Journal articles: 'Pan-African orogeny'

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Ephraim, Bassey E., Barth N. Ekwueme, Mohssen Moazzen, and Monir Modjarrad. "P-T conditions of Pan-African orogeny in southeastern Nigeria." Central European Geology 51, no. 4 (2008): 359–78. http://dx.doi.org/10.1556/ceugeol.51.2008.4.5.

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Takigami, Yutaka. "Consideration of the Pan-African Orogeny from 40Ar-39Ar Age Results." Gondwana Research 4, no. 4 (2001): 796. http://dx.doi.org/10.1016/s1342-937x(05)70580-3.

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Okpoli, C. C., and D. Oludeyi. "Aeromagnetic Mapping of Iwo Region of Southwestern Nigeria for Lithostructural Delineation." Pakistan Journal of Geology 3, no. 2 (2019): 20–30. http://dx.doi.org/10.2478/pjg-2019-0008.

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AbstractThe IGRF filtered Aeromagnetic data over Iwo, southwestern part of Nigeria within the basement complex was subjected to reduction to magnetic equator filtering, residual filtering, upward and downward continuation filtering, automatic gain control filtering, tilt angle derivative, second vertical derivative, analytical signal and Euler deconvolution. This reveals the geologic information such as structural trend. Based on the result of the total magnetic intensity map, reduction to equator map, analytical signal map and residual magnetic intensity map, it can be concluded that; The rocks in the study area have a trend of approximately northeast-southwest direction as seen on the upward continuation map. Most of the delineated lineaments found within the study area strike mostly in NNE-SSW, NE-SW and NW-SE with minor trend of E-W and ENE-WSW direction. Structural lineament orientation suggested that they were products of Pan-African orogeny (NE-SW, NW-SE and NNE-SSW trends) and pre-Pan-African orogeny (NNW-SSE and E-W trend). The interpretation of the aeromagnetic dataset gave an insight into the regional geology and structural trends of the area.

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Weerakoon, M. W. K., K. Shuto, and H. Kagami. "Pan–African Orogeny in Sri Lanka: The Eppawala Carbonatite and Surrounding Rocks." Gondwana Research 2, no. 2 (1999): 312. http://dx.doi.org/10.1016/s1342-937x(05)70162-3.

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Bartlett, J. M. "Tectonic and Thermal Evolution of South India During the Pan-African Orogeny." Mineralogical Magazine 58A, no. 1 (1994): 55–56. http://dx.doi.org/10.1180/minmag.1994.58a.1.32.

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Abdel-Rahman, A. M. "Petrogenesis of anorogenic peralkaline granitic complexes from eastern Egypt." Mineralogical Magazine 70, no. 1 (2006): 27–50. http://dx.doi.org/10.1180/0026461067010311.

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AbstractThe Pan-African orogenic shield rocks of eastern Egypt were intruded by several anorogenic within- plate granitic complexes, including Mounts Abu-Kharif and El-Dob. These two massifs were emplaced at the intersection of a fault system and a shear zone. The two massifs are made up of hypersolvus peralkaline granites, consisting essentially of perthitic alkali feldspar (55–65 vol.%), quartz (30–35%), and alkali amphibole (ferrorichterite to arfvedsonite; 5–12%), with accessory zircon, apatite and ilmenite. The rocks are evolved in composition, are relatively enriched in Nb (53–75 ppm), Y (34–72 ppm), Zr (421–693 ppm), Ga (26–29 ppm), and the REE (294–562 ppm), and depleted in Al, Mg, Ca, Sr, Ba and Eu. The REE patterns are sub-parallel, LREE-enriched over HREE, and show prominent negative Eu anomalies. The rocks exhibit mineralogical and chemical traits typical of within-plate A-type granites. Rb-Sr radiometric age dating produced a Cambrian age of 522±21 Ma, and an initial 87Sr/86Sr ratio of 0.7080±0.0042. Thus, the investigated peralkaline granitic rocks were emplaced following the termination of the Pan-African orogeny. The rocks are interpreted to have formed in an extensional tectonic environment during a phase of cooling, relaxation, crustal attenuation, and fracturing of the newly-formed shield.Results of geochemical modelling indicate that the magma may have formed by a large degree of batch partial melting (F = 0.57) of Pan-African calc-alkaline shield rocks, which had been metasomatized possibly by a Na-rich fluid. The volatile flux may have caused fenitization-type reactions along fissures and re-activated Pan-African fractures prior to anatexis, and is considered to have played a role as an important agent of heat transfer. Shear heating, caused possibly by a rapid change in the direction of plate motions beneath eastern Egypt during the Early Palaeozoic, is likely to have produced temperatures necessary for crustal anatexis. The confining pressure must have been released by fissuring of the crust. Magma ascent may have been facilitated by reactivation of pre-existing Pan-African fractures.

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Ntiharirizwa, Seconde, Philippe Boulvais, Marc Poujol, et al. "Geology and U-Th-Pb Dating of the Gakara REE Deposit, Burundi." Minerals 8, no. 9 (2018): 394. http://dx.doi.org/10.3390/min8090394.

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The Gakara Rare Earth Elements (REE) deposit is one of the world’s highest grade REE deposits, likely linked to a carbonatitic magmatic-hydrothermal activity. It is located near Lake Tanganyika in Burundi, along the western branch of the East African Rift. Field observations suggest that the mineralized veins formed in the upper crust. Previous structures inherited from the Kibaran orogeny may have been reused during the mineralizing event. The paragenetic sequence and the geochronological data show that the Gakara mineralization occurred in successive stages in a continuous hydrothermal history. The primary mineralization in bastnaesite was followed by an alteration stage into monazite. The U-Th-Pb ages obtained on bastnaesite (602 ± 7 Ma) and on monazite (589 ± 8 Ma) belong to the Pan-African cycle. The emplacement of the Gakara REE mineralization most likely took place during a pre-collisional event in the Pan-African belt, probably in an extensional context.

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Torremans, Koen, Philippe Muchez, and Manuel Sintubin. "Non-cylindrical parasitic folding and strain partitioning during the Pan-African Lufilian orogeny in the Chambishi–Nkana Basin, Central African Copperbelt." Solid Earth 9, no. 4 (2018): 1011–33. http://dx.doi.org/10.5194/se-9-1011-2018.

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Abstract. A structural analysis has been carried out along the south-east margin of the Chambishi–Nkana Basin in the Central African Copperbelt, hosting the world-class copper and cobalt (Cu–Co) Nkana orebody. The geometrically complex structural architecture is interpreted to have been generated during a single NE–SW-oriented compressional event, clearly linked to the Pan-African Lufilian orogeny. This progressive deformation resulted primarily in asymmetric multiscale parasitic fold assemblages, characterised by non-cylindrical NW–SE-oriented periclinal folds that strongly interfere laterally, leading to fold linkage and bifurcation. The vergence and amplitude of these folds consistently reflect their position along an inclined limb of a NW-plunging megascale first-order fold. A clear relation is observed between the intensity of parasitic folding and the degree of shale content in the Copperbelt Orebody Member (COM), which hosts most of the ore. Differences in fold amplitude, wavelength and shape are explained by changes in mechanical stratigraphy caused by lateral lithofacies variation in ore-bearing horizons. In addition, strong differences in strain partitioning occur within the deforming basin, which is interpreted to be in part controlled by changes in mechanical anisotropy in the layered rock package. This work provides an essential backdrop to understand the influence of the Lufilian orogeny on metal mineralisation and (re-)mobilisation in the Copperbelt.

