Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9524464 | Journal