Geochemistry - Seeing through tectonic plates

摘要

Anyone living near the Pacifi c coast or on one of its islands such as Japan almost certainly lives in the vicinity of some active volcano. It may be possible to see a volcano spewing steam and — if one is fortunate — even erupting. But the ongoing unrest deep beneath the surface that ultimately leads to volcanism is invisible. Along most of the circum-Pacifi c region, one oceanic plate is sinking very slowly beneath another continental or oceanic one, releasing fl uids in response to the relatively high ambient temperatures. However, near central Japan, two oceanic plates are subducting with some overlap in a setting not unlike two sloppily stacked saucers. On page 380 of this issue, Nakamura and co-authors1 use geochemical data from volcanic rocks to identify distinct signatures of fl uids that originate from each of the subducting plates and fi nd that the upper plate does not appear to inhibit fl uid rising up from the underlying one.