EVOLUÇÃO MAGMÁTICA DA INTRUSÃO BÁSICA NO POÇO 1UN30 E SUA INTERAÇÃO COM O ARENITO ENCAIXANTE, NA PORÇÃO NORTE DA BACIA DO PARNAÍBA (N E NE DO BRASIL)

Magmatic evolution of basic intrusion in the well 1UN30 and its interaction with the enclosing sandstone, in the northern of the Parnaíba Basin

Abstract

This work was developed as a result of petrographic, chemical and litogeochemical analysis of the 1UN30 well, drilled in the Parnaíba Basin. The petrography indicates that the igneous rock has glomeroporphyrytic texture and essential mineralogy of plagioclase and pyroxene with olivine and opaque minerals as accessories. The sandstone is a quartzarenite to subarkose with framework of the quartz, K-feldspar and opaque minerals, and interstices filled by tremolite and clay minerals. The igneous rock, by litogeochemical, is an intraplate tholeiitic basalt. Analysis of MEV pointed the clay minerals as belonging to the illite-smectite group and identified minerals of chlorite group. Through the textures and chemical analysis of the grains, two phases of plagioclase formation are identified. The most calcic phase occurs as corroded and zoned core with thick sieve textured. The other consists at the edges of corroded cores or in isolated crystals, zoned and with fine sieve texture. It concludes that the rock was formed by four evolutionary events: the first phase of crystallization; rapid decompression during rising of the magma chamber; mix with a warmer and rich in calcium magma; and the second phase of crystallization. The interaction with the magma formed tremolite and clay minerals in the sandstone, maintaining the anterior sedimentary aspect, in a process called contact diagenesis.