Transvaal Supergroup inliers: geology, tectonic development and relationship with the Bushveld complex, South Africa

Several deformed Transvaal Supergroup inliers occur in the Bushveld complex. The most prominant are the Crocodile River dome and the Rooiberg fragment in the western Transvaal basin and the Dennilton-Marble Hall dome and Stavoren fragment in the eastern Transvaal basin. Several other smaller Transvaal Supergroup inliers are situated in the Bushveld complex to the east and west of the central inliers. The geology and tectonic relationship of these inliers with the Bushveld complex imposed important constraints on the tectonic evolution of the Transvaal basin and the subsequent distribution of the Bushveld complex.The central inliers are subdivided into two groups. The Crocodile River, Marble Hall and Dennilton domes consist of highly deformed, lower Transvaal strata that were subjected to low-grade metamorphism. The domes were formed by interference folding that was accentuated by the intrusion of the Bushveld complex. They acted as physical barriers to the emplacement of the mafic rocks of the Bushveld complex in the centre of the Transvaal basin.The Rooiberg and Stavoren fragments are synforms of upper Transvaal strata. The strara that comprise them are less deformed than those in the domes. These fragments were subjected to low-grade metamorphism because of the intrusion of Bushveld granite beneath them. They acted as roof pendants to the emplacement of the Bushveld complex.Other smaller Transvaal Supergroup inliers in the Transvaal basin are shown to be either attached or detached structures, depending on their tectonic setting and relation to the Bushveld complex.     

新疆西博格达山周缘地区中新生代沉积岩源区和构造背景

沉积岩中的碎屑组分及相对稳定的微量元素和稀土元素可以反映物源信息,广泛应用于沉积源区的确定和构造背景的分析。本文通过对西博格达山周缘地区侏罗纪至古近纪沉积地层的碎屑岩岩石学和微量元素与稀土元素分析,揭示盆地沉积岩的源岩来自上地壳,岩性以长英质岩石为主,混合部分安山质及基性岩石。源区构造背景应为岩浆弧和再循环造山带,其中岩浆弧起主导作用。本文的分析结果为研究博格达山的构造演化过程及其机制提供了有力的证据,并且对准噶尔盆地油气勘探具有一定指导意义。     

中扬子北缘上侏罗统-白垩系沉积岩地球化学特征与构造背景分析

沉积岩中的微量元素和稀土元素特征对沉积环境、沉积物的物源和构造背景具有十分重要的示踪与指示作用。对采自中扬子北缘晚侏罗世-白垩纪地层的泥质岩样品中微量元素和稀土元素进行了测试与分析,结果表明,研究区微量元素中的深源元素普遍低于地壳粘土岩中的平均值,说明沉积物的来源为陆源物质。而典型陆源元素Zr、Hf的平均含量远高于地壳粘土岩中的平均含量,反映了大量的陆源物质的快速堆积。上侏罗统与下白垩统泥质岩的微量元素特征相似,而上白垩统则发生了明显的变化,表现为深源性微量元素含量较上白垩统明显降低,而陆源性微量元素含量显著增加,反映早晚白垩世之间沉积背景发生了变化。纵向上,稀土元素的变化规律显示,上白垩统与下白垩统的稀土元素特征具明显的差异,表现为Eu的负异常明显减小,Ce的负异常增大,轻稀土富集程度降低,反映了沉积作用分异度较低的特点。La-Th-Sc、Th-Co-Zr／10和Th-Sc—Zr／10构造环境判别图及La／Th-Hf和Th／Sc-Sc比值图表明,中扬子北缘晚侏罗世．白垩纪沉积岩物源区的构造背景以大陆岛弧型为主,可能也存在类似被动大陆边缘构造背景。     

