| 1. |
- Baratoux, L., et al.
(author)
-
New U–PB baddeleyite ages of mafic dyke swarms of the west African and amazonian cratons : Implication for their configuration in supercontinents through time
- 2019
-
In: Springer Geology. - Singapore : Springer Singapore. - 2197-9553 .- 2197-9545. ; , s. 263-314
-
Book chapter (peer-reviewed)abstract
- Eight different generations of dolerite dykes crosscutting the Paleoproterozoic basement in West Africa and one in South America were dated using the high precision U–Pb TIMS method on baddeleyite. Some of the individual dykes reach over 300 km in length and they are considered parts of much larger systems of mafic dyke swarms representing the plumbing systems for large igneous provinces (LIPs). The new U–Pb ages obtained for the investigated swarms in the southern West African Craton (WAC) are the following (oldest to youngest): 1791 ± 3 Ma for the N010° Libiri swarm, 1764 ± 4 Ma for the N035° Kédougou swarm, 1575 ± 5 for the N100° Korsimoro swarm, ~1525–1529 Ma for the N130° Essakane swarm, 1521 ± 3 Ma for the N90° Sambarabougou swarm, 915 ± 7 Ma for the N070° Oda swarm, 867 ± 16 Ma for the N355° Manso swarm, 202 ± 5 Ma and 198 ± 16 Ma for the N040° Hounde swarm, and 200 ± 3 Ma for the sills in the Taoudeni basin. The last ones are related to the Central Atlantic Magmatic Province (CAMP) event. The Hounde swarm is oblique to the dominant radiating CAMP swarm and may be linked with the similar-trending elongate Kakoulima intrusion in Guinea. In addition, the N150° Käyser swarm (Amazonian craton, South America) is dated at 1528 ± 2 Ma, providing a robust match with the Essakane swarm in a standard Amazonia-West African craton reconstruction, and resulting in a combined linear swarm >1500 km by >1500 km in extent. The Precambrian LIP barcode ages of c. 1790, 1765–1750, 1575, 1520, 915. 870 Ma for the WAC are compared with the global LIP record to identify possible matches on other crustal blocks, with reconstruction implications. These results contribute to the refinement of the magmatic ‘barcode’ for the West African and Amazonian cratons, representing the first steps towards plausible global paleogeographic reconstructions involving the West African and Amazonian cratons.
|
|
| 2. |
- de Kock, M. O., et al.
(author)
-
The precambrian mafic magmatic record, including large igneous provinces of the kalahari craton and its constituents : A paleogeographic review
- 2019
-
In: Springer Geology. - Singapore : Springer Singapore. - 2197-9553 .- 2197-9545. ; , s. 155-214
-
Book chapter (peer-reviewed)abstract
- The study of Precambrian dyke swarms, sill provinces and large igneous provinces on the Kalahari craton in southern Africa has expanded greatly since the pioneering work initiated almost four decades ago. The main contributors to this progress have been a large number of precise U–Pb crystallization ages of mafic rocks, published in a number of recent papers. This information is compiled here into a series of maps that provide a nearly 3 billion year intraplate magmatic record of the Kalahari craton and its earlier constituents, the proto-Kalahari, Kaapvaal and Zimbabwe cratons. We also review their possible paleogeographic relations to other cratons or supercontinents. This review provides a more accessible overview of individual magmatic events, and mostly includes precise U–Pb ages of mafic dykes and sills, some of which can be linked to stratigraphically well-constrained volcanic rocks. The extrusion ages of these volcanic units are also starting to be refined by, among others, in situ dating of baddeleyite. Some mafic dyke swarms, previously characterized entirely on similarity in dyke trends within a swarm, are found to be temporally composite and sometimes consist of up to three different generations. Other mafic dyke swarms, with different trends, can now be linked to protracted volcanic events like the stratigraphically well preserved Mesoarchean Nsuze Group (Pongola Supergroup) and Neoarchean Ventersdorp Supergroup. Following upon these Archean events, shorter-lived Proterozoic large igneous provinces also intrude the Transvaal Supergroup, Olifantshoek Supergroup and Umkondo Group, and include the world’s largest layered intrusion, the Bushveld Complex. Longer-lived late Paleoproterozoic magmatic events are also preserved as mafic intrusions and lava units within the Waterberg and Soutpansberg groups as well as the granitic basement. Many gaps in our knowledge of the Precambrian mafic record of the Kalahari craton remain, but further multi-disciplinary studies combining the latest advances in U–Pb geochronology and both paleomagnetism and geochemistry will help solve the Precambrian paleogeographic puzzle.
|
|
| 3. |
- Samal, Amiya K., et al.
