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2. Allanite U–Pb dating places new constraints on the high‐pressure to high‐temperature evolution of the deep Himalayan crust.
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Wood, Eleni, Warren, Clare J., Kunz, Barbara E., Argles, Tom W., Bidgood, Anna, Halton, Alison, Hammond, Samantha J., Millar, Ian L., and Roberts, Nick M. W.
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GARNET ,URANIUM-lead dating ,MELT infiltration ,ORTHOPYROXENE ,PLAGIOCLASE ,INDICATORS & test-papers - Abstract
During continental collision, crustal rocks are buried, deformed, transformed and exhumed. The rates, timescales and tectonic implications of these processes are constrained through the sequence and conditions of metamorphic reactions in major and accessory phases. Petrographic, isotopic and elemental data from metabasite samples in NW Bhutan, eastern Himalaya, suggest initial equilibration under high‐pressure (plagioclase‐absent and rutile‐present) conditions, followed by decompression to lower pressure conditions at high‐temperatures that stabilized plagioclase, orthopyroxene and ilmenite. Field observations and chemical indicators suggest equilibration under the lower pressure conditions is likely linked to the infiltration of melt from the host metasedimentary rocks. The metabasites preserve two metamorphic growth stages of chemically‐and petrographically distinct allanite that temporally overlap two stages of zircon growth. Allanite cores and zircon mantles grew at c. 19 ± 2 and 17–15.5 Ma respectively, linked texturally and chemically to the high‐pressure evolution. Symplectitic rims on embayed allanite cores, wholly symplectized Aln–Ilm and Aln–Cpx grains, and high U zircon rims grew at c. 15.5–14.5 Ma, linked chemically to the presence of melt and lower pressure, high‐temperature conditions. A single garnet Lu–Hf date is interpreted as geologically meaningless, with the bulk rock composition modified by melt infiltration after garnet formation. The open system evolution of these rocks precludes precise determination of the reactive bulk composition during metamorphic evolution and thus absolute conditions, especially during the early high‐pressure evolution. Despite these limitations, we show that combined geochemical and petrographic datasets are still able to provide insights into the rates and timescales of deep orogenic processes. The data suggest a younger and shallower evolution for the NW Bhutan metabasites compared to similar rocks in the central and eastern Himalayas. [ABSTRACT FROM AUTHOR]
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- 2024
- Full Text
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3. Forty-Ninth Rochester Mineralogical Symposium: Contributed Papers in Specimen Mineralogy—Part 2.
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MINERALOGY , *PHOSPHATE minerals , *CALCITE crystals , *MINERALS , *SILICATE minerals , *SULFIDE minerals , *ZIRCON - Abstract
The acicular quartz was the first mineral to form, and crystals can be found protruding from quartz of normal morphology that grew around them. This would lead to the change from earlier crystallizing As-bearing sulfide minerals (arsenopyrite) to later-forming arsenide minerals (löllingite) in the core zone as the sulfur anions became depleted. The pegmatite has the highest mineral species count, currently 183 (Falster et al. [2]), in the state of Maine. [Extracted from the article]
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- 2022
- Full Text
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4. Scientific paper zircon-based coating for the applications in Lost Foam casting process
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Prstić Aurel, Aćimović-Pavlović Zagorka, Andrić Ljubiša, Stojanović Jovica, and Terzić Anja
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sand casting ,Lost Foam casting process ,refractory coating ,zircon ,Chemical engineering ,TP155-156 ,Chemical industries ,HD9650-9663 - Abstract
In this work, a possibility to develop a new zircon-based refractory coating for casting applications was investigated. Optimization of the coating composition with controlled rheological properties was attained by application of different coating components, particularly by application of a new suspension agent and by alteration of coating production procedure. Zircon powder with particle size of 25x10-6 m was used as filler. The zircon sample was investigated by means of the following methods: X-ray diffraction analysis, diffraction thermal analysis and polarized microscope. The shape and grain size were analyzed by means of the PC program package OZARIA 2.5. It was shown that application of this type of water-alcohol-based coating had a positive influence on surface quality, structural and mechanical properties of the castings of cast iron obtained by pouring into sand molds by means of the expandable patterns method (Lost Foam casting process).
- Published
- 2012
- Full Text
- View/download PDF
5. Reply to the comments by Ramírez‐Fernández et al. (DOI: 10.1002/gj.4266) on paper "Microtexture and U–Pb geochronology of detrital zircon grains in the Chachalacas beach, Veracruz State, Gulf of Mexico" by Armstrong‐Altrin et al. (2021)
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Armstrong‐Altrin, John S., Ramos‐Vázquez, Mayla A., Nadia‐Yutzi, Hermenegildo R., and Madhavaraju, Jayagopal
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GEOLOGICAL time scales , *ZIRCON , *BEACHES , *CENOZOIC Era , *VOLCANIC fields , *PETROLOGY - Abstract
Based on the comparison of zircon ages with source terranes, they inferred that the likely source for Cenozoic zircon grains was the Eastern Alkaline Province of Mexico, which comprises various volcanic fields of Cenozoic age. Armstrong-Altrin et al. (2021) reported the detrital zircon grain surface features, chemistry, and U-Pb ages in the Chachalacas beach sediments, Gulf of Mexico. Armstrong-Altrin et al. (2020) discussed the U-Pb ages of detrital zircon grains, which we reported from the Chachalacas beach in the western Gulf of Mexico. [Extracted from the article]
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- 2022
- Full Text
- View/download PDF
6. Comments on the paper 'The nature of 'Svecofennian' zircon in the Belomorian Mobile Belt and some geological implications' by A.A. Shchipanskii and A.I. Slabunov
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A. V. Berezin, Sergey G. Skublov, and A. E. Mel’nik
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010504 meteorology & atmospheric sciences ,Archean ,Geochemistry ,Metamorphism ,Crust ,010502 geochemistry & geophysics ,01 natural sciences ,Plate tectonics ,Precambrian ,Geophysics ,Geochemistry and Petrology ,Eclogite ,Geology ,0105 earth and related environmental sciences ,Zircon - Abstract
Eclogites were relatively recently found in the Belomorian Mobile Belt (BMB) (Volodichev et al., 2004; Shchipanskii et al., 2005; Konilov et al., 2004). The very first isotopic dates (Volodichev et al., 2004; Mints et al., 2010) were obtained for these rocks in the northwestern (in the Salma and Kuru-Vaara areas) and central (Gridino area) portions of BMB and corresponded to the Archean: approximately 2.72–2.87 Ga. Because no crustal eclogites older that 2.0 Ga (Moller et al., 1995) had been known before these dates were obtained, these eclogites were regarded as unique. It is commonly believed that no crustal eclogites could be formed in the Archean because the crust was then relatively thin (Kroner, 2010), and hence, the find of crustal eclogites of Archean age in BMB called for a fundamental revision of geodynamic reconstructions of the crustal evolution and was one of the main arguments invoked to support the hypothesis that currently operating geodynamic mechanisms of plate tectonic can be extrapolated to the Early Precambrian (Rozen et al., 2008). However, these finds were practically immediately followed by serious doubts that the primary estimates of the timing of the eclogite metamorphism in the Belomorian Belt may be incorrect (Mitrofanov et al., 2009; and others).
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- 2017
7. Review of paper: Interpretation of zircon corona textures from metapelitic granulites of Ivrea-Verbano Zone, Northern Italy: Two-stage decomposition of Fe-Ti oxides
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Fernando Corfu
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Ti oxides ,Corona (optical phenomenon) ,Stage (stratigraphy) ,Geochemistry ,Granulite ,Decomposition ,Geology ,Interpretation (model theory) ,Zircon ,Northern italy - Published
- 2017
8. Detrital zircon geochronology and polycyclic sediment sources, Upper Jurassic – Lower Cretaceous of the Scotian Basin, southeastern Canada 1This article is one of a series of papers published in this CJES Special Issue on the theme of Mesozoic–Cenozoic geology of the Scotian Basin
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Georgia Pe-Piper, David J.W. Piper, Greg Strathdee, Mike Tubrett, and Stavros Triantafyllidis
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Provenance ,Paleontology ,Paleozoic ,Geochronology ,General Earth and Planetary Sciences ,Mesozoic ,Cenozoic ,Cretaceous ,Geology ,Zircon ,Terrane - Abstract
Sources of Tithonian–Albian sediment in the Scotian Basin are interpreted from detrital zircon geochronology to test previous hypotheses about the sources and pathways of sediment to thick deltaic successions that are important hydrocarbon reservoirs. Sediment provenance influences reservoir quality, but also provides information on tectonism during rifting of the North Atlantic Ocean. More than 760 zircons were dated by laser ablation U–Pb methods from nine offshore wells and one borehole on land and were characterized by external morphology, internal zoning, and Th/U ratio. A Meguma terrane source to the LaHave Platform was confirmed by peaks in detrital zircon abundance at 550–650 Ma, 1.0–1.2 Ga, and ∼2.1 Ga. Samples from the Sable Subbasin show a large peak in detrital zircon abundance at ∼1050 Ma, with lower peaks from 400–650, ∼1480, ∼1650, ∼1860 Ma and 2.7 Ga, characteristic of inboard Appalachian terranes of Laurentide affinity. Many late Paleozoic to Neoproterozoic zircons are euhedral or subhedral, and apparently first cycle, as are a few older zircons that indicate transport from the rising rift shoulder in southern Labrador as far north as the Makkovik Province (∼1860 Ma). About half the zircons are rounded and polycyclic. Samples from the Abenaki Subbasin are similar, but late Paleozoic to Neoproterozoic zircons are rare and ∼40% of the Mesoproterozoic zircons are subhedral, implying a different Laurentide source through the Humber valley. Euhedral–subhedral unzoned zircons yielded two groups of Cretaceous dates: ∼105 Ma from the Cree Member, and ∼120 Ma from the Missisauga Formation.
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- 2012
9. Laurentia-derived detritus in the Badger Group of central Newfoundland: deposition during closing of the Iapetus Ocean1This article is one of a series of papers published in CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.2Geological Survey of Canada Contribution 20110273
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Cees R. van Staal, Vicki McNicoll, and John W.F. Waldron
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Paleontology ,Paleozoic ,Ordovician ,General Earth and Planetary Sciences ,Detritus (geology) ,Laurentia ,Crust ,Geology ,Zircon ,Terrane ,Katian - Abstract
The Dunnage zone of central Newfoundland records the closing of an oceanic tract — the Iapetus Ocean. Within this tract, the Red Indian line separates arc terranes developed close to Laurentia (Notre Dame subzone) from those associated with the peri-Gondwanan terrane Ganderia (Exploits subzone). Sandstones and conglomerates of the Badger Group were deposited on the Exploits subzone, southeast of the Red Indian line, from Late Ordovician (Katian) to early Silurian (Llandovery) time. Two samples were collected from the base and top of the Badger Group for detrital zircon U/Pb dating. The lower sample yielded detrital zircon populations with a large statistical peak at ca. 1.0 Ga, and other features characteristic of derivation from Laurentian sources. Paleozoic zircons with ages from Late Cambrian to Late Ordovician were probably derived from the Notre Dame arc on the margin of Laurentia. The upper sample yielded a comparable age distribution, but with a much smaller proportion of Mesoproterozoic relative to Paleozoic detrital zircon. These results date the earliest arrival of Laurentia-derived detritus on the peri-Gondwanan Exploits subzone crust in the early Katian (ca. 455 Ma). However, the absence, in both samples, of Neoproterozoic grains suggests that there was still a seaway separating the Gander margin from arc terranes accreted to Laurentia until at least the middle Llandovery (ca. 436 Ma).
