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Статті в журналах з теми "Palaeoproterozoic boundary"
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Vogel, D. C., R. S. James, and R. R. Keays. "The early tectono-magmatic evolution of the Southern Province: implications from the Agnew Intrusion, central Ontario, Canada." Canadian Journal of Earth Sciences 35, no. 7 (July 1, 1998): 854–70. http://dx.doi.org/10.1139/e98-031.
Повний текст джерелаАнотація:
The Palaeoproterozoic Southern Province comprises a thick, continental rift related volcanic-sedimentary sequence along the southern margin of the Archaean Superior Province. The Agnew Intrusion (50 km2), which is a member of the East Bull Lake suite of layered intrusions, occurs adjacent to the Superior Province - Southern Province boundary in central Ontario, Canada, and provides an opportunity to examine the early tectono-magmatic evolution of a Palaeoproterozoic rifting event. The Agnew Intrusion is a well-exposed, 2100 m thick, layered gabbronoritic to leucogabbronoritic pluton. It was the product of at least four recognizable, but chemically similar, high-Al2O3 and low-TiO2 magma pulses. Structural data, coupled with excellent stratigraphic correlations between the Agnew Intrusion and other East Bull Lake suite layered intrusions, suggest that these plutons are erosional remnants of one or more sill-like bodies that may originally have formed an extensive, subhorizontal mafic sheet. We argue on the basis of field evidence that the early evolution of the Southern Province was characterized by a large, mantle plume induced magmatic event that gave rise to a Palaeoproterozoic continental flood basalt province. However, the incompatible trace element characteristics of the Agnew Intrusion parental magma (i.e., large ion lithophile and light rare earth element enrichment and high field strength element depletion) are more typical of modern subduction-modified subcontinental lithospheric mantle. Given that this is a prevailing geochemical signature of mafic rocks in the Archaean-Palaeoproterozoic, we suggest that there was a fundamental difference in both the composition and structure between the ancient and more modern mantle. "Subduction-like" geochemical signatures may have been imparted to the entire developing mantle during early Earth differentiation.
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Roelofse, F., H. de Bruiyn, D. Cornell, and M. Kristofferson. "Lithostratigraphy of the Palaeoproterozoic Verena Granite." South African Journal of Geology 123, no. 1 (March 1, 2020): 117–28. http://dx.doi.org/10.25131/sajg.123.0007.
Повний текст джерелаАнотація:
Abstract The Verena Granite forms part of the Palaeoproterozoic Lebowa Granite Suite of the Bushveld Complex and was named after the village of Verena in the Mpumalanga Province of South Africa. It occurs over an area of ~600 km2 and is intrusive into the Rooiberg Group, the Rashoop Granophyre Suite and the Klipkloof Granite. It is in turn intruded by the Makhutso Granite, the youngest known granite of the Lebowa Granite Suite. The Verena Granite is characterised by its coarse to very coarse-grained nature, its pinkish to reddish colours and its porphyritic texture defined by the presence of large perthitic K-feldspar phenocrysts within a finer grained groundmass of plagioclase (An8-15) and quartz. Geochemically it can be classified as an A-type granite that straddles the boundary between metaluminous and peraluminous compositions. The granite is enriched in REEs relative to chondrite and shows strong fractionation of the LREEs, a distinct negative Eu anomaly and little fractionation of the HREEs. U-Pb dating presented here places the age of the Verena Granite at 2052 ± 9 Ma, which is the same as that of the published 2054 ± 2 Ma age of the Nebo Granite. Currently no consensus exists regarding the petrogenesis of the Verena Granite. Doubts have been cast on a genetic link between the Verena Granite and the remainder of the Nebo Granite. A genetic link between the Klipkloof Granite and the Verena Granite appears likely, with the former possibly representing the rapidly chilled roof of the magmas that crystallised to form the latter. Lu-Hf isotope data on zircons are consistent with that from other units of the Lebowa Granite Suite. It also supports the unconventional model involving a common enriched mantle origin for all mafic and felsic units of the Bushveld Complex, with minimal input from older crust.
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ANDERSEN, TOM. "Age, Hf isotope and trace element signatures of detrital zircons in the Mesoproterozoic Eriksfjord sandstone, southern Greenland: are detrital zircons reliable guides to sedimentary provenance and timing of deposition?" Geological Magazine 150, no. 3 (November 16, 2012): 426–40. http://dx.doi.org/10.1017/s0016756812000623.