扬子西南缘盐边群时代及构造环境: 来自碎屑沉积岩的约束

出露于扬子地块西南缘的盐边群为一套火山-沉积岩系,其深入研究对探讨扬子西缘新元古代构造环境具有重要意义.本文对盐边群中碎屑沉积岩进行了较系统的岩石学、碎屑物质组成和地球化学研究,并从小坪组和乍古组中各选取了1件变质砂岩样品进行锆石U-Pb年龄和Hf同位素分析.变质砂岩主要由棱角状-次棱角状火山岩岩屑、石英和长石矿物碎屑组成.碎屑沉积岩Al2O3/SiO2值为0.12～0.4,K2O/Na2O值范围为0.14 ～9.45(其中板岩K2O/Na2O值多大于1.0,而变质砂岩中多数样品的K2O/Na2O值小于1.0).所有样品具有轻-中等程度的轻重稀土元素分异((La/Yb)N=1.6 ～9.37),多数样品具有明显的负Eu异常.εNd(t)值范围为-1.77～ +5.01.变质砂岩碎屑锆石U-Pb年龄峰值为900～ 910Ma,同时存在少量太古代-古元古代碎屑锆石.小坪组和乍古组变质砂岩中年轻碎屑锆石206pb/238U年龄加权平均值分别为888±8Ma和884±14Ma.碎屑物质组成、地球化学和锆石U-Pb年龄结果共同表明,盐边群碎屑沉积为近源沉积,物源区主要为岛孤中酸性火山岩和花岗岩.结合关刀山岩体(857Ma)和荒田组玄武岩(880～830Ma)研究结果,进一步限定盐边群的时代为880～830Ma,形成于弧后盆地环境,其沉积物源区为华夏地块向扬子地块俯冲过程中,扬子西南缘形成的火山岛孤.     

Geochemistry of Neogene sedimentary rocks from Borneo Basin,East Malaysia: Paleo-weathering,provenance and tectonic setting

Multi-element geochemistry and mineralogy are used to characterize the chemical composition, degree of paleo-weathering, provenance and tectonic settings of the Neogene sedimentary rocks of Borneo Basin of east Malaysia. Sedimentary rocks are classified as extremely weathered sandstones (i.e. wacke, arkose, litharenite, Fe-sandstone and quartz arenite). Wacke, arkose, litharenite and Fe-sandstone are characterized by post-depositional K-metasomatism and zircon enrichment through sediment recycling. Geochemical characteristics suggest a mixed-nature provenance for the sandstones and the variable tectonic settings possibly mirror the complexity of the basin. Enriched Cr in quartz arenite and Fe-sandstone are related to the contribution from ophiolite or fractionation of Cr-bearing minerals.     

柴窝铺盆地及其北缘地区中新生代沉积岩源区构造背景和物源属性研究

沉积岩中的碎屑组分及主量元素、微量元素和稀土元素可以反映物源信息,广泛应用于沉积源区的确定、构造背景的分析。通过对柴窝铺盆地及北缘地区侏罗纪至古近纪沉积地层的碎屑岩岩石学和地球化学分析,揭示了盆地沉积岩的原岩来自上地壳,岩性以长英质岩石为主,并混合进了部分安山质及基性岩石。源区构造背景为活动大陆边缘,因其原岩是在大陆岛弧环境下形成的,所以部分构造背景显示为大陆岛弧。本次研究不仅可以为柴窝铺盆地及北天山的构造演化过程及其机制提供有力证据,并且对柴窝铺油气勘探具有一定指导意义。     

Economic potential of the Rooiberg Group: volcanic rocks in the floor and roof of the Bushveld Complex

Volcanic rocks of the Rooiberg Group are preserved in the floor and roof of the mafic Rustenburg Layered Suite of the Bushveld Complex. Field and geochemical characteristics of these volcanic rocks imply that they are genetically related to the Rustenburg Layered Suite. Four major ore-forming events are identified in the Rooiberg Group. The first phase was accompanied by volcanic hosted, fault controlled, hydrothermal copper mineralisation, which is found in the lowermost portion of the Rooiberg Group, underlying the Rustenburg Layered Suite. This type of mineralisation is tentatively linked to initial Rustenburg Layered Suite intrusions. Stratabound arsenic mineralisation that possibly formed in response to contact metamorphism, characterises the second phase, and occurred after extrusion of the Damwal Formation, possibly due to shallow granophyric intrusion. The third mineralising event occurred in response to contact metamorphism during the final stages of the Rustenburg Layered Suite, where especially Pb and Zn were introduced into the felsite roof rocks. This type of mineralisation affected the majority of the Rooiberg Group, but is most pronounced towards the contact with the Rustenburg Layered Suite. The fourth phase is restricted to the Rooiberg Group in the Nylstroom area and is linked to the granite intrusions of the Lebowa Granite Suite, from which Sn and F were introduced into the uppermost felsite succession. Mineralisation in the Rooiberg Group appears to be controlled by the character and intrusion level of the associated Bushveld magmas. Different styles of mineralisation in Rooiberg Group volcanic rocks are encountered at various stratigraphic levels. Major primary volcanogenic ore deposits appear to be absent.     

