scholarly journals Radiometric age determinations in the Kærven area, Kangerdlugssuaq, Bast Greenland Tertiary igneous Province: 40Ar/39 Ar, Kl Ar and Rb/Sr isotopic results

1991 ◽  
Vol 38 ◽  
pp. 183-201
Author(s):  
Paul Martin Holm
Keyword(s):  
Isotope Analysis ◽  
Alkali Feldspar ◽  
Magmatic Activity ◽  
Sr Isotopes ◽  
Sr Isotope ◽  
Stepwise Heating ◽  
Alkaline Intrusion ◽  
Igneous Province ◽  
Age Determinations ◽  
Alkali Feldspars

The Kærven syenite complex was emplaced as part of the magmatic activity related to continental rifling in the Paleogene. Radiometric age determinations have been carried out on samples from selected parts of the complex, which consists of more !han 10 significant units. Five amphiboles and two alkali feldspar have been analysed by the 40Arl'9Ar method with stepwise heating, five amphiboles and one biotite K/Ar analyses are presented together with Rb/Sr isotope analysis of 6 amphiboles, 2 biotites, 3 alkali feldspars and 32 whole rocks. The results reveal that a Iate, probably 36 Ma, thermal event caused Ar-loss in the alkali feldspars and excess 40Ar-gain in variable amounts in the analysed minerals. Also the Sr isotopes were disturbed by the secondary heating. Crystallisation ages for parts of the Kærven complex can be established as 58 ± 1 Ma, while other units have younger ages of 56.1 ± 0.8 Ma and 50.4 ± 0.8 Ma. The age for the early Kærven rocks is significantly older than other recorded syenites in the Kangerdlugssuaq area and is comparable only to the estimated age of the initiation of basaltic volcanism along the East Greenland coast at 57 Ma. An Rb/Sr isochron for four nordmarkite whole rocks and a 40Ar/39 Ar age plateau of an amphibole from one nordmarkite date the part of the Kangerdlugssuaq alkaline intrusion adjacent to the Kærven complex as 54.6 ± 2.4 Ma. This is older than other parts of the Kangerdlugssuaq intrusion, and indicate that this intrusion was multiple and emplaced over several million years

The Highwood Mountains potassic igneous province, Montana: mineral fractionation trends and magmatic processes revisited

2012 ◽  
Vol 76 (4) ◽  
pp. 1005-1051 ◽  
Author(s):  
C. M. B. Henderson ◽  
F. R. Richardson ◽  
J. M. Charnock
Keyword(s):  
Major Element ◽  
Magma Mixing ◽  
Alkali Feldspar ◽  
Bulk Rock ◽  
Magma Chambers ◽  
Igneous Province ◽  
Rock Analysis ◽  
Volatile Loss ◽  
Primary Magmas ◽  
Alkali Feldspars

AbstractPotassium-rich mafic dykes and lavas from the Highwood Mountains Igneous Province, USA were studied by electron-microprobe and bulk-rock analysis. For the mafic phonolites, compositional trends for olivine and augite phenocrysts and groundmass biotite, alkali feldspar and titanomagnetites are presented and substitution mechanisms discussed. Phenocrysts of biotite and augite in the minettes are also characterized, together with groundmass alkali feldspar and titanomagnetite. The alkali feldspars and biotites are commonly enriched in Ba. Olivine, clinopyroxene and biotite phenocrysts are generally quite magnesium-rich, which is consistent with the primitive natures of the least evolved rocks.Bulk-rock major-element compositions are combined with modal and microprobe data for the principal phenocrysts to calculate model residual liquid compositions for mafic phonolites, minettes and a syenitic rock. On the basis of phase-equilibria, it is suggested that the main controls of differentiation are polybaric involving crystallization during transport of primary magmas from the mantle for the minettes, and low-pressure differentiation for the mafic phonolites. Whereas magma mixing might have contributed to petrogenesis, many of the disequilibrium features exhibited by clinopyroxene and biotite phenocrysts can also be attributed to pre-existing phenocrysts undergoing decompression melting during magma uprise from its mantle source, followed by rapid crystal growth and episodic volatile loss in sub-volcanic magma chambers.

