Crustal contamination and insights into diachronous changes toward modern tectonics: evidence from Hf-Nd-O-Pb isotope of sanukitoids from the Amazonian craton

Abstract

<p>Archean sanukitoids provide crucial insights into crust-mantle interactions during the early Earth’s geodynamic evolution. However, the role of crustal contamination in their genesis remains uncertain. Sanukitoids identified in the Sapucaia subdomain of the southern Carajás Province are represented by two plutons Água Limpa and Água Azul, collectively referred to as the Água Limpa sanukitoid suite. These plutons are compositionally similar to low-Ti sanukitoids (< 0.63 % TiO₂) and their zircon isotopic data record a short period of magmatic activity around ca. 2.87 Ga. Sanukitoids zircons reveal <em>ε</em>_Hf(<em>t</em>) values ranging from –3.31 to + 2.14, Hf and Nd model ages between 2.91 Ga and 3.28 Ga, whole-rock <em>ε</em>_Nd(<em>t</em>) values from –1.64 to + 1.76, and <em>δ</em>¹⁸O values ranging from 5.0 ‰ to 7.6 ‰. The Pb isotopic compositions in K-feldspar (<em>µ</em> > 10) suggests a Mesoarchean mantle source affected by slight crustal contribution and/or contamination. Result of geochemical modelling indicates that the sanukitoids were formed by ∼ 15 % partial melting of mantle peridotite previously enriched by ∼ 30 % of slab-derived melts, with orthopyroxene, garnet, clinopyroxene, phlogopite, and magnetite as residual phases. The integration of our data with previously published results leads us to suggest that modern-style plate tectonics may have initiated along the northern Carajás Province during the Mesoarchean, while the Rio Maria domain to the south remained dominated by mantle plume-driven crustal growth and vertical tectonics.<br></p>