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1
Gower, Charles F., and Thomas E. Krogh. "A U–Pb geochronological review of the Proterozoic history of the eastern Grenville Province." Canadian Journal of Earth Sciences 39, no. 5 (May 1, 2002): 795–829. http://dx.doi.org/10.1139/e01-090.
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The geological evolution of the eastern Grenville Province can be subdivided into three stages. During the first stage, namely pre-Labradorian (> 1710 Ma) and Labradorian (17101600 Ma) events, a continental-marginal basin was created and subsequently destroyed during accretion of a magmatic arc formed over a south-dipping subduction zone. Subduction was short-lived and arrested, leading to a passive continental margin. The second stage addresses events between 1600 and 1230 Ma. The passive margin lasted until 1520 Ma, following which a continental-margin arc was constructed during Pinwarian (15201460 Ma) orogenesis. Elsonian (14601230 Ma) distal-inboard, mafic and anorthositic magmatism, decreasing in age northward, is explained by funnelled flat subduction, possibly associated with an overridden spreading centre. As the leading edge of the lower plate advanced, it was forced beneath the Paleoproterozoic Torngat orogen root between the Archean Superior and North Atlantic cratons, achieving its limit of penetration by 1290 Ma. Static north-northeast-trending rifting then ensued, with mafic magmatism flanked by felsic products to the north and south. Far-field orogenic effects heralded the third stage, lasting from 1230 to 955 Ma. Until 1180 Ma, the eastern Grenville Province was under the distal, mild influence of Elzevirian orogenesis. From 1180 to 1120 Ma, mafic and anorthositic magmatism occurred, attributed to back-arc tectonism inboard of a post-Elzevirian Laurentian margin. Quiescence then prevailed until Grenvillian (1080980 Ma) continentcontinent collision. Grenvillian orogenesis peaked in different places at different times as thrusting released stress, thereby precipitating its shift elsewhere (pressure-point orogenesis). High-grade metamorphism, thrusting and minor magmatism characterized the Exterior Thrust Zone, in contrast to voluminous magmatism in the Interior Magmatic Belt. Following final deformation, early posttectonic anorthositicalkalicmafic magmatism (985975 Ma) and late posttectonic monzoniticsyenitegranite magmatism (975955 Ma) brought the active geological evolution of this region to a close.
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Nardi, Lauro V. S., Jorge Plá-Cid, Maria de Fátima Bitencourt, and Larissa Z. Stabel. "Geochemistry and petrogenesis of post-collisional ultrapotassic syenites and granites from southernmost Brazil: the Piquiri Syenite Massif." Anais da Academia Brasileira de Ciências 80, no. 2 (June 2008): 353–71. http://dx.doi.org/10.1590/s0001-37652008000200014.
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The Piquiri Syenite Massif, southernmost Brazil, is part of the post-collisional magmatism related to the Neoproterozoic Brasiliano-Pan-African Orogenic Cycle. The massif is about 12 km in diameter and is composed of syenites, granites, monzonitic rocks and lamprophyres. Diopside-phlogopite, diopside-biotite-augite-calcic-amphibole, are the main ferro-magnesian paragenesis in the syenitic rocks. Syenitic and granitic rocks are co-magmatic and related to an ultrapotassic, silica-saturated magmatism. Their trace element patterns indicate a probable mantle source modified by previous, subduction-related metasomatism. The ultrapotassic granites of this massif were produced by fractional crystallization of syenitic magmas, and may be considered as a particular group of hypersolvus and subsolvus A-type granites. Based upon textural, structural and geochemical data most of the syenitic rocks, particularly the fine-grained types, are considered as crystallized liquids, in spite of the abundance of cumulatic layers, schlieren, and compositional banding. Most of the studied samples are metaluminous, with K2O/Na2O ratios higher than 2. The ultrapotassic syenitic and lamprophyric rocks in the Piquiri massif are interpreted to have been produced from enriched mantle sources, OIB-type, like most of the post-collisional shoshonitic, sodic alkaline and high-K tholeiitic magmatism in southernmost Brazil. The source of the ultrapotassic and lamprophyric magmas is probably the same veined mantle, with abundant phlogopite + apatite + amphibole that reflects a previous subduction-related metasomatism.
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Soper, N. J. "The Newer Granite problem: a geotectonic view." Geological Magazine 123, no. 3 (May 1986): 227–36. http://dx.doi.org/10.1017/s0016756800034725.
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AbstractThe Siluro–Devonian suite of granitic plutons in the British Caledonides known as the Newer Granites, together with their associated extrusive rocks, represent one of the most extensively researched examples of calc-alkaline magmatism apparently related to orogeny. Although recent chemical studies have credibly interpreted some of the Scottish intrusions and volcanic rocks as part of a continental-margin magmatic arc generated by the subduction of lapetus oceanic lithosphere beneath Laurentia, insurmountable problems of distribution and timing arise when attempts are made to relate the magmatic activity as a whole to a traditional two-plate collision model for the orogeny.Newer Granite magmatism is here discussed in the context of more mobilistic models for the post-Grampian evolution of the British Caledonides which involve E–W closure between Laurentia and Baltica, terminated by collision in the Silurian, followed by the northward accretion of Gondwana-derived terranes in the early Devonian. The former produced the Main Caledonian tectonometamorphism of the Northern Highlands of Scotland, the latter the Late Caledonian deformation of the slate belts in the paratectonic Caledonides. These models imply much more complex convergence geometries which can, in principle, account for the whole Newer Granite suite as a series of subduction-generated magmatic arcs overlapping in space and time.The model proposed involves three late Caledonian magmatic arcs in addition to the Ordovician ‘Borrowdale arc’ which is not considered in this paper. One is related to Laurentia–Baltica convergence with westward subduction beneath the Scottish sector of the Laurentian margin in the Ordovician and Early Silurian, which generated the early members of the Newer Granite suite in the Highlands; a second is related to northward Silurian–early Devonian subduction at the Solway Line, which generated the younger Newer Granites and volcanic rocks north of the Highland Border; and a third, related to northward accretion of the Armorican terrane in early Devonian time, produced intrusive and extrusive magmatism as far south as Southeast Ireland and the English Midlands.
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Ross, Gerald M. "Evolution of Precambrian continental lithosphere in Western Canada: results from Lithoprobe studies in Alberta and beyond." Canadian Journal of Earth Sciences 39, no. 3 (March 1, 2002): 413–37. http://dx.doi.org/10.1139/e02-012.
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The Precambrian lithosphere of western Canada was assembled into the present crustal configuration between ca. 2.01.78 Ga by plate collisions, sometimes accompanied by arc magmatism, with subsequent cooling of the lithosphere since ca. 1.7 Ga. Collisional processes inferred along preserved plate sutures include (1) subduction of oceanic lithosphere and accretion of Proterozoic arc crust to the western Rae Province; (2) marginal basin consumption and tectonic entrapment of the Hearne Province between coeval subductioncollision zones; and (3) amagmatic marginal basin closure, perhaps analogous to the roots of small collisional orogens, such as the Pyrenees. Seismic reflection profiles acquired during the Lithoprobe Alberta Basement Transect have captured images of syn- to post-collisional structures along these sutures and evidence for crustal-scale thrust imbrication and rigid body accretion of Archean crust with preservation of precollisional tectonic fabric. The degree to which lithospheric mantle beneath Archean crustal blocks was preserved during these collisions is unknown, although tectonic geometries imply significant thermal and (or) mechanical interaction. Post-collisional, intrusive mafic magmatism is imaged widely in both seismic reflection and refraction surveys. These magmatic events are demonstrably Proterozoic, based on crosscutting relationships seen on seismic reflection profiles and geochronology of lower crustal xenoliths, and are comparable in scale to Phanerozoic igneous provinces (e.g., large igneous provinces) but have little preserved surface manifestation. Reactivation of Precambrian basement structures is limited or very subtle, reflecting strength control by the mantle on stress transmission and crustal failure. Long-wavelength elastic deformation of the crust during the Phanerozoic occurred in regions associated with, or adjacent to, Proterozoic mafic magmatism, suggesting local rheologic control of anomalous Phanerozoic paleotopography.
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Castillo, P. R. "The cause and source of post-subduction arc magmatism in Baja California, Mexico." Geochimica et Cosmochimica Acta 70, no. 18 (August 2006): A88. http://dx.doi.org/10.1016/j.gca.2006.06.089.
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Trubelja, Fabijan, Klaus Peter Burgath, and Vesna Marchig. "Triassic Magmatism in the Area of the Central Dinarides (Bosnia and Herzegovina): Geochemical Resolving of Tectonic Setting." Geologia Croatica 57, no. 2 (2004): 159–70. http://dx.doi.org/10.4154/gc.2004.13.
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Triassic magmatic rocks in the Central Dinarides in Bosnia and Herze-govina are known from two separate geotectonic units: (1) the AdriaticCarbonate Platform (Outer Dinarides) and (2) the Palaeozoic–Triassicallochthonous complex. They are assigned to the same regional, genetic and geochemical unit. Their emplacement age is inferred from contacts with the surrounding marble and sedimentary rocks (post-Anisian for intrusives and Ladinian for effusives).The magmatic rocks display different levels of emplacement and crystallization (intrusive, effusive and dyke rocks). They represent different stages of magmatic differentiation, from gabbro/basalt via diorite/andesite to granodiorite/dacite and granites. The most frequent dyke rock is diabase. Pillow basalts indicate eruption under subaquaticconditions. Pyroclastic rocks within the volcano-sedimentary unit point to the temporary explosive character of orogenic magmatic activity. Most rocks are affected and modified by post-magmatic alteration and hydrothermal fluids. This led to the formation of spilite, keratophyre, quartz keratophyre and rarely K spilite.New geochemical data support the opinion that subduction was the main process which triggered the Triassic magmatic activity in the Central Dinarides. Although some of the investigated rocks reveal MORB characteristics (in the selected geochemical discriminations), most samples are enriched in all elements which are reported as characteristicfor arc magmatism at convergent margins including incorporationof sediments.
