Pan-African Tectonothermal Event Research Articles

Source and age of the Ngaye banded iron formations, Adamawa Yadé Domain, Central Cameroon: Constraints from whole-rock geochemistry and U-Pb zircon geochronology

The Ngaye inlier of the Adamawa Yadé Domain is located in the Central African Fold Belt, adjacent to the Nyong Complex at the northern margin of the Congo craton, in central Cameroon. This area consists of metamorphosed granite-greenstone associations comprising amphibole- and pyroxene-rich banded iron formations (BIFs), amphibolites, and migmatitic gneisses. This study reports detailed petrographic, whole-rock geochemical, and LA-ICP-MS U-Pb zircon data for the Ngaye BIFs and associated amphibolites to better constrain their source, tectonic setting, and age. Amphibole-rich BIFs exhibit high REE-Y content and uncommon LREE-enriched patterns. In contrast, pyroxene-rich BIFs display combined low REE-Y content, seawater-like patterns, and positive Eu anomalies, suggesting a mixture of seawater and hydrothermal fluids during their deposition. The geochemical data of associated amphibolites suggest a back-arc setting for the Ngaye metavolcanosedimentary sequence, similar to that of the Nyong Complex. LA-ICP-MS U-Pb zircon dating of amphibole-rich BIFs indicate a maximum depositional age of ca. 2186 Ma and subsequent metamorphism at ca. 2038 Ma, overlapping with that of metavolcanosedimentary sequences from the Nyong Complex. Neoproterozoic age of ca. 598 Ma obtained for these BIFs is interpreted as the Pan-African metamorphic/hydrothermal imprint. This finding suggests that the post-depositional fluid overprint was probably related to the regional Pan-African tectono-thermal event.

NEW DATA ON THE GEOLOGICAL STRUCTURE AND PRECAMBRIAN EVOLUTION OF THE DENMAN GLACIER WEST SIDE MOUNTAIN FRAME (EAST ANTARCTICA): FIRST PALEOARCHEAN AGE FOR PLAGIOGNEISES

Mountain frame of the Denman Glacier is a little explored and at the same time an most essential region of East Antarctica in the context of studying the Precambrian geological history and geodynamic evolution of the Archean protocratons of East Antarctica. Present paper provides original U–Pb isotope geochronology data from zircons of metamorphic and intrusive rocks sampled from the Denman Glacier western flank outcrops. Geodynamic interpretation of geochronology data are also presented. For the first time, for such East Antarctic location, crystallization time (3355 ± 5.4 Ma) for plagiogneisses magmatic protolith was obtained. The Davis Paleoarchean protocraton in the Archean time interval of evolution was subject to multistage polymetamorphism in the intervals ~3100–3000, 2900–2800 Ma ago. The late stage is associated with crustal extension, which is marked by syntectonic intrusion of ultramafic dikes and pyroxenite sills (2827 ± 6 Ma). The formation time of granite veins and subalkaline granitoid pluthons corresponds to the time of tectono-thermal activisation in the interval of 550–510 Ma traced also along significant part of East Antarctic (the Pan-African tectono-thermal event). The Davis terrane shows a significant similarity in the time of formation and evolution of geodynamic processes with the Paleo-Mesoarchean protocratons of East Antarctica, as well as India and Australia.

Constraining the timing of deep magmatic pulses from diamondiferous kimberlite and related rocks in the South China Continent and implications for diamond exploration

Mantle-derived magmas provide windows to the deep earth, and precise dating of the deep magmatic rocks such as kimberlite and related lithologies is crucial to attaining a better understanding of the mantle evolution and mantle-crust interaction in conjunction with global geodynamic cycle. Here we report a geochronology investigation of the diamondiferous kimberlite and related rocks from the southeastern side of the Yangtze Craton in China with the aim to constrain the deep mantle magma emplacement patterns and mantle evolution through time. Ultrabasic magmatic events occurred intermittently between 492 and 441 Ma, as inferred from apatite U-Pb dating and phlogopite 40Ar-39Ar dating. Combined with the previous data, two pulses of diamondiferous magmatism (ca. 488 Ma and ca. 450 Ma) are identified. The emplacement ages and patterns of these deep-seated diamondiferous magmas are unrelated to the reported Pan-African tectonothermal event (peak at ca. 522 Ma), Kwangsian Orogeny (peak at ca. 435 Ma), and Emeishan plume event (peak at ca. 260 Ma) in the South China Continent. Instead, we infer that the kimberlite and associated rocks in the South China Continent may be related to the upwellings from the edges of the Large Low Shear Velocity Province located at the core-mantle boundary at that time. The lack of magmatic event during 760 to 460 Ma and the existence of the thick lithosphere (>175 km) beneath the South China Continent are suitable for lithospheric diamond formation during the Early Paleozoic. These data suggest that future diamond exploration should be focused on the kimberlites emplaced during the Cambrian–Ordovician transition on the southeastern side of the former Yangzte Craton.

