7 research outputs found
The Grenvillian Namaqua fold belt adjacent to the western Kaapvaal Craton: 2. Archaean Craton and supercontinent connections
No full textA 2.023 Ga age for the Vredefort impact event and a first report of shock metamorphosed zircons in pseudotachylitic breccias and Granophyre
No full textLarge Meteorite Impacts and Planetary Evolution
No full textOne of the major paper topics was the Sudbury project.sponsored by Barringer Crater Company ... [and others]PARTIAL CONTENTS: Melt Production in Large-Scale Impact Events: Calculations of Impact-Melt Volumes and Crater Scaling / M.J. Cintala and R.A.F. Grieve--Melt Production in Large-Scale Impact Events: Planetary Observations and Implications / M. Cintala and R.A.F. Grieve--Structural Review of the Vredefort Dome / W.P. Colliston and W.U. Reimold--Intrusive Origin of the Sudbury Igneous Complex: Structural and Sedimentological Evidence / E.J. Cowan and W.M. Schwerdtner--Enhanced Magnetic Field Production During Oblique Hypervelocity Impacts / D.A. Crawford and P.H. Schultz--Impactite and Pseudotachylite from Roter Kamm Crater, Namibia / J.J. Degenhardt Jr., P.C. Buchanan, and A.M. Reid--Sudbury Project (University of Milnster-Ontario Geological Survey): (4) Isotope Systematics Support the Impact Origin / A. Deutsch, D. Buhl, P. Brockmeyer, R. Lakomy, and M. Flucks--Noril'sk/Siberian Plateau Basalts and Bahama Hot Spot: Impact Triggered? / R.S. Dietz and J.F. McHone--Mobilization of the Platinum Group Elements by Low-Temperature Fluids: Implications for Mineralization and the Iridium Controversy / K. Dowling, R.R. Keays, M.W. Wallace, and V.A. Gostin--Does the Bushveld-Vredefort System (South Africa) Record the Largest Known Terrestrial Impact Catastrophe? / W.E. Elston--Ruthenium/Iridium Ratios in the Cretaceous-Tertiary Boundary Clay: Implications for Global Dispersal and Fractionation Within the Ejecta Cloud / N.J. Evans, W.D. Goodfellow, D.C. Gregoire, and J. Veizer--Diaplectic Transformation of Minerals: Vorotilov Drill Core, Puchezh-Katunki Impact Crater, Russia / V.I. Feldman--Breccia Dikes from the Beaverhead Impact Structure, Southwest Montana / P.S. Fiske, S.B. Hougen, and R.B. Hargraves
Reply to comments by W.P. Colliston, A.E. Schoch, and H.E. Praekelt on our paper on metasediments from the Areachap and Kakamas Terranes and the stratigraphic integrity of the Areachap Group. (SAJG, 110, 575-584 (2007)
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
Reconstructing the glacial history of Upgang, North Yorkshire: a North Sea ice lobe readvance during the termination of the last glacial maximum?
No full textAround Great Britain at the end of the Last Glacial Maximum (LGM) there is evidence for a number of glacial readvances, specifically in the Irish Sea Basin and Eastern Scotland. These readvances have been correlated with Heinrich Event 1 (HI) (16.1 - 17.6 cal. years BP; Bond et al. 1992). However, the presence of a synchronous HI readvance on the Yorkshire coast has not been investigated, although it is known from previous work that a number of readvances occurred during the end of the LGM. Therefore, this study aims to establish, firstly, if a readvance signal exists in Yorkshire and, secondly, if this signal can be correlated with HI. In order to achieve this, the coastal section of Upgang in North Yorkshire is examined using a multi-proxy approach. This involves the study of the sediments, clast form, clast fabric and clast lithological analysis along with geochemistry and geomorphological mapping. The sequence at Upgang shows a distinct advance - retreat - readvance signal. Two lower subglacial tills, Dl and D2 represent an initial ice advance and are a glaciotectonite or overrun proglacial thrust feature and a subglacial traction till respectively. Deposited above these is an extensive sand and gravels lithofacies association, indicative of an infilled lake after the ice had retreated. This lithofacies also represents the increasingly ice proximal nature of the site with the Upper facies representing proglaeial subaerial sandur sedimentation. The section is capped by the readvance till, D3, another subglatial traction till. Using local vegetation and varve records from Kildale and the Tees Estuary a proxy climate record is produced. This along with Ше correlation of the Upgang tills with those at Dimlmgton allows the production of a chronostratigraphic framework. This shows that the initial ice advance occurred shortly after 21 000 cal. years BP. The readvance then occurred around 16 ООО cal. years BP in conjunction with a deterioration in climate. Therefore, this readvance is tentatively correlated with Heinrich Event 1， which is also seen as the mechanism for other Last Glacial Maximum readvances around Great Britain, although without absolute dating control no great certainty can be placed upon this
