Paleomagnetic Evidence for a Paleoproterozoic Rotational Assembly of the North Australian Craton in the Leadup to Supercontinent Formation. Issue 22 (17th November 2022) - Kirscher, U.
Abstract: The kinematics of the Paleoproterozoic assembly of Earth's first supercontinent, Nuna, are still debated. We present new paleomagnetic results from two Paleoproterozoic rock formations in the North Australia Craton (NAC) that exemplify cratonic assembly processes in the leadup to Nuna formation. Our new paleomagnetic data for the 1, 825 Ma Plum Tree Creek Volcanics of the proto‐NAC and the layered mafic‐ultramafic 1, 855 Ma Toby intrusion of the Kimberley Craton suggest their amalgamation just prior to ca. 1.8 Ga through a scissor‐like ocean closure to form the NAC, in accord with geological records. Comparing these new results with extant poles from Australia and other major cratons suggests similarly minor relative plate motions between ca. 1.9 and 1.65 Ga during craton and supercontinent formation. A global reconstruction suggests that these events could be related to a major slab‐suction event leading to Nuna formation. Plain Language Summary: Earth's evolution is characterized by the recurring assembly of most tectonic plates into one single supercontinent. There is mounting evidence that at least three supercontinents existed throughout Earth history. This cycle of supercontinents potentially played an important role for the evolution of life and is inextricably connected to plate tectonics. However, we still don't understand how and when exactly the supercontinent cycle initiated. We present here new paleomagnetic data allowing us the most precise paleogeographic reconstruction for the time interval before the first of the three known supercontinents formed. Our data reveals a small‐scale collisional assembly of the Australian cratons in the vicinity of the formation of other major cratons at that time. Our global reconstruction using the most up to date paleomagnetic data set can be interpreted as evidence for a model where all cratons formed over a mantle downwelling structure that ultimately lead to the initiation of the supercontinent cycle. Key Points: Two new high‐quality Paleoproterozoic paleopoles for the North Australian Craton are presented The new paleomagnetic data suggest a scissor‐like assembly of the North Australian Craton Our new kinematic model proposes a situation prior to the formation of the first supercontinent related to a major slab‐suction event