Journal articles on the topic 'Neoproterozoic quartzites'
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ŽÁČKOVÁ, ELIŠKA, JIŘÍ KONOPÁSEK, JAN KOŠLER, and PETR JEŘÁBEK. "Detrital zircon populations in quartzites of the Krkonoše–Jizera Massif: implications for pre-collisional history of the Saxothuringian Domain in the Bohemian Massif." Geological Magazine 149, no. 3 (September 13, 2011): 443–58. http://dx.doi.org/10.1017/s0016756811000744.
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AbstractAge spectra of detrital zircons from metamorphosed quartzites of the Krkonoše–Jizera Massif in the northeastern part of the Saxothuringian Domain were obtained by U–Pb laser ablation inductively coupled plasma mass spectrometry dating. The zircon ages cluster in the intervals of 450–530 Ma and 550–670 Ma, and show individual data between 1.6 and 3.1 Ga. Zircons in the analysed samples are predominantly of Cambrian–Ordovician and Neoproterozoic age, and the marked peak at c. 525–500 Ma suggests a late Cambrian maximum age for the sedimentary protolith. Detritus of the quartzites probably originated from the erosion of Cambrian–Ordovician granitoids and their Neoproterozoic (meta)sedimentary or magmatic country rocks. The lack of Neoproterozoic (meta)sedimentary rocks in the central and eastern part of the Krkonoše–Jizera Massif suggests that the country rocks to voluminous Cambrian–Ordovician magmatic bodies were largely eroded during the formation of early Palaeozoic rift basins along the southeast passive margin of the Saxothuringian Domain. The detrital zircon age spectra confirm the previous interpretation that the exposed basement, dominated by Neoproterozoic to Cambrian–Ordovician granitoids, was overthrust during Devonian–Carboniferous subduction–collision processes by nappes composed of metamorphosed equivalents of the uppermost Cambrian–Devonian passive margin sedimentary formations. Only a negligible number of Mesoproterozoic ages, typically from the Grenvillian event, supports the interpretation that the Saxothuringian Neoproterozoic basement has an affinity to the West African Craton of the northwestern margin of Gondwana.
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Sharafeldin, Hani E., and Alexander A. Vercheba. "Perspective of gold-bearing deposits in the ferruginous-siliceous formations of Egypt and Kursk Magnetic Anomaly." RUDN Journal of Engineering Researches 20, no. 2 (December 15, 2019): 174–83. http://dx.doi.org/10.22363/2312-8143-2019-20-2-174-183.
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Banded ferruginous-siliceous formations (FSF) are confined to the Precambrian basement of the Arabian-Nubian Shield within the central part of the Eastern Desert of Egypt. Gold mineralization is spatially associated with banded ferruginous quartzite, representing one of the most ancient manifestations of gold ore. The Precambrian rocks are combined into deposits complex of the Neoproterozoic Pan-African megacycle of the territory development. Banded iron-silicate rocks occur in sedimentary-volcanogenic rocks that were formed in the subduction trough zones, and are represented by metamorphosed ferruginous quartzites, jaspilites and schists. FSF show tectonic dislocations, shear cracks, and fracture cracks made by gold-quartz-sulphide mineralization. Promising for the identification of gold-bearing mineralization in the rocks of the FSF can be iron-silicate deposits with the occurrence of epigenetic hydrothermal activity as a result of activation of the submarine volcanism of the tholeiitic type.
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A Nwos Prisca-Gaelle, Bien, Mounchili Ibrahim, Apouamoun Yiagnigni Roland, Etoundi Jean, Ndongue Constantin, and Meying Arsene. "THE CONTRIBUTION OF REMOTE SENSING AND AEROMAGNETISM TO GOLD PROSPECTING: THE CASE OF THE MEIGANGA ZONE, CAMEROON." International Journal of Advanced Research 9, no. 5 (May 31, 2021): 775–93. http://dx.doi.org/10.21474/ijar01/12903.
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In order to optimize gold prospecting in the Meiganga zone located in the Adamaoua region of Cameroon, aeromagnetic and remote sensing prospecting was carried out in the eastern and southern parts. The remote sensing approach on a Landsat 8 OLI/TIRS image highlighted areas of maximum gold concentration. Thus, ferric ion bearing minerals are located in the North-West, silicate minerals bearing ferrous ions are in the Centre while clay minerals are in the North-East and East. The principal component analysis revealed important structural information. The PCA Spatial Map (PC1, PC2, PC3) showed the plutonic formations composed of anatexis and anatexis granites, vegetation cover (at the date of image acquisition: February 22, 2019), areas of permanent water circulation or accumulation, and metamorphic and sedimentary formations namely gneisses, quartzites, schists and superficial clay formations. A Landsat SRTM (Shuttle Radar Topography Mission) image was also used to enhance the lineaments through the Sobel filter to highlight the geomorphological (cliffs, valleys, ...) and topographic (river network, ridge and drainage segment) structures. The aeromagnetic approach was also important. The study of the modified magnetic field (CM) showed 4 ranges: very high, high, medium and low. The Total Magnetic Anomalies (TMI) of the area are subdivided into 2 ranges large positive anomalies (221.1-103.0 nT) located in the lower part of NE-SW orientation, small positive anomalies (103.0-(-)89.7 nT) located in the upper part of NE-SW orientation. The reduced total magnetic anomaly at the equator shows a fairly similar distribution to the total magnetic anomaly with the large positive anomalies in almost the entire lower part. Superimposed on the geological map, Neoproterozoic pre- to syn-tectonic granitoids (C) are superimposed on the large positive anomalies and Neoproterozoic conglomerates, quartzites, sedimentary shales and volcanosedimentary rocks (A) and Neoproterozoic syn-tectonic granitoids (B) are superimposed on the large and small positive anomalies. The grid of the reduced residual equatorial anomaly (ARRE) confirms that the local geology is strongly magnetic (gneiss and quartzite). The filters of the derivatives allowed to establish a map of magnetic lineaments of major orientation N045° and minor orientation N130°. The horizontal gadient superimposed on the local maxima showed the presence of deep structures oriented NE-SW. The analytical signal superimposed on the local maxima highlights the metamorphic basement consisting of rocks with strong magnetism. The application of Euler deconvolution localizes the depth of the sources of linear anomalies.
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Barrote, Vitor Rodrigues, Carlos Alberto Rosiere, Vassily Khoury Rolim, João Orestes Schneider Santos, and Neal Jesse Mcnaughton. "The Proterozoic Guanhães banded iron formations, Southeastern border of the São Francisco Craton, Brazil: evidence of detrital contamination." Geologia USP. Série Científica 17, no. 2 (August 1, 2017): 303. http://dx.doi.org/10.11606/issn.2316-9095.v17-352.
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The Guanhães banded iron formation (BIF) bearing succession occurs as tectonic slices, juxtaposed to Archean TTG granite-gneissic basement rock, developed during the Neoproterozoic-Cambrian Brasiliano collage. The succession has a maximum depositional age of ~2.18 Ga, from detrital zircons in quartzite, and consists of quartzites, schists, BIFs, gneiss and amphibolite, all metamorphosed under amphibolite facies conditions. The Guanhães BIF shows HREE enrichment and consistent positive Eu anomaly (PAAS-normalized REE+Y). Two types of contamination were observed in the samples. The first is contamination by an exotic detrital component, which resulted in low Y/Ho (<30) and Pr/Yb (SN) ratios. Evidence of such contamination, combined with inferred stratigraphic stacking data, indicates that the Guanhães BIFs were deposited on a shallow marine environment. The second type of contamination resulted in higher Eu-anomalies, positive Ce-anomalies, and higher REE+Y concentrations, possibly due to the interaction between later magmatic fluids and the Guanhães BIF. A strong Cambrian event is recorded in zircon age data. The uncontaminated samples display REE+Y distribution similar to other Precambrian BIFs, particularly those from the Morro-Escuro Sequence and the Serra da Serpentina Group, without true Ce-anomalies and Y/Ho close to seawater values (45). Geochronological and geochemical data presented in this paper strongly suggest a correlation between the Guanhães supracrustal succession and the Serra da Serpentina and Serra de São José Groups.
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Dias, Tatiana Gonçalves, Fabrício de Andrade Caxito, Antônio Carlos Pedrosa-Soares, Ross Stevenson, Ivo Dussin, Luiz Carlos da Silva, Fernando Alkmim, and Márcio Pimentel. "Age, provenance and tectonic setting of the high-grade Jequitinhonha Complex, Araçuaí Orogen, eastern Brazil." Brazilian Journal of Geology 46, no. 2 (June 2016): 199–219. http://dx.doi.org/10.1590/2317-4889201620160012.
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ABSTRACT: The Jequitinhonha Complex of the northeastern Araçuaí orogen is an extensive sedimentary unit metamorphosed in the amphibolite-granulite facies transition around 580-545 Ma. The unit consists of Al-rich (kinzigitic) paragneisses with decametric intercalations of graphite gneisses and quartzites, and centimetric to metric lenses of calcsilicate rocks. A new detrital zircon U-Pb age spectrum is reported for a sample of quartzite, and whole-rock geochemical (major and trace elements, 9 samples) and Sm-Nd isotope data (10 samples) for Jequitinhonha Complex paragneiss. Together with published data these show that: (1) the geochemistry of paragneiss samples of the Jequitinhonha Complex are similar to those of passive margin sedimentary protoliths; (2) detrital zircon data yield U-Pb age populations between ca. 0.9 and 2.5 Ga; and (3) Sm-Nd TDM model ages range from 1.6 to 1.8 Ga and εNd(575 Ma) around -7.5. The data reveal a mixture of Cryogenian to Mesoproterozoic rift-related igneous rocks with the Palaeoproterozoic-Archaean basement rocks of the São Francisco-Congo palaeocontinent as the main source areas, and also support the correlation between the Jequitinhonha Complex and the passive margin units of the upper Macaúbas Group, constituting the precursor basin of the orogen. Our results, with the absence of ophiolites in the Jequitinhonha Complex, reinforce the interpretation that the São Francisco-Congo palaeocontinent was not divided to the north of the focused region, suggesting an ensialic termination of a gulf during the Neoproterozoic.
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Wang, Lu, Stephen T. Johnston, and Nengsong Chen. "New insights into the Precambrian tectonic evolution and continental affinity of the Qilian block: Evidence from geochronology and geochemistry of metasupracrustal rocks in the North Wulan terrane." GSA Bulletin 131, no. 9-10 (April 15, 2019): 1723–43. http://dx.doi.org/10.1130/b35059.1.
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Abstract The Qilian block, one of the Precambrian terranes in the Qinling-Qilian-Kunlun orogenic system, is a critical region for reconstruction of the overall architecture and tectonic evolution of NW China. This investigation of zircon U-Pb and Lu-Hf isotopes and whole-rock geochemistry of a metasupracrustal sequence in the North Wulan terrane provides new insights into the Qilian block. A Statherian–Calymmian unit (ca. 1.67–1.5 Ga), dominated by Al- and Si-rich gneisses, arkosites, quartzites, and amphibolites with minor calc-silicate rocks and marbles, is interpreted to have been deposited during continental rifting. Detrital zircons show two main age populations of 2685–2276 and 2098–1761 Ma with mostly negative εHf(t) values (–14.0 to +3.6). The sources are characterized by mixed felsic to intermediate igneous rocks as well as recycled components and are interpreted as being derived from the Tarim craton because of the age distribution of their detrital zircons. A Stenian–Tonian unit (ca. 1.1–0.9 Ga) consists mainly of felsic gneisses, quartzites, calc-silicate rocks, marbles, metavolcanic rocks, and amphibolites. The metasedimentary rocks yielded detrital zircon ages clustering at ca. 1.64, 1.43, 1.3–1.2, 1.1, and 0.94 Ga with predominantly positive εHf(t) values (–7.1 to +9.7). One metavolcanic rock has an age of ca. 1110 Ma and εHf(t) values of +6.5 to +9.1. The provenance is dominated by local syndepositional arc-related igneous rocks with older detritus possibly from Laurentia, again based on the age distribution of the detrital zircons. The Central Qilian and Hualong terranes show strong affinities with the North Wulan terrane and together constituted a single coherent Qilian block prior to their involvement in the Qilian–North Qaidam orogen. The Qilian block was probably once part of the Tarim craton and had a strong linkage to South Tarim, which drifted from North Tarim during the breakup of Columbia in the early Mesoproterozoic. We suggest that, from the late Mesoproterozoic to early Neoproterozoic, the South Tarim–Qilian formed an active continental margin located close to Laurentia during the assembly of Rodinia. The final collision occurred in the early Neoproterozoic with the formation of a significant continent that included the reunified Tarim-Qilian as well as Qaidam-Kunlun and Qinling terranes, Alxa block, Kyrgyz-Chinese Tianshan, and Yili block.
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Soulaimani, Abderrahmane, Mohamed Bouabdelli, and Alain Piqué. "The Upper Neoproterozoic-Lower Cambrian continental extension in the Anti-Atlas (Morocco)." Bulletin de la Société Géologique de France 174, no. 1 (January 1, 2003): 83–92. http://dx.doi.org/10.2113/174.1.83.