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- 2012
10. Preservation of terranes during the assembly of the Annieopsquotch Accretionary Tract: Inferences from the provenance of a Middle Ordovician ophiolite to arc transition, central Newfoundland Appalachians1Geological Survey of Canada Contribution 20100463.2This article is one of a series of papers published in this CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology
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John M. Hanchar, Vicki McNicoll, April M. Coombs, and Alex Zagorevski
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geography ,Provenance ,geography.geographical_feature_category ,Volcanic arc ,Geochemistry ,Ophiolite ,Paleontology ,Basement (geology) ,Geochronology ,Ordovician ,General Earth and Planetary Sciences ,Geology ,Terrane ,Zircon - Abstract
The Newfoundland Appalachians are a classic area for studying the record of arc development and terrane accretion processes with excellent exposure to different crustal levels that are minimally deformed and metamorphosed. This area also provides a link between the once continuous Appalachian and Caledonian orogens. The Annieopsquotch Accretionary Tract lies along the Red Indian Line, within the peri-Laurentian realm of the central Newfoundland Appalachians. The Darriwilian (468–461 Ma) tectonostratigraphic units of the Annieopsquotch Accretionary Tract are commonly characterized by polymictic volcanogenic conglomerate horizons. A conglomerate horizon at the interface between a suprasubduction zone ophiolite and its calc-alkaline volcanic arc cover sequence is herein investigated for zircon and geochemical provenance. Geochronology revealed a maximum age of deposition of 467 ± 4 Ma with zircon inheritance ranging from ca. 500 to 2800 Ma, consistent with a peri-Laurentian continental basement source. Four types of volcanogenic conglomerate clasts are noted on the basis of lithogeochemistry: arc andesite; calc-alkaline basalt; tholeiitic basalt; and non-arc rhyodacite. Tholeiitic basalt clasts are likely locally derived, perhaps from the underlying Skidder Formation. Other volcanic clasts do not have any known geochemical equivalents in the Annieopsquotch Accretionary Tract and hence appear to be exotic. The dominant zircon population suggests that the exotic clasts were derived from a ca. 467 Ma peri-Laurentian andesitic volcanic arc that once formed part of the Annieopsquotch Accretionary Tract.
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- 2012
11. Ordovician A-type plutons in the Antigonish Highlands, Nova Scotia1This article is one of a series of papers published in CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology
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Sandra M. Barr, Michael A. Hamilton, J. B. Murphy, and E. A. Escarraga
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Gabbro ,Pluton ,Ordovician ,Geochemistry ,General Earth and Planetary Sciences ,Mafic ,Hypersolvus ,Alkali feldspar ,Amphibole ,Geology ,Zircon - Abstract
Previously unrecognized A-type granitoid and gabbroic rocks cover an area of ∼100 km 2 in the central Antigon- ish Highlands in Avalonian northern mainland Nova Scotia. The granitoid rocks in this suite occur, together with minor gab- bro, in separate mappable bodies named the Brora Lake, Haggarts Lake, West Barneys River, McGraths Mountain, and Leadbetter Road plutons and are the focus of this study. They are mainly alkali feldspar granite and quartz syenite with var- ied texture and modal mineralogy. Close spatial association, gradational contact relations, and magma-mingling relationships suggest that all of these rocks, including the gabbro, are coeval. Hence a U-Pb (zircon) age of 469.4 +/- 0.5 Ma obtained for a quartz syenite sample from the Brora Lake pluton is interpreted to indicate a Middle Ordovician age for all of these granitoid and gabbroic rocks. Most granitic and quartz syenitic samples have hypersolvus texture, characterized by strongly perthitic alkali feldspar, and some also contain interstitial granophyre, both features indicative of shallow emplacement. Mafic minerals include iron-rich calcic and calcic-sodic amphibole, hedenbergite, and in some samples fayalite. Most of the rocks have high concentrations of K, Na, P, Ti, and Fe and are alkalic, with agpaitic indices as high as 0.98. Discrimination diagrams indicate that they are A-type granitoid rocks formed in a within-plate extensional setting. Age correlatives of these A-type granitoid and gabbroic rocks are not yet known elsewhere in Avalonia. The available data suggest that this ca. 470 Ma magmatism occurred while Avalonia was a separate microcontinent in the Rheic Ocean. Resume : Des roches gabbroiques et granitoides de type A, auparavant non reconnues, recouvrent un secteur d'environ 100 km 2 dans les hautes terres centrales d'Antigonish dans la partie continentale septentrionale de l'Avalonie en Nouvelle
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- 2012
12. Scientific paper zircon-based coating for the applications in Lost Foam casting process
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Aurel Prstić, Anja Terzić, Jovica Stojanović, Ljubiša Andrić, and Zagorka Aćimović-Pavlović
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0209 industrial biotechnology ,Materials science ,General Chemical Engineering ,02 engineering and technology ,zircon ,engineering.material ,law.invention ,020901 industrial engineering & automation ,Coating ,law ,Sand casting ,0202 electrical engineering, electronic engineering, information engineering ,lcsh:Chemical engineering ,lcsh:HD9650-9663 ,sand casting ,Metallurgy ,lcsh:TP155-156 ,020206 networking & telecommunications ,Lost Foam casting process ,Casting ,Grain size ,refractory coating ,engineering ,Particle size ,Cast iron ,Lost-foam casting ,lcsh:Chemical industries ,Zircon - Abstract
In this work, a possibility to develop a new zircon-based refractory coating for casting applications was investigated. Optimization of the coating composition with controlled rheological properties was attained by application of different coating components, particularly by application of a new suspension agent and by alteration of coating production procedure. Zircon powder with particle size of 25x10-6 m was used as filler. The zircon sample was investigated by means of the following methods: X-ray diffraction analysis, diffraction thermal analysis and polarized microscope. The shape and grain size were analyzed by means of the PC program package OZARIA 2.5. It was shown that application of this type of water-alcohol-based coating had a positive influence on surface quality, structural and mechanical properties of the castings of cast iron obtained by pouring into sand molds by means of the expandable patterns method (Lost Foam casting process).
- Published
- 2012
13. The Pikwitonei Granulite Domain, Manitoba: a giant Neoarchean high-grade terrane in the northwest Superior ProvinceThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.N. Machado, T.E. Krogh, and W. Weber are deceased
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Nuno Machado, Larry M. Heaman, M. T. Corkery, Ch. O. Böhm, Thomas E. Krogh, and W. Weber
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Metamorphic rock ,Geochronology ,Geochemistry ,General Earth and Planetary Sciences ,Charnockite ,Granulite ,Protolith ,Geology ,Zircon ,Terrane ,Gneiss - Abstract
The Pikwitonei Granulite Domain located at the northwestern margin of the Superior Province is one of the largest Neoarchean high-grade terranes in the world, with well-preserved granulite metamorphic assemblages preserved in a variety of lithologies, including enderbite, opdalite, charnockite, and mafic granulite. U–Pb geochronology has been attempted to unravel the protolith ages and metamorphic history of numerous lithologies at three main localities; Natawahunan Lake, Sipiwesk Lake, and Cauchon Lake. The U–Pb age results indicate that some of the layered enderbite gneisses are Mesoarchean (3.4–3.0 Ga) and the more massive enderbites are Neoarchean. The high-grade metamorphic history of the Pikwitonei Granulite Domain is complex and multistage with at least four episodes of metamorphic zircon growth identified: (1) 2716.1 ± 3.8 Ma, (2) 2694.6 ± 0.6 Ma, (3) 2679.6 ± 0.9 Ma, and (4) 2642.5 ± 0.9 Ma. Metamorphic zircon growth during episodes 2 and 3 are interpreted to be regional in extent, corresponding to M1 amphibolite- and M2 granulite-facies events, respectively, consistent with previous field observations. The youngest metamorphic episode at 2642.5 Ma is only recognized at southern Cauchon Lake, where it coincides with granite melt production and possible development of a major northeast-trending deformation zone. The timing and multistage metamorphic history recorded in the Pikwitonei Granulite Domain is similar to most Superior Province high-grade terranes and marks a fundamental break in Archean crustal evolution worldwide at the termination of prolific global Neoarchean greenstone belt formation.
- Published
- 2011
14. Geochronology and geochemistry of Precambrian gneisses, metabasites, and pegmatite from the Tobacco Root Mountains, northwestern Wyoming craton, MontanaThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.T.E. Krogh deceased April 2008
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David F.HessD.F. Hess, Robert E.JohnsonR.E. Johnson, Peter S. Dahl, Thomas E. Krogh, Sandra L. Kamo, and Thomas B. Hanley
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geography ,geography.geographical_feature_category ,Archean ,Metamorphic rock ,Geochemistry ,engineering.material ,Craton ,Geochronology ,engineering ,General Earth and Planetary Sciences ,Geology ,Terrane ,Zircon ,Gneiss ,Hornblende - Abstract
The Middle Mountain Metamorphic Domain of the Montana Metasedimentary Terrane, northwestern Wyoming Craton, within the northwestern Tobacco Root Mountains, mainly comprises migmatized tonalitic gneiss interlayered with amphibolitic (hornblende) gneiss, both of which are cut by metamorphosed mafic rocks. Together, these gneisses are defined as Middle Mountain Gneiss. Archean tonalitic gneiss from west of, and amphibolitic gneiss from east of, the Bismark Fault give, from chemically and air-abraded zircon grains, U–Pb ID–TIMS ages of 3325.5 ± 1.7 and 3340 Ma, respectively. These results reflect primary magmatic ages and show that the Middle Mountain Gneiss extends into the northern area of the Central Fault Block, between the Bismark and Mammoth faults. Older crustal processes in the tonalitic gneiss are evidenced by inherited grains, the oldest of which is >3460 Ma. A metabasite hosted in tonalitic gneiss in the Bismark Fault selvage zone yields a zircon age of 2468 Ma, which is interpreted as the time of metamorphism. This date and other ca. 2470 Ma dates known in the region reflect a series of thermotectonic events designated here as the Beaverhead – Tobacco Root Orogeny. Geochemical evidence in the Central Fault Block metabasites suggests that their >2470 Ma precursors evolved in a back-arc – arc-rift setting, whereas their equivalents west of the Bismark Fault were largely mid-ocean ridge basalt-related tholeiites and east of the Central Fault Block were back-arc tholeiites showing some continental affinity. The metabasite was metamorphosed, deformed, and intruded by pegmatite at 1756 Ma during the Big Sky Orogeny. This orogenic event also produced new zircon growth in Archean tonalitic gneiss. Monazite with an age of 75 Ma, found at one location, reflects nearby intrusion of the Cretaceous Tobacco Root Batholith.
