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1
Stephens, Michael B., and Stefan Bergman. "Chapter 2 Regional context and lithotectonic framework of the 2.0–1.8 Ga Svecokarelian orogen, eastern Sweden." Geological Society, London, Memoirs 50, no. 1 (2020): 19–26. http://dx.doi.org/10.1144/m50-2017-2.
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AbstractSix separate lithotectonic units, referred to from north to south as the Överkalix, Norrbotten, Bothnia–Skellefteå, Ljusdal, Bergslagen and Småland units, are identified inside the western part of the 2.0–1.8 Ga Svecokarelian orogen, Fennoscandian Shield, Sweden. Apart from the boundary between the Norrbotten and Bothnia–Skellefteå lithotectonic units in northern Sweden, which is defined on the basis of a change in crustal basement from Neoarchean (and possibly older) in the NE (Norrbotten) to juvenile Paleoproterozoic crust further south (Bothnia–Skellefteå), all the boundaries are defined by shear zones or combinations of zones that, in places, form broader shear belts up to several tens of kilometres thick. The identification of lithotectonic units provides a necessary foundation for a more detailed synthesis of the tectonic evolution of the 2.0–1.8 Ga orogeny in northern Europe, emphasizing in particular the allochthoneity between most of these units inside this part of the orogen.
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Chauvel, C., N. T. Arndt, S. Kielinzcuk, and A. Thom. "Formation of Canadian 1.9 Ga old continental crust. I: Nd isotopic data." Canadian Journal of Earth Sciences 24, no. 3 (March 1, 1987): 396–406. http://dx.doi.org/10.1139/e87-042.
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A Nd isotopic study was carried out on 1.9−1.8 Ga rocks from two parts of the Trans-Hudson Orogen in northern Canada. The first part is the Reindeer Lake Zone in the Churchill Province in Saskatchewan, where a variety of volcanic, granitoid, and sedimentary rocks are preserved in several lithotectonic belts that border a reworked Archean craton to the northwest. The second area comprises the Ottawa and Belcher islands, in Hudson Bay, and the Fox River volcanics, in Manitoba. These form part of the Circum-Superior Belt, a band of basaltic volcanics and sedimentary rocks that overlies the Archean Superior craton.From U–Pb zircon ages, Pb–Pb ages, and Sm–Nd ages, Nd initial isotopic compositions were calculated for all analyzed samples. In the Saskatchewan terrains, we obtained a large range of εNd values, from +5 to −8. The highest values (+4 to +5) come from two volcanic-dominated belts (Flin Flon and Western la Ronge), lower values (~+2) characterize intervening sediment-dominated domains (Eastern La Ronge, Glennie Lake, and Kisseynew), and still lower values (−1 to −4) were found in migmatitic and granitoid belts adjacent to the reworked Archean craton in the northwest. Each lithotectonic belt has its own characteristic, restricted range of εNd values, and, with few exceptions, there is no correlation between εNd and rock type; i.e., in individual belts, volcanics, granites, and sediments have very similar εNd values.In the Circum-Superior Belt, three lava flows from the Ottawa Islands have εNd values ranging from +4.5 to 0, and samples from the Belcher Islands have values ranging from +3.5 to −9.These results are explained by mixing between mantle-derived rocks and variable amounts of Archean continental crustal rocks. Assuming that 1.9 Ga ago the mantle had an εNd value of +5 and Archean crust had an εNd value of −12, we calculate proportions of Archean crustal material in Trans-Hudson rocks ranging from ~2 to 35 %, increasing systematically toward the Archean platform. The mean Archean component is about 8%: this area of Proterozoic continental crust is clearly dominated by material derived directly from the mantle.The similarity between the εNd values of sediments, granites, and volcanics in the Trans-Hudson Orogen suggests that sedimentary processes played a dominant role in transporting Archean detritus from eroding Archean continental areas into basins, where it mixed with mantle-derived volcanic material and melted to form granitoids.
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Kozlov, N. E., N. O. Sorokhtin, N. E. Kozlova, and Eu V. Martynov. "Geological structure of the Ustoyarvi region (North-Western part of the Russian Arctic)." Vestnik MGTU 25, no. 1 (March 31, 2022): 12–26. http://dx.doi.org/10.21443/1560-9278-2022-25-1-12-26.
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The paper presents data on geology and composition of rocks from the Ustoyarvi region (the North-Western Arctic zone of Russian Federation). Their compositional analysis (including mathematical evaluation of the similarity/difference measure) provided much reliable conclusion that the rocks from this area, which are presumably attributed to the Ustoyarvi structure (Ustoyarvinsky Greenstone Belt) were similar to those from the Ura-Guba area in the Kolmozero-Voronya Belt and continued it. In addition, it has been shown that from west to east lithotectonic units in the adjacent (Suormussky) Block become gradually impregnated with tectonic wedges of rocks of the Ustoyarvi Greenstone Belt. It indicates increasing collisional interaction between rock associations with a varied genesis. P-T formation parameters have been specified for komatiites from greenstone belts, i. e. the Kolmozero-Voronya, Ura-Guba, Ustoyarvi and Western Litsa area. It has been defined that komatiites of the Ustoyarvi Greenstone Belt were formed under pressure of about 5 hPa, komatiites of the Ura-Guba area - about 4.5 hPa, komatiites of the Kolmozero-Voronya - about 2 hPa. Thus, komatiites of the Ustoyarvi Greenstone Belt are more high-pressure formations.
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Stephens, Michael B., Ulf Bergström, and Carl-Henric Wahlgren. "Chapter 14 Regional context and lithotectonic framework of the 1.1–0.9 Ga Sveconorwegian orogen, southwestern Sweden." Geological Society, London, Memoirs 50, no. 1 (2020): 337–49. http://dx.doi.org/10.1144/m50-2018-17.
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AbstractThe 1.1–0.9 Ga Sveconorwegian orogen in southwestern Scandinavia belongs to the global system of mountain belts established during the assembly of the supercontinent Rodinia. An overall north–south structural trend and five lithotectonic units bounded by crustal-scale shear zones characterize this orogen. In Sweden, the Eastern Segment abuts the orogen's cratonic foreland eastwards and is separated from the Idefjorden terrane westwards by a ductile shear zone, up to 5 km thick, displaying a sinistral transpressive component. These two lithotectonic units differ on the basis of their pre-Sveconorwegian accretionary tectonic evolution, and the timing of Sveconorwegian high-pressure metamorphism, anatexis and polyphase deformation. High-pressure granulites and migmatites formed at c. 1.05–1.02 Ga in the Idefjorden terrane; eclogites, high-pressure granulites and migmatites at c. 0.99–0.95 Ga in the Eastern Segment. Magmatic activity and crustal extension progressed westwards at c. 0.98–0.92 Ga. Prior to or at 0.93–0.91 Ga, greenschist facies shear deformation with top-to-the-foreland movement affected the frontal part of the orogen. Geodynamic uncertainties concern the affinity of the Idefjorden terrane relative to Fennoscandia (Baltica), the character of the Sveconorwegian orogenesis, and the contiguous or non-contiguous nature of the erosional fronts of the late Mesoproterozoic–early Neoproterozoic orogens in Sweden and Canada.
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Stephens, Michael B. "Chapter 1 Introduction to the lithotectonic framework of Sweden and organization of this Memoir." Geological Society, London, Memoirs 50, no. 1 (2020): 1–15. http://dx.doi.org/10.1144/m50-2019-21.
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AbstractThe solid rock geology of Sweden comprises three principal components: (1) Proterozoic and (locally) Archean rocks belonging to the western part of the Fennoscandian Shield; (2) Phanerozoic and (locally) Neoproterozoic sedimentary cover rocks deposited on top of this ancient crust; and (3) the early to mid-Paleozoic (0.5–0.4 Ga) Caledonide orogen. Earlier compilations have applied different principles for the subdivision of the geology in the Fennoscandian Shield and the Caledonide orogen. A uniform lithotectonic framework has been developed here. Crustal segments affected by orogenesis have been identified and their ages determined by the youngest tectonothermal event. Four ancient mountain belts and six orogenies are preserved. Solid rocks outside the orogens have been assigned to different magmatic complexes or sedimentary successions based on their time of formation and tectonic affiliation. This approach allows relicts of older mountain-building activity to be preserved inside a younger orogen – for example, the effects of the Archean (2.8–2.6 Ga) orogeny inside the 2.0–1.8 Ga Svecokarelian orogen and Paleo–Mesoproterozoic (1.7–1.5 and 1.5–1.4 Ga) mountain-building processes inside the 1.1–0.9 Ga Sveconorwegian orogen. Sweden's five largest mineral districts are addressed in the context of this new lithotectonic framework, which forms the architecture to the contents of the chapters in this Memoir.
