Petrogenesis of the alkaline and calcalkaline monogenetic volcanism in the northern sector of the Michoacán-Guanajuato Volcanic Field (Central Mexico)

- Two alkaline series coeval with calcalkaline volcanism are identified in the MGVF.
- A petrogenetic AFC model is proposed for each differentiation series.
- OIB-like magmas are interpreted to derive from a sublithospheric enriched source.
- A heterogeneous mantle wedge could generate “mild-alkaline” and calcalkaline magmas.
- A tear in the Cocos plate is inferred to allow ascent of sublithospheric magmas.

In the Michoacán-Guanajuato Volcanic Field, Quaternary monogenetic alkaline volcanism is mostly present in its northern sector in association with coeval calcalkaline volcanism. Their respective geochemical signatures reveal the existence of two suites of differentiated alkaline lavas, one with a typical OIB-like signature and another that displays intermediate characteristics with the coeval calcalkaline lavas. Petrogenetic modelling supports that each suite followed independent fractionation paths from distinct initial magmas with no interaction between them. In all cases similar AFC processes prevailed with ~ 30% crystallization and contamination (r ~ 0.3) with heterogeneous granitic and rarely granulitic components, involving different paragenetic assemblages mainly controlled by olivine, plagioclase, pyroxenes as well as some minor phases such as apatite and oxides. The geochemical characteristics of the initial magmas suggest that they derived from distinct mantle sources.The approximate N-S distribution of alkaline volcanism in the area, which coincides with a major geodynamic boundary at about the 101° W longitude, both at crustal levels and also concerning the configuration of the Cocos plate in the area, supports the existence of some disruption of the subducting plate that would favour the ascent of enriched sublithospheric melts. These would either ascend to the surface to produce OIB-like magmas or act as metasomatic agents in the mantle wedge, also influenced by components derived from the subducting slab. Such a hybrid mantle would represent the source of both the calcalkaline and the intermediate mildly alkaline melts, resulting from selective sampling (by different degrees of melting) from compositionally distinct domains within the mantle wedge.