Pan-African metamorphism and magmatism in the Prydz Belt,East Antarctica:a geochronological perspective

The Prydz Belt in East Antarctica underwent extensive reworking during the late Neoprotertozoic–early Paleozoic Pan-African orogeny,which is characterized by granulite facies,clockwise P–T paths,and high dT/dP values.This study compiles the existing age and composition data of zircon and monazite from metamorphic rocks and links their key characteristics to the metamorphic evolution of the Prydz Belt.The frequency of zircon U–Pb ages starts to increase noticeably from~555 Ma,peaking between 530 Ma and 520 Ma,followed by a dramatic decline after 520 Ma.High Th/U values(>0.1)of zircon are observed from~545 Ma,displaying a noticeable increasing trend in Th/U values before a rapid decline from~520 Ma.The frequency of monazite ages progressively increases from~540 Ma,reaching its peak at 515 Ma,and then rapidly decreases after 490 Ma.Combined with the crystallization behaviors of zircon and monazite,this study suggests that the systematic changes in Th/U values of zircon after 545 Ma indicate a transition in the thermal regime of the Prydz Belt towards the cooling stage.Abundant growth of zircon and monazite corresponds to the post-peak cooling process,while the crystallization peak of monazite lags behind that of zircon by~5–15 Ma,which indicates a relatively low cooling rate.Though the granitic intrusions accompanied the entire metamorphic evolution,the majority of them are younger than 520 Ma.The results suggest that the Pan-African event likely peaked at~555–545 Ma and gradually cooled to near-solidus conditions at~520–510 Ma,with a relatively slow average cooling process.

Geochemistry and Geochronology of Peraluminous High-K Granitic Leucosomes of YaoundéSeries (Cameroon): Evidence for a Unique Pan-African Magmatism and Melting Event in North Equatorial Fold Belt

Geochemical and geochronological studies have been carry out on the leucosomes of Yaoundé series with the aims to identify the magma sources and to indicate their production periods and emplacement within the formations of the Pan-African North-Equatorial Fold Belt (PANEFB) in Cameroon. The Yaoundé series belongs to the Southern domain of the PANEFB and it is composed of migmatites in which two types of granitic leucosomes (in situ leucosomes and injected leucosomes) have been distinguished. These rocks display characteristic of calc-alkaline (in situ leucosomes) and high-K calc-alkaline to shoshonitic series (injected leucosomes). All the rocks are peraluminous with in situ leucosomes conform to S-type and injected leucosomes conform to I- and S-type granitoids. Major and trace elements composition reveal that in situ leucosomes derived from the partial melting of the host metapelite whereas injected leucosomes derived from the melting of metagreywacke. These sources are similar to those of granitoids from central and northern domains of the PANEFB. Th-U-Pb dating by electron microprobe (EMP) and LA-ICP-MS U-Pb dating on zircon have been used to constraints the melting event and emplacement of leucosomes in Yaoundé series. Th-U-Pb monazite dating, undertaken in two samples of leucosomes, gives two groups of monazite ages. The older group gives an age of 658 Ma whereas the age of younger group is 592 Ma. U-Pb dating of zircons from the leucosomes reveals a Pan-African age ranging from 626 to 654 Ma whereas zircons from metapelitic host rock reveal the overprinting of an early Pan-African event 911 - 1127 Ma on Palaeoproterozoic (2127 Ma) inheritance. These data clearly indicate that the host rocks of leucosomes of Yaoundé series have been firstly metamorphosed during Tonien-Stenien period (911 - 1127 Ma) and reveal the existence of extended unique melting event (592 and 658 Ma) in the Yaoundé series which is contemporaneous with the magmatism responsible for the emplacement of granitoids in the other domains of the PANEFB.

