages of the Metamorphic Rocks in the Namaqualand Metamorphic Complex, South Africa

Rb-Sr and Sm-Nd isotopic studies were carried out for metamorphic rocks in the Namaqualand Metamorphic Complex, South Africa. The metamorphic rocks give the Rb-Sr mineral isochron ages (whole-rock - biotite - felsic fractions) of 844±85 Ma and 811.6±6.6 Ma for the lower granulite zone and of 776.5±5.4 Ma for the upper granulite zone. The rocks yield the Sm-Nd mineral isochron ages of 1071±18 Ma (whole-rock - garnet - felsic fractions) and 1067±158 Ma (whole-rock - hornblende - biotite rich fraction - felsic fractions) for the lower granulite zone and of 1052.0±3.6 Ma and 1002.5±1.4 Ma (whole-rock - garnet - felsic fractions) for the upper granulite zone. These age data suggest that the granulite facies metamorphism took place at 1060-1000 Ma, and that the rocks cooled down at 850-780 Ma. The Sr and Nd isotopic compositions of metamorphic rocks are different between the lower and upper granulite zones.     

Corona textures in Proterozoic olivine melanorites of the Equeefa Suite,Natal Metamorphic Province,South Africa

Summary Olivine-plagioclase and phlogopite-plagioclase coronas have been identified from olivine melanorites of the Mid- to Late Proterozoic Equeefa Suite in southern Natal, South Africa. Olivine, in contact with plagioclase, is mantled by a shell of clear orthopyroxene, in turn rimmed by pale green (pargasitic) clinoamphibole. Locally a third rim, composed of a fine pargasite-spinel symplectite is developed adjacent to the plagioclase. The second corona reaction has produced greenish-brown pargasite at phlogopite-plagioclase interfaces. A third, less obvious reaction, between olivine and phlogopite is also noted. Analytical data of all the mineral phases present, along with the coronas, are given. Two-pyroxene thermometry yields magmatic core temperatures ( 1120°C), with rim compositions indicating equilibration at 850°C. Consistent with this, the modelled olivine-plagioclase reaction occurs between 830–1050°C with a_waterbetween 0.1 and 1.0 at 7 kbar. The three reactions took place during a prolonged history of cooling and partial hydration of the magmatic olivine melanorites from over 1000°C down to 600°C. The P-T conditions indicated by the reactions suggest this cooling process was essentially isobaric, indicating that the area was not subjected to rapid uplift or burial throughout this entire period.

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Korona-Texturen in proterozoischen Olivin-Melanoriten der Equeefa Suite, Natal Metamorphic Province, Südafrika

Zusammenfassung Aus Olivin-Melanoriten der mittel- bis spätproterozoischen Equeefa Suite im südlichen Natal, Südafrika, wurden Olivin-Plagioklas und Phlogopit-Plagioklas-Koronartexturen beobachtet. Olivin, der mit Plagioklas im Kontakt steht, wird von einem klaren Saum vom Orthopyroxen ummantelt, der seinerseits von blaßgrünem (pargasitischem) Klinoamphibol umsäumt wird. Stellenweise ist ein dritter Saum, bestehend aus feinkörnigem symplektitischem Pargasit-Spinell im Kontakt mit Plagioklas ausgebildet. Die zweite koronabildende Reaktion resultiert in Bildung eines grünbraunen Pargasites an Phlogopit-Plagioklas Kornkontakten. Eine dritte, weniger auffällige Reaktion zwischen Olivin und Phlogopit wurde ebenfalls beobachtet. Zwei-Pyroxen-Thermometrie ergab magmatische Temperaturen der Kernbereiche ( 1120°C) und belegt eine Gleichgewichtseinstellung in den Randzonen bei ca. 850°C. Olivin-Plagioklas-Modellreaktionen liegen ebenfalls in einem Temperaturbereich von 830–1050°C bei Wasseraktivitäten von 0.1 bis 1.0 und einem Druck von 7 kbar. Die drei Reaktionen liefen im Zuge einer länger andauernden Abkühlung unter teilweiser Hydratisierung der magmatischen Melanorite in einem Temperaturbereich von 1000°C bis ca. 600°C ab. Die aus den Reaktionen ableitbaren P-T-Bedingungen sprechen für eine im wesentlichen isobare Abkhlungsgeschichte und zeigen, daß dieses Gebiet wáhrend dieser gesamten Periode keiner raschen Hebung bzw. keiner Versenkung unterworfen worden ist.

