TTG petrogenesis and U–Pb SHRIMP zircon geochronology constraints on the tectonic regime and formation of the Mesoarchean crust from the Ourilândia–Tucumã area in the Carajás Province, Amazonian Craton, Brazil

Abstract

Tonalite–trondhjemite–granodiorite (TTG) magmatism marked crucial episodes in early crustal growth and cratonization worldwide; petrogenetic processes, tectonic configurations, and sources of TTGs are the focus of continuous debate. Here, we present a geochemical and geochronological (zircon U–Pb SHRIMP) study of TTG granitoids to determine their petrogenesis and to better constrain the crustal evolution of Carajás Province. New evidence of preserved TTG crust in the Ourilândia–Tucumã area, which is composed of tonalite–trondhjemites, is presented. The tonalite has an emplacement age of 3.0 Ga. These rocks are consistent with low- and medium- to high-pressure TTGs. Our modeling of the sources that gave rise to these TTGs revealed that the origin of the trondhjemites was related to the 13 % partial melting of an amphibolite/eclogite source at high pressure (approximately 1.5 GPa) in the garnet/rutile stability zone. The tonalite data also suggest 16–22 % partial melting of a metabasaltic crust at medium–low pressures (approximately 1.0 GPa), with little or no influence from garnet in the residue. The source had an affinity with the metabasalts in the greenstone belt sequence of the Tucumã–Gradaús Group. The proposed geodynamic setting of the Carajás Province TTG crust evolved from stagnant lid tectonics to mobile lid tectonics. Drip tectonics occurred over 30–50 Ma, aborted low-angle subduction began to occur, and as the crust became thicker and more resistant, increasingly steep subduction occurred.