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Pundir, Shailendra, Vikas Adlakha, Santosh Kumar, and Saurabh Singhal. "Closure of India–Asia collision margin along the Shyok Suture Zone in the eastern Karakoram: new geochemical and zircon U–Pb geochronological observations." Geological Magazine 157, no. 9 (February 24, 2020): 1451–72. http://dx.doi.org/10.1017/s0016756819001547.
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AbstractNew whole-rock geochemical analyses along with laser ablation multi-collector inductively coupled plasma mass spectrometry U–Pb zircon ages of the granite–rhyolite from the Karakoram Batholith, exposed along the Shyok Valley, NW India, have been performed to understand the timing and geochemical evolution of these magmatic bodies and their implications for the geodynamic evolution of the Karakoram Batholith. New geochronological data on granites and rhyolites along with previously published geochronological data indicate that the Karakoram Batholith evolved during Albian time (~110–100 Ma) owing to the subduction of Tethys oceanic lithosphere along the Shyok Suture Zone. This region witnessed a period of no magmatism during ~99–85 Ma. Following this, the Kohistan–Ladakh arc and Karakoram Batholith evolved as a single entity in Late Cretaceous and early Palaeogene times. Late Cretaceous (~85 Ma) rhyolite intrusions within the Karakoram Batholith show calc-alkaline subduction-related signatures with a highly peraluminous nature (molar A/CNK = 1.42–1.81). These intrusions may have resulted from c. ~13.8 % to ~34.5 % assimilation of pre-existing granites accompanied by fractional crystallization during the ascent of the magma. The contamination of mantle wedge-derived melts with crust of the active continental margin of the Karakoram most likely enhanced the high peraluminous nature of the rhyolite magma, as has been constrained by assimilation fractional crystallization modelling. Two granite samples from the contact of the Shyok Metamorphic Complex and Karakoram Batholith indicate that the post-collisional Miocene magmatism was not only confined along the Karakoram Fault zone but also extends ~30 km beyond the Shyok–Muglib strand.
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Pease, V., J. H. Scarrow, I. G. Nobre Silva, and A. Cambeses. "Devonian magmatism in the Timan Range, Arctic Russia — subduction, post-orogenic extension, or rifting?" Tectonophysics 691 (November 2016): 185–97. http://dx.doi.org/10.1016/j.tecto.2016.02.002.
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Whalen, Joseph B. "The Topsails igneous suite, western Newfoundland: an Early Silurian subduction-related magmatic suite?" Canadian Journal of Earth Sciences 26, no. 12 (December 1, 1989): 2421–34. http://dx.doi.org/10.1139/e89-207.
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The Topsails igneous suite contains several Late Ordovician to Early Silurian volcanic and intrusive sequences, which overlie and intrude Early to Middle Ordovician oceanic and arc rocks. The oldest components of this suite may represent calc-alkaline, continental-arc magmatism. The younger components are bimodal, with felsic compositions vastly predominating, and include a major (> 2200 km2) alkaline (A-type) granite complex. These felsic components have similarities to peralkaline suites formed in unusual subduction-related settings. Younger mafic components resemble within-plate basalts emplaced in a continental setting.Silurian magmatic activity in the Canadian Appalachians is widespread, includes diverse magmatic types, and has contrasting metamorphic and tectonic overprinting, even in contiguous areas. These features and the probability of major post-Silurian displacements in the orogen render correlation and interpretation difficult. Tectonic models that consider basin closure and major plate movements to be complete by Middle Ordovician time fail to adequately explain the Silurian activity. Available data best fit a model that relates Late Ordovician to Silurian magmatic activity to the opening and closing of small, discontinuous basins, portions of which may have been floored by oceanic crust.
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Sommer, Carlos A., Evandro F. Lima, Lauro V. S. Nardi, Joaquim D. Liz, and Breno L. Waichel. "The evolution of Neoproterozoic magmatism in Southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins." Anais da Academia Brasileira de Ciências 78, no. 3 (September 2006): 573–89. http://dx.doi.org/10.1590/s0001-37652006000300015.
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The Neoproterozoic shoshonitic and mildly alkaline bimodal volcanism of Southernmost Brazil is represented by rock assemblages associated to sedimentary successions, deposited in strike-slip basins formed at the post-collisional stages of the Brasilian/Pan-African orogenic cycle. The best-preserved volcano sedimentary associations occur in the Camaquã and Campo Alegre Basins, respectively in the Sul-riograndense and Catarinense Shields and are outside the main shear belts or overlying the unaffected basement areas. These basins are characterized by alternation of volcanic cycles and siliciclastic sedimentation developed dominantly on a continental setting under subaerial conditions. This volcanism and the coeval plutonism evolved from high-K tholeiitic and calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, and its evolution were developed during at least 60 Ma. The compositional variation and evolution of post-collisional magmatism in southern Brazil are interpreted as the result mainly of melting of a heterogeneous mantle source, which includes garnet-phlogopite-bearing peridotites, veined-peridotites with abundant hydrated phases, such as amphibole, apatite and phlogopite, and eventually with the addition of an asthenospheric component. The subduction-related metasomatic character of post-collisional magmatism mantle sources in southern Brazil is put in evidence by Nb-negative anomalies and isotope features typical of EM1 sources.
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Ross, Gerald M., and David W. Eaton. "Proterozoic tectonic accretion and growth of western Laurentia: results from Lithoprobe studies in northern Alberta." Canadian Journal of Earth Sciences 39, no. 3 (March 1, 2002): 313–29. http://dx.doi.org/10.1139/e01-081.
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The western Canadian Shield of northern Alberta is composed of a series of continental slivers that were accreted to the margin of the Archean Rae hinterland ca. 1.92.0 Ga., preserving a unique record of continental evolution for the interval 2.12.3 Ga. This part of Laurentia owes its preservation to the accretionary style of tectonic assembly south of the Great Slave Lake shear zone, which contrasts with indentationescape processes that dominate the Paleoproterozoic record farther north. The Buffalo Head and Chinchaga domains form the central core of this region, comprising a collage of ca. 23252045 Ma crustal elements formed on an Archean microcontinental edifice, and similar age crust is preserved as basement to the Taltson magmatic zone. The distribution of magmatic ages and inferred collision and subduction zone polarity are used to indicate closure of intervening oceanic basins that led to magmatism and emplacement of continental margin arc and collisional belts that formed from ca. 1998 to1900 Ma. Lithoprobe crustal seismic profiles complement the existing geochronologic and geologic databases for northern Alberta and elucidate the nature of late stages of the accretionary process. Crustal-scale imbrication occurred along shallow eastward-dipping shear zones, resulting in stacking of arc slivers that flanked the western Buffalo Head terrane. The seismic data suggest that strain is concentrated along the margins of these crustal slivers, with sparse evidence for internal penetrative deformation during assembly. Post-collisional mafic magmatism consisted of widespread intrusive sheets, spectacularly imaged as regionally continuous subhorizontal reflections, which are estimated to extend over a region of ca. 120 000 km2. The form of such mid-crustal magmatism, as subhorizontal sheets (versus vertical dykes), is interpreted to represent a style of magma emplacement within a confined block, for which a tectonic free face is unavailable.
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Soder, Christian G., and Rolf L. Romer. "Post-collisional Potassic–Ultrapotassic Magmatism of the Variscan Orogen: Implications for Mantle Metasomatism during Continental Subduction." Journal of Petrology 59, no. 6 (June 1, 2018): 1007–34. http://dx.doi.org/10.1093/petrology/egy053.
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Dolzodmaa, Boldbaatar, Yasuhito Osanai, Nobuhiko Nakano, and Tatsuro Adachi. "Zircon U–Pb geochronology and geochemistry of granitic rocks in central Mongolia." Mongolian Geoscientist 50 (June 2, 2020): 23–44. http://dx.doi.org/10.5564/mgs.v50i0.1327.
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The Central Asian Orogenic Belt had been formed by amalgamation of voluminous subduction–accretionary complexes during the Late Neoproterozoic to the Mesozoic period. Mongolia is situated in the center of this belt. This study presents new zircon U–Pb geochronological, whole-rock major and trace element data for granitoids within central Mongolia and discusses the tectonic setting and evolution of these granitic magmas during their formation and emplacement. The zircon U–Pb ages indicate that the magmatism can be divided into three stages: the 564–532 Ma Baidrag granitoids, the 269–248 and 238–237 Ma Khangai granitoids. The 564–532 Ma Baidrag granitoids are adakitic, have an I-type affinity, and were emplaced into metamorphic rocks. In comparison, the 269–248 Ma granitoids have high-K, calc-alkaline, granodioritic compositions and are I-type granites, whereas the associated the 238–237 Ma granites have an A-type affinity. The 564–532 Ma Baidrag and 269–248 Ma Khangai granitoids also both have volcanic arc-type affinities, whereas the 238–237 Ma granites formed in a post-collisional tectonic setting. These geochronological and geochemical results suggest that arc magmatism occurred at the 564–532 Ma which might be the oldest magmatic activity in central Mongolia. Between the Baidrag and the Khangai, there might be paleo-ocean and the oceanic plate subducted beneath the Khangai and produced voluminous granite bodies during the 269–248 Ma. After the closure of the paleo-ocean, the post collisional granitoids were formed at the 238–237 Ma based on the result of later granitoids in the Khangai area.
