69 research outputs found
Isotope analysis of crystalline impact melt rocks from Apollo-16 station-11 and station-13, North Ray crater
No full textDiscovery of mafic impact melt in the center of the Vredefort dome:archetype for continental residua of early Earth cratering?
No full textMelting by impact heating is thought to have been a significant process in the modification of early planetary crusts; however, crustally derived melt bodies in ancient terrestrial crust are frequently presumed to be absent due to erosion. Here we demonstrate that in the central basement uplift of the 2.020 Ga Vredefort impact basin (South Africa), components of mafic impact melt have survived amid Archean gneiss as decimeter-scale dikes and lenses of variably foliated gabbronorite. Zircon microstructural, trace element, and isotopic analyses (U-Pb, Lu-Hf) of the gabbronorite reveal a dominant population of 2.02 Ga unshocked igneous zircon with apparent Ti-in-zircon temperatures of 800-900 °C, similar to those from the mafic sublayer of the Sudbury impact melt sheet. Highly negative subchondritic σHf values of -1.4 ± 1.1 to -7.9 ± 1.4 are consistent with a depleted mantle model age of ca. 3 Ga and gabbronorite derivation from the once superjacent Witwatersrand basin lithologies. The recrystallized igneous mineral textures and Archean felsic gneiss inclusions in the gabbronorite are attributable to the effects of emplacement and crater modification following ̃20 km elevation of the central uplift. Long mistaken as preimpact basement, the setting and characteristics of the Vredefort gabbronorite may provide new benchmarks in the search for remnants of large cratering events and melt residua on Earth's cratons.</p
A late Cretaceous 40Ar-39Ar age for the Lappajarvi impact crater, Finland
No full textWe report on a 40Ar — 39Ar study of karnaite from the ⁓ 17 km Lappajarvi impact crater, Finland. Four samples from a 3,000 m profile across the crater center give rather well defined age plateaux and indicate complete degassing at the time of the impact event. The mean age is 77 m.y., much younger than geologically derived age estimates.
ARK: https://n2t.net/ark:/88439/y062490
Permalink: https://geophysicsjournal.com/article/186
 
Scientific comment on: uundja et al., 2007 : Magnetic imaging of the Vredefort impact crater, South Africa, EPSL 261, 456-468
No full textComment on “Anatomy of impactites and shocked zircon grains from Dhala reveals Paleoproterozoic meteorite impact in the Archean basement rocks of Central India” by Li et al., 2018, Gondwana Research, 54, 81–101
No full textCatastrophic events & mass extinctions, impacts and beyond
No full textsponsors University of Vienna, Austria, Lunar and Planetary Institute ... [and others]international organizing and program committee, Walter Alvarez [and others] ; local organizing committee, Christian Koeberl [and others]PARTIAL CONTENTS: Global Distribution of Chicxulub Ejecta / P. Claeys, W. Kiessling, and W. Alvarez--Long-Term Environmental Perturbations Following a Late Eocene Impact? Evidence from the Massignano GSSP, Italy / R. Coccioni, D. Basso, H. Brinkhuis, S. Galeotti, S. Gardin, S. Monechi, and S. SpezzaJerri--Radio Search for Extrasolar Cometary Impacts at 22 GHz (Water MASER Emission) / C.B. Cosmovici, S. Pogrebenko, S. Montebugnoli, and G. Maccaferri--Comparison of the Chemical Composition Between Bosumtwi Rocks and Ivory Coast Tektites: Search for a Meteoritic Component in Impact Breccias / X. Dai, C. Koeberl, W.U. Reimold, and I. McDonal
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