(author)
-
Neoarchean-mesoproterozoic mafic dyke swarms of the indian shield mapped using google earth™ images and arcgis™, and links with large igneous provinces
- 2019
-
In: Springer Geology. - Singapore : Springer Singapore. - 2197-9545 .- 2197-9553. ; , s. 335-390
-
Book chapter (peer-reviewed)abstract
- We present dyke swarm maps generated using Google Earth™ images, ArcGIS™, field data, and available geochronological ages of Neoarchean-Mesoproterozoic (ranging in age from ~2.80 to ~1.10Â Ga) mafic dyke swarms and associated magmatic units of the different Archean cratons of the Indian shield which represent the plumbing system of Large Igneous Provinces (LIPs). The spatial and temporal distributions together with the trends of the dyke swarms provide important informations about geodynamics. Twenty four dyke swarms (17 have been precisely dated), mostly mafic in nature, have been mapped from the different cratons and named/re-named to best reflect their location, trend, distribution and distinction from other swarms. We have identified 14 distinct magmatic events during the Neoarchean-Mesoproterozoic in the Indian shield. These intraplate magmatic events (many of LIP scale) of the Indian shield and their matches with coeval LIPs on other crustal blocks suggest connections of the Indian shield within known supercontinents, such as Kenorland/Superia (~2.75–2.07Â Ga), Columbia/Nuna (1.90–1.38Â Ga), and Rodinia (1.20–0.72Â Ga). However, further detailed U–Pb geochronology and associated paleomagnetism are required to come to any definite constraints on the position of the Indian cratons within these supercontinents.
|
|
| 4. |
- Wabo, H., et al.
(author)
-
Constraining the chronology of the mashishing dykes from the eastern kaapvaal craton in South Africa
- 2019
-
In: Springer Geology. - Singapore : Springer Singapore. - 2197-9553 .- 2197-9545. ; , s. 215-261
-
Book chapter (peer-reviewed)abstract
- The present study focuses on NNE-trending dykes (sites LDA to LDJ) that occur near Mashishing in the eastern Kaapvaal craton. The Mashishing dykes were previously considered to be coeval and regarded as the extension of the 1.875–1.835Â Ga Black Hills dyke swarm into the sedimentary rocks of the Pretoria Group. Thin sections exhibit well-preserved igneous textures, with primary minerals (e.g., hornblende, clinopyroxene, plagioclase) extensively altered to secondary minerals in most cases. Our dykes can be petrographically grouped as pyroxenite (LDB and LDC), dolerite (LDH) and diorite (remainder of samples). REE and multi-element profiles of pyroxenites and two of the diorites (LDI and LDJ) suggest a common origin of the four dykes, but show no similarity with known mafic units of the Kaapvaal craton. An age estimate between 2208 and 2276Â Ma for dyke LDB, obtained from two overlapping amphibole 40Ar/39Ar plateau results, indicates that these four dykes predates the ~2.05Â Ga Bushveld event. The six remaining dykes have similar chemistry to either the ~2.06Â Ga Dullstroom Lavas (LDG), the 1.875–1.835Â Ga Black Hills dyke swarm (LDH) or the ~1.11Â Ga Umkondo dolerites (LDA, LDD, LDE and LDF). An U–Pb baddeleyite date of 1867 ± 10Â Ma for dyke LDH confirms it as a member of the Black Hills dyke swarm. Demagnetization of eighty-three specimens reveals five stable magnetizations carried by titanomagnetite. Two of these are regarded as magnetic overprints while three magnetizations are likely representative of primary remanences. The corresponding virtual geomagnetic poles (Lat.−26.84°N, Long. 31.66°E; Lat. 26.07°N, Long. 11.01°E, and Lat. 55.84°N, Long. 65.02°E) resemble those from the ~2.23Â Ga Hekpoort Formation, the ~1.88–1.83Â Ga post-Waterberg intrusions, and the ~1.11Â Ga Umkondo dolerites respectively. The above results suggest that the Mashishing dykes, despite similar trends, constitute swarms of different generations.
|
|
| 5. |
- Walker, M. J. C., et al.
(author)
-
Formal Subdivision of the Holocene Series/Epoch
- 2014
-
In: STRATI 2013. - Cham : Springer International Publishing. - 2197-9545. - 9783319043630 ; , s. 983-987
-
Conference paper (peer-reviewed)abstract
- This proposal, by a Working Group of Integration of ice-core, marine, and terrestrial records (INTIMATE) and the Subcommission on Quaternary Stratigraphy (SQS) of the International Commission on Stratigraphy (ICS), is for a formal subdivision of the Holocene Series/Epoch. Although previous attempts to subdivide the Holocene have proved inconclusive, recent developments in Quaternary stratigraphy, notably the definition of the Pleistocene-Holocene boundary and the emergence of formal subdivisions of the Pleistocene Series/Epoch, mean that it may be timely to revisit this matter. The Quaternary literature reveals a widespread but variable informal usage of a tripartite division of the Holocene ("early", "middle" or "mid-", and "late"), and we propose that this de facto subdivision should now be formalised to ensure consistency in stratigraphic terminology. We advocate a formal Early-Middle Holocene boundary at 8200 a BP and a formal Middle-Late Holocene boundary at 4200 a BP, each of which is linked to a Global Stratotype Section and Point (GSSP).
|
|
