Mafic microgranular enclaves trace the origin of post-collisional magmatism

Abstract

Mafic microgranular enclaves (MME) appear associated with most post-collisional batholiths around the world. Together with the mafic-intermediate (sanukitoid) and granitic suites, it constitutes one of the most common features of post-collisional magmatism. MME are considered to represent a mafic endmember with mantle affinity related to granite petrogenesis. Hence, they constitute an ideal tracer of the mantle involvement in crustal-scale processes. However, their exact relationship with the host granitic post-collisional suite and the role of such mantle remains unclear. In this regard, abundant MME in Los Pedroches batholith (Iberian Massif) can provide valuable constrains to this problem. Using new MME data, we provide a comparative study between MME and the mafic-intermediate (sanukitoid) suite of post-collisional batholiths, revealing an accurate overlap between the two groups. A common geochemical signature consisting of high MgO and K2O and low CaO is evidenced, pointing to a potential genetic link between MME and the sanukitoid suite in a modified mantle source. Further information provided by cotectic experimental liquids and petrographical evidence point to cotectic differentiation and orthopyroxene restite self-contamination as the main responsible mechanisms for the particular geochemistry of the series. Once the role of the mantle in MME formation and their magmatic evolution are characterized, their potential relationship with the host granites is established using isotopic criteria. Implications for post-collisional batholith petrogenesis is then discussed in a qualitative manner, suggesting a heterogeneous yet common origin for all post-collisional magmatism.