Повний текст джерелаАнотація:
AbstractThe Gardar Rift in southern Greenland developed within Palaeoproterozoic rocks of the Ketilidian orogen, near its boundary with the Archaean craton. The Eriksfjord Formation was deposited atc. 1.3 Ga on a basement ofc. 1.8 Ga Julianehåb I-type granite. Detrital zircons from the lower sandstone units shows a range of ages and εHfcompatible with proto sources within the Archaean craton and the Nagssugtoquidian mobile belt north and east of the craton; zircons that can be attributed to juvenile Ketilidian sources are less abundant. This suggests a predominance of distant sources, probably by recycling of older and no longer preserved cover strata. A significant fraction ofc. 1300 Ma zircons have εHfbetween 0 and −38. Rather than originating from a hitherto unknown igneous body within the Gardar Rift, these are interpreted as Palaeoproterozoic to late Archaean zircons that have lost radiogenic lead during diagenesis and post-depositional thermal alteration related to Gardar magmatism. Although the sediments originate from sources within Greenland, the age and initial Hf isotope distribution of Palaeoproterozoic and Archaean zircons mimics that of granitoids from the Fennoscandian Shield. This may reflect parallel evolution and possible long-range exchange of detritus in Proterozoic supercontinent settings. The lesson to be learned is that detrital zircon age data should not be used to constrain the age of sedimentary deposition unless the post-depositional history is well understood, and that recycling of old sediments, long-range transport and parallel evolution of different continents make detrital zircons unreliable indicators of provenance.
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SHEPPARD, S., T. J. GRIFFIN, I. M. TYLER, and R. W. PAGE. "High- and low-K granites and adakites at a Palaeoproterozoic plate boundary in northwestern Australia." Journal of the Geological Society 158, no. 3 (May 2001): 547–60. http://dx.doi.org/10.1144/jgs.158.3.547.
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LAMMINEN, JARKKO, TOM ANDERSEN, and JOHAN PETTER NYSTUEN. "Provenance and rift basin architecture of the Neoproterozoic Hedmark Basin, South Norway inferred from U–Pb ages and Lu–Hf isotopes of conglomerate clasts and detrital zircons." Geological Magazine 152, no. 1 (May 2, 2014): 80–105. http://dx.doi.org/10.1017/s0016756814000144.
Повний текст джерелаАнотація:
AbstractThe Neoproterozoic Hedmark Basin in the Caledonides of South Norway was formed at the western margin of the continent Baltica by rifting 750–600 Ma ago. The margin was destroyed in the Caledonian Orogeny and sedimentary basins translated eastwards. This study uses provenance analysis to map the crustal architecture of the pre-Caledonian SW Baltican margin. Conglomerate clasts and sandstones were sampled from submarine fan, alluvial fan and terrestrial glacigenic sedimentary rocks. Samples were analysed for U–Pb isotopes and clast samples additionally for Lu–Hf isotopes. The clasts are mainly granitesc. 960 Ma and 1680 Ma old, coeval with the Sveconorwegian Orogeny and formation of the Palaeoproterozoic Transscandinavian Igneous Belt (TIB). Mesoproterozoic (Sveconorwegian) ages are abundant in the western part of the basin, whereas Palaeoproterozoic ages are common in the east. Lu–Hf isotopes support crustally contaminated source for all clasts linking them to Fennoscandia. Detrital zircon ages of the sandstones can be matched with those from the granitic clasts except for ages within the range 1200–1500 Ma. These ages are typically found in the present-day Telemark, SW Norway. The sandstones and conglomerate clasts in the western part of the Hedmark Basin were sourced from the Sveconorwegian domain in the present SW Norway or its continuation to the present-day NW. The conglomerate clasts in the eastern part of the Hedmark Basin were sourced mainly from the TIB domain or its northwesterly continuation. The Hedmark Basin was initiated within the boundary of two domains in the basement: the TIB and the Sveconorwegian domains.
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DICKIN, ALAN, and ROBERT NORTH. "Nd isotope mapping of the Allochthon Boundary Thrust on the shores of Georgian Bay, Ontario: significance for Grenvillian crustal structure and evolution." Geological Magazine 152, no. 6 (March 31, 2015): 993–1008. http://dx.doi.org/10.1017/s0016756815000114.
