Geochemical and fractal analysis of enclaves in the Dehe-Bala intrusion, (Northwestern Iran): a new concept in the interpretation of the crust–mantle interaction process

Abstract

The Dehe-Bala intrusion is one of the remarkable intrusions of granodiorite rocks with I-type affinity and abundant mafic microgranular enclaves (MMEs) in the Buin Zahra area, Qazvin, Iran. The MMEs, composed of diorite and quartz-monzodiorites, are haphazardly widespread in the granodiorites. The Dehe-Bala Granodiorites (DBG) usually are characterized by high contents of SiO 2 (64.2–66.9), Na 2 O (3–3.23), K 2 O (3.49–4), Mg# 4.84 and Th/Ta ratio (»7.9). In comparison to the DBG, the MMEs can be distinguished by their lower value of SiO 2 (52.8–58.2), K 2 O (1.4–3.8) and higher Mg# (0.4–0.46). All these characteristics show a different composition of the DBG and MMEs, more importantly, can argue in favor of a magma mixing/mingling origin in the DBG. The enrichment in total REEs and HFSEs in the MMEs clearly reflects a marked diffusional process from the felsic to mafic magma that could have been achieved by chemical exchange during the magma mixing/mingling process. The fractal dimensions ( D box ) of MMEs differ from 1.14 to 1.29 with the highest frequency at 1.29. The textural heterogeneity and geochemical features combined with high D box values in the MMEs compared with the DBG show lower degrees of mixing/mingling between mantle-derived mafic and lower crust-derived felsic magmas.