UPb ages of zircon rims: A new analytical method using the air-abrasion technique

Aleinikoff, John N.; Winegarden, Donald L.; Walter, Marianne

doi:10.1016/0168-9622(90)90015-5

Cited by 12 publications

(4 citation statements)

References 30 publications

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“…Foliated, gray, medium-grained biotite trondhjemite collected from an outcrop on the south side of NH Route 110, about 8 km northwest of Berlin, NH (Moench et al, 1995, site (Steiger and J€ a ager, 1977). a Abbreviations: E (elongate), NM (non-magnetic), D (diamagnetic), A (abraded), M (magnetic), C (clear), P (prismatic), R (round), Dust (fine-grained material collected during abrasion in ceramic mill; Aleinikoff et al, 1990).…”

Section: A2 Resultsmentioning

confidence: 99%

“…Foliated, gray, medium-to coarse-grained granite collected from a roadcut 7 km north of Lancaster, NH (Moench et al, 1995, site O-11, northern). Five zircon fractions were analyzed, including two fractions composed of material removed from the rims of grains (see Aleinikoff et al, 1990 for methodology) ( Table 3). The isotopic data are colinear with intercept ages of 442 AE 4 and )5 AE 59 Ma (MSWD ¼ 0.52).…”

Section: A2 Resultsmentioning

confidence: 99%

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Stratigraphy, geochronology, and accretionary terrane settings of two Bronson Hill arc sequences, northern New England

Moench¹,

Aleinikoff²

2003

Physics and Chemistry of the Earth, Parts A/B/C

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The Ammonoosuc sequence is defined by the Middle Ordovician Ammonoosuc Volcanics near Littleton, NH, the type area, northeast to Milan, NH, and Oquossoc, ME; it also includes black slate of the Partridge Formation (C. bicornis--zone graptolites, $457 Ma). Related metamorphosed intrusives are the tonalitic Joslin Turn pluton (469 AE 2 Ma), the Cambridge Black granitic pluton (468 AE 3 Ma), and gabbro, tonalite (467 AE 4 Ma), and sheeted diabase of the Chickwolnepy intrusions. These intrusives cut lowermost Ammonoosuc (therefore >469 Ma). Probable uppermost Ammonoosuc is dated at 465 AE 6 and 461 AE 8 Ma. Successively below the Ammonoosuc are the Dead River and Hurricane Mountain Formations (flysch and melange), and the Jim Pond Formation (484 AE 5 Ma) and Boil Mountain Complex (both ophiolite), which are structurally underlain by the Neoproterozoic(?) Chain Lakes massif.The Quimby sequence is defined by the Lower Silurian(?) to Upper Ordovician Quimby Formation, composed of bimodal volcanics (443 AE 4 Ma) and sulfidic shale and graywacke that lie conformably to unconformably above the Ammmonoosuc Volcanics and Partridge Formation. Also in the Quimby sequence are several granitic to sparsely gabbroic plutons of the Highlandcroft (441-452 Ma) and Oliverian (435-456 Ma) Plutonic Suites, which intrude the Dead River, Ammonoouc and Partridge, but not the Quimby Formation.Based on faunal, paleolatitude, and isotopic data, the Ammonoosuc sequence and its correlatives and underlying sequences formed off the southern Laurentian margin, but northwest of the principal Iapetan suture, or Red Indian line. The Boil MountainJim Pond-Hurricane Mountain sequence was ramped northwestward over the Chain Lakes massif at $475 Ma, on the basal Boil Mountain surface. This obduction probably occurred slightly before obduction on the Baie Vert-Brompton surface (BBL), farther NW, over the Laurentian margin, and was followed by Dead River flysch sedimentation, which ended with the abrupt onset of Ammonoosuc-sequence arc magmatism at $470 Ma. Ammonoosuc eruptions probably ended at $460 Ma, when Iapetus closed along the Red Indian line.During a following magmatic hiatus of $3-5 m.y., now represented by portions of the Partridge Formation that overlie the Ammonoosuc Volcanics, subduction polarity reversed, and subduction resumed below the northwest-dipping Brunswick subduction complex (BSC) of New Brunswick, Canada. Quimby-sequence magmatism ($456-435 Ma) on the newly accreted Laurentian margin occurred above the BSC, whose footwall is now buried to the southeast by mainly Silurian clastic sediments of the MerrimackFredericton trough, deposited in the ''Fredericton Sea''. In Silurian to Early Devonian time, the NW-dipping BSC footwall was paired with a SE-dipping subduction zone that produced arc magmas of the Coastal Volcanic belt, built on the composite Avalon and adjacent peri-Avalonian terranes. Orogen-normal extension produced by rapid rollback of both subduction zones narrowed the Fredericton Sea, produced the Central Maine and Connecti...