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Abstract Introduction. – In the Anti-Atlas, south of Morocco (fig. 1), the Precambrian terrains are usually divided into several “series” (fig. 2) : the Paleoproterozoic (PI) is an old crystalline basement, at least Eburnean ; the Neoproterozoic (PII) is constituted by metasedimentary rocks, quartzites and limestones, indicative of a shelf, in which volcano-sedimentary and volcanic flows are intercalated, laterally grading to an ophiolitic complex along the Sirwa-Bou Azzer axis. These PII rocks have been deformed in the course of the Panafrican orogeny ; above the underlying upper Proterozoic terrains and in major unconformity on the Panafrican structures, the Saghro group (PII3) and Ouarzazate group (PIII) series are volcanic and volcano-clastic sequences, often considered as late-Panafrican molasses. Above them, the Tata group (Adoudounian), constituted by marine carbonates and siltstones, represents the earliest Cambrian. Recent structural and sedimentological observations Recent observations have been realized through all the Anti-Atlas, of which the present note gives only examples that are the most significant and easily accessible. They show that the PII3 conglomerates were not everywhere deposited around Panafrican paleoreliefs ; they often contain large bodies of quartzites embedded within the conglomerates (fig. 3). Clearly, the PII3 is an olistostrome at the base of the PIII détrital and volcanic series, which were deposited at the base of active faults. The development of these reliefs took place several tens of millions of years after the end of the Panafrican paroxysm and therefore the PII3 and the PIII are post-Panafrican deposits, unrelated to the Panafrican orogeny. Study of synsedimentary structures (folds, faults, progressive unconformities : fig. 4 to 7) reveals the extensive character of this faulting event that extends even in basal Cambrian. Between the PII3 series and PIII an angular unconformity due to tilting can exist, but we did not find there plicative structures clearly related to the compressive late-Panafrican « B2 » phase sometimes described in the litterature. In the western Anti-Atlas, the extension is pure, with a NW-SE direction ; it is N-S in the central Anti-Atlas and it is transtensive according to N070°E faults, en échelon between sinistral N110°E trending faults in the central-eastern Anti-Atlas. In the detail, nevertheless, the synsedimentary structures suggest slidings from raised zones that correspond to the future inliers (fig. 7). Magmatic and metallogenic activity This extension accompanies various events : (1) a marine transgression, from west to east ; (2) the emplacement of extrusive magmas, first calco-alkaline then tholeiitic ; (3) an hydrothermal activity responsible for the concentration of Co, Au, Cu, etc. These concentrations were in the past attributed to various episodes, from the pre-Panafrican extension to the Hercynian compression. In fact, they result from the circulation of hydrothermal solutions that deposited, in the superficial levels of the crust, products extracted from the PIII magmas or the PII Proterozoic serpentines. The circulations took place in the old compressive structures (e.g. the Panafrican foliation) reopened during the extensive episode described above. Discussion and conclusion : the late Proterozoic-early Cambrian rifting The crustal extension that affected the Anti-Atlas started during the late Proterozoic, after the end of the main Panafrican deformation. Its tectonic significance is discussed with regard to the Panafrican orogeny : either a late Panafrican extension, bracketed between two compressive deformations and possibly related to a thinning of the orogenic crust, or a post-Panafrican extension, unrelated to compressive phases, described as a synrift event. In the Anti-Atlas, it developed through late Proterozoic and early Cambrian times. It aborted at the end of the early Cambrian. Evidences of a comparable extension are found in northern Morocco, western Europe and as far in the Middle East, i.e. all along the northern margin of the paleo-Gondwana.
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Alexeiev, D. V., A. K. Khudoley, and S. A. DuFrane. "Paleoproterozoic and Neoproterozoic Quartzites of the Kyrgyz North Tianshan: Age Determination according to the Results of Detrital Zircon Dating." Doklady Earth Sciences 491, no. 2 (April 2020): 191–94. http://dx.doi.org/10.1134/s1028334x20040017.
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El Aouli, El Hassan, Dominique Gasquet, and Moha Ikenne. "Le magmatisme basique de la boutonniere d'Igherm (Anti-Atlas occidental, Maroc); un jalon des distensions neoproterozoiques sur la bordure nord du craton ouest-africain." Bulletin de la Société Géologique de France 172, no. 3 (May 1, 2001): 309–17. http://dx.doi.org/10.2113/172.3.309.
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Abstract In the Igherm inlier (western Anti-Atlas, Morocco) doleritic dyke swarms with various directions and gabbroic intrusive bodies were emplaced during Neoproterozoic times, cutting across either Eburnean micaschists and granites or Panafrican limestones and quartzites. All these rocks were deformed by the main Panafrican schistosity and covered by molassic and volcanic Upper Neoproterozoic series. The primary mineralogical assemblages (plagioclase, augite, olivine...) of the mafic rocks are nearly completely replaced by secondary assemblages (albite, actinolite, chlorite, epidote, calcite, quartz, leucoxene, magnetite, hematite...). However, three main groups have been recognized by the means of relative chronology and petrography. The group 1 is earlier, as shown by the intrusive character of the dykes of the other two groups into its gabbroic bodies. Using incompatible trace elements and rare earth elements it appears that this magmatism is truly heterogeneous and that the three groups have different magmatic affinities. The group 1 corresponds to tholeiitic dolerites and gabbros characterized by intersertal and ophitic textures and by high contents in Fe 2 O 3 (12.16 to 16.64%), TiO 2 (1.46 to 2.5%), Zr (90 to 174 ppm), Nb (7 to 13 ppm), Y (21.68 to 38.74 ppm) and V (264 to 419 ppm). The REE contents are low (Sigma REE = 49 to 137 ppm) and the REE patterns are flat [1.99<(La/Yb) N <4.56] showing a relative slight enrichment in LREE and no anomaly in Eu (0.89>Eu/Eu (super *) <1.11). These features as the TiO 2 vs FeO (super *) /MgO and V vs Ti/1000 diagrams are characteristic of anorogenic intraplate magmas. The group 2 corresponds to calc-alkaline dolerites and gabbros showing fine-grained intersertal textures and high contents of Al 2 O 3 (14.10 to 20.64%) and low contents of Fe 2 O 3 (8.35 to 12.91%), TiO 2 (0.68 to 1.41%), Zr (66 to 106 ppm), Nb (5 to 7 ppm), Y (16.41 to 20.75 ppm) and V (144 to 264 ppm). The REE contents vary from 67 to 155 ppm and the REE patterns are fractionated (2.78<(La/Yb) N <6.62) with a strong enrichment in LREE. The slight positive Eu anomaly (0.91<Eu/Eu (super *) <1.37) is related to the wealth of plagioclases frequently observed in these rocks. The TiO 2 contents of these rocks and their low FeO (super *) /MgO ratios give them a calc-alkaline affinity similar to that of calc-alkaline orogenic basalts related to an oceanic subduction. The group 3 corresponds to alkaline dolerites characterized by fine-grained intersertal textures with high contents of TiO 2 (3.85 to 3.97%), P 2 O 5 (0.66 to 0.77%), Nb (33 to 39 ppm), Zr (262 to 287 ppm), Y (39.6 to 47.7 ppm) and REE (Sigma REE = 205 to 218 ppm). The REE patterns are fractionated (7.77<La/Yb) N <6.65) without no Eu anomaly (0.99<Eu/Eu (super *) <1.02). The Ti/V and Y/Nb ratios (65.26 to 74.95 and 1.19 to 1.22, respectively) are those of alkaline rocks found in intraplate environments. The detailed petrographical, geochemical and field studies of the Igherm inlier show that the mafic magmatism is more complex than previously described. The mafic tholeiitic and alkaline magmatism occurring in the Igherm inlier is also present in the other inliers of the Moroccan Anti-Atlas during Neoproterozoic times. On the other hand the calc-alkaline Neoproterozoic mafic magmatism is very rare elsewhere in the Anti-Atlas except in the Siroua Massif and locally in the Bas Draa and Tagragra d'Akka inliers (western Anti-Atlas). The geodynamical environment of this mafic magmatism is linked to a strong extensional tectonic regime occurring at the northern border of the West African craton during Neoproterozoic times. This regime is related to the oceanic opening described in Central Anti-Atlas and to the emplacement of the ophiolites of Bou Azzer and Siroua or occurs immediately after the oceanic opening. The chemical heterogeneities observed in the three defined groups can be related to heterogeneities of mantellic sources and/or various partial melting ratios of the sub-continental mantle. We can assume that this major fissural magmatic event, not precisely dated, is equivalent to that observed in the other Neoproterozoic provinces in Hoggar, Cameroon, north America and Brazil.
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JASTRZĘBSKI, MIROSŁAW, ANDRZEJ ŻELAŹNIEWICZ, IZABELLA NOWAK, MENTOR MURTEZI, and ALEXANDER N. LARIONOV. "Protolith age and provenance of metasedimentary rocks in Variscan allochthon units: U–Pb SHRIMP zircon data from the Orlica–Śnieżnik Dome, West Sudetes." Geological Magazine 147, no. 3 (November 2, 2009): 416–33. http://dx.doi.org/10.1017/s0016756809990501.
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AbstractNew U–Pb sensitive high-mass resolution ion microprobe (SHRIMP) data from detrital zircons within the Orlica–Śnieżnik Dome provide new insights into the stratigraphic and palaeogeographic position of assumed relict Precambrian basement preserved in the Variscan collisional orogen of the West Sudetes, SW Poland. Hitherto, the Młynowiec Formation and the Stronie Formation within the Orlica–Śnieżnik Dome were assumed to represent two metavolcano-sedimentary successions of Proterozoic and early Palaeozoic age, respectively. However, when previous U–Pb data and mapping data from the Orlica–Śnieżnik Dome are combined with the new detrital zircon isotopic ages both from paragneisses within the Młynowiec Formation and from light-coloured quartzites and mica schists within the Stronie Formation, the result strongly suggests that the protoliths of these two formations actually form a continuous succession. This continuous succession is herein designated the Młynowiec–Stronie Group. The rocks of this group were deposited during middle Cambrian–early Ordovician times (c.520–470 Ma), presumably at the northern edge of West Gondwana after the 10–20 Ma period of tectonic quiescence that followed the terminal stage of the Cadomian collisions. Monotonous Młynowiec metagreywackes form the lower part of the succession, and the lithologically diverse schistose Stronie Formation forms its upper part. The change from greywacke (Młynowiec) to volcano-sedimentary (Stronie) facies coincided with the onset of rather short-lived volcanic activity which climaxed around 505–495 Ma and which supplied the volcanogenic components to the Stronie Formation. No ‘Cadomian unconformity’ has been observed in the region. Xenocrystic zircons from the Młynowiec–Stronie Group retain records of Archaean (3.0–2.3 Ga), Palaeoproterozoic (2.1–1.8 Ga) and Neoproterozoic to early Cambrian (660–530 Ma) zircon-forming events. These zircon ages, together with the lack of 1.7–1.2 Ga zircon ages, suggest that the source areas for the metasedimentary rocks may have been the West Africa craton, which therefore differs from the Amazonian affinity of the adjacent Brunovistulia Terrane. Nevertheless, two zircons,c.1.0 and 1.1 Ga old, respectively, indicate that the Młynowiec–Stronie Group sedimentary basin must have still been within the delivery reach of detritus ultimately derived from the Grenvillian-age belt(s). The detrital components of the supracrustal formations of the Orlica–Śnieżnik Dome were mainly derived from Neoproterozoic zircon-bearing crystalline rocks that were accreted to, and included in, the Cadomian basement in several intrusive pulses that culminated at 660–640 Ma, 620 Ma and 570–530 Ma.
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Sunkari, Emmanuel Daanoba, Basiru Mohammed Kore, and Samuel Edem Kodzo Tetteh. "Petrography and structural features of the Precambrian basement rocks in the Benin-Nigerian Shield, NW Nigeria: Implications for their correlation with South Atlantic Precambrian terranes." AIMS Geosciences 8, no. 4 (2022): 503–24. http://dx.doi.org/10.3934/geosci.2022028.