Distribution domains of the Pan-African event in East Antarctica and adjacent areas

The Pan-African event is widely distributed in East Antarctica （EA） craton, including both the coastal regions and interior of the EA. From aspects of the shear zones, granites, pegmatites, time of high-grade metamorphism and detrital zircon age peaks of the downflowing sediments from the inland, the Pan-African event in the EA and adjacent areas in the Gondwana reconstruction, like SE Africa, southern India and SW Australia, was described in the paper. The water or fluid available along the shear zones was responsible for retrogression of the earlier, e.g., Grenville age, high-grade outcrops to later Pan-African amphibolite to granulite facies metamorphism. In geochemistry, the granites are generally anorogenic, ocassionally with some gabbros or dolerite dykes, showing sign of bimodal feature. Meanwhile, the event has influenced most isotopic systems, including the U-Pb, Sm-Nd, Rb-Sr and Ar-Ar systems, giving Pan-African apparent ages. Spatially, the Pan-African event is demonstrated from possibly local granitic magmatism, to wider medium-high grade metamorphism, and mostly widespread in resetting for some isotope systems, suggesting the prevailing thermal effect of the event. Before Gondwana formation, local depressions in the EA may have been filled with sediments, implying the initial breakup period of the Rodinia. The later Pan-Gondwana counterrotating cogs shaped the interstitial fold belts between the continent blocks and formed a set of shear zones. The mafic underplating in the Gondwana may be responsible for the typical features of the Pan-African event. The event may be an overwhelmingly extensional and transcurrent tectonics in mechanism and is a possible response of the plate movement surrounding the continent swarms in the non-stable interior of the yet consolidated Gondwana.

The U-Pb Geochronology and Lu-Hf Isotope Compositions of Detrital Zircons from the Nanhua Group of the Longsheng Region,South China and their Implications for Pan-African Events

It is unclear whether the South China blocks have an affinity with continental Gondwana due to a lack of direct Pan-African magmatic and metamorphic features.In this study,we conducted U-Pb geochronological and Lu-Hf isotopic analyses for detrital zircons from a sandstone of the Chang'an Formation of the Nanhua Group in the Longsheng region of northern Guangxi,with the aim of constraining the timing of sedimentation and information as to its source,as well as seeking evidence for Pan-African events in the South China blocks.The results show that the ages of detrital zircons peaked at 654.7±6.2 Ma,773.2±4.1 Ma and 821.9±6.5 Ma,with some at 920–870 Ma;the youngest age indicates the existence of the Pan-African thermal event.The ε_(Hf)(t)and T_(DM2) values demonstrate that the study area has experienced three stages of crustal growth at 3.0–2.4 Ga,2.1–1.5 Ga and 1.3–0.9 Ga.With intensively distributed Neoproterozoic mafic-ultramafic and granitic plutons emplaced at 830–810 Ma along the southwestern section of the Jiangnan Orogenic Belt and positiveεHf(t)values from a large group of zircon grains,it is proposed that the sediments of the Chang'an Formation(of Nanhua Group)were largely sourced from the southeastern margin of the Yangtze block.Comparison with the zircon age spectra of the Cathaysian block shows that about 79%of the Pan-African aged detrital zircon grains that have TDM2=1352–1031 Ma andεHf(t)=3.68–8.79,were sourced from the recycled Grenvillian crust of the Cathaysian block,suggesting that the Cathaysian block had a close connection with Gondwana.

Structural Organization and Tectono-Metamorphic Evolution of the Pan-African Suture Zone: Case of the Kabye and Kpaza Massifs in the Dahomeyide Orogen in Northern Togo (West Africa)

The Kabye and Kpaza Massifs correspond to two main granulitic suites in the suture zone of the Pan-African Dahomeyide orogenic belt, in northern Togo. The Kabye Massif is composed of an important west verging nappe pile subdivided into two petrographic units. The nappes in its western petrographic unit are made up of leucocratic garnetbearing granulites defined as the “Lassa-Soumdina Granulites” (GLS). The eastern petrographic unit consists of mela-nocratic granulites, with metagabbroic structures, called the “Ketao-Sirka Granulites” (GKS). These two petrographic units are separated by the Panalo Mylonitic Zone (ZMP). This major west verging zone includes a syn-Dn + 2 dextral shear contact. The Kpaza Massif comprises nappes of melanocratic granulites (GKM), comparable to the GKS of the Kabye Massif. All these granulitic nappes include boudins of pyroxenites or meta-anorthosites, and ultramafic rocks represented by serpentinites, talcschists, actinolite- and chlorite-schists which generally mark thrust soles. The GLS nappes are thrust over the Kara-Niamtougou orthogneissic unit (UKN) which is considered as the easternmost structural unit of the Dahomeyide external zone. On the other hand, the GKS nappes underlie those of the Binah meta-volcano sedimentary Complex (CB) which belongs to the Dahomeyide internal zone. As regards the Kpaza Massif, it occurs as a geologic window tectonically enclosed in the Mono Complex nappes (CM) corresponding to the southern part of the CB. The organization of the Kabye and Kpaza Massifs, as west verging nappe piles, and their relationships with the surrounding structural units express the tangential and folding tectonics that structured the Pan-African belt in northern Togo. The microstructures and mineral parageneses of the granulites and associated rocks in these two massifs indicate a polyphase tectono-metamorphic evolution: a syn-Dn granulitization (collision phase);a syn-Dn + 1 amphibolitization (obduction or tangential phase);and a syn- to post-Dn + 2 greenschist facies retrogressive metamorphism (post-nappe folding phase).