     

Poverty, vulnerability and the impact of flooding in the Limpopo Province, South Africa

The article evaluates household vulnerability after the 2000 flood in two poor communities of the Limpopo Province, South Africa. The study analyses the forms of vulnerability which disasters such as floods present. Using data gathered from a survey of households, the study presents the impacts, coping and adapting strategies of households after the 2000 flood. The article argues that beyond the concern over socio-economic circumstances as the major determinant of household vulnerability, the management of the disaster can serve to perpetuate vulnerability.     

青海南祁连科克岩体地球化学特征及其形成时代

为探讨南祁连喀克图蒙克山科克岩体的构造属性,对南祁连喀克图蒙克山中奥陶世科克岩体进行了详细的地球化学和定年研究。研究结果表明,该岩体主体岩性为正长花岗岩,具有高SiO_2(68.41%～73.10%)、高Al_2O_3(13.03%～14.35%)的特征,亏损高场强元素Nb、P、Ti和重稀土元素,发育明显的负Eu异常,反映岩石经历了强烈的分离结晶作用,其稀土元素配分曲线类型与壳源花岗岩相似;构造成因分类图解表明,这些花岗岩属同碰撞环境的产物。LA-ICP-MS锆石U-Pb测年结果表明,岩体形成于461±2.7Ma,时代为中奥陶世,表明该岩体的源岩为壳源或壳幔混合的产物。结合区域地质特征认为,该岩体为同碰撞作用的产物,佐证了南祁连地块在奥陶纪处于挤压状态,对进一步研究南祁连造山带的演化具有重要意义。     

南秦岭白龙江群中花岗岩脉群年代学、地球化学特征及地质意义

秦岭造山带南缘勉略缝合带北侧发育近东西向展布的印支期花岗岩带,出露于南秦岭志留系白龙江群中花岗岩脉群,属于该花岗岩带的一部分,其宽度多为1~8m不等,呈北西西-南东东向延伸,主要岩性为花岗闪长斑岩-石英闪长斑岩组合。笔者对南秦岭志留系白龙江群中密集出露的花岗岩脉体进行了详细的LA-ICP-MS锆石U-Pb年代学及岩石地球化学研究,结果表明,白龙江群中花岗闪长斑岩脉结晶年龄为（210.44±0.47）Ma,属晚三叠世。地球化学特征显示这些脉体相对高K2O、Sr含量及Zr/Y值,富集LREE和LILE,亏损HFSE,里特曼指数（σ）为1.41~2.73,具高钾钙碱性I型花岗岩特征。此外,它们明显亏损Nb、Ta及Ti,低Y、Yb,具有较高的（La/Yb）N值,表明它们可能为地壳增厚背景下,下地壳拆沉作用导致减薄地壳中以基性岩为主的源岩部分熔融的产物,可能存在幔源岩浆的贡献。综合区域地质资料研究认为,出露于南秦岭白龙江群中的花岗岩脉群形成于后碰撞构造环境,是华北板块与扬子板块碰撞造山之后挤压体制向伸展体制转换阶段的产物。     

鲁西隐伏含铁岩系——前寒武纪济宁岩群地球化学特征及沉积环境

济宁岩群是分布于山东省鲁西南地区的隐伏浅变质地层,埋深大于900m,由变火山碎屑岩组、含铁岩组和千枚岩组组成,是一套海相火山-沉积岩系。岩石中SiO2、Al2O3、Fe2O3、K2O等亲陆元素含量高,岩石化学的成熟度指数不高,反映其源岩是鲁西TTG岩系;m值(4.75～31.86)和MnO/TiO2(0.05～0.2)值低,指示了海陆过渡性近岸浅海陆架沉积环境。富集轻稀土、重稀土平坦、铕异常不明显;微量元素K、Rb、Ba富集,贫Nb、Ti和P、Cr。Sr/Ba值(主要为0.16～0.77)小,指示沉积时的盐度较低;V/(V+Ni)值较高(>0.46),形成于还原环境。岩石的δ13CV-PDB=-4.7‰～-15‰,δ18OV-PDB=-12.1‰～-18.8‰,δ30SiNBS-28=-0.8‰～-1.2‰,数值较低,显示了热水沉积特征。济宁岩群是受华北克拉通1.8Ga大陆裂解事件影响形成的裂谷型热水沉积。     

