Banca de DEFESA: JOYCE LORENA OLIVEIRA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : JOYCE LORENA OLIVEIRA
DATE: 26/08/2021
TIME: 09:00
LOCAL: videoconferência
TITLE:

Geology and petrogenesis of the Miocene alkaline volcanism of Serra Preta region, Pedro Avelino / RN, NE Brazil

KEY WORDS:

intraplate magmatism; alkaline magma; Miocene; dike system; NE Brazil

PAGES: 69
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geologia
SUMMARY:

Cenozoic intracontinental magmatism in Rio Grande do Norte outcrop as small plugs, necks, dikes and flows of basaltic composition. These rocks compose the northwesternmost tip of the Macau-Queimadas Trend, a ca. 200 km long tectono-magmatic province. Part of this volcanism also intrudes the sedimentary rocks of the Potiguar Basin, leading to thermal contact aureoles that contribute to hydrocarbon maturation and remobilization. In the eastern portion of Pedro Avelino/RN, three igneous bodies with different geometries intrude Cretaceous sandstones and carbonates of the Potiguar Basin. The aim of this research is to characterize the petrogenesis and the emplacement mechanism of these rocks through field relationships, petrography and whole-rock geochemistry (major, trace and rare earth elements). The surface expression of the larger body, namely Serra Preta, was previously interpreted as plateau-type. However, reinterpretation of field data and of remote sensing images suggest the emplacement of NNW-SSE and NE-SW dike sets is tectonically controlled. In terms of petrography, these rocks are predominantly volcanic to subvolcanic olivine basalts, as well as late differentiate nepheline microgabbros. The groundmass is crypto- to microcrystalline and is composed of microlithes of augite, plagioclase (~An50), opaques and interstitial glass. Whole-rock geochemistry show that these rocks are alkaline and relatively primitive, with high Mg# (65-79), MgO (12-19 wt. %) and Ni (>200 ppm), low SiO2 (39-43%) and have normative nepheline + olivine ± leucite. They are classified as strongly silica-undersaturated basanites, melanephelinites and olivine basalts. Chondrite normalized diagrams show enrichment of light rare earth elements (LaN/YbN ~36-18) and enriched in Large Ion Lithophile Elements (LILE), with negative anomalies of Rb, K and Hf. Geochemical modeling indicates that these rocks are the product of low degrees of partial melting (<10%) of a phlogopite-amphibole-bearing garnet-lherzolite source enriched in LILE. Fractional crystallization of ca. 80% is responsible for the most evolved compositions, with a cumulate composed of clinopyroxene, nepheline, magnetite, apatite, perovskite, leucite and Ca-plagioclase. Miocene local stresses were responsible for the reactivation of brittle structures that acted as conduits for those mantle-derived magmas. 

BANKING MEMBERS:
Externo à Instituição - ALCIDES NÓBREGA SIAL - UFPE
Interno - 2042352 - FREDERICO CASTRO JOBIM VILALVA
Interno - 350630 - ZORANO SERGIO DE SOUZA