Distribution of the Pan-African Domains in East Antarctica and Adjacent Areas

The Pan-African event is widely distributed in East Antarctica craton. Many terranes or outcrops of the craton bear more or less signs of the event. From characteristics of the shear zones, granites, pegmatites, feature and time of high grade metamorphism and detrital zircon ages peaks of the downflowing sediments from the plateau, the Pan-African event in the East Antarctica and adjacent areas in the Gondwana reconstruction, like SE Africa, southern India and SW Australia, wasdistributed as special zones or areas in many localities, including both the coastal regions and interior of the East Antarctica. In geochemistry, the granites are generally anorogenic, ocassionally with some gabbros or dolerite dykes, showing sign of bi-modal feature. The water or fluid available along the shear zones were responsible for retrogression of the earlier, e.g., Grenville age, high grade outcrops to later Pan-African amphibolite facies metamorphism. Meanwhile, the Pan-African event has influenced most isotopic systems, including the U-Pb, Sm-Nd, Rb-Sr and Ar-Ar systems, giving younger apparent ages. Manifestation of the Pan-African event is distributed from possibly locally granitic magmatism, to wider medium-high grade metamorphism, and mostly widespread in resetting for some isotope systems, suggesting the prevailing thermal effect.Before Gondwana formation, local depressions in the East Antarctica could be filled with sediments, implying the initial breakup period of the Rodinia. The later Pan-Gondwana counterrotating cogs shaped the interstitial fold belts between continent blocks and formed a set of shear zones. The mafic underplating in the Gondwana may be responsible for the widespread granites, pegmatites and more or less isotopic resetting due to strong thermal effect from the deep. That is, the Pan-African event is a possible response of the plate movement surrounding the continent swarms in the non-stable interior of theyet consolidated Gondwana.The Pan-African event may be an overwhelmingly extensional and transcurrent tectonics in mechanism.

The Chromitites Associated with the Pan-African Ophiolites in Egypt

Ophiolites components occur in Pan-African belt in Central Eastern Desert(CED)and South Eastern Desert(SED.The ultramafic components are severely serpentinized and in some areas occur as small fresh

Compositional Variations and Tectonic Settings of Podiform Chromitites Associated with Ultramafic Rocks of the Pan-African Proterozoic Ophiolites from South Eastern Desert, Egypt