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Williams, Howard R. "Subprovince accretion tectonics in the south-central Superior Province." Canadian Journal of Earth Sciences 27, no. 4 (April 1, 1990): 570–81. http://dx.doi.org/10.1139/e90-053.
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Development of tectonic subprovinces as shear-bounded granite–greenstone and sediment-dominated terranes during the late Archaean is reviewed and interpreted from relationships between portions of the Wabigoon, Wawa, and Quetico subprovinces.Greenstone-dominated subprovinces (Wabigoon and Wawa) are complex successions of tholeiites, 2.76–2.70 Ga calc-alkaline volcanic centres, and derived sediments. Supracrustal rocks aggregated on a scale of tens of kilometres, forming homoclines, locally upright folded, intruded by granitoids, exhibiting variable fabric trends and strains, and cut by transcurrent shear zones. Small-scale (10–100 km) accretion juxtaposed these varied supracrustal sequences, which were engulfed granitoid magmas, to form greenstone belts.Sediment-dominated subprovinces (Quetico) are metamorphosed wacke sequences deposited during and after the volcanic climax in the period 2.70–2.69 Ga. Overthrust imbrication at both the Wabigoon–Quetico and the Quetico–Wawa contacts occurred along north-dipping shears, now vertical. Continued right-lateral convergence at subprovince margins induced progressive shortening within the Quetico Subprovince, producing a regional planar fabric. Abukuma–style metamorphism, migmatite formation, and S-type granite intrusions occurred during the period 2.67–2.65 Ga.Greenstone-belt developments, terminated during large-scale (100–1000 km) late neo-Archæan accretion, are preserved within elongate, batholith-dominated terranes separated by metasedimentary migmatite belts. Geochronological, lithotectonic, and metamorphic patterns on a scale of hundreds of kilometres are permissive of an accretionary model of greenstone terrane coalescence in which formation of long-lived, complex volcanic arcs and a complementary fore-arc accretionary prism culminated in large-scale accretion and the formation of stable continental crust.
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Ketchum, J. W. F., G. R. Dunning, and N. G. Culshaw. "U–Pb geochronologic constraints on Paleoproterozoic orogenesis in the northwestern Makkovik Province, Labrador, Canada." Canadian Journal of Earth Sciences 34, no. 8 (August 1, 1997): 1072–88. http://dx.doi.org/10.1139/e17-087.
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A 45 km wide, shear-zone-bounded segment of the northwestern Makkovik Province, Labrador, is underlain by Archean gneisses derived from the adjacent Nain craton. This lithotectonic block (Kaipokok domain) was reworked at high metamorphic grade, overthrust by supracrustal sequences (Lower Aillik and Moran Lake groups), and intruded by granitoid plutons during the Paleoproterozoic. Initial amphibolite-facies reworking of the Kaipokok domain at 1896 ± 6 Ma is indicated by U–Pb ages of metamorphic zircon from a foliated Kikkertavak metadiabase dyke. This is one of the oldest Paleoproterozoic tectonic events dated thus far in northeast Laurentia and may be linked with ca. 1890 Ma plutonism documented elsewhere in the Kaipokok domain. Intrusion of granitoid plutons at [Formula: see text], 1877 ± 5, and [Formula: see text] in the Kaipokok Bay area postdates early thick- and thin-skinned thrusting (possibly east to northeast directed) that involved Lower Aillik Group strata. U–Pb titanite ages of 1866–1847 Ma in part record a metamorphic event that followed this plutonic–tectonic activity. These early events are temporally and kinematically difficult to reconcile with accretion of juvenile Makkovikian terranes in the southeast and may instead be related to early stages of the ca. 1.91–1.72 Ga Torngat orogeny along the western margin of the Nain craton. In contrast, high-grade metamorphism, dextral shearing, and northwestward thrusting between 1841 and 1784 Ma, including crystallization of an Iggiuk granitic vein at 1811 ± 8 Ma, are in accord with accretion of Makkovikian terranes in a dextral transpressional regime (Makkovikian orogeny sensu stricto). Coeval sinistral transpression in the Torngat orogen suggests that both otogenic belts accommodated relative northward tectonic escape of the Nain craton during this interval.
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Clarke, D. Barrie, Andrew S. Henry, and Mike A. Hamilton. "Composition, age, and origin of granitoid rocks in the Davin Lake area, Rottenstone Domain, Trans-Hudson Orogen, northern Saskatchewan." Canadian Journal of Earth Sciences 42, no. 4 (April 1, 2005): 599–633. http://dx.doi.org/10.1139/e04-067.
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The Rottenstone Domain of the Trans-Hudson orogen is a 25-km-wide graniticmigmatitic belt lying between the La Ronge volcanicplutonic island arc (18901830 Ma) to the southeast and the ensialic Wathaman Batholith (1855 Ma) to the northwest. The Rottenstone Domain consists of three lithotectonic belts parallel to the orogen: (i) southeast gently folded migmatized quartzo-feldspathic metasedimentary and mafic metavolcanic rocks intruded by small concordant and discordant white tonalitemonzogranite bodies; (ii) central intensely folded and migmatized metasedimentary rocks and minor metavolcanic rocks intruded by largely discordant, xenolith-rich, pink aplite-pegmatite monzogranite bodies; and (iii) northwest steeply folded migmatized metasedimentary rocks cut by subvertical white tonalitemonzogranite sheets. Emplacement of granitoid rocks consists predominantly of contiguous, orogen-parallel, steeply dipping, syntectonic and post-tectonic sheets with prominent magmatic schlieren bands, overprinted by parallel solid-state deformation features. The white granitoid rocks have A/CNK (mol Al2O3/(mol CaO + Na2O + K2O)) = 1.141.22, K/Rb ≈ 500, ΣREE (sum of rare-earth elements) < 70 ppm, Eu/Eu* > 1, 87Sr/86Sri ≈ 0.7032, and εNdi ≈ 2. The pink monzogranites have A/CNK = 1.111.16, K/Rb ≈ 500, ΣREE > 90 ppm, Eu/Eu* < 1, 87Sr/86Sri ≈ 0.7031, and εNdi ≈ 2. The white granitoid rocks show a wider compositional range and more compositional scatter than the pink monzogranites, reflecting some combination of smaller volume melts, less homogenization, and less control by crystalmelt equilibria. All metavolcanic, metasedimentary, and granitic rocks in the Rottenstone Domain have the distinctive geochemical signatures of an arc environment. New sensitive high-resolution ion microprobe (SHRIMP) UPb geochronology on the Rottenstone granitoid rocks reveals complex growth histories for monazite and zircon, variably controlled by inheritance, magmatism, and high-grade metamorphism. Monazite ages for the granitoid bodies and migmatites cluster at ~1834 and ~1814 Ma, whereas zircon ages range from ~2480 Ma (rare cores) to ~19001830 Ma (cores and mantles), but also ~18181814 Ma for low Th/U recrystallized rims, overgrowths, and rare discrete euhedral prisms. These results demonstrate that at least some source material for the granitic magmas included earliest Paleoproterozoic crust (Sask Craton?), or its derived sediments, and that Rottenstone granitic magmatism postdated plutonism in the bounding La Ronge Arc and Wathaman Batholith. We estimate the age of terminal metamorphism in the Davin Lake area to be ~1815 Ma. Petrogenetically, the Rottenstone migmatites and granitoid rocks appear, for the most part, locally derived from their metasedimentary and metavolcanic host rocks, shed from the La Ronge Arc, Sask Craton, and possibly the Hearne Craton. The Rottenstone Domain was the least competent member in the overthrust stack and probably underwent a combination of fluid-present melting and fluid-absent decompression melting, resulting in largely syntectonic granitoid magmatism ~18351815 Ma, analogous to granite production in the High Himalayan gneiss belt.
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Leclair, A. D., S. B. Lucas, H. J. Broome, D. W. Viljoen, and W. Weber. "Regional mapping of Precambrian basement beneath Phanerozoic cover in southeastern Trans-Hudson Orogen, Manitoba and Saskatchewan." Canadian Journal of Earth Sciences 34, no. 5 (May 1, 1997): 618–34. http://dx.doi.org/10.1139/e17-049.