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<abstract> <p>This study investigated the petrographic and structural features of the Precambrian (Neoproterozoic) basement rocks of the Benin-Nigerian Shield that crop out in northwestern Nigeria within Kanoma and its environs to give an insight into the evolution and deformational episodes that pervaded them. The major rock types in the area are schists and quartzites, which have been intruded by granitic rocks that appear to be metamorphosed. The origin of these rocks is attributed to the Eburnean Precambrian orogenic episode and the Pan-African orogeny, which started and ended with the intrusion of the granite suites. The dominant mineralogy associated with the rock types includes quartz, orthoclase, plagioclase, microcline, biotite, chlorite, and very few accessory minerals. The schist shows the dominance of quartz, feldspars (alkali and plagioclase), biotite, muscovite, chlorite, and opaque minerals. The quartzite is typically dominated by quartz that appears recrystallized in places, whereas the meta-granite contains quartz, feldspars (alkali and plagioclase), biotite, and opaque minerals. Structural features such as joints, quartz veins with minor folds, and faults observed in the lithological units have a predominant N-S trend and are the imprints of the last tectonic event (Pan-African orogeny). The level of deformation in Kanoma led to the development of N to NNE trending moderately (S<sub>1</sub>) to steeply (S<sub>2</sub>) dipping foliations in the schist. The evolution of these deformational mechanisms from moderately dipping foliations to steeply dipping foliations along the N to NNE- trend is associated with late orogenic uplift and exhumation following oblique convergence during the Pan-African orogeny. Structural overprinting relations recognized within Kanoma and its environs allow us to decipher the geologic structures into three successive Pan-African deformational events (D1–D3). D1 fabrics are manifested by simple anticline micro folds in the schist. The D2 structures are the predominant ones in the area comprising the N-S directional joints and faults. The D3 phase of deformation is a progressive one, which started as N-S high angle thrusts and thrust-related folds that resulted from the NE–SW contraction during the orogenic episodes. The studied rocks can be correlated with the Pan-African and Brasiliano belts based on their overlapping features.</p> </abstract>
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Natal’in, Boris A., Gürsel Sunal, Erkan Gün, Bo Wang, and Yang Zhiqing. "Precambrian to Early Cretaceous rocks of the Strandja Massif (northwestern Turkey): evolution of a long lasting magmatic arc." Canadian Journal of Earth Sciences 53, no. 11 (November 2016): 1312–35. http://dx.doi.org/10.1139/cjes-2016-0026.
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The Strandja Massif, northwestern Turkey, forms a link between the Balkan Zone of Bulgaria, which is correlated with the Variscan orogen in Europe, and the Pontides, where Cimmerian structures are prominent. Five fault-bounded tectonic units form the massif structure. (1) The Kırklareli Unit consists of the Paleozoic basement intruded by the Carboniferous to Triassic Kırklareli metagranites. It is unconformably overlain by Permian and Triassic metasediments. (2) The Vize Unit that is made of Neoproterozoic metasediments, which are intruded by Cambrian metagranites, and overlain by the pre-Ordovician molasse. Unconformably laying the Ordovician quartzites pass upward into quartz schists and then to alternating marble and chert of, possibly, latest Devonian age. Rocks of the Vize Unit are intruded by the late Carboniferous metagranites. The Vize Unit may be correlated with the passive continental margin of the Istanbul Zone. (3) The Mahya accretionary complex and (4) the paired Yavuzdere magmatic arc were formed in the Carboniferous. (5) Nappes consisting of the Jurassic dolomites and marbles thrust to the north in late Jurassic – early Cretaceous time. They occupy the highest structural position on all above-mentioned tectonic units. Tectonic subdivision of the Strandja Massif is supported by new 18 ages of magmatic and detrital zircons. The long duration of subduction-related magmatism in the region and its continuity in the Triassic contradicts with the widely accepted ideas about the dominance of the passive continental margin settings in the tectonic evolution of the Strandja Massif. The massif is interpreted as a fragment of the long-lived, Cambrian to Triassic Silk Road magmatic arc. At least since the late Paleozoic this arc evolved on the northern side of Paleo-Tethys.
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Franz, Gerhard, Giulio Morteani, Axel Gerdes, and Dieter Rhede. "Ages of protolith and Neoproterozoic metamorphism of Al-P-bearing quartzites of the Veredas formation (Northern Espinhaço, Brazil): LA-ICP-MS age determinations on relict and recrystallized zircon and geodynamic consequences." Precambrian Research 250 (September 2014): 6–26. http://dx.doi.org/10.1016/j.precamres.2014.05.011.
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Barr, Sandra M., Deanne Van Rooyen, Brent V. Miller, Chris E. White, and Susan C. Johnson. "Detrital zircon signatures in Precambrian and Paleozoic sedimentary units in southern New Brunswick – more pieces of the puzzle." Atlantic Geology 55 (October 2, 2019): 275–322. http://dx.doi.org/10.4138/atlgeol.2019.010.
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Southern New Brunswick consists of a complex collage of fault-bounded belts of Late Neoproterozoic igneous and metamorphic rocks, Early Paleozoic sedimentary, metamorphic and igneous units, and overlying Carboniferous sedimentary rocks. The area also contains the boundary between the Avalonian and Ganderian terranes as interpreted in the northern Appalachian orogen. New detrital zircon ages reported here provide improved understanding of depositional ages and provenance of diverse Neoproterozoic to Carboniferous rocks in this complex area. Detrital zircon data from samples with Neoproterozoic maximum depositional ages indicate a dominantly Gondwanan provenance with a strong influence from the Amazonian craton. However, quartzite from The Thoroughfare Formation on Grand Manan Island contains dominanly 2 Ga zircon grains, consistent with derivation from the West African Craton. The age spectrum is similar to that from the Hutchins Island Quartzite in the Isleboro block in Penobscot Bay, Maine, strengthening the previously proposed correlation between the two areas. Cambrian samples also show prominent peri-Gondwanan provenance with strong influence from Ediacaran to Early Cambrian arc magmatism. The maximum depositional ages of these samples are consistent with previous interpretations of Cambrian ages based on fossil correlations and field data. A Carboniferous sample from Avalonia shows a significant contribution from Devonian magmatism as the youngest detrital component, although its depositional age based on field relationships is Carboniferous. The results exemplify the need to integrate multiple datasets in making interpretations from detrital zircon data.
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Gehling, James G., and J. Keith Rigby. "Long expected sponges from the Neoproterozoic Ediacara fauna of South Australia." Journal of Paleontology 70, no. 2 (March 1996): 185–95. http://dx.doi.org/10.1017/s0022336000023283.
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New fossils from the Neoproterozoic Ediacara fauna of South Australia are interpreted as the oldest known hexactinellid sponges. They occur within the Ediacara Member of the Rawnsley Quartzite (Pound Subgroup) from several locations in the Flinders Ranges. The new genus,Palaeophragmodictya, is characterized by disc-shaped impressions preserving characteristic spicular networks and is reconstructed as a convex sponge with a peripheral frill and an oscular disc at the apex.
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Lewis, Reed S., Jeffrey D. Vervoort, Russell F. Burmester, and Peter J. Oswald. "Detrital zircon analysis of Mesoproterozoic and Neoproterozoic metasedimentary rocks of north-central Idaho: implications for development of the Belt–Purcell basin." Canadian Journal of Earth Sciences 47, no. 11 (November 2010): 1383–404. http://dx.doi.org/10.1139/e10-049.
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The authors analyzed detrital zircon grains from 10 metasedimentary rock samples of the Priest River complex and three other amphibolite-facies metamorphic sequences in north-central Idaho to test the previous assignment of these rocks to the Mesoproterozoic Belt–Purcell Supergroup. Zircon grains from two samples of the Prichard Formation (lower Belt) and one sample of Cambrian quartzite were also analyzed as controls with known depositional ages. U–Pb zircon analysis by laser ablation — inductively coupled plasma — mass spectrometry reveals that 6 of the 10 samples contain multiple age populations between 1900 and 1400 Ma and a scatter of older ages, similar to results reported from the Belt–Purcell Supergroup to the north and east. Results from the Priest River metamorphic complex confirm previous correlations with the Prichard Formation. Samples from the Golden and Elk City sequences have significant numbers of 1500–1380 Ma grains, which indicates that they do not predate the Belt. Rather, they are probably from a relatively young, southwestern part of the Belt Supergroup (Lemhi subbasin). Non-North American (1610–1490 Ma) grains are rare in these rocks. Three samples of quartzite from the Syringa metamorphic sequence northwest of the Idaho batholith contain zircon grains younger than the Belt Supergroup and support a Neoproterozoic age. A single Cambrian sample has abundant 1780 Ma grains and none younger than ∼1750 Ma. These results indicate that the likely protoliths of many high-grade metamorphic rocks in northern Idaho were strata of the Belt–Purcell Supergroup or overlying rocks of the Neoproterozoic Windermere Supergroup and not basement rocks.
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Seybold, Lina, Wolfgang Dörr, Claudia A. Trepmann, and Jochen Krahl. "New constraints from U–Pb dating of detrital zircons on the palaeogeographic origin of metasediments in the Talea Ori, central Crete." Geological Magazine 157, no. 9 (January 13, 2020): 1383–408. http://dx.doi.org/10.1017/s0016756819001365.
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AbstractHigh-pressure low-temperature metamorphic sediments of the Phyllite–Quartzite unit sensu stricto and the Talea Ori group are investigated in the field, microstructurally and by U–Pb dating of detrital zircons to shed light on their palaeogeographic origin. Zircon age spectra with ages >450 Ma of the Phyllite–Quartzite unit sensu stricto indicate a palaeogeographic origin at the northern margin of East Gondwana. In contrast, the lower stratigraphic, siliciclastic formations of the Talea Ori group show a high number of well-rounded Cambrian to Early Carboniferous aged zircons and a Neoproterozoic zircon age spectrum with East Gondwana affinity. Based on the comparison of zircon age data, a possible distal sediment source is the Sakarya Zone at the southern active margin of Eurasia. To reconcile the zircon data with the geological observations we propose different alternative models, or a combination of these, including sediment transport from the Sakarya Zone and/or a westerly source towards the northern margin of Gondwana as well as terrane-displacement of the Sakarya Zone. Also, a palaeogeographic origin of the Talea Ori group at the southern active margin of Eurasia cannot be excluded. This alternative, however, would not be consistent with the usually assumed association of the Talea Ori group with the Plattenkalk unit characterized by a palaeogeographic origin at the northern margin of Gondwana.
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Malone, D. H., J. P. Craddock, P. K. Link, B. Z. Foreman, M. A. Scroggins, and J. Rappe. "Detrital zircon geochronology of quartzite clasts, northwest Wyoming: Implications for Cordilleran Neoproterozoic stratigraphy and depositional patterns." Precambrian Research 289 (February 2017): 116–28. http://dx.doi.org/10.1016/j.precamres.2016.12.011.
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van Rooyen, D., S. M. Barr, C. E. White, and M. A. Hamilton. "New U–Pb age constraints on the geological history of the Ganderian Bras d’Or terrane, Cape Breton Island, Nova Scotia." Canadian Journal of Earth Sciences 56, no. 8 (August 2019): 829–47. http://dx.doi.org/10.1139/cjes-2018-0248.
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The northern Appalachian orogen preserves evidence of a complex history of amalgamation of terranes with both Laurentian and Gondwanan affinities. The Ganderian Bras d’Or terrane of central Cape Breton Island is not well represented elsewhere in the orogen and its relationship to other Ganderian terranes is enigmatic, particularly with respect to its pre-Neoproterozoic history. The Boisdale Hills and Kellys Mountain areas contain the oldest metamorphic rocks in the Bras d’Or terrane. Quartzite units in the Boisdale Hills have detrital zircon populations with ages ranging from 3.2 to ca. 1 Ga. Paragneiss units from the Kellys Mountain area contain Meso- to Neoproterozoic detrital zircons, in which the youngest grains indicate that the maximum depositional age is <600 Ma. The detrital zircon populations of rocks from both areas are consistent with Gondwanan provenance for the protoliths, most likely the Amazonian craton. New U–Pb dates for subduction-related dioritic to granodioritic plutons in the Boisdale Hills yielded ages of 560 to ca. 540 Ma. Sedimentary, bimodal volcanic and plutonic rocks from the Bourinot belt in the Boisdale Hills and related plutons in the Kellys Mountain area have ages of ca. 510–490 Ma and are interpreted to have formed during extension related to separation of Ganderia from Gondwana. The southeastern Bras d’Or terrane preserves rocks formed in Pan-African subduction zones on a former passive margin of Gondwana as well as rocks formed during the initial stages of rifting of Ganderia from Gondwana and the subsequent opening of the Rheic Ocean.
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Lindsay, J. F. "Heavitree Quartzite, a Neoproterozoic (ca800–760 Ma), high‐energy, tidally influenced, ramp association, Amadeus Basin, central Australia." Australian Journal of Earth Sciences 46, no. 1 (February 1999): 127–39. http://dx.doi.org/10.1046/j.1440-0952.1999.00693.x.
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Smith, Loren H., Alan J. Kaufman, Andrew H. Knoll, and Paul Karl Link. "Chemostratigraphy of predominantly siliciclastic Neoproterozoic successions: a case study of the Pocatello Formation and Lower Brigham Group, Idaho, USA." Geological Magazine 131, no. 3 (May 1994): 301–14. http://dx.doi.org/10.1017/s0016756800011079.
