New constraints on paleoreconstructions through geochronology of mafic dyke swarms in North Atlantic Craton

Sammanfattning: Earth history is punctuated by a series of events of supercontinent amalgamation and break-up. Fragments of old continents display rifted margins and orogenic sutures that testify their involvement in supercontinent cycles. Periods of break-up are associated with widespread magmatism due to extensional thinning and rifting of the lithosphere and in some instances the arrival of mantle plumes. Mantle plumes are thought to, at least in part, be responsible for Large Igneous Provinces (LIPs for short), voluminous short-lived outburst of mafic magmatism, whose products are continental flood basalts and oceanic plateaus, layered intrusions, sills and dykes. While continental flood basalts and oceanic plateaus are sensitive to subsequent erosion and subduction, the plumbing system of LIPs comprising deep-seated intrusions, sills and dykes have a high preservation potential. Thus, these events should be possible to trace back in time through multiple supercontinent cycles. LIPs typically have temporal scales of a few million years, but spatial scales of several hundred to thousand kilometers. After break-up and subsequent ocean basin opening, the products of LIPs may end up on different continents. Ancient crustal fragments, or cratons, have experienced a number of magmatic events, and thus have their individual record. Cratons that were once adjacent in a single landmass should share a part of their magmatic record during the interval of time they were connected. Because mafic rocks contains trace amounts of baddeleyite (ZrO2), and because baddeleyite incorporate abundant uranium but only neglible amounts of lead in its crystal structure, we can age determine mafic intrusions using U-Pb geochronology. H Date: 2016-05-16 ence, we can elucidate these events, craton by craton, and compare them to each other. Multiple individual age matches between different cratons suggest a common ancestry in a supercontinent or supercraton. In addition, dyke swarms provide geometric information as they often display radiating or parallel patterns. Fragments of ancient supercontinents or larger landmasses can thus theoretically be reconstructed by comparing geometry of dyke swarm matches in the magmatic record. My PhD-project has been focused on Paleoproterozoic mafic dykes from the present-day southern Greenland part of the Archean North Atlantic Craton (NAC). Precise U-Pb baddeleyite age determinations of multiple events of dyke emplacement are presented in this thesis at ca. 2500, 2375−2365, 2215−2210, 2165−2160, 2125 and 2050−2020 Ma. This magmatic record show temporal correlations with a number of Archaean cratons worldwide, and notably share multiple matches with Superior and Dharwar cratons in present day Canada and India, respectively. A tentative paleoreconstruction of possible cratonic configurations of North Atlantic, Superior and Dharwar cratons during the time interval 2.37−2.17 Ga is presented in the context of supercraton Superia.