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Perpétuo, Marcela Paschoal, Wagner da Silva Amaral, Felipe Grandjean da Costa, Evilarde Carvalho Uchôa Filho, and Daniel Francisco Martins de Sousa. "Geochemistry of the Serra das Melancias Pluton in the Serra da Aldeia Suite: a classic post-collisional high Ba-Sr granite in The Riacho do Pontal Fold Belt, NE Brazil." Brazilian Journal of Geology 46, no. 2 (2016): 221–37. http://dx.doi.org/10.1590/2317-4889201620160002.

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ABSTRACT: The Serra da Aldeia Suite is composed by circular or oval-shaped plutons, intrusive in meta-sedimentary and meta-volcanosedimentary rocks in the Riacho do Pontal Fold Belt, NE Brazil. The Serra das Melancias Pluton, belonging to Serra da Aldeia Suite, is located southeastern of Piaui state, near Paulistana city. These plutons represent a major magmatic expression in this area and contain important information about the late magmatic/collisional geologic evolution of the Brasiliano Orogeny. Based on petrographic and geochemical data, three facies were defined in the Serra das Melancias Pluton: granites, syenites and quartz monzonites. The rocks display high-K and alkaline to shoshonitic affinities, are metaluminous and show ferrous character. They are enriched in Light Rare Earth Elements and Large Ion Lithophile Elements, with negative anomalies in Nb, Ta and Ti. Their high Ba, Sr, K/Rb, low Rb, relatively low U, Th, Nb to very low Heavy Rare Earth Elements and Y resemble those of typical high Ba-Sr granitoids. The geochemical data suggest the emplacement of Serra das Melancias Pluton in a transitional, late to post-orogenic setting in the Riacho do Pontal Fold Belt during the late Brasiliano-Pan African Orogeny.

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Rai, Abhishek, V. K. Gaur, S. S. Rai, and K. Priestley. "Seismic signatures of the Pan-African orogeny: implications for southern Indian high-grade terranes." Geophysical Journal International 176, no. 2 (2009): 518–28. http://dx.doi.org/10.1111/j.1365-246x.2008.03965.x.

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Shellnutt, J. Gregory, Ngoc Ha T. Pham, Steven W. Denyszyn, Meng-Wan Yeh, and Tung-Yi Lee. "Timing of collisional and post-collisional Pan-African Orogeny silicic magmatism in south-central Chad." Precambrian Research 301 (October 2017): 113–23. http://dx.doi.org/10.1016/j.precamres.2017.08.021.

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Liu, W. C., Z. G. Zhou, X. X. Zhang, and X. G. Zhao. "SHRIMP zircon geochronological constraints on a Pan-African orogeny in the Yadong Area, Southern Tibet." Geochimica et Cosmochimica Acta 70, no. 18 (2006): A365. http://dx.doi.org/10.1016/j.gca.2006.06.738.

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13

Xue, Er-Kun, Wei Wang, Mei-Fu Zhou, Manoj K. Pandit, Si-Fang Huang, and Gui-Mei Lu. "Late Neoproterozoic–early Paleozoic basin evolution in the Cathaysia Block, South China: Implications of spatio-temporal provenance changes on the paleogeographic reconstructions in supercontinent cycles." GSA Bulletin 133, no. 3-4 (2020): 717–39. http://dx.doi.org/10.1130/b35588.1.

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Abstract The role of the Cathaysia Block, South China, and its linkage with orogenesis in the Rodinia and Gondwana supercontinents remain unresolved because of uncertainties in its paleoposition in supercontinental reconstructions. The lithostratigraphic, geochronologic, geochemical (including isotopic), and paleocurrent data on late Neoproterozoic to early Paleozoic sub-basins in the Cathaysia Block reveal spatio-temporal, tectono-sedimentary, and provenance diversity that show linkages with previously adjacent terranes and orogens in East Gondwana. An abundance of siliceous and conglomeratic rocks, local unconformities, and pinch-out in certain layers indicate a late Cryogenian proximal deposition, late Ediacaran transgression, and Middle Cambrian uplift. Cryogenian to early Ordovician strata contain predominantly 1000–900 Ma (late Grenvillian age) detrital zircon population, whereas 1300–1050 Ma (early Grenvillian age) zircons are only dominant in strata earlier than late Ediacaran. Besides, 850–700 Ma zircons are the most prominent group in the Middle Cambrian strata along with an occasional increase in the 650–500 Ma (Pan-African age) zircons. The Grenvillian age zircon groups exhibit significant sediment input from the eastern Indian terrane (990–950 Ma) and western Australia (1300–1050 Ma), underlining the fact that the Cathaysia Block was located between these two terranes in the northern part of East Gondwana. The diminishing contribution of early Grenvillian components in the late Ediacaran strata can be linked to the Pinjarra Orogeny (550–520 Ma), which led to uplift that blocked the transport of detritus from Australia. Middle Cambrian provenance variation with high abundance of 850–700 Ma components indicates the presence of intrinsic sediment from the Wuyishan terrane of South China. Given that the Cathaysia Block was a passive continental margin, this change was caused by the uplift of the southeastern Cathaysia Block, which was related to the far-field stress effects of the late phase of the Kuunga Orogeny (530–480 Ma). The decrease in abundance of early Grenvillian and Pan-African zircons in space implies that they were transported into the basins through independent drainage systems. This is consistent with the local and temporal variations in paleocurrent orientations during the Cambrian, further implying diverse and complex drainage systems in the southwestern Cathaysia Block during this period.

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Castaing, C., C. Triboulet, J. L. Feybesse, and P. Chèvremont. "Tectonometamorphic evolution of Ghana, Togo and Benin in the light of the Pan-African/Brasiliano orogeny." Tectonophysics 218, no. 4 (1993): 323–42. http://dx.doi.org/10.1016/0040-1951(93)90322-b.

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Ulrich Igor, Owono Amougou Olivier, Ndougsa Mbarga Theophile, Meying Arsène, et al. "Evidence of Major Structural Features over the Pan-African Domain in the Bertoua-Mbangue Area (East Cameroon) from a Multiscale Approach of Modeling and Interpretation of Aeromagnetic Data." International Journal of Geophysics 2019 (March 3, 2019): 1–12. http://dx.doi.org/10.1155/2019/9148678.