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AbstractIsotopic chemostratigraphy has proven successful in the correlation of carbonate-rich Neoproterozoic successions. In successions dominated by siliciclastic rocks, chemostratigraphy can be problematic, but if thin carbonates punctuate siliciclastic strata, useful isotopic data may be obtained. The upper Pocatello Formation and lower Brigham Group of southeastern Idaho provide an opportunity to assess the potential and limitations of isotopic chemostratigraphy in overwhelmingly siliciclastic successions. The 5000 m thick succession consists predominantly of siliciclastic lithologies, with only three intervals that contain thin intercalated carbonates. Its depositional age is only broadly constrained by existing biostratigraphic, sequence stratigraphic and geochronometric data. The lowermost carbonates include a cap dolomite atop diamictites and volcanic rocks of the Pocatello Formation. The δ13C values of these carbonates are distinctly negative ( −5 to −3), similar to carbonates that overlie Neoproterozoic glaciogenic rocks worldwide. Stratigraphically higher carbonates record a major positive δ13C excursion to values as high as +8.8 within the carbonate member of the Caddy Canyon Quartzite. The magnitude of this excursion is consistent with post-Sturtian secular variation recorded elsewhere in the North American Cordillera, Australia, Svalbard, Brazil and Namibia, and exceeds the magnitude of any post-Varanger δ13C excursion documented to date. In most samples, Sr-isotopic abundances have been altered by diagenesis and greenschist facies metamorphism, but a least-altered value of approximately 0.7076 supports a post-Sturtian and pre-Marinoan/Varanger age for upper Pocatello and lower Brigham rocks that lie above the Pocatello diamictite. Thus, even though available chemostratigraphic data are limited, they corroborate correlations of Pocatello Formation diamictites and overlying units with Sturtian glaciogenic rocks and immediately post-Sturtian successions in western North America and elsewhere.
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Levell, Bruce K., Howard D. Johnson, Daniel S. Collins, and Marijn Cappelle. "Deposition and preservation of fluvio‐tidal shallow‐marine sandstones: A re‐evaluation of the Neoproterozoic Jura Quartzite (western Scotland)." Sedimentology 67, no. 1 (August 8, 2019): 173–206. http://dx.doi.org/10.1111/sed.12639.
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Meireles, Carlos, A. J. D. Sequeira, Paulo Castro, and Narciso Ferreira. "Novos dados sobre a lito-estratigrafia do Grupo Beiras (Schist Greywacke Complex) na região de Góis- Arganil-Pampilhosa da Serra (Portugal Central)." Cadernos do Laboratorio Xeolóxico de Laxe. Revista de Xeoloxía Galega e do Hercínico Peninsular 37 (December 9, 2013): 105–23. http://dx.doi.org/10.17979/cadlaxe.2013.37.0.3585.
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No decurso dos levantamentos geológicos realizados na região de Góis (Portugal Central) uma nova unidade foi reconhecida no topo da Formação Boque-Serpins, caracterizada pela presença de níveis de quartzitos entrelaçados com xistos, agora chamados pela Formação Colmeal. A sua caracterização formal é agora apresentada e as suas implicações geológicas regionais são discutidas no contexto da sequência metasedimentar neoproterozóica do Grupo das Beiras (Supergrupo Dúrico-Beirão ou "Complexo Xisto-Grauvaque"). Os levantamentos geológicos em curso confirmam que a sequência, desde a base até ao topo, das formações Caneiro, Boque-Serpins e Colmeal, apresentam o mesmo padrão estrutural e de deformação, comum às três unidades. Note-se que estas unidades, definidas no sector sul de Coimbra - Lousã - Góis, têm uma ampla representação cartográfica regional, uma vez que já foram mapeadas e reconhecidas desde Arganil até à Sertã, a sul. A oeste, estender-se-ão até ao limite com as metáforas da Zona Ossa-Morena estabelecidas pela falha da chave dextral de Porto-Tomar.
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Laflamme, Marc, James G. Gehling, and Mary L. Droser. "Deconstructing an Ediacaran frond: three-dimensional preservation of Arborea from Ediacara, South Australia." Journal of Paleontology 92, no. 3 (March 14, 2018): 323–35. http://dx.doi.org/10.1017/jpa.2017.128.
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AbstractExquisitely preserved three-dimensional examples of the classic Ediacaran (late Neoproterozoic; 570–541 Ma) frond Charniodiscus arboreus Jenkins and Gehling, 1978 (herein referred to as Arborea arborea Glaessner in Glaessner and Daily, 1959) are reported from the Ediacara Member, Rawnsley Quartzite of South Australia, and allow for a detailed reinterpretation of its functional morphology and taxonomy. New specimens cast in three dimensions within sandy event beds showcase detailed branching morphology that highlights possible internal features that are strikingly different from rangeomorph and erniettomorph fronds. Combined with dozens of well-preserved two-dimensional impressions from the Flinders Ranges of South Australia, morphological variations within the traditional Arborea morphotype are interpreted as representing various stages of external molding. In rare cases, taphomorphs (morphological variants attributable to preservation) represent composite molding of internal features consisting of structural supports or anchoring sites for branching structures. Each primary branch consists of a central primary branching stalk from which emerge several oval secondary branches, which likely correspond to similar structures found in rare two-dimensional specimens. Considering this new evidence, previous synonymies within the Arboreomorpha are no longer justified, and we suggest that the taxonomy of the group be revised.
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Schoenborn, William A., Christopher M. Fedo, and G. Lang Farmer. "Provenance of the Neoproterozoic Johnnie Formation and Stirling Quartzite, southeastern California, determined by detrital zircon geochronology and Nd isotope geochemistry." Precambrian Research 206-207 (June 2012): 182–99. http://dx.doi.org/10.1016/j.precamres.2012.02.017.
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FUMES, Regiane Andrade, George Luiz LUVIZOTTO, Renato MORAES, and Edson Ricardo Maia FERRAZ. "PETROGRAFIA, QUÍMICA MINERAL E GEOTERMOBAROMETRIA DE METAPELITO DO GRUPO CARRANCAS NA NAPPE DE LUMINÁRIAS (MG)." Geosciences = Geociências 36, no. 4 (January 17, 2018): 639–54. http://dx.doi.org/10.5016/geociencias.v36i4.12150.
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A Nappe Luminárias corresponde a estrutura alongada de orientação NNE-SSW, situada na porção sul do Orógeno Brasília e de idade neoproterozoica, na borda sul do Cráton do São Francisco. Tal estrutura é composta por metapelitos e quartzitos do Grupo Carrancas. O presente trabalho foca na caracterização metamórfica das suas rochas da, utilizando petrografia, química mineral e termobarometria. A paragênese observada na porção norte é Cld+Chl+Ky+Rt+Qtz+Ms; na porção centro norte é St+Grt+Rt+Qtz+Ms e na porção sul é Grt+Ky+St+Rt+Qtz+Ms. Biotita, clorita e ilmenita retrometamórficas são obervadas no centro-norte e sul. A granada apresenta aumento de almandina e piropo em direção às bordas. As condições obtidas pelo método average PT do THERMOCALC na porção centro-norte são de 591±59 ˚C e 8,3±1,8 kbar para o pico metamórfico e 571±20 ˚C e 10,1±4,8 kbar) para o retrometamorfismo. Na porção sul foi obtido 608±47 ˚C e 11,8±2,8 kbar para o pico metamórfico. Os resultados indicam a presença de gradiente metamórfico com condições variando de fácies xisto-verde na porção norte e centro-norte a fácies anfibolito/eclogito na porção sul.
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Dyck, Brendan, Marc St-Onge, Michael P. Searle, Nicole Rayner, David Waters, and Owen M. Weller. "Protolith lithostratigraphy of the Greater Himalayan Series in Langtang, Nepal: implications for the architecture of the northern Indian margin." Geological Society, London, Special Publications 483, no. 1 (September 20, 2018): 281–304. http://dx.doi.org/10.1144/sp483.9.
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AbstractReconstruction of the protolith lithostratigraphy of amphibolite-facies metasedimentary rocks of the Greater Himalayan Series (GHS) in Nepal documents a single, long-lived passive-margin succession that was deposited along the northern margin of the Indian Craton. In the Langtang area, Paleoproterozoic gneisses are unconformably overlain by a succession of upper Neoproterozoic–Ordovician fluvio-deltaic quartzite, basinal pelite and psammitic beds that grade upsection into micaceous semipelite and pelite. U–Pb zircon geochronology yields maximum depositional ages between c. 815 and 460 Ma for the GHS in Langtang. Regional variations in the composition and thickness of the GHS along the length of the Himalaya are attributed to siliciclastic depocentres centred on Zanskar in northern India, Langtang and Everest in central to western Nepal, which contrast with coeval marine carbonate shelf deposition in the Annapurna region. The protolith lithostratigraphy documented for Langtang provides a coherent framework for interpreting subsequent Cenozoic Himalayan deformation, specifically the homogeneously distributed layer-normal shortening (i.e. flattening) and layer-parallel stretching (i.e. transport-parallel stretching) that characterizes the GHS. Within the context of a single protracted northern Indian marginal sedimentary succession, the distinction between the Lesser, Greater and Tethyan Himalaya is structural rather than lithostratigraphic in origin.
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GUPTA, SHEKHAR, R. V. Singh, Rahul Banerjee, and M. B. Verma. "Facies Architecture and Sedimentary Structures in the drill cores of Uranium Bearing Sediments of Banganapalle Formation of Palnad Sub-basin, Guntur District, Andhra Pradesh." Journal of The Indian Association of Sedimentologists 38, no. 1 (June 30, 2021): 109–18. http://dx.doi.org/10.51710/jias.v38i1.128.
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The Banganapalle Formation, the lowest member of the Neoproterozoic Kurnool Group of rocks, resting over the basement granites, has been identified as the host rock for uranium in Koppunuru area in the western part of Palnad sub-basin. The uppermost arenite facies of the Banganapalle Formation is exposed on surface and shows only few bedform indicators like ripple marks, planer laminations etc. Down-hole lithological examinations on course of core drilling in Koppunuru and adjoining areas identified five recognizable lithofacies of Banganapalle Formation, viz. basal conglomerate unit, quartzite-shale intercalated facies, and two quartz arenite facies separated by a grey shale dominated argillaceous facies.
The polymictic conglomerate, with unsorted grit to pebble size clasts of granite, shale, quartzite, vein quartz and dolerite indicate short distance transportation and derivation from nearby granitoids traversed by quartz reef/dolerite dykes. Cyclic repetitions of arenaceous and argillaceous sediments in Banganapalle lithocolumn above the basal conglomerates point to alternate rhythmic marine transgression and regression regimes. These units can also be discriminated based on their sedimentary texture, bedforms and several soft-sedimentary penecontemporaneous deformational structures (PCD) like load structure, convolute bedding/laminations, and slump structures such as micro-slips, gravity faults and folds. These syn-sedimentary structures clearly indicate perturbation and submergence of the basin contemporaneous to deposition. Cross-beds suggests change in current direction/intensity while bi-directional symmetrical ripples in outcrops of upper arenite facies suggests that the Banganapalle sediments are derived from the basement granitoids exposed to the north as well as upper Cuddapah sediments to its west. Overall, the sedimentary structures, textural and composition variation of the lithounits suggest deposition of these sediments in marginal marine, inter- to supra-tidal flat environment. The porous and permeable nature of the quartz arenite and the basal conglomerates and the presence of available reductants in the form of sulphides and carbonaceous matter make them the best suited loci for fluid movement and precipitation of uranium.
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Miao, Laicheng, Mingshuai Zhu, Chenghao Liu, Munkhtsengel Baatar, Chimidtseren Anaad, Shunhu Yang, and Xingbo Li. "Detrital-Zircon Age Spectra of Neoproterozoic-Paleozoic Sedimentary Rocks from the Ereendavaa Terrane in NE Mongolia: Implications for the Early-Stage Evolution of the Ereendavaa Terrane and the Mongol-Okhotsk Ocean." Minerals 10, no. 9 (August 22, 2020): 742. http://dx.doi.org/10.3390/min10090742.
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The Mongol-Okhotsk orogenic belt (MOB) is considered to be the youngest division of the huge Central Asian Orogenic Belt, but its origin and evolution are still enigmatic. To better understand the history of the MOB, we conducted U-Pb geochronological analyses of detrital-zircon grains from Neoproterozoic-Paleozoic sedimentary sequences as well as a volcanic suite in the Ereendavaa terrane, the southern framing unit of the MOB, in NE Mongolia. Our results show that the protoliths of the quartzite assemblage of the Ereendavaa terrane basement (or proto-Ereendavaa terrane) was deposited after ca. 1.15 Ga on a passive continental margin. The detrital-zircon age spectra of the Silurian and Devonian sedimentary sequences of the terrane demonstrate that the source areas were dominated by proximal Cambrian-Ordovician arc rocks, likely resulting from the northward subduction of the Kherlen Ocean lithosphere beneath the Ereendavaa terrane. Based on a combination of our new data with those published, we show that the Mongol-Okhotsk Ocean split from an early Paleozoic domain during, or after, the early Silurian by a mantle plume, and developed an Andean-type margin along its northern rim possibly at Middle Devonian times, and a bidirection subduction system in mid-Carboniferous at approximately 325 Ma. This bipolar subduction of the Mongol-Okhotsk Ocean might have lasted until the Triassic.