- Published
- 2011
15. Lifetime of an ocean island volcano feeder zone: constraints from U–Pb dating on coexisting zircon and baddeleyite, and 40Ar/39Ar age determinations, Fuerteventura, Canary IslandsThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh
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Maria Ovtcharova, François BussyF. Bussy, Michael CoscaM. Cosca, Urs Schaltegger, Eric Lewin, James Allibon, and Denise Bussien
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geography ,Plateau ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Geochemistry ,Thermal ionization mass spectrometry ,010502 geochemistry & geophysics ,01 natural sciences ,Baddeleyite ,Paleontology ,13. Climate action ,Magma ,Geochronology ,General Earth and Planetary Sciences ,Mafic ,Amphibole ,Geology ,0105 earth and related environmental sciences ,Zircon - Abstract
High-precision isotope dilution – thermal ionization mass spectrometry (ID–TIMS) U–Pb zircon and baddeleyite ages from the PX1 vertically layered mafic intrusion Fuerteventura, Canary Islands, indicate initiation of magma crystallization at 22.10 ± 0.07 Ma. The magmatic activity lasted a minimum of 0.52 Ma. 40Ar/39Ar amphibole dating yielded ages from 21.9 ± 0.6 to 21.8 ± 0.3, identical within errors to the U–Pb ages, despite the expected 1% theoretical bias between 40Ar/39Ar and U–Pb dates. This overlap could result from (i) rapid cooling of the intrusion (i.e., less than the 0.3 to 0.6 Ma 40Ar/39Ar age uncertainties) from closure temperatures (Tc) of zircon (699–988 °C) to amphibole (500–600 °C); (ii) lead loss affecting the youngest zircons; or (iii) excess argon shifting the plateau ages towards older values. The combination of the 40Ar/39Ar and U/Pb datasets implies that the maximum amount of time PX1 intrusion took to cool below amphibole Tc is 0.8 Ma, suggesting PX1 lifetime of 520 000 to 800 000 Ma. Age disparities among coexisting baddeleyite and zircon (22.10 ± 0.07/0.08/0.15 Ma and 21.58 ± 0.15/0.16/0.31 Ma) in a gabbro sample from the pluton margin suggest complex genetic relationships between phases. Baddeleyite is found preserved in plagioclase cores and crystallized early from low silica activity magma. Zircon crystallized later in a higher silica activity environment and is found in secondary scapolite and is found close to calcite veins, in secondary scapolite that recrystallised from plagioclase. close to calcite veins. Oxygen isotope δ18O values of altered plagioclase are high (+7.7), indicating interaction with fluids derived from host-rock carbonatites. The coexistence of baddeleyite and zircon is ascribed to interaction of the PX1 gabbro with CO2-rich carbonatite-derived fluids released during contact metamorphism.
- Published
- 2011
16. High-precision U–Pb age and geochemistry of the mineralized (Ni–Cu–Co) Suwar intrusion, YemenThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh
- Author
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Lucia ThenyL. Theny, Sean A. Crowe, Charles Fipke, John D. Greenough, and Sandra L. Kamo
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Intrusion ,Gabbro ,Geochronology ,Geochemistry ,General Earth and Planetary Sciences ,Thermal ionization mass spectrometry ,Isotope dilution ,Geology ,Zircon - Abstract
High-precision U–Pb isotope dilution – thermal ionization mass spectrometry (ID–TIMS) geochronology on chemically abraded zircon grains from a noritic gabbro of the Ni-bearing Suwar mafic–ultramafic layered complex, northwestern Yemen, gives a mean 206Pb/238U age of 638.46 ± 0.73 Ma (2σ; MSWD = 1.4). At Wadi Qutabah, ∼30 km to the north, a similar mafic sample has an identical age of 638.58 ± 0.51 Ma (2σ; MSWD = 0.32), which supports the possibility of there being a single, large intrusive complex with an estimated areal extent of ∼250 km2. This is supported by geochemical data of samples from each locality, which are postkinematic, gabbroic rocks that contain variable amounts of cumulus olivine, plagioclase, orthopyroxene, and ilmenite with intercumulus augite, hornblende, and Ni-sulphides. Straight rare Earth element (REE) patterns, Ba/La ∼30, Rb/Ba ∼0.04, and negative primitive-mantle-normalized P anomalies resemble EM1 (Enriched Mantle 1) of oceanic island basalts and Archean subcontinental mantle lithosphere. The mineralogy and magmatic/tectonic discrimination diagrams suggest within-plate continental tholeiitic and noritic cumulates typical of a rift setting for both intrusions. The complex intrudes retrograded, amphibolite-facies paragneiss of the Pan-African Afif lithotectonic terrane, and is generally undeformed and unaltered, and, therefore, unaffected by the Pan-African orogeny. Emplacement of the 639 Ma complex occurred during a tensional tectonic regime on the Arabian Peninsula and marks the time of proto-Iapetan rifting. The estimated size of the intrusion, its noritic composition, and Archean subcontinental lithospheric mantle signature and its position in thin Proterozoic lithosphere abutting Archean cratonic rocks, give it the key characteristics of known, mostly Proterozoic, intrusions that host world-class Ni–Cu–Co ore deposits.
- Published
- 2011
17. U–Pb zircon geochronology of eclogites from the Scandian Orogen, northern Western Gneiss Region, Norway: 14–20 million years between eclogite crystallization and return to amphibolite-facies conditionsThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh
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Sandra L. Kamo, Kim KwokK. Kwok, Thomas E. Krogh, Peter Robinson, and Michael P. Terry
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Tectonics ,Continental collision ,Subduction ,Geochronology ,Geochemistry ,General Earth and Planetary Sciences ,Eclogite ,Geology ,Metamorphic facies ,Gneiss ,Zircon - Abstract
Reconstructing tectonic histories involving continental collision, subduction, and exhumation at plate-tectonic rates of ∼1 cm/year, requires precise U–Pb zircon geochronology. The Western Gneiss Region has exceptional exposures of high-pressure (HP) and ultra-high-pressure (UHP) rocks. The strategy adopted here involved sampling eclogite and associated late unstrained pegmatites to acquire the time of eclogite crystallization and subsequent exhumation, respectively. The oldest eclogite sampled is 415 ± 1 Ma from layered, probably UHP eclogite at Tevik, Averøya, also with a garnet–hornblende assemblage at 410 ± 1 Ma. The Flem Gabbro eclogite margin, with implied UHP conditions, is 410 ± 2 Ma. Hornblende eclogite at Seth, Lepsøya, never at UHP, is 412 ± 2 Ma. These compare to Devonian ages of 401 ± 1 Ma for overgrowths on Proterozoic baddeleyite in Selnes Gabbro, 402 ± 2 Ma for coesite eclogite at Hareidlandet, 405–400 Ma for coesite eclogite at Flatraket, and 405 ± 2 Ma for near-UHP eclogite at Hjelmelandsdalen. The 415 Ma eclogite at Tevik compares to granitic pegmatite in the same outcrop at 395.2 ± 1.3 Ma and to pegmatite in eclogite at Aspøya at 395.3 ± 2 Ma. The 410 Ma age at Flem compares to nearby pegmatite in eclogite at 396 ± 4 Ma. Collectively, these results imply 14–20 million years between deep eclogite crystallization at ∼130 km and return to amphibolite-facies conditions at ∼30 km, with crystallization of locally derived granitoid melts. Nearby garnet-pyroxenite records older ages (∼430) and greater depths (∼200 km), but on similar exhumation paths at ∼0.4–0.7 cm/year.
- Published
- 2011
18. New zircon shock phenomena and their use for dating and reconstruction of large impact structures revealed by electron nanobeam (EBSD, CL, EDS) and isotopic U–Pb and (U–Th)/He analysis of the Vredefort domeThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh
- Author
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Desmond E. Moser, I. Barker, R. M. Flowers, J.R. Hart, C. L. Cupelli, John R. Bowman, and J. L. Wooden
- Subjects
Paleontology ,Geochronology ,Geochemistry ,General Earth and Planetary Sciences ,Geology ,Zircon ,Electron backscatter diffraction - Abstract
Integrated electron nanobeam (EBSD, CL, EDS) and isotopic measurements (U–Pb, (U–Th)/He) of zircon from the collar and centre of the 80 km wide central uplift of the 2020 ± 3 Ma Vredefort impact structure reveal new shock features in a microstructural progression related to impact basin formation and degree of U–Pb age resetting: (1) planar fractures in {1K0} and {1K2} orientation during initial shock wave compression; (2) curviplanar fractures in {1K1} orientation, now annealed, which host glassy inclusions of partial melt of the host rock; (3) microtwin lamellae in an orientation of 65° about [110], attributed to shock wave rarefaction; (4) nucleation of impact-age crystallites, possibly on microtwins, during post-shock heating by impact melt; and (5) crystal-plastic deformation linked to crater modification of the core of the central uplift. Planar fracturing and microtwinning ≥20 GPa in “cold shock” zircon in granitoid at a radial distance of 25 km failed to reset zircon age. Single-grain ID–TIMS data extend between pre-impact age of 2077 ± 11 Ma and a secondary Pb-loss event at ca. 1.0 Ga — the latter reflecting Kibaran igneous activity between 1.110 and 1.021 Ga. Age resetting by the impact event operated in an ∼15 km wide “hot shock” zone of impact-elevated temperatures ≥700 °C at the core of the central uplift. Mechanisms include internal recrystallization, defect-accelerated Pb diffusion via shock microstructures and melt films, and late crystal-plastic deformation. Igneous zircons from a 2019 ± 2 Ma foliated norite impact melt yield a mean (U–Th)/He date of 923 ± 61 Ma, indicating exposure of the present surface after this time.
- Published
- 2011
19. Extending the Krogh legacy: development of the CA–TIMS method for zircon U–Pb geochronologyThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh
- Author
-
James M. Mattinson
- Subjects
Sample selection ,Paleontology ,Honour ,Air abrasion ,Honor ,media_common.quotation_subject ,Geochronology ,General Earth and Planetary Sciences ,Art history ,Geology ,Theme (narrative) ,Zircon ,media_common - Abstract
Tom Krogh was without a doubt the most influential U–Pb geochronologist of the modern era. His career was marked by a continuing series of breakthroughs, both revolutionary and evolutionary. His legacy is such that every lab around the world uses the methods he developed. After some fascinating insights into chemical leaching effects in zircon, Tom largely dropped this approach in favor of his enormously successful air abrasion technique, coupled with careful sample selection at the individual grain level. Here, I describe continued experiments with leaching and “step-wise dissolution” techniques, and how a series of alternating steps forward and setbacks eventually led to a new “chemical abrasion” or “CA–TIMS” method for selectively removing those domains within zircon that have lost Pb. Continuing to strive for improvements in analytical technique is perhaps the best way to honor Tom’s many contributions and extend his legacy.