The Precambrian podiform chromitites associated with ophiolites are abundant in Pan-African belt in central Eastern Desert(CED)and south Eastern Desert(SED),Egypt and range from 690 to 890 Ma in age.The studied chromitites associated with Neoproterozoic ophiolites are distributed in southern Eastern Desert,Egypt in Baranis-Shalaten sheet and occur as lenticular bodies with variable dimensions in ultramafic component(serpentinites).We present geochemical and mineralogical data from three areas of ophiolites and associated chromitites namely Gebel Abu Dahr(D),Gebel Arais(A)and Gebel Anbat in the Wadi Hodein area(H)(Fig.1).The paper studies the compositional variations and tectonic settings of podiform chromitites associated with ultramafic rocks,in addition to the alteration process of chromite during metamorphism.The ophiolite in the present areas is composed of the ultramafic rocks(mainly serpentinites)with minor relics of fresh dunite and harzburgite.All these rocks are affected by metamorphism and subsequent retrograde during subduction and exhumation.Six samples selected from the serpentinites geochemically analyzed for major,trace and some REE elements and the geochemical results reflect that harzburgite and dunite compositions are typical of depleted mantle peridotite.Microprobe analyses and SIMS investigations were carried out for three massive podiform chromitite ore bodies and disseminated chromites in serpentinites(1215 spot probe analyses),and silicate minerals in serpentinite rocks such as serpentine and olivine(102 spots).Serpentine minerals are mainly antigorite with some chrysotile in serpentinite rocks and in chromitites,mainly filling cross-cutting veins.In this study,we consider that the alteration occurred in two stages:during the first one chromite reacted with olivine and water to form Cr-and Fe-rich,porous chromite and chlorite;during the second event magnetite filled the pores,created in the porous chromite and defused into this chromite to form homogeneous magnetite.According to this,the composition of chromite is a key factor controlling the metamorphic reaction between olivine and chromite because if the primary chromite is very poor in Al,the chlorite-forming reaction hardly takes place.In this case,during the second event,the addition of magnetite only contributes to create a magnetite corona around the former chromite grains without any diffusion at the chromite-magnetite boundary as suggested by Gerbilla et al.(2012).Barnes(2000)studied the chromite in komatiites and modification during green schist to mid amphibolite facies metamorphism.He suggested that the chromite cores continually equilibrated with magnetite rims document metamorphic grade conditions.Barnes(2000)suggested that the relative proportions of Cr3+,Al3+and Fe3+of chromite are not affected by metamorphism up to lower temperature amphibolite facies implying restricted mobility of these elements occurred under lower amphibolite facies.So,the chromite in lower temperature amphibolite facies preserves its primary igneous chemistry and can be used to estimate the metamorphic grade.Sack and Ghiorso(1991)and Barnes(2000)suggested that all chromite cores are equilibrated at temperature below^500–550℃corresponding to lowest amphibolite facies metamorphism and reflect magmatic composition not influenced by metamorphism.In this study,there is no alteration but only nearly pure magnetite deposition and development with restricted Cr-solubility at<500℃in the chromite rims on crystal boundaries and within fractures as shown in Fig 2a,b.Also magnetite alters later to hematite.The podiform chromitites are common in the Moho transition zone(MTZ)to the mantle section of ophiolites or harzburgite dominant peridotite massifs(e.g.,Arai,1997;Miura et al.,2012).They have been interpreted as a product of peridotite/melt reaction and subsequent melt mixing within the MTZ to the upper mantle;they are basically magmatic cumulates that formed at the upper mantle level(e.g.,Arai and Yurimoto,1994;Zhou et al.,1994).They are thus a good marker of peridotite/melt reaction(e.g.,Arai,1997).The Pan-African podiform chromitites mayh ave formed in the same way as the Phanerozoic,namely by melt-harzburgite reaction and subsequent melt mixing.The podiform chromatites and disseminated chromites are high-Cr chromites and have range in Cr#(Cr/Cr+Al)atomic ratio from 0.75 to 0.95 and low Ti with boninitic affinity(Fig.3a),indicating an island arc setting in supra-subduction zone setting.The present massive chromitites and disseminated chromites in serpentinites fall in the field of chromites de Bou Azer,chromites de Cordoba,Argentinia in the Cr#versus Mg#diagram(Fig.3 b,c)(Gervilla et al.,2012)The studied chromatites contain some grains of platinumgroup minerals(PGM)such as sulfides(Os-rich laurite)and Os–Ir alloy as shown in Fig.4 and as reported in South Eastern Desert by Ahmed(2007).