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Melo, Marilane Gonzaga de, Éder Carlos Moreira, Fábio Simplicio, Gláucia Nascimento Queiroga, Letícia Garcia D’Agostim, and Marco Paulo de Castro. "Trace-element composition of pyrite and its implications for hydrothermal process within the Mesoproterozoic metasedimentary sequences of the São Francisco Craton, northeastern Brazil." Geologia USP. Série Científica 22, no. 1 (March 31, 2022): 93–108. http://dx.doi.org/10.11606/issn.2316-9095.v22-183067.
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The distribution of trace elements in pyrite has been documented for the first time in quartz veins hosted in the Mesoproterozoic metasedimentary sequence of the Tombador Formation, São Francisco Craton, northeast Brazil. In this study, Electron Microprobe Analyses (EPMA) were used to determine the trace-element compositions of pyrite in these hydrothermal quartz veins. Three pyrite types have been distinguished and interpreted from petrographical relationships and trace-element patterns. Pre-existing pyrite (Py1), derived from the host-rock quartzite, is Ni-poor with concentrations varying from 600 – 6,100 ppm. Elongated syn-tectonic pyrite (Py2) has similar trace-element composition to the Py1, with Ni amounts ranging between 830 and 7,870 ppm. In contrast, possibly post-tectonic, euhedral to subhedral hydrothermal pyrite (Py3), contains higher contents of Ni (7,970 – 26,120 ppm). Mafic and/or metasedimentary rocks from the Espinhaço Supergroup were probably the source of Ni for this fluid-flow event. Fluid generation is related to the devolatilization of the base of the thickened crust, with migration of fluids by preexisting structures. Several shear zones and large-scale NNW-trending folds were developed during the inversion of the Espinhaço basin, as a result of the ca. 0.6 Ga Brasiliano orogenic event. Regional fluid movement through the crust at this time is supported by several mineralized veins and hydrothermal deposits in the São Francisco Craton and adjacent Neoproterozoic belts.
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Kanygina, Nadezhda A., Andrey A. Tretyakov, Kirill E. Degtyarev, Victor P. Kovach, Sergei Yu Skuzovatov, Kwan-Nang Pang, Kuo-Lung Wang, and Hao-Yang Lee. "Late Mesoproterozoic–early Neoproterozoic quartzite–schist sequences of the Aktau–Mointy terrane (Central Kazakhstan): Provenance, crustal evolution, and implications for paleotectonic reconstruction." Precambrian Research 354 (March 2021): 106040. http://dx.doi.org/10.1016/j.precamres.2020.106040.
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Amato, Jeffrey M. "Detrital zircon ages from Proterozoic, Paleozoic, and Cretaceous clastic strata in southern New Mexico, U.S.A." Rocky Mountain Geology 54, no. 1 (May 1, 2019): 19–32. http://dx.doi.org/10.24872/rmgjournal.54.1.19.
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ABSTRACT U-Pb ages were obtained from detrital zircon grains from Proterozoic, Ordovician, Devonian, Pennsylvanian, and Cretaceous clastic sedimentary rocks in southern New Mexico and are compared to previously published data from Proterozoic, Cambrian, Permian, and other Cretaceous strata. This provides the first combined data set from most of the known pre-Cenozoic clastic formations in southern New Mexico, albeit in a reconnaissance fashion. Proterozoic quartzite, conglomerate, and lithic sandstone yield mostly 1.65-Ga zircon ages that were derived from the Mazatzal province, with minor 1.8–1.7-Ga zircon ages from the Yavapai province. The Cambrian–Ordovician Bliss Sandstone is dominated by Grenville-age grains and Cambrian grains inferred to be locally derived. Newly acquired ages from the Ordovician Cable Canyon Sandstone are dominated by 1.7–1.6-Ga Mazatzal province zircon grains, whereas new data from the Devonian Percha Shale indicate subequal contributions from 1.7–1.6-Ga and ~1.4-Ga sources, along with 1.8–1.7-Ga zircon ages. Both of these formations likely had mainly distal sources as the Precambrian basement in the region was largely buried by older Paleozoic strata. New data from a sandstone in the Pennsylvanian La Tuna Formation show mostly Yavapai grains and minor Paleozoic zircon grains, including Cambrian zircon grains sourced from the nearby Florida Mountains landmass postulated to have been exposed during Pennsylvanian time. The Permian ‘Abo tongue’/Robledo Mountains Formation of the Hueco Group has mostly Neoproterozoic and Grenville-age zircon grains and was derived from Ancestral Rocky Mountain uplifts that did not have a large ~1.4-Ga component. The Aptian Hell-to-Finish Formation of the Bisbee Group has mostly Yavapai-aged zircon grains in the pre-1000-Ma age group, but younger Albian- and Campanian-age sandstones have mostly Grenville-age zircon grains. New data from the Albian Beartooth Quartzite indicate syndepositional volcanic grains at 102 Ma and support correlations with the Mojado Formation rather than the younger Dakota Sandstone. Archean zircon ages are rare overall in all of the strata in southern New Mexico, but zircon grains with ages of ~2.74 Ga are most abundant. These grains could have been derived from basement rocks in the Wyoming or Superior provinces, or recycled from sediment originally derived from those sources.
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Carvalho, Manuela de Oliveira, Claudio de Morisson Valeriano, Pamela Alejandra Aparicio González, Gustavo Diniz Oliveira, and Agnes Impiccini. "The thrust contact between the Canastra and Vazante groups in the Southern Brasília Belt: structural evolution, white mica crystallinity and implications for the Brasiliano orogeny." Brazilian Journal of Geology 46, no. 4 (December 2016): 567–83. http://dx.doi.org/10.1590/2317-4889201620160052.
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ABSTRACT: Two regional thrust-sheets of Neoproterozoic metasedimentary rocks occur in the Southern Brasília Belt, northwest Minas Gerais. The lower one comprises the Vazante Group, that is formed in the studied area, from base to top, by the Serra do Garrote (metapelites interlayered with carbonaceous phyllite), Serra do Poço Verde (beige to pink stromatolitic metadolomite with interlayered greenish slates), Morro do Calcário (gray stromatolitic metadolomite interlayered with gray slates) and Serra da Lapa (phyllite with dolarenitic lenses interlayered with slates) formations. The upper thrust sheet consists of the Canastra Group (Paracatu formation): laminated sericite phyllites and carbonaceous phyllites interlayered with quartzite. The Braziliano orogeny resulted in four phases of contractional deformation, associated with low-grade metamorphism. The first two (D1 and D2) are ductile, while the third and fourth ones (D3 and D4) are brittle-ductile. D1 developed a slaty S1 cleavage subparallel to the primary layering, with shallow to steep dips to NW. D2 developed a crenulation cleavage (S2) that dips moderately to NW and is associated with tight to isoclinal folds. D3 and D4 phases developed crenulations and open folds and kink bands. S3 dips steeply to NW, while S4 has moderate to steep dips to NE and SW. White mica crystallinity (Kübler index) measurements in metapelites indicate that both the Canastra and Vazante groups reached anchizone/epizone conditions, and metamorphic discontinuities along thrusts indicate that the peak of metamorphism is pre or syn-thrusting.
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Verhaert, Michèle, Atman Madi, Abdelaziz El Basbas, Mohamed Elharkaty, Abdellah Oummouch, Lahcen Oumohou, Annelies Malfliet, Lhou Maacha, and Johan Yans. "Genesis of As-Pb-Rich Supergene Mineralization: The Tazalaght and Agoujgal Cu Deposits (Moroccan Anti-Atlas Copperbelt)." Economic Geology 115, no. 8 (October 23, 2020): 1725–48. http://dx.doi.org/10.5382/econgeo.4779.
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Abstract In the Moroccan Anti-Atlas, sulfide deposits hosted by Neoproterozoic to Cambrian formations underwent significant weathering, leading to the formation of supergene profiles. In the Tazalaght Cu-As deposit, three mineralogical steps are distinguished: (1) the replacement of hypogene sulfides (chalcopyrite, pyrite, tennantite) by supergene sulfides (bornite, chalcocite) in the large cementation zone; (2) the formation of oxidized minerals (malachite, azurite, olivenite, and chenevixite, mainly) in a more oxidizing and neutral environment; and (3) the precipitation of goethite, hematite, and quartz in the gossan. In the Cu-As-Pb-V deposit of Agoujgal, the mineralogical units are spatially less confined than at Tazalaght. The narrow cementation zone hosts chalcocite, resulting from the weathering of hypogene chalcopyrite, pyrite, tennantite and galena, while the much more extended and diversified oxidized zone is rich in Cu and Pb carbonates, arsenates, sulfates, phosphates, vanadates, and oxides. Goethite, hematite, mottramite, and late calcite occur in the gossan. Both deposits are characterized by As-rich secondary ores that were formed through similar processes, despite some mineralogical and chemical variations highlighting the influence of the host rocks on weathering. The restricted oxidized mineralization at Tazalaght and the Agoujgal cementation zone most likely arise from the contrasting omnipresence of quartzite at Tazalaght that could not enable a fast and effective neutralization of the fluid’s acidity, and the large amounts of dolomitic host rocks that could be dissolved at Agoujgal. At both sites, the weathering of tennantite through a boxwork texture records the transition from the cementation zone (chalcocite), the oxidized zone (arsenates), and the gossan, and reflects the fluids evolution with time.
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Chew, David M., Nicola Fallon, Christine Kennelly, Quentin Crowley, and Michael Pointon. "Basic volcanism contemporaneous with the Sturtian glacial episode in NE Scotland." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 100, no. 04 (December 2009): 399–415. http://dx.doi.org/10.1017/s1755691009009037.
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ABSTRACTThe Dalradian Supergroup contains three distinct glacigenic units, formerly termed ‘Boulder Beds’, which are correlated with widespread Neoproterozoic glaciations. The oldest and thickest unit, the Port Askaig Formation, marks the Appin–Argyll group boundary of the Dalradian Supergroup and has been correlated with the Middle Cryogenian (Sturtian) glaciation. The Auchnahyle Formation, a diamictite-bearing sequence near Tomintoul in NE Scotland, exhibits strong lithological similarities to the Port Askaig Formation. Both these glacigenic ‘Boulder Bed’ units contain abundant dolomite clasts in their lower parts and more granitic material at higher levels. Both metadiamictite units are overlain by thick shallow-marine quartzite units. C isotope data from Appin Group carbonate strata below the Auchnahyle Formation support this correlation. U–Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) detrital zircon data from the Auchnahyle Formation metadiamictite differ slightly from the Port Askaig Formation, but are similar to detrital zircon spectra obtained from the Macduff Formation, a diamictite unit in the younger Southern Highland Group of the Dalradian Supergroup; both apparently reflect derivation from local basement rocks. No detritus younger than 0·9 Ga is observed, so the data do not constrain significantly the depositional age of the glacial strata. A thin tholeiitic pillow basalt unit in the lower part of the Auchnahyle Formation is geochemically distinct from pre-tectonic metadolerite sills and from basic metavolcanic rocks up-section. A Sturtian (c. 720–700 Ma) age for the Auchnahyle Formation metadiamictite would imply that this basaltic volcanism represents the oldest recorded volcanic activity in the Dalradian Supergroup and is inferred to represent an early, local phase of proto-Iapetan rifting within the Rodinian supercontinent.
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Higgins, A. K. "East Greenland Caledonides: stratigraphy, structure and geochronology." Geological Survey of Denmark and Greenland (GEUS) Bulletin 6 (December 30, 2004): 1–4. http://dx.doi.org/10.34194/geusb.v6.4814.
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The East Greenland Caledonides extend from 70° to 81°30′N, and have been the subject of a series of regional mapping programmes between 1968 and 1998. The entire orogen is now covered by five published 1:500 000 geological map sheets. The six papers in this bulletin concern a variety of topics relating mainly to Kronprins Christian Land (79°–81°30′N) and the Kong Oscar Fjord region (72°–75°N).The paper by Smith et al. on Lower Palaeozoic stratigraphy proposes amendments to several stratigraphical units that occur in Kronprins Christian Land and nearby Lambert Land. In the Kong Oscar Fjord region, two new formations are defined for quartzite and limestone/dolostone units that crop out in foreland windows, and the Lower Palaeozoic succession of the fjord region of East Greenland is formally placed in the Kong Oscar Fjord Group. The second paper by Smith et al. describes and formally defines the Neoproterozoic Rivieradal Group of Kronprins Christian Land. The paper by Higgins et al. analyses the thinskinned fold-and-thrust belt that marks the transition between foreland and orogen in Kronprins Christian Land, and presents a balanced cross-section restoration.The two geochronological papers by Thrane report the results of ion microprobe zircon analyses from orthogneisses in the Charcot Land window (72°N), and results of reconnaissance Pb-Pb dating by the stepleaching method.The final paper by Higgins & Leslie reviews the history of geological research in the Eleonore Sø and Målebjerg areas of the Kong Oscar Fjord region (72°–75°N). Recognition that the two areas are part of the Caledonian foreland implies that the two thrust sheets structurally overlying the Eleonore Sø and Målebjerg windows have large displacements (~ 100 km each), and that the 'stockwerke' concept of the orogen that focused on in situ vertical movements can finally be laid to rest.
