The History of the Pacific Superplume

To understand the birth place and episodic activity of the Pacific superplume, we reconstructed the paleogeograhy of continents and oceanic plates from 1.0 Ga supercontinent Rodinia until now by adopting the most confident available data set to determine paleopositions of oceanic plateaus, seamounts, and oceanic arc, in addition to major continents, by using plate trajectory for the last 150Ma and for the farther back to 1.0Ga, by the paleomagnetic constraints tied with geologic connections. Our main focus is the frequency change of ancient activity of plume rocks that are now preserved in the accretionary complex around the circum-Pacific orogenic belts. Several conclusions are led through our reconstruction. (1) Cretaceous oceanic plateaus which present widespread in western Pacific (e.g., Manihiki Plateau, Shatsky Rise, Hess Rise, Mid-Pacific Mountain, Nauru Basin) are traced back and concentrated to the present active region of the Pacific superplume. This suggests that those were once formed a huge composite volcanoes as large as 4000 km x 2400 km across during the Cretaceous by superplume activity. These are equivalent to Australia or Tharsis bulge volcanic complex on Mars. The estimated thickness of oceanic crust ca. 30-40 km suggests that major parts may have been above sea-level during the Cretaceous time. The Cretaceous global warming may be related to this hyper-active superplume event which have carried mantle CO₂ to the surface of 3.2 x 10²¹ g, assuming 0.3 wt% x 350 million km³ (magma volume) x 3.07 g/cm³ during 150-75 Ma. This CO₂ output amount occupies as much as 37 wt% among the total output from mantle estimated by using erupted basaltic volume estimated by Larson (1991, Geology, 549-550) and present output rate of CO₂. The similar episodic activity of Pacific superplume seems to have occurred at 750-700 Ma, 550-500Ma, 300-250Ma by considering the frequency of occurrences of greenstones in the accretionary complexes of the world. (2) Rodinia rifted and separated at 750Ma on the similar latitude to present active region of the Pacific superplume. This suggests that Pacific superplume may be born at 750Ma to break-up supercontinent Rodinia to support the original idea by Maruyama (1994, J. Geol. Soc. Japan, 100, 24-49) as African superplume may be born at 250-200 Ma to break-up Pangea. (3) At 1000Ma, the Grenvillian orogens cemented amalgamated collisional continents to form the supercontinent Rodinia. This suggests that the large amounts of oceanic slab must have subducted along the Grenvillian sutures and might have caused the birth of Pacific superplume.