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The aim of this study is to investigate crustal structures from East Cameroon, using aeromagnetic data. The modeling of aeromagnetic data is conducted using the Oasis Montaj 8.0 software. The total magnetic intensity map reduced to the equator (RTE-TMI) shows important anomalies features, namely, the Northern East magnetic anomalies of high amplitude, the Southwest where very low values of the magnetic intensity were observed, and a corridor with negative values relatively high, separating the anomalies. The horizontal gradient map shows on the one hand brittle and folded structures carried out in the area of study and on the other hand various rectilinear, narrow, and short-wave anomalies that can be classified as a family of little faults. The maxima observed on the RTE-TMI maps are correlated to intrabasement contacts; and the map derived from Euler’s solutions permitted to evaluate the depth of the geological accidents observed from the other filters. This map also reveals new faults with a depth greater than 5000 m. The lineaments identified in the Southwestern part could be linked to the Pan-African orogeny and seem to correspond to deep-seated basement structures, which are referred to the tectonic boundary between Congo Craton and the Pan-African orogeny belt. A 23/4-D modeling confirmed the observations derived from the RTE-TMI and HGM maps analyses. It shows intrusive bodies composed of gneiss and porphyroid granite and some domes with their roof situated at various depths not exceeding 1800 m from the surface. The structural map of the study area shows the trending of the structural features observed, namely, NE-SW, NW-SE, ENE-WSW, and WNW-ESE, respectively, while the E-W and N-S are secondary orientation of the observed tectonic evidence. Moreover, circular anomalies observed over the area are assimilated to intrusions of high magnetic materials or to granitic domes.

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Domingos, Nitzschia R. R., Walter E. Medeiros, and Roberto G. Oliveira. "Geophysical evidence for doming during the Pan-African/Brasiliano orogeny in the Seridó belt, Borborema Province, Brazil." Precambrian Research 350 (November 2020): 105870. http://dx.doi.org/10.1016/j.precamres.2020.105870.

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Bousquet, Romain, Rachid El Mamoun, Omar Saddiqi, Bruno Goffé, Andreas Möller, and Atman Madi. "Mélanges and ophiolites during the Pan-African orogeny: the case of the Bou-Azzer ophiolite suite (Morocco)." Geological Society, London, Special Publications 297, no. 1 (2008): 233–47. http://dx.doi.org/10.1144/sp297.11.

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Rainaud, C., S. Master, R. A. Armstrong, D. Phillips, and L. J. Robb. "Monazite U–Pb dating and 40Ar–39Ar thermochronology of metamorphic events in the Central African Copperbelt during the Pan-African Lufilian Orogeny." Journal of African Earth Sciences 42, no. 1-5 (2005): 183–99. http://dx.doi.org/10.1016/j.jafrearsci.2005.08.007.

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Rocha, Marcelo Peres, Paulo Araújo de Azevedo, Marcelo Assumpção, Antônio Carlos Pedrosa-Soares, Reinhardt Fuck, and Monica Giannoccaro Von Huelsen. "Delimiting the Neoproterozoic São Francisco Paleocontinental Block with P-wave traveltime tomography." Geophysical Journal International 219, no. 1 (2019): 633–44. http://dx.doi.org/10.1093/gji/ggz323.

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SummaryThe São Francisco Paleocontinental Block (SFPB) represents part of the Congo-São Francisco Paleocontinent (CSFP), amalgamated around 2 Ga. In the Neoproterozoic, a branched continental rift system evolved to ocean basins around most edges of the SFPB that remained only partially linked to the Congo Paleocontinent by means of the Bahia-Gabon Continental Bridge. After the Brasiliano—Pan-African orogeny, two relatively preserved CSFP sectors formed the São Francisco and Congo cratons, surrounded by Neoproterozoic orogenic belts. Recent results of upper mantle P-wave seismic tomography allowed us to suggest a delimitation in lithospheric depths of the Neoproterozoic SFPB, which comprise the São Francisco Craton, and that this would have been connected with the Congo Paleocontinent along the Araçuaí Belt. It is characterized by high-velocity anomalies and its boundaries with other blocks are marked by low-velocity anomalies at lithospheric depths. We tested the resolution of the tomographic results through synthetic models obtained by a ray tracing scheme using the observed ray configuration. We observe that the lateral resolution is adequate, but the method used was not able to set the depth reached by the SFPB. Our results indicate that the SFPB area in lithospheric depths is larger than the surface area ascribed to the São Francisco craton, and thus, the SFPB basement deeply extends beneath neighboring orogenic regions, suggesting that these Neoproterozoic mobile belts, such as Araçuaí Orogen and the Brasilia Fold Belt, reworked the continental crust. We observe a low-velocity anomaly in the SFPB central region, corresponding to the Pirapora aulacogen. Our results have a good spatial correspondence with the low Bouguer anomalies used to define the SFPB in previous studies. The limits of the SFPB are consistent with deviation of the mantle flow, as suggested by SKS fast polarization.

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Goscombe, B., R. Armstrong, and J. M. Barton. "Tectonometamorphic Evolution of the Chewore Inliers: Partial Re-equilibration of High-grade Basement during the Pan-African Orogeny." Journal of Petrology 39, no. 7 (1998): 1347–84. http://dx.doi.org/10.1093/petroj/39.7.1347.

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Grantham, G. H., A. B. Moyes, and D. R. Hunter. "The age, petrogenesis and emplacement of the Dalmatian Granite, H.U. Sverdrupfjella, Dronning Maud Land, Antarctica." Antarctic Science 3, no. 2 (1991): 197–204. http://dx.doi.org/10.1017/s0954102091000238.

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The ∼470 Ma Dalmatian Granite forms sheet-like bodies intruded discordantly into orthogneisses, paragneisses and calcareous rocks belonging to the ∼1000 Ma Jutulrora, Sveabreen and Fuglefjellet formations respectively. The Dalmatian Granite is muscovite + biotite bearing. Two varieties are recognized, one that is magnetite-bearing and another that is characterized by tourmaline nodules. At some localities, development of the tourmaline-bearing variety is spatially associated with the presence of carbonates. Physical conditions of emplacement for the Dalmatian Granite are estimated to be approximately 700°C and 6kbar with pH2O = Pload. The emplacement of the granite is considered to have occurred syntectonically during D3 approximately 470 Ma ago. The granites are therefore similar in age to Pan African age granites in Mozambique as well as Ross Orogeny age granites in the Transantarctic Mountains.

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Itano, Keita, Tsuyoshi Iizuka, Qing Chang, Jun-Ichi Kimura, and Shigenori Maruyama. "U–Pb chronology and geochemistry of detrital monazites from major African rivers: Constraints on the timing and nature of the Pan-African Orogeny." Precambrian Research 282 (September 2016): 139–56. http://dx.doi.org/10.1016/j.precamres.2016.07.008.

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Motta, João Gabriel, Norberto Morales, and Walter Malagutti Filho. "Geophysical perspective on the structural interference zone along the Neoproterozoic Brasília and Ribeira fold belts in West Gondwana." Brazilian Journal of Geology 47, no. 1 (2017): 3–19. http://dx.doi.org/10.1590/2317-4889201720160144.

