Abstract

Granite plutons are fundamental building blocks of the Earth’s crust, and most non-plutonic rocks descended from plutonic ancestors. The centuries-old textbook understanding of plutons, reinforced by myriad “big red blob” cartoons, is that they are the frozen remains of rapidly intruded, km-scale tanks of magma, and that such tanks underlie active volcanoes. In this talk I will argue that this central concept about the Earth is contradicted by a growing body of data from multiple fields; that big-red-blob cartoons are misleading and pernicious; and that as a consequence many of the underpinnings of petrology need to be rethought. Oops! Recognition that plutons are emplaced in small increments and that most are heavily modified by a metamorphic overprint reconciles pluton geology with data from geochemistry, geochronology, geophysics, geodetics, and volcanology. It is time to move beyond big red blobs.