Mineral chemistry and petrology of mantle peridotites from the Qala En Nahal-Umm Saqata ophiolite, Gedarif State, Sudan

The study area of this research some 70 km southwest of Gedarif city, Gedarif State, in eastern Sudan. With a geological position, it is located within two major lithological associations, representing two different crustal entities: Saharan Metacraton (SMC) in the west and the Arabian Nubian Shield (ANS) to the east. The main objective of the study is a petrological investigation of the mantle peridotites within Qala En Nahal-Umm Saqata area. The relatively large-scale exposed masses of mantle’s peridotite, include mainly the Utash mass and the Umm Saqata mass in the south and the Qala en Nahal mass and the Fau mass in the north of the area. Petrographically, they are mostly serpentinite. They have low-contents of Al2O3, CaO, TiO2O, MgO, Na2O and K2O, all consistent with depleted mantle materials, and similar to the metamorphic peridotites. The analyzed serpentine minerals are mainly pseudomorphic serpentines with subordinate antigorite, which may suggest that the parent minerals were first retrogressed to form lizardite and chrysotile. Subsequently, progressive metamorphism has recrystallized these minerals into antigorite. The chromites from the study area have high Cr# (Cr# varies from 0.51 to 0.87), most probably representing the primary phase which is similar to chromian spinels in mantle-derived peridotites. The presence of podiform chromites in the studied serpentinites is e typical of supra-subduction ophiolites, with Cr# similar to those of forearc ophiolites and boninite-derived chromites. Qala En Nahal-Umm Saqata mantle peridotites were formed in a forearc setting, during the subduction initiation that developed as a result of southeastward-dipping subduction zone. They possibly represent ensimatic, thrusted material, after the collision of the Nubian-Arabian Shield with the older sialic continental Saharan Metacraton during the late Proterozoic, Pan-African tectono-thermal event. These investigations were carried out supported by the Peoples’ Friendship University of Russia (RUDN University), Moscow, Russia and the Faculty of Petroleum and Minerals, Al Neelain University, Sudan. The publication has been prepared with the support of the «RUDN University Program 5–100». To all we express our thanks and appreciations.

Detrital zircon age spectra of the Yungou Formation and its constrain to the related block affinity, western Yunnan

滇西允沟岩组为一套低绿片岩相的泥质浅变质岩，岩性以云母石英片岩、云母石英千枚岩、云母片岩、细晶灰岩为主，局部夹硅质岩，一直以来被认为是前寒武纪变质基底的重要组成部分。其原岩以碎屑岩为主，含有部分灰岩、白云岩，是一套形成于特提斯洋被动大陆边缘的半深海-深海沉积物，因此，是研究特提斯洋构造演化的重要窗口。但是，对允沟岩组的形成时代至今仍存在较大争议，为此本文选取允沟岩组中的片岩进行了碎屑锆石U-Pb精确定年。分析结果表明，允沟岩组原岩沉积时代为新元古代晚期-寒武纪期间（551~491Ma），主要由新太古代、新元古代及少量古元古代碎屑物质组成。其中，大量太古宙晚期碎屑锆石表明其源区有太古宙基底的存在，而1749Ma这组碎屑锆石可能与哥伦比亚超大陆聚散有关，956Ma和848Ma这两组锆石记录的事件可能是对罗迪尼亚超大陆三阶段裂离事件的前两期的响应。此外，还含有少量泛非运动信息，但泛非运动对其源区的影响极其有限。结合前人研究成果和本文碎屑锆石年龄谱，显示允沟岩组形成于原特提斯洋的被动陆缘，与印度板块、南羌塘地块具有显著的亲缘性。;The Yungou Formation in western Yunnan Province, a suit of metapelites of lower greenschist facies, consists dominantly of mica quartz schist, mica quartz phyllite, mica schist and fine crystalline limestone, with some siliceous rocks. It has always been considered as an important part of the Precambrian metamorphic basement. The protoliths are mainly clastic rocks with some limestone and dolomite, belonging to a set of semi-deep sea sediments formed in the passive continental margin of the Tethys Ocean. So the Yungou Formation witnessed the origin, development and extinction of the Tethys Ocean, and played a great role in understanding the tectonic evolution of the Tethys Ocean. However, its forming age is still under controversial. In this paper, the zircon U-Pb dating of schists from the Yungou Formation, southwestern Yunnan Province, has been carried out. The analysis results show that the depositional age of the protolith of the Yungou Formation is in Late Neoproterozoic-Cambrian (551~491Ma), and mainly composed of Neoarchean, Neoproterozoic and some Paleoproterozoic detrital rocks. The discovery of massive Neoarchean detrital zircons indicates the existence of the Archean basement in the source area. The 1749Ma zircons may be related to the Columbia Supercontinent from assembly to breakup. The zircons of 956Ma and 848Ma may be a response to the former two stages of the three-stage-rifting evolution of the Rodinia Supercontinent. In addition, the dating result also revealed the existence of pan-African tectono-thermal event, but its impact on the source region of the Yungou Formation is extremely limited. Combined with previous study, the U-Pb age spectra of detrital zircons shows that the Yungou Formation developed on the passive continental margin of the Proto-Tethys Ocean and when it deposited this block has the good affinity of the Indian and South Qiangtang blocks.