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Olivarius, Mette, Thomas F. Kokfelt, Henrik Friis, J. Richard Wilson, and Mette Olivarius. "Proterozoic basement and Palaeozoic sediments in the Ringkøbing–Fyn High characterized by zircon U–Pb ages and heavy minerals from Danish onshore wells." Bulletin of the Geological Society of Denmark 63 (May 29, 2015): 29–44. http://dx.doi.org/10.37570/bgsd-2015-63-04.
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New data from the Proterozoic basement and scattered Palaeozoic sediments in the Ringkøbing–Fyn High including zircon U–Pb geochronometry, heavy mineral compositions and whole rock geochemistry is presented here to provide a frame of reference for detrital provenance studies. The Ringkøbing–Fyn High is a WNW–ESE trending structural high including subcropping basement rocks, and the results indicate that it is a southerly extension of the Fennoscandian Shield. The zircon data show matching age distribution patterns in crystalline basement rocks obtained from two drill sites, the Glamsbjerg-1 and Grindsted-1 wells. They both record a characteristic Telemarkian accretionary event at 1.51 and 1.48 Ga and a Sveconorwegian metamorphic overprinting at 1.08 Ga. Furthermore, the dominant age intervals in the Glamsbjerg High (1.55–1.48 Ga) and the Grindsted High (1.51–1.44 Ga) suggest that rocks of the Gothian orogeny (that ended at 1.52 Ga) are only present in the eastern part of the Ringkøbing–Fyn High. Thus, the buried basement in central Denmark may be youngest towards the west, which is consistent with the general westward age progression trend in the Sveconorwegian Orogen. The basement breccia in the Arnum-1 well on the southern flank of the Ringkøbing–Fyn High has zircon ages (c. 1.54–1.53 Ga) that resemble those of gneiss in the Glamsbjerg High. The conglomeratic sandstone in the Ringe-1 well on the Glamsbjerg High has a dual age distribution as the matrix has late Palaeoproterozoic to early Mesoproterozoic ages, whereas the granitic clasts have a distinct middle Neoproterozoic age (c. 0.76 Ga) that may indicate an Avalonian source. The quartzite in the Slagelse-1 well on the northern flank of the Ringkøbing–Fyn High has a broad age span with late Palaeoproterozoic to late Mesoproterozoic zircon ages. Supplementary material: Detailed documentation of U/Pb analytical procedures, results and analysed zircon spots are available below.
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Goodman, S., A. Crane, M. Krabbendam, A. G. Leslie, and A. Ruffell. "Correlation of depositional sequences in a structurally complex area: the Dalradian of Glenn Fearnach to Glen Shee, Scotland." Transactions of the Royal Society of Edinburgh: Earth Sciences 87, no. 4 (1996): 503–13. http://dx.doi.org/10.1017/s0263593300018162.
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ABSTRACTThe stratigraphy of the Neoproterozoic Dalradian Supergroup has been formalised at group, subgroup and formation level, based largely on mapping in the SW Highlands of Scotland. Elsewhere, there has been a tendency for the lithostratigraphy to be fitted into this framework, implying that the lithostratigraphy represents basin-wide changes in depositional environment. The pitfalls of this ‘layer-cake’ approach are illustrated by interpreting the geology of the Gleann Fearnach to Glen Shee area of the Central Highlands, using the published maps of the adjacent regions. Attempts to correlate units into the Braemar area in the NE and into the Pitlochry area in the SW show considerable mismatch between the maps covering these areas, which has in the past led to invocation of geometrically unlikely arrangements of faults and slides to explain the lithostratigraphical distribution.The present study is the result of a different approach adopted during remapping of the Gleann Fearnach to Glen Shee area. Some basin-wide events, here suggested to be associated with key sequence stratigraphic surfaces, were identified. These principally relate to the deposition of Appin Quartzite, Boulder Bed and Ben Lawers Schist precursor sediments. Between these reference units the stratigraphy has been determined by detailed field mapping, and variation from the standard stratigraphy explained in terms of both the position within the depositional sequence and palaeogeography during deposition. This has led to an integrated solution which works on both sedimentological and structural grounds. There are local implications for the stratigraphy and structural geology elsewhere in the Scottish Dalradian, but, more importantly, it is an approach which must be more widely applied in order to make wider correlations beyond the British Dalradian to the rest of the Laurentian margin.
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Gannaway Dalton, C. Evelyn, Katherine A. Giles, Mark G. Rowan, Richard P. Langford, Thomas E. Hearon, and J. Carl Fiduk. "Sedimentologic, stratigraphic, and structural evolution of minibasins and a megaflap formed during passive salt diapirism: The Neoproterozoic Witchelina diapir, Willouran Ranges, South Australia." Journal of Sedimentary Research 90, no. 2 (February 20, 2020): 165–99. http://dx.doi.org/10.2110/jsr.2020.9.
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ABSTRACT This study documents the growth of a megaflap along the flank of a passive salt diapir as a result of the long-lived interaction between sedimentation and halokinetic deformation. Megaflaps are nearly vertical to overturned, deep minibasin stratal panels that extend multiple kilometers up steep flanks of salt diapirs or equivalent welds. Recent interest has been sparked by well penetrations of unidentified megaflaps that typically result in economic failure, but their formation is also fundamental to understanding the early history of salt basins. This study represents one of the first systematic characterizations of an exposed megaflap with regards to sub-seismic sedimentologic, stratigraphic, and structural details. The Witchelina diapir is an exposed Neoproterozoic primary passive salt diapir in the eastern Willouran Ranges of South Australia. Flanking minibasin strata of the Top Mount Sandstone, Willawalpa Formation, and Witchelina Quartzite, exposed as an oblique cross section, record the early history of passive diapirism in the Willouran Trough, including a halokinetically drape-folded megaflap. Witchelina diapir offers a unique opportunity to investigate sedimentologic responses to the initiation and evolution of passive salt movement. Using field mapping, stratigraphic sections, petrographic analyses, correlation diagrams, and a quantitative restoration, we document depositional facies, thickness trends, and stratal geometries to interpret depositional environments, sequence stratigraphy, and halokinetic evolution of the Witchelina diapir and flanking minibasins. Top Mount, Willawalpa, and Witchelina strata were deposited in barrier-bar-complex to tidal-flat environments, but temporal and spatial variations in sedimentation and stratigraphic patterns were strongly influenced from the earliest stages by the passively rising Witchelina diapir on both regional (basinwide) and local minibasin scales. The salt-margin geometry was depositionally modified by an early erosional sequence boundary that exposed the Witchelina diapir and formed a salt shoulder, above which strata that eventually became the megaflap were subsequently deposited. This shift in the diapir margin and progressive migration of the depocenter began halokinetic rotation of flanking minibasin strata into a megaflap geometry, documenting a new concept in the understanding of deposition and deformation during passive diapirism in salt basins.
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Uhlein, Alexandre, Fabrício de Andrade Caxito, Julio Carlos Destro Sanglard, Gabriel Jubé Uhlein, and Guilherme Labaki Suckau. "ESTRATIGRAFIA E TECTÔNICA DAS FAIXAS NEOPROTEROZÓICAS DA PORÇÃO NORTE DO CRATON DO SÃO FRANCISCO." Geonomos, February 8, 2013. http://dx.doi.org/10.18285/geonomos.v19i2.38.
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Apresenta-se uma síntese da estratigrafia e tectônica das faixas dobradas neoproterozóicas da margem norte do Cráton do São Francisco. A Faixa Rio Preto, que ocorre na margem noroeste, no noroeste da Bahia e sul do Piauí, é constituída pela Formação Formosa (mica xistos granatíferos, xistos verdes, anfibolitos) de idade paleoproterozóica (~1,9 Ga) e pela Formação Canabravinha (metadiamictitos, quartzitos, mica xistos) de idade neoproterozóica (850-600 Ma). A deformação neoproterozóica originou uma estrutura complexa em leque assimétrico divergente, entre 600 e 540 Ma atrás. A Faixa Riacho do Pontal, que ocorre na margem norte do cráton, entre os estados da Bahia, Pernambuco e Piauí, é constituída pelo Grupo Casa Nova, com biotita xistos granatíferos, carbonatos, quartzitos e rochas metavulcânicas (xistos verdes, anfibolitos, metaultrabasitos) intensamente deformados em estilo tangencial na porção externa da faixa dobrada, com vergência para o cráton, e transcorrente destrógira (Lineamento de Pernambuco) em sua porção interna. Intrusões graníticas sin a tardi-colisionais sugerem que a deformação tangencial ocorreu entre 668 e 555 Ma atrás. A Faixa Sergipana, situada na margem nordeste do Cráton do São Francisco, nos estados de Sergipe e Alagoas, é constituída pelos Grupos Miaba (quartzitos, metapelitos, metacarbonatos), Vaza-Barris (metadiamictitos, metacarbonatos, metassiltitos e filitos) e Macururé (metaritmitos, biotita xistos, quartzitos), especialmente na região centro-sul. Estas unidades estratigráficas foram envolvidas em importante deformação tangencial vergente para o cráton, a aproximadamente 630-560 Ma atrás. As faixas Rio Preto, Riacho do Pontal e Sergipana representam um sistema orogênico de mais de 1000 km de extensão, desenvolvido diacronicamente na margem norte do Cráton do São Francisco, durante o Neoproterozóico.Palavras-chave: Faixas dobradas neoproterozóicas, estratigrafia, geologia estrutural, geotectônica. ABSTRACT: STRATIGRAPHY AND TECTONICS OF THE NEOPROTEROZOIC FOLD BELTS IN THE NORTHERN SÃO FRANCISCO CRATON. We present a stratigraphic and tectonic review of the neoproterozoic fold belts in the northern São Francisco Craton. The Rio Preto fold belt, which occurs in the northwestern margin of the São Francisco Craton, in Bahia and Piauí states, is represented by the paleoproterozoic (~1,9 Ga) Formosa Formation (schists, quartzites, greenschists and amphibolites), and the neoproterozoic (850-600Ma) Canabravinha Formation (metadiamictites, quartzites and schists). The neoproterozoic deformation originated a complex assymetrical doubly-vergent fan structure, between 600 and 540 Ma ago. The Riacho do Pontal fold belt, which occurs in the northern margin of the São Francisco Craton, in Bahia, Pernambuco and Piauí states, is represented by the Casa Nova Group, with biotite schists, carbonates, quartzites and metavolcanics (green schists, amphybolites, metaultrabasics) highly deformed in a craton-verging tangencial style at the outer parts of the fold belt and in dextral transcurrent style at its inner parts (Pernambuco lineament). Syn to late collisional granitic intrusions suggests that the tangencial deformation occurred in between 667 and 555 Ma ago. The Sergipana fold belt, situated in the northestern margin of São Francisco Craton, in Sergipe and Alagoas states, is represented by the Miaba (quartzites, metapelites and metacarbonates), Vaza-Barris (metadiamictites, metacarbonates, metasiltites and phyllites) and Macururé (metarithmytes, biotite schists, quartzites) groups. These units are involved in an important craton-verging tangencial deformation, developed in between 630 and 560 Ma ago. The Rio Preto, Riacho do Pontal and Sergipana fold belts represent a 1000 km wide orogenic system developed in the northern margin of the São Francisco Craton, during the Neoproterozoic.Keywords: Neoproterozoic fold belts, stratigraphy, structural geology, geotectonics
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Aracema, Laurenn Wolochate, Ana Carolina Neves, Juliana Cristina Henriques Ferreira, Antônio Carlos Pedrosa-Soares, Lydia Maria Lobato, and Carlos Maurício Noce. "NOVAS EVIDÊNCIAS DE REMANESCENTES OCEÂNICOS NA FAIXA ARAÇUAÍ: AS ROCHAS META-ULTRAMÁFICAS DE SÃO JOSÉ DA SAFIRA." Geonomos, July 1, 2000. http://dx.doi.org/10.18285/geonomos.v8i1.148.
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Neoproterozoic oceanic slivers have been characterized in the Araçuaí Belt, eastern Brazil. Close to the SãoJosé da Safira town, Minas Gerais State, meta-ultramafic rocks consist of serpentinite with preservedperidotite cores, talc-anthophyllite schists, a diopside-rich rock, and tremolite schist. They are closelyassociated with banded iron formation (magnetic oxide, sulfide and silicate types), muscovite schist andgraphite schist. This rock assemblage is interpreted as an ophiolitic mélange emplaced by thrusts betweentwo different units. One of them, correlated to the Salinas Formation, consists of quartz-mica schist (withgarnet, staurolite, kyanite, and/or sillimanite), sedimentary-derived calc-silicate rock, and sparseorthoamphibolite. The unit correlated to the Capelinha Formation consists of orthoquartzite, hematite andmica quartzites. All described rocks were transported from NE to SW in response to a dextral, obliquethrustsystem. Geochemical data from metaultramafic rocks of São José da Safira indicate an ophioliticorigin. The comparison with data from other Neoproterozoic oceanic remnants (Abadiânia and Fuchuan)corroborates this interpretation.