- Published
- 2011
20. High-precision U–Pb zircon ID–TIMS dating of two regionally extensive bentonites: Cenomanian Stage, Western Canada Foreland BasinThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh
- Author
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I. Barker, A. Guy Plint, Sandra L. Kamo, and Desmond E. Moser
- Subjects
Paleontology ,Stratigraphy ,Stage (stratigraphy) ,Geochronology ,Geochemistry ,General Earth and Planetary Sciences ,Thermal ionization mass spectrometry ,Cenomanian ,Foreland basin ,Cretaceous ,Geology ,Zircon - Abstract
The stratigraphy of Cretaceous rocks in the Western Canada Foreland Basin is well constrained by dense borehole data that allow three-dimensional mapping of transgressive–regressive events, paleogeography, and subsidence patterns. However, it is difficult to estimate rates of change or to place events in a precise temporal framework because very few of the many bentonite beds have been dated using modern techniques. In this study, two bentonites, of at least regional extent, were dated using isotope dilution – thermal ionization mass spectrometry (ID–TIMS) U–Pb methods on chemically abraded zircon crystals. The older bentonite correlates with the “X” bentonite of the late middle Cenomanian and yields an age of 95.87 ± 0.10 Ma. The Bighorn River Bentonite, which lies just below the Cenomanian–Turonian boundary, yields an age of 94.29 ± 0.13 Ma and is interpreted to equate with the “B” bentonite and bed 80 at Pueblo, Colorado. Both bentonites dated here are older than the previously reported 40Ar/39Ar ages from correlative United States samples, supporting the observation that 40Ar/39Ar ages may systematically underestimate ages of Cretaceous bentonites by ∼1%, as suggested by other recent studies. The X bentonite immediately precedes a major late middle Cenomanian eustatic transgression that inundated the Dunvegan delta complex. The new ages for the X and Bighorn River bentonites indicate an average minimum subsidence rate of ∼0.27 mm/year in the most proximal part of the Cenomanian foredeep in northeast British Columbia during this time. The new age of the Bighorn River Bentonite, coupled with the orbitally tuned time scale of Sageman et al. (2006) , suggests a Cenomanian–Turonian boundary age of 94.12 ± 0.13 Ma.
- Published
- 2011
21. Age and significance of Grenvillian and Silurian orogenic events in the Finnmarkian Caledonides, northern NorwayThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh
- Author
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Trond H. Torsvik, Lewis D. Ashwal, Torgeir B. Andersen, Fernando Corfu, and M. Gerber
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Metamorphic rock ,Monazite ,Geochronology ,Titanite ,Geochemistry ,engineering ,General Earth and Planetary Sciences ,Metamorphism ,engineering.material ,Migmatite ,Geology ,Zircon ,Nappe - Abstract
The concepts concerning the origin of the Caledonides of northern Norway have changed rapidly in the last decade thanks largely to the application of modern geological and isotopic methods. This contribution presents U–Pb data obtained by ID–TIMS (isotope dilution – thermal ionization mass spectrometry) on zircon, titanite, and monazite from plutonic and metamorphic rocks. The Gjesvær Migmatite Complex of the Kalak Nappe Complex is shown to be of Grenvillian age, with granite and leucosome emplaced at about 970 Ma in a succession of psammites and amphibolites. It then underwent metamorphism and partial melting at about 425 Ma during Caledonian thrusting. Dating of granitic and gabbroic rocks that intrude the mainly turbiditic Hellefjord Group of the overlying Magerøy Nappe yields ages of 440–435 Ma, confirming that this unit is a correlative of the rocks on the island of Magerøy. A superimposed set of events at 430–425 Ma caused metamorphism forming pegmatites and local leucosome proving that the Magerøy Nappe, and the underlying Kalak Nappe Complex were juxtaposed on Baltica by that time. The age structure and other geological and paleomagnetic constraints suggest that the nappes originated along the Laurentian and perhaps Gondwanan margins and were brought to intersect Baltica by Cordilleran-type terrane translations along sinistral transform fault systems during the oblique convergence of Baltica and Laurentia.
- Published
- 2011
22. Evolution of early crust in chondritic or non-chondritic Earth inferred from U–Pb and Lu–Hf data for chemically abraded zircon from the Itsaq Gneiss Complex, West GreenlandThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh
- Author
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Yuri AmelinY. Amelin, Der-Chuen LeeD.-C. Lee, and Sandra L. Kamo
- Subjects
Geochronology ,Geochemistry ,General Earth and Planetary Sciences ,Crust ,Mafic ,Thermal ionization mass spectrometry ,Protolith ,Geology ,Planetary differentiation ,Zircon ,Gneiss - Abstract
Zircon grains in rocks collected from the Itsaq Gneiss Complex, southwest Greenland, were analyzed for U–Pb and Lu–Hf in the same grain using isotope dilution – thermal ionization mass spectrometry (TIMS) and multicollector – inductively coupled plasma – mass spectrometry (MC–ICP–MS). Grains were pretreated using chemical abrasion or air abrasion to assure that only zircon material unaffected by the migration of parent and daughter elements was analyzed. The data are consistent with derivation of all studied rocks from a single enriched mantle source or mafic crustal protolith with 176Lu/177Hf of 0.022 ± 0.003 that was repeatedly melted and produced tonalitic magmas. The assessment of the primary mantle source from which this mafic protolith was derived, at or before 3.85 Ga, greatly depends on the assumed composition of the bulk silicate Earth. Using the currently accepted Lu–Hf bulk Earth parameters based on the analysis of chondrites yields εHf(T) of 0 to +1 for the 3.80–3.86 Ga rocks, suggesting that the protolith was derived from mantle that underwent moderate depletion shortly before 3.9 Ga. However, using alternative models of the bulk silicate Earth composition, i.e., that account for the possible irradiation-induced accelerated decay of 176Lu in the early Solar System, and (or) loss of the products of early planetesimal or planetary differentiation, can lead to widely variable interpretations of the enrichment or depletion history of the mantle source of the Itsaq protolith.
- Published
- 2011
23. High-precision U–Pb geochronology of the Butedale pluton, British ColumbiaThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh
- Author
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Steven W. DenyszynS.W. Denyszyn, Paul R. Renne, Sarah J. Brownlee, and Roland Mundil
- Subjects
Series (stratigraphy) ,Paleomagnetism ,Batholith ,Pluton ,Geochronology ,Geochemistry ,General Earth and Planetary Sciences ,Thermal ionization mass spectrometry ,Shear zone ,Geology ,Zircon - Abstract
The Butedale pluton, a ca. 100 km long compositionally zoned batholith, is part of the Coast Plutonic Complex that extends the length of the Canadian Pacific coast. Its age and thermal history are relevant to the Butedale pluton’s role as a test case of the Baja–BC hypothesis, as paleomagnetic evidence suggests that it may have formed thousands of kilometres to the south and moved northward along what is now the Coast Shear Zone. High-resolution U–Pb (chemical abrasion – thermal ionization mass spectrometry (CA–TIMS), zircon) analysis of rocks across the width of the Butedale pluton indicates that it is actually made up of at least two distinct magmatic events that formed the West Butedale pluton (ca. 95 Ma) and the East Butedale pluton (ca. 85 Ma). The East Butedale pluton was reheated by the emplacement of a younger adjacent pluton, which may have caused partial Pb loss and resulting excess scatter of 206Pb/238U zircon ages within individual samples. The West Butedale pluton may be the same age as, and part of, the nearby Ecstall pluton, thereby doubling the length of the Ecstall pluton to ca. 200 km. Single-grain, high-precision U–Pb analysis of zircon reveals previously unknown complexity and detail of emplacement and thermal history in the Butedale plutons.
- Published
- 2011
24. Detrital zircon geochronology and provenance of Devono-Mississippian strata in the northern Canadian Cordilleran miogeoclineThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.Northwest Territories Geoscience Office Contribution 0047. Geological Survey of Canada Contribution 20100432
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Yvon Lemieux, Antonio Simonetti, and Thomas HadlariT. Hadlari
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Paleontology ,Provenance ,Honour ,Series (stratigraphy) ,Carboniferous ,media_common.quotation_subject ,Geochronology ,Geological survey ,General Earth and Planetary Sciences ,Devonian ,Geology ,Zircon ,media_common - Abstract
U–Pb ages have been determined on detrital zircons from the Upper Devonian Imperial Formation and Upper Devonian – Lower Carboniferous Tuttle Formation of the northern Canadian Cordilleran miogeocline using laser ablation – multicollector – inductively coupled plasma – mass spectrometry. The results provide insights into mid-Paleozoic sediment dispersal in, and paleogeography of, the northern Canadian Cordillera. The Imperial Formation yielded a wide range of detrital zircon dates; one sample yielded dominant peaks at 1130, 1660, and 1860 Ma, with smaller mid-Paleozoic (∼430 Ma), Neoproterozoic, and Archean populations. The easternmost Imperial Formation sample yielded predominantly late Neoproterozoic – Cambrian zircons between 500 and 700 Ma, with lesser Mesoproterozoic and older populations. The age spectra suggest that the samples were largely derived from an extensive region of northwestern Laurentia, including the Canadian Shield, igneous and sedimentary provinces of Canada’s Arctic Islands, and possibly the northern Yukon. The presence of late Neoproterozoic – Cambrian zircon, absent from the Laurentian magmatic record, indicate that a number of grains were likely derived from an exotic source region, possibly including Baltica, Siberia, or Arctic Alaska – Chukotka. In contrast, zircon grains from the Tuttle Formation show a well-defined middle Paleoproterozoic population with dominant relative probability peaks between 1850 and 1950 Ma. Additional populations in the Tuttle Formation are mid-Paleozoic (∼430 Ma), Mesoproterozoic (1000–1600 Ma), and earlier Paleoproterozoic and Archean ages (>2000 Ma). These data lend support to the hypothesis that the influx of sediments of northerly derivation that supplied the northern miogeocline in Late Devonian time underwent an abrupt shift to a source of predominantly Laurentian affinity by the Mississippian.
