Mineral chemistry of the Água Limpa suite: Insights into petrological constraints and magma ascent rate of Mesoarchean sanukitoids from the Sapucaia terrane (Carajás Province, southeastern Amazonian Craton, Brazil)

Abstract

The Água Limpa suite is comprised of two E‒W elongated sanukitoid-affinity plutons named the Água Azul and Água Limpa, exposed along with other intrusive granitic bodies and typifying Mesoarchean granitic activity in the Sapucaia terrane (Carajás Province). In the present study, the T-P-fO2-H2Omelt conditions, viscosity of magma and upward magma transport rate were retrieved on the basis of mineral chemistry and partial dissolution of magmatic epidote. The mafic mineral assemblage is dominated by amphibole (magnesio-hornblende, tremolite, pargasite and magnesiohastingsite compositions), in addition to magmatic epidote (Ps of 25–32%) and magnesio-biotite. Titanite, apatite, zircon, magnetite, ilmenite and chalcopyrite are the main accessory phases. The apatite saturation thermometer indicates at least initial crystallization temperatures between 903 and 850 °C. The Al-in-amphibole geobarometer provided temperatures varying from 1039 to 718 °C and 984 to 707 °C for the Água Limpa and Água Azul plutons, respectively. A variation in pressure from 625 to ∼100 MPa was obtained for both plutons, related to the deep crustal level of formation and shallow depths of emplacement. Experimental studies carried out on similar magma compositions indicate the parental Água Limpa suite magmas were water-rich (> 6 wt% dissolved H2O) and crystallized under high oxygen fugacity conditions (0.3 ≤ NNO ≤ 2.5). Partial corrosion of the magmatic epidote in these two plutons occurred within a timeframe of no more than 1–9 years, corresponding to upward magma transport rates of 1481–13,333 m/year. A structurally controlled network of conduits associated at the mesoscale pervasive migration developed during the active deformation stage (faults and shear zones), and small-scale diking probably acted as pathways for magma transfer through distinct pulses that underwent subsequent crystallization before reaching the hot continental crust at peak metamorphism, and permitted survival of the epidote that was out of equilibrium at the low pressure of final emplacement. The Água Limpa suite reveals strong mineralogical and geochemical affinities with the sanukitoids from the Rio Maria suite and the Ourilândia complex of the Carajás Province and differs from the sanukitoids from other cratons in terms of age and geological setting.