南辽河群斜长角闪岩的地球化学特征及地质意义:以三家子地区为例

基于详细的野外地质调查,对南辽河群下部里尔峪组斜长角闪岩进行了岩相学和地球化学研究。岩相学研究表明,南辽河群下部里尔峪组斜长角闪岩属于正变质岩。地球化学研究显示,这些斜长角闪岩原岩属于高铁拉斑玄武岩系列(Nb/Y=0.16~0.4),SiO_2含量为47.27%~50.68%,具有较低的TiO_2含量(0.92%~1.61%),亏损高场强元素(Nb、Ta、Zr、Hf等),表明其原岩形成于岛弧或活动大陆边缘,而非前人所说的大陆裂谷。综合岩相学和地球化学特征,初步认为其岩石成因与活动大陆边缘有关。     

湖北宜昌崆岭群孔兹岩系地球化学特征

湖北宜昌崆岭群孔兹岩系由富铝片岩-片麻岩及榴线英岩类、长英质岩类及镁铁质麻粒岩类组成,其原岩分别为黏土岩、砂岩-杂砂岩和泥灰岩,富铝片麻岩的稀土元素分配型式接近北美页岩组合样(NASC),Eu显示负异常,而Ce基本无异常.富铝片麻岩和榴线英岩的微量元素分配形式与澳大利亚后太古代页岩(PAAS)接近.根据风化参数CIW,与NASC、PAAS相近的稀土和微量元素的分布特征以及高w(LREE)/w(HREE)值与Eu负异常综合判断崆岭群孔兹岩系的原岩属于以花岗质岩石为蚀源区的陆屑沉积岩.根据富铝片麻岩和榴线英岩的δ(Ce)值(NASC标准化)及岩组中的石墨推断其原岩沉积环境为还原条件,根据δ(Ce)值(球粒陨石标准化)和镁铝含量比进一步判断其原岩沉积为大陆边缘的陆海过渡-海水沉积.由大量的碎屑沉积-少量化学沉积-有不同程度的化学沉积加入的大量碎屑沉积的沉积建造与岩组中石墨的变化推测该孔兹岩系原岩的形成可能与阜平、五台等旋回(期)的前吕梁旋回(期)黄陵-川中古陆块(或扬子陆块) 的陆核形成有关.     

Geochemistry of South African On- and Off-craton, Group I and Group II Kimberlites: Petrogenesis and Source Region Evolution

Bulk-rock geochemical compositions of hypabyssal kimberlites,emplaced through the Archaean Kaapvaal craton and ProterozoicNamaqua–Natal belt, are used to estimate close-to-primarymagma compositions of Group I kimberlites (Mg-number = 0·82–0·87;22–28 wt % MgO; 21–30 wt % SiO₂; 10–17 wt% CaO; 0·2–1·7 wt % K₂O) and Group II kimberlites(Mg-number = 0·86–0·89; 23–29 wt %MgO; 28–36 wt % SiO₂; 8–13 wt % CaO; 1·6–4·6wt % K₂O). Group I kimberlites are distinguished from GroupII by their lower Ba/Nb (<12), Th/Nb (<1·1) andLa/Nb (<1·1) but higher Ce/Pb (>22) ratios. Thedistinct rare earth element patterns of the two types of kimberlitesindicate a more highly metasomatized source for Group II kimberlites,with more residual clinopyroxene and less residual garnet. Thesimilarity of Sr and Nd isotope ratios and diagnostic traceelement ratios (Ce/Pb, Nb/U, La/Nb, Ba/Nb, Th/Nb) of Group Ikimberlites to ocean island basalts (OIB), but more refractoryMg-numbers and Ni contents, are consistent with derivation ofGroup I kimberlites from subcontinental lithospheric mantle(SCLM) that has been enriched by OIB-like melts or fluids. Sourceenrichment ages and plate reconstructions support a direct associationof these melts or fluids with Mesozoic upwelling beneath southernAfrica of a mantle plume(s), at present located beneath thesouthern South Atlantic Ocean. In contrast, the geochemicalcharacteristics of both on- and off-craton Group II kimberlitesshow strong similarity to calc-alkaline magmas, particularlyin their Nb and Ta depletion and Pb enrichment. It is suggestedthat Group II kimberlites are derived from both Archaean andProterozoic lithospheric mantle source regions metasomatizedby melts or fluids associated with ancient subduction events,unrelated to mantle plume upwelling. The upwelling of mantleplumes beneath southern Africa during the Mesozoic, at the timeof Gondwana break-up, may have acted as a heat source for partialmelting of the SCLM and the generation of both Group I and GroupII kimberlite magmas. KEY WORDS: kimberlite; geochemistry; petrogenesis; mantle plumes; South Africa     