- Published
- 2011
25. Neoarchean high-potassium granites of the Boothia mainland area, Rae domain, Churchill Province: U–Pb zircon and Sm–Nd whole rock isotopic constraintsThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh
- Author
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Léopold Nadeau, J.J. Ryan, Alana M. Hinchey, and William J. Davis
- Subjects
Series (stratigraphy) ,Sequence (geology) ,Honour ,media_common.quotation_subject ,Geochronology ,Geochemistry ,General Earth and Planetary Sciences ,Regionally Extensive ,Sedimentary rock ,Mainland ,Geology ,Zircon ,media_common - Abstract
The Boothia mainland region of the north-central Rae domain is underlain by remnants of a Neoarchean volcano sedimentary sequence dismembered by two regionally extensive Neoarchean high-potassium granitoid suites with rare occurrences of a structurally interleaved, Paleoproterozoic sedimentary cover sequence. The granitoids and their gneissic equivalents are dominated by variably deformed and metamorphosed I-type, metaluminous, polyphase, commonly porphyritic to augen, biotite ± hornblende monzogranite, and subordinate granodiorite, with rare tonalite. New geochronological results, the first for this area, demonstrate that the widespread Neoarchean granitoid plutonism is dominantly 2.61–2.59 Ga, with a less prominent 2.66 Ga plutonic event. The age of zircon recrystallization suggests that ca. 2.60 Ga Archean metamorphism and fabric development (S1) affected the 2.66 Ga plutons prior to or contemporaneously with intrusion of the voluminous ca. 2.6 Ga suite. εNd(t) for the ca. 2.61–2.59 Ga suite range from 1.4 to –1.9, overlapping with the ca. 2.66 Ga suite that range from 1.4 to 1.5. The Nd isotopic data, coupled with the presence of inherited ca. 2.65, 2.70, and 2.85–2.90 Ga zircon, suggests recycling of older, Neoarchean to Mesoarchean crust in the formation of these suites. Metaplutonic rocks preserve Paleoproterozoic deformation (F4 and F5) and amphibolite-facies metamorphism, sporadically recorded in zircon rims that formed at 1.81 Ga. This event strongly reoriented the Neoarchean fabrics in metaplutonic rocks, generally without the development of a new coaxial Paleoproterozoic fabric, and we attribute this strain and metamorphism to the Hudsonian orogeny.
- Published
- 2011
26. Note on the paper by Guochun Zhao, Simon A. Wilde, Sanzhong Li, Min Sun, Matthew L. Grant and Xuping Li, 2007, 'U–Pb zircon age constraints on the Dongwanzi ultramafic–mafic body, North China, confirm it is not an Archean ophiolite'
- Author
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Timothy M. Kusky and J.H. Li
- Subjects
Geophysics ,Space and Planetary Science ,Geochemistry and Petrology ,Ultramafic rock ,Archean ,Earth and Planetary Sciences (miscellaneous) ,North china ,Geochemistry ,Mafic ,Ophiolite ,Geology ,Zircon - Published
- 2008
27. Comment to paper: Timing of magmatism and metamorphism in the Gruinard Bay area of the Lewisian gneiss complex: comparison with the Assynt Terrane and implications for terrane accretion by G.J. Love, P.D. Kinny and C.R.L. Friend (Contr Mineral Petrol (2004) 146:620–636)
- Author
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Corfu, F.
- Subjects
- *
MAGMATISM , *METAMORPHISM (Geology) , *GNEISS , *ZIRCON , *PETROLOGY , *MINERALOGY , *VOLCANISM - Abstract
The article comments on the paper "Timing of Magmatism and Metamorphism in the Gruinard Bay Area of the Lewisian Gneiss Complex: Comparisons with the Assynt Terrane and Implications for Terrane Accretion" by C. R. L. Friend, P. D. Kinny and G. J. Glove. According to the author, the paper expands the readers' understanding of the geological relations in the Complex at Badcall Bay, Lochinver and Gruinard Bay in Northern Scotland. The paper also presents new insights on the systematics of zircon in high-grade rocks, however, it also contains some dubious interpretations that ignore or misrepresents available evidence.
- Published
- 2007
- Full Text
- View/download PDF
28. Comments on the papers by Bailie et al. concerning the age and deposition of the Bushmanland Group (South African Journal of Geology, 110, 59-86) and single zircon ages of the Aggeneys Granite Suite (South African Journal of Geology, 110, 87-110)
- Author
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W.P. Colliston, A.E. Schoch, and H.E. Praekelt
- Subjects
Paleontology ,Sequence (geology) ,Structural mapping ,Suite ,Group (stratigraphy) ,Geology ,Context (language use) ,Archaeology ,Zircon - Abstract
The authors of the two papers fulfill a long-felt need for accurate isotopic data on the Bushmanland Group and the contiguous granitic gneisses, not to mention a wealth of new geochemical analyses. The samples that were used, were collected in the eighties by Lipson (reported in a thesis, 1990) and by Duncan et al . (provided in an unpublished report, 1985). We much appreciate the new data but believe that the stratigraphic sampling context is fundamentally flawed, constraining the interpretation of analytical results. The stratigraphic framework that we prefer is based on detailed as well as regional sequence and structural mapping, elucidated in several previous publications (Strydom et al. , 1987; Colliston et al. , 1986; 1989 …
- Published
- 2008
29. Reply to the comment of Fügenschuh et al. on the paper 'Estimating displacement along the Brenner Fault and orogen-parallel extension in the Eastern Alps' by Rosenberg and Garcia, Int J Earth Sci (Geol Rundsch) (2011) 100:1129-1145.
- Author
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Rosenberg, Claudio and Garcia, Sebastian
- Subjects
- *
GEOLOGIC faults , *ZIRCON , *FISSION track dating , *MYLONITE , *STRUCTURAL geology , *ESTIMATES , *STRATIGRAPHIC geology - Abstract
The article offers the authors insight on their reply to the comment by Fügenschuh and colleagues on their paper titled "Estimating displacement along the Brenner Fault and orogen-parallel extension in the Eastern Alps." The authors note that the zircon fission track ages in the footwall of Brenner Fault (BF) in Eastern Alps reflect the antiform of Tauern Window (TW). They cite that there is a link between ductile mylonites and brittle faulting. They say that the trend of ductile mylonitic belt continues into the Austroalpine Units as exhumation was insufficient to attain brittle/ductile transition. They mention the tectonic omissions and the new estimate of extension based on stratigraphic omissions at Brenner Pass in Austria.
- Published
- 2012
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30. 207Pb/206Pb zircon ages and the evolution of the Singhbhum Craton, eastern India: an ion microprobe study1This paper is dedicated to Prof. A.K. Saha, one of the senior co-authors, who passed away after submission of the paper.1
- Author
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S. Ray, A.K. Saha, M. Wiedenbeck, J. N. Goswami, S. Mishra, and M.P. Deomurari
- Subjects
geography ,geography.geographical_feature_category ,Lithology ,Continental crust ,Metamorphic rock ,Geochemistry ,Geology ,Plutonism ,Craton ,Geochemistry and Petrology ,Sedimentary rock ,Zircon ,Gneiss - Abstract
We used an ion microprobe to measure 207 Pb / 206 Pb ages of single zircons from four key lithologies from the Singhbhum Craton of eastern India. Detrital zircons from the oldest recognized sedimentary sequence of the craton (the Older Metamorphic Group) yielded 3.5–3.6 Ga ages, indicating that crustal formation had already been initiated by 3.6 Ga in this region. This data also established an older limit of 3.5 Ga for the age of sediment deposition. The first appearance of extensive continental crust in the Singhbhum region, marked by the emplacement of the Older Metamorphic Tonalite Gneisses, is dated at ∼3.44 Ga. Our data from both of these units reveal that a 3.2 Ga event induced overgrowths within each of these pre-existing zircon populations. We determine an age of 3328±7 Ma for the Singhbhum Granite (phase II), the most widespread of this granite's three phases. The emplacement of the two phases of the Mayurbhanj Granite, marking the youngest major episode of acid plutonism in this craton, took place in rapid succession at ∼3.1 Ga, marking the broad-scale stabilization of this terrain.
- Published
- 1999
31. A database of detrital zircon U–Pb ages and Hf isotopic compositions from the Tarim, West Kunlun, Pamir, Tajik and Tianshuihai terranes.
- Author
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Zhang, Shijie, Hu, Xiumian, Zhang, Jinrong, Li, Qing, Xu, Yiwei, Yu, Yuyang, and Han, Liqin
- Subjects
DATABASES ,ZIRCON ,ISOTOPIC analysis ,LITERARY sources ,RESEARCH personnel - Abstract
With the development of detrital zircon U–Pb ages and Hf isotope analysis as conventional sedimentological research methods, a large number of studies have been conducted in the Tarim, West Kunlun, Tajik, Pamir and Tianshuihai regions and abundant data have been accumulated. Summarizing these data to characterize sedimentary units and source regions is more important than local studies of specific geological epochs; therefore, we compiled a database of detrital zircon U–Pb ages and Hf isotope analyses from the Tarim, West Kunlun, Pamir, Tajik and Tianshuihai terranes. The database contains data from 90 papers, including 35,281 individual U–Pb ages and 4,181 Hf isotope analyses. The database records the literature source, petrologic sample information, regional geological information, geographic coordinates and analytical parameters for each data point in as much detail as possible to allow readers to review, process, analyse and use the data. The database relies on the Deep‐time Digital Earth (DDE) platform and uses an open database update system to enable sharing and collaborative building. We encourage other researchers to contribute relevant published data to facilitate wider use. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
32. Comments on the paper by D.H. Cornell and A. Pettersson (SAJG, 110, 575-584 (2007)
- Author
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A.E. Schoch, W.P. Colliston, and H.E. Praekelt
- Subjects
Craton ,geography ,Tectonics ,Paleontology ,geography.geographical_feature_category ,Geology ,Context (language use) ,Terrane ,Zircon - Abstract
The authors are to be congratulated on excellent new zircon dates that contribute to terrane demarcation in the eastern part of the Namaqua mobile belt. Because we were involved in terrane definition of the mobile belt for some time ( e.g. Colliston et al. , 1992), we are very interested in all new isotopic data that can place time constraints on the details of the tectonic history of the region. Hopefully these results will lead to more investigations of a similar nature. We agree in broad context with the synthesis of the authors according to which crustal blocks were accreted against the craton from the west (Cornell and Pettersson, Figure 4) but think that it is already possible to supply more detail. Caution is however advised in terrane demarcation lacking mesoscopic field control and based on only a few firm dates. Mapping of …
- Published
- 2008
33. Response to the papers by Bailie et al. concerning the age and deposition of the Bushmanland Group (South African Journal of Geology, 110, 59-86) and single zircon ages of the Aggeneys Granite Suite (South African Journal of Geology, 110, 87-110)
- Author
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Russell Bailie, David G. Reid, and Richard Armstrong
- Subjects
Tectonics ,Paleontology ,Suite ,Geology ,Thrust fault ,Zircon ,Terrane ,Structural complexity - Abstract
We appreciate the comments by Colliston et al . (2008) on our recent publications concerning the age and deposition of the Bushmanland Group and the age of the Aggeneys Granite Suite (Bailie et al ., 2007a; b). We welcome the debate around the geological significance of the analytical results but note that this can vary according to the stratigraphic/structural models that themselves evolve. We agree with Colliston et al . (2008) that the Namaqua mobile belt is highly structurally complex, being divided into a number of terranes bounded by major thrust faults and with complex stratigraphic relationships that require disciplined and detailed study. It has, nevertheless, being shown by previous authors (Rozendaal, 1975; Joubert, 1986; Ryan et al . 1986; Lipson, 1990; Laccasie et al ., 2006) that despite the structural complexity of the area that various lithological units are consistent across large areas of Namaqualand, albeit that they have been duplicated by thrusting, faulting, shearing and other tectonic events. Colliston et al . (2008) argue for a “preferable” stratigraphic framework. This preferable stratigraphic framework is, however, arguable and not factual. We have used a stratigraphic subdivision proposed by previous authors and do not prefer to follow the exceedingly complex proposed stratigraphic framework of Colliston et al . (2008) and previous publications of theses authors. The samples used in our …
