PROTEROZOIC ASSEMBLY OF THE WESTERN GUYANA SHIELD: EVIDENCES FROM ITS U-PB–HF–O ISOTOPIC RECORD (Invited Presentation)

The Guyana Shield comprises the northern half of the Amazonian Craton, one of the largest Precambrian crustal nuclei on Earth. Since the late 80’s, the long-term evolution of Amazonia has been attributed to progressive lateral growth by accretion of juvenile Proterozoic arcs around an ancient Archean core. Nevertheless, the K-Ar, Rb-Sr, Sm-Nd and U-Pb isotopic data upon which this interpretation was built and has evolved over time derive mostly from samples of the Central Brazilian Shield (southern half of the Amazonian Craton), while geochronologic and isotopic data from the Guyana Shield have remained comparatively scarce.

Recent U-Pb–Hf–O isotopic results from multiple units and sampling localities across the purported Proterozoic tectonic boundaries in the Guyana Shield have started to shed light into a different story, one where pervasive reworking of older crustal material of inferred early Paleoproterozoic to possibly Neoarchean age has played a much larger role in the Proterozoic crustal development of northern Amazonia than what the widely-accepted model predicts. Although some hypothesized tectonic boundaries projected from the Central Brazilian Shield seem to be represented in the Guyana Shield (e.g., limit between the Ventuari-Tapajos and Rio Negro-Juruena provinces near the Colombia-Venezuela border), other provinces are much broader and isotopically complex than previously thought (e.g., Rio Negro-Juruena–like domains) or seem to be entirely absent or poorly represented (e.g., Rondonian-San Ignacio–like domains). The Proterozoic assembly of Amazonia culminated with its collisional incorporation to the Rodinia Supercontinent in the earliest Neoproterozoic, resulting in the high-grade reworking of the long-lived accretionary margin of the Putumayo Orogen, a late Meso- to early Neoproterozoic collisional orogenic belt which has also revealed a contrasting tectonometamorphic history with respect to its SW Amazonian relative, the Sunsás-Aguapeí orogen. This talk seeks to summarize the progress made over the past one and a half decades to improve our understanding on the Proterozoic tectonic and crustal development history of the Guyana Shield, and to highlight some of the key issues that remain to be addressed moving forward.