Metamorphic and Thermal History of a Fore-Arc Basin: the Fossil Bluff Group, Alexander Island, Antarctica

The Himalia Ridge Formation (Fossil Bluff Group), AlexanderIsland is a 2·2-km-thick sequence of Upper Jurassic–LowerCretaceous conglomerates, sandstones and mudstones, derivedfrom an andesitic volcanic arc and deposited in a fore-arc basin.The metamorphic and thermal history of the formation has beendetermined using authigenic mineral assemblages and vitrinitereflectance measurements. Metamorphic effects include compaction,pore-space reduction, cementation and dissolution and replacementof detrital grains by clay minerals (smectite, illite/smectite,corrensite and kaolinite), calcite, chlorite, laumontite, prehnite,pumpellyite, albite and mica, with less common quartz, haematite,pyrite and epidote. The authigenic mineral assemblages exhibita depth-dependence, and laumontite and calcite exhibit a strongantipathetic relationship. Detrital organic matter in the argillaceouslayers has vitrinite reflectance values (R_o) ranging from 2·3to 3·7%. This indicates considerable thermal maturation,with a systematic increase in reflectivity with increasing depth.There is good correlation of metamorphic mineral assemblageswith chlorite crystallinity and vitrinite reflectance values—allindicating temperatures in the range of 140 ± 20°Cat the top of the sequence to 250 ± 10°C at the baseof the sequence. The temperatures suggest a geothermal gradientof 36–64°C/km and a most likely gradient of 50°C/km.It is suggested that this higher-than-average gradient for afore-arc basin resulted either from rifting during basin formationor from a late-stage arc migration event. KEY WORDS: Antarctica; diagenesis; fore-arc basin; low-temperature metamorphism; vitrinite reflectance     

Evaluating the Provenance of Metasedimentary Rocks of the Jiangxian Group from the Zhongtiao Mountain Using Whole-Rock Geochemistry and Detrital Zircon Hf Isotope

Abstract：In this study, whole-rock geochemical and Nd isotopic data, as well as detrital zircon Hf isotopes of Palaeoproterozoic metasedimentary rocks from the Jiangxian Group are presented to evaluate the characteristics of their provenance and the tectonic history. The major and trace element compositions are comparable to Post-Archean upper continental crust (PA-UCC), but have slight enrichment in the LILE, with the exception of Cs and Sr, and a slight depletion in ferromagnesian elements, HFS elements, such as Nb and Ta, and some major elements, such as CaO and Na2O. The geochemical data reveal that the collected metasedimentary rocks have experienced intermediate source weathering with chemical index of alteration values ranging from 72 to 78, varying degrees of K-metasomatism, and post-depositional loss of Na, as well as negligible sorting, and are derived from the weathering of mostly felsic and non-mafic rocks. The selected Lu–Hf isotopic analysis on detrital zircon points to both the Trans-North China Orogen and Eastern Block of the north China craton as the most likely sources for the metasedimentary rocks of the Jiangxian Group. However, a contribution of detritus from the Western Block of the north China craton can be ruled out. The sediments were probably deposited in a back-arc basin within an active continental margin setting.     