Lake basin closure and episodic inflow as recorded by radiogenic Sr isotopes: Eocene Green River Formation in the Piceance Creek Basin, Colorado

2020 ◽  
Vol 57 (4) ◽  
pp. 355-373
Author(s):  
Kuwanna Dyer-Pietras
Keyword(s):  
Isotope Analysis ◽  
Green River Formation ◽  
Lake Basin ◽  
Sr Isotopes ◽  
Sr Isotope ◽  
Green River ◽  
White River ◽  
Core Deposits ◽  
The Difference ◽  
Lacustrine Basins

Lacustrine basins are excellent archives of lake evolution, and deposits record the uplift and weathering histories of the surrounding terrain. The application of Sr isotopes has been tested in several lacustrine basins, both modern and ancient, based on the premise that lakes are well mixed, and shifting Sr isotopes may suggest changes in lake provenance. In the Eocene lacustrine Green River Formation in the Piceance Creek Basin of Colorado, Sr isotope analysis of carbonate mudstones indicates that radiogenic Sr in the center of the Piceance lake decreased during the evolution of the lake, from 52.8–48.4 Ma. Because deposition in the basin center occurred away from the influence of episodic alluvial inflow at the basin margin, Sr isotope evolution in the Piceance lake after basin closure is recorded in the John Savage #24-1 core deposits, not the Anvil Points deposits. Sr isotope analysis of carbonate mudstones at Anvil Points below 55 m shows fluctuating radiogenic Sr values that record episodic inflow from the White River Uplift. This inflow is responsible for the difference in radiogenic Sr trends recorded between the basin center and margin. Above 55 m, fluctuating Sr isotope values at Anvil Points record episodic inflow from the White River Uplift, without inflow of Paleozoic and Mesozoic carbonates. The boundary at 55 m records the hydrologic closure of the Uinta and Piceance lakes around 52 Ma, when lake level lowered beneath the basin sill and the lakes were no longer connected across the Douglas Creek Arch. A significant increase in radiogenic Sr across the 55-m-boundary records this transition from open to closed hydrology, reflecting a loss of dissolved Sr sourced from Paleozoic and Mesozoic carbonates.

Accuracy of laser-ablation (LA)-MC-ICPMS Sr isotope analysis of (bio)apatite – a problem reassessed

2016 ◽  
Vol 31 (1) ◽  
pp. 259-269 ◽  
Author(s):  
Wolfgang Müller ◽  
Robert Anczkiewicz
Keyword(s):  
Laser Ablation ◽  
Isotope Analysis ◽  
Sr Isotope ◽  
Plasma Laser ◽  
Interference Correction

Accurate in situ Sr isotope analysis of (bio)apatite via ‘robust-plasma’ laser-ablation MC-ICPMS with negligible 40Ca31P16O and reliable 87Rb interference correction.

scholarly journals THE COMPREHENSIVE STUDY OF CREMATIONS IN THE 1st CENTURY BC – 2nd CENTURY AD FROM THE BURIAL VAULTS OF THE EASTERN NECROPOLIS IN PHANAGORIA

2020 ◽  
Author(s):  
Н.Г. Свиркина ◽  
С.А. Володин
Keyword(s):  
Chemical Analysis ◽  
Urban Population ◽  
Isotope Analysis ◽  
Southern Europe ◽  
Sr Isotope ◽  
Preliminary Results ◽  
Key Characteristics ◽  
Comprehensive Study

В статье представлены предварительные результаты комплексного биоархеологического исследования серии трупосожжений I в. до н. э. – II в. н. э., обнаруженных в склепах Восточного некрополя Фанагории. Результаты определения основных характеристик сожженных останков сравниваются с данными о кремациях из некрополей Западной и Южной Европы, что позволило наметить основные черты общеримской традиции сожжения покойных, которой придерживалось и городское население столицы Азиатского Боспора. Помимо этого был проведен химический анализ состава «припеканий» на костях изучаемой серии, и оказалось, что данные аномалии на останках являются следами контакта с керамическими изделиями во время сожжения. В ходе анализа изотопов стронция было сделано предположение о низкой мобильности изученных индивидов. The paper contains preliminary results of the comprehensive bioarchaeological study of the cremations dating back to 1st century BC – 2nd century AD which were discovered in the burial vaults of Eastern Necropolis in Phanagoria. Key characteristics of the cremated remains are compared with the cremation data from necropolises of Western and Southern Europe. This analysis helped identify main characteristics of the general Roman tradition of cremating the deceased practiced by the urban population of the Asian Bosporus capital. Besides, chemical analysis of the composition of the ‘burns’ on the bones of the studied series was performed. This analysis demonstrated that such anomalies on the remains represent traces of the contact with ceramic items during cremation. The Sr isotope analysis suggested low mobility of the individuals examined.

