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Sills máfi cos da Suíte Intrusiva Huanchaca - SW do Cráton Amazônico: registro de magmatismo fi ssural relacionado à ruptura do Supercontinente Rodínia

2012; Sociedade Brasileira de Geologia; Volume: 42; Issue: 1 Linguagem: Inglês

10.25249/0375-7536.2012421111129

2177-4382

Gabrielle Aparecida de Lima, Maria Zélia Aguiar de Sousa, Amarildo Salina Ruiz, Manoel S. D’Agrella-Filho, Paulo Vasconcelos,

Geography and Environmental Studies

The Ricardo Franco hill is comprised by sub-horizontal layers of the Aguapeí Group (Fortuna, Vale da Promissão and Morro Cristalina Formations, from bottom to top), mafic sills from the Huanchaca Intrusive Suite, and cherts and silexites of Tramposo Unit. This work presents geologic, petrographic, geochemical and geochronological (Ar-Ar) data of mafic sills belonging to the Huanchaca Intrusive Suite inserted in the Paraguá Terrane, SW of Amazonian Cráton, and discuss the possible tectonic significance of this igneous event. Two sills are identifi ed intruding mudstones of the Vale da Promissão Formation. Petrographically, the mafic rocks are isotropic, fine to medium grained and greenish-gray to black color. They show equi to inequigranular textures and gabbroic composition. Geochemically the sills are subalkaline tholeiitic basalts and tectonically they are related to a continental intraplate environment. The magnesium index (mg #) values vary between 0.25 and 0.38, indicating evolved basaltic magmas. Data 40Ar-39Ar isotopic ages indicate plateaus of 1040 ± 40 Ma for amphibole and 948 ± 5 Ma for plagioclase, the first (amphibole) is the best estimate of the age of injection of sills. The sills and mafic dykes Huanchaca, along with Rancho de Prata and Rio Perdido Intrusives Suites and sills (Salto do Céu Intrusive Suite) of the southwestern sector of the Amazonian Cráton, all described as diabases and gabbros of tholeiitic affinity, form a large igneous province (LIP), generated by crustal extension with a NNW displacement vector, preceding the dispersion of Rodinia Supercontinent.