Resumo

ROMERO-CONDOR, Christian et al. Petrography and geochemistry of the Naiza intrusive, Cordillera Cutucú, Ecuador. Bol. geol. [online]. 2023, vol.45, n.3, pp.15-36.  Epub 16-Nov-2023. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v45n3-2023001.

On the Ecuadorian Andes, the Jurassic magmatism record outcrops extensively to the south of the Subandean Zone. These intrusive rocks have been grouped indiscriminately in the Zamora Batholith, defined as an N-S trend. The 100 km long intrusive rocks belt is considered magmatic roots of a long-lived, calc-alkaline, metaluminous continental arc dated to Lower Jurassic (180 to 162 Ma). However, the Zamora batholith and contemporaneous sedimentary rocks were affected by multiple intrusions, which have high scientific and economic interest due to their mineralization style. Recently, in northwest Indanza, in the Naiza sector, a granitoid emplaced in sedimentary rocks of the Chapiza Formation and volcanic rocks of the Misahuallí Formation, was dated at 148.34±1.65 Ma. The Naiza intrusive is a quartz-monzonite composed by plagioclase (oligoclase-andesine), feldspar (microcline), quartz, biotite, and hornblende. Geochemical data indicate that this intrusive has an alkaline to high K calc-alkaline affinity and metalluminic character. Rare earth patterns show enrichment of LREE concerning HREE. Positive anomalies of Rb, and Th, accompanied by negative anomalies of Eu, and Nb, are standard patterns in continental margin magmatic arc environments. Anomalies positive for Pb indicate cortical contamination. The Y, La, and Nb contents suggest that the Naiza intrusive corresponds to a late-post magmatic to a post-magmatic episode in an intra-continental domain.

Palavras-chave : Jurassic magmatism; Subandean zone; Indanza; Ecuador.

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