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The northern edge of Phanerozoic platformal rocks of the Western Canada Sedimentary Basin overlies the Flin Flon Belt (Trans-Hudson Orogen) in Manitoba and Saskatchewan. A program of regional mapping of the Phanerozoic-covered basement has been undertaken, involving the integration of high-resolution aeromagnetic and gravity data with extensive drill core information. Several major domains are recognized in the buried basement, each with a distinct lithotectonic character and potential field anomaly pattern. Three lithotectonic domains in the buried basement (Clearwater, Athapapuskow, and Amisk Lake domains) are characterized by northerly-trending positive gravity and aeromagnetic anomalies and correlate with the 1.92–1.83 Ga volcanic and plutonic rocks of the exposed Flin Flon Belt (Amisk collage and Snow Lake assemblage). An upper amphibolite grade orthogneiss complex (Namew Gneiss Complex), containing calc-alkaline intrusive rocks ranging in age from 1.88 to 1.83 Ga and screens derived from the older volcano-sedimentary rocks, is interpreted as the middle crust of a 1.88–1.84 Ga arc exposed in the Flin Flon Belt. Discordant intrusive complexes, such as the 1.830 Ga Cormorant Batholith, are centred on magnetic–gravity lows and truncate the structural trend of adjacent lithotectonic domains. Correlation of Flin Flon Belt geology with that beneath the Phanerozoic cover shows that its constituent lithotectonic elements have north–south strikes of up to 150 km, and form a predominantly east-dipping crustal section, consistent with Lithoprobe seismic reflection profiles.
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Wahlgren, Carl-Henric, and Michael B. Stephens. "Chapter 7 Småland lithotectonic unit dominated by Paleoproterozoic (1.8 Ga) syn-orogenic magmatism, Svecokarelian orogen." Geological Society, London, Memoirs 50, no. 1 (2020): 207–35. http://dx.doi.org/10.1144/m50-2017-19.
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AbstractThe Småland lithotectonic unit in the 2.0−1.8 Ga Svecokarelian orogen, southeastern Sweden, is dominated by a c. 1.81−1.77 Ga alkali–calcic magmatic suite (the Transscandinavian Igneous Belt or TIB-1). At least in its central part, the TIB-1 suite was deposited on, or emplaced into, c. 1.83–1.82 Ga calc-alkaline magmatic rocks with base metal sulphide mineralization and siliciclastic sedimentary rocks (the Oskarshamn–Jönköping Belt). Ductile deformation and metamorphism under low- to medium-grade conditions affected the Oskarshamn–Jönköping Belt prior to c. 1.81 Ga. Both suites were subsequently affected by low-grade ductile deformation, mainly along steeply dipping, east–west to NW–SE shear zones with dip-slip and dextral strike-slip displacement. Sinistral strike-slip NE–SW zones are also present. In the northern part of the lithotectonic unit, 1.9 Ga magmatic rocks, c. 1.87–1.81 Ga siliciclastic sedimentary rocks and basalt, and c. 1.86–1.85 Ga granite show fabric development, folding along steep NW–SE axial surfaces and medium- or high-grade metamorphism prior to c. 1.81 Ga and, at least partly, at c. 1.86–1.85 Ga; base metal sulphide, Fe oxide and U or U–REE mineralizations also occur. Magmatism and siliciclastic sedimentation along an active continental margin associated with subduction-related, accretionary tectonic processes is inferred over about 100 million years.
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Alvarez, Vincenzo Costanzo, and David J. Dunlop. "A regional paleomagnetic study of lithotectonic domains in the Central Gneiss Belt, Grenville Province, Ontario." Earth and Planetary Science Letters 157, no. 1-2 (April 1998): 89–103. http://dx.doi.org/10.1016/s0012-821x(98)00028-4.
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ZHAO, GUOCHUN, ALFRED KRÖNER, SIMON A. WILDE, MIN SUN, SANZHONG LI, XUPING LI, JIAN ZHANG, XIAOPING XIA, and YANHONG HE. "Lithotectonic elements and geological events in the Hengshan–Wutai–Fuping belt: a synthesis and implications for the evolution of the Trans-North China Orogen." Geological Magazine 144, no. 5 (June 19, 2007): 753–75. http://dx.doi.org/10.1017/s0016756807003561.
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The Hengshan–Wutai–Fuping belt is located in the middle segment of the Trans-North China Orogen, a Palaeoproterozoic continental collisional belt along which the Eastern and Western blocks amalgamated to form the North China Craton. The belt consists of the medium- to high-grade Hengshan and Fuping gneiss complexes and the intervening low- to medium-grade Wutai granite–greenstone terrane, and most igneous rocks in the belt are calc-alkaline and have affinities to magmatic arcs. Previous tectonic models assumed that the Hengshan and Fuping gneiss assemblages were an older basement to the Wutai supracrustal rocks, but recent studies indicate that the three complexes constitute a single, long-lived Neoarchaean to Palaeoproterozoic magmatic arc where the Wutai Complex represents an upper crustal domain, whereas the Hengshan and Fuping gneisses represent the lower crustal components forming the root of the arc. The earliest arc-related magmatism in the belt occurred at 2560–2520 Ma, marked by the emplacement of the Wutai granitoids, which was followed by arc volcanism at 2530–2515 Ma, forming the Wutai greenstones. Extension driven by widespread arc volcanism led to the development of a back-arc basin or a marginal sea, which divided the belt into the Hengshan–Wutai island arc (Japan-type) and the Fuping relict arc. At 2520–2480 Ma, subduction beneath the Hengshan–Wutai island arc caused partial melting of the lower crust to form the Hengshan tonalitic–trondhjemitic–granodioritic (TTG) suites, whereas eastward-directed subduction of the marginal sea led to the reactivation of the Fuping relict arc, where the Fuping tonalitic–trondhjemitic–granodioritic suite was emplaced. In the period 2360–2000 Ma, sporadic phases of isolated granitoid magmatism occurred in the Hengshan–Wutai–Fuping region, forming 2360 Ma, c. 2250 Ma and 2000–2100 Ma granitoids in the Hengshan Complex, the c. 2100 Ma Wangjiahui and Dawaliang granites in the Wutai Complex, and the 2100–2000 Ma Nanying granitoids in the Fuping Complex. At c. 1920 Ma, the Hengshan–Wutai island arc underwent an extensional event, possibly due to the subduction of an oceanic ridge, leading to the emplacement of pre-tectonic gabbroic dykes that were subsequently metamorphosed, together with their host rocks, to form medium- to high-pressure granulites. At 1880–1820 Ma, the Hengshan–Wutai–Fuping arc system was juxtaposed, intensely deformed and metamorphosed during a major and regionally extensive orogenic event, the Lüliang Orogeny, which generated the Trans-North China Orogen through collision of the Eastern and Western blocks. The Hengshan–Wutai–Fuping belt was finally stabilized after emplacement of a mafic dyke swarm at 1780–1750 Ma.
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Shellnutt, J. G. "The enigmatic continental crust of North-Central Africa: Saharan Metacraton or Central Sahara Shield?" South African Journal of Geology 124, no. 2 (June 1, 2021): 383–90. http://dx.doi.org/10.25131/sajg.124.0047.
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Abstract The continental crust of North-Central Africa between the Tuareg and Arabian-Nubian shields and south to the Central African Orogenic Belt is enigmatic due to the few bedrock exposures especially within the central region. The current understanding, based on a review of geochronology and isotope geochemistry, is that the central Sahara region is a large, coherent craton that was ‘highly remobilized’ during the Late Neoproterozoic amalgamation of Gondwana and referred to as the Saharan Metacraton. However, new data from the Guéra, Ouaddaï, and Mayo Kebbi massifs and the Lake Fitri inlier of Chad suggest that it may be a composite terrane of older cratonic blocks or microcontinents with intervening Mesoproterozoic to Neoproterozoic domains and referred to as the ‘Central Sahara Shield’. It is postulated that the older crust and juvenile crust were sutured together along a Pan-Gondwana collisional belt (Central Sahara Belt) that bisects the central Sahara region. The ‘Central Sahara Shield’ hypothesis suggests the Chad Lineament, a narrow arcuate gravity anomaly within central Chad, could be a collisional belt suture zone and that it may explain the existence of the relatively juvenile crust that typifies southern and eastern Chad. The new data improves upon the existing knowledge and challenges the lithotectonic paradigm of the Saharan Metacraton. Further investigations are required to fully characterize the crust of the central Sahara region and to test the contrasting hypotheses.
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JASTRZĘBSKI, MIROSŁAW. "New insights into the polyphase evolution of the Variscan suture zone: evidence from the Staré Město Belt, NE Bohemian Massif." Geological Magazine 149, no. 6 (February 28, 2012): 945–63. http://dx.doi.org/10.1017/s0016756812000040.
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AbstractForming a northern continuation of the Moldanubian Thrust Zone, the Staré Město Belt comprises an E-verging thrust stack of three narrow lithotectonic units that exhibit variations in their respective P–T records. The upper and lower units form the respective margins of the hanging wall and footwall of the suture zone and are dominated by amphibolite grade metasedimentary successions. The middle unit is defined by an elongated body of MORB-like amphibolites that contains inserts of migmatized mica schists. Integrating both structural studies and pseudosection modelling in the MnNCKFMASH system shows that the present-day tectonic architecture of the Staré Město Belt is the result of a polyphase Variscan evolution. During a frontal, WNW–ESE-directed (in present-day coordinates) collision between the Bohemian Massif terranes and the Brunovistulian terrane, the metasedimentary rocks of the Staré Město Belt experienced tectonic burial to depths corresponding to 7–9 kbar. The continuous indentation and underthrusting of the Brunovistulian terrane led to top-to-the-ESE folding and uplift of these rocks to depths corresponding to 5.5–6.0 kbar at peak temperature. At depths corresponding to 5.5 kbar, the Staré Město Belt underwent subsequent dextral (top-to-the-NNE) shearing that was locally associated with nearly isobaric heating, possibly related to the emplacement of a Carboniferous tonalite body in the axial part of the Staré Město Belt. Subsequent tectonic compression resulted in the Variscan WNW-dipping metamorphic foliations becoming locally (N)NE- or ESE-dipping.