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Section: A2 Resultsmentioning

confidence: 99%

Section: A2 Resultsmentioning

confidence: 99%

Stratigraphy, geochronology, and accretionary terrane settings of two Bronson Hill arc sequences, northern New England

Moench¹,

Aleinikoff²

2003

Physics and Chemistry of the Earth, Parts A/B/C

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“…7). Physical techniques, such as over-pressurized air abrasion in closed chambers, also efficiently remove the external 4 He*-enriched rim (Aleinikoff et al 1990).…”

Section: Removing the Implanted 4 He* Componentmentioning

confidence: 99%

Cosmogenic 3He in terrestrial rocks: a review

Blard¹

2023

Preprint

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This review article summarizes the state of the art of cosmogenic 3He (3Hec), with a focus on the most efficient methods for measuring this cosmogenic noble gas in terrestrial samples. After briefly reviewing the scientific applications and production pathways of cosmogenic 3He, I summarize the most important theoretical and practical aspects of 3He analyses and describe the best strategies for correcting for non-cosmogenic 3He components in minerals. I also review our knowledge of 3Hec production rates and explore potential new applications for future studies.Our ability to accurately and precisely measure cosmogenic 3He is mainly constrained by the level of the non-cosmogenic 3He background (i.e., magmatic, radiogenic, nucleogenic, and atmospheric 3He), and thus by the geological characteristics of the samples. Constructing 3He vs. 4He isochrons by analyzing several aliquots from the same sample constitutes a useful and overlooked method that is advantageous because it obviates the often-complicated step of vacuum crushing. This method also allows the direct and joint determination of cosmogenic 3He and the magmatic 3He/4He ratio. I perform numerical modeling to explore the impact of the non-cosmogenic 3He components on the final uncertainties and detection limits of 3He dating. Reducing the magmatic component by selecting phenocrysts in the 100–500 m size fraction improves the precision of cosmogenic 3He analyses. Moreover, it is important to measure U, Th, and Li concentrations in the analyzed minerals and their host rocks to ensure proper corrections for radiogenic 4He and nucleogenic 3He, improving both the accuracy and precision of the method.After summarizing the most important aspects of 3He analytical techniques, including the best 3Hec extraction techniques and the key parameters of noble gas mass spectrometry that result in accurate and precise helium isotopic measurements, I also review 3Hec production rates and their spatial variability. The global database of absolute calibration sites yields a world-wide average 3Hec production rate in olivine and pyroxene of 124 ± 11 at g−1 yr−1 using the LSD scaling and the online CREp calculator (https://crep.otelo.univ-lorraine.fr/#/). Cross-calibrations against 10Be indicate that the ratio of the production rate of 3Hec in olivine/pyroxene to that of 10Be in quartz is 33 ± 2 and increases by less than 7% between sea level and 5,000 m elevation. This important observation demonstrates that 3He in olivine/pyroxene and 10Be in quartz can be considered as synchronized chronometers. However, 3Hec/10Be cross-calibrations based on 3Hec in accessory minerals (zircon, garnet, kyanite, apatite) yield unexpectedly high 3He/10Be production ratios of 40–60 above 3,000 m elevation. As the capture of cosmogenic thermal neutrons by 6Li is unlikely to explain this excess, I discuss other plausible mechanisms that should be explored, such as 3Hec inherited from previous exposure episodes, unrecognized specific reaction pathways, or the impact of snow cover. New cross-calibration data obtained by measuring 3Hec against other cosmogenic nuclides in different settings will advance our understanding of cosmogenic nuclide production rates and improve the accuracy and precision of applications relying on cosmogenic 3He. Other improvements could extend the applicability of the 3He geoscientific toolbox; for example, coupling 3He with radioactive cosmogenic nuclides (10Be, 36Cl, 53Mn) will allow paleoaltimetry or the determination of burial ages or paleo-depths in intermediate and mafic terrains.

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“…For olivine and pyroxene,Bromley et al, (2014) proposed a chemical treatment in which minerals are leached for 2 hours in a 3% HF:10% HCl acid solution in an ultrasonic bath at 40 °C. Physical techniques, such as over-pressurized air abrasion in closed chambers, also efficiently remove the external 4 He*-enriched rim(Aleinikoff et al, 1990).…”

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confidence: 99%

Cosmogenic 3He in terrestrial rocks: A review

Blard

2021

Chemical Geology

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This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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UPb ages of zircon rims: A new analytical method using the air-abrasion technique

Cited by 12 publications

References 30 publications

Stratigraphy, geochronology, and accretionary terrane settings of two Bronson Hill arc sequences, northern New England

Stratigraphy, geochronology, and accretionary terrane settings of two Bronson Hill arc sequences, northern New England

Cosmogenic 3He in terrestrial rocks: a review

Cosmogenic 3He in terrestrial rocks: A review

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