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AbstractNearly 50 new Nd isotope analyses are presented for the Shawanaga region of Georgian Bay, Ontario, to study crustal evolution in the Grenvillian Central Gneiss Belt. Depleted mantle (TDM) Nd model ages are used to map a major Grenvillian tectonic boundary, the Allochthon Boundary Thrust (ABT), which in the Shawanaga area separates gneisses with TDM ages above and below 1.65 Ga. This is lower than the 1.8 Ga age cut-off observed further north, and is attributed to a southward increase in Mesoproterozoic magmatic reworking of an original Palaeoproterozoic continental margin, causing a progressive southward decrease in Nd model ages. Between Shawanaga Island and Franklin Island, Nd isotope mapping yields an ABT trajectory that closely matches published geological mapping, and passes within 100 m of four retrogressed eclogite bodies typically associated with the thrust boundary. This validation of the method gives confidence in the mapped trajectory south of Snake Island, where sparse outcrop inhibits lithological mapping. The new results suggest that published 1.7–1.9 Ga TDM ages in the Lower Go Home domain of the Central Gneiss Belt further south are also indicative of parautochthonous crust. Hence, we propose that the main ramp of the ABT is located in the immediate hangingwall of the Go Home domain, much further south than generally recognized. This has important implications for the large-scale crustal structure of the SW Grenville Province, suggesting that the ABT ramp has a similar curved trajectory to the Grenville Front and the Central Metasedimentary Belt boundary thrust.
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Zheng, Binsong, Chuanlong Mou, Renjie Zhou, Xiuping Wang, Zhaohui Xiao, and Yao Chen. "Nature and origin of the volcanic ash beds near the Permian–Triassic boundary in South China: new data and their geological implications." Geological Magazine 157, no. 4 (December 3, 2019): 677–89. http://dx.doi.org/10.1017/s001675681900133x.
Повний текст джерелаАнотація:
AbstractPermian–Triassic boundary (PTB) volcanic ash beds are widely distributed in South China and were proposed to have a connection with the PTB mass extinction and the assemblage of Pangea. However, their source and tectonic affinity have been highly debated. We present zircon U–Pb ages, trace-element and Hf isotopic data on three new-found PTB volcanic ash beds in the western Hubei area, South China. Laser ablation inductively coupled plasma mass spectrometry U–Pb dating of zircons yields ages of 252.2 ± 3.6 Ma, 251.6 ± 4.9 Ma and 250.4 ± 2.4 Ma for these three volcanic ash beds. Zircons of age c. 240–270 Ma zircons have negative εHf(t) values (–18.17 to –3.91) and Mesoproterozoic–Palaeoproterozoic two-stage Hf model ages (THf2) (1.33–2.23 Ga). Integrated with other PTB ash beds in South China, zircon trace-element signatures and Hf isotopes indicate that they were likely sourced from intermediate to felsic volcanic centres along the Simao–Indochina convergent continental margin. The Qinling convergent continental margin might be another possible source but needs further investigation. Our data support the model that strong convergent margin volcanism took place around South China during late Permian – Early Triassic time, especially in the Simao–Indochina active continental margin and possibly the Qinling active continental margin. These volcanisms overlap temporally with the PTB biocrisis triggered by the Siberian Large Igneous Province. In addition, our data argue that the South China Craton and the Simao–Indochina block had not been amalgamated with the main body of Pangea by late Permian – Early Triassic time.
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Boukhalfa, Zakaria, Abderrezak Bouzid, Yixian Xu, Abderrahmane Bendaoud, Bo Yang, Mohamed Hamoudi, Said Sofiane Bougchiche, et al. "Magnetotelluric investigation of the Precambrian crust and intraplate Cenozoic volcanism in the Gour Oumelalen area, Central Hoggar, South Algeria." Geophysical Journal International 223, no. 3 (September 12, 2020): 1973–86. http://dx.doi.org/10.1093/gji/ggaa432.
Повний текст джерелаАнотація:
SUMMARY The Tuareg Shield was assembled by oceanic closures and horizontal movements along mega-shear zones between approximately 20 terranes during the Pan-African Orogeny (750–550 Ma). Although there is an ongoing debate about its origin, the exhumation of the Tuareg Shield is assumed to be related to Cenozoic intraplate volcanism. The Gour Oumelalen is a key region of the Tuareg Shield and is located in the northeastern part of the Egéré-Aleksod terrane, corresponding to the eastern boundary of the Archean–Palaeoproterozoic microcontinent LATEA (Central Hoggar). The eastern boundary of the study area corresponds to a Neoproterozoic suture zone separating two old microcontinents, LATEA and the Orosirian Stripe. We deployed two magnetotelluric (MT) profiles consisting of 33 broad-band MT stations and combined these with aeromagnetic data, aiming to define the crustal structure in detail. The resistivity cross-sections obtained from the 3-D inversion of full impedance tensor and tipper data from stations along the profiles, confirm the main Precambrian faults, some of which are covered by Quaternary sediments and hence, have not yet been deciphered. The cross-sections also highlight the Cretaceous–Quaternary sedimentary basins represented by low resistivities. The upper crust is typically cratonic with a high electrical resistivity. On the contrary, the lower crust shows a drastic drop in resistivity (<10 Ωm). The most plausible hypothesis is that the study area corresponds to a Cretaceous rifting zone. The Cretaceous magmatic event and its related fluids and mineralization as well as the recent fluids associated with Cenozoic volcanism, are plausible causes of a very conductive lower crust. However, we cannot exclude other reasons such as: (i) a high-temperature and strongly sheared mobile belt or (ii) a contribution of inheritance involving Pan-African events that affected this former suture area.
