According to the seismology study, the lower continental crust has grown through the underplating of basaltic magma. There are strong reflectors in the lower continental crust, which is widespread, have been interpreted as flow, sills, and layered mafic intrusions. Supporting this conclusion, some shallow reflectors have been traced to the surface and identified \cite{Percival_1992}. Single basalt flows can be up to 100km thick and cover thousands of square kilometers. Uplifted segments studies and crustal xenolith studies show mafic intrusions in the lower crust, some considerably younger than their host rocks \cite{Rudnick_1995,Rudnick_1995a}.
A further possible source of juvenile crust is crustal underplating related to the eruption of continental flood basalts. As stated by the study in North Atlantic Igneous province, extensive volumes of mafic magma were emplaced along the transition between continental and oceanic crust. Both submarine and subaerial volcanism occurred along more that 2600km of the propagating coastlines in the North Atlantic (the coasts of Greenland and Europe) during the early Tertiary. Similar widespread volcanism, nut more prolonged, occurred along the eastern coast of North America during the opening of this part of the Atlantic in the Mesozoic (White et al., 1987).