**3. The crust**

The Earth is divided into at least 12 main plates of the oceanic or continental type, delimited by distension and compression margins and in some cases by transform faults (**Figure 5**, [18]). **Figure 6** shows the distribution of active volcanism in diverse geodynamic settings (subduction, rift, and hotspot). Crustal end-members are of fundamental importance to understanding the magma evolution on the earth's surface, especially for the continental crust. Lately, we have enjoyed the model of Steve Sparks and collaborator (deep and hot intrusion zone [20–22]). The model clarifies how the volcanic rocks were originated either from metasomatized mantle source with the classical signature and/or by crustal contamination. A detailed explanation of trace elements and isotopes of volcanic systems come anyway, can be in their hand [23]. The continental crust of Wedepohl [19] (**Figure 6**) still can be taken as the best example to use and to perceive the Conrad and Moho discontinuities as the region where the basaltic magma intrudes, stagnate, and evolve through the surface. The bulk continental crust of Wedepohl [19] has a tonalitic composition with distinctly higher concentrations of incompatible elements. A dioritic bulk crust was suggested by Taylor and Mclennan [24] in contrast to Wedepohl [19]. If we make a section from New Zealand to South America (i.e., Chile), we can observe five types of tectonic margin—(a) subduction, oceanicoceanic plates, (b) hotspot, (c) oceanic rift, (d) subduction oceanic-continental plates, (e) continental rift (**Figure 7**, [18]; a, b, c, d, e are partial melting zone with the production of basaltic magmas). Although other lithotypes are also present, we can surely say that partial melting could be the Holy Grail of Igneous Petrology.

#### **Figure 5.**

*Plate tectonic with larger and smaller plates and with the location of all the volcanic activity (modified from Schmincke [14]).*
