Petrologia e gravimetria do segmento Norte do Batólito Acari, faixa Seridó: condições de alojamento e estruturação profunda

Abstract

The Acari Batholith stands out in the geological and metallogenetic evolution of the Seridó Belt both for its extension and facies diversity, as well as for the historical association of its northern portion, the Serra do Dorna Granite (SDG), with scheelite mineralization in the Brejuí-Boca de Laje District. However, the batholith's deep structure and thermobarometric evolution within the Seridó Belt context still require more detailed investigations. This study addresses these gaps through two main approaches. The first approach consists of 2.5D forward gravity modelling of the central-northern portion of the Acari Batholith, where negative gravity anomalies indicate its feeder zone. For this purpose, ten E-W oriented profiles with 2 km spacing were modeled using GM-SYS extensions in Seequent Oasis Montaj®. The second approach integrates petrographic and lithogeochemical aspects of the SDG granites, including 1:50,000-scale geological mapping to identify magmatic facies, field relationships, and structures. Thermobarometric estimates were performed based on whole-rock geochemical data. The SDG consists of equigranular to microporphyritic granites, while porphyritic granites and diorites predominate in the batholith's central portion. Gravity modelling results reveal two roots in the northeastern segment of the Acari Batholith, aligned in the NE-SW direction. The northern root is located outside the outcrop area, between the Acari Batholith and the Acauã Stock, at 1150 m depth. The southern root is deeper (1930 m) and lies beneath the batholith's outcrop area near Serra da Lagoa Seca. Although separated at the surface by a thin cover of mica schists, the Acari Batholith and Acauã Stock constitute the same magmatic system at depth. Thermobarometric estimates indicate crystallization temperatures between 909 and 702°C and pressures between 2.6 and 3.5 kbar, consistent with regional calibrations for the batholith's host mica schists. The maximum pressures represent an emplacement depth of 13.5 km, reflecting the depth reached by Seridó Group metasedimentary rocks during the peak of the D3 metamorphic-deformational event. The eastward displacement of the batholith's roots suggests a higher thermal gradient in this direction, whose influence is manifested in the hightemperature/low-pressure assemblages of the host mica schists (sillimanite + cordierite). In summary, the results demonstrate how the integration of gravity modeling and thermobarometry provides a more robust understanding of the Acari Batholith's structure and emplacement, as well as its relationship with the Seridó Belt's tectonometamorphic context.