河南嵩山地区元古宙五佛山群沉积岩的地球化学特征及其对物源区和构造环境的制约

河南嵩山地区位于华北克拉通南缘,保存有较为完整的太古宙-古元古代变质结晶基底和之后的沉积盖层。五佛山群直接角度不整合覆盖于新太古界登封群和古元古界嵩山群之上,为嵩山地区结晶基底之上分布广泛的第一沉积盖层。其主要由(长石)石英砂岩组成,夹少量的粉砂质页岩、泥岩和薄层灰岩。从下而上岩性相变明显,代表两次较大的沉积旋回。地球化学特征上,五佛山群砂岩的SiO₂含量(70.18%~95.21%)明显比泥质岩(20.79%~52.27%)高,但Fe₂O₃、MgO、CaO和K₂O含量比泥质岩低,表明泥质岩中含有较多的基性组分和富钾矿物。泥质岩的稀土总量(∑REE=131×10^-6~169×10^-6)比砂岩(∑REE=7.30×10^-6~158×10^-6)高,反映泥质岩中较高含量的粘土矿物对稀土元素具有较强的吸附作用。砂岩样品的成分变异指数(ICV=0.89~3.59)较低,说明其成熟度较高,为稳定构造环境下沉积的产物。泥质岩的ICV值为4.04~17.50,SiO₂/Al₂O₃比值(3.90~5.58)和La/V比值较低(0.45~0.65),说明其成熟度较低,形成环境相对比较活动。较低的化学蚀变指数(CIA=7.52~66.1)反映碎屑沉积岩 的源区遭受相对较弱的化学风化作用,其中砂岩(CIA=27.6~66.1)的化学风化强度比泥质岩(CIA=7.52~24.9)高。五佛山群碎屑沉积物主要来源于古元古代中酸性组分,有少量基性组分的加入。其下部和中部的砂岩与华北南缘同时代的沉积地层均形成于被动大陆边缘的沉积环境,说明华北克拉通南缘在熊耳群之后进入了一个稳定的沉积阶段。而五佛山群上部泥质岩形成于与大陆岛弧相关的沉积盆地,显示地壳活动性增强,沉积环境上暗示由被动大陆边缘向活动大陆边缘过渡的过程,可能与秦岭造山带形成初期的板 块活动有关。     

张家界地区志留系岩石地球化学与构造背景

张家界地区志留系出露有兰多弗里统及文洛克统,其中兰多弗里统泥岩中SiO₂含量平均61.59%,SiO₂/Al₂O₃值平均3.63,K₂O/ Na₂O值平均4.80,Al₂O₃/(K₂O+Na₂O)值平均3.49,∑REE含量平均238.58×10^-6,LREE含量平均213.89×10^-6, LREE/HREE值平均8.68, B含量平均98.29×10^-6,B/Ga值平均3.99,Th/U值平均5.61。通过构造环境判别图解认为: 兰多弗里统泥岩以活动大陆边缘物源为主,混入部分大陆岛弧物源,其古老物源则可能来自被动大陆边缘; 已经拼合在一起的华夏、扬子陆块,在志留纪时期继续向北西挤压,形成多处隆升(黔中隆起、雪峰隆起等),随着进一步挤压,雪峰隆起升出海面,为张家界地区提供了泥质沉积物,挤压导致岛弧形成并提供了部分物源。     

Trace element characteristics of graywackes and tectonic setting discrimination of sedimentary basins