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Sidik, Ouattara Aboubakar, Coulibaly Yacouba, and Kouadio Fossou J-L. H. "Les Altérations Hydrothermales Associées À La Minéralisation Aurifère Du Gisement De Dougbafla (District d’Oumé-Hiré, Centre-Ouest De La Côte d’Ivoire)." European Scientific Journal, ESJ 13, no. 30 (October 31, 2017): 108. http://dx.doi.org/10.19044/esj.2017.v13n30p108.
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The Dougbafla gold deposit is located in the West-Central part of Côte d’Ivoire at about 240 km from Abidjan, on the Birimian greenstone belt of Fettèkro (West African craton). The lithologies of this deposit can be divided into three lithotectonic units which correspond to volcanic, sedimentary, and plutonic assemblages metamorphosed in the shale facies. Hydrothermalism, on the one hand, caused a pervasive alteration of the primary paragenesis marked by sericitic, silica, and carbonate alteration. On the other hand, it causes a vein alteration materialized by quartz veins. These hydrothermal alterations induced two types of gold mineralization in the Dougbafla deposit. These are: (i) disseminated gold and sulphide mineralization in the granophyre associated with sericite, silica and dolomite alteration in which no quartz vein has been reported; this type however is controlled by the intrusion of granophyre and (ii) a quartz vein mineralization controlled by deformation.
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Biswal, T. K. "The Lithotectonic Setting of the Eastern Ghat Mobile Belt and Adjoining Craton in Western Orissa, India: An Example of Mesoproterozoic Fold-Thrust Belt." Gondwana Research 1, no. 3-4 (October 1998): 410–12. http://dx.doi.org/10.1016/s1342-937x(05)70858-3.
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Amanipoor, Hakimeh. "ACTIVE DEFORMATION DELINEATED BY GEOMORPHIC AND SEDIMENTARY RESPONSE OF RIVERS, CENTRAL ZAGROS FOLD – THRUST BELT, SW IRAN." Geodesy and Cartography 41, no. 3 (October 6, 2015): 137–44. http://dx.doi.org/10.3846/20296991.2015.1086143.
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The mountain generation in Iran is because of continental collision between the Arabian and Eur-asia plate. Southwestern Iran shows active shorten that its evidences is deformation of crust and frequent earthquakes. At depth, active basement of the Zagros fold-thrust-belt in southwestern Iran, which are covered by folding of the Phanerozoic sediments, affected by some blind thrusted faults that have seismic nature. The Zagros fold-thrust-belt can be divided into 4 lithotectonic units including Sanandaj-Sirjan Zone (SSZ), Imbricate Zone (IZ), Zagros Fold Belt (ZFB), and Molasse Cover Sequence (MCS); this dividing and classification is based on geomorphology landscape, drainage pattern, rate of tectonics and stratigraphic records. Each tectonic unit characterized by especial abnormal forces in river systems. Active tectonics has the most important role to control the river systems by changing of channels incline. Change in the drainage pattern, channels cut, longitudinal profile, anomalous changes of sinuosity, changing of the side form and forming of terrace, change of river direction, compact meanders, cutting of meanders and geomorphology features of the rivers are responds to the active tectonics of region that are studied using remote sensing, DEM and field observations. These parameters are used to understand the vertical movement in the study area. Existing structures, especially growing anticlines and blind thrusted faults in the Zagros fold-thrust-belt, which cut the river channels and sometimes put them in parallel, are used in the study of their effect on the longitudinal and transverse tilt of morphological changes.
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Hanmer, Simon, and Sally McEachern. "Kinematical and rheological evolution of a crustal-scale ductile thrust zone, Central Metasedimentary Belt, Grenville orogen, Ontario." Canadian Journal of Earth Sciences 29, no. 8 (August 1, 1992): 1779–90. http://dx.doi.org/10.1139/e92-140.
Full textAbstract:
The Central Metasedimentary Belt boundary thrust zone is a 10 km thick, 200+ km long, stack of crystalline thrust sheets, enclosed by an anastomosing network of ductile thrust zones, formed at mid- to deep-crustal depths in the southwest Grenville orogen, Ontario. It has behaved as a coherent upper amphibolite facies thrust zone, accommodating northwestward transport of the Central Metasedimentary Belt, the largest lithotectonic entity in this part of the orogen, by coherent and contemporaneous displacements. The earliest thrusting was well under way by ca. 1.19–1.18 Ga and the boundary thrust zone was reactivated at ca. 1.08–1.05 Ga. The early thrusting records the closure of a back-arc basin within the Central Metasedimentary Belt, which closed at ca. 1.19–1.18 Ga. The younger thrusting may reflect continental collision to the southeast of the exposed Grenville and represent intraplate reactivation of the boundary thrust zone, which acted as an older, crustal-scale zone of weakness. Transverse mid- to deep-crustal thrusting was apparently contemporaneous with longitudinal (orogen-parallel) shearing at higher structural levels. The rheological behaviour of the deforming media may have influenced the localization of both the upper and lower limits of the boundary thrust zone at the time of its initiation. The upper limit coincides with a chain of relatively stiff metagabbro bodies, which may have acted as a barrier to the upward migration of fluids responsible for syntectonic nephelinization at the top of the thrust zone.
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Berger, J., O. Féménias, J. C. C. Mercier, and D. Demaiffe. "A Variscan slow-spreading ridge (MOR-LHOT) in Limousin (French Massif Central): magmatic evolution and tectonic setting inferred from mineral chemistry." Mineralogical Magazine 70, no. 2 (April 2006): 175–85. http://dx.doi.org/10.1180/0026461067020322.
Full textAbstract:
AbstractThe Limousin ophiolite (French Massif Central) occurs as elongate bodies forming a (nearly) continuous suture zone between two major lithotectonic units of the French Variscan belt. The mantle section of the ophiolite is made of diopside-bearing harzburgite, harzburgite and dunite characteristic of a lherzolite-harzburgite ophiolite type (LHOT). The plutonic section is essentially composed of troctolites, wehrlites and gabbros locally intruded by ilmenite-rich mafic dykes. All the rocks were strongly affected by an ocean-floor hydrothermal metamorphism. The composition and evolution of primary magmatic phases (olivine, clinopyroxene, plagioclase and spinel) throughout the lowermost magmatic sequence correspond to those described in oceanic cumulates (ODP data). The Limousin ophiolite is thus of MOR type instead of SSZ type. The whole lithological section, the mineral chemistry, the extensive hydrothermal oceanic alteration and the relatively thin crustal section are typical of a slow-spreading ridge ocean (i.e. Mid-Atlantic ridge). Comparison of the Limousin ophiolite with other ophiolites from European Variscides suggests that the oceanic domain was actively spreading during the Late Palaeozoic and extended from the Armorican massif to the Polish Sudetes.
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Wodicka, N., R. A. Jamieson, and R. R. Parrish. "The Parry Sound domain: a far-travelled allochthon? New evidence from U–Pb zicon geochronology." Canadian Journal of Earth Sciences 33, no. 7 (July 1, 1996): 1087–104. http://dx.doi.org/10.1139/e96-083.
Full textAbstract:
We report U–Pb zircon ages for metaplutonic and metasedimentary rocks from three lithotectonic assemblages within the Parry Sound allochthon of the Central Gneiss Belt, southwestern Grenville Orogen: the basal Parry Sound, interior Parry Sound, and Twelve Mile Bay assemblages. Magmatic crystallization ages for granitic to tonalitic gneisses from the basal Parry Sound assemblage fall in the range 1400–1330 Ma. Younger intrusions include the Parry Island anorthosite dated at 1163 ± 3 Ma and a crosscutting mafic dyke bracketed between 1151 and 1163 Ma. Dated at [Formula: see text] a tonalitic gneiss from the overlying interior Parry Sound assemblage is slightly younger than the older group of rocks from the basal Parry Sound assemblage. 207Pb/206Pb ages for zircons from a quartzite of the basal Parry Sound assemblage range from 1385 Ma to the Neoarchaean. An absolute maximum age for this quartzite is 1436 ± 17 Ma. In contrast, detrital zircons from a quartzite of the Twelve Mile Bay assemblage constrain the age of deposition at post-ca. 1140–1120 Ma. We speculate that Grenvillian-age zircons within this quartzite were derived from rocks in the Adirondack Highlands and Frontenac terrane, implying that part of the Parry Sound domain and these terranes were contiguous during deposition of the quartzite. Our data support previous interpretations that the Parry Sound domain is allochthonous with respect to its surroundings, and suggest that the most likely source region of the basal Parry Sound domain lies southeast of the Central Gneiss Belt, within the Central Metasedimentary Belt boundary thrust zone or the Adirondack Highlands. This implies the possibility of 100–300 km of displacement of the domain. Emplacement of the Parry Sound domain into its present position must have occurred relatively late in the orogen's history, by about 1080 Ma.