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ABSTRACT: The Brasília and Ribeira fold belts have been established in south-southwestern São Francisco Craton during the Brasiliano-Pan African orogeny (0.9-0.5 Ga - Tonian to Cambrian), and played an important role in West Gondwana continent assembly. The region is given by a complex regional fold and thrust belt superposed by shearing during the orogeny late times, with superposing stress fields forming a structural interference zone. These thrust sheets encompasses assemblies from lower- to upper-crust from different major tectonic blocks (Paranapanema, São Francisco), and newly created metamorphic rocks. Re-evaluation of ground gravity datasets in a geologically constrained approach including seismology (CRUST1 model) and magnetic data (EMAG2 model) unveiled details on the deep- crust settings, and the overall geometry of the structural interference zone. The Simple Bouguer Anomaly map shows heterogeneous density distribution in the area, highlighting the presence of high-density, high metamorphic grade rocks along the Alterosa suture zone in the Socorro-Guaxupé Nappe, lying amid a series of metasedimentary thrust scales in a regional nappe system with important verticalization along regional shear zones. Forward gravity modeling favors interpretations of structural interference up North into Guaxupé Nappe. Comparison to geotectonic models shows similarities with modern accretionary belts, renewing the discussion.

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Fotze, Quentin Marc Anaba, Charles Antoine Basseka, Anatole Eugene Djieto Lordon, Albert Eyike Yomba, Yves Shandini, and Jean Marie Tadjou. "Geophysical Data Processing for the Delineation of Tectonic Lineaments in South Cameroon." Earth Science Research 8, no. 2 (2019): 1. http://dx.doi.org/10.5539/esr.v8n2p1.

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The processing of aeromagnetic and gravity data of the Northern part of Congo Craton (South Cameroon region), between latitudes 2&deg;30&rsquo;-3&deg;30&rsquo; N and longitudes 12&deg;-13&deg; E, permitted the determination of the structural features ccurring within the Precambrian basement (Ntem Complex) southwards and the Pan-African belt (Yaounde Group) northwards. The maxima of the Horizontal Gradient within the study area, were obtained using the Blakely and Simpson method (1986). Those maxima were used to trace the magnetic lineaments of the study area. Furthermore, the Total Horizontal derivative of the Tilt derivative applied on the residual grid of Bouguer anomaly guaranteed the enhancement of linear structures which were automatically extracted using the CET Grid Analysis algorithm. The superimposition of both magnetic and gravity lineaments allowed us to display the structural framework of the area, whose major trending directions are E-W, ENE-WSW, and NE-SW. These major lineament directions are likely to be linked to one or more than a single tectonic event such as the ENE-WSW/NE-SW trends, considered as the subduction direction of the Congo craton beneath the Pan-African belt. These trends may be linked to the Eburnean orogeny and are also said to be connected to the Central African Shear Zone (CASZ). The geophysical lineaments identified in the study are defined as potential targets along which mineralization may have been formed, considering the economic potential of the area.

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GUIMARÃES, IGNEZ DE PINHO, CÍCERA NEYSI DE ALMEIDA, ADEJARDO FRANCISCO DA SILVA FILHO, and JOÃO MARIA MARTINS DE ARAÚJO. "GRANITOIDS MARKING THE END OF THE BRASILIANO (PAN - AFRICAN) OROGENY WITHIN THE CENTRAL TECTONIC DOMAIN OF THE BORBOREMA PROVINCE." Revista Brasileira de Geociências 30, no. 1 (2000): 177–81. http://dx.doi.org/10.25249/0375-7536.2000301177181.

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Miyazaki, T., H. Kagami, K. Shuto, and T. Morikiyo. "Geochronological and Geochemical Characterization of Some Alkaline Plutons from Tamil Nadu, South India: Implications for the Pan-African Orogeny." Gondwana Research 1, no. 1 (1997): 154. http://dx.doi.org/10.1016/s1342-937x(05)70019-8.

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Li, Xian-Hua, Yi Chen, Jean Pierre Tchouankoue, et al. "Improving geochronological framework of the Pan-African orogeny in Cameroon: New SIMS zircon and monazite U-Pb age constraints." Precambrian Research 294 (June 2017): 307–21. http://dx.doi.org/10.1016/j.precamres.2017.04.006.

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Liégeois, Jean Paul, Louis Latouche, Mustapha Boughrara, Jacques Navez, and Michel Guiraud. "The LATEA metacraton (Central Hoggar, Tuareg shield, Algeria): behaviour of an old passive margin during the Pan-African orogeny." Journal of African Earth Sciences 37, no. 3-4 (2003): 161–90. http://dx.doi.org/10.1016/j.jafrearsci.2003.05.004.

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Dwivedi, Shyam Bihari, Kevilhoutuo Theunuo, and Ravi Ranjan Kumar. "Characterization and metamorphic evolution of Mesoproterozoic granulites from Sonapahar (Meghalaya), NE India, using EPMA monazite dating." Geological Magazine 157, no. 9 (2020): 1409–27. http://dx.doi.org/10.1017/s0016756819001389.

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AbstractThis paper presents three different age domains, obtained by electron microprobe monazite dating, for granulitic gneisses collected from the Shillong-Meghalaya Gneissic Complex in Sonapahar, NE India, which contain radioactive materials, e.g. thorium (3.32–7.20 wt %), uranium (0.133–1.172 wt %) and lead (0.101–0.513 wt %). The microprobe analyses of monazite grains in the rock samples show that the monazites have three different ages ranging from Mesoproterozoic to Neoproterozoic. The oldest age (1571 ± 22 Ma) represents a peak metamorphic event, the youngest dominant age indicates the Pan-African tectonic event (478 ± 7 Ma) and the intermediate age marks the Grenvillian orogeny (1034 ± 91 Ma) or may be a mixing artefact; these ages are located at the cores, rims and intermediate parts of the monazite grains, respectively. The equilibrium mineral phases calculated for the granulitic gneisses from Sonapahar lie in a P–T range from 5.9 kbar/754 °C to 8.3 kbar/829 °C in the NCKFMASH system. Plotting the P–T conditions of the granulitic gneisses reveals a clockwise P–T path. Two major metamorphic events are observed in Sonapahar. The M1 metamorphic stage is represented by peak mineral assemblages of prograde garnet-forming reactions (8.2 kbar/∼713 °C) during Mesoproterozoic time (1571 ± 22 Ma). The M2 metamorphic stage featured decompression (3.9 kbar/∼701 °C) in which garnet–sillimanite broke down to form cordierite along an isothermal decompression path during the Pan-African tectonic event (478 ± 7 Ma).

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Perron, Paul, Michel Guiraud, Emmanuelle Vennin, et al. "Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins (Reggane, Ahnet, Mouydir and Illizi basins, Hoggar Massif)." Solid Earth 9, no. 6 (2018): 1239–75. http://dx.doi.org/10.5194/se-9-1239-2018.