Contribution of Columbia and Gondwana Supercontinent assembly- and growth-related magmatism in the evolution of the Meghalaya Plateau and the Mikir Hills, Northeast India: Constraints from U-Pb SHRIMP zircon geochronology and geochemistry

The Meghalaya Plateau and the Mikir Hills constitute a northeastern extension of the Precambrian Indian Shield. They are dominantly composed of Proterozoic basement granite gneisses, granites, migmatites, granulites, the Shillong Group metasedimentary cover sequence, and Mesozoic-Tertiary igneous and sedimentary rocks. Medium to coarse grained, equigranular to porphyritic Cambrian granite plutons intrude the basement granite gneisses and the Shillong Group. U-Pb SHRIMP zircon geochronology and geochemistry of the granite gneisses and granites have been carried out in order to understand the nature and timing of granite magmatism, supercontinent cycles, and crustal growth of the Meghalaya Plateau and Mikir Hills. Zircons from the Rongjeng granite gneiss record the oldest magmatism at 1778±37Ma. An inherited zircon core has an age of 2566.4±26.9Ma, indicating the presence of recycled Neoarchaean crust in the basement granite gneisses. Zircons from the Sonsak granite have two ages: 523.4±7.9Ma and 1620.8±9.2Ma, which indicate partial assimilation of an older granite gneiss by a younger granite melt. Zircons from the Longavalli granite gneiss of the Mikir Hills has a crystallization age of 1430.4±9.6Ma and a metamorphic age of 514±18.6Ma. An inherited core of a zircon from Longavalli granite gneiss has an age of 1617.1±14.5Ma. Zircons from younger granite plutons have Cambrian mean ages of 528.7±5.5Ma (Kaziranga), 516±9.0Ma (South Khasi), 512.5±8.7Ma (Kyrdem), and 506.7±7.1Ma and 535±11Ma (Nongpoh). These plutons are products of the global Pan-African tectonothermal event, and their formation markedly coincides with the later stages of East Gondwana assembly (570–500Ma, Kuunga orogen). The older inherited zircon cores (2566.4±26.9Ma, 1758.1±54.3Ma, 1617.1±14Ma) imply a significant role for recycled ancient crust in the generation of Cambrian granites. Thus the Meghalaya Plateau and Mikir Hills experienced major felsic magmatic episodes at ~1800Ma, ~1600Ma, ~1400Ma, and ~500Ma with recycling of Neoarchaean crust, and later contributions from Paleo-Mesoproterozoic granite gneiss sources. A 258±20Ma lower intercept age of the Rongjeng granite gneiss perhaps indicates a Permo-Triassic thermal imprint on the Meghalaya Plateau. The granite gneisses and granites have peraluminous to metaluminous compositions, and syn-orogenic to post-collisional affinities. We conclude that the orogenic history of the Meghalaya Plateau and the Mikir Hills records crustal growth of the Columbia and Gondwana supercontinents as noted in other Pan-African-Indian-Prydz-Brasiliano orogens.

Age and P–T evolution of the Neoproterozoic Turkel Anorthosite Complex, Eastern Ghats Province, India

Massif-type anorthosite complexes constitute a distinct component of the Proterozoic Eastern Ghats Province in India. They intruded the poly-deformed and poly-metamorphic granulite facies terrane near its western and northern tectonic contacts with the Archaean Bastar and Singhbhum cratons, respectively. Following their emplacement, the complexes were variously affected by high-grade metamorphism and deformation. The Turkel Anorthosite Complex comprises an anorthosite–leuconorite diapir encircled by voluminous crust-derived quartz–monzonite intrusions hosted within an expansive batholithic complex of megacrystic K-feldspar granite and remnants of an older gneissic unit. This contribution evaluates the pressure-temperature history of the anorthosite complex based on textural relations, paragenetic characteristics, and mineral chemistry, and provides for the first time, constraints on the timing of emplacement and subsequent metamorphism of the rocks through in situ U–Pb dating of zircon from several members of the suite.Emplacement of the Turkel Anorthosite Complex occurred after the fabric-defining late Mesoproterozoic deformation (D1–D3) and high-grade metamorphism of the country rocks and was shortly preceded by the surrounding expansive intrusion of the megacrystic K-feldspar granite. The leuconorite-anorthosite suite crystallized at 980±8Ma while the other components including the monzonite, quartz–monzonite, and ferrodiorite were emplaced later between 956±6 and 945±5Ma. The post-intrusion evolution of the complex is characterized by partial re-equilibration of the igneous parageneses and textures during an initial episode of cooling and decompression from the magmatic crystallization stage (1100–950°C, 12–7kbar) towards the ambient thermobaric regime, and following prolonged slow cooling by an episode of renewed compressional deformation (late-D3; ca. 750°C, 6.5–7.0kbar) that caused the thorough high-grade recrystallization of the rocks and produced the monophase planar fabric of the complex. U–Pb spot ages from metamorphic domains of zircon grains constrain the age of this metamorphism to 901–879Ma. The complex was moderately affected by the late Neoproterozoic to early Palaeozoic Pan-African tectonothermal event which led to internal tectonic segmentation and westward thrusting of the Khariar and Rampur domains of the northern Eastern Ghats Province onto the Bastar craton.

Geochronology of granitic rocks from the Ruangwa region, southern Tanzania – Links with NE Mozambique and beyond