Magnetic Characterization of Amphibolites from the Fomopéa Pluton(West Cameroon):Their Implication in the Pan-African Deformation of the Central African Fold Belt

The Fomopea granitic pluton is emplaced in gnessic and amphibolitic basement. These gneissic and amphibolitic basement rocks are represented in the pluton＇s body as sub-rounded, elongated or stretched xenoliths. Amphibolitic xenoliths display testimonies of two main tectonic events namely： （i） El flattening deformation event characterized by a NW-SE to E-W foliation with a best pole at 246/57 and a mineral stretched lineation with a best line at 293/47; and （ii） E2 compressive event typified by （1） N-S to NNE-SSW steeply dipping foliation; （2） S-type flexion-fold indicating a sinistral shear movement. These amphibolite rocks indicate a magnetic susceptibility magnitude （Km） range from 418 ~SI to 90092 IISI for 87% of the stations showing a ferromagnetic behavior. K-T curves reveal the presence of Ti-poor magnetite as susceptibility mineral carrier. Magnetic foliation and lineation suggest that the N-S strike direction observed in the Bamendou amphibolite is, as pointed out elsewhere in the Central African Fold Belt, of paramount importance in the tectonic evaluation of the Fomopea area, since it has most likely acted as major deformation phase in the second tectonic event in the belt.

Petrography and Mineralogy of the Quartz and Quartz-Feldspar Sulphide Veins in the Pan-African Syenitic Massif of Guider (North Cameroon)

In the syenitic pluton of Guider (593 ± 4 Ma) in the North-West Cameroon domain of Central African Fold Belt, mineralized N-S to NE-SW vertical or sub-vertical quartz and quartz feldspar veins has been recently identified. In this contribution, we present petrography and mineralogy of these veins, in order to constrain their genesis and emplacement mechanisms based on detailed field work, petrographic studies and chemical characterization of minerals by using an electron probe microanalyser (EPMA). Field observations and vein microstructures show that the emplacement of the veins has been controlled by the dextral N-S trending strike-slip shear zones related to the regional D2 deformation phase. The results of mineralogical analysis reveal the co-presence of silicates and metallic minerals that include magnetite, ilmenite, pyrite, bismuthite, galena (very rare) and sulphide complexes (BiPbS, BiAgPbS, FeBiPbCuS, BiFe(TeS), FeBiPbS, BiPbCuS). The gangue is represented by quartz (quartz 1, quartz 2 and quartz 3), feldspars, sericite, chlorite, yellowish brown clay minerals, and hematite. The textural relationships between sulphides, quartz and alteration products show that the mineralization is essentially syn- to late-D2 and suggest that syenitic country rock and dextral shear zones have played an important role in the metallogenesis of these veins. This mineralization shows characteristics for copper-bearing calc-alkaline deposits, but differs from these by its more extensive alteration and its abundance in hematite. Substitutions of Al(IV) by Si(IV) in sericite associated with the sulphide mineralization and cataclastic deformation suggest that the temperature of trapping of the fluids is between 230&#176;C and 275&#176;C.

From Nationalist Rebellion to Pan-African Liberation: A Theory of the Apartheid Endgame in South Africa

Why did the apartheid’s endgame favor the African National Congress (ANC) over other contenders? This article advances a path dependence argument, hypothesizing Mandela’s 1962 trip across Africa as a “critical juncture” whose arc of counter-intuitive developments narrowed the ruling National Party’s bargaining options down to its worst enemy—Mandela’s ANC.

Mapping Structurally Controlled Alterations Sparked by Hydrothermal Activity in the Fatira–Abu Zawal Area,Eastern Desert,Egypt

The Eastern Desert of Egypt suffered a protracted period of deformation triggered by cratonization of the new juvenile crust known as the Arabian Nubian Shield(ANS),which has been proposed for potential gold discoveries associated with the corresponding tectonic event.The Fatira area,on the border of Egypt’s Northern and Central Eastern Deserts,is covered with metavolcanic rocks twisted by a dextral relocation of the Fatira Shear Zone(FSZ)relative to the Barud magmatic body.The recent study evaluated many deformed post-orogenic granitic intrusions and felsite dikes associated with promising mineralization localities,notably orogenic gold deposits.The combination of various field observations and remote sensing data,followed by the analysis of aeromagnetic enhanced maps,allowed the differentiation of distinct lithologies,structural features,and hydrothermal alterations in the study area.Additionally,the integrated results obtained from the different interpretation techniques are utilized to identify and confirm the previously supposed mineralized localities in the Fatira and Abu Zawal areas and predict other matched localities.The final ASTER,Sentinel 2 hydrothermal alteration,and orientation entropy heat maps demonstrate the association between these mineralized regions and major structures related to the FSZ late stage of deformation rather than other structures studied throughout the area of interest.