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Ketchum, J. WF, and A. Davidson. "Crustal architecture and tectonic assembly of the Central Gneiss Belt, southwestern Grenville Province, Canada: a new interpretation." Canadian Journal of Earth Sciences 37, no. 2-3 (April 2, 2000): 217–34. http://dx.doi.org/10.1139/e98-099.
Full textAbstract:
The Central Gneiss Belt, southwestern Grenville Province, is characterized by parautochthonous crust in the north and allochthonous lithotectonic domains in the south. Despite nearly two decades of study, the basal décollement to allochthonous domains transported from the southeast, known as the allochthon boundary thrust, has not been precisely located throughout much of the belt. Between Lake Nipissing and Georgian Bay where its surface trace is known, it separates 1.24 Ga Sudbury metadiabase in the footwall from eclogite remnants and 1.17-1.15 Ga coronitic olivine metagabbro confined to its hanging wall. On the premise that this relationship can be used to trace the allochthon boundary thrust elsewhere in the Central Gneiss Belt, we have sought to extend the known distribution of these mafic rock types, making use of field, petrographic, and geochemical criteria to identify them. New occurrences of all three mafic types are identified in a region extending from south of Lake Nipissing to western Quebec, and the mutually exclusive pattern of occurrence is maintained within this region. Structural trends and reconnaissance mapping of high-strain zones that appear to represent a structural barrier to the mafic suites suggest that the allochthon boundary thrust lies well to the north of its previously suggested location. Our preferred surface trace for it passes around the southern end of the Powassan batholith and through the town of North Bay before turning east to join up with the Lac Watson shear zone in western Quebec. This suggests that a large segment of "parautochthonous" crust lying north of, and including, the Algonquin domain is in fact allochthonous. The mutually exclusive distribution of the mafic suites points to significant separation of allochthonous and parautochthonous components prior to the Grenvillian orogeny, in accord with models of pre-Grenvillian continental rifting proposed by others. Despite a relative abundance of geological and geochronological data for the Central Gneiss Belt and a mafic rock distribution that appears to successfully locate a major tectonic boundary, we emphasize the need for additional field and laboratory work aimed at testing our structural model.
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AO, S. J., W. J. XIAO, C. M. HAN, X. H. LI, J. F. QU, J. E. ZHANG, Q. Q. GUO, and Z. H. TIAN. "Cambrian to early Silurian ophiolite and accretionary processes in the Beishan collage, NW China: implications for the architecture of the Southern Altaids." Geological Magazine 149, no. 4 (October 20, 2011): 606–25. http://dx.doi.org/10.1017/s0016756811000884.
Full textAbstract:
AbstractThe mechanism of continental growth of the Altaids is currently under debate between models invoking continuous subduction-accretion or punctuated accretion by closure of multiple ocean basins. We use the Yueyashan–Xichangjing ophiolite belt of the Beishan collage (southern Altaids) to constrain the earliest oceanic crust in the southern Palaeo-Asian Ocean. Five lithotectonic units were identified from S to N: the Huaniushan block, a sedimentary passive margin, the structurally incoherent Yueyashan–Xichangjing ophiolite complex, a coherent sedimentary package and the Mazongshan island arc with granitic rocks. We present a structural analysis of the accretionary complex, which is composed of the incoherent ophiolitic melange and coherent sedimentary rocks, to work out the tectonic polarity. A new weighted mean206Pb–238U age of 533 ± 1.7 Ma from a plagiogranite in the Yueyashan–Xichangjing ophiolite indicates that the ocean floor formed in early Cambrian time. Furthermore, we present new geochemical data to constrain the tectonic setting of the Yueyashan–Xichangjing ophiolite. The Yueyashan–Xichangjing ophiolite was emplaced as a result of northward subduction of an oceanic plate beneath the Mazongshan island arc to the north in late Ordovician to early Silurian time. Together with data from the literature, our work demonstrates that multiple overlapping periods of accretion existed in the Palaeozoic in the northern and southern Altaids. Therefore, a model of multiple accretion by closure of several ocean basins is most viable.
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Maxeiner, Ralf O., Tom II Sibbald, William L. Slimmon, Larry M. Heaman, and Brian R. Watters. "Lithogeochemistry of volcano-plutonic assemblages of the southern Hanson Lake Block and southeastern Glennie Domain, Trans-Hudson Orogen: evidence for a single island arc complex." Canadian Journal of Earth Sciences 36, no. 2 (February 1, 1999): 209–25. http://dx.doi.org/10.1139/e98-037.
Full textAbstract:
This paper describes the geology, geochemistry, and age of two amphibolite facies volcano-plutonic assemblages in the southern Hanson Lake Block and southeastern Glennie Domain of the Paleoproterozoic Trans-Hudson Orogen of east-central Saskatchewan. The Hanson Lake assemblage comprises a mixed suite of subaqueous to subaerial dacitic to rhyolitic (ca. 1875 Ma) and intercalated minor mafic volcanic rocks, overlain by greywackes. Similarly with modern oceanic island arcs, the Hanson Lake assemblage shows evolution from primitive arc tholeiites to evolved calc-alkaline arc rocks. It is intruded by younger subvolcanic alkaline porphyries (ca. 1861 Ma), synvolcanic granitic plutons (ca. 1873 Ma), and the younger Hanson Lake Pluton (ca. 1844 Ma). Rocks of the Northern Lights assemblage are stratigraphically equivalent to the lower portion of the Hanson Lake assemblage and comprise tholeiitic arc pillowed mafic flows and felsic to intermediate volcaniclastic rocks and greywackes, which can be traced as far west as Wapawekka Lake in the south-central part of the Glennie Domain. The Hanson Lake volcanic belt, comprising the Northern Lights and Hanson Lake assemblages, shows strong lithological, geochemical, and geochronological similarities to lithotectonic assemblages of the Flin Flon Domain (Amisk Collage), suggesting that all of these areas may have been part of a more or less continuous island arc complex, extending from Snow Lake to Flin Flon, across the Sturgeon-Weir shear zone into the Hanson Lake Block and across the Tabbernor fault zone into the Glennie Domain.
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Klasner, J. S., and E. R. King. "Precambrian basement geology of North and South Dakota." Canadian Journal of Earth Sciences 23, no. 8 (August 1, 1986): 1083–102. http://dx.doi.org/10.1139/e86-109.
Full textAbstract:
Combined analysis of drill-hole, gravity, and magnetic data indicates that the buried Precambrian basement rocks of the Dakotas can be divided into several lithotectonic terranes. Eastern North Dakota and northeastern South Dakota are underlain by Archean gneiss. Except for the Black Hills region of South Dakota, where Archean rocks are also exposed, the western third of both Dakotas is underlain mainly by Early Proterozoic gneiss and metasedimentary rocks. Part of this region is underlain by Archean crust with an Early Proterozoic tectonic overprint. A broad transition zone of strongly overprinted Archean crust occurs between the Proterozoic rocks to the west and the Archean rocks to the east. South central South Dakota is underlain by an Early Proterozoic batholith. Early Proterozoic felsic volcanic rocks occur in southeast South Dakota. The bootheel portion of South Dakota contains a diverse assemblage of basement rocks that are partly Archean in age.Churchill Province rocks of the Trans-Hudson foldbelt project into the western Dakotas. The Thompson nickel belt and the Pickwitonei gneiss belt correlate with the western and eastern halves, respectively, of the transition between Archean and Proterozoic crust, and the Archean Glennie – Hanson Lake microcontinent of the Churchill Province likely extends into western North Dakota. Archean rocks of Minnesota extend into the eastern Dakotas, and the Wyoming craton extends to the Black Hills region. The Cheyenne foldbelt projects into southwest South Dakota. The Penokean foldbelt of Michigan and Wisconsin does not extend into the Dakotas, but it most likely extends into northwest Iowa.Tectonic evolution of the Early Proterozoic terrane in the Dakotas was most likely similar to plate tectonic models for the evolution of the Trans-Hudson foldbelt in the Churchill Province. As in the Churchill Province, the western Dakotas are underlain by Early Proterozoic rocks, but it is not known whether these rocks formed as a result of rifting and subsequent closure of a once extensive Archean crust or as a result of collision of once widely separated blocks of Archean crust.