New U–Pb zircon LA-ICP-MS data are presented for 4 granitoid bodies which intrude high grade gneisses of the previously unmapped Ruangwa region in southern Tanzania. The study area forms part of the late Neoproterozoic East African Orogen (EAO). The oldest unit, a coarse-grained migmatitic granitic orthogneiss gave an early Neoproterozoic (Tonian) crystallization age of 899±9/16Ma, which is similar to, but significantly younger than, Stenian-Tonian basement ages in areas relatively nearby. Crust of this age may extend as far north as the major Phanerozoic Selous Basin, north of which Archaean protolith ages predominate (the “Western Granulites”), except for the juvenile Neoproterozoic “Eastern Granulites”, which are not represented in the study area. To the south, the Tonian crust of the study area provides a tentative link with the Marrupa Complex in NE Mozambique. A granite pluton, dated at 650±5/11Ma is broadly coeval with the main Pan-African tectono-thermal event in the East African Orogen that is recorded across Tanzania north of the Selous Basin. Zircons in this granite contain inherited cores at ca. 770Ma. This age is within the range of dates obtained from south and west of the study area from juvenile granitoid orthogneisses which might be related to a widespread, but poorly understood, early phase of Gondwana assembly along an Andean-type margin.South of the study area, in NE Mozambique, the latest orogenic events occurred at ca. 550Ma, and are sometimes attributed to the Ediacaran-aged “Kuunga Orogeny”. While metamorphic dates of this age have been recorded from the EAO north of the Selous Basin, magmatic rocks of this event have not been recognized in Tanzania. The two youngest granitoids of the present study are thus the first 500–600Ma igneous rocks reported from the region. A weakly deformed very coarse-grained granite pluton was dated at 591±4/10Ma, while a very late, cross-cutting, undeformed granite dyke gave an intrusive age of 549±4/9Ma.The granitoids ages presented in this study contain elements that are characteristic of the northern, Tanzania-Kenya, segment of the East African Orogen and of the southern, Mozambique, segment. The Tonian orthogneiss sample is typical of (but somewhat younger than) the Marrupa Complex of NE Mozambique. No zircon inheritance was recorded in the sample, typical of the juvenile Marrupa Complex. On the other hand, the ca. 650Ma granite pluton has an age that is typical of the northern segment of the orogen; this is the first recorded granite of that age intruded into the Tonian-dominated crust of southern Tanzania or NE Mozambique. The two younger granites have provided dates that are typical of the southern segment of the orogen, and that of the Kuunga Orogen. The study area thus appears to represent an area of transitional crust straddling two complex and contrasting segments of the East African Orogen, with elements of both segments present and evidence for a ca. 770Ma event which appears to be quite widespread and may relate to the early phases of Gondwana amalgamation in southern East Africa.

Application of remote sensing in exploration for uranium mineralization in Gabal El Sela area, South Eastern Desert, Egypt

This research aims at integrating remote sensing data and field studies to prospect for radioactive materials at Gabal El Sela area, South Eastern Desert of Egypt. This area is a part of the Arabo-Nubian shield, which is constituted by Late Precambrian basement rocks and developed during the Pan African tectono-thermal event. Geological interpretation of Landsat ETM+ image and field studies revealed that the study area is mainly covered by ophiolitic ultramafic rocks, intermediate metavolocanics, granodiorites, biotite granites and garnetiferous muscovite granites. These rocks are injected by pegmatitic and quartz veins and cut by acidic and basic dykes. The processed Landsat ETM+ data enable also to identify uraniferous alteration zones hosted in the granitic rocks (using band ratio 5/7, 4/5, 3/1 in RGB, density slicing and supervised classification techniques). The measured reflectance values (DNs) of six spectral bands of Landsat ETM+ for all exposed rock types in the study area show that the alteration zones have the highest reflectance values. The study recorded the presence of uranium mineralizations in alteration zones associating with the granitic rocks occurring along ENE–WSW trending shear zones. Three uranium-bearing alteration zones hosted in granitic rocks were detected. These zones are characterized by ferrugination, silicification, grizenization and kaolinitization. The most promising alteration zones (Site 1) occurs at the northeastern part of Gabal El Sela and is characterized by very high radioactive anomalies (up to 5000ppm eU). Microprobe analyses of samples collected from these alteration zones reveal the presence of uraninite crystals. It seems that the high fractures density of the granitic rocks acted as good channels for the ascending hydrothermal fluids and the percolating meteoric water, that leached the uranium minerals disseminated all over the rocks and redeposited them along the fractures of the shear zones. This study demonstrates the utility of orbital remote sensing data for finding unknown mineralized zones in the Eastern Desert of Egypt and similar arid regions.

Pan-African decompressional P-T path recorded by granulites from central Dronning Maud Land, Antarctica

A high-grade metamorphic complex is exposed in Filchnerfjella (6–8°E), central Dronning Maud Land. The metamorphic evolution of the complex has been recovered through a study of textural relationships, conventional geothermobarometry and pseudosection modelling. Relicts of an early, high-P assemblage are preserved within low-strain mafic pods. Subsequent granulite facies metamorphism resulted in formation of orthopyroxene in rocks of mafic, intermediate to felsic compositions, whereas spinel + quartz were part of the peak assemblage in pelitic gneisses. Peak conditions were attained at temperatures between 850–885 °C and 0.55–0.70 GPa. Reaction textures, including the replacement of amphibole and garnet by symplectites of orthopyroxene + plagioclase and partial replacement of garnet + sillimanite + spinel bearing assemblages by cordierite, indicate that the granulite facies metamorphism was accompanied and followed by decompression. The observed assemblages define a clock-wise P-T path including near-isothermal decompression. During decompression, localized melting led to formation of post-kinematic cordierite-melt assemblages, whereas mafic rocks contain melt patches with euhedral orthopyroxene. The granulite facies metamorphism, decompression and partial crustal melting occurred during the Cambrian Pan-African tectonothermal event.

