Article
Geochemistry & Geophysics
Sanna Holm-Alwmark, Fred Jourdan, Ludovic Ferriere, Carl Alwmark, Christian Koeberl
Summary: This study focuses on the Puchezh-Katunki impact structure in Russia, accurately dating its formation to 195.9 +/- 1.0 Ma using 40Ar/39Ar data. The research challenges previous temporal correlations between the impact event and multiple extinction events, emphasizes the importance of careful sample preparation and methodology in overcoming 40Ar issues, and highlights the need for caution when suggesting connections between specific impact events and extinction events.
GEOCHIMICA ET COSMOCHIMICA ACTA
(2021)
Article
Geochemistry & Geophysics
Allan Silva Gomes, Paulo Marcos Vasconcelos, Teresa Ubide, Eleonora Maria Gouvea Vasconcellos
Summary: The high-Ti Paranapanema sequence in the Parana Large Igneous Province is characterized by a series of pahoehoe lava flows, some of which contain unique mafic segregation structures. The study of two pegmatite occurrences and their host basalts reveals that the pegmatites are more fractionated and enriched in various elements compared to the enclosing lavas. Additionally, age differences observed in plagioclase phenocrysts from the pegmatites and whole-rock fragments from the enclosing lavas are likely due to hydrothermal alteration rather than differences in crystallization age.
Article
Geochemistry & Geophysics
Allan Silva Gomes, Paulo Marcos Vasconcelos, Isabela de Oliveira Carmo
Summary: The presence of secondary phases in volcanic rocks and intrusive units may pose challenges for high resolution 40Ar/39Ar geochronology. Acid treatment is used to remove alteration products, but it has minimal impact on the accuracy of age determinations. Effective separation of atmospheric and radiogenic gases can successfully mitigate deleterious effects associated with alteration phases.
Article
Geosciences, Multidisciplinary
B. Eid, F. Lhuillier, S. A. Gilder, J. A. Pfaender, E. F. Gebru, D. Assbichler
Summary: The research findings from investigating the eruption history of the Ethiopia-Yemen Traps revealed that the local extrusion rate of the Afar plume head exceeded the average rate of the entire plume. The high titanium concentrations in the basalts suggest a faster local extrusion rate near the Afar plume axis.
GEOPHYSICAL RESEARCH LETTERS
(2021)
Review
Geosciences, Multidisciplinary
Yang Wu, Xiu-Juan Bai, He-Sheng Shi, Li-Yan He, Hua-Ning Qiu
Summary: This paper provides a review of dating methods relying on the K-Ar and Rb-Sr isotopic decay systems applied in sedimentary rocks. It discusses the sample preparation and analytical techniques associated with these methods and summarizes their applications in various sedimentary settings. The paper also highlights the use of Rb-Sr and 40Ar/39Ar dating in determining depositional ages and trapped ancient atmospheric argon components in chert.
EARTH-SCIENCE REVIEWS
(2023)
Article
Geology
Igor M. Villa, Giulia Bosio
Summary: The substoichiometric potassium concentrations and low alkali occupation observed in biotite phenocrysts from marine tephra layers are likely the result of diagenetic alteration caused by exposure to interstitial water and brine intrusions. This alteration has been shown to affect potassium-argon ages, leading to discordance, high step ages, and anomalies in elemental ratios. The preferential leaching of potassium from the phyllosilicate interlayers and the shielding of radiogenic Ar* in the tetrahedral-octahedral-tetrahedral (T-O-T) phyllosilicate layer are proposed as mechanisms for the observed discrepancies.
Article
Geography, Physical
Alan L. Deino, Clifford Heil, John King, Lindsay J. McHenry, Ian G. Stanistreet, Harald Stollhofen, Jackson K. Njau, Joshua Mwankunda, Kathy D. Schick, Nicholas Toth
Summary: The Olduvai Gorge Coring Project in Tanzania drilled cores at three sites in the Olduvai Basin, developing a chronostratigraphic framework. Through dating, paleomagnetic stratigraphy, and tephrochemical correlation, they obtained realistic age estimates. The age models revealed varying sedimentation rates in the basin's history and provided new estimates for the basal contacts of upper stratigraphic units in Olduvai Gorge.
PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY
(2021)
Article
Geosciences, Multidisciplinary
Hugo K. H. Olierook, Jasmine Gale, Franco Pirajno, Fred Jourdan, Christopher L. Kirkland, Noreen J. Evans, Bradley J. McDonald, Mark Krejci, Qiang Jiang, Anusha Shantha Kumara, Celia Mayers, R. Adam Frew, Hugo Kaag, Brent I. A. McInnes
Summary: This study investigates the magmatism and plate motions in the Late Triassic period in the New England Orogen in Australia. Through dating and geochemical analysis, it is found that the Late Triassic magmatism is closely related to lithospheric delamination, rather than slab roll-back. This finding is significant for understanding the tectonic and magmatic activity in the New England Orogen.