Petrology, Age and Geodynamic Implication of the Panafrican Granitoids Associated with the Glito-Kpatala Shear Zone (South-East Togo)

The granitic plutons associated with the Glito-Kpatala shear zone are composed of biotite and amphibole granodiorites, biotite granites, two-mica granites and aplitic granites, which are very poorly represented. The chemical and mineralogical compositions of these facies indicate that they are I type and belong to high-K calc-alkaline series, with a chemical metaluminous character displayed by the granodiorites relative to the biotite and two-mica facies whose chemical compositions vary between metaluminous and peraluminous caracter. The Th/Ta (14.04 - 43.82 ppm, mean = 26.05), Th/U (2.58 to 15.05 ppm, mean = 5.85 ppm), Zr/Hf (25.27 to 37.21, mean = 30.67 ppm) and Rb/Sr (0.16 to 4.32;mean = 1.67 ppm) ratios of these granitoids reveal a strong crustal involvement in their magmatogenesis. Variations in CaO/Na2O (0.47 - 1.44 ppm), Rb/Sr (0.14 - 0.27 ppm), Rb/Ba (0.07 - 0.14 ppm) and Sr/Y (38.21 - 174.42 ppm) ratios indicate that biotite and amphibole granodiorites with their excessive Ni (135.37 - 139.51 ppm) and Cr (395.73 - 447.74 ppm) were derived from a mafic to intermediate lower continental crust where garnet and/or amphibole were stable residual assemblage minerals. The moderate Sr/Y ratios (1.81 - 9.47 ppm) and low transition elements Ni (1 - 6.44 ppm) and Cr (7.89 - 13.47 ppm) contents in both the two-mica and biotite granites are consistent with their emplacement at relatively shallow depths in the upper to mean continental crust, at pressures below 10 Kbar. In the two-mica granites, moderate CaO/Na2O (0.20 - 0.57 ppm, mean = 0.38 ppm) and Rb/Ba (0.39 - 1.37, mean = 0.84 ppm) ratios and quite varied Rb/Sr (1.53 - 4.23 ppm, mean = 2.85 ppm) ratios indicate a predominant derivation from psammitic and pelitic metasediments rather than metagreywackes. These low ratios (0.25 ≤ CaO/Na2O ≤ 0.32, mean = 0.28 ppm;0.31 ≤ Rb/Ba ≤ 0.44, mean = 0.39 ppm;1.11 ≤ Rb/Sr ≤ 1.78, mean = 0.39 ppm) in biotite granites are more consistent with melting from a metagreywacke-derived source. Evidence for the contribution of mantle-derived mafic magma with granitic magma in the plutons studied is materialized by the presence of magmatic enclaves in both granodiorites and two-mica granites, the volcanic arc geochemical signatures displayed by the plutons in geotectonic diagrams and Nb/Ta ratios (14.14 - 34.61 ppm) closer to mantle estimates. Geochemical data and radiometric dating elements suggest that the granitoids studied can be integrated into the pan-African late magmatic episode, which corresponds between 606 and 583 Ma, to the activity of transcurrent ductile strike-slips and to the synchronous emplacement of high K calc-alkaline plutons in a post-collisional context.

Criticism of Colonialism and the Colonial Memory Work in Germany

Colonialism is an ideological system that was not only contrary to traditional African law(family law,popular law,etc.),but was also incompatible with the dignity of man.Colonial tyranny in Africa began with the political implementation of the decisions adopted at the Berlin Conference of 1884/85,its essential principles of international law being the inviolability and the purity of colonial borders.Thus the European colonial powers managed to avoid wars of aggression and prevent uprisings by African people.Since the dominant theories of colonialism were Eurocentric,they could scarcely contribute to adequately investigating the nature of colonialism,let alone adequately describing its dimension in Africa.Instead of examining the shades of the colonial system from different cultural perspectives to inform people objectively,Eurocentric theories prevented any attempt at truth about colonial injustice.Unfortunately,some Europeans still tend to endorse the colonial injustice system in Africa with cheap and cynical Downplaying terms.The fact that colonial policy has a long history,however,in no way indicates that it should necessarily be accepted or legitimized.On the contrary,since its inception colonialism met with violent and intellectual opposition until African countries attained national sovereignty and territorial integrity.This article demonstrates the significance colonialism has in Africans’intellectual discourse and shows how the colonial question is discussed in Germany.