U–Pb geochronology and geochemistry of the bedrocks and moraine sediments from the Windmill Islands: Implications for Proterozoic evolution of East Antarctica

Zircon LA-ICP-MS U–Pb geochronology and geochemistry on representative bedrocks and moraine sediments in the Windmill Islands in Wilkes Land, East Antarctica were performed to characterize the age and origin of main rocks as well as the lithology and age of ice-covered basement in this sector of East Antarctica. Zircon U–Pb dating on two garnet-bearing granite gneisses and one foliated garnet-bearing granite from Bailey Peninsula yield weighted mean 207Pb/206Pb ages of 1247±13Ma, 1258±12Ma and 1242±13Ma, respectively, which are interpreted as emplacement ages of these rocks. Igneous inherited zircons in these rocks yield a weighted mean 207Pb/206Pb age of 1372±13Ma, indicating existence of a ca. 1.37Ga igneous activity in the Windmill Islands. Both garnet-bearing granite gneisses and foliated garnet-bearing granites from Bailey Peninsula are characterized by similar geochemical and isotopic compositions and were likely produced by partial melting of predominantly Paleoproterozoic ancient crustal materials at 1.24–1.25Ga. Zircon U–Pb analyses on two charnockite samples from Robinson Ridge yield weighted mean 207Pb/206Pb ages of 1196±8Ma and 1205±13Ma, respectively, indicating emplacement of the Ardery Charnockite at ca. 1.20Ga. The charnockites were likely produced by partial melting of the ancient mafic lower crust heated by underplated basaltic magma during the D2 cycle at late stage of the granulite facies metamorphism, and some lithospheric mantle materials could be involved during formation of these rocks. U–Pb analyses of detrital zircons from sand-sized moraine sediments yield concordant 207Pb/206Pb ages mainly ranging from ca. 1368Ma to ca. 1107Ma with main magmatic zircon populations at ca. 1107Ma, 1150–1160Ma, ca. 1196Ma, 1231–1255Ma, ca. 1317Ma and ca. 1368Ma, respectively. Some old zircon populations at ca. 1411Ma to ca. 2360Ma, which are considered to be derived from recycling of the Proterozoic metapsammitic gneiss rocks, have been identified. Their zircon Hf isotopic model ages (TDMC) are mainly around 1.6–2.4Ga. The absence of Archean zircons in moraines suggests that the crust of Law Dome and inland areas of Wilkes Land are dominated by Palaeo-Mesoproterozoic rocks, which is consistent with the vast majority of the Nd–Hf isotopic data presented. Abundant Mesoproterzoic zircons from ca. 1107Ma to ca. 1533Ma in moraines indicate the crustal rocks in the Windmill Island and its inland areas are mainly formed in the Mesoproterozoic. The ages and Hf isotopic compositions of these moraine zircons are comparable with those of the bedrocks in the Windmill Islands, indicating that subglacial rock compositions of Law Dome and the inland areas of Wilkes Land are similar to the rock composition of the Windmill Islands area. Law Dome and the inland areas of Wilkes Land are probablly a similar Mesproterozoic high-grade metamorphic terrane as the Windmill Islands in East Antarctica. Our results also confirmed that there is no evidence for Pan-African tectonothermal events and the Windmill Islands and its inland areas are not affected by Pan-African tectonism and magmatism.

A new tectonic and temporal framework for the Tanzanian Shield: Implications for gold metallogeny and undiscovered endowment

The lack of new gold discoveries in recent times has prompted suggestions that Tanzania is mature or approaching maturity, in terms of gold exploration. New tectonic–metallogenic subdivisions proposed in this study are used to explain gold-endowment, assess gold exploration maturity, and suggest the potential for new discoveries from the following three regions: 1) the Lake Victoria Region, comprising the gold-endowed East Lake Victoria and Lake Nyanza Superterranes of <2.85Ga greenschist–amphibolite facies granitoid-greenstone terranes in >3.11Ga continental crust. These superterranes are separated by the gold-poor, Mwanza–Lake Eyasi Superterrane, comprising deeply eroded and/or exhumed terranes of gneissic-granulite belts and widespread granitoid plutons; 2) the Central Tanzania Region, comprising the Moyowosi–Manyoni Superterrane, which is largely composed of granitoid and migmatitic–gneissic terranes, and the Dodoma Basement and Dodoma Schist Superterranes, these are underlain by extensive, >3.2Ga migmatitic-gneisses and granitoid belts with interspersed, relatively narrow, <2.85Ga greenschist–amphibolite facies greenstone and schist belts. The Central Tanzania Region also includes the East Ubendian–Mtera Superterrane, comprising the East Ubendian Terrane of predominantly Paleoproterozoic belts with cryptic Archean age components, and the ~2.85–3.0Ga Isanga–Mtera Terrane of thrust-transported migmatitic ortho- and para-gneisses; and 3) Proterozoic Tanzania Regions, comprising various Archean terranes which were once sutured to the Tanzania Craton prior to later Proterozoic orogenic and tectonic events that separated them from the craton and thermally reworked them. These include the Archean Nyakahura–Burigi Terrane in the Northwestern Tanzania Proterozoic Orogen and the Kilindi–Handeni Superterrane in the Southern East African Orogen of Tanzania.The major metallogenic significance of the new tectonic subdivisions is the recognition of under-explored belts: 1) in the gold-endowed East Lake Victoria and Lake Nyanza Superterranes, Lake Victoria Region. Here deeply weathered belts in the Musoma–Kilimafedha, Kahama–Mwadui and Nzega–Sekenke Terranes and belts, situated in tectono-thermally reworked crustal blocks such as the Iaida–Haidon, Singida–Mayamaya and Mara–Mobrama Terranes, are predicted to be prospective; 2) in the Dodoma Basement Superterrane, Central Tanzania Region, where relatively thin, juvenile granitoid-greenstone belts, similar to the ~2815–2660Ma Mazoka Belt in the Undewa–Ilangali Terrane, contain small-scale gold systems with analogous terrane-scale geologic settings and evolution histories to those of gold-hosting greenstone belts in the Sukumaland Terrane, Lake Victoria Region. The overall geologic–geometric setting of the greenstone belts in the Central Tanzania Region (Mazoka-type) is comparable to those of the gold-hosting juvenile granitoid-greenstone belts in the South West and Youanmi Terranes, Yilgarn Craton, Western Australia, and North Superior and North Caribou Superterrane, northwestern Superior Craton, Canada; and 3) in the Proterozoic Tanzanian Regions, where terranes that lie in close geographic proximity and regional strike extension to the gold-endowed Lake Nyanza Superterrane are likely to be most prospective. They include the Archean Nyakahura–Burigi Terrane in unroofed thrust windows of the Mesoproterozoic Karagwe–Ankolean Belt of northwestern Tanzania, and the Kilindi–Handeni Superterrane where Archean proto-crust has been reworked by Pan-African tectonothermal events in the Southern East African Orogen.