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Ali, Shehata, Rainer Abart, M. I. Sayyed, Christoph A. Hauzenberger, and Mabrouk Sami. "Petrogenesis of the Wadi El-Faliq Gabbroic Intrusion in the Central Eastern Desert of Egypt: Implications for Neoproterozoic Post-Collisional Magmatism Associated with the Najd Fault System." Minerals 13, no. 1 (December 22, 2022): 10. http://dx.doi.org/10.3390/min13010010.
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The late Neoproterozoic gabbroic intrusion of the Wadi El-Faliq area in the central Eastern Desert of Egypt (north Arabian–Nubian Shield; henceforth, ANS) is a fresh, undeformed elliptical body elongated in a NW–SE trend following the main sinistral strike-slip faults of the Najd fault system. Mineralogical and geochemical evidence suggest that they were derived from hydrous tholeiitic mafic magmas with arc-like geochemical fingerprints resembling the post-collisional gabbroic intrusions in Saudi Arabia. Despite the arc-like signatures, their fresh and undeformed nature, together with the field relationships, indicates that the studied gabbroic intrusion post-dates the main collisional phase, supporting its emplacement after subduction ceased and during the post-collisional stage. As a result, the arc-like signatures were possibly transmitted from the earlier ANS subduction episode. Indeed, the high (La/Sm)N, and negative-Nb and positive-Pb anomalies suggest contributions from subduction components. Lithospheric delamination was possibly facilitated by the Najd faults and shear zones formed during the post-orogenic crustal extension associated with the Pan-African orogenic collapse. The delamination process could have generated a rapid upwelling and melting of the asthenosphere mantle. The melt-rock reaction process likely played an important role in the genesis of the studied rocks through the interaction of the asthenosphere melts with lithosphere mantle rocks during ascent. The HREE fractionation suggests a probable mixing between melts from both spinel- and garnet-bearing peridotites. We suggest that the Wadi El-Faliq gabbroic intrusion was likely emplaced due to the stretching and thinning of the lithosphere during the extensional tectonism following the Pan-African orogeny.
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Muhtar, M. N., Chang-Zhi Wu, M. Santosh, Ru-Xiong Lei, Lian-Xing Gu, Si-Meng Wang, and Kai Gan. "Late Paleozoic tectonic transition from subduction to post-collisional extension in Eastern Tianshan, Central Asian Orogenic Belt." GSA Bulletin 132, no. 7-8 (December 23, 2019): 1756–74. http://dx.doi.org/10.1130/b35432.1.
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Abstract Late Paleozoic large-scale transcurrent tectonics and synkinematic intrusions are prominent features in the Eastern Tianshan segment of the southwestern Central Asian Orogenic Belt. However, the spatial and temporal relationship between synkinematic intrusions and crustal-scale shear zones remains unclear. Here we report petrology, geochemistry, and geochronology of the Qiziltag pluton associated with the Kanggur-Huangshan Shear Zone (KHSZ) with a view to characterize the spatial and temporal relationship between synkinematic intrusions and large-scale transcurrent shearing. Field relations and zircon U-Pb ages indicate that the Qiziltag pluton was formed through two stages of magmatism, with earlier stage granitoids (gneissic biotite granite: 288.9 ± 1.9 Ma, biotite monzogranite: 291.5 ± 1.7 Ma, K-feldspar granite: 287.9 ± 3.1 Ma), and later stage bimodal intrusions (biotite quartz monzonite: 278.5 ± 1.8 Ma, gabbro: 278.1 ± 2.3 Ma). The earlier stage granitoids are high-K calc-alkaline, enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs; e.g., Rb, Th, and U), and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti). Combined with their depleted isotopic compositions (εNd(t) = +6.29 to +7.48) and juvenile model ages (TDM2 = 450–610 Ma), we infer that the granitoids were derived from juvenile lower crust in a post-collisional tectonic transition (from compression to extension). The structural and temporal features indicate that the earlier stage (ca. 290 Ma) granitoids formed prior to the regional large-scale dextral strike slip. The later stage bimodal intrusions are dominated by biotite quartz monzonite as the felsic member and gabbro as the mafic component. The biotite quartz monzonite is high-K calc-alkaline with enriched LREEs and LILEs (e.g., Rb, Th, and U), and depleted HFSEs (e.g., Nb, Ta, and Ti), whereas the gabbro is subalkalic with depleted LREEs and HFSEs (e.g., Nb and Ta), resembling normal mid-ocean ridge basalt features. The bimodal intrusions show similar isotopic compositions (εNd(t) = +6.41 to +6.72 and εHf(t) = +9.55 to + 13.85 for biotite quartz monzonite; εNd(t) = +9.13 to +9.69 and εHf(t) = +4.80 to +14.07 for gabbro). These features suggest that the later stage (ca. 280 Ma) bimodal intrusions were derived from partial melting of depleted mantle and anatectic melting of lower crust materials induced by synchronous underplating of basaltic magma in a post-collisional extension. The structural features of the bimodal intrusions indicate that the later stage (ca. 280 Ma) magmatism was coeval with the development of the KHSZ. In conjunction with spatial and temporal evolution of magmatism and sedimentary records of Eastern Tianshan, we infer that transition between the northward closure of the North Tianshan Ocean and subsequent collision between the Central Tianshan Massif and the Qoltag Arc belt occurred at ca. 300 Ma.
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He, Chuan, Songlin Gong, Lu Wang, Nengsong Chen, M. Santosh, and Qinyan Wang. "Protracted post-collisional magmatism during plate subduction shutdown in early Paleoproterozoic: Insights from post-collisional granitoid suite in NW China." Gondwana Research 55 (March 2018): 92–111. http://dx.doi.org/10.1016/j.gr.2017.11.009.
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Sepahi, Ali, Hossein Shahbazi, Wolfgang Siebel, and Ahmad Ranin. "Geochronology of plutonic rocks from the Sanandaj-Sirjan zone, Iran and new zircon and titanite U-Th-Pb ages for granitoids from the Marivan pluton." Geochronometria 41, no. 3 (September 1, 2014): 207–15. http://dx.doi.org/10.2478/s13386-013-0156-z.
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Abstract The Sanandaj-Sirjan zone of Iran is a metamorphic belt consisting of rocks which were metamorphosed under different pressure and temperature conditions and intruded by various plutons ranging in composition from gabbro to granite. The majority of these granitoids formed along the ancient active continental margin of the Neo-Tethyan ocean at the southeastern edge of the central Iranian microplate. Geochronological data published in recent years indicate periodic plutonism lasting from Carboniferous through Mesozoic to late-Paleogene times (from ca. 300 to ca. 35 Ma) with climax activity during the mid- and late-Jurassic. The age constraints for plutonic complexes, such as Siah-Kouh, Kolah-Ghazi, Golpayegan (Muteh), Azna, Aligoodarz, Astaneh, Borujerd, Malayer (Samen), Alvand, Almogholagh, Ghorveh, Saqqez, Marivan, Naqadeh and Urumieh, clearly indicate the periodic nature of magmatism. Therefore, the Sanandaj-Sirjan zone preserves the record of magmatic activity of a complete orogenic cycle related to (1) Permocarboniferous(?) rifting of Gondwana and opening of the Neo-Tethyan ocean, (2) subduction of the oceanic crust, (3) continental collision and (4) post-collision/post-orogenic activities. The formation of the Marivan granitoids, northwestern Sanandaj-Sirjan zone, for which we present U-Pb zircon and titanite ages of ca. 38 Ma, can be related to the collisional and post-collisional stages of this orogenic cycle.
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Guo, Zhengfu, Marjorie Wilson, Lihong Zhang, Maoliang Zhang, Zhihui Cheng, and Jiaqi Liu. "The role of subduction channel mélanges and convergent subduction systems in the petrogenesis of post-collisional K-rich mafic magmatism in NW Tibet." Lithos 198-199 (June 2014): 184–201. http://dx.doi.org/10.1016/j.lithos.2014.03.020.
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Zhang, Yunying, Chao Yuan, Min Sun, Xiaoping Long, Zongying Huang, Yingde Jiang, Pengfei Li, and Long Du. "Two late Carboniferous belts of Nb-enriched mafic magmatism in the Eastern Tianshan: Heterogeneous mantle sources and geodynamic implications." GSA Bulletin 132, no. 9-10 (January 7, 2020): 1863–80. http://dx.doi.org/10.1130/b35366.1.
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Abstract Identification of subduction to post-collisional tectonic transitions is critical to the study of orogenic belts. To characterize such a transition in the Tianshan Orogenic Belt, a systematic study was conducted on the late Carboniferous (305–301 Ma) Hongshankou dolerite and Dikan’er basalt of Eastern Tianshan. The Hongshankou dolerites have relatively high Ti and Nb contents, akin to Nb-enriched arc basalts. Based on the Nb/La ratios, these dolerites can be divided into low-Nb/La (0.35–0.40) and high-Nb/La (0.67–1.4) groups, which were likely derived respectively from slab melt-metasomatized mantle wedge and a mixed mantle source involving depleted super-slab and enriched sub-slab asthenospheric components. Like the low-Nb/La dolerites, the Dikan’er basalts possess low Nb/La (0.42–0.46) ratios, suggesting a mantle source previously modified by slab components. In addition, the Dikan’er basalts have variable Nb contents and can be grouped into normal arc basalts and Nb-rich basalts that can be attributed to a common mantle source with different degrees of mantle melting, as demonstrated by the positive correlations of La/Sm with La and Nb. By integrating available data, two late Carboniferous belts of Nb-enriched mafic magmatism are recognized in the Eastern Tianshan, with one in the Yamansu arc (336–301 Ma) and the other in the Bogda Mountains (305–301 Ma). The former is characterized by low Nb/La (<0.6) ratios, reflecting derivation from mantle metasomatized by slab-derived melt during a subduction process; the latter exhibits an abrupt Nb/La increase from 0.6 to 1.4, indicating significant input of sub-slab asthenospheric mantle that was probably induced by slab break off. Accordingly, we propose that the tectonic transition from subduction to post-collision in the Eastern Tianshan occurred in the latest Carboniferous (305–301 Ma) and was marked by the abrupt input of deep and enriched asthenospheric mantle.