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Corfu, F., S. L. Jackson, and R. H. Sutcliffe. "U–Pb ages and tectonic significance of late Archean alkalic magmatism and nonmarine sedimentation: Timiskaming Group, southern Abitibi belt, Ontario." Canadian Journal of Earth Sciences 28, no. 4 (April 1, 1991): 489–503. http://dx.doi.org/10.1139/e91-043.
Full textAbstract:
The paper presents U–Pb ages for zircons of the calc-alkalic to alkalic igneous suite and associated alluvial–fluvial sedimentary rocks of the Timiskaming Group in the late Archean Abitibi greenstone belt, Superior Province. The Timiskaming Group rests unconformably on pre-2700 Ma komatiitic to calc-alkalic volcanic sequences and is the expression of the latest stages of magmatism and tectonism that shaped the greenstone belt. An age of 2685 ± 3 Ma for the Bidgood quartz porphyry, an age of about 2685–2682 Ma for a quartz–feldspar porphyry clast in a conglomerate, and ages ranging from 2686 to 2680 Ma for detrital zircons in sandstones appear to reflect an early stage in the development of the Timiskaming Group. The youngest detrital zircons in each of three sandstones at Timmins, Kirkland Lake, and south of Larder Lake define maximum ages of sedimentation at about 2679 Ma; the latter sandstone is cut by a porphyry dyke dated by titanite at [Formula: see text], identical to the 2677 ± 2 Ma age for a volcanic agglomerate of the Bear Lake Formation north of Larder Lake. Similar ages have previously been reported for syenitic to granitic plutons of the region. The dominant period of Timiskaming sedimentation and magmatism was thus 2680–2677 Ma. Xenocrystic zircons found in a porphyry and a lamprophyre dyke have ages of 2750–2720 Ma, which correspond to the ages of the oldest units in the belt, predating the volumetrically dominant ca. 2700 Ma greenstone sequences. The presence of these xenocrysts and the onlapping of the Timiskaming Group on all earlier lithotectonic units of the southern Abitibi belt support the concept that the 2700 Ma ensimatic sequences were thrust onto older assemblages during a phase of compression that culminated with the generation of tonalite and granodiorite at about 2695–2688 Ma. Published geochemical data for the Timiskaming igneous suite, notably the enrichments in large-ion lithophile elements and light rare-earth elements and the relative depletion of Nb, Ta, and Ti compare with the characteristics of suites at modern convergent settings such as the Eolian and the Banda arcs and are consistent with generation of the melts from deep metasomatized mantle in the final stages of, or after cessation of, subduction. Late- and post-Timiskaming compression caused north-directed thrusting and folding. Turbiditic sedimentary units of the Larder Lake area which locally structurally overly the alluvial–fluvial sequence and were earlier thought to be part of the Timiskaming Group, appear to be older "flyschoid" sequences, possibly correlative with sedimentary rocks deposited in the Porcupine syncline at Timmins between 2700 and 2690 Ma.
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James, Donald T., and James K. Mortensen. "An Archean metamorphic core complex in the southern Slave Province: basement–cover structural relations between the Sleepy Dragon Complex and the Yellowknife Supergroup." Canadian Journal of Earth Sciences 29, no. 10 (October 1, 1992): 2133–45. http://dx.doi.org/10.1139/e92-169.
Full textAbstract:
Archean rocks in the Fenton Lake – Brown Lake area, southern Slave Province, are subdivided into two lithotectonic domains: a supracrustal domain, which consists mainly of the Archean Yellowknife Supergroup, and a gneiss–granite domain. The latter is composed of gneissic and metaigneous rocks of the Sleepy Dragon Complex, determined to be basement to the Yellowknife Supergroup, and granite plutons, including the 2641 ± 3.5 Ma Suse Lake granite and the 2583.5 ± 1 Ma Morose Granite. Volcanic rocks of the Cameron River Belt and greywacke–mudstone turbiditic metasedimentary rocks of the Burwash Formation constitute the supracrustal domain.A late Archean, amphibolite- to greenschist-facies, ductile to local brittle, high-strain zone separates the domains. Kinematic indicators demonstrate that the zone experienced two kinematically opposed episodes of displacement. The older episode involved pre- to synthermal peak thrusting of the supracrustal rocks over the gneiss–granite domain. Thrusting is kinematically and temporally consistent with late Archean, pre- to synthermal peak, regional contractional deformation. Structural and metamorphic relations and kinematic indicators suggest that thrusting and regional contraction were followed shortly by intrusion of the peraluminous Morose Granite and thereafter by a late syn- to post-thermal peak episode of extension, resulting in tectonic unroofing of the gneiss–granite domain.The sequential history of contraction and attendant regional metamorphism, granite intrusion, and, ultimately, extensional collapse, which is documented in the Archean rocks in the area, is a common feature of Phanerozoic collisional orogens. Moreover, the tectonic history of the gneiss–granite domain is broadly similar to the evolution of metamorphic core complexes in the North American Cordillera.
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Davis, D. W., and J. R. Bartlett. "Geochronology of the Belmont Lake Metavolcanic Complex and implications for crustal development in the Central Metasedimentary Belt, Grenville Province, Ontario." Canadian Journal of Earth Sciences 25, no. 11 (November 1, 1988): 1751–59. http://dx.doi.org/10.1139/e88-166.
Full textAbstract:
U–Pb analyses of zircon and titanite were carried out on eight rocks from the Belmont Lake Metavolcanic Complex, a volcano-sedimentary sequence in the Central Metasedimentary Belt of the Grenville Province of southeastern Ontario. The ages of concordant supracrustal rocks within the complex do not accord with stratigraphic position.The youngest volcanic age is [Formula: see text] from a rhyolite near the base of the sequence. The oldest age, [Formula: see text], is from a dacite in the middle. This is overlain by a rhyolite [Formula: see text] in age. A rhyolite at the top of the sequence appears to contain zircon inherited from a source about 1870 Ma old. The complex is therefore interpreted as comprising a lithotectonic sequence composed of structurally interleaved segments of contrasting age. Tectonic emplacement of these segments was most likely along previously unrecognized thrust faults.The supracrustal rocks were subjected to at least two major deformational events as well as a late metamorphism. The earliest event was probably associated with thrusting. The age of the youngest volcanic unit, [Formula: see text], is an upper age estimate for this event. A lower estimate is probably given by the age of the Cordova Gabbro, 1242 ± 3 Ma. The later event, including peak regional metamorphism, should be younger than [Formula: see text], the age of a sheared, recrystallized felsic sill intruded into the supracrustal rocks, and older than [Formula: see text], the age of the undeformed and unmetamorphosed Belmont Granite.Titanite fractions in the Belmont Granite and a volcanic andesite both give an age of 1071 ± 5 Ma. The age from titanite in the Belmont Granite may be due to thermal resetting during slow cooling. Titanite in the andesite is secondary and may have grown as a result of late metamorphic reactions.The youngest age measured, 1039 ± 5 Ma, is from a concordant analysis of a single zircon grain found within the oldest rhyolite. This may be an example of zircon growth from low-temperature, late-metamorphic fluids.
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Tourigny, Ghislain, Claude Hubert, A. C. Brown, and Robert Crépeau. "Structural geology of the Blake River Group at the Bousquet mine, Abitibi, Quebec." Canadian Journal of Earth Sciences 25, no. 4 (April 1, 1988): 581–92. http://dx.doi.org/10.1139/e88-056.
Full textAbstract:
In the Bousquet mining district, metamorphosed volcanic rocks of the Blake River Group (BRG) exhibit discrete strain features resulting from three generations of structures—D1, D2, and D3. Deformation D1 formed an east–west-trending, subvertical, penetrative schistosity that is coplanar with the axial plane of associated folds. This foliation contains a linear fabric plunging steeply westward, and mineral lineations are subparallel to fold axes and to intersection lineations.Defomations D2 and D3 formed a crenulation cleavage and a set of conjugate kink bands, respectively. The cleavage is oriented east–northeast, and the kink bands are oriented northeast–southwest and northwest–southeast. Both deformations distorted earlier-formed structures to a minor extent. A conjugate set of minor strike-slip faults with orientations similar to the kinks are the youngest structures found in BRG rocks.The volcanic sequence is composed of two lithotectonic domains juxtaposed along fault-related contacts. Each domain exhibits distinctive strain features attributed mainly to a broad network of anastomosing faults. This network of faults disrupted strata and destroyed many internal stratigraphic features, especially in domain 2; it relates to late stages of D1.Domain 1, occupying the northern half of the BRG in the mine area, represents a zone of weakly sheared tholeiitic basalts 750 m thick and is overlain by 150 m of felsic volcaniclastic rocks. Primary textures and structures indicate that this domain forms a south-facing homoclinal succession.Domain 2 is characterized by a strongly strained, 500 m wide belt of anastomosing faults adjacent to the southern margin of domain 1. Narrow bands of schist, mylonite, and phyllonite straddle fault zones and surround less-deformed, lozenge-shaped blocks of metamorphosed volcanic and (or) volcaniclastic rocks.The lack of syngenetic structures and textures, together with intense faulting and transposition, restricts stratigraphic correlations throughout the BRG as well as correlations between this volcanic succession and the adjacent sedimentary units. Structural evidence presented here complicates the original stratigraphic scheme commonly applied to volcano-sedimentary assemblages in the Rouyn–Val D'Or area. It is proposed that faulting is responsible for the spatial distribution of lithologies previously interpreted as resulting from folding phenomena in the Bousquet mining district. Gold mineralization is concentrated in bands of deformed rocks in the fault zones of domain 2 at the Bousquet mine.