- Published
- 2008
34. A global zircon U–Th–Pb geochronological database.
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Wu, Yujing, Fang, Xianjun, and Ji, Jianqing
- Subjects
EARTH system science ,DATABASES ,ZIRCON ,CRUST of the earth ,CONTINENTAL crust - Abstract
Since the start of the 21st century, the widespread application of ion probes has promoted the mass output of high-precision and high-accuracy U–Th–Pb geochronological data. Zircon, as a commonly used mineral for U–Th–Pb dating, widely exists in the continental crust and records a variety of geological activities. Due to the universality and stability of zircon and the long half-lives of U and Th isotopes, zircon U–Th–Pb geochronology can provide nearly continuous records for almost the entirety of Earth's history and is thus essential to studying the growth and evolution of the continental crust and Earth system evolution. Here, we present a database of zircon U–Th–Pb geochronology that samples the global continental crust and spans nearly all of Earth's history. This database collects ∼2 000 000 geochronology records from ∼12 000 papers and dissertations. This paper describes the compiled raw data, presents the relationship between dating error and zircon age, compares the error levels of different dating instruments, and discusses the impact of sampling bias on data analysis as well as how to evaluate and minimize this impact. In addition, we provide an overview of the temporal and spatial distribution of global zircon ages and provide key insights into the potential research value of zircon ages for Earth system science, such as crustal evolution, plate tectonics, and paleoclimate changes, as well as commercial use in mining and energy exploration. Overall, this data collection provides us with a comprehensive platform with which to study zircon chronological data in deep time and space. The described zircon database is freely available via Zenodo at 10.5281/zenodo.7387566 (Wu et al., 2023). [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
35. Multidimensional Scaling of Varietal Data in Sedimentary Provenance Analysis.
- Author
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Vermeesch, P., Lipp, A. G., Hatzenbühler, D., Caracciolo, L., and Chew, D.
- Subjects
MULTIDIMENSIONAL scaling ,PROVENANCE (Geology) ,COMPOSITION of sediments ,PRINCIPAL components analysis ,MINERAL properties ,SPHENE - Abstract
Varietal studies of sedimentary provenance use the properties of individual minerals or mineral groups. These are recorded as lists of numerical tables that can be difficult to interpret. Multidimensional Scaling (MDS) is a popular multivariate ordination technique for analyzing other types of provenance data based on, for example, detrital geochronology or petrography. Applying MDS to varietal data would allow them to be treated on an equal footing with those other provenance proxies. MDS requires a method to quantify the dissimilarity between two samples. This paper introduces three ways to do so. The first method ("treatment‐by‐row") turns lists of (compositional) data tables into lists of vectors, using principal component analysis. These lists of vectors can then be treated as "distributional" data and subjected to MDS analysis using dissimilarity measures such as the Kolmogorov‐Smirnov statistic. The second method ("treatment‐by‐column") turns lists of compositional data tables into multiple lists of vectors, each representing a single component of the varietal data. These multiple distributional data sets are subsequently subjected to Procrustes analysis or 3‐way MDS. The third method uses the Wasserstein‐2 distance to jointly compare the rows and columns of varietal data. This arguably makes the best use of the data but acts more like a "black box" than the other two methods. Applying the three methods to a detrital titanite data set from Colombia yields similar results. After converting varietal data to dissimilarity matrices, they can be combined with other types of provenance data, again using Procrustes analysis or 3‐way MDS. Plain Language Summary: The source of modern or ancient sediment can be determined by examining either the overall characteristics of the sediment or the chemical composition of individual sediment particles. With the help of recent analytical advancements, geologists can now analyze the complete chemical makeup of single grains of sand or silt. These types of data sets, known as "varietal" data sets, have the ability to uncover differences between sediments that are not visible through traditional methods. However, varietal data are incompatible with the statistical methods that geologists typically use to determine the origin of sediment. This paper addresses this issue by presenting three methods for quantifying the differences between varietal data sets, which is a crucial step in any further statistical analysis. Testing these methods on a varietal data set from Colombia shows similar outcomes. By using the techniques described in this paper, varietal data can now be combined with other conventional methods for determining sediment origin. Key Points: Varietal data are defined as lists of compositional tablesGiven an appropriate dissimilarity measure, varietal data can be subjected to multidimensional scalingThis paper introduces three ways to quantify the pairwise dissimilarity of varietal data [ABSTRACT FROM AUTHOR]
- Published
- 2023
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36. Postcollisional Molybdenum Porphyry Mineralization in the Middle Tien Shan: First Isotopic U–Pb Zircon Data for Rocks from the Molo-Sarychat Pluton (Eastern Kyrgyzstan).
- Author
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Soloviev, S. G., Kryazhev, S. G., Semenova, D. V., Kalinin, Yu. A., and Bortnikov, N. S.
- Subjects
METALLOGENY ,IGNEOUS intrusions ,ZIRCON ,PORPHYRY ,MINERALIZATION ,MOLYBDENUM ,METAMORPHIC rocks - Abstract
The paper presents the first isotopic U–Pb study data (LA–ICP–MS method) of zircon from intrusive rocks of the Molo-Sarychat pluton situated along the deep-seated fault system of the "Nikolaev Line" in the eastern Kyrgyzstan. The intrusive rocks from this pluton belong to the high-potassic calc-alkaline to shoshonitic series. Intense Mo(–W–Cu–Au) (mainly molybdenum-porphyry) mineralization is spatially and genetically associated with this pluton. Together with the other Au, W and Cu deposits and occurrences, this mineralization is part of the extended metallogenic belt of Tien Shan; however, occurrences of molybdenum-porphyry mineralization are still rare in this belt. The concordant isotopic U–Pb ages of zircon autocrysts indicate the crystallization of quartz monzonite (293.3 ± 4.2 Ma) and monzogranite (286.6 ± 2.4 Ma) in the Early Permian. Zircon antecrysts dated at 306–320 Ma are also present. The crystallization age obtained corresponds to a post-collisional epoch of the development of this territory but the presence of the antecrysts expands the pluton emplacement to the Late Carboniferous-Early Permian, which, as a result, spanned over initially subduction-related and then post-collisional tectonic settings. Correspondingly, a post-collisional setting of the Mo(–W–Cu–Au) (molybdenum-porphyry) mineralization is established; it is related to the pluton studied and was formed after the emplacement of quartz monzonite (early stage) and monzogranite (late stage). Significant enrichment in Mo can be related to its progressing accumulation during magmatic differentiation causing the emplacement of quartz monzonite and especially monzogranite. These processes occurred under the more mature post-collisional tectonic regime, with possible formation of intermediate magma chambers in the Paleoproterozoic metamorphic rocks and ancient granitoids. The age dates determined for rocks from the Molo-Sarychat pluton are similar to those identified for the igneous and metasomatic rocks of the large Kumtor gold deposit that is also associated with the "Nikolaev Line." [ABSTRACT FROM AUTHOR]
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- 2024
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37. Metamorphic P–T conditions and ages of garnet-biotite schists in the Dahongshan Group from the southwestern Yangtze Block.
- Author
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Ma, Jun-xiao, Yang, Guang-shu, Yan, Yong-feng, Xu, Xiao-Fei, Ren, Yun-hua, Zhao, Hui, Zheng, Xiao-jun, and Qin, Yuan
- Subjects
RODINIA (Supercontinent) ,SUBDUCTION ,PHASE equilibrium ,PLAGIOCLASE ,ZIRCON ,URANIUM-lead dating ,GARNET - Abstract
The Dahongshan Group, situated at the southwestern margin of the Yangtze Block, represents a geological unit characterized by relatively high-grade metamorphism in the region. This paper investigates the garnet-biotite schist from the Laochanghe Formation of the Dahongshan Group, employing an integrated approach that includes petrological analysis, phase equilibrium modeling, and zircon U–Pb dating. The schist is mainly composed of garnet, biotite, plagioclase, quartz, rutile, and ilmenite. Phase equilibrium modeling revealed the peak metamorphic conditions of 8–9 kbar and 635–675 °C. By further integrating the prograde metamorphic profile of garnet and geothermobarometric results, a clockwise P–T metamorphic evolution path is constructed, which includes an increase in temperature and pressure during the prograde stage. LA–ICP–MS zircon U–Pb dating and zircon Ti thermometry constrains the post-peak metamorphic age of 831.2 ± 7.2 Ma. Integrated with previously reported results, it is revealed that the southwestern margin of the Yangtze Block experienced a large-scale regional metamorphism during the Neoproterozoic (890–750 Ma), which is related to the collisional orogenic process. This may be associated with the late-stage assembly of the Rodinia supercontinent or with local compression and subduction processes during the breakup of the Rodinia supercontinent. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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38. Late Paleozoic Potassic Intrusions of the Eastern Part of the Nikolaev Line and Associated W–Mo–Cu–Au Mineralization: First Isotopic U–Pb Zircon Data (LA-ICP-MS Method) for Rocks from the Adyrtor Intrusions (Middle Tien Shan, Eastern Kyrgyzstan)
- Author
-
Soloviev, S. G., Kryazhev, S. G., Semenova, D. V., Kalinin, Y. A., and Bortnikov, N. S.