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Pipera, K., A. Koroneos, T. Soldatos, G. Poli, and G. Christofides. "Origin of the High-K Tertiary magmatism in Northern Greece: Implications for mantle geochemistry and geotectonic setting." Bulletin of the Geological Society of Greece 47, no. 1 (September 5, 2013): 416. http://dx.doi.org/10.12681/bgsg.11017.
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Tertiary plutonic and volcanic rocks cropping out in the Rhodope Massif (N. Greece) are studied using existing and new geochemical and isotopic data. Most of these rocks belong to the post-collisional magmatism formed as part of the prolonged extensional tectonics of the Rhodope region in Late Cretaceous– Paleogene time. This magmatism is considered to be of mantle origin; however, the character of the mantle source is controversial. Rock bulk chemistry and compositional variations show magmas with calc-alkaline to high-K calc-alkaline and shoshonitic features associated with magmatism at convergent margins. Initial 87Sr/86Sr, 143Nd/144Nd ratios, Pb isotopes and REE composition of the mafic rocks indicate mainly an enriched mantle source, even if some rocks indicate a depleted mantle source. Low- and High-K mafic members of these rocks coexist indicating a strongly heterogeneous mantle source. The High-K character of some of the mafic rocks is primarily strongly related to mantle enrichment by subduction-related components, rather than crustal contamination. The geochemical characteristics of the studied rocks (e.g Ba/Th,Th/Yb,Ba/La, U/Th, Ce/Pb) indicate that primarily sediments and/or sediment melts, rather than fluid released by the subducted oceanic crust controlled the source enrichment under the Rhodope Massif.
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Rabayrol, Fabien, Craig J. R. Hart, and Derek J. Thorkelson. "Temporal, spatial and geochemical evolution of late Cenozoic post-subduction magmatism in central and eastern Anatolia, Turkey." Lithos 336-337 (July 2019): 67–96. http://dx.doi.org/10.1016/j.lithos.2019.03.022.
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DRAUT, AMY E., PETER D. CLIFT, DAVID M. CHEW, MATTHEW J. COOPER, REX N. TAYLOR, and ROBYN E. HANNIGAN. "Laurentian crustal recycling in the Ordovician Grampian Orogeny: Nd isotopic evidence from western Ireland." Geological Magazine 141, no. 2 (March 2004): 195–207. http://dx.doi.org/10.1017/s001675680400891x.
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Because magmatism associated with subduction is thought to be the principal source for continental crust generation, assessing the relative contribution of pre-existing (subducted and assimilated) continental material to arc magmatism in accreted arcs is important to understanding the origin of continental crust. We present a detailed Nd isotopic stratigraphy for volcanic and volcaniclastic formations from the South Mayo Trough, an accreted oceanic arc exposed in the western Irish Caledonides. These units span an arc–continent collision event, the Grampian (Taconic) Orogeny, in which an intra-oceanic island arc was accreted onto the passive continental margin of Laurentia starting at ∼ 475 Ma (Arenig). The stratigraphy corresponding to pre-, syn- and post-collisional volcanism reveals a progression of εNd(t) from strongly positive values, consistent with melt derivation almost exclusively from oceanic mantle beneath the arc, to strongly negative values, indicating incorporation of continental material into the melt. Using εNd(t) values of meta-sediments that represent the Laurentian passive margin and accretionary prism, we are able to quantify the relative proportions of continent-derived melt at various stages of arc formation and accretion. Mass balance calculations show that mantle-derived magmatism contributes substantially to melt production during all stages of arc–continent collision, never accounting for less than 21% of the total. This implies that a significant addition of new, rather than recycled, continental crust can accompany arc–continent collision and continental arc magmatism.
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Searle, Michael P. "Tectonic evolution of the Caledonian orogeny in Scotland: a review based on the timing of magmatism, metamorphism and deformation." Geological Magazine 159, no. 1 (October 15, 2021): 124–52. http://dx.doi.org/10.1017/s0016756821000947.
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AbstractClassic tectonic models for the Caledonian orogeny in Scotland involve Ordovician collision of Laurentia–Midland Valley arc (Grampian orogeny), followed by middle Silurian collision of Laurentia–Baltica (Scandian orogeny) and 500–700 km of sinistral displacement along the Great Glen fault separating the Northern Highlands (Moine Supergroup) from the Grampian Highlands (Dalradian Supergroup). A review of the timing of magmatic and metamorphic rocks across Scotland allows a simpler explanation that fits with a classic Himalayan-style continent–island arc–continent collision. Late Cambrian – Early Ordovician NW-directed ophiolite obduction (Highland Border complex) coincided with the ending of stable continental shelf sedimentation along the eastern margin of Laurentia. Following collision between Laurentia and the Midland Valley arc–microcontinent in Early Ordovician time, crustal thickening and shortening led to almost continuous regional metamorphism from c. 470 to 420 Ma, rather than two discrete ‘orogenies’ (Grampian, Scandian). U–Pb monazite and garnet growth ages indicating prograde metamorphism, and S-type granites related to melting of crustal protoliths are coeval in the Grampian and Northern Highlands terranes. There is no evidence that the Great Glen fault was a terrane boundary, and strike-slip shearing post-dated emplacement of Silurian – Early Devonian granites. Late orogenic alkaline granites (c. 430–405 Ma) in both Moine and Dalradian terranes are not associated with subduction. They are instead closely related to regional alkaline appinite–lamprophyric magmatism resulting from simultaneous melting of lower crust and enriched lithospheric mantle. Caledonian deformation and metamorphism in northern Scotland, with continuous SE-directed subduction, show geometry and time scales that are comparable to the Cenozoic India–Kohistan arc–Asia collisional Himalayan orogeny.
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Chenin, Pauline, Suzanne Picazo, Suzon Jammes, Gianreto Manatschal, Othmar Müntener, and Garry Karner. "Potential role of lithospheric mantle composition in the Wilson cycle: a North Atlantic perspective." Geological Society, London, Special Publications 470, no. 1 (March 6, 2018): 157–72. http://dx.doi.org/10.1144/sp470.10.
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AbstractAlthough the Wilson cycle is usually considered in terms of wide oceans floored with normal oceanic crust, numerous orogens result from the closure of embryonic oceans. We discuss how orogenic and post-orogenic processes may be controlled by the size/maturity of the inverted basin. We focus on the role of lithospheric mantle in controlling deformation and the magmatic budget. We describe the physical properties (composition, density, rheology) of three types of mantle: inherited, fertilized and depleted oceanic mantle. By comparing these, we highlight that fertilized mantle underlying embryonic oceans is mechanically weaker, less dense and more fertile than other types of mantle. We suggest that orogens resulting from the closure of a narrow, immature extensional system are essentially controlled by mechanical processes without significant thermal and lithological modification. The underlying mantle is fertile and thus has a high potential for magma generation during subsequent tectonic events. Conversely, the thermal state and lithology of orogens resulting from the closure of a wide, mature ocean are largely modified by subduction-related arc magmatism. The underlying mantle wedge is depleted, which may inhibit magma generation during post-orogenic extension. These end-member considerations are supported by observations derived from the Western Europe–North Atlantic region.
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Dusel-Bacon, Cynthia, and John M. Murphy. "Apatite fission-track evidence of widespread Eocene heating and exhumation in the Yukon-Tanana Upland, interior Alaska." Canadian Journal of Earth Sciences 38, no. 8 (August 1, 2001): 1191–204. http://dx.doi.org/10.1139/e01-015.
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We present an apatite fission-track (AFT) study of five plutonic rocks and seven metamorphic rocks across 310 km of the YukonTanana Upland in east-central Alaska. Samples yielding ~40 Ma AFT ages and mean confined track lengths > 14 µm with low standard deviations cooled rapidly from >120°C to <50°C during a 35 Ma period, beginning at about 40 Ma. Data from samples yielding AFT ages >40 Ma suggest partial annealing and, therefore, lower maximum temperatures (~90105°C). A few samples with single-grain ages of ~20 Ma apparently remained above ~50°C after initial cooling. Although the present geothermal gradient in the western YukonTanana Upland is ~32°C/km, it could have been as high as 45°C/km during a widespread Eocene intraplate magmatic episode. Prior to rapid exhumation, samples with ~40 Ma AFT ages were >3.82.7 km deep and samples with >50 Ma AFT ages were >3.32.0 km deep. We calculate a 440320 m/Ma minimum rate for exhumation of all samples during rapid cooling. Our AFT data, and data from rocks north of Fairbanks and from the Eielson deep test hole, indicate up to 3 km of post-40 Ma vertical displacement along known and inferred northeast-trending high-angle faults. The predominance of 4050 Ma AFT ages throughout the YukonTanana Upland indicates that, prior to the post-40 Ma relative uplift along some northeast-trending faults, rapid regional cooling and exhumation closely followed the Eocene extensional magmatism. We propose that Eocene magmatism and exhumation were somehow related to plate movements that produced regional-scale oroclinal rotation, northward translation of outboard terranes, major dextral strike-slip faulting, and subduction of an oceanic spreading ridge along the southern margin of Alaska.