Metallogenic Mechanism and Tectonic Setting of Tungsten Mineralization in the Yangbishan Deposit in Northeastern China

The Yangbishan iron-tungsten deposit in the Shuangyashan area of Heilongjiang Province is located in the center of the Jiamusi Massif in northeastern China. The rare earth element and trace element compositions of the scheelite show that it formed in a reducing environment and inherited the rare earth element features of the ore-forming fluid. The geochemical characteristics of the gneissic granite associated with the tungsten mineralization show that the magma formed in this reducing environment and originated from the partial melting of metamorphosed shale that contained organic carbon and was enriched with tungsten. In addition, in situ Hf isotopic analysis of zircons from the gneissic granite indicates that they probably originated from the partial melting of a predominantly Paleo-Mesoproterozoic crustal source. According to LA-ICP-MS zircon dating, the Yangbishan ore- related gneissic granite has an Early Paleozoic crystallization age of 520.6 ＋ 2.8 Ma. This study, together with previous data, indicates that the massifs of northeastern China, including Erguna, Xing＇an, Songliao, Jiamusi, and Khanka massifs, belonged to an orogenic belt that existed along the southern margin of the Siberian Craton during the late Pan-African period. The significant continental movements of this orogeny resulted in widespread magmatic activity in northeastern China from 530 Ma to 470 Ma under a tectonic setting that transitioned from compressional syn-collision to extensional post- collision.

Metamorphism and zircon U-Pb dating of high-pressure pelitic granulites from glacial moraines in the Grove Mountains, East Antarctica

The Grove Mountains are an inland continuation of the Prydz Belt in East Antarctica. Detailed metamorphic petrological and zircon U-Pb geochronological studies are performed on the high-pressure （HP） pelitic granulites from glacial moraines in the Grove Mountains. The metamorphic peak mineral assemblage of the HP pelitic granulites is characterized by garnet ＋ kyanite ＋ K-feldspar ＋ biotite ＋ plagioclase ＋ quartz, and the subsequent medium-pressure （MP） granulite facies retrogression is characterized by sillimanite replacing kyanite, the formation of the biolite ＋ sillimanite symplectite in the matrix. These mineral assemblages and their P-T estimates based on the P-T pseudosection constructed in MnNCKFMASHT system define a clockwise P-T path involving metamorphic peak of 11.6–13.6 kbar at 817–834°C followed by a near-isothermal decompression of 6.7–7.5 kbar at 806–828°C, comparable with those of associated HP mafic granulites from glacial moraines in the Grove Mountains. Zircon U-Pb dating, coupled with available metamorphic age data obtained for HP mafic granulites, reveals HP metamorphism occurred at 540–545 Ma. Combining the previous research results, the HP pelitic granulites and contemporary HP mafic granulites were widely distributed in glacial moraines from the Grove Mountains, suggesting at least part of the Grove Subglacial Highlands underwent Pan-Afrian HP granulite facies metamorphism, which provides new evidence for a collisional tectonic setting of the Pan-Afrian Prydz Belt.

Petrography and Geochemical Characterization of Dolerites from Figuil (Northern Cameroon) and Léré(Southwestern Chad)

