Australia: The Land Where Time Began

A biography of the Australian continent 

Deep mantle plume - Convective Upwelling beneath the Pacific Ocean

According to the authors¹ the mantle is believed to convect as a whole, with material flow across the upper mantle phase transitions of olivine at depths of 410 and 60 km, though convection details, especially in the case of mantle plumes and upwelling, are not well constrained. In this study the authors¹ used seismic shear wave reflections from the underside of these phase boundaries that are dependent on temperature and composition, which they resolved to be flat beneath the Pacific Ocean, apart from beneath regions of subduction and volcanic hotspots. Beneath the Hawaiian hotspot the boundaries are closer together, as they are in a larger region of the South Pacific that has a number of hotspots flanking it. Beneath this region is the southern part of the large-scale slow shear velocity province in the lowermost mantle. Originating in the lowermost mantle and impinging on the 600 km discontinuity in the South Pacific Ocean, a large plume head, or a cluster of several plumes is consistent with phase boundary topography that has been observed and patterns of subduction. It is suggested by the authors¹ that this feature may be related to volcanic eruptions that produce large volumes of magma, such as the flood basalts of the Ontong Java Plateau from the Cretaceous that have been proposed to originate in the South Pacific Ocean.

Sources & Further reading

Schmerr, Nicholas, Edward Garnero, and Allen McNamara. "Deep Mantle Plumes and Convective Upwelling beneath the Pacific Ocean." Earth and Planetary Science Letters 294, no. 1–2 (5/15/ 2010): 143-51.