The graywackes of Paleozoic turbidite sequences of eastern Australia show a large variation in their trace element characteristics, which reflect distinct provenance types and tectonic settings for various suites. The tectonic settings recognised are oceanic island arc, continental island arc, active continental margin, and passive margins. Immobile trace elements, e.g. La, Ce, Nd, Th, Zr, Nb, Y, Sc and Co are very useful in tectonic setting discrimination. In general, there is a systematic increase in light rare earth elements (La, Ce, Nd), Th, Nb and the Ba/Sr, Rb/Sr, La/Y and Ni/Co ratios and a decrease in V, Sc and the Ba/Rb, K/Th and K/U ratios in graywackes from oceanic island arc to continental island arc to active continental margin to passive margin settings. On the basis of graywacke geochemistry, the optimum discrimination of the tectonic settings of sedimentary basins is achieved by La-Th, La-Th-Sc, Ti/Zr-La/Sc, La/Y-Sc/Cr, Th-Sc-Zr/10 and Th-Co-Zr/10 plots. The analysed oceanic island arc graywackes are characterised by extremely low abundances of La, Th, U, Zr, Nb; low Th/U and high La/Sc, La/Th, Ti/Zr, Zr/Th ratios. The studied graywackes of the continental island arc type setting are characterised by increased abundances of La, Th, U, Zr and Nb, and can be identified by the La-Th-Sc and La/Sc versus Ti/Zr plots. Active continental margin and passive margin graywackes are discriminated by the Th-Sc-Zr/10 and Th-Co-Zr/10 plots and associated parameters (e.g. Th/Zr, Th/Sc). The most important characteristic of the analysed passive margin type graywackes is the increased abundance of Zr, high Zr/Th and lower Ba, Rb, Sr and Ti/Zr ratio compared to the active continental margin graywackes.     

浙黔桂地区寒武纪硅质岩的地球化学特征及其形成背景

本文采用常量和稀土元素地球化学方法对浙黔桂地区寒武纪硅质岩的形成背景进行了研究。研究表明,硅质岩的A12O3/（A12O3＋Fe2O3）为0.56~0.87;Ce/Ce＊为0.74±0.19;Lan/Cen为0.90~1.58;Lan/Ybn平均为6.38,轻稀土明显富集,这些特征表明研究区硅质岩形成于大陆边缘环境或大陆边缘与深海过渡带。形成于裂陷盆地初期的硅质岩,比古华南残留洋盆和扬子陆块边缘的硅质岩轻稀土元素更加富集。构造拉张期形成的硅质岩为热液成因硅质岩,其稀土配分模式显示出轻稀土相对亏损、Eu正异常特征;构造稳定期形成的硅质岩为沉积成因硅质岩,稀土配分模式显示出轻稀土相对富集、Eu弱负异常特征。由硅质岩稀土配分模式的差异性反映出寒武纪时期的拉张为幕式拉张。位于扬子地台边缘的硅质岩所具有的Ce负异常,暗示着江南造山带寒武纪后曾发生过由东向西的大规模逆冲推覆。     

Petrographic and geochemical characteristics of the Paleogene sedimentary rocks from the North Jiangsu Basin,Eastern China: implications for provenance and tectonic setting

The petrography and geochemistry (major, trace, and rare earth elements) of clastic sedimentary rocks from the Paleogene Dainan Formation (E₂ d) in the North Jiangsu Basin, eastern China, are investigated to trace their provenance and to constrain their tectonic setting. The studied samples are characterized by LREE enrichment, flat HREE, and negative Eu anomaly similar to the upper continental crust composed chiefly of felsic components in the source area. Petrographic observation indicates that the sandstones contain predominant metamorphic and sedimentary clasts that were derived from peripheral recycled orogen and intrabasinal materials. The trace element ratios (Co/Th, La/Sc, La/Th, and Th/U) and the La-Th-Sc ternary plot further confirm that the sandstones are derived from granitic gneiss sources from recycled orogen and the intrabasinal mixed sedimentary provenance. The granitic gneiss source rocks may have derived from the Proterozoic granitic gneiss denuded in the eastern Dabie-Sulu orogen; and the intrabasinal provenance may come from the underlying strata during the Late Paleocene Wubao movement. The chemical index of alteration (CIA) and A-CN-K plot show that these source rocks may have experienced weak to medium chemical weathering. Analysis on tectonic setting of the source area suggests an active continental margin, which is intimate with tectonic feature of the Dabie-sulu orogen and the Yangtze block. In summary, we suggest that the North Jiangsu Basin is an ideal site for the study of the coupling between the uplift of the orogen and the subsidence of the foreland basin.     

