Pre-Rhyacian lithostructural targets of the transversal zone (central domain) of the Borborema Province

Abstract

The Borborema Structural Province is situated in ther northernmost part of the South American Platform, from the northernmost side of Bahia State (to the south) up to the Ceará-Piaui boundary areas.(to the north and northwest). Unde geological conceptions, this province is a branching system of Neoproterozoic orogens, presenting different types of "structural/tectonic highs" from the Paleoproterozoic and Archean basements, of different origins and magnitudes. In these basement inliers there are known occurrences of some Archean "seed nuclei", as well as , there many other indications of ancient basement nuclei, all of them demanding geological and geochronological researches.This Neoproterozoic "region of folding" (russian sense) presents a fan-like distribution of their structural trends, very different of the original late-orogenic one. This was caused by the stiking activity of "escape tectonic" (or "extrusion") of the Ediacaran Cambrian times. So doing, all structural trends use to reach the coast line as perpendicular lines. Besides the extent of this "region of folding" (lithotypes and structural lines) under the continental shelf , this contiuity is known in the northwestern Afican territory, from Gana (Accra City) up to Gabão (to the south, Bata City) We are awared that both Archean and Siderian rock types are inserted in this Neoproterozoic structural province as relicts elements (of previous structural assemblages). We have continuously witnessed these occurrences. The tectonic, magmatic and thermal reworking of these ancient domains due the imposed conditions of post-Rhazcian tectonic-magmatic cycles has systematically been observed. So, besides the attempts for of finding out new occurrences of Archean and Siderian protoliths, the study of those reworking processes are among the aims of this research project. We are conscious that this study will be a fair additional contribution .The selected área for the research studies for the next two years comprises the central subprovince of the Borborema province, the so-called Zona Transversal, positioned between the coordinates 6º 30´S e 8º 30´S (parallels) and 34º 30´ W e 40º 30´W (meridians). About 30 sheets (ca. 3.000 km2 each one) of recent geological mapping (scales 1/100,000) are now available, covering the entire area of the subprovince. We have followed step by step, very closed, this process of geological mapping, The authors (proponents) know some occurrences of Archean and Siderian rock types both in the subprovinces north (Setentrional Segment, Central Ceará terrane) and south (PEAL massif, basement of Rio Capibaribe and Riacho do Pontal fold belts) of the Tansversal Zone. The central idea is to discriminate all potential targets of these occurrences inside of the Transversal Zoning, using for that all data of previous researches and the subsides of the now available geological maps. We intend to improve the knowledge of such older lithostructural types, both in terms of real extent and the role in the crustal evolution. The proponents of this research project have a good experience in terms of the regional geology and geochronology of the province as a whole. The same is true about the use of the isotopic methods Sm-Nd (WR, as pathfinder and U-Pb LASER ABLATION (for lithotypes and precedence studies). (AU)