Segments and Super-Units in the Coastal Batholith of Peru

By analogy with rock-stratigraphic nomenclature the plutonic rocks of the linear Coastal Batholith of Peru can be grouped into units (formations) which can further be grouped into super-units (groups). Such an hierarchical system enables the Coastal Batholith to be divided into three compositionally distinct segments 200, 400, and 900 km in length. Segmentation is thought to reflect discontinuities in a subduebion zone, with magmatism in each segment possessing its own unique episodicity of emplacement and spatial distribution. Within each super-unit differences in the time of arrival of the magmas in the upper crust produce magmatic diachronism. On the basis of an upper mantle/ lower crustal melting hypothesis it seems that within each segment, which takes of the order of 70 m.y. to emplace, the super-units are the product of separate melt cells, each of "which exists spasmodically over a period of ca. 10 m.y. The melt cells provided progressively more acidic magma with time, whilst decreasing in areal extent.