西藏雅鲁藏布缝合带三叠系朗杰学群沉积岩古生物、地球化学特征及其物源区和构造背景分析

随着近年来对朗杰学群的解体,发现前人对于朗杰学群、涅如组、修康群及洛林岩群的研究存在混淆,研究对象是否为朗杰学群应重新审慎,同时,几者是否为同一构造背景产物仍存在较大争议。本文对朗杰学群命名地(贡嘎县姐德秀镇-朗杰学乡一带)的朗杰学群重矿物特征、地球化学特征及古生物化石进行了研究。朗杰学群砂岩主量元素和微量元素化学成分低于地壳克拉克值,SiO₂含量平均为74.14%,K₂O/Na₂O值平均为0.70,反映砂岩成熟度较低,没有经历明显的成岩后生改造;化学蚀变指数(CIA)较集中,平均为71.55,属低级-中等风化程度,指示气候和构造环境都处于相对稳定状态;古环境分析显示,100Mg/Al₂O₃值平均为7.85,CaO/Fe+CaO值平均为0.314,表明朗杰学群形成于中等盐度的深水厌氧环境,且由北向南沉积水体逐渐加深;重矿物以锆石为主,其次为金红石,分选磨圆较差,ATi指数为93.3～98.97,ZTR指数为48.01～85.75,反映朗杰学群物源区的火山岩较为丰富,且搬运距离较...     

青海南部曲麻莱县加容检德工卡侵入岩序列特征及其构造环境

加容检德工卡侵入岩序列由石英闪长岩-英云闪长岩-花岗闪长岩-正长花岗岩组成。岩石化学成分表现为从中基性到酸性的演化及岩浆向富硅、富碱方向演化。稀土元素特征表现为轻稀土元素富集;微量元素特征表现为富集大离子亲石元素Rb、K、Ba、Th,而Sr、Nb、Ta略显亏损,Ti、P较强亏损。构造环境为同碰撞花岗岩,时代为早白垩世。     

Geochemistry and tectonic setting of mafic rocks from the Othris Ophiolite,Greece

We present new geochemical analyses of minerals and whole rocks for a suite of mafic rocks from the crustal section of the Othris Ophiolite in central Greece. The mafic rocks form three chemically distinct groups. Group 1 is characterized by N-MORB-type basalt and basaltic andesite with Na- and Ti-rich clinopyroxenes. These rocks show mild LREE depletion and no HFSE anomalies, consistent with moderate degrees (~15%) of anhydrous partial melting of depleted mantle followed by 30–50% crystal fractionation. Group 2 is represented by E-MORB-type basalt with clinopyroxenes with higher Ti contents than Group 1 basalts. Group 2 basalts also have higher concentrations of incompatible trace elements with slightly lower HREE contents than Group 1 basalts. These chemical features can be explained by ~10% partial melting of an enriched mantle source. Group 3 includes high MgO cumulates with Na- and Ti-poor clinopyroxene, forsteritic olivine, and Cr-rich spinel. The cumulates show strong depletion of HFSE, low HREE contents, and LREE enrichments. These rocks may have formed by olivine accumulation from boninitic magmas. The petrogenesis of the N-MORB-type basalts and basaltic andesites is in excellent agreement with the melting conditions inferred from the MOR-type peridotites in Othris. The occurrence of both N- and E-MORB-type lavas suggests that the mantle generating the lavas of the Othris Ophiolite must have been heterogeneous on a comparatively fine scale. Furthermore, the inferred parental magmas of the SSZ-type cumulates are broadly complementary to the SSZ-type peridotites found in Othris. These results suggest that the crustal section may be genetically related to the mantle section. In the Othris Ophiolite mafic rocks recording magmatic processes characteristic both of mid-ocean ridges and subduction zones occur within close spatial association. These observations are consistent with the formation of the Othris Ophiolite in the upper plate of a newly created intra-oceanic subduction zone. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Compressive deformation in the floor rocks to the Bushveld Complex (South Africa): evidence from the Rustenburg Fault Zone

The north-northwest-south-southeast striking Rustenburg Fault Zone in the western Transvaal Basin, South Africa, has been extensively mapped in order to unravel its tectonic history. In post-Pretoria Group times, but before the intrusion of the Bushveld Complex at 2050 Ma, the area surrounding the fault zone was subjected to two compressive deformational events. The shortening direction of the first event was directed northeast-southwest, producing southeast-northwest trending folds, and the shortening direction of the second was directed north-northwest - south-southeast, producing east-northeast - west-southwest trending folds. The second set of folds refolded the first set to form typical transitional Type 1-Type 2 interference folding. This compression ultimately caused reactivation of the Rustenburg Fault, with dextral strike-slip movement displacing the Pretoria Group sediments by up to 10.6 km. The subsequent intrusion of the Bushveld Complex intensely recrystallised, and often ponded against the strata along the fault zone. The fault rocks within the fault zone were also recrystallised, destroying any pre-existing tectonic fabric. Locally, the fault zone may have been assimilated by the Bushveld Complex. After the intrusion of the Bushveld Complex, little movement has occurred along the fault, especially where the fault passes under areas occupied by the Bushveld Complex. It is thought that the crystallisation of the Bushveld Complex has rheologically strengthened the neighbouring strata, preventing them from being refaulted. This model is at variance with previous assumptions, which suggest that continuous regional extension during Pretoria Group sedimentation culminated in the intrusion of the Bushveld Complex.     