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Petrie, Meredith Blair, Jane A. Gilotti, William C. McClelland, Cees Van Staal, and Sierra J. Isard. "Geologic Setting of Eclogite-facies Assemblages in the St. Cyr Klippe, Yukon–Tanana Terrane, Yukon, Canada." Geoscience Canada 42, no. 3 (July 29, 2015): 327. http://dx.doi.org/10.12789/geocanj.2015.42.073.
Full textAbstract:
The St. Cyr area near Quiet Lake hosts well preserved to variably retrogressed eclogite found as sub-metre to hundreds of metre-long lenses within quartzofeldspathic schist in south-central Yukon, Canada. The St. Cyr klippe consists of structurally imbricated, polydeformed and polymetamorphosed units of continental arc crust and ultramafic–mafic rocks. Eclogite-bearing quartzofeldspathic schist forms thrust slices in a 30 km long by 6 km wide, northwest-striking outcrop belt. The schist unit comprises metasedimentary and felsic intrusive rocks that are intercalated on the metre to tens of metres scale. Ultramafic rocks, serpentinite and associated greenschist-facies metagabbro form imbricated tectonic slices within the eclogite-bearing quartzofeldspathic unit, which led to a previously held hypothesis that eclogite was exhumed within a tectonic mélange. The presence of phengite and Permian zircon crystallized under eclogite-facies metamorphic conditions in the quartzofeldspathic host rocks indicate that the eclogite was metamorphosed in situ together with the schist as a coherent unit that was part of the continental arc crust of the Yukon–Tanana terrane, rather than a mélange associated with the subduction of oceanic crust of the Slide Mountain terrane. Petrological, geochemical, geochronological and structural similarities link St. Cyr eclogite to other high-pressure localities within Yukon, indicating the high-pressure assemblages form a larger lithotectonic unit within the Yukon–Tanana terrane.RÉSUMÉLa région de St-Cyr renferme des éclogites bien conservées à légèrement rétrogradées qui se présentent sous forme de lentilles allant de la fraction de mètre à quelques centaines de mètres de longueur, au sein d’un schiste quartzofeldspathique du centre-sud du Yukon au Canada. La klippe de St-Cyr est structurellement constituée d’unités imbriquées, polydéformées et polymétamorphisées de croûte d’arc continental et de roches ultramafiques à mafiques. Les schistes quartzofeldspathiques à lentilles d’éclogites forment des écailles de chevauchement d’une bande de 30 km de longueur par 6 km de largeur de direction nord-ouest. Les schistes sont constitués de roches métasédimentaires et de roches intrusives felsiques intercalées à des intervalles qui vont du mètre à quelques dizaines de mètres. Les roches ultramafiques, serpentinites et métagabbros au facies à schiste vert forment des écailles tectoniques imbriquées au sein de l’unité quartzofeldspathique à lentilles d’éclogite, d’où une précédente hypothèse voulant que les éclogites soient un produit d’exhumation à partir d’un mélange tectonique. La présence de phengite et de zircon permien cristallisé sous conditions métamorphiques du faciès à éclogite au sein de la roche hôte quartzofeldspathique indiquent que l’éclogite a été métamorphisée en place, avec le schiste comme unité cohérente du terrane de croûte d’arc continental de Yukon–Tanana, plutôt qu’un mélange associé à une subduction de croûte océanique du terrane de Slide Mountain. Des similarités pétrologiques, géochimiques, géochronologiques et structurales lient les éclogites de St-Cyr à d’autres lieux de hautes pressions au Yukon, ce qui indique que les assemblages de hautes pressions forment une unité lithotectonique plus grande au sein du terrane de Yukon–Tanana.
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Hibbard, James, and Paul Karabinos. "Disparate Paths in the Geologic Evolution of the Northern and Southern Appalachians: A Case for Inherited Contrasting Crustal/Lithospheric Substrates." Geoscience Canada 40, no. 4 (December 20, 2013): 303. http://dx.doi.org/10.12789/geocanj.2013.40.021.
Full textAbstract:
Modern understanding of the tectonic evolution of the Appalachian orogen allows for recognition of most of the first-order lithotectonic elements and events of the mountain belt. Comparison of these features and events along the length of the orogen indicates that the northern and southern segments display distinct first-order differences. Contrasts between these segments existed from the onset of the Appalachian cycle. It has been recognized that Mesoproterozoic basement rock types south of approximately Pennsylvania are different from those to the north and more recently it has been shown that basement rocks in each area display distinct Nd and Pb isotopic signatures. Also, an early, ca. 770–680 Ma, Cryogenian stage of rifting is recorded in the southern Appalachians, but is not documented in the northern part of the orogen. During the Paleozoic Appalachian cycle, the accretion of peri-Gondwanan terranes was partitioned; Carolinia and Suwannee are confined to the southern Appalachians, and Ganderia, Avalonia, and Meguma to the northern Appalachians. Consequential to this partitioning, associated magmatism and some of the attendant tectonism is asymmetrically distributed between the two segments of the orogen. The terminal Appalachian collisional event, the Carboniferous Alleghanian orogeny, is distinctly different in the two segments of the orogen. The volumes of Alleghanian magmatic rocks in the northern and southern Appalachians are distributed asymmetrically and Carboniferous tectonic styles contrast sharply between the two regions. In addition, there is a modern first-order topographic change in the foreland of the orogeny. The southern foreland is characterized by a continuous, elevated plateau, whereas north of the New York promontory, foreland topography is more varied. Throughout the Appalachian cycle, all of these varied first-order changes occur in the vicinity of the New York promontory, suggesting that the promontory represents an enduring, fundamental boundary in the orogen. The nature and duration of differences between the northern and southern segments of the orogen indicate that this boundary was not an extrinsic ephemeral feature, such as a plate triple junction or hot spot. Rather, we suggest that an intrinsic difference in the Laurentian crustal/lithospheric(?) substrate present from the outset of the Appalachian cycle, as reflected by contrasts in the Mesoproterozoic basement in each segment, could be the root cause of these significant contrasts.SOMMAIREL’état actuel des connaissances sur l’évolution tectonique de l’orogène appalachien nous permet de reconnaître la plupart des éléments et des événements lithotectoniques de premier niveau de la chaîne de montagnes. La comparaison de ces caractéristiques et événements tout au long de l'orogène permet de distinguer des différences de premier ordre entre les segments nord et sud. Des contrastes entre ces segments ont existé depuis le début des Appalaches. Il a été reconnu que les roches de type socle du Mésoprotérozoïque à partir du sud de la Pennsylvanie environ, diffèrent de celles au nord, et plus récemment, il a été démontré que les roches de socle dans chacun de ces segments ont des signatures isotopiques Nd et Pb distinctes. En outre, un début de phase de distension au Cryogénien (770-680 Ma env.) est présent dans le segment sud des Appalaches, mais n'est pas documenté dans le segment nord de l'orogène. Durant le cycle paléozoïque des Appalaches, l'accrétion des terranes péri-Gondwana a été partagé; les terranes de Carolinia et de Suwannee sont confinés au segment sud des Appalaches, alors que ceux de Ganderia, d’Avalonie, et de Meguma sont confinés au segment nord des Appalaches. Conséquence de cette répartition, le magmatisme associé ainsi qu’une partie du diastrophisme relié sont répartis de manière asymétrique entre les deux segments de l'orogène. La phase terminale de collision des Appalaches, l'orogenèse Carbonifère alléghanienne, est nettement différente dans les deux segments de l'orogène. Les volumes des roches magmatiques alléghaniennes dans les Appalaches septentrionales et méridionales sont répartis de manière asymétrique et les styles tectoniques carbonifères contrastent fortement entre ces deux régions. En outre, on observe une différence topographique de premier ordre dans l’état actuel de l'avant-pays de l'orogenèse. Le segment sud de l'avant-pays est caractérisé par un plateau élevé continu, alors qu’au nord du promontoire de New York, la topographie d'avant-pays est plus diversifiée. Tout du long du cycle des Appalaches, tous ces changements variés de premier ordre existent au pourtour du promontoire de New York, ce qui permet de penser que le promontoire représente une frontière déterminante durable dans l'orogène. La nature et la persistance de ces différences entre les segments nord et sud de l'orogène indiquent que cette limite n'était pas une caractéristique éphémère extrinsèque, comme une jonction triple de plaque ou un point chaud. Nous suggérons plutôt qu'une différence intrinsèque dans la croûte/substrat lithosphérique(?) laurentien existait dès le début du cycle des Appalaches, comme en témoignent les contrastes dans le socle mésoprotérozoïque dans chaque segment, et pourrait être la cause de ces contrastes significatifs.