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Abstract. The Paleozoic intracratonic North African Platform is characterized by an association of arches (ridges, domes, swells, or paleo-highs) and low subsidence rate syncline basins of different wavelengths (75–620 km). The Reggane, Ahnet, Mouydir and Illizi basins are successively delimited from east to west by the Amguid El Biod, Arak-Foum Belrem, and Azzel Matti arches. Through the analysis of new unpublished geological data (i.e., satellite images, well logs, seismic lines), the deposits associated with these arches and syncline basins exhibit thickness variations and facies changes ranging from continental to marine environments. The arches are characterized by thin amalgamated deposits with condensed and erosional surfaces, whereas the syncline basins exhibit thicker and well-preserved successions. In addition, the vertical facies succession evolves from thin Silurian to Givetian deposits into thick Upper Devonian sediments. Synsedimentary structures and major unconformities are related to several tectonic events such as the Cambrian–Ordovician extension, the Ordovician–Silurian glacial rebound, the Silurian–Devonian Caledonian extension/compression, the late Devonian extension/compression, and the Hercynian compression. Locally, deformation is characterized by near-vertical planar normal faults responsible for horst and graben structuring associated with folding during the Cambrian–Ordovician–Silurian period. These structures may have been inverted or reactivated during the Devonian (i.e., Caledonian, Mid–Late Devonian) compression and the Carboniferous (i.e., pre-Hercynian to Hercynian). Additionally, basement characterization from geological and geophysics data (aeromagnetic and gravity maps), shows an interesting age-dependent zonation of the terranes which are bounded by mega-shear zones within the arches–basins framework. The old terranes are situated under arches while the young terranes are located under the basins depocenter. This structural framework results from the accretion of Archean and Proterozoic terranes inherited from former orogeny (e.g., Pan-African orogeny 900–520 Ma). Therefore, the sedimentary infilling pattern and the nature of deformation result from the repeated slow Paleozoic reactivation of Precambrian terranes bounded by subvertical lithospheric fault systems. Alternating periods of tectonic quiescence and low-rate subsidence acceleration associated with extension and local inversion tectonics correspond to a succession of Paleozoic geodynamic events (i.e., far-field orogenic belt, glaciation).

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Aminatou, Fagny Mefire, Nkouandou Oumarou Faarouk, Temdjim Robert, et al. "New K–AR ages of tchabal mbabo alkaline volcano massif, Cameroon volcanic line and adamawa plateau (central Africa)." International Journal of Advanced Geosciences 4, no. 2 (2016): 62. http://dx.doi.org/10.14419/ijag.v4i2.6516.

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Tchabal Mbabo in Central Africa is a voluminous volcano massif composed of alkali lava series. K-Ar geochronology data obtained from three samples of basanite - trachyandesite composition defined at least two volcanic activities. The first at end Eocene (38.22 ± 0.80 Ma) and the second during Oligocene (28.88 ± 0.61 and 28.60 ± 0.60Ma). The distribution of different ages along the Cameroon Volcanic Line is difficult to council with any migration of magmatic activity, as previously suggested. The most realistic scenario for the formation of Cameroon Line is that the ascent of lavas has been favored by the crustal discontinuities inherited from the Pan-African orogeny and reactivated during Mesozoic and Cenozoic. ICP MS and ICP AES analyses show that basanite lavas are the result of 2 % melting of sub-lithospheric mantle source containing garnet and phlogopite phases; the trachyandesites are formed by fractional crystallization of K-feldspar, amphibole, clinopyroxene and Fe-Ti oxides.

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Rahaman, M. A., I. A. Tubosun, and J. R. Lancelot. "U-Pb geochronology of potassic syenites from Southwestern Nigeria and the timing of deformational events during the Pan-African Orogeny." Journal of African Earth Sciences (and the Middle East) 13, no. 3-4 (1991): 387–95. http://dx.doi.org/10.1016/0899-5362(91)90102-5.

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33

Montero, P., F. Bea, F. González-Lodeiro, C. Talavera, and M. J. Whitehouse. "Zircon ages of the metavolcanic rocks and metagranites of the Ollo de Sapo Domain in central Spain: implications for the Neoproterozoic to Early Palaeozoic evolution of Iberia." Geological Magazine 144, no. 6 (2007): 963–76. http://dx.doi.org/10.1017/s0016756807003858.

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AbstractDating the pre-Middle Ordovician metavolcanic rocks and metagranites of the Ollo de Sapo Domain has, historically, been difficult because of the small compositional variation, the effects of the Variscan orogeny and, as revealed in this paper, the unusually high fraction of inherited zircon components. The first reliable zircon data (U–Pb ion microprobe and Pb–Pb stepwise evaporation) indicate that the Ollo de Sapo volcanism spanned 495±5 Ma to 483±3 Ma, and was followed by the intrusion of high-level granites from 483±3 Ma to 474±4 Ma. In both metavolcanic rocks and metagranites, no less than 70–80% of zircon grains are either totally Precambrian or contain a Precambrian core overgrown by a Cambro-Ordovician rim. About 80–90% of inherited zircons are Early Ediacaran (602–614 Ma) and derived from calc-alkaline intermediate to felsic igneous rocks generated at the end of the Pan-African arc–continent collision. In the Villadepera region, located to the west, both the metagranites and metavolcanic rocks also contain Meso-Archaean zircons (3.0–3.2 Ga) which ultimately originated from the West African Craton. In the Hiendelaencina region, located to the east, both the metagranites and metavolcanic rocks lack Meso-Archaean zircons, but they have two different inherited zircon populations, one Cryogenian (650–700 Ma) and the other Tonian (850–900 Ma), which suggest older-than-Ediacaran additional island-arc components. The different proportion of source components and the marked variation of the 87Sr/86Srinit. suggest, at least tentatively, that the across-arc polarity of the remnants of the Pan-African arc of Iberia trended east–west (with respect to the current coordinates) during Cambro-Ordovician times, and that the passive margin was situated to the west.

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Qaoud, Nedal. "Geochemistry of the Um Had Plutonites, Central Eastern Desert, Egypt: Implications for Magma Evolution, and Tectonic Setting." Journal of Geography and Geology 6, no. 2 (2014): 36. http://dx.doi.org/10.5539/jgg.v6n2p36.

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Geochemistry of gabbroid and granitoid plutonites from the Um Had area indicates island arc subalkaline basic magma with tholeiitic affinity and calc-alkaline, metaluminous and slightly peraluminous magma, respectively. Although different in age both plutonite types were emplaced under compressional regime, where subduction-related environment was dominant. They were formed under relatively low to moderate water-vapour pressure (1–5 k-bars) at moderate depths (20–30 km). Biotite granites were formed at a relatively high temperature range (800–840 °C), while biotite-muscovite granites were formed under relatively moderate temperature conditions (760–800 °C). These two units may represent evolution from island arc to active continental margin. It is suggested that island arc gabbros might have sourced the late subduction-related calc-alkaline granitoids during the waning stages of the pan-African orogeny. The I-type nature of the investigated plutonites in the study area and elsewhere suggests the juvenile character of the basement complex of the Eastern Desert of Egypt.

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Gomes, Cristiane H., and Delia Almeida. "New insights into the Gondwana breakup at the Southern South America by apatite fission-track analyses." Advances in Geosciences 47 (January 21, 2019): 1–15. http://dx.doi.org/10.5194/adgeo-47-1-2019.

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Abstract. Apatite fission-track (AFT) analyses, applied to Southern Brazil and Uruguay samples, was employed aiming to understand the low temperature history of the Dom Feliciano Belt Segment. The Dom Feliciano Belt formed during the Neoproterozoic to Early Paleozoic, linked to the Brasiliano/Pan-African Orogeny. Twenty-four samples were dated, and confined track lengths of twenty samples were measured. The spatial distribution of ages shows three domains with different evolution cut by shear zones and, or suture zones in the Dom Feliciano Belt. The Western Domain exhibits AFT ages > 250 Ma (Permian to Devonian) while the Eastern Domain shows AFT ages < 230 Ma (Paleogene to Triassic). In the Central Domain, the AFT ages range from ∼196 to 130 Ma (Jurassic to Early Cretaceous). The thermal modeling in the domains revealed a complex evolution, with cooling and reheating phases, and a denudation of ∼2600 m. The AFT ages clearly postdate the Gondwanide, Paraná-Etendeka and Rio Grande Cone exhumation history of the Dom Feliciano Belt.