Geochemistry, tectonic setting and metamorphism of mid-triassic volcanic rocks of Greece

Mid-Triassic volcanic rocks are preserved in about eight localities in the nappes of the external Hellenides, and are also widespread in the Pelagonian zone of central Greece. Most have suffered low-grade metamorphism. Immobile trace elements from 35 samples, 80 major element analyses, and pyroxene analyses show that these rocks are the product of an eastward dipping subduction zone. The subducted ocean was perhaps analogous to the Pennine zone of the Alps. The Othris and Pindos ophiolites are probably contemporaneous products of related back-arc extension.Metamorphic mineral assemblages in volcanic rocks of the Phyllite Series of the external Hellenides indicate high-pressure, low-temperature conditions, probably related to a second subduction that occurred prior to the main phase of Hellenide nappe emplacement in the Miocene.     

The sedimentary rocks of macaronesia

In all the archipelagos forming Macaronesia, volcanis predominate, but pre-Quaternary sediments are also present, though playing a humble role.Calcareous deposits have by far the greatest significance throughout the known stratigraphic record. Tertiary occurrences tend to be thin, show more gentle dips, whereas the Mesozoics attain thicknesses of 400 m (certain), attitudes steeper, often vertical.To date, Mesozoics are recognized only in Maio (Cape Verde), are possible in S. Nicolau (Cape Verde) and Fuerteventura (Canary Islands). Whether strata as old as Jurassic is present in these three islands is a moot point. Ample arguments, pro and con, have been presented for Maio; there is meagre evidence in S. Nicolau; pure conjecture in Fuerteventura.Beginning with the Neogene, the stratigraphic record for Macaronesia is more substantial, the Vindobonian being present or then strongly suspected in all archipelagos.The sedimentary rocks in these islands have not aroused the same interests as the volcanics, and undeniably they are of far less importance as regards rock constitution. The status of investigations varies widely within the different islands, and as of the present, we must frankly recognize that our knowledge of the sedimentaries is only of reconnaissance standard.

---

Zusammenfassung Auf allen Inselgruppen, die man als Makaronesen zusammenfaßt, überwiegen vulkanische Gesteine; prä-quartäre Sedimente gibt es — in geringem Umfang — ebenfalls.Kalkablagerungen haben, nach den bekannten stratigraphischen Zeugnissen zu urteilen, die größte Bedeutung. Tertiär ist in geringer Mächtigkeit und schwach geneigt vertreten, während das Mesozoikum bis zu 400 m nachgewiesene Mächtigkeit erreicht und verstellt, oft vertikal auftritt.Bisher ist Mesozoikum nur in Maio (Kapverden) bekannt, möglicherweise auch in S. Nicolau (Kapverden) und Fuerteventura (Kanarische Inseln). Ob Schichten jurassischen Alters und den drei Inseln vorkommen, ist umstritten. Argumente dafür und dagegen sind für Maio reichlich zusammengetragen worden; für S. Nicolau gibt es magere Hinweise, für Fuerteventura nur Vermutungen.Seit dem Neogen sind die stratigraphischen Zeugnisse auf den makaronesischen Inseln umfangreicher; so ist Vindobon auf allen Inselgruppen vorhanden oder sein Vorkommen mindestens sehr wahrscheinlich gemacht.Die sedimentären Gesteine haben auf den Inseln nicht das gleiche Interesse gefunden wie die vulkanischen, und sie sind auch ganz sicher von geringerer Bedeutung, soweit es sich um ihren Gesteinscharakter handelt. Der Forschungsstand ist innerhalb der Inseln sehr unterschiedlich, und wir müssen eingestehen, daß zur Zeit unser Wissen über die sedimentären Gesteine sieh noch im Anfangsstadium befindet.

