New evidence of a magmatic arc in the southern Brasilia Belt, Brazil: The Serra da Agua Limpa batholith (Socorro-Guaxupe Nappe)

This paper presents a detailed description of the Neoproterozoic Serra da Agua Limpa batholith (SALB) and the interpretation of its genesis. The batholith, located along the border of the states of Minas Gerais and Sao Paulo, was involved in the Socorro-Guaxupe Nappe, a tectonic unit that integrates the southern Brasilia Belt. The tectonic evolution of this nappe is related to the convergence and subsequent collision between the Paranapanema paleocontinent, representing the upper plate, with the Sao Francisco paleocontinent, resulting in the construction of the southern Brasilia Belt. The active margin of the Paranapanema paleocontinent developed during the pre-collisional stage a magmatic arc composed of batholithic igneous bodies. The Socorro-Guaxupe Nappe represents this active margin and SALB is one of those bodies. U-Pb dating (Laser Ablation, LA-ICP-MS) in zircon was performed in five samples of SALB. The results are as follows: sample RDTM 62, 667 +/- 10 Ma; RDPA 44, 645 +/- 5 Ma; RDPA 46, 630 +/- 12 Ma; VAC 10, 631 +/- 7 Ma and RDIT 41, 635 +/- 8 Ma. These ages indicate that the body crystallized between 670 and 630 Ma, with predominance of ages in the interval 645-630 Ma, demonstrating that the magmatic event that formed the arc lasted at least 40 myr. Younger ages, measured in rims of zircon grains, mainly in the range 625-600 Ma were interpreted as metamorphic ages. The lithogeochemical analyses indicate that the I-type rocks of the Serra da Agua Limpa batholith belong to the high K calc-alkaline series, and are metaluminous to slightly peraluminous. Tectonic environment diagrams also indicate that the batholith was produced in a volcanic arc setting which is confirmed by negative anomalies of elements of high ionic potential (HFS) in multi-element diagrams. Whole rock Sm-Nd isotope analyses show highly negative epsilon(Nd) values (-12 to -7), indicating significant crustal contamination or origin of the magma by melting of enriched lower crust. (C) 2014 Elsevier Ltd. All rights reserved.