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36

Oyebamiji, Abiola, Adeniyi JohnPaul Adewumi, Tehseen Zafar, Adegbola Odebunmi, Philips Falae, and Oluwafemi Fadamoro. "Petrogenetic and Compositional Features of Rare Metal Pan-African Post-Collisional Pegmatites of Southwestern Nigeria; A Status Review." Contemporary Trends in Geoscience 7, no. 2 (2018): 166–87. http://dx.doi.org/10.2478/ctg-2018-0012.

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Abstract This research reviews the geology, petrogenesis, compositional trends and geochronology of the rare-metal pegmatite of southwestern Nigeria. The source of these pegmatites is still presently debated which have been explained as either product of highly fractionated molten material or anatexis of the local crust. However, published works of past authors have been compiled to give a detailed understanding of the formation of the mineral deposits. The basement complex of southwestern Nigeria comprises of Precambrian rocks of amphibolite, the hornblende gneiss and the granite gneisses which were formed as a result of the opening and closing of the ensialic basin with significant, extensive subduction during the Pan-African orogeny. The pegmatites in this region have shown internal zoning and a high degree of evolution from the border zone to the core zone during the crystallization and solidification of the felsic granite to pegmatite melt. The rare-metal pegmatites have distinct chemical compositions and mineralogy, containing quartz, biotite, muscovite, microcline, garnet with localized tourmaline, tantalite and columbite. These pegmatites vary significantly by their bulk-rock and mineral chemistry which indicates a more peraluminous attribute and enrichments of lithophile elements of Rb, Cs, Ta and Ba. Previous K/Ar isotopic ages (502.8±13.0 Ma and 514.5±13.2 Ma) suggest that the pegmatites are related to the post-collisional phase of intensive metasomatism. Adopted from previous studies, a five-stage conceptual model of evolution which is widely accepted have been proposed for the origin of the pegmatites.

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Wang, Yong, Yong-hong Shi, Bai-lin Chen, Ren-wen Tan, Yun Gao, and Jing-hui Shen. "Zircon U-Pb age of Fengxian acid pyroclastic rocks and its enlightenment to the existence of Pan-African orogeny in the West Qinling Orogenic Belt, China." China Geology 3, no. 4 (2019): 1–3. http://dx.doi.org/10.31035/cg2018130.

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BAUER, W., W. FIELITZ, J. JACOBS, C. M. FANNING, and G. SPAETH. "Mafic Dykes from Heimefrontfjella and implications for the post-Grenvillian to pre-Pan-African geological evolution of western Dronning Maud Land, Antarctica." Antarctic Science 15, no. 3 (2003): 379–91. http://dx.doi.org/10.1017/s0954102003001391.

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Two groups of geochemical different dykes have been identified in the Grenville-aged basement of Heimefrontfjella. The first group comprises dykes of continental tholeiite composition which probably intruded during the final stage of indentation of the Kaapvaal—Grunehogna Craton into Laurentia. One dyke of this group yielded an U—Pb zircon SHRIMP age of 1033 ± 7 Ma. The second group has an E-type MORB composition and may be related to ocean floor basalts of the Mozambique Ocean between East and West Gondwana. A preliminary U—Pb SHRIMP age of 586 ± 7 Ma for a single zircon crystal was obtained from a dyke of the second group. During the Pan-African orogeny both dyke groups underwent metamorphism and tectonism at different grades: up to amphibolite-facies in the eastern and southern Heimefrontfjella, and at greenschist-facies in the western and northern Heimefrontfjella. The older dykes may be correlated with the Equeefa suite of southern Natal whereas the younger dyke group is not correlatable with any known mafic intrusions or lava flows in adjacent regions.

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39

Triantafyllou, Antoine, Julien Berger, Jean-Marc Baele, et al. "The Tachakoucht–Iriri–Tourtit arc complex (Moroccan Anti-Atlas): Neoproterozoic records of polyphased subduction-accretion dynamics during the Pan-African orogeny." Journal of Geodynamics 96 (May 2016): 81–103. http://dx.doi.org/10.1016/j.jog.2015.07.004.

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40

Ménot, R. P., and K. F. Seddoh. "The eclogites of the Lato hills, south Togo, West Africa: Relics from the early tectonometamorphic evolution of the Pan-African orogeny." Chemical Geology 50, no. 1-3 (1985): 313–30. http://dx.doi.org/10.1016/0009-2541(85)90126-3.

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41

Greenough, John D., Sandra L. Kamo, Lucia Theny, Sean A. Crowe, and Charles Fipke. "High-precision U–Pb age and geochemistry of the mineralized (Ni–Cu–Co) Suwar intrusion, YemenThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh." Canadian Journal of Earth Sciences 48, no. 2 (2011): 495–514. http://dx.doi.org/10.1139/e10-067.

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High-precision U–Pb isotope dilution – thermal ionization mass spectrometry (ID–TIMS) geochronology on chemically abraded zircon grains from a noritic gabbro of the Ni-bearing Suwar mafic–ultramafic layered complex, northwestern Yemen, gives a mean 206Pb/238U age of 638.46 ± 0.73 Ma (2σ; MSWD = 1.4). At Wadi Qutabah, ∼30 km to the north, a similar mafic sample has an identical age of 638.58 ± 0.51 Ma (2σ; MSWD = 0.32), which supports the possibility of there being a single, large intrusive complex with an estimated areal extent of ∼250 km2. This is supported by geochemical data of samples from each locality, which are postkinematic, gabbroic rocks that contain variable amounts of cumulus olivine, plagioclase, orthopyroxene, and ilmenite with intercumulus augite, hornblende, and Ni-sulphides. Straight rare Earth element (REE) patterns, Ba/La ∼30, Rb/Ba ∼0.04, and negative primitive-mantle-normalized P anomalies resemble EM1 (Enriched Mantle 1) of oceanic island basalts and Archean subcontinental mantle lithosphere. The mineralogy and magmatic/tectonic discrimination diagrams suggest within-plate continental tholeiitic and noritic cumulates typical of a rift setting for both intrusions. The complex intrudes retrograded, amphibolite-facies paragneiss of the Pan-African Afif lithotectonic terrane, and is generally undeformed and unaltered, and, therefore, unaffected by the Pan-African orogeny. Emplacement of the 639 Ma complex occurred during a tensional tectonic regime on the Arabian Peninsula and marks the time of proto-Iapetan rifting. The estimated size of the intrusion, its noritic composition, and Archean subcontinental lithospheric mantle signature and its position in thin Proterozoic lithosphere abutting Archean cratonic rocks, give it the key characteristics of known, mostly Proterozoic, intrusions that host world-class Ni–Cu–Co ore deposits.