- Subjects
IGNEOUS intrusions ,ZIRCON ,METALLOGENY ,LASER ablation inductively coupled plasma mass spectrometry ,METAMORPHIC rocks ,PALEOZOIC Era ,MINERALIZATION - Abstract
The paper presents first data on isotopic U–Pb study (LA-ICP-MS method) of zircon from intrusive rocks of the Adyrtor intrusions – a group of small intrusives situated in the easternmost part of the deep-seated fault system of the "Nikolaev Line." Here, these intrusions cut through one of the oldest (1.8–2.6 Ga) complexes of the basement rocks of Tien Shan (metamorphic rocks of the "Kuilyu suite"). These intrusive rocks belong to the high-potassic calc-alkaline to shoshonitic series, with some geochemical signatures also of anorogenic (A-type) magmatism. These intrusions are accompanied by skarn and porphyry W–Mo–Cu–Au mineralization. Together with the other Au, W, and Cu deposits and occurrences, they are parts of the extended metallogenic belt of Tien Shan. The concordant isotopic U–Pb age data for zircon autocrysts indicate the crystallization of quartz syenite (330.7 ± 4.3 Ma) and quartz monzonite (329.5 ± 5.8 Ma) in the latest Early Carboniferous. The distinct W–Mo specialization of ore mineralization related to the intrusions studied is in agreement with the post-collisional tectonic setting during their emplacement, despite their older or similar age compared to the ore-bearing plutons in more western segments of the Middle Tien Shan, which corresponded to a subduction-related setting. This supports the possibility of the "scissor-like" (from east to west) closure of the Turkestan paleoocean that resulted in the earlier cessation of subduction in the eastern Tien Shan compared to the western Tien Shan. The rocks also contain zircon xenocrysts with older (on the order of 1.7–2.6 Ga) age, which is in agreement with the age of the host metamorphic rocks of the Tarim craton basement. This highlights the possibility of magma chamber development in the continental crust, together with the magma chambers in the metasomatically-enriched subcontinental upper mantle, the latter being common for high-potassic magmatism. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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39. Short Paper: The depositional age of the Dalradian Supergroup: U-Pb and Sm-Nd isotopic studies of the Tayvallich Volcanics, Scotland
- Author
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Alex N. Halliday, Colin M. Graham, M. Aftalion, and P. Dymoke
- Subjects
Dalradian ,Volcanic rock ,geography ,Igneous rock ,Precambrian ,geography.geographical_feature_category ,Absolute dating ,Geochemistry ,Metamorphism ,Geology ,Orogeny ,Zircon - Abstract
Zircons from a keratophyre associated with the Tayvallich Volcanics in the Dalradian rocks of the SW Scottish Highlands have been dated by U-Pb methods, yielding an age of 595 ± 4 Ma. This age indicates that most or all of the Dalradian is Precambrian in age, and that Dalradian sedimentation may have lasted for about 200 million years. The age also constrains the time interval between cessation of Dalradian sedimentation and subsequent crustal thickening and regional metamorphism during the Grampian Orogeny. Sm-Nd isotopic data for the Tayvallich Volcanins and related metadolerite sills yield initial oNd values of +2 to +4, which are thought to reffect the effects of melting of lithospheric mantle.
- Published
- 1989
40. <Original Papers>Research on the Rare Metal Resources (I) : Caldasite from Pocos de Caldas as a Zirconium Resources
- Subjects
Zircon ,Thorium ,Metallurgy ,Uranium ,Chlorination ,Caldasite ,Zirconium ,Baddeleyite ,Hafnium ,Metamictization ,Distillation - Abstract
The zirconium deposit of the Pocos de Caldas Plateau is north of São Paulo, Brasil, on the boundary between the States of Minas Gerais and São Paulo. The zirconium ore was formed as a mixture of baddeleyite (ZrO_2) and zircon (ZrSiO_4) which was identified as caldasite from the microscopic, X-ray and electron microprobe studies. This ore also contained a high content of uranium and thorium oxides, enough for nuclear fuel resources from the γ-ray spectrometry. The ore shows stable behavior in the TG-DTA studies but the metamictization by the α radiation damage from uranium and thorium seems to have occurred. The possible production process of zirconium from the caldasite was discussed mainly in the distillation process. Finally the evaluation of the caldasite as a zirconium resource was conducted from the metallurgical point of view.
- Published
- 1986
41. State-of-the-art and perspectives in the heavy mineral industry of Sri Lanka
- Author
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K. A. G. Sameera, H.C.S. Subasinghe, and Amila Sandaruwan Ratnayake
- Subjects
Heavy minerals ,020209 energy ,Economics, Econometrics and Finance (miscellaneous) ,02 engineering and technology ,Sustainable utilisation ,010501 environmental sciences ,engineering.material ,01 natural sciences ,Placer deposit ,Environmental protection ,0202 electrical engineering, electronic engineering, information engineering ,health care economics and organizations ,0105 earth and related environmental sciences ,Sri Lanka ,Original Paper ,Heavy mineral ,Mineral resource classification ,Value addition ,Rutile ,engineering ,Environmental science ,Leucoxene ,Sillimanite ,Social Sciences (miscellaneous) ,Ilmenite ,Zircon - Abstract
Heavy minerals have become an essential commodity in modern-day technology. The objective of this study is to examine the current status of the heavy mineral industry of Sri Lanka. The present study also examines the economic viability of potential heavy mineral placer deposits, based on geochemical data. Field investigations suggested the occurrence of heavy minerals as beach-placers, and inland/raised beach deposits along the coastline of Sri Lanka. Geochemical results showed the enrichment of TiO2, Fe2O3, Al2O3, and trace elements, and depletion of other major oxides such as Na2O, K2O, MnO, MgO, CaO, and P2O5. Consequently, it suggests the abundance of ilmenite, leucoxene, rutile, sillimanite, garnet, and rare earth element (REE)-bearing heavy minerals in potential placer deposits. In contrast, this study illustrates the exported quantity (in the weight ratio of 35:3:1) of ilmenite, rutile, and zircon minerals during the last decade. Ilmenite is the dominant heavy mineral in Sri Lanka, and thus, its production and price volatilisations are essential to understand the current status and predict the future behaviour of the heavy mineral industry. Statistical observations suggest that the global production and unit price variations of ilmenite have increased gradually from 1950 to 2015. Besides, the forecasted variations in annual global production and unit price changes of ilmenite indicate healthy compound annual growth rates of 1.27% and 1.43%, respectively. However, Sri Lanka has less contribution (< 1%) to global ilmenite production. Consequently, the value addition of ilmenite must be highly encouraged with at least an immediate stage (e.g. synthetic rutile). The present study also highlights possible value addition stages of available heavy mineral resources (low-, intermediate-, or high-level value addition), and discusses action plans to improve the quality of the heavy mineral industry of Sri Lanka. In recommendations, imposing sustainable regulations and policies would uplift the heavy mineral industry of Sri Lanka. For example, value addition to local heavy minerals and terminating raw commodity export are highly recommended.
- Published
- 2021
42. Zircon UPb versus RbSr whole-rock age data from eastern finland: A critical comment on the papers of Barbey & Martin and Martin, Precambrian research, vol. 35, 1987
- Author
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Matti Vaasjoki
- Subjects
Plate tectonics ,Precambrian ,Geochemistry and Petrology ,Absolute dating ,Proterozoic ,Archean ,Geochemistry ,Geology ,Baltic Shield ,Crust ,Zircon - Abstract
Discussion et reponse sur les articles «The role of komatiites in plate tectonics. Evidence from the Archean and early Proterozoic crust in the eastern Baltic Shield Precambrien» par Barbey P. et Martin H., 1987, 35, p. 1-14 et «Evolution and composition of granitic rocks controlled by time-dependent changes in petrogenetic processes: examples from the Archean of eastern Finland», par Martin H, 1987, 35, p. 257-276
- Published
- 1988
43. Comments on the papers by Bailie et al. concerning the age and deposition of the Bushmanland Group (South African Journal of Geology, 110, 59-86) and single zircon ages of the Aggeneys Granite Suite (South African Journal of Geology, 110, 87-110).
- Author
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Colliston, W. P., Schoch, A. E., and Praekelt, H. E.
- Subjects
SEDIMENTATION & deposition ,ROCKS ,GEOLOGICAL time scales ,SEQUENCE stratigraphy ,ZIRCON - Abstract
The authors comment on two papers concerning the age and deposition of the Bushmanland Group in South Africa. According to the authors, the samples employed in the two papers for isotopic analyses are related to their stratigraphic sequence. The authors admit the difficulty of dating zircons in metamorphic rocks but thinks that a good advance has been made concerning possible ages of the provenance rocks of the Bushmanland Group.
- Published
- 2008
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44. New Data on the U–Pb (LA-ICP-MS) Isotopic Age of Zircon from Intrusive Rocks of the Kuru-Tegerek Skarn Au–Cu–Mo Deposit, Middle Tien Shan, Kyrgyzstan.
- Author
-
Soloviev, S. G., Kryazhev, S. G., Semenova, D. V., Kalinin, Yu. A., and Bortnikov, N. S.
- Subjects
METALLOGENY ,SKARN ,GEOLOGICAL time scales ,ZIRCON ,LASER ablation inductively coupled plasma mass spectrometry ,METAMORPHIC rocks - Abstract
The paper presents new isotopic U–Pb data (LA-ICP-MS method) of zircon from the main types of intrusive rocks at the Kuru-Tegerek gold-copper-molybdenum skarn deposit situated in the Chatkal segment of the Middle Tien Shan. This and other gold, copper, tungsten and molybdenum deposits are parts of the extended Late Paleozoic metallogenic belt of Tien Shan. The concordant isotopic U–Pb values obtained for zircon autocrysts from the rocks of sequential intrusive phases span over the interval from approximately 323 to 311 Ma. This interval comprises the crystallization of gabbro-diorite (from 323.5 ± 2.5 Ma to 323.2 ± 6.8 Ma) and tonalite (from 321.4 ± 3.8 Ma to 311 ± 3.8 Ma). The age dates obtained for these zircon autocrysts correspond to the emplacement of these moderate-potassic intrusions in the Late Carboniferous and are almost coincident with the isotopic dates previously known for the high-potassic intrusions of the porphyry Cu–Au–Mo deposits of the Almalyk mineralized cluster (Kurama segment of the Middle Tien Shan), which were also emplaced in the Late Carboniferous (about 330–310 Ma). This corresponds to the subduction tectonic regime occurred in this region in relation to the steep-dipping (in the Kurama segment) or flat (in the Chatkal segment) subduction of a tectonic plate toward the north, under the structures of the Kazakhstan–North Tien Shan continental massif and accreted segments of the Middle Tien Shan. The intrusive rocks studied at the Kuru-Tegerek deposit contain also zircon xenocrysts (including these in the core of complex crystals) with the isotopic U–Pb age of some 1.9–2.1 Ga. These dates are in agreement with the age of metamorphic rocks in the Tarim craton basement and indicate the presence of the ancient continental crust in this segment of the Middle Tien Shan. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
45. A Complex Meso–Cenozoic History of Far-Field Extension and Compression: Evidence from Fission Track Analysis in the Helanshan Mountain Tectonic Belt, NW China.