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Gradim, Daniel Tavares, Gláucia Nascimento Queiroga, Tiago Amâncio Novo, Carlos Maurício Noce, Antônio Carlos Pedrosa-Soares, Antônio Wilson Romano, Maximiliano Martins, Fernando Flecha de Alkmim, Camila Franco Basto, and Moisés Abraão Suleiman. "GEOLOGIA DA REGIÃO DE JEQUERI-VIÇOSA (MG), ORÓGENO ARAÇUAÍ MERIDIONAL." Geonomos, February 11, 2013. http://dx.doi.org/10.18285/geonomos.v19i2.47.
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RESUMO: A característica fundamental da região de Jequeri-Viçosa, situada no extremo sul do Orógeno Araçuaí, é a abundância de rochas metamórficas, ortoderivadas e paraderivadas, de fácies anfibolito alto e granulito. O embasamento paleoproterozóico é representado, a oeste, por ortognaisses tonalíticos a graníticos do Complexo Mantiqueira e, a leste, por ortognaisses charno-enderbíticos do Complexo Juiz de Fora. Ambos os complexos incluem anfibolitos e exibem intensidades variáveis de migmatização. O contato entre eles é marcado pela zona de cisalhamento transpressiva destral de Abre Campo, interpretada como uma sutura paleoproterozóica reativada no Neoproterozóico. O Anfibolito Santo Antônio do Grama e rochas meta-ultramáficas associadas (Córrego do Pimenta) representam restos ofiolíticos ediacaranos, colocados ao longo da Zona de Cisalhamento de Abre Campo. Assentada sobre o embasamento, na parte oeste da área, ocorre uma associação metavulcano-sedimentar neoproterozóica do Grupo Dom Silvério, composta por xistos diversos e quartzito. Na porção leste da área mapeada, a cobertura metassedimentar neoproterozóica é atribuída ao Grupo Andrelândia que inclui paragnaisse migmatítico e raro quartzito. Corpos de hidrotermalito quartzoso, indiscriminadamente associados às unidades do embasamento e da cobertura neoproterozóica, ocorrem ao longo de zonas de cisalhamento. Hidrotermalitos ferruginosos associam-se ao Complexo Mantiqueira na Zona de Cisalhamento de Ponte Nova. O granito foliado a milonitizado da Serra dos Vieiras parece ser um produto de fusão parcial do paragnaisse Andrelândia. Completam o quadro geológico os pegmatitos da Suíte Paula Cândico e diques de diabásio mesozóicos.Palavras-chave: Paleoproterozóico, Neoproterozóico, Orógeno AraçuaíABSTRACT: GEOLOGY OF THE JEQUERI-VIÇOSA REGION, MINAS GERAIS STATE, SOUTHERN ARAÇUAÍ OROGEN. This paper focuses on the southwestern sector of the Araçuaí orogen in a region located close to the boundary with the northern Ribeira orogen. This region is rich in ortho- and para-derived metamorphic rocks of the high amphibolite and granulite facies. The Paleoproterozoic basement includes, to the west, tonalitic to granitic orthogneisses of the Mantiqueira Complex and, to the east, enderbitic to charnockitic orthogneisses of the Juiz de Fora Complex. Both complexes also include amphibolite enclaves and show several rates of partial melting. The contact between them is marked by the dextral transpressional Abre Campo shear zone, considered to be a Paleoproterozoic suture reactivated during the Neoproterozoic Era. The Santo Antônio do Grama Amphibolite and associated meta-ultramafic rocks (Córrego do Pimenta) are Ediacaran ophiolite slivers emplaced along the Abre Campo shear zone. In the western part of the region, the Paleoproterozoic basement is locally covered by a metavolcano-sedimentary assemblage composed of amphibolite facies schist and quartzite of the Neoproterozoic Dom Silvério Group. To the east, the Neoproterozoic cover comprises the migmatized paragneiss and rare quartzite of the Andrelândia Group. The Serra dos Vieiras foliated to mylonitic granite seems to be formed from the partial melting of the Andrelândia paragneiss. Pegmatites of the Paula Cândido Suite and Mesosozic diabase dikes complete the geologic framework of the mapped area.Keywords: Paleoproterozoic, Neoproterozoic, Araçuaí Orogen
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Reusch, Douglas N., Christopher S. Holm-Denoma, and John F. Slack. "U–Pb zircon geochronology of Proterozoic and Paleozoic rocks, North Islesboro, coastal Maine (USA): links to West Africa and Penobscottian orogenesis in southeastern Ganderia?" Atlantic Geology, July 14, 2018, 189–221. http://dx.doi.org/10.4138/atlgeol.2018.007.
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Within the Ganderian inlier of Penobscot Bay, coastal Maine, the Islesboro fault block occupies a central position between the St. Croix terrane of continental affinity and, to the east, the Ellsworth terrane of oceanic affinity. New field, petrographic, geochemical, and U–Pb LA-ICP-MS geochronological data on detrital and magmatic zircon grains constrain the provenance and transfer history of these terranes from Gondwana to the Appalachian margin of Laurentia. On North Islesboro, the Coombs Limestone and Hutchins Island Quartzite (new name), intruded by E-MORB amphibolite, constitute a newly recognized local inlier of Proterozoic basement. Together with the nearby Seven Hundred Acre Island Formation, these mature, carbonate-rich strata record deposition on a low-latitude passive margin. Abundant detrital zircon grains in the Hutchins Island Quartzite, all older than ca. 1.8 Ga, have a predominant population at ca. 2.0 Ga and a small peak between ca. 2.8 Ga and 2.4 Ga, an age spectrum strikingly similar to those of both the Paleoproterozoic Taghdout Quartzite in Morocco, on the West African craton, and basement rocks from Georges Bank, offshore Massachusetts. The overlying Neoproterozoic–Cambrian Islesboro Formation records a second period of extension (interstratified EMORB greenstone) synchronous with accumulation of interbedded siliciclastic and carbonate sediment, prior to recumbent folding. At the base of the moderately deformed Turtle Head Cove (new name) cover sequence, immature greywacke has a youngest zircon population of ca. 515 Ma, large late Neoproterozoic populations (ca. 624 Ma and 678 Ma), a small peak at 1.2 Ga, a moderate number of ca. 1.5 Ga to 2.0 Ga grains, and a few Late Archean grains. Compared with many similar Ganderian age spectra reported from Vermont to New Brunswick, which are all consistent with a source in either the Amazonian or West African cratons, this new age spectrum most closely resembles those from quartzites in the Grand Manaan and Brookville terranes of coastal New Brunswick. Significantly, exotic blocks lithologically indistinguishable from Proterozoic strata on Islesboro occur in the St. Croix terrane within a Lower Ordovician black shale mélange at the base of the Penobscot Formation, suggesting that the St. Croix terrane, Islesboro block, and Ellsworth terrane were initially juxtaposed by Penobscottian thrusting prior to the Middle Ordovician. Subsequently, the Islesboro block was isolated between the bounding post-Silurian, pre-Late Devonian Turtle Head and Penobscot Bay dextral strike-slip faults. Along the North Islesboro fault, a fault-bounded lens of foliated pyritic felsic volcanic and volcaniclastic rock, dated at ca. 372 Ma and containing Devonian to Archean detrital zircons, records late Paleozoic deformation recognized previously in coastal New Brunswick but not in Penobscot Bay.
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Silva, Sebastião Milton P. da, Álvaro P. Crósta, Francisco J. F. Ferreira, Hartmut Beurlen, Adalene M. Silva, and Marcelo R. R. da Silva. "IDENTIFICAÇÃO GAMAESPECTROMÉTRICA DE PLACERES RUTILO-MONAZÍTICOS NEOPROTEROZÓICOS NO SUL DA FAIXA SERIDÓ, NORDESTE DO BRASIL." Revista Brasileira de Geofísica 28, no. 1 (March 6, 2010). http://dx.doi.org/10.22564/rbgf.v28i1.1853.
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Dados digitais de um aerolevantamento gamaespectrométrico cobrindo seqüência crustal Neoproterozóica da Faixa Seridó (FSe) foram processados e analisados juntamente com medidas de gamaespectrometria terrestre, fotos aéreas e dados geológicos de campo, objetivando a caracterização e o mapeamento litogeofísico de granitos pegmatíticos e campos de pegmatitos associados, bem como de litologias e unidades litoestratigráficas do Grupo Seridó. A interpretação das imagens individuais e ternária dos canais do urânio (eU), do tório (eTh) e do potássio (K), além das razões eU/eTh e eTh/K, possibilitou a identificação de anomalias de tório associadas a metaconglomerados e metarenitos intercalados nos quartzitos da Formação Equador, constituídos de fragmentos e seixos de quartzo, muscovita e concentrações de minerais pesados, dominantemente hematita, ilmenita, monazita, rutilo, titanita e zircão. A análise semiquantitativa em grãos minerais de duas amostras dessas rochas, por microscopia de varredura eletrônica (MEV-EDS), revelou teores máximos de 79,4% de ThO2 e 87,7% de ETR (Ce, La, Nd) em monazitas; 99,2% de TiO2 em ilmenita e rutilo e 1,81 % de Hf02 em zircão. Também foram identificadas anomalias de tório em sedimentos de idade cenozóica na mesma região.Keywords : gamaespectrometria; sensoriamento remoto; placeres rutilo-monazíticos; Província Borborema; Faixa Seridó.ABSTRACTAerial gamma-ray survey data covering Neoproterozoic supracrustal sequences in the Seridó Belt were processed and analyzed together with ground gamma-ray data, air photos and geological data for lithogeophysical characterization and mapping of granitic rocks, related pegmatites fields and lithological units of Seridó Group. Interpretation was based on individual and ternary images of the three radio-elements and the eU/eTh and eTh/K ratios, and allowed the discovery of thorium anomalies associated with coarse-grained metarenites and metaconglomerates facies intercalated with quartzites of the Equador Formation. High contents of iron oxides, ilmenite, monazite, rutile, titanite and zircon were identified by ore microscopy of polished sections in the metaconglomerate's matrix. Semiquantitative scanning electron microscopy (SEM) analyses in minerals of two samples revealed up to 79.4% of Th02 and 87.7% of REE in monazites; up to 99.2% of Ti02 in ilmenite and rutile and up to 1.81 % of HfO2 in zircon. Gamma-ray anomalies due to thorium were also identified in association with sediments of Cenozoic age in the region.Keywords : gamma-ray spectrometry; remote sensing; rutile-monazite placers; Borborema Province; Seridó Belt.
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Craddock, John P., Timothy Paulsen, Renata de Silva Schmitt, Stephen T. Johnston, Paul M. Myrow, and Nigel C. Hughes. "Amalgamation of Gondwana: Calcite Twinning and Finite Strains from the early to late Paleozoic Buzios, Ross, Kurgiakh, and Gondwanide Orogens." Geological Society, London, Special Publications 531, no. 1 (November 3, 2022). http://dx.doi.org/10.1144/sp531-2022-165.
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Abstract Oriented carbonate (calcite twinning strains; n=78 with 2414 twin measurements) and quartzites (finite strains, n=15) were collected around Gondwana to study the deformational history associated with the amalgamation of the supercontinent. The Buzios orogen (545-500 Ma), within interior Gondwana, records the high-grade collisional orogen between São Francisco craton (Brazil) and Congo-Angola craton (Angola-Namibia) and twinning strains in calcsilicates record a SE-NW shortening fabric parallel to thrust transport. Along Gondwana's southern margin, the Saldanian-Ross-Delamerian orogen (590-480 Ma) is marked by a regional unconformity that cuts into deformed Neoproterozoic-Ordovician sedimentary rocks and associated intrusions. Cambrian carbonate is preserved in the central part of the southern Gondwana margin, namely in the Kango inlier of the Cape fold belt and the Ellsworth, Pensacola and Transantarctic Mountains. Paleozoic carbonate is not preserved in the Ventana Mountains, Argentina; Islas Malvinas/Falkland Islands or Tasmania. Twinning strains in these Cambrian carbonate strata and synorogenic veins record a complex, overprinted deformation history with no stable foreland strain reference. The Kurgiakh orogen (490 Ma) along Gondwana's northern margin is also defined by a regional Ordovician unconformity throughout the Himalaya; these rocks record a mix of layer-parallel and layer-normal twinning strains with a likely Himalayan (40 Ma) strain overprint and no autochthonous foreland strain site. Conversely, the Gondwanide orogen (250 Ma) along Gondwana's southern margin has three foreland (autochthonous) sites for comparison with 59 allochthonous thrust belt strain analyses. From west to east: finite strains from Devonian quartzite preserve a layer-parallel shortening (LPS) strain rotated clockwise in the Ventana Mountains, Argentina; the frontal (calcite twins) and internal (quartzite strains) samples in the Cape belt preserve a LPS fabric that is rotated clockwise from the autochthonous N-S horizontal shortening in the foreland strain site; Falkland Devonian quartzite shows the same clockwise rotation of the LPS fabric; Permian limestone and veins in Tasmania record a thrust transport-parallel LPS fabric. Early amalgamation of Gondwana (Ordovician) is preserved by local layer-parallel and layer-normal strain without evidence of far-field deformation whereas the Gondwanide orogen (Permian) is dominated by layer-parallel shortening, locally rotated by dextral shear along the margin, that propagated across the supercontinent.