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Bertrand, Jean-Michel, J. Christopher Roddick, Martin J. van Kranendonk, and Ingo Ermanovics. "U–Pb geochronology of deformation and metamorphism across a central transect of the Early Proterozoic Torngat Orogen, North River map area, Labrador." Canadian Journal of Earth Sciences 30, no. 7 (July 1, 1993): 1470–89. http://dx.doi.org/10.1139/e93-127.
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The Early Proterozoic Torngat Orogen resulted from the oblique collision of the Archean Nain and southeastern Rae provinces and evolved in four stages: (0) deposition of platformal supracrustal assemblages followed by subduction-related arc magmatism in the margin of the Rae Province; (I) crustal thickening and nappe tectonics; (II) sinistral transpression and formation of the Abloviak shear zone; (III) uplift on steeply dipping, east-verging mylonites along the eastern orogenic front.U–Pb geochronology on zircon and monazite from major rock units and syntectonic intrusions indicates that arc magmatism at ca. 1880 Ma was followed by 40 Ma. of deformation and high-grade metamorphism from ca. 1860 to 1820. Subsequent uplift and final cooling occurred ca. 1795 – 1770 Ma. Several ages of mineral growth that correspond to distinct structural and metamorphic events have been recognized: (1) 1858 – 1853 Ma zircon and monazite dates are interpreted as the minimum age of stage I and peak metamorphic conditions; (2) 1844 Ma zircons from anatectic granitoids in the Tasiuyak gneiss complex (TGC), syntectonic with stage II deformation, are interpreted to date the formation of the Abloviak shear zone; (3) 1837 Ma magmatic zircons from an intrusive granite vein deformed along the western contact of the TGC represent a discrete intrusive event; (4) 1825 – 1822 Ma metamorphic overgrowths and newly grown zircons in granitic veins from the western portion of the orogen (Lac Lomier complex) represent a period of renewed transpressional deformation; (5) 1806 Ma magmatic zircons from a post-stage II granite emplaced along the eastern edge of the Abloviak shear zone defines the transition between stage II and stage III events; (6) 1794 – 1773 Ma zircons from leucogranites and pegmatites that are associated with uplift of the orogen (stage III). 1780 – 1740 Ma dates for monazite and a 40Ar/39Ar hornblende age correspond to the latest stages of uplift and cooling of the orogen.
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BUZZI, L., L. GAGGERO, L. GROZDANOV, S. YANEV, and F. SLEJKO. "High-Mg potassic rocks in the Balkan segment of the Variscan belt (Bulgaria): implications for the genesis of orogenic lamproite magmas." Geological Magazine 147, no. 3 (October 27, 2009): 434–50. http://dx.doi.org/10.1017/s0016756809990550.
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AbstractUltrapotassic plutons from several domains of the Variscan orogenic belt have been in turn interpreted as syn- to post-orogenic due to their age spread, but assessment of their geodynamic setting and source regions is still open to interpretation. In the Svoge region (Bulgaria), at the southern margin of the Balkan orogen, peralkalic plutons are hosted within Ordovician pelites. The main intrusion, with lamproitic affinity, which hosts monzodiorite xenoliths and a polyphase syenite suite, was emplaced at a shallow level.40Ar–39Ar dating by step-heating of amphibole and biotite yielded a Early Carboniferous intrusion age for the main body (337 ± 4 and 339.1 ± 1.6 Ma). The lamproite intrusion is silica-rich compared with bona fide lamproites and characterized by moderate LILE and LaN/YbNenrichments. Sr and Nd isotopic data (initial ϵNdin the range −4.87 to −5.88) suggest an origin in a depleted lithospheric mantle, possibly refertilized by eo-Variscan subduction. The high-K syn-tectonic plutonism in several zones of the Variscan orogen (Bohemian, Austro-Alpine, Vosges, French and Corsica domains) is consistent with a derivation of high-K magmatism from partial melting of metasomatized mantle following the subduction along the collision front between Gondwana and Laurasia.
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Bogossian, Jessica, Anthony I. S. Kemp, and Steffen G. Hagemann. "Linking Gold Systems to the Crust-Mantle Evolution of Archean Crust in Central Brazil." Minerals 11, no. 9 (August 30, 2021): 944. http://dx.doi.org/10.3390/min11090944.
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The Goiás Archean Block (GAB) in central Brazil is an important gold district that hosts several world-class orogenic gold deposits. A better comprehension of the crustal, tectono-magmatic, and metallogenic settings of the GAB is essential to accurately define its geological evolution, evaluate Archean crustal growth models, and target gold deposits. We present an overview of gold systems, regional whole-rock Sm-Nd analyses that have been used to constrain the geological evolution of the GAB, and augment this with new in situ zircon U-Pb and Hf-O isotope data. The orogenic gold deposits show variable host rocks, structural settings, hydrothermal alteration, and ore mineralogy, but they represent epigenetic deposits formed during the same regional hydrothermal event. The overprinting of metamorphic assemblages by ore mineralogy suggests the hydrothermal event is post-peak metamorphism. The metamorphic grade of the host rocks is predominantly greenschist, locally reaching amphibolite facies. Isotope-time trends support a Mesoarchean origin of the GAB, with ocean opening at 3000–2900 Ma, and reworking at 2800–2700 Ma. Crustal growth was dominated by subduction processes via in situ magmatic additions along lithospheric discontinuities and craton margins. This promoted a crustal architecture composed of young, juvenile intra-cratonic terranes and old, long-lived reworked crustal margins. This framework provided pathways for magmatism and fluids that drove the gold endowment of the GAB.
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Seghedi, Ioan, Liviu Maţenco, Hilary Downes, Paul R. D. Mason, Alexandru Szakács, and Zoltán Pécskay. "Tectonic significance of changes in post-subduction Pliocene–Quaternary magmatism in the south east part of the Carpathian–Pannonian Region." Tectonophysics 502, no. 1-2 (April 2011): 146–57. http://dx.doi.org/10.1016/j.tecto.2009.12.003.
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Macdonald, Ray, and Douglas J. Fettes. "The tectonomagmatic evolution of Scotland." Transactions of the Royal Society of Edinburgh: Earth Sciences 97, no. 3 (September 2006): 213–95. http://dx.doi.org/10.1017/s0263593300001450.
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ABSTRACTScotland has a magmatic record covering much of the period 3100–50 Ma. In this review, we pull together information on Scotland's igneous rocks into a continuous story, showing how magmatic activity has contributed to the country's structural development and assessing whether the effects of older magmatic events can be recognised in later episodes.The oldest igneous rocks are part of supracrustal sequences within the Lewisian Gneiss Complex, formed when Scotland was part of the supercontinent Kenorland. The supracrustal rocks were intruded between 3100 and 2800 Ma by granodiorites and tonalites, which were metamorphosed and deformed in a major tectonothermal event between 2700 and 2500 Ma. The break-up of Kenorland (2400–2200 Ma) was marked by the intrusion of mafic dyke swarms of tholeiitic affinity. The convergence of continental masses to form the supercontinent Columbia resulted, at ∼1900 Ma, in a series of subduction-related volcanic rocks and gabbro–anorthosite masses. Subsequent continent–continent collision formed a series of granite–pegmatite sheets at ∼1855 Ma and ∼1675 Ma and reworked much of the earlier rocks in the amphibolite facies. Columbia was breaking up by 1200 Ma, an event marked by remnants of basaltic magmatism in the NW of the country. Re-assembly of the continental fragments to form the supercontinent Rodinia resulted in the Grenville Orogeny, which in Scotland was marked by basement reworking but no confirmed magmatic activity. Early attempts to split Rodinia produced a rift-related, bimodal, mafic–felsic sequence in the Moine Supergroup of the Northern Highlands, at least some of the mafic rocks having mid-ocean ridge basalt affinities. Crustal thickening during a disputed orogenic event, the Knoydartian, may have caused regional migmatisation. The final break-up of Rodinia occurred in Scotland at ∼600 Ma, when very extensive tholeiitic magmatism characterised the later parts of the Dalradian Supergroup, while a series of granites intruded the Moine and Dalradian successions.Ordovician and Silurian times saw the closure of the Iapetus Ocean and the convergence of Laurentia, Avalonia and Baltica. The collision of a major arc system with Laurentia caused the Grampian event (480–465 Ma) of the Caledonian Orogeny, marked by ophiolite obduction, the generation of (largely) anatectic granites, volcanism in the Midland Valley and Southern Uplands, and intrusion of a major gabbro–granite suite in the NE. The late-Caledonian events (435–420 Ma) were largely post-collisional and were marked by the emplacement of alkaline igneous intrusions in the NW, calc-alkaline granitic intrusions over much of the country, widespread volcanic activity and regional dyke swarms. Laurentia, Avalonia and Baltica amalgamated to form the supercontinent Laurussia. Magmatic activity recommenced at 350 Ma, when intra-plate alkaline magmatism affected much of southern Scotland, in particular, through into Permian times. The alkaline magmatism was interrupted at ∼295 Ma by a short-lived event in which tholeiitic magmas were intruded as sills and dykes in a swarm ∼200 km wide. In the early Palaeogene, lithospheric attenuation related to proto-North Atlantic formation and the splitting of Pangaea was complemented by the arrival of the Iceland mantle plume. Huge volumes of mafic magma were emplaced as lava fields, central complexes and regional swarms, locally increasing crustal thickness by 30%
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MOUMBLOW, R. M., G. A. ARCURI, A. P. DICKIN, and C. F. GOWER. "Nd and Pb isotope mapping of crustal domains within the Makkovik Province, Labrador." Geological Magazine 156, no. 5 (April 3, 2018): 833–48. http://dx.doi.org/10.1017/s0016756818000195.
