Geocronologia Rb-Sr e Características Geoquímicas dos Diques Máficos da Região de Nova Lacerda e Conquista D’Oeste (MT), Porção Sudoeste do Craton Amazônico

Abstract

In the Nova Lacerda and Conquista D’Oeste regions, Mato Grosso State, SW part of the Amazonian Craton, mafi c dikes trending NNW intrude the Nova Lacerda Granite (1462 ± 12 Ma), within the Jauru Domain, in the Rondonia-San Ignacio Province (1.55 - 1.3 Ga). The mafi c swarm comprises diabases, metadiabases and amphibolites. Metadiabases originated from uralitization of diabases. These rocks have tholeiitic affi nity and predominant basaltic composition. Some samples are andesi-basalts. The ages of diabases and metabasites are 1380 ± 32 Ma and 1330 ± 120 Ma respectively. Geochemical data indicate that the compositional variation of diabases and metadiadases is due to fractional crystallization of evolved tho- leiitic magmas. The origin of the basaltic magmas is related to a heterogeneous mantle source.