Article
Geochemistry & Geophysics
Augustin Dekoninck, Gilles Ruffet, Julien Baptiste, Robert Wyns, Simon Philippo, Yishen Zhang, Olivier Namur
Summary: This study discusses the hydrothermal formation of romanechite in the Romane`che Mn deposit and the significance of its age by combining ore petrogenesis and 40Ar/39Ar ages. The study confirms the feasibility of romanechite 40Ar/39Ar dating and identifies a period of at least c. 7.6 My of discontinuous hydrothermal activity in the Massif Central.
Article
Geography, Physical
Sander L. Hilgen, Eduard Pop, Shinatria Adhityatama, Tom A. Veldkamp, Harold W. K. Berghuis, Indra Sutisna, Dida Yurnaldi, Guillaume Dupont-Nivet, Tony Reimann, Norbert Nowaczyk, Klaudia F. Kuiper, Wout Krijgsman, Hubert B. Vonhof, Dian Rahayu Ekowati, Gerrit Alink, Ni Luh Gde Dyah Mega Hafsari, Olafianto Drespriputra, Alexander Verpoorte, Remco Bos, Truman Simanjuntak, Bagyo Prasetyo, Josephine C. A. Joordens
Summary: This study aims to establish an accurate age control for the fossils found at the Trinil site in Java, Indonesia. By applying various dating methods and documenting new stratigraphic sections, the researchers identified two distinct fossil-rich channel fills with ages ranging from 830-773 ka to 450 +/- 110 ka. The presence of fossils from different time periods challenges the assumption of a homogeneous biostratigraphic unit at the Trinil site.
QUATERNARY SCIENCE REVIEWS
(2023)
Article
Geochemistry & Geophysics
P. W. Ball, G. G. Roberts, D. F. Mark, D. N. Barfod, N. J. White, B. H. Lodhia, M. M. Nahdi, S. Garni
Summary: Harrat Rahat is the largest volcanic field in Saudi Arabia and has been active from around 10 Ma to the present day. Recent eruptions at Harrat Rahat have been extensively studied, but the evolution of its oldest lava flows, known as the Shawahit Basalt, is poorly understood. In this study, we collected and analyzed samples from Harrat Rahat, focusing on the Shawahit unit. We found that the volcanic activity at Harrat Rahat was initiated by a mantle plume beneath a thinned lithosphere, and the changes in geochemistry can be attributed to a decrease in melt productivity and contamination.
Article
Geosciences, Multidisciplinary
Lucas Albanese Valore, Otavio Augusto Boni Licht, Eleonora Maria Gouvea Vasconcellos, Bruno Guimaraes Titon
Summary: In continental flood basalt provinces (CFBPs), primary volcaniclastic deposits formed by explosive hydrovolcanism challenge traditional views of CFB evolution. This study focused on interflow beds at Sertanópolis in the Paraná Igneous Province to better understand the setting. Detailed geological mapping and petrographic studies identified four interflow units with fine-grained facies including vesiculated clastic rocks and well-defined stratification. The presence of pyroclastic breccias suggests multiple pyroclastic density currents formed each interflow unit.
JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH
(2023)
Article
Geosciences, Multidisciplinary
R. Spikings, A. Paul, C. Vallejo, P. Reyes
Summary: The gabbros and ultramafic rocks of the Huargualla Gabbro unit in Ecuador were derived from asthenospheric sources with minor crustal contamination and formed part of the Central Iapetus Magmatic Province. These rocks represent the only igneous record of Iapetus rifting north of the Huancabamba deflection in South America. The age and composition of the Huargualla Gabbro unit is consistent with the reconstruction by Tegner et al. (2019), suggesting juxtaposition of Baltica and northwestern Gondwana within Panotia.
Article
Geochemistry & Geophysics
M. O. Naumenko-Dezes, I. M. Villa, Y. Rolland, S. Gallet, P. Lanari
Summary: Museum-grade mica megacrysts from the Phalaborwa phlogopite and Rubikon pegmatite were studied for their compositional and chronological heterogeneities. The research revealed that the micas had significant variations in both element concentrations and ages within individual subgrains. The recrystallization processes were likely triggered by post-magmatic hydrothermal events, leading to variable loss of argon at a subgrain scale. These observations suggest that thorough petrological investigations and 40Ar/39Ar systematics are essential for diagnosing recrystallization events.
Article
Geochemistry & Geophysics
Qiang Jiang, Fred Jourdan, Hugo K. H. Olierook, Renaud E. Merle, Chrystele Verati, Celia Mayers
Summary: 40Ar/39Ar geochronology is crucial for determining the timing of basaltic events due to the lack of suitable minerals for other dating techniques. Plagioclase, a common mineral in basalts, is often altered, affecting the accuracy of dating results. Even a small amount of alteration can lead to younger ages, and the Ca/K ratios of plagioclase play a role in the sensitivity of age determination to alteration. Inspecting age spectra, Ca/K ratios, and degassing curves can help identify alteration signatures in plagioclase samples.
GEOCHIMICA ET COSMOCHIMICA ACTA
(2021)