Petrologia e geoquímica das rochas plutônicas da região de Conceição -Itaporanga (PB)

Abstract

The igneous rocks of the Conceição-Itaporanga region (W of the State of Paraíba) are intrusive in metamorphic rocks of the basement and of the Piancó Alto Brígida fold belt, which is inserted in the Caririana folded region of northeastern Brazil. These rocks are represented by K-diorite, tonalite, granodiorite and granite, and are placed in metasedimentary rocks of the Cachoeirinha Group and gneisses of the Uauá Group and are considered to be post-tectonic in the Brasiliano cycle. Chemically these rocks have a special character where K-diorite, with a high K content, and tonalite, granodiorite and granite have a much more mafic chemistry than many other granitic rocks. The chemical compositions of these rocks when placed in the diagrams of variation of elements versus the modified Larsen Index and in the AFM diagram, show several trends that are not compatible with differentiation. Comparing the mineralogical associations of tonalitic, granodioritic and granitic rocks in the Conceição-Itaporanga region, with experimental work in granodiorite and granitic systems, it is observed that the most probable temperatures for crystallization of granodiorite magma are 680°-780° at a pressure of 8Kb. For the origin of K-diorites, it is assumed that they were formed from a primary K-rich magma, while the most likely genesis of tonalitic, granodiorite and granitic rocks is by partial melting in the crust from mafic gneisses or rocks. meta-basalt.