---

Résumé Le matériel volcanique domine dans les îles de l'archipel des Macaronesia. Les sédiments pré-quaternaires sont aussi présents, bien que jouant un rôle plus modeste.Les formations calcaires sont de loin les plus représentatives des dépôts reconnus de la colonne stratigraphique. Les dépôts cénozoiques sont généralement peu épais et présentent de faibles pendages, tandis que ceux du Mésozoique atteignent des épaisseurs de 400 m (démontrées), et des pendages importants, atteignant souvent la verticale.Jusqu'à présent, les dépôts mésozoiques ont été reconnus uniquement à Maio (Cap Vert), sont possibles à S. Nicolau (Cap Vert) et Fuerteventura (Iles des Canaries). La présence de Jurassique dans ces trois îles est encore un sujet de controverse. De nombreux arguments, positifs ou négatifs, ont été présentés concernant l'île de Maio; les arguments positifs sont légèrement dominants à S. Nicolau; le problème est à l'état de pure hypothèse à Fuerteventura.On peut faire débuter sans ambiguité la colonne stratigraphique des îles de l'archipel Macaronesia au Néogène, le Vindobonien étant présent ou fortement suspecté dans toutes les archipels.Les roches sédimentaires dans ces îles n'ont pas suscité le même intérêt que les roches volcaniques, et indéniablement leur importance est moindre. L'état d'avancement de ces travaux varie largement d'une île à l'autre, mais à l'heure actuelle, nous devons reconnaître qu'ils en sont seulement au stade de la reconnaissance.

---

, , , , - . , . , 400 ; - . Maio, , . S. Nicolau Fuertaventura. - — : , . Maio; . S. Nicolau , Fuertaventura . . , - . , , . .

     

An overview of the geology of the Transvaal Sequence and Bushveld Complex,South Africa

The Late Archaean-Early Proterozoic Transvaal Sequence is preserved within the Transvaal, Kanye and Griqualand West basins, with the 2050 Ma Bushveld Complex intrusive into the upper portion of the succession within the Transvaal basin. Both Transvaal and Bushveld rocks are extensively mineralized, the former containing large deposits of iron, manganese, asbestos, andalusite, gold, fluorine, lead, zinc and tin ores, and the latter some of the World's major occurrences of PGE, chromium and vanadium ores. Transvaal sedimentation began with thin, predominantly clastic sedimentary rocks (Black Reef-Vryburg Formations) which grade up into a thick package of carbonate rocks and BIF (Chuniespoort-Ghaap-Taupone Groups). These lithologies reflect a carbonate-BIF platform sequence which covered much of the Kaapvaal craton, in reaction to thermal subsidence above Ventersdorp-aged rift-related fault systems. An erosional hiatus was followed by deposition of the clastic sedimentary rocks and volcanics of the Pretoria-Postmasburg-Segwagwa Groups within the three basins, under largely closed-basin conditions. An uppermost predominantly volcanic succession (Rooiberg Group-Loskop Formation) is restricted to the Transvaal basin. A common continental rift setting is thought to have controlled Pretoria Group sedimentation, Rooiberg volcanism and the intrusion of the mafic rocks of the Rustenburg Layered Suite of the Bushveld Complex. The dipping sheets of the Rustenburg magmas cut across the upper Pretoria Group stratigraphy and lifted up the Rooiberg lithologies to form the roof to the complex. Subsequent granitic rocks of the Lebowa and Rashoop Suites of the Bushveld Complex intruded both upper Rustenburg rocks and the Rooiberg felsites.     

中祁连西段托赖岩群变质岩的原岩恢复及其构造环境

对托赖岩群变质岩的岩石特征及地球化学进行研究,结果显示,托赖岩群中的片岩、片麻岩、石英岩、大理岩的原岩为沉积岩,其中片岩、片麻岩原岩为砂质岩、杂砂岩;石英岩原岩为石英砂屑岩;大理岩原岩为灰岩、白云岩。斜长角闪岩原岩为中基性火山岩,岩性为玄武安山岩。变质基性火山岩的构造环境判别结果表明,其形成于板内环境,作为托赖岩群中的特殊夹层,暗示托赖岩群沉积岩的原岩形成环境与变质火山岩的构造环境一致。