Geometry of fold interference patterns in Wadi Kharit area, South Eastern Desert, Egypt

Fold interference patterns and superimposed relations are common in the Neoproterozoic basement rocks of Egypt. They are the products of complex Precambrian orogenies formed by collision and accretionary island arcs onto a pre-Pan-African continent to the west of the River Nile. Fold interference patterns and superimposed folds affected the unmetamorphosed to slightly metamorphosed volcaniclastic rocks in Wadi Kharit area during the Pan-African tectono-thermal events (600–450 Ma). Superimposed folding in Wadi Kharit area resembles in many respects that of recorded in Hafafit Shear Zone. The difference is in the degree of deformation and grade of metamorphism. Fold interference patterns and superimposition in Wadi Kharit area are formed by a single phase of deformation rather than a polyphase of deformation. Most of the fractures and associated normal faults dissected Wadi Kharit area are of fold-related faulting, which are reactivated post-dating igneous intrusions.

Genesis of wollastonite- and grandite-rich skarns in a suite of marble-calc-silicate rocks from Sittampundi, Tamil Nadu: constraints on the P–T–fluid regime in parts of the Pan-African mobile belt of South India

The Pan-African tectonothermal activities in areas near Sittampundi, south India, are characterized by metamorphic changes in an interlayered sequence of migmatitic metapelites, marble and calc-silicate rocks. This rock sequence underwent multiple episodes of folding, and was intruded by granite batholiths during and subsequent to these folding events. The marble and the calc-silicate rocks develop a variety of skarns, which on the basis of mineralogy; can be divided into the following types: Type I: wollastonite + clinopyroxene (mg# = 71–73) + grandite (16–21 mol% Adr) + quartz ± calcite, Type II: grandite (25–29 mol% Adr ) + clinopyroxene (mg# = 70) + calcite + quartz, and Type III: grandite (36–38 mol% Adr) + clinopyroxene (mg# = 55–65) + epidote + scapolite + calcite + quartz. Type I skarn is 2–10 cm thick, and is dominated by wollastonite (>70 vol%) and commonly occurs as boudinaged layers parallel to the regional foliation Sn1 related to the Fn1 folds. Locally, thin discontinuous lenses and stringers of this skarn develop along the axial planes of Fn2 folds. The Type II skarn, on the other hand, is devoid of wollastonite, rich in grandite garnet (40–70 vol%) and developed preferentially at the interface of clinopyroxene-rich calc-silicates layers and host marble during the later folding event. Reaction textures and the phase compositional data suggest the following reactions in the skarns: 1. calcite + SiO2 → wollastonite + V, 2. calcite + clinopyroxene + O2 → grandite + SiO2 + V, 3. scapolite + calcite + quartz + clinopyroxene + O2 → grandite + V and 4. epidote + calcite + quartz + clinopyroxene + O2 → grandite + V Textural relations and composition of phases demonstrate that (a) silica metasomatism of the host marble by infiltration of aqueous fluids (XCO2 11 kbar and >950°C) inferred for the Pan-African tectonothermal events from the neighboring areas. Field and petrological attributes of these skarn rocks are consistent with the infiltration of aqueous fluid predominantly during the Fn1 folding event at or close to the ‘peak’ metamorphic conditions. Petrological features indicate that the buffering capacity of the rocks was lost during the formation of type I and II skarns. However, the host rock could buffer the composition of the permeated fluids during the formation of type III skarn. Aqueous fluids derived from prograde metamorphism of the metapelites seem to be the likely source for the metasomatic fluids that led to the formation of the skarn rocks.

Genesis of secondary uranium minerals associated with jasperoid veins, El Erediya area, Eastern Desert, Egypt