Geomorphological palaeoenvironments of the Sneeuberg Range,Great Karoo,South Africa

Sedimentary sequences within headwater valleys on the landward side of the Great Escarpment of South Africa are elucidated and their significance as indicators of environmental change is assessed. This study focuses on the Sneeuberg Range, the most prominent mountain range in the semi‐arid central Great Karoo. Valley fills of a hitherto unrecognised complexity and of a greater age than any previously recorded in the central Great Karoo are reported. Three phases of deposition spanning the Late Pleistocene up to the present are documented from sites where gully erosion has incised the valley fills. The earliest depositional phase is represented by deeply weathered, calcretised gravel deposits, which probably were emplaced by debris flow and fluvial processes in the form of a fan. These deposits subsequently were buried by finer grained, largely unconsolidated sediment, with much of this emplacement occurring during the Holocene. There is evidence for phases of landscape stability and instability within this facies. Finally, sheetwash has removed fine‐grained sediments from valley flanks and has deposited it either on valley bottoms, or in presently active gullies. This process appears to be ongoing, and is the subject of current investigation. The sedimentary deposits are interpreted as representing a wide range of palaeoenvironmental conditions that have prevailed within the central Great Karoo since the penultimate glaciation. Copyright © 2003 John Wiley & Sons, Ltd.     

河北平山小觉地区阜平岩群浅粒岩深熔作用的地球化学研究

新太古代阜平岩群浅粒岩遭受深熔作用改造形成一些不同规模和形状的浅色体。与溶融母岩相比，其稀土元素和高场强元素含量相对较低，但大多数情况下具有相似的元素分布模式。然而，深熔作用刚开始时形成的浅色体，其元素含量、分布模式与熔融母岩完全不同，Nd同位素组成存在较大差别。随着深熔作用的进行，两者Nd同位素组成的差异越来越小，最后几乎完全消失。残余相副矿物，特别是锆石和磷灰石，对深熔浅色体的元素、Nd同位素组成的变化起了重要的作用。     

Management and sediment dynamics of the St. Lucia Estuary mouth,Zululand, South Africa

St. Lucia Estuary is on the subtropical, predominantly microtidal Zululand coast of South Africa. Lake St. Lucia's surface area fluctuates between 420 and 215 km² and has a mean depth of less than 1 m. The 21-km-long narrows connects Lake St. Lucia with the Indian Ocean. Tidal effects penetrate 14 km up the narrows. The St. Lucia system has changed substantially since the 1930s due to bad farming techniques within its catchment. Large amounts of sediment were deposited in the estuary mouth, resulting in relocation of the Mfolozi River mouth to the south at Mapelane. The St. Lucia catchment was subjected to two devastating floods in the last ten years: Cyclone Domoina during February 1984 and the September 1987 cutoff low flood. After floods scoured out the estuary, marine sand advanced up the estuary at a rate of 1200 m/y as a series of flood-tidal deltas. Over 600,000 m³ of sediment accumulated in the St. Lucia Estuary mouth from February 1988 to November 1989. Of this amount, 466,000 m³ of sediment was removed by dredging, although this has not stopped the shoaling. During high rainfall years, the estuary mouth is able to maintain an open outlet to the sea, but as lake levels drop, shoaling causes the mouth to constrict and eventually close. Without the dredging program the mouth would ultimately close during low rainfall years, causing management problems.     

赤峰东南部建平群斜长角闪岩黑云母矿物化学特征及地质意义

利用电子探针、激光剥蚀-电感耦合等离子体质谱测试技术,对赤峰东南部建平群斜长角闪岩中黑云母的常量元素、微量(稀土)元素进行了测试分析。研究表明:赤峰东南部建平群斜长角闪岩中的黑云母主量元素以富Fe、Mg为特征,为高铁镁云母;黑云母稀土元素含量低,轻重稀土分馏较强,δEu、δCe均值为正,为选择Ce、Nd的配分型矿物;黑云母中Rb、Ba、Pb和Cs等大离子亲石元素富集,特别是Cs、Ba明显富集,而Sr略有亏损;高场强元素Zr、Hf、Sc等亏损,较富集的元素为U、Th、Nb、Ta元素;亏损的亲铁元素为Cr、Ni,而显著富集的元素为V、Ti;亲硫元素Cu亏损而Zn明显富集;分散元素Ga有明显的富集。