- Author
-
Wu, Cheng, Wang, Yu, Yuan, Wanming, and Zhou, Liyun
- Subjects
OROGENIC belts ,AGE groups ,SUBDUCTION ,LITHOSPHERE ,ZIRCON ,APATITE - Abstract
The Helanshan Mountain tectonic belt (HTB) is an intraplate deformation belt along the northwestern border of the Ordos Block in the North China Craton. When and why this intracontinental tectonic belt formed, its subsequent uplift and erosion, and the relationships between ranges and adjacent basins remain unclear. To better assess the connections between the temporal and structural activity in HTB, apatite fission-track (AFT) and zircon fission-track (ZFT) analyses were conducted in this study. The lack of adequate FT data from the HTB is a source of contention and dispute. This paper collected samples for AFT and ZFT techniques from the central and southern HTB, trying to improve the research. The ZFT and AFT ages could be divided into the following 7 groups: 279 Ma, 222–213 Ma, 193–169 Ma, 151–147 Ma, 130–109 Ma, 92–77 Ma, and 65–50 Ma. The inverse modeling results of AFT indicate 4 fast cooling episodes of 170–120 Ma, 120–95 Ma, 66–60 Ma, and ~10–8 Ma to the present. Combining the results of FT analysis with radial plot and inverse modeling of AFT, the following eight age groups are believed to reveal the distinct tectonic activities in HTB: the first age group of 279 Ma mainly represented the back-arc extension of the southern HTB; the age group of 222–213 Ma was bounded with NNE-SSE trending contraction between the South China block and North China Craton; the event of 193–169 Ma responded to the post-orogenic collapse followed after the second event; the 151–147 Ma group was interpreted as the eastward extrusion induced by the subduction between Qiangtang and Lhasa blocks; the Early Cretaceous (130–109 Ma) group was not only affected by the rollback of the Pacific Plate, but also denoted the collapse of the thickened lithosphere formed in the Late Jurassic; the Late Cretaceous (92–77 Ma) group was attributed to long-distance impact from the subduction of the Pacific Plate beneath the Eurasian Plate; the event during 65–50 Ma was a correspondence to far-field effect of the onset collision between the Eurasian and Indian Plates; and from 10–8 Ma to the present, the progressive collision of the Indian and Eurasian Plates have a significant impact on the HTB and the northeastern Tibetan Plateau. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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46. Isotopic U–Pb Age of Zircon (LA-ICP-MS Method) from Igneous Rocks of the Chorukh-Dairon W–Mo(–Cu–Au) Deposit (Tajikistan): First Evidences for Post-Collisional Ore Formation in the Kurama Segment of the Middle Tien Shan.
- Author
-
Soloviev, S. G., Kryazhev, S. G., Semenova, D. V., Kalinin, Yu. A., and Bortnikov, N. S.
- Subjects
METALLOGENY ,IGNEOUS rocks ,LASER ablation inductively coupled plasma mass spectrometry ,ZIRCON ,SKARN ,MONZONITE - Abstract
The paper presents isotopic U–Pb zircon data (LA-ICP-MS method) for the main types of high-potassic intrusive rocks of the Chorukh-Dairon W–Mo(–Cu–Au) skarn deposit situated in the Kurama segment of the Middle Tien Shan near the largest porphyry Cu–Mo–Au deposits of the Almalyk mineralized cluster. Together with the other Au, W, Mo and Cu deposits, all these deposits are parts of the extended Late Paleozoic metallogenic belt of Tien Shan. The concordant isotopic U–Pb zircon data obtained for the rocks of successive intrusion phases in the Chorukh-Dairon pluton span from about 298 Ma to 290 Ma. This interval included crystallization of monzodiorite (295.1 ± 3.3 Ma), quartz syenite (294.7 ± 2.3 Ma), quartz monzonite (294.1 ± 2.1 Ma), and monzogranite (293.0 ± 3.0 Ma). These dates correspond to the pluton emplacement at the Late Carboniferous-Early Permian boundary and highlight its younger age compared to the productive high-potassic intrusions of the porphyry Cu–Mo–Au deposits in the Almalyk mineralized cluster, the latter assigned to the Late Carboniferous (about 337–313 Ma and partially to 308–297 Ma). By contrast to the latter, which were intruded in the subduction-related environment, the emplacement of the high-potassic rock of the Chorukh-Dairon pluton occurred in the transitional subduction-related to post-collisional environment or even under an actual post-collisional regime. This allows distinguishing two pulses of ore-bearing Carboniferous-Permian high-potassic calc-alkaline to shoshonitic series magmatism in the Middle Tien Shan. Consistently, there is a metallogenic evolution in the region that was expressed in the transition from porphyry Cu–Mo–Au deposits associated with subduction-related potassic magmatism, and likely evolving toward epithermal Au-Ag deposits, to essentially tungsten (W–Mo–Cu–Au) deposits associated with younger potassic magmatism occurring rather in the post-collisional environment. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
47. Petrogenesis of late triassic high-silica granites in the North Qiangtang terrane, central Tibetan Plateau.
- Author
-
Changjun Ji, Bin Liu, Yun Chen, Zhenhan Wu, Chong Chen, Fangyang Hu, and Gong-Jian Tang
- Subjects
ZIRCON ,GRANITE ,PETROGENESIS ,TURBIDITES ,NONFERROUS metals ,CONTINENTAL crust - Abstract
Although high-silica granites can provide unique insights into the maturity of the continental crust and rare metal enrichment, the origin of high-silica granitic magmatism remains uncertain. In this paper, we present an integrated study of zircon U-Pb geochronology and trace elements, whole-rock geochemistry, and Sr-Nd isotopes for two typical high-silica granites (namely, the Longbao granitic porphyry and the Yushu granite) found in the North Qiangtang terrane, central Tibetan Plateau. Zircon geochronological data indicate that these high-silica granites crystallized at 217-214 Ma. All the samples from the Longbao granitic porphyry and the Yushu granite exhibited high SiO
2 , low MgO, depletion of Ba, Nb, Sr, P, and Ti, and enrichment of Th and U. They exhibited relatively high (87 Sr/86 Sr)i ratios of 0.7120-0.7136 and low eNd (t) values of -8.58 ~ -7.58; together with their old ages according to the two-stage Nd model (1.6-1.7 Ga), these features indicate the involvement of crustal materials. Geochemical and isotopic variation indicated that the high-silica granites studied were mainly produced by the dehydration melting of a muscovite (Ms)-bearing source, and that the Triassic turbidites might be a good candidate for the magma source. Combining this evidence with new regional studies, it can be concluded that partial melting of Triassic turbidites induced by slab roll-back might be the key factor controlling the origin of Late Triassic magmatism in the North Qiangtang terrane. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
- View/download PDF
48. Identification of the Sedimentary Sources and Origin of Uranium for Zhiluo Formation of the Tarangaole U Deposit, Northeastern Ordos Basin.
- Author
-
Li, Guang-Yao, Xue, Chun-Ji, Zhu, Qiang, Yang, Jian-Wen, and Zhao, Xiao-Bo
- Subjects
HEAVY minerals ,ZIRCON ,URANIUM ,CLASTIC rocks ,URANIUM mining ,PROVENANCE (Geology) ,URANIUM-lead dating ,CHEMICAL weathering - Abstract
The large-sized Tarangaole uranium deposit and its neighboring Daying and Nalinggou deposits, located in the northeastern margin of the Ordos Basin, constitutes a major uranium resource base in northern China. In order to further clarify the sedimentary material source, uranium source and regional sediment–tectonic setting of the uranium-fed clastic rocks (i.e., Zhiluo Formation(J
2 z)) in the district, this paper carried out whole-rock geochemistry, heavy minerals composition and in situ U-Pb dating of detrital zircons for sandstones from the lower section of the Zhiluo Formation. The results have shown that the average chemical differentiation index (CIA) for the host rocks is 73.16 and the chemical weathering degree is moderate. Heavy minerals are mainly composed of ilmenite, garnet, chlorpyrite, zircon, pyrite, apatite, hematite, etc. The U-Pb dating of detrital zircon generally indicates three age peaks, i.e., 260~Ma, 1850~Ma and 2450~Ma, respectively. In conclusion, the source rocks may have been formed at active continental margins, e.g., in a continental margin arc environment. The sedimentary materials mainly come from khondalite series, TTGs, granulite, and mafic–ultramafic intrusive rocks distributed among the Daqing–Ula Mountains and adjacent areas, etc. The Late Paleozoic U-rich intermediate and acidic magmatic rocks spreading over the eastern part of the Ula–Daqing and Wolf mountains have provided the main uranium sources for the formation of major U deposits in the northern Ordos Basin. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
- View/download PDF
49. A synthesis of available detrital zircon data from Turkey, Cyprus and Greek peninsula.
- Author
-
Chen, Guohui, Li, Chao, Shi, Yifan, and Zha, Kaijie
- Subjects
ZIRCON ,PENINSULAS ,PUBLISHED articles ,SCIENCE publishing ,ISOTOPES - Abstract
This paper describes the assembly of an updated dataset of detrital zircon geochronology and Lu–Hf isotopes for Turkey, Cyprus and Greek peninsula. This first version of the dataset documented 286 samples with detrital zircon U–Pb data and 70 samples with zircon Lu–Hf isotopes from 42 published articles. These samples are mainly distributed in seven geologic‐tectonic units in the Eastern Mediterranean Tethyan region. The compilation of dataset will be periodically accessed in the Deep‐Time Digital Earth repository, containing more updated raw data of (un)published scientific research. We believe that the construction of such a dataset is fundamental to studies of clastic strata and also to understanding of crustal evolution in the Eastern Mediterranean region. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
50. Application of Raman Spectroscopy for Studying Shocked Zircon from Terrestrial and Lunar Impactites: A Systematic Review.
- Author
-
Zamyatin, Dmitry A.
- Subjects
RAMAN spectroscopy ,ZIRCON ,LUNAR craters ,IMPACT craters ,SCIENCE databases ,WEB databases - Abstract
A highly resistant mineral, zircon is capable of preserving information about impact processes. The present review paper is aimed at determining the extent to which Raman spectroscopy can be applied to studying shocked zircons from impactites to identify issues and gaps in the usage of Raman spectroscopy, both in order to highlight recent achievements, and to identify the most effective applications. Method: Following PRISMA guidelines, the review is based on peer-reviewed papers indexed in Google Scholar, Scopus and Web of Science databases up to 5 April 2022. Inclusion criteria: application of Raman spectroscopy to the study of shocked zircon from terrestrial and lunar impactites. Results: A total of 25 research papers were selected. Of these, 18 publications studied terrestrial impact craters, while 7 publications focused on lunar breccia samples. Nineteen of the studies were focused on the acquisition of new data on geological structures, while six examined zircon microstructures, their textural and spectroscopic features. Conclusions: The application of Raman spectroscopy to impactite zircons is linked with its application to zircon grains of various terrestrial rocks and the progress of the electron backscatter diffraction (EBSD) technique in the early 2000s. Raman spectroscopy was concluded to be most effective when applied to examining the degree of damage, as well as identifying phases and misorientation in zircon. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
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