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"Metamorphism in allochthonous and autochthonous terranes of the western United States." Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences 331, no. 1620 (June 30, 1990): 549–70. http://dx.doi.org/10.1098/rsta.1990.0089.
Full textAbstract:
The haphazard accretion of exotic terranes during continental reassembly results in a crustal college typified by genetically unrelated lithotectonic belts. Profound chronologic, lithologic, geochemical, and metamorphic breaks characterize such suture zones. However, post-metamorphic differential vertical uplift and erosion can generate a marked discontinuity in grade within a single lithotectonic entity, and in contrast, post-amalgamation recrystallization of an exotic terrane assembly can produce an isofacial metamorphic overprint. Thus the tectonic context of metamorphic mineral parageneses must be interpreted with caution. In spite of the presence of allochthonous terranes, the western U.S. Cordillera in general is characterized by gradual sectorial enlargements towards the modern edge of the continent, by coherent, broadly continuous isotopic or geochemical provinces, and by systematic oceanward decreases in the metamorphic intensities of the constituent lithic assemblages, both within a belt, and across a series of belts. These relationships hold over a wide range of scales, from that of a physiographic province to that of a quadrangle-sized area. Examples described include chronologic, isotopic, igneous and metamorphic belts of (1) the entire western conterminous U.S. Cordillera, (2) the Phanerozoic Sierran-Klamath basement terrane assembly, and (3) the Great Valley and Franciscan sedimentary couplet derived from the late Mesozoic Sierra Nevada-TClamath arc. For these cases, systematic recrystallization-deformation trends and nearly in situ growth of sialic crust are evident. Mapped metamorphic and structural discontinuities reflect dislocations involving spatially associated, co-evolving continental lithotectonic units, and, except for fartravelled oceanic fragments, do not imply wholesale juxtaposition of exotic, genetically unrelated terranes.
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"Chapter 4 The Loch Maree Group." Geological Society, London, Memoirs 26, no. 1 (2002): 29–44. http://dx.doi.org/10.1144/gsl.mem.2002.026.01.04.
Full textAbstract:
The supracrustal rocks of the Loch Maree Group (LMG) consist of a variety of metasedimentary rocks interbanded with amphibolites considered to be of volcanic origin. The metasedimentary rocks fall into two distinct categories: a) schistose semipelites, which form the main part of the outcrop; and b) narrow bands of different rock types, including siliceous, carbonate-bearing and graphitic rocks, occurring in close association with the metavolcanic amphibolites. Both the compositional banding and the dominant foliation throughout the LMG outcrop are steeply dipping and trend uniformly NW-SE.The sequence of lithotectonic rock units from SW to NE (structurally upwards) is shown in the cross-section (Fig. 4.1) and briefly described in Table 4.1. The original names of the lithotectonic units (Park 1964) are retained for convenience. The depositional age of the LMG is presumed to be around 2.0 Ga, based on a Sm-Nd model age (O'Nions et al. 1983) and detrital zircon dates (Whitehouse et al. 1991 a, 2001) (see below).Semipelites form several distinct NW-trending belts separated by amphibolite sheets. The most prominent belt comprises the Flowerdale schist unit (see map) which occupies a broad belt about 700 m in width, extending in a northwesterly direction across the Gairloch district, but ending north of the mapped area, where the two amphibolites from either side converge, 3.5 km north of the Gairloch-Poolewe road. This belt is offset in the centre of the area by the Flowerdale fault, and has a total exposed length of about 15 km. Southwest of this belt is the
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Cartwright, Samuel F. A., David P. West, Jr., and William H. Amidon. "Depositional constraints from detrital zircon geochronology of strata from multiple lithotectonic belts in south-central Maine, USA." Atlantic Geology, April 15, 2019, 093–136. http://dx.doi.org/10.4138/atlgeol.2019.003.
Full textAbstract:
The bedrock geology of south-central Maine is characterized by a series of fault-bounded lithotectonic terranes that were accreted onto the Laurentian margin during Silurian-Devonian orogenesis. The multiple phases of deformation and metamorphism associated with this tectonism obscured most primary features in the protolith rocks, leading to uncertainties in their pre-accretionary history. Here we present the results of detrital zircon geochronology from five of these terranes and make interpretations on their depositional ages, sediment provenance, and tectonic setting of deposition.Detrital zircon from Silurian rocks of the Vassalboro Group in the eastern-most portion of the Central Maine basin indicate sediment input in an extensional setting from both Laurentian and Ordovician sources. Results from Ordovician rocks of the Casco Bay Group of the Liberty-Orrington belt support earlier findings that these rocks have strong peri-Gondwanan affinities. Detrital zircon from the Appleton Ridge Formation and Ghent phyllite of the Fredericton trough are consistent with a peri-Gondwanan sediment source with no evidence of Laurentian sediment input. These findings are consistent with that of Dokken et al. (2018) for older Fredericton trough strata (i.e., Digdeguash Formation) east of the Fredericton fault in southern New Brunswick. Two samples from the Jam Brook complex reveal extreme differences in depositional age (Ordovician vs. Mesoproterozoic) and tectonic affinity and support the hypothesis that this narrow belt represents a fault complex containing a wide variety of stratigraphic units. Detrital zircon from Ordovician rocks of the Benner Hill Sequence indicate a peri-Gondwanan sediment source with no Laurentian input.Collectively, the pre-Silurian rocks of the Liberty-Orrington belt, Jam Brook complex, Benner Hill Sequence, and Late Ordovician-Early Silurian strata from the Appleton Ridge and Ghent phyllite in the Fredericton trough show peri-Gondwanan affinities with no evidence of Laurentian sediment input. This suggests a barrier exisited between the Laurentian margin and these peri-Gondwanan terranes prior to about 435 Ma. In contrast, Silurian strata from the eastern portion of the Central Maine basin do show evidence of a Laurentian sediment source, along with deposition in an extensional setting (lacking in all other samples), thus signaling a fundamental change in tectonic regime.
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Fu, Changlei, Zhen Yan, Jonathan C. Aitchison, Wenjiao Xiao, Solomon Buckman, Bingzhang Wang, Qingguo Zhai, and Bo Cao. "Short-lived intra-oceanic arc-trench system in the North Qaidam belt (NW China) reveals complex evolution of the Proto-Tethyan Ocean." GSA Bulletin, October 29, 2021. http://dx.doi.org/10.1130/b36127.1.
Full textAbstract:
Recognition of any intra-oceanic arc-trench system (IOAS) could provide invaluable information on the tectonic framework and geodynamic evolution of the vanished ocean basin. The Tanjianshan Complex and mafic-ultramafic rocks along the North Qaidam ultra-high pressure metamorphic belt in NW China record the subduction process of the Proto-Tethyan Ocean. Four lithotectonic units, including island arc, ophiolite, forearc basin, and accretionary complex, are recognized based on detailed field investigation. They rest on the northern margin of the Qaidam block and occur as allochthons in fault contact with underlying high-grade metamorphic rocks. The ophiolite unit mainly consists of ultramafic rocks, 527−506 Ma gabbro, 515−506 Ma plagiogranite, dolerite, and massive lava. High-Cr spinels in serpentinite, dolerite with forearc basalt affinity, and boninitic lava collectively indicate a forearc setting. The accretionary complex, exposed to the south of the ophiolite complex and island arc, is highly disrupted and contains repeated slices of basalt, 495−486 Ma tuff, chert, limestone, and mélange. Tuffs with positive zircon εHf(t) values indicate derivation from a nearby juvenile island arc. These lithotectonic units, as well as the back-arc basin, are interpreted to constitute a Cambrian IOAS that formed during the northward subduction of the Proto-Tethyan Ocean. Combined with regional geology, we propose a new geodynamic model involving short-lived Mariana-type subduction and prolonged Andean-type subduction to account for the complex evolution of the Proto-Tethyan Ocean. The reconstruction of a relatively complete IOAS from the North Qaidam belt not only reveals a systematic evolution of intra-oceanic subduction but also advances our understanding of the subduction and accretion history of the Proto-Tethyan Ocean.