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42

Boukhalfa, Zakaria, Abderrezak Bouzid, Yixian Xu, et al. "Magnetotelluric investigation of the Precambrian crust and intraplate Cenozoic volcanism in the Gour Oumelalen area, Central Hoggar, South Algeria." Geophysical Journal International 223, no. 3 (2020): 1973–86. http://dx.doi.org/10.1093/gji/ggaa432.

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SUMMARY The Tuareg Shield was assembled by oceanic closures and horizontal movements along mega-shear zones between approximately 20 terranes during the Pan-African Orogeny (750–550 Ma). Although there is an ongoing debate about its origin, the exhumation of the Tuareg Shield is assumed to be related to Cenozoic intraplate volcanism. The Gour Oumelalen is a key region of the Tuareg Shield and is located in the northeastern part of the Egéré-Aleksod terrane, corresponding to the eastern boundary of the Archean–Palaeoproterozoic microcontinent LATEA (Central Hoggar). The eastern boundary of the study area corresponds to a Neoproterozoic suture zone separating two old microcontinents, LATEA and the Orosirian Stripe. We deployed two magnetotelluric (MT) profiles consisting of 33 broad-band MT stations and combined these with aeromagnetic data, aiming to define the crustal structure in detail. The resistivity cross-sections obtained from the 3-D inversion of full impedance tensor and tipper data from stations along the profiles, confirm the main Precambrian faults, some of which are covered by Quaternary sediments and hence, have not yet been deciphered. The cross-sections also highlight the Cretaceous–Quaternary sedimentary basins represented by low resistivities. The upper crust is typically cratonic with a high electrical resistivity. On the contrary, the lower crust shows a drastic drop in resistivity (&lt;10 Ωm). The most plausible hypothesis is that the study area corresponds to a Cretaceous rifting zone. The Cretaceous magmatic event and its related fluids and mineralization as well as the recent fluids associated with Cenozoic volcanism, are plausible causes of a very conductive lower crust. However, we cannot exclude other reasons such as: (i) a high-temperature and strongly sheared mobile belt or (ii) a contribution of inheritance involving Pan-African events that affected this former suture area.

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Thomas, William A., George E. Gehrels, Kurt E. Sundell, et al. "Detrital zircons and sediment dispersal in the eastern Midcontinent of North America." Geosphere 16, no. 3 (2020): 817–43. http://dx.doi.org/10.1130/ges02152.1.

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Abstract Results of detrital-zircon analyses (U-Pb ages and initial Hf values, εHft) of Mississippian–Pennsylvanian sandstones in the Michigan, Illinois, and Forest City basins are remarkably similar to data for coeval sandstones in the Appalachian basin, indicating dispersal of sediment from the Appalachian orogen through the Appalachian basin to the eastern Midcontinent during the late Paleozoic. The similarities of results include matches of the two most prominent age groups (1300–950 Ma and 490–350 Ma), as well as matches of the less abundant age groups. Comparisons of the data are from observations of probability density plots and multidimensional scaling of U-Pb age data and of εHft values. Despite the dominance of an Appalachian signature in all samples, some samples contain grains with ages that suggest intermittent additional sources. Four samples (three ranging in depositional age from Morrowan to Atokan–Desmoinesian in the Illinois basin, and one of Desmoinesian age in the Forest City basin), in addition to typical Appalachian age distributions, have prominent age modes between 768 and 525 Ma, corresponding in age to Pan-African/Brasiliano rocks in Gondwanan accreted terranes in the Appalachian orogen, suggesting intermittent dispersal from the Moretown terrane of the northern Appalachians. Sandstones in the Appalachian basin and those in the Midcontinent basins have very few grains with ages that correspond to the Alleghanian orogeny in the Appalachian orogen. Nevertheless, three sandstones each in the Illinois basin and Forest City basin with depositional ages of 312–308 Ma have a few zircon grains in the age range of 321 ± 5 to 307 ± 4 Ma. The nearly identical crystallization and depositional ages suggest reworking at the depositional sites of air-fall volcanic ash from the Alleghanian orogen, rather than fluvial transport from the orogen. The basal Pennsylvanian sandstones lap onto a regional unconformity around the northern rims of the Illinois and Forest City basins, suggesting sources for recycled grains. Along the northern edge of the Illinois basin, Ordovician sandstones beneath the unconformity may have contributed minor concentrations of Superior-age zircons in the basal Pennsylvanian sandstones. Basal Pennsylvanian sandstones in the Forest City basin lap onto Mississippian strata, suggesting possible recycling of zircons from eroded Mississippian sandstones.

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44

Suchý, V., I. Sýkorová, K. Melka, J. Filip, and V. Machovič. "Illite ‘crystallinity’, maturation of organic matter and microstructural development associated with lowest-grade metamorphism of Neoproterozoic sediments in the Teplá-Barrandian unit, Czech Republic." Clay Minerals 42, no. 4 (2007): 503–26. http://dx.doi.org/10.1180/claymin.2007.042.4.08.

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AbstractMetamorphic grade, palaeothermal history and the influence of tectonic strain on clay minerals and organic matter transformation were studied in the eastern part of the Teplá-Barrandian unit in the Czech Republic. The metamorphic grade of pelitic sediments ranges from the lower anchizone (IC ~0.30–0.36Δº2θ) to the lowermost epizone (IC ~0.24–0.26Δº2θ). Increase in metamorphic grade is paralleled by the development of anastomosing cleavage and lenticular quartz grains in the anchizone which give way to slaty cleavage and dynamically recrystallized ribbon quartz grains in the lower epizone. White mica in highly strained rocks generally has greater IC values whereas chlorite displays reduced values in deformed and cleaved samples. The organic matter dispersed in the sediments represents a complex assemblage of highly matured particles of uncertain origin, pyrobitumen and ‘transitional matter’. The reflectance of organic fragments generally varies from 3.1% to 7.7% of Rmax which suggests anthracite to meta-anthracite rank progrades to semigraphite in higher-grade samples, although the overall link between Rmax and IC values is weak, if present at all. Newly formed shear-induced graphite appears abruptly near the anchizone-epizone boundary and correlates with the onset of plastic deformation and dynamic recrystallization of quartz grains in the host sediments.Maximum metamorphic temperatures within the Neoproterozoic sequence in the range of 250–350ºC were attained during the Cadomian (Pan-African) orogeny at 540–550 Ma. Apatite fission-track analysis reveals a subsequent decrease in rock temperature over the period 340–350 Ma that persisted throughout the late Palaeozoic. The most recent episode of accelerated cooling occurred between 20 and 40 Ma, corresponding with the regional uplift of the Bohemian Massif due to the Alpine orogeny.

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45

Naydenov, Kalin V., Jeremie Lehmann, Kerstin Saalmann, et al. "New constraints on the Pan-African Orogeny in Central Zambia: A structural and geochronological study of the Hook Batholith and the Mwembeshi Zone." Tectonophysics 637 (December 2014): 80–105. http://dx.doi.org/10.1016/j.tecto.2014.09.010.

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46

Heilbron, Monica, Beatriz Paschoal Duarte, and José Renato Nogueira. "The Juiz De Fora Granulite Complex of the Central Ribeira Belt, SE Brazil: A Paleoproterozoic Crustal Segment Thrust During the Pan-African Orogeny." Gondwana Research 1, no. 3-4 (1998): 373–81. http://dx.doi.org/10.1016/s1342-937x(05)70853-4.