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Mazur, Stanislaw, Sandra Piazolo, and G. Ian Alsop. "Structural analysis of the northern Nagssugtoqidian orogen, West Greenland: an example of complex tectonic patterns in reworked high-grade metamorphic terrains." Geological Survey of Denmark and Greenland (GEUS) Bulletin 11 (December 5, 2006): 163–78. http://dx.doi.org/10.34194/geusb.v11.4929.
Повний текст джерелаАнотація:
Structural analysis of the deeply eroded northern flank of the Palaeoproterozoic Nagssugtoqidian orogen shows marked regional variations in both the orientation and type of fabrics, as is characteristic of Precambrian high-grade terrains subjected to polyphase deformation. Here we investigate the relationship between strain, metamorphic grade, and the resulting structural patterns. The study area south of Aasiaat in West Greenland consists of amphibolite- to granulite-grade Archaean orthogneisses and relatively thin supracrustal units. The regional foliation displays a WSW–ENE to SW–NE strike associated with steep to moderate dips towards the WNW or SSE. Lineation trends are WSW–ENE and generally plunge gently towards the WSW. Mesoscopic fold hinges are usually colinear with the regional lineation. A systematic change in the plunge of lineations occurs across the south-western part of the study area. Towards the south, the lineation plunge progressively increases, despite the generally uniform strike of foliation. This southward increase of lineation pitch is typically associated with the transition from L > S or L = S shape fabrics in rocks characterised by a low pitch, to S > L or S fabrics in the zone of moderate to high pitch. The structural patterns point to subdivision of the study area into a southern domain mostly characterised by S or S > L shape fabrics and a moderate to high angle of lineation pitch, and a northern domain showing L > S or L = S fabrics and low angles of lineation pitch. This subdivision corresponds well with the map scale boundary between granulite facies rocks in the south and amphibolite facies rocks farther north. The observed structural pattern may be explained by two alternative tectonic models: (1) northward indentation of the previously cooled granulite block into the rheologically weaker amphibolite domain, and (2) strain partitioning within a mid-crustal transpression zone. In model 2 the northern domain represents a localised zone dominated by strike-slip kinematics, whereas the southern domain shows evidence of mostly coaxial shortening. Recent geochronology supports the indentator model in spite of limited available data. Despite the details and structural complexities of the two tectonic models, the granulite and amphibolite facies domains seem to form autochthonous segments of a crustal section linked by a transitional zone that was only reactivated and reworked during indentation or transpression. The Nagssugtoqidian compression was effectively transferred across this zone towards the northern amphibolite domain that suffered penetrative deformation during the Palaeoproterozoic event. The N–S shortening was accommodated through folding, indentation and/or strike-slip displacements, rather than by thrusting and folding as seen south of the study area.
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Korstgård, John A., Bo Møller Stensgaard, and Thorkild M. Rasmussen. "Magnetic anomalies and metamorphic boundaries in the southern Nagssugtoqidian orogen, West Greenland." Geological Survey of Denmark and Greenland (GEUS) Bulletin 11 (December 5, 2006): 179–84. http://dx.doi.org/10.34194/geusb.v11.4930.