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AbstractThe Makkovik Province of eastern Labrador represents part of an accretionary orogen active during an early stage in the development of the Palaeoproterozoic southern Laurentian continental margin. New Nd isotope data for the eastern Makkovik Province suggest that accreted juvenile Makkovik crust was generated in the Cape Harrison domain during a single crust-forming event at c. 2.0 Ga. Pb isotope data support this model, and show a strong similarity to radiogenic crustal signatures in the juvenile Palaeoproterozoic crust of the Ketilidian mobile belt of southern Greenland. As previously proposed, an arc accretion event at c. 1.9 Ga triggered subduction-zone reversal and the development of an ensialic arc on the composite margin. After the subduction flip, a temporary release of compressive stress at c. 1.87 Ga led to the development of a retro-arc foreland basin on the downloaded Archean continental edge, forming the Aillik Group. Unlike previous models, a second arc is not envisaged. Instead, a compressive regime at c. 1.82 Ga is attributed to continued ensialic arc plutonism on the existing margin. The tectonic model for the Makkovikian orogeny proposed here is similar to that for the Ketilidian orogeny. Major- and trace-element analyses suggest that much of the magmatism in the Makkovik orogen results from post-accretionary ensialic arc activity, and that few vestiges remain of the original accreted volcanic arc. This pattern of arc accretion and intense post-accretion reworking is common to many accretionary orogens, such as the South American Andes and North American Cordillera.
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Syafitri, A., I. G. B. E. Sucipta, A. N. Arifa, A. Saepuloh, and S. Widiyantoro. "Tectonic Setting of Mount Agung, Bali: Insight From Petrology and Geochemistry Analysis." IOP Conference Series: Earth and Environmental Science 1047, no. 1 (July 1, 2022): 012005. http://dx.doi.org/10.1088/1755-1315/1047/1/012005.
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Abstract One of the longest arcs in the world originated from the complexity of subduction zones is the Sunda Arc that covers 80% of Indonesia's active volcanoes, from the Andaman, Sumatra, Java, and the Lesser Sunda Islands. Previous research in magmatism in Sunda Arc has conceded that the continental crust is in the west and becomes progressively oceanic towards the east. However, recent research has suggested that continental basement is more widespread than previously thought. Therefore, this study aims to re-evaluate the tectonic setting of Mount Agung, Bali, part of the Lesser Sunda Islands. Based on the results of published geochemistry data analysis and our petrological and/or mineralogical data, we found that Mount Agung was influenced by three cogenetic magmas and can be divided into 4 eruption periods, i.e., pre- 3200±60 BP, 3200±60 – 1870±40 BP, 1870±40 – 1040±50 BP, and post-1040±50 BP. These calc-alkaline magmas were derived from partial melting caused by the subduction of the Indo-Australian Plate within the Eurasian Plate. It produced basalt to dacite rocks with SiO2 varying between 51 and 63 wt%. As seen from the spider diagram, Rb, Ba, Th, K, and La – Sm contents are enriched, while Eu – Lu experienced depletion. In addition, the Nb content shows a negative anomaly, which is a characteristic of volcanic products from convergent plate boundaries. Based on the ratio of Zr to Zr/Y, it introduces that Mount Agung is affected by continental arcs. La/Sm to Th/Nb diagram reveals that in the older period (pre-1040±50 BP), the magma differentiation process is subduction-related enrichment, while in the younger period (post-1040±50 BP), there may be a slight influence from the presence of crustal contamination. Thus, these analyses presume that Bali Island has a continental basement (micro-continent basement), which may become the eastern end boundary of Sundaland.
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Glukhov, A. N., V. V. Priymenko, and A. A. Samsonov. "The age and tectonic position epithermal gold mineralization Omolon Massif (North-East Asia)." Moscow University Bulletin. Series 4. Geology 1, no. 6 (January 29, 2022): 61–69. http://dx.doi.org/10.33623/0579-9406-2021-6-61-69.
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Some aspects of the genesis of industrially important Paleozoic epithermal gold deposits of the Omolon massif are considered. According to the results of Ar-Ar dating of ores, their age is 20–30 Ma younger than that of the volcanic complexes of the Kedonian volcanic belt of the Devonian, with which this mineralization is traditionally associated. For the Paleozoic continental marginal magmatism of the Omolon massif, we have identified a stage of post-subduction rifting, characterized by the formation of volcano-plutonic associations of shoshonite-latite series. The authors suppose that it was at this stage, the chronological boundaries of which are determined as 335–286 Ma, that the ores under consideration were formed. The paragenetic connection with riftogenic shoshonite-latite series explains such specific features of the Paleozoic epithermal gold mineralization of the Omolon massif, such as high gold-silver ratio, low ore sulfide content, widespread development of fluorite and tellurides, low values of the primary Sr isotope ratio (0,703–0,706).
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Wang, Ruirui, Zhiqin Xu, M. Santosh, and Bo Zeng. "Mid-Neoproterozoic magmatism in the northern margin of the Yangtze Block, South China: Implications for transition from subduction to post-collision." Precambrian Research 354 (March 2021): 106073. http://dx.doi.org/10.1016/j.precamres.2020.106073.
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DUGGEN, S., K. HOERNLE, P. VAN DEN BOGAARD, and D. GARBE-SCHÖNBERG. "Post-Collisional Transition from Subduction- to Intraplate-type Magmatism in the Westernmost Mediterranean: Evidence for Continental-Edge Delamination of Subcontinental Lithosphere." Journal of Petrology 46, no. 6 (February 25, 2005): 1155–201. http://dx.doi.org/10.1093/petrology/egi013.
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Wang, Ruirui, Zhiqin Xu, M. Santosh, and Bo Zeng. "Mid-Neoproterozoic magmatism in the northern margin of the Yangtze Block, South China: Implications for transition from subduction to post-collision." Precambrian Research 354 (March 2021): 106073. http://dx.doi.org/10.1016/j.precamres.2020.106073.
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Zhang, Lihong, Zhengfu Guo, Maoliang Zhang, Zhihui Cheng, and Yutao Sun. "Post-collisional potassic magmatism in the eastern Lhasa terrane, South Tibet: Products of partial melting of mélanges in a continental subduction channel." Gondwana Research 41 (January 2017): 9–28. http://dx.doi.org/10.1016/j.gr.2015.11.007.
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Hildebrand, Robert S., and Joseph B. Whalen. "The mid-Cretaceous Peninsular Ranges orogeny: a new slant on Cordilleran tectonics? I: Mexico to Nevada." Canadian Journal of Earth Sciences 58, no. 8 (August 2021): 670–96. http://dx.doi.org/10.1139/cjes-2020-0154.
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The Peninsular Ranges orogeny occurred during the mid-Cretaceous at ∼100 Ma and affected rocks from southern Mexico to Alaska. The event resulted from the closing of an Early Cretaceous marine arc trough, named the Bisbee–Arperos seaway in Mexico and Arizona, and the Cinko Lake arc trough in the Sierra Nevada. The trough was an ocean that formed after the Late Jurassic – Early Cretaceous Nevadan orogeny and associated post-collisional magmatism. It was open for ∼40 million years and closed by westward subduction. Here, we focus initially on the most complete cross section, located in southwestern Mexico, where a west-facing Albian carbonate platform, with subjacent siliciclastic rocks built on the western margin of North America, was pulled down into a trench at 100 Ma, buried in hemipelagic mud and Cenomanian flysch, then overthrust from the west by rocks of the 140–100 Ma Santiago Peak – Alisitos arc and its substrate, the Guerrero Superterrane, which collectively document westerly subduction. This tectonically thickened collision zone was exhumed and intruded by 99–84 Ma distinctive post-collisional tonalite–granodiorite plutonic complexes, all with Sr/Y > 20, Sm/Yb > 2.5, Nb/Y > 0.4, and La/Yb > 10. These geochemical features are typical of slab failure, not arc magmas. The post-collisional plutons, previously considered to represent arc flare-ups, were derived from melting of the descending slab following arc-continent collision. Remnants of the arc, basin, related east-vergent 100 Ma thrusts, flexural foredeep, and 99–84 Ma slab failure plutons are traced from the Peninsular Ranges, through the Mojave Desert to the Sierra Nevada where similar rocks, relations, and ages occur. Along the western, back-arc, side of the orogen after collision and slab break-off, but during exhumation, east-dipping reverse faults with >10 km of east-side up movement shed 100–85 Ma plutonic and other debris westward from the hinterland into troughs such as the Valle and Great Valley. We extend our synthesis northward, from west-central Nevada to Alaska, in Part II.
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Bussy, François, Jean Hernandez, and Jürgen Von Raumer. "Bimodal magmatism as a consequence of the post-collisional readjustment of the thickened Variscan continental lithosphere (Aiguilles Rouges-Mont Blanc Massifs, Western Alps)." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 91, no. 1-2 (2000): 221–33. http://dx.doi.org/10.1017/s0263593300007392.
