Slab failure-related magmatism in the Pinheiro Machado Complex, southern Dom Feliciano Belt, Brazil

Abstract

In the Dom Feliciano Belt, Brazil, the Pinheiro Machado Complex (PMC) includes diorites, tonalites, granodiorites, syenogranites and granites, whose evolution is related to several magmatic pulses and complex petrogenetic processes. Two magmatic stages were identified (early and late), resulting in different rock subgroups. The geochemical data showed that the early magmatism was chemically affected by partial melting. Geochemical modelling results suggest that fractional crystallization processes with assimilation of around 40% from the crustal basement and the decoupling of assimilated magma are crucial for the PMC rocks' genesis. Geochemical data also show that during the early magmatism, the subsequent process of early diorite anatexis developed by heating and continuous activity of the underlying magma chamber possibly occurred at a melting rate of 5%–10%. The hybrid rocks have contributions from the mixing process related to early terms, showing geochemical correlations in the major element curves, for the early diorite and syenogranitic melt members, at 60%–50% and 50%–40%, respectively. Slab failure tectonic context is related to the multi-intrusive events dynamics recorded in the studied rocks. Recharge and melting events of the recently formed crust due to the constant heating of new pulses of deep slab melting would explain the magmatic interactions observed in the Complex. The results demonstrate that the studied rocks crystallized in an open system, including mixing processes to form hybrid rocks, physical disaggregation and assimilation of early intrusions, truncation, dragging and erosion of early mushes by younger pulses.