Повний текст джерелаАнотація:
Within the southern Nagssugtoqidian orogen in West Greenland metamorphic terrains of both Archaean and Palaeoproterozoic ages occur with metamorphic grade varying from low amphibolite facies to granulite facies. The determination of the relative ages of the different metamorphic terrains is greatly aided by the intrusion of the 2 Ga Kangâmiut dyke swarm along a NNE trend. In Archaean areas dykes cross-cut gneiss structures, and the host gneisses are in amphibolite to granulite facies. Along Itilleq strong shearing in an E–W-oriented zone caused retrogression of surrounding gneisses to low amphibolite facies. Within this Itivdleq shear zone Kangâmiut dykes follow the E–W shear fabrics giving the impression that dykes were reoriented by the shearing. However, the dykes remain largely undeformed and unmetamorphosed, indicating that the shear zone was established prior to dyke emplacement and that the orientation of the dykes here was governed by the shear fabric. Metamorphism and deformation north of Itilleq involve both dykes and host gneisses, and the metamorphic grade is amphibolite facies increasing to granulite facies at the northern boundary of the southern Nagssugtoqidian orogen. Here a zone of strong deformation, the Ikertôq thrust zone, coincides roughly with the amphibolite–granulite facies transition. Total magnetic field intensity anomalies from aeromagnetic data coincide spectacularly with metamorphic boundaries and reflect changes in content of the magnetic minerals at facies transitions. Even the nature of facies transitions is apparent. Static metamorphic boundaries are gradual whereas dynamic boundaries along deformation zones are abrupt.
Дисертації з теми "Palaeoproterozoic boundary"
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Rowe, S. E. "Mechanism of formation and age of the Ayyarmalai A-type charnockite – granite association from the south-eastern Palghat- Cauvery Shear System, southern India." Thesis, 2010. http://hdl.handle.net/2440/104030.
Повний текст джерелаАнотація:
This item is only available electronically.The Ayyarmalai A-type charnockite and A-type alkali granite lies on the south-eastern margin of the Palghat-Cauvery Shear System and provides an example of co-magmatism that was later overprinted with granulite facies metamorphism at ~2.45-2.5Ga. The Palghat-Cauvery Shear System represents an intriguing zone with Neoproterozoic aged granulites (~800-500 Ma) to the south and Archaean granulites (~3000-2500 Ma) to the north; the origins of which are still often disputed. This study presents whole rock major and trace element compositions, mineral chemistry, pressure-temperature estimates and whole rock Sm-Nd, Rb-Sr, Pb-Pb and δ18O isotopic compositions of this A-type charnockite-granite association found at Ayyarmalai, Tamil Nadu, Southern India. The subsequent data from this study suggests that: (1) the Ayyarmalai charnockites from the Palghat-Cauvery Shear System have zircon ages that are synchronous with events in the Northern Granulite Terrain; (2) The Dharwar Craton is a strong candidate for the protolith of these rocks; (3) Evidence of a Neoproterozoic-Cambrian granulite metamorphic event (~520 Ma) appears to be absent in these rocks questioning the existence or location of a Neoproterozoic - Cambrian suture zone proposed for the Palghat-Cauvery Shear System recently. U-Pb zircon ages show zoned igneous cores ~2.65-2.68 Ga ages in both rock types defining the crystallisation age, while the large metamorphic rim overgrowths date the Archaean granulite metamorphic event at ~2.45 - 2.5 Ga. Geochemical data of the Ayyarmalai charnockites reveal a very primitive, unfractionated REE pattern with no Eu-anomaly, ferroan, high K-calc-alkaline, with moderate enrichment of LREE with respect to HREE and fall within the field of high Ba-Sr type granitoids. Extraction of Pyroxene- Hornblende rich cumulates resulted in an intermediate charnockites driving the crystallisation towards the final A-type alkali granite. The A-type alkali granites show a more fractionated REE pattern with a significant Eu-anomaly, ferroan, high-K- calc-alkaline, with enrichment of LREE and depletion in the low Ba-Sr type granitoids. εNd and Nd model ages indicate a highly evolved protolith (εNd(0) =-25.15 to -33.14) that encountered a crustal Archaean source (2.89-3.09 Ga) causing contamination as the magmas ascended. Harker diagrams, Nd data (isochron age, ~2519 Ma) and U-Pb zircon crystallisation ages suggest a co-magmatic relationship between the charnockite and alkali granite. Conventional geothermometry/barometry suggest minimum pressure-temperature conditions existed at 740 – 750°C and P=5.61 – 5.84 kbar. The data presented from this study is consistent with a magmatic origin of these charnockites favouring the early crystallisation of orthopyroxene. The correlation with the data from the Dharwar Craton suggest that the study region may have encountered Dharwar Craton on magmatic ascent causing crustal contamination
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2010
Частини книг з теми "Palaeoproterozoic boundary"
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Mohanty, S. "Redox State of Atmosphere and Ocean at the Archaean-Palaeoproterozoic Boundary: A Case Study from the Sausar Belt, Central India." In Society of Earth Scientists Series, 57–77. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-89698-4_4.
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