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High Precision U-Pb zircon and monazite dating in the Aiguilles Rouges–Mont Blanc area allowed discrimination of three short-lived bimodal magmatic pulses: the early 332 Ma Mg–K Pormenaz monzonite and associated 331 Ma peraluminous Montées Pélissier monzogranite; the 307 Ma cordierite-bearing peraluminous Vallorcine and Fully intrusions; and the 303 Fe-K Mont Blanc syenogranite. All intruded syntectonically along major-scale transcurrent faults at a time when the substratum was experiencing tectonic exhumation, active erosion recorded in detrital basins and isothermal decompression melting dated at 327-320 Ma. Mantle activity and magma mixing are evidenced in all plutons by coeval mafic enclaves, stocks and synplutonic dykes. Both crustal and mantle sources evolve through time, pointing to an increasingly warm continental crust and juvenile asthenospheric mantle sources. This overall tectono-magmatic evolution is interpreted in a scenario of post-collisional restoration to normal size of a thickened continental lithosphere. The latter re-equilibrates through delamination and/or erosion of its mantle root and tectonic exhumation/erosion in an overall extensional regime. Extension is related to either gravitational collapse or back-arc extension of a distant subduction zone.
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Belgrano, Thomas M., Larryn W. Diamond, Yves Vogt, Andrea R. Biedermann, Samuel A. Gilgen, and Khalid Al-Tobi. "A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence." Solid Earth 10, no. 4 (July 29, 2019): 1181–217. http://dx.doi.org/10.5194/se-10-1181-2019.
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Abstract. Numerous studies have revealed genetic similarities between Tethyan ophiolites and oceanic “proto-arc” sequences formed above nascent subduction zones. The Semail ophiolite (Oman–U.A.E.) in particular can be viewed as an analogue for this proto-arc crust. Though proto-arc magmatism and the mechanisms of subduction initiation are of great interest, insight is difficult to gain from drilling and limited surface outcrops in marine settings. In contrast, the 3–5 km thick upper-crustal succession of the Semail ophiolite, which is exposed in an oblique cross section, presents an opportunity to assess the architecture and volumes of different volcanic rocks that form during the proto-arc stage. To determine the distribution of the volcanic rocks and to aid exploration for the volcanogenic massive sulfide (VMS) deposits that they host, we have remapped the volcanic units of the Semail ophiolite by integrating new field observations, geochemical analyses, and geophysical interpretations with pre-existing geological maps. By linking the major-element compositions of the volcanic units to rock magnetic properties, we were able to use aeromagnetic data to infer the extension of each outcropping unit below sedimentary cover, resulting in a new map showing 2100 km2 of upper-crustal bedrock. Whereas earlier maps distinguished two main volcanostratigraphic units, we have distinguished four, recording the progression from early spreading-axis basalts (Geotimes), through axial to off-axial depleted basalts (Lasail), to post-axial tholeiites (Tholeiitic Alley), and finally boninites (Boninitic Alley). Geotimes (“Phase 1”) axial dykes and lavas make up ∼55 vol % of the Semail upper crust, whereas post-axial (“Phase 2”) lavas constitute the remaining ∼45 vol % and ubiquitously cover the underlying axial crust. Highly depleted boninitic members of the Lasail unit locally occur within and directly atop the axial sequence, marking an earlier onset of boninitic magmatism than previously known for the ophiolite. The vast majority of the Semail boninites, however, belong to the Boninitic Alley unit and occur as discontinuous accumulations up to 2 km thick at the top of the ophiolite sequence and constitute ∼15 vol % of the upper crust. The new map provides a basis for targeted exploration of the gold-bearing VMS deposits hosted by these boninites. The thickest boninite accumulations occur in the Fizh block, where magma ascent occurred along crustal-scale faults that are connected to shear zones in the underlying mantle rocks, which in turn are associated with economic chromitite deposits. Locating major boninite feeder zones may thus be an indirect means to explore for chromitites in the underlying mantle.
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Lebedev, V. A., A. V. Parfenov, and A. I. Yakushev. "Neogene–Quaternary Magmatism of the Çaldıran Plain and its Vicinity (Eastern Turkey): an Example of Post-Collisional Transition from Subduction to Intraplate Type." Petrology 26, no. 5 (September 2018): 469–91. http://dx.doi.org/10.1134/s0869591118050053.
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Moritz, Robert, Hervé Rezeau, Maria Ovtcharova, Rodrik Tayan, Rafael Melkonyan, Samvel Hovakimyan, Vagif Ramazanov, et al. "Long-lived, stationary magmatism and pulsed porphyry systems during Tethyan subduction to post-collision evolution in the southernmost Lesser Caucasus, Armenia and Nakhitchevan." Gondwana Research 37 (September 2016): 465–503. http://dx.doi.org/10.1016/j.gr.2015.10.009.
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Ali, Shehata, and Abdullah S. Alshammari. "Genesis of gabbroic intrusions in the Arabian Shield, Saudi Arabia: mineralogical, geochemical and tectonic fingerprints of the Neoproterozoic arc magmatism." Geological Magazine 158, no. 9 (April 12, 2021): 1639–56. http://dx.doi.org/10.1017/s0016756821000182.
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AbstractThe Arabian Shield of Saudi Arabia represents part of the Arabian–Nubian Shield and forms an exposure of juvenile continental crust on the eastern side of the Red Sea rift. Gabbroic intrusions in Saudi Arabia constitute a significant part of the mafic magmatism in the Neoproterozoic Arabian Shield. This study records the first detailed geological, mineralogical and geochemical data for gabbroic intrusions located in the Gabal Samra and Gabal Abd areas of the Hail region in the Arabian Shield of Saudi Arabia. Geological field relations and investigations, supported by mineralogical and geochemical data, indicate that the gabbroic intrusions are generally unmetamorphosed and undeformed, and argue for their post-collisional emplacement. Their mineralogical and geochemical features reveal crystallization from hydrous, mainly tholeiitic, mafic magmas with arc-like signatures, which were probably inherited from the previous subduction event in the Arabian–Nubian Shield. The gabbroic rocks exhibit sub-chondritic Nb/U, Nb/Ta and Zr/Hf ratios, revealing depletion of their mantle source. Moreover, the high ratios of (Gd/Yb)N and (Dy/Yb)N indicate that their parental mafic melts were derived from a garnet-peridotite source with a garnet signature in the mantle residue. This implication suggests that the melting region was at a depth exceeding ∼70–80 km at the garnet stability field. They have geochemical characteristics similar to other post-collisional gabbros of the Arabian–Nubian Shield. Their origin could be explained by adiabatic decompression melting of depleted asthenosphere that interacted during ascent with metasomatized lithospheric mantle in an extensional regime, likely related to the activity of the Najd Fault System, at the end of the Pan-African Orogeny.
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Fadaeian, Mohammad, Ahmad Jahangiri, Songjian Ao, Amin Allah Kamali, and Wenjiao Xiao. "Geochemistry and Petrogenesis of Shoshonitic Dyke Swarm in the Northeast of Meshkinshahr, NW Iran." Minerals 12, no. 3 (February 28, 2022): 309. http://dx.doi.org/10.3390/min12030309.
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The study area is located in Ardabil province in the northeast of Meshkinshahr city. More than 200 small and large Eocene-age dykes form outcrops in this area. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U–Pb zircon analyses yield a consistent age of 44.3 ± 1.8 Ma for the dyke swarms. These dykes include tephritic, andesitic and basaltic compositions, and show enrichment in LREEs (relative to HREEs) and are characterized by enrichment in LILEs and depletion in HFSEs. Petrological observations, along with major, rare earth and trace elements geochemistry, suggest that the dykes have a shoshonitic signature. All the rocks are highly enriched in incompatible trace elements and have variable Sr–Nd isotopes. Enrichment in incompatible elements and other geochemical features for the dyke swarm rocks suggest that a metasomatized subcontinental lithospheric mantle is the magma source. The negative Nb–Ta–Ti anomalies in the rocks are comparable with the features of subduction-related magmatism and contamination with ancient crustal components. The radiogenic 87Sr/86Sr isotopic values of the rocks imply the involvement of slab terrigenous sediments and/or a continental lithosphere. Isotopically, the volcanic rocks exhibit a binary trend, representing 1–5% mixing between the primary mantle and sediment melts. Our melting models suggest that there are residual garnet + spinel in the source, which are incompatible with the partial melting of amphibole- and/or phlogopite-bearing lherzolites. The geochronological, geochemical and isotopic data for the northeast Meshkinshahr dyke swarms suggest that these Late Eocene magmas were derived from a small degree of partial melting of a subduction-metasomatized lithospheric mantle source in a post-collisional setting.
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Gao, Mingdi, Haijin Xu, Junfeng Zhang, and Stephen F. Foley. "Experimental interaction of granitic melt and peridotite at 1.5 GPa: Implications for the origin of post-collisional K-rich magmatism in continental subduction zones." Lithos 350-351 (December 2019): 105241. http://dx.doi.org/10.1016/j.lithos.2019.105241.
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Vanderhaeghe, Olivier, Oscar Laurent, Véronique Gardien, Jean-François Moyen, Aude Gébelin, Cyril Chelle-Michou, Simon Couzinié, Arnaud Villaros, and Mathieu Bellanger. "Flow of partially molten crust controlling construction, growth and collapse of the Variscan orogenic belt: the geologic record of the French Massif Central." BSGF - Earth Sciences Bulletin 191 (2020): 25. http://dx.doi.org/10.1051/bsgf/2020013.
