Is the rate of supercontinent assembly changing with time?
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To address the question of secular changes in the speed of the supercontinent cycle, we use two major databases for the last 2.5 Gyr: the timing and locations of collisional and accretionary orogens, and average plate velocities as deduced from paleomagnetic and paleogeographic data. Peaks in craton collision occur at 1850 and 600 Ma with smaller peaks at 1100 and 350 Ma. Distinct minima occur at 1700–1200, 900–700, and 300–200 Ma. There is no simple relationship in craton collision frequency or average plate velocity between supercontinent assemblies and breakups. Assembly of Nuna at 1700–1500 Ma correlates with very low collision rates, whereas assemblies of Rodinia and Gondwana at 1000–850 and 650–350 Ma, respectively correspond to moderate to high rates. Very low collision rates occur at times of supercontinent breakup at 2200–2100, 1300–1100, 800–650, and 150–0 Ma. A peak in plate velocity at 450–350 Ma correlates with early stages of growth of Pangea and another at 1100 Ma with initial stages of Rodinia assembly following breakup of Nuna. A major drop in craton numbers after 1850 Ma corresponds with the collision and suturing of numerous Archean blocks. Orogens and passive margins show the same two cycles of ocean basin closing: an early cycle from Neoarchean to 1900 Ma and a later cycle, which corresponds to the supercontinent cycle, from 1900 Ma to the present. The cause of these cycles is not understood, but may be related to increasing plate speeds during supercontinent assembly and whether or not long-lived accretionary orogens accompany supercontinent assembly. LIP (large igneous province) age peaks at 2200, 2100, 1380 (and 1450?), 800, 300, 200 and 100 Ma correlate with supercontinent breakup and minima at 2600, 1700–1500, 1100–900, and 600–400 Ma with supercontinent assembly. Other major LIP age peaks do not correlate with the supercontinent cycle. A thermochemical instability model for mantle plume generation can explain all major LIP events by one process and implies that LIP events that correspond to the supercontinent cycle are independent of this cycle. The period of the supercontinent cycle is highly variable, ranging from 500 to 1000 Myr if the late Archean supercratons are included. Nuna has a duration of about 300 Myr (1500–1200 Ma), Rodinia 100 Myr (850–750 Ma), and Gondwana–Pangea 200 Myr (350–150 Ma). Breakup durations are short, generally 100–200 Myr. The history of angular plate velocities, craton collision frequency, passive margin histories, and periodicity of the supercontinent cycle all suggest a gradual speed up of plate tectonics with time.
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