Things you can do from home during a pandemic: A geochronological review of... - Åke Johansson скачать в хорошем качестве

Things you can do from home during a pandemic: A geochronological review of... - Åke Johansson

Things you can do from home during a pandemic: A geochronological review of magmatism along the external margin of Columbia and in the Grenville-age orogens forming the core of Rodinia Åke Johansson, and many others Swedish Museum of Natural History, Stockholm A total of 4212 magmatic U-Pb ages in the range 2300 to 800 Ma have been compiled from orogenic belts along the external margin of the supercontinent Columbia (ca. 1800-1300 Ma) and from the subsequent collisional orogens forming the core of the supercontinent Rodinia (ca. 1000-600 Ma). The age data are derived from Laurentia (North America and Greenland, n = 1208), Baltica (NE Europe, n = 1922), Amazonia (central South America, n = 628), Kalahari (southern Africa and Dronning Maud Land in East Antarctica, n = 265) and western Australia (n = 199). Laurentia, Baltica and Amazonia (and possibly other cratons) most likely formed an external active continental margin of Columbia from its assembly at ca 1800 Ma until its dispersal at ca 1260 Ma, after which all cratons studied were involved in the Rodinia-forming Grenvillian orogeny. However, the magmatic record is not smooth and even but highly irregular, with marked peaks and troughs, both for the individual cratons or continents and for the combined data set. The magmatic peaks typically range in time from a few tens of million years up to around hundred million years, with troughs of comparable length. Some magmatic peaks are observed on multiple cratons, whether by coincidence or because of paleogeographic proximity and common geodynamic setting, while others are not. The best correlation, 0.617, is observed between Baltica and Amazonia, consistent with (but not definitive proof of) them being close neighbours during the Proterozoic. Correlation factors between the other cratons, also between Laurentia and Baltica, are much lower, below 0.15. The detailed evolution before and during the final Grenvillian collision is also largely diachronous between all continents involved. After 900 Ma, magmatic activity had ceased in all areas investigated, attesting to the position of most of them within the stable interior of Rodinia.