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We present here a tectonic-geodynamic model for the generation and flow of partially molten rocks and for magmatism during the Variscan orogenic evolution from the Silurian to the late Carboniferous based on a synthesis of geological data from the French Massif Central. Eclogite facies metamorphism of mafic and ultramafic rocks records the subduction of the Gondwana hyperextended margin. Part of these eclogites are forming boudins-enclaves in felsic HP granulite facies migmatites partly retrogressed into amphibolite facies attesting for continental subduction followed by thermal relaxation and decompression. We propose that HP partial melting has triggered mechanical decoupling of the partially molten continental rocks from the subducting slab. This would have allowed buoyancy-driven exhumation and entrainment of pieces of oceanic lithosphere and subcontinental mantle. Geochronological data of the eclogite-bearing HP migmatites points to diachronous emplacement of distinct nappes from middle to late Devonian. These nappes were thrusted onto metapelites and orthogneisses affected by MP/MT greenschist to amphibolite facies metamorphism reaching partial melting attributed to the late Devonian to early Carboniferous thickening of the crust. The emplacement of laccoliths rooted into strike-slip transcurrent shear zones capped by low-angle detachments from c. 345 to c. 310 Ma is concomitant with the southward propagation of the Variscan deformation front marked by deposition of clastic sediments in foreland basins. We attribute these features to horizontal growth of the Variscan belt and formation of an orogenic plateau by gravity-driven lateral flow of the partially molten orogenic root. The diversity of the magmatic rocks points to various crustal sources with modest, but systematic mantle-derived input. In the eastern French Massif Central, the southward decrease in age of the mantle- and crustal-derived plutonic rocks from c. 345 Ma to c. 310 Ma suggests southward retreat of a northward subducting slab toward the Paleotethys free boundary. Late Carboniferous destruction of the Variscan belt is dominantly achieved by gravitational collapse accommodated by the activation of low-angle detachments and the exhumation-crystallization of the partially molten orogenic root forming crustal-scale LP migmatite domes from c. 305 Ma to c. 295 Ma, coeval with orogen-parallel flow in the external zone. Laccoliths emplaced along low-angle detachments and intrusive dykes with sharp contacts correspond to the segregation of the last melt fraction leaving behind a thick accumulation of refractory LP felsic and mafic granulites in the lower crust. This model points to the primordial role of partial melting and magmatism in the tectonic-geodynamic evolution of the Variscan orogenic belt. In particular, partial melting and magma transfer (i) triggers mechanical decoupling of subducted units from the downgoing slab and their syn-orogenic exhumation; (ii) the development of an orogenic plateau by lateral flow of the low-viscosity partially molten crust; and, (iii) the formation of metamorphic core complexes and domes that accommodate post-orogenic exhumation during gravitational collapse. All these processes contribute to differentiation and stabilisation of the orogenic crust.
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Chen, Hanzhi, Mingcai Hou, Fuhao Xiong, Hongwei Tang, and Gangqiang Shao. "Petrogenesis and Geodynamic Implications of Miocene Felsic Magmatic Rocks in the Wuyu Basin, Southern Gangdese Belt, Qinghai-Tibet Plateau." Minerals 11, no. 6 (June 21, 2021): 655. http://dx.doi.org/10.3390/min11060655.
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Miocene felsic magmatic rocks with high Sr/Y ratios are widely distributed throughout the Gangdese belt of southern Tibet. These provide a good opportunity to explore the magmatic process and deep dynamic mechanisms that occurred after collision between the Indo and the Asian plates. In this paper, felsic volcanic rocks from the Zongdangcun Formation in the Wuyu Basin in the central part of the southern Gangdese belt are used to disclose their origin. Zircon U-Pb geochronology analysis shows that the felsic magmatism occurred at ca. 10.3 ± 0.2 Ma, indicating that the Zongdangcun Formation formed during the Miocene. Most of these felsic magmatic rocks plot in the rhyolite area in the TAS diagram. The rhyolite specimens from the Zongdangcun Formation have the characteristics of high SiO2 (>64%), K2O, SiO2, and Sr contents, a low Y content and a high Sr/Y ratio, and the rocks are rich in LREE and depleted in HREE, showing geochemical affinity to adakitic rocks. The rocks have an enriched Sr-Nd isotopic composition (εNd(t) = −6.76 to −6.68, (87Sr/86Sr)i = 0.7082–0.7088), which is similar to the mixed product of the juvenile Lhasa lower continental crust and the ancient Indian crust. The Hf isotopes of zircon define a wide compositional range (εHf(t) = −4.19 to 6.72) with predominant enriched signatures. The Miocene-aged crustal thickness in southern Tibet, calculated on the basis of the Sr/Y and (La/Yb)N ratios was approximately 60–80 km, which is consistent with the thickening of the Qinghai-Tibet Plateau. The origin of Miocene felsic magmatic rocks with high Sr/Y ratios in the middle section of the Gangdese belt likely involved a partial melting of the thickened lower crust, essentially formed by the lower crust of the Lhasa block, with minor contribution from the ancient Indian crust. After comprehensively analyzing the post-collisional high Sr/Y magmatic rocks (33–8 Ma) collected from the southern margin of the Gangdese belt, we propose that the front edge tearing and segmented subduction of the Indian continental slab may be the major factor driving the east-west trending compositional changes of the Miocene adakitic rocks in southern Tibet.
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Gower, Charles F., Urs Schärer, and Larry M. Heaman. "The Labradorian orogeny in the Grenville Province, eastern Labrador, Canada." Canadian Journal of Earth Sciences 29, no. 9 (September 1, 1992): 1944–57. http://dx.doi.org/10.1139/e92-152.
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Two minor intrusions within the Hawke River terrane in the Grenville Province, eastern Labrador, have upper intercept U–Pb ages as follows: (i) [Formula: see text] for a megacrystic intermediate dyke and (ii) 1622 ± 3 Ma for a pegmatite dyke. The upper intercepts date time of emplacement and the lower intercepts (508 and 320 Ma, respectively) record the timing of early Paleozoic events in the region. A third sample, a sillimanite-bearing pelitic gneiss from the Paradise metasedimentary gneiss belt in the Hawke River terrane, yielded a range of ages between 1647 and 1627 Ma from seven single zircon analyses. The zircons in the metasedimentary gneiss are interpreted as detrital because of their variation in morphology, the range of ages obtained, and their extreme variation in U content. A detrital origin implies that the sedimentary protolith must have been deposited after 1627 Ma, and is therefore not the same age as morphologically similar metasedimentary gneiss that occurs as enclaves within pre-1670 Ma migmatized quartz diorite. The timing of the post-1627 Ma high-grade metamorphic event that subsequently affected the gneiss is not known. It is unlikely to have been Grenvillian, as other evidence denies the likelihood that the Hawke River terrane was affected by more than moderate Grenvillian metamorphism. Using the emplacement ages of the minor intrusions, coupled with previous U–Pb dating and unequivocal field relationships, the following history is proposed. An early (northward subduction?) event, which possibly should be defined as being pre-Labradorian, occurred at ca. 1710 Ma and included distal magmatism in the Makkovik Province. There were two short-lived, closely related calc-alkaline plutonic events at 1677 and 1670 Ma, then mafic dyke injection and migmatization. These events are interpreted to reflect the times of rapid island-arc formation (over a southward-dipping subduction zone) from a mantle reservoir having a chondritic isotopic signature. After local granitoid emplacement at 1663 Ma (succeeded by further mafic dyke injection and then megacrystic dyke injection at 1660 Ma?), there was a widespread, major felsic magmatic event at ca. 1650 Ma. This was followed by another phase of mafic dyke injection and amphibolite facies metamorphism, which ended by ca. 1646 Ma. These events are interpreted to record the time of accretion of the island arcs to proto-Laurentia. A final Labradorian felsic magmatic event occurred between 1632 and 1622 Ma and is considered to be related to postcollisional anatectic plutonism and crustal thickening. This crustal thickening resulted in erosion that led to the deposition and burial of sediments in the Paradise metasedimentary belt.
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Bédard, Jean H. "Parental magmas of Grenville Province massif-type anorthosites, and conjectures about why massif anorthosites are restricted to the Proterozoic." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 100, no. 1-2 (March 2009): 77–103. http://dx.doi.org/10.1017/s1755691009016016.
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ABSTRACTTrace element inversion modelling of Grenvillean anorthosite massifs and associated rocks yield NMORB-normalised trace element profiles enriched in highly incompatible elements; commonly with negative Nb and Th anomalies. Model melts can be divided into subtypes that cannot be linked through fractional crystallisation processes. Most model melts are depleted in the heavy rare-earth elements and can be explained by partial melting of arc basaltic sources (5–60 melting ) with garnet-bearing residues. Some of the model melts have flat NMORB-normalised profiles (for rare-earth elements), have high compatible element contents, and might have been derived from mantle fertilised by arc magmatism, followed by low-pressure fractional crystallisation. Intermediate Ce/Yb types may represent mixtures of these end-members, or less probably, variations in the crustal source composition and residual assemblage. The active tectonic context now favoured for the Grenville Province appears to be inconsistent with plume or thermal insulation models. The heat source for crustal and mantle melting could record either post-orogenic thermal relaxation of a tectonically-thickened arc crust, or basaltic underplating caused by delamination of a mantle root or subduction slab beneath this arc crust. In this context, pre-Proterozoic anorthosites may be lacking, because prior to ca. 2·5 Ga, the crust may have been too weak to be thickened tectonically. The absence of post-Proterozoic anorthosites may be due to the secular decrease in radiogenic heating and cooling of the mantle and crust.
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Xue, Shengchao, Kezhang Qin, Chusi Li, Dongmei Tang, Qingfei Wang, and Xinshui Wang. "Permian bimodal magmatism in the southern margin of the Central Asian Orogenic Belt, Beishan, Xinjiang, NW China: Petrogenesis and implication for post-subduction crustal growth." Lithos 314-315 (August 2018): 617–29. http://dx.doi.org/10.1016/j.lithos.2018.06.021.
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