Produção Nacional
ENXAMES DE DIQUES MÁFICOS DO QUADRILÁTERO FERRÍFERO E ESPINHAÇO MERIDIONAL, MINAS GERAIS, BRASIL
2017; Sociedade Brasileira de Geologia; Volume: 25; Issue: 2 Linguagem: Inglês
ISSN
2177-4382
AutoresAdalene Moreira Silva, Farid Chemale, Raul Minas Kuyumjian, Larry M. Heaman,
Tópico(s)Geochemistry and Elemental Analysis
ResumoMafic dikes are abundant in the Quadrilatero Ferrifero and Southern Espinhaco regions, southeastern State of Minas Gerais. The dikes range from 1,7 Ga to 120 Ma and form at least three swarms that differ in trend, mineralogy, composition and age. The oldest swarnrhas a baddeleyite U/Pb age of 1,7 Ga (Ibirite Gabbro) and K- Ar age of about 1 ,7- 1 ,5 Ga (schists), trends north-south, the dikes vary in width from centimeters to meters, and are deformed and metamorphosed to cnlorite-sericke-quartz-plagioclase schist or are some meters wide and contain plagioclase, augite,- ilmenite, quartz and traces of baddeleyite. These dikes are enriched in LREE [(La/Sm)N =3,68 -6.39], and depleted to enriched in HREE [(Dy/Yb)N = 0,82 - 1,29]. These dikes (and sills also) are related to the opening of the Espinhaco Basin. Nprthwest-and northeast-trending mafic dikes have a U/Pb age of about 906 Ma. They are commonly ten meters wide, and are of metagabbro with relict igneous textures and containing altered plagioclase (Ans-52), amphibole, epidote, ilmenite, quartz, and apatite. Samples of this dike swarm are slightly enriched in LREE and HREE with a (La/Sm)N = 1 .32 to 2.2 and (Dy/Yb)N = 1 .36 to 1 .88, respectively, and also show small negative europium anomaly. Sills, stocks, plugs, laccoliths and phaccoliths with compositions similar to dikes are present in the study area. The Sm-Nd data indicate negative ENU (T) (+ 1 .34 and - 3.20) and model ages (T DM ) of ca. 2.59 and 1 .35 Ga. These dikes may be related the first stages of the Panafrican/Brasiliano event. North-south, east-west, northwest and northeast trending Phanerozoic dikes are of diabase composed of plagioclase (An«)), augite and magnetite. They show moderate LREE (La/Sm)N = 2,53, and slight HREE enrichments, (Dy/Yb)N = 1,47. These dikes have a K/Ar age of about 120 Ma and may be related to the fragmentation of Gondwanaland. The Quadrilatero Ferrifero and Southern Espinhaco dikes are tholeitic and exhibit prominent iron-enrichment. Some trace element distributions are similar to continental rift basalts. They represent significant amounts of mafic melts formed during the beginning of ample extensional tectonic regimes. There are significant variations in incompatible and partially compatible element abundances both within and between dike swarms, which is due not only to heterogeneous mantle sources, but also to crustal contamination.
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