This work presents the petrographic and geochemical data of the dolerite dykes crosscutting the Pan-African basement of Figuil (North-Cameroon) and Léré (South-West Chad) in order to approach their petrogenesis and their emplacement context. Two groups of dolerites have been highlighted by petrographic and geochemical studies. These groups were discriminated by their TiO2, Fe2O3, REE, Ba, Nb, Zr, La and Hf contents which are relatively higher in group I;group II, on the other hand, has higher MgO, Mg#, Sc, Ni and Cr contents. The mineralogical assemblage of these dolerites is made up by plagioclases, pyroxenes, olivine, oxides, amphibole, biotite and sometimes pyrite, calcite, apatite, epidote and chlorite. The behaviour of the major and trace elements suggest that studied dolerites have an evolution dominated by fractional crystallization. Most dolerite samples show higher REE concentrations and (La/Yb)N > 8.7, (Tb/Yb)N > 1.9 and Dy/Yb > 2 ratios characterizing a garnet-bearing mantle. The difference in incompatible elements between the two groups is explained by the degree of partial melting of the same source which becomes more important over time. Low (Ce/Yb)N values (3.3 - 11.58) also suggest relatively low partial melting degree of the source. Fractional crystallization process was possibly combined with minor crustal contamination as shown by enrichment of Th/Yb from group II to Group I that might be due to turbulent magma emplacement. The chemical compositions of these dolerites are similar to that of continental tholeiites with slightly moderate negative Nb-Ta anomalies which are attributed to crustal contamination of magmas. As other dolerites of Cameroon, continental tholeiitic signature of the studied dolerites is evidenced in geotectonic discrimination diagrams with Group II dolerite compositions falling within the field of tholeiitic basalts and group I within the field of alkali basalts.

Granitoid Rocks in Guider Area(North Cameroon):Contribution of Petrography and Structural Analysis

The study area is located around Guider and belongs to the Northern Cameroon Pan-African fold belt.It is essentially made of three generations of granitoids.The first generation G1 comprises diorites,tonalites and granodiorites.The second one G2 is constituted by biotite granites and biotite-muscovite granites deformed in the solid-state.The third generation G3 is constituted by biotite-syenites,monzosyenites,and leucogranites. All the granitoids are cross cut by aplite veins

Geochemical Characterization of Mineralized Pegmatites around Wowyen Areas,Akwanga,Northcentral Nigeria

This study aims to account for the petrogenesis and mineralization of pegmatites around the Wowyen area,northcentral basement complex,Nigeria.Field studies,petrography and whole rock geochemistry(Major oxides were estimated by X-Ray Fluorescence while the trace elements were estimated by Inductively Coupled Plasma Mass Spectrometry)where the methods adopted.The pegmatites around Wowyen area are emplaced in the remobilized belt of the Nigerian Basement complex.They are predominantly complex pegmatites(rare-metal pegmatites)which are intruded in the biotite-muscovite gneiss while the simple pegmatites intruded more in the migmatitic banded gneiss.The major components of the complex pegmatites are quartz,albite and muscovite and tourmaline.The accessory constituents are garnet;ilmenites;cassiterite-columbite-tantalite oxides in contrast to quartz,microcline and biotite of the simple pegmatites.The complex pegmatites show higher peraluminous than the simple pegmatites,however,higher fractionation is observed in the complex pegmatites than the simple pegmatites.The complex pegmatites are rather enriched in rare elements such as Li,Rb,B,Cs,Sn,Nb,Be and Ta and show low ratios in Al/Ga and K/Rb than the simple pegmatites.The pegmatites are likely product of sedimentary origin and originated from post-collisional tectonic event.

Petrology and geochemical framework of dolerites dykes of Temte, North Cameroon, Central Africa

The Temtebasement in North Cameroon is crosscut by dyke swarms with N 20°–40°trending,including dykes 15–30 m wide,up to 3 km-long.Representative rocks exhibit intersertal to sub-ophitic textures.Electron microprobe analyses identified diopside,augite,pargasite,biotite,Ti-magnetite,plagioclase,and sanidine.Whole-rock ICP-MS and ICP-AES chemical analyses showed compositions of basaltic andesite,basaltic trachyandesite and trachyandesite in composition.Igneous differentiation was likely governed by fractional crystallization associated with limited fluid metasomatism.Some lavas could have been moderately contaminated by crustal materials during feeding of local cracks through turbulent magma flows.Discrimination geochemical diagrams and immobile trace and REE element ratios show that the mantle source of Temtedolerites was a deep phlogopitebearing EMII mantle component and has undergone moderate to high partial melting rate.Correlations of fieldwork and analytical data with previous results evidence the Temtedolerite dyke swarms as fingerprints of crustal extension accompanying regional uplift in an active continental margin when early rifting led to the formation of the Poli marginal basin.