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Knauer, Luiz Guilherme. "O SUPERGRUPO ESPINHAÇO EM MINAS GERAIS: CONSIDERAÇÕES SOBRE SUA ESTRATIGRAFIA E SEU ARRANJO ESTRUTURAL." Geonomos, February 16, 2013. http://dx.doi.org/10.18285/geonomos.v15i1.109.
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This article presents data and interpretations on the Espinhaço Supergroup in Minas Gerais, emphasizingstratigraphic and structural data of the Serra do Espinhaço, where arise sequences from Archean (granites/gnaisses/migmatites and units of lower metamorphic degree) to Neoproterozoic. Espinhaço Supergroup hasit’s development in the end of the Paleoproterozoic until the Mesoproterozoic, and in the Meridional Sectionit’s base is represented by the Guinda Group, with quartzites, phylites and metaconglomerates/breccias offluvial to shallow marine origins, presenting intercalations of metavolcanics and real paleosoils (part ofhematitic phylites). Above arise eolian metasediments of the Galho do Miguel Formation and the marine tofluvial metasediments of the Conselheiro Mata Group. At the Setentrional Sector, three big groups, mainlypresenting continental characteristics (compatible with the opening of a rift), can be recognized formingthis super group in the setentrional sector of the mountain rage: Metavulcanossedimentar Unit, InferiorMetassedimentar Unit and Superior Metassedimentar Unit. The region is structured by a system of inversefaults/ ductile shear zones that cause frequent stratigraphic inversions and that spread marked blocks internallyby open folds to closed with West vergence. The analysis of quantity of deformation proves the non-axialcharacter of these mass transportations, and confirms the location of part of the shear zones.
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Degler, Reik, Tiago Amâncio Novo, Bernhard Schulz, and Gláucia Nascimento Queiroga. "P- T PATH RECONSTRUCTION IN NEOPROTEROZOIC GARNET-BEARING PARAGNEISSES FROM A METASEDIMENTARY SUCCESSION OF THE SOUTH WESTERN ARAÇUAÍ OROGEN, MINAS GERAIS, BRAZIL." Geonomos, December 31, 2015. http://dx.doi.org/10.18285/geonomos.v23i2.709.
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Abstract: This paper focuses on pressure- and temperature path analyses in paragneisses from a metasedimentary succession (MSS) in the south western Araçuaí orogen. The sampling area is limited by the Abre Campo shear zone (West) and the Rio Doce Magmatic Arc (East). This region is rich in ortho-derived metamorphic basement rocks (Mantiqueira and the Juiz de Fora complexes) and para-derived metamorphic rocks, including paragneisses interlaid by quartzites, which form the MSS. The sampled rocks are mainly compost of quartz, plagioclase, garnet, K-Feldspar, orthopyroxene and sillimanite. Measurement spot profiles through garnet porphyroblasts show a certain zonation characterised by decrease in pyrope and the increase in almandine from the core to the rim. This implies retrograde growth. Metamorphic conditions are of high amphibolite- to granulite facies with maximum pressure of ca. 6 kbar and maximum temperature of ca. 700°C. The data suggest that the cores of the garnet porphyroblasts of MSS started to grow during the final deformation stage of the Araçuaí orogen (south western part); the event of decompression is captured in the rims of the porphyroblasts and related to the gravitational collapse in the Cambrian. Keywords: P-T path, metasedimentary succession, geothermobarometry, Araçuaí orogenResumo: RECONSTRUÇÃO DE TRAJETÓRIAS P-T EM PARAGNAISSES GRANADÍFEROS NEOPROTEROZÓICOS DA UMA SUCESSÃO METASSEDIMENTAR NO SUDOESTE DO ORÓGENO ARAÇUAÍ, MINAS GERAIS, BRASIL. Este estudo foca analises de caminhos de pressão e temperatura em paragnaisses de sucessão metassedimentar (SMS) da região sudoeste do Orógeno Araçuaí. A área de amostragem é limitada pela zona de cisalhamento de Abre Campo a oeste e pelo Arco Magmático Rio Doce a leste. A região é rica em rochas metamórficas de alto grau ortoderivadas (complexos Mantiqueira e Juiz de Fora do embasamento) e paraderivadas; incluindo paragnaisses intercalados a quartzitos, que formam o SMS. As rochas amostradas são compostas por quartzo, plagioclásio, granada, feldspato potássio, ortopiroxênio e sillimanita. Perfis de pontos de análise em porfiroblastos de granada mostram certo zoneamento caracterizado pela redução de piropo e por aumento de almadina do núcleo para borda; isto implica em crescimento de cristal sob condições de metamorfismo retrógrado. Condições metamórficas são de fácies anfibolito alto a granulito com um máximo de pressão de ca. 6 kbar e com temperatura máxima de ca. 700°C. Os dados sugerem que porfiroblastos de granada da SMS têm nucleação e início de crescimento durante o final da etapa deformacional principal compressiva do Orógeno Araçuaí (região sudoeste do orógeno); o evento de descompressão captado em bordas dos porfiroblastos foi relacionando ao colapso gravitacional no Cambriano. Palavras-chave: Trajetórias P-T, sucessão metassedimentar, geotermobarometria, Orógeno Araçuaí
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Queiroga, Gláucia, Tiago Novo, and A. C. Pedrosa-Soares. "MAPEAMENTO GEOLÓGICO DA REGIÃO DA SERRA DOS TURVOS, CARATINGA (MG), SETOR SUL DO ORÓGENO ARAÇUAÍ." Geonomos, July 31, 2012. http://dx.doi.org/10.18285/geonomos.v20i1.23.
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A área de estudo situa-se na parte sul do núcleo cristalino do Orógeno Araçuaí, próximo à fronteira com o Orógeno Ribeira. A característica fundamental da região é a abundância de rochas de alto grau metamórfico, na transição de fácies anfibolito-granulito. Uma cobertura metassedimentar neoproterozóica é a unidade dominante e está representada por paragnaisse migmatítico, bandado, com intercalações de quartzito, formação ferrífera micácea e formação ferrífera maciça. Corpos de anfibolito, pegmatito e charnockito também ocorrem na área. A principal estrutura dúctil é a foliação (Sn) regional, paralela ao bandamento composicional do granada-biotita paragnaisse. Fraturas são abundantes no quartzito e formação ferrífera maciça. As formações ferríferas são ricas em magnetita e formam corpos lenticulares com espessura decamétrica a centimétrica, concordantes com o bandamento composicional do granada-biotita paragnaisse. Preliminarmente, interpreta-se a gênese dessas formações ferríferas como sedimentar, durante a deposição dos protolitos areno-pelíticos do paragnaisse.Palavras-chave: metamorfismo de alto grau, formação ferrífera, Orógeno Araçuaí. ABSTRACT: GEOLOGICAL MAPPING OF THE SERRA DOS TURVOS REGION, CARATINGA (MG), SOUTHERN SECTION OF THE ARAÇUAÍ OROGEN. The study area is located in the southern part of the crystalline core of the Araçuaí orogen, close to the boundary with the Ribeira orogen. The main feature of the region is the abundance of high-grade metamorphic rocks of the amphibolite-granulite facies transition. A Neoproterozoic sedimentary cover is the dominant unit in the area and consists of migmatitic banded paragneiss with intercalations of quartzite, mica-bearing iron formation and massive iron formation. Amphibolite, pegmatite and charnockite bodies are also found in the area. The main ductile structure is the regional foliation (Sn) which is parallel to the compositional banding of the garnet-biotite paragneiss. Fractures are abundant in the quartzite and massive iron formation. The iron formations form lenticular bodies ranging in thickness from centimeters to decameters, which are concordant to the banding and foliation of the garnet-biotite paragneiss. Accordingly to field data, a sedimentary genesis can be suggested for the iron formations.Keywords: high grade metamorphism, iron formation, Araçuaí Orogen
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Fraga, Lucio Mauro Soares, Soraya de Carvalho Neves, Gabriela Luiza Pereira Pires, Adriano Luiz Tibães, and Alexandre Uhlein. "ESTROMATÓLITOS COLUNARES NA BASE DO GRUPO MACAÚBAS, NORDESTE DA SERRA DO ESPINHAÇO (MG): PALEONTOLOGIA E AMBIENTE DE SEDIMENTAÇÃO." Geonomos, July 31, 2013. http://dx.doi.org/10.18285/geonomos.v21i1.254.
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Na região nordeste da Serra do Espinhaço Meridional são encontrados metassedimentos da base do Grupo Macaúbas,constituídos por quartzitos, camadas de metapelitos e rochas metacarbonáticas, depositadas em diferentes ambientes de sedimentação:continental, transicional e marinho. Na Formação Domingas ocorrem camadas de metapelitos contendo lentes isoladas de dolomitos comum rico conteúdo paleontológico formado por estruturas estromatolíticas colunares. Em trabalhos de campo recentes foram encontradas edescritas duas lentes de dolomitos na região de Inhaí (região da Fazenda Boqueirão) e uma lente já conhecida, localizada na calha do RioJequitinhonha. Nestas regiões foram descritas a morfologia e a geometria das estruturas biogênicas, além da petrografia das rochascarbonáticas e das rochas metapelíticas associadas. Este estudo concentra-se na descrição dos morfotipos de estromatólitos, classificadosde acordo com sua macro e mesoestrutura, conforme o grau de herança laminar e o tipo de ramificações encontradas. Desta forma, foramidentificados dois morfotipos distintos de estromatólitos onde, as formas cônicas sem ramificações, apresentaram alto grau de herançalaminar, sendo então classificados como Conophyton garganicum. As formas ramificadas, geralmente com dicotomas paralelos e decrescimento muito convexo, foram classificadas como Jacutophyton. A geometria dos corpos dolomíticos, o conteúdo paleontológico e suaposição estratigráfica associada a sedimentação pelítica, sugerem que estas rochas foram formadas a partir de precipitações bioquímicasem águas pouco profundas (submaré rasa) dentro de um ambiente costeiro.Palavras Chaves: Estromatólito; Grupo Macaúbas; Proterozóico; Conophyton; Jacutophyton. ABSTRACTCOLUMNAR STROMATOLITES AT THE BASE OF MACAÚBAS GROUP, NORTHEST OF ESPINHAÇO RIDGE (MG): PALEONTOLOGYAND SEDIMENTARY ENVIRONMENT- The rocks at the base of the Macaúbas Group that outcrop in the northeastern of Espinhaço Ridge areconstituted mainly by quartzites followed by layers of metapelites and metacarbonates rocks, deposited in fluvial, marine and coastalenvironments, of Neoproterozoic age. At the top of metapelites layers of the Domingas Formation, occur isolated lens of dolomitescontaining a rich paleontological content composed of columnar estromatolitics structures. After recently field trips where they wereidentified news lenses of dolomites in the Boqueirão Farm (Inhaí/Diamantina region) and the lens already know, in the Jequitinhonha river,trough was described the morphology and geometry of biogenic structures found, besides the petrography of carbonates and metapeliticrocks associated. In this study the stromatolites were classified by the macro and mesostructures, depending on the degree of laminar andheritage branch type found. In this way, were described two distinct morphotypes of stromatolites where conical shapes without branches,showed a high degree of laminar heritage, being so classed as Conophyton garganicum. The branched shapes, usually with paralleldicotomas and convex growth were classified as Jacutophyton. The geometry of the dolomitic bodies, the paleontological content andstratigraphic position association of pelitic sedimentation, suggest that these rocks were formed from biochemical precipitation in waterssufficiently deep (subtidal shallow) within a coastal environment.Keywords: Stromatolites; Macaúbas Group; Proterozoic; Conophyton; Jacutophyton.
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Barr, Sandra M., and James K. Mortensen. "Neoproterozoic U–Pb (zircon) and 40Ar/39Ar (muscovite) ages from granitic pegmatite clasts, basal Ross Island Formation, Grand Manan Island, New Brunswick, Canada." Atlantic Geology, July 28, 2019, 265–74. http://dx.doi.org/10.4138/atlgeol.2019.009.
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Zircon grains from a granitic pegmatite clast from conglomerate at the base of the Ross Island Formation on Grand Manan Island indicate an igneous crystallization age of 664.1 ± 4.6 Ma. The clast also contains abundant older inherited grains back to the Archean. Muscovite in the same clast and an additional similar clast yielded cooling ages of 607.0 ± 3.7 Ma and 619.6 ± 4.1 Ma, respectively, providing a maximum depositional age for the host conglomerate of the Ross Island Formation. The similarity in age to pegmatite in the Seven Hundred Acre Island Formation in Penobscot Bay, Maine, supports earlier correlations between the two areas based on similarities in Neoproterozoic quartzite and carbonate units.