Geochemical implications from Sr isotopes and K-Ar age determinations for the cook-austral islands chain

1984 ◽  
Vol 104 (1-2) ◽  
pp. 145-154 ◽  
Author(s):  
Jun-Ichi Matsuda ◽  
Kenji Notsu ◽  
Jun Okano ◽  
Katsumi Yaskawa ◽  
Leonard Chungue
Keyword(s):  
Sr Isotopes ◽  
Austral Islands ◽  
Age Determinations

scholarly journals Mid-infrared spectroscopy of alkali feldspar samples for space application

2020 ◽  
Vol 114 (5) ◽  
pp. 453-463 ◽  
Author(s):  
Maximilian P. Reitze ◽  
Iris Weber ◽  
Herbert Kroll ◽  
Andreas Morlok ◽  
Harald Hiesinger ◽  
...  
Keyword(s):  
Alkali Feldspar ◽  
Reference Database ◽  
Space Application ◽  
X Ray Diffraction ◽  
Exchange Method ◽  
Infrared Measurements ◽  
Planetary Bodies ◽  
Terrestrial Planetary Bodies ◽  
End Members ◽  
Alkali Feldspars

Abstract Feldspars are major components of terrestrial planetary surfaces. For future space application and the setup of a comprehensive reference database, Na- and K-rich alkali feldspars, NaAlSi3O8 – KAlSi3O8, have been investigated by infrared reflectance spectroscopy. We related the feldspar spectra to the chemical composition and state of Al,Si order/disorder. The infrared measurements were analyzed with respect to band shifts and peak shapes using the autocorrelation function. Natural samples served as starting materials. Some samples were treated by the alkali exchange method to produce pure end-members, which were then heated to generate various states of Al,Si disorder. X-ray diffraction (XRD) methods served to determine the Al,Si distribution. Our autocorrelation allowed to differentiate between the compositional and the order/disorder influences seen in the spectra in the wavelength range between 7 μm up to 14 μm (1429 cm− 1 to 714 cm− 1). Space missions often analyze the surfaces of planetary bodies using remote sensing. Therefore, our results are essential to characterize and distinguish alkali feldspars on the surfaces of terrestrial planetary bodies like Mercury.

The feldspars of the Rosses Granite Complex, Donegal, Ireland

1966 ◽  
Vol 35 (275) ◽  
pp. 975-982 ◽  
Author(s):  
A. Hall
Keyword(s):  
Low Temperature ◽  
Structural State ◽  
Alkali Feldspar ◽  
Temperature State ◽  
Granite Complex ◽  
Higher Temperature ◽  
Alkali Feldspars

SummaryAn examination has been made of the composition and structural state of the feldspars in each of the units of the Rosses granite complex. The compositions of the plagioclases are systematically related to the compositions of the rocks, but the alkali feldspars are much more uniform as a result of postmagmatic recrystallization. In the granites both alkali feldspar and plagioclase are in low-temperature structural states, but alkali feldspar phenocrysts from one of the porphyry dykes associated with the complex show a higher-temperature state.

Partition coefficients of alkali and alkaline-earth elements between alkali feldspar phenocrysts and their lava matrix

1978 ◽  
Vol 42 (321) ◽  
pp. 63-67 ◽  
Author(s):  
Renzo De Pieri ◽  
Sergio Quareni
Keyword(s):  
Partition Coefficients ◽  
Alkaline Earth ◽  
Alkali Feldspar ◽  
Single Peak ◽  
Wide Spread ◽  
Alkaline Earth Elements ◽  
The Difference ◽  
Two Peaks ◽  
To Receive ◽  
Alkali Feldspars

SummaryPlots of partition coefficients (mineral/ matrix) against ionic radius of the alkali and alkaline earth elements in forty-four alkali feldspars from rhyolites and trachytes show two kinds of diagram, one for homogeneous alkali feldspars with a single peak, and the other for cryptoperthites with a wide spread of points, which cannot represent a single peak, but may probably be explicable in terms of two peaks. The difference in behaviour does not seem to be due to the chemical composition, but is apparently related to the crystallo-graphic features of the alkali feldspar structures. In particular the presence of two peaks in the diagrams of the cryptoperthites seems to be due to the existence of lattice positions suited to receive bigger ions (K, Ba, Rb) and smaller ions (Na, Ca, Sr) in the potassic and sodic domains.

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