Uranium mineralization in the El Erediya area, Egyptian Eastern Desert, has been affected by both high temperature and low temperature fluids. Mineralization is structurally controlled and is associated with jasperoid veins that are hosted by a granitic pluton. This granite exhibits extensive alteration, including silicification, argillization, sericitization, chloritization, carbonatization, and hematization. The primary uranium mineral is pitchblende, whereas uranpyrochlore, uranophane, kasolite, and an unidentified hydrated uranium niobate mineral are the most abundant secondary uranium minerals. Uranpyrochlore and the unidentified hydrated uranium niobate mineral are interpreted as alteration products of petscheckite. The chemical formula of the uranpyrochlore based upon the Electron Probe Micro Analyzer (EPMA) is $$ ^{A} {\left( {{\text{U}}_{{1.07}} {\text{Ca}}_{{0.28}} {\text{Pb}}_{{0.03}} {\text{Na}}_{{0.21}} {\text{Mg}}_{{0.02}} } \right)}_{{\Sigma 1.6}} \;^{B} {\left( {{\text{Nb}}_{{0.57}} {\text{Si}}_{{0.62}} {\text{Zr}}_{{0.35}} {\text{P}}_{{0.20}} {\text{Fe}}_{{0.17}} {\text{Al}}_{{0.06}} {\text{Ti}}_{{0.03}} } \right)}_{{\Sigma 2}} $$ . It is characterized by a relatively high Zr content (average ZrO2 = 6.6 wt%). The average composition of the unidentified hydrated uranium niobate mineral is $$ ^{{\text{U}}} {\left( {{\text{U}}_{{1.89}} {\text{Ca}}_{{0.49}} {\text{Pb}}_{{0.13}} {\text{Na}}_{{0.06}} {\text{Mg}}_{{0.02}} } \right)}_{{\Sigma 2.59}} \;^{{{\text{Nb}}}} {\left( {{\text{Nb}}_{{1.31}} {\text{Fe}}_{{0.34}} {\text{Si}}_{{0.14}} {\text{P}}_{{0.10}} {\text{Ti}}_{{0.05}} {\text{Zr}}_{{0.03}} {\text{Al}}_{{0.03}} } \right)}_{{\Sigma 2.0}} $$ , where U and Nb represent the dominant cations in the U and Nb site, respectively. Uranophane is the dominant U6+ silicate phase in oxidized zones of the jasperoid veins. Kasolite is less abundant than uranophane and contains major U, Pb, and Si but only minor Ca, Fe, P, and Zr. A two-stage metallogenetic model is proposed for the alteration processes and uranium mineralization at El Erediya. The primary uranium minerals were formed during the first stage of the hydrothermal activity that formed jasperoid veins in El Eradiya granite (130–160 Ma). This stage is related to the Late Jurassic–Early Cretaceous phase of the final Pan-African tectono-thermal event in Egypt. After initial formation of El Erediya jasperoid veins, a late stage of hydrothermal alteration includes argillization, dissolution of iron-bearing sulfide minerals, formation of iron-oxy hydroxides, and corrosion of primary uranium minerals, resulting in enrichment of U, Ca, Pb, Zr, and Si. During this stage, petscheckite was altered to uranpyrochlore and oxy-petscheckite. Uranium was likely transported as uranyl carbonate and uranyl fluoride complexes. With change of temperature and pH, these complexes became unstable and combined with silica, calcium, and lead to form uranophane and kasolite. Finally, at a later stage of low-temperature supergene alteration, oxy-petscheckite was altered to an unidentified hydrated uranium niobate mineral by removal of Fe.

Multi-stage emerald formation during Pan-African regional metamorphism: The Zabara, Sikait, Umm Kabo deposits, South Eastern desert of Egypt

The genesis of gem-quality deep green emeralds of Zabara, Sikait and Umm Kabo (South Eastern Desert, Egypt) is to date a controversial topic. The emerald-bearing biotite schists and quartz lenses are interpreted alternatively as a product of (i) thrust-fault-shear zone – controlled large scale alkali-metasomatism driven by post-magmatic fluid flow or of (ii) a large scale interaction between syntectonic pegmatitic magma or hydrothermal fluids with pre-existing basic to ultrabasic rocks, or of (iii) a syn- to post-tectonic regional metamorphism and small scale blackwall metasomatism. Detailed microstructural and chemical analyses of the Egyptian emeralds and their host rocks show that three generations of beryl can be distinguished: a colourless pegmatitic beryl; a pale green Cr-poor beryl crystallized from pegmatite-related hydrothermal fluids; and a deep green Cr- and Mg-rich emerald. The crystallization of the Cr- and Mg-rich emerald was controlled by the very local availability of Cr, Mg and Be-rich metamorphic fluids during the Pan-African tectono-thermal event. Emerald-rich quartz lenses demonstrate that those fluids locally did mobilize quartz, too. The pale green emeralds found within the pegmatites in association with colourless beryl are the product of a mobilization of colourless pegmatitic beryl and/or phenakite by late pegmatitic fluids slightly enriched in Cr by an interaction with the Cr-rich country rocks. The late pegmatitic fluids are typically Na-rich as is demonstrated by the pervasive albitization of the pegmatites. The complex interplay of magmatic and regional metamorphic events during the genesis of the Egyptian emeralds/beryls makes it impossible through stable oxygen isotope data to relate their genesis to the one or the other event.

Electron microprobe chemical ages of monazite from Qinling Group in the Qinling Orogen: Evidence for Late Pan-African metamorphism?

Electron microprobe chemical dating was carried out on monazites enclosed in two generations of mineral paragenesis of St + Ky + Grt and Sil + And + Grt + St, respectively, from the Qinling Group. Two different ages, 520±23 Ma and 435±9 Ma, were obtained from these monazites. This indicates that the Qinling Group experienced a metamorphism during the Early Cambrian, which is probably in response to the Late Pan-African subduction-accretion tectonothermal event.