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47

Andriampenomanana, Fenitra, Andrew A. Nyblade, Michael E. Wysession, et al. "Seismic velocity and anisotropy of the uppermost mantle beneath Madagascar from Pn tomography." Geophysical Journal International 224, no. 1 (2020): 290–305. http://dx.doi.org/10.1093/gji/ggaa458.

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SUMMARY The lithosphere of Madagascar records a long series of tectonic processes. Structures initially inherited from the Pan-African Orogeny are overprinted by a series of extensional tectonic and magmatic events that began with the breakup of Gondwana and continued through to the present. Here, we present a Pn-tomography study in which Pn traveltimes are inverted to investigate the lateral variation of the seismic velocity and anisotropy within the uppermost mantle beneath Madagascar. Results show that the Pn velocities within the uppermost mantle vary by ±0.30 km s–1 about a mean of 8.10 km s–1. Low-Pn-velocity zones (&lt;8.00 km s–1) are observed beneath the Cenozoic alkaline volcanic provinces in the northern and central regions. They correspond to thermally perturbed zones, where temperatures are estimated to be elevated by ∼100–300 K. Moderately low Pn velocities are found near the southern volcanic province and along an E–W belt in central Madagascar. This belt is located at the edge of a broader low S-velocity anomaly in the mantle imaged in a recent surface wave tomographic study. High-Pn-velocity zones (&gt;8.20 km s–1) coincide with stable and less seismically active regions. The pattern of Pn anisotropy is very complex, with small-scale variations in both the amplitude and the fast-axis direction, and generally reflects the complicated tectonic history of Madagascar. Pn anisotropy and shear wave (SKS) splitting measurements show good correlations in the southern parts of Madagascar, indicating coherency in the vertical distribution of lithospheric deformation along Pan-African shear zone as well as coupling between the crust and mantle when the shear zones were active. In most other regions, discrepancies between Pn anisotropy and SKS measurements suggest that the seismic anisotropy in the uppermost mantle beneath Madagascar differs from the vertically integrated upper mantle anisotropy, implying a present-day vertical partitioning of the deformation. Pn anisotropy directions lack the coherent pattern expected for an incipient plate boundary within Madagascar proposed in some kinematic models of the region.

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Soper, N. J. "Neoproterozoic sedimentation on the northeast margin of Laurentia and the opening of Iapetus." Geological Magazine 131, no. 3 (1994): 291–99. http://dx.doi.org/10.1017/s0016756800011067.

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AbstractVery thick shallow water sedimentary sequences were deposited in Neoproterozoic time along the future margins of Laurentia. On the eastern margin these include the Eleonore Bay and Hecla Hoek sequences of Greenland and Svalbard; these are described and their geotectonic context briefly reviewed. They present both geotectonic and geodynamic problems: why did subsidence continue for some 300 Ma prior to the opening of Iapetus, and how could 15–20 km of sediment be accommodated in an ensialic environment?Prolonged slow stretching appears to have affected the eastern margin of Laurentia while the western (Cordilleran) margin progressed through the rift-drift transition as the Pacific opened. It is proposed that expansion of the Pacific was associated with both the convergence of Proto-Gondwanan continental terranes during the Pan-African orogeny (the extended SWEAT hypothesis) and also the maintenance of very slow extension rates on the future Iapetus margin. The strain-hardening effect of slow stretching may have been inhibited by a continuous basin-fill of juvenile heat-producing Grenville detritus. The onset of subduction in the Pacific freed up this margin; major rifting took place between East Greenland and possibly the Tornquist margin of Baltica in Vendian time, followed by the opening of northern Iapetus.

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Mbaihoudou, Diontar, Kwékam Maurice, Fozing Eric Martial, Kagou Dongmo Armand, and Tcheumenak Kouémo Jules. "Petrology and Geochemical Characteristic of Granitoids From Guéra Massif in the Central Part of Chad: An Example of Mixing Magmas." Earth Science Research 9, no. 2 (2020): 66. http://dx.doi.org/10.5539/esr.v9n2p66.

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The granitoids of Gu&eacute;ra Massif are composed of biotite-granite, amphibole-biotite granite and gabbro-diorite and commonly contain micro granular mafic enclaves which vary from monzogabbro to syenite composition. They are metaluminous, high-K calc-alkaline to shoshonitic series. Gabbro-diorite rocks are magnesian while amphibole-biotite granites are magnesian to ferroan, and biotite granites are ferroan. They are enriched in LREEs relative to HREE and display negative anomalies in Nb, Ta and Ti. Fields relationships, petrology and geochemistry indicate that mixing and mingling processes could be more relevant for the genesis of granitoids associated to fractional crystallization. Thus, the presence of mafic enclaves of gabbro-diorite composition in the granites, the resumption of alkaline feldspar xenocrystals in the gabbro-diorites, as well as the linear correlation between the granites and the gabbro-diorites and the intermediate position of the mafic enclaves between the two formations, enable us to propose magmatic mixing as the major process that presided over the evolution of the Gu&eacute;ra granitoids. The delamination of the continental lithosphere during the post-collisional phase of the Pan-African orogeny would have caused the partial melting of the subduction-modofied mantle and lower continental crust and thus produced the magmas of the Gu&eacute;ra granitoids.

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Motoki, Akihisa, Thais Vargas, Woldemar Iwanuch, Susanna Eleonora Sichel, Alex Balmant, and José Ribeiro Aires. "Tectonic breccia of the Cabo Frio area, State of Rio de Janeiro, Brazil, intruded by Early Cretaceous mafic dyke: evidence of the Pan-African brittle tectonism?" Rem: Revista Escola de Minas 64, no. 1 (2011): 25–35. http://dx.doi.org/10.1590/s0370-44672011000100003.

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This paper presents the field descriptions and microscopic observations of a tectonic breccia in the basement gneiss of the Cabo Frio and Arraial do Cabo areas, State of Rio de Janeiro, Brazil, and its intrusive contact with the Early Cretaceous mafic dyke. At the sea cliff close to the Ilha do Japonês, there is an excellent contact outcrop between them. The tectonic breccia zone is 10 to 20m wide and has N30ºE direction. The breccia clasts are angular and characterized by auto-brecciation texture, and composed of breccia with similar aspect of the host tectonic breccia. The matrix is firmly consolidated by hydrothermalism and following silicification. The mafic dyke is 7 to 10m wide and of N45ºE direction. Along the contact, the dyke chilled margin featured by fine-grained basalt and prismatic joints can be observed. At the Conchas Beach and Arraial do Cabo city, there are four outcrops demonstrating the mafic dyke intrusion into the consolidated tectonic breccias. These outcrops prove that the tectonic breccias are older than the Early Cretaceous tholeiitic dykes. The fault breccias could have been formed during the brittle-phase tectonism of the last stage of the Pan-African Orogeny by hydrothermalism without magmatic activities, namely tectonic hydrothermalism. The existence of the clasts constituent of the breccia that are composed of breccia suggests that the fault movement and following hydrothermalism occurred repeatedly.

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Journal articles on the topic 'Pan-African orogeny'

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