Mineralogy, geochemistry and petrology of an amphibolite-facies aluminum-phosphate and borosilicate (APB)-bearing quartzite from the Mesoproterozoic Itremo Group (Central Madagascar)

The present paper reports the whole rock and mineral chemistry, textural relations and the mineral reactions under greenschist to amphibolite facies conditions of the Aluminum-Phosphate and -Borosilicate (APB)-bearing Mesoproterozoic quartzite of the Itremo Group (central Madagascar) and discusses the genesis of the protolith as well as the metamorphic P-T-conditions. The Itremo Group consists from bottom to top of a micaschist formation (metapelite and metasiltstone) (approximate to 500 m), a quartzite (approximate to 1000 m), and a stromatolitic dolomitic marble formation (> 1000 m). In the quartzite cross bedding and ripple marks document a deposition in a shallow continental shelf environment. Lazulite, augelite, trolleite, svanbergite, goyazite, crandallite, berlinite, tourmaline, apatite, celestine, anhydrite, muscovite and dumortierite with the minor constituents zircon, monazite and xenotime in addition to quartz are the rock-forming minerals. Boron and Sr have been supplied to the protolith of the quartzite by submarine hydrothermal fluids or by rivers fed by B and Sr-rich thermal springs. Using textures, stability data for augelite, trolleite, berlinite, lazulite, scorzalite, dumortierite, muscovite, kyanite and temperature data from the literature the P-T conditions of Panafrican metamorphism, which produced the prograde APB-parageneses can be approximated as 3.8 kbar and about 475 degrees C. Deposition and metamorphism of the protolith can be summarized as: i.) deposition of clay-bearing sand in a shallow continental shelf environment, ii.) chemical precipitation of phosphates and of phosphorus-rich iron hydroxides by oxidizing marine pore waters, iii.) reductive dissolution of the Fe-oxyhydroxides with crystallization of authigenic Al-phosphates in early diagenesis, iv) metamorphic overprint and crystallization during the Panafrican tectonothermal event, v) hydration reactions, element mobilisation and consequent retrograde resetting of prograde mineral equilibrium by postorogenic fluid circulation at the end of the Panafrican tectonothermal event.

Ultrahigh-temperature mafic granulites from Panrimalai, south India: Constraints from phase equilibria and thermobarometry

The Panrimalai area constitutes part of the granulite-facies rocks of the Madurai block in the Southern Granulite Terrain (SGT), India. Garnet-bearing mafic granulites in Panrimalai occur as small enclaves within charnockite. The common stable assemblage during peak metamorphism contains hornblende, garnet, orthopyroxene, clinopyroxene, quartz and plagioclase. The resorption of garnet in various reaction textures and the development of spectacular orthopyroxene–plagioclase and hornblende–plagioclase symplectites characterize the subsequent stages of metamorphism. Application of multi-equilibrium calculation procedures for mineral core compositions of the early assemblage yields near peak conditions at ≥ 900 °C at 9 kbar. These estimates are the highest yet reported in mafic granulites from the Madurai block. The post-peak P– T path is constructed for the mafic granulites based on observed microstructural relations and thermobarometric results is characterized by a steep clockwise decompressional P– T segment from ≥ 9 to < 4.5 kbar. Constraints from model Nd ages provide evidence for Paleoproterozoic magmatism restricted to the Madurai block in the Southern Granulite Terrain. The early part of the crustal evolution of the Panrimalai granulites could be coeval with the Paleoproterozoic event. Subsequent development of symplectitic assemblages via near-isothermal decompression can be ascribed to a distinctly later tectonic event. Available U–Pb and Sm–Nd mineral dates suggest a widespread Pan-African tectonothermal event in the SGT. Given the general recognition of ultrahigh-temperature (UHT) and isothermal decompression (ITD) in Pan-African age metamorphism in the East-African–Antarctic Orogen (EAAO) , the Panrimalai UHT history is considered to be part of this record.

Mesoproterozoic rifting and Pan-African continental collision in SE India: evidence from the Khariar alkaline complex

The suture zone between the Bhandara craton and the granulite-facies rocks of the Eastern Ghats Province in SE India contains a number of deformed alkaline and tholeiitic intrusives. The Khariar alkaline complex is one of the several occurrences which intruded in the Mesoproterozoic (1,480±17 Ma, 2σ) and was deformed during the Pan-African tectonothermal event. The geochemical signatures indicate a rift-related setting for the magmatic activity. The nepheline syenite parent magma may have been produced by in-mantle fractionation of clinopyroxene and Ti-rich amphibole from a basanitic primary magma derived from an enriched spinel lherzolite mantle source in the sub-continental lithosphere. Geochemical variations in the Khariar alkaline suite can be modeled by the fractionation of clinopyroxene, amphibole, titanite, zircon, apatite and allanite. The Mesoproterozoic alkaline magmatism at Khariar marks the initiation of a NE-SW rift which formed several craton margin basins and opened an ocean towards the south. The sediments of the cratogenic basins and the Eastern Ghats Province were deposited in these rift-related basins. A K-Ar age of 1,330±53 Ma from glauconites in sandstone suggests that the NW-SE trending Godavari–Pranhita graben formed at approximately the same time as the rift at the craton margin. If the two are related, the Godavari–Pranhita graben may represent the failed arm of a rift system in which the NE-SW arm was the active segment. The granulite-facies deformation and metamorphism of the Eastern Ghats Province sediments may be related to an episode of Grenvillian basin inversion. The Mesoproterozoic rifting and Grenvillian basin closure may thus represent two well-defined parts of a Wilson cycle i.e. the opening and closure of an ocean. The Khariar and other alkaline bodies were, however, deformed during a Pan-African collisional event associated with the westward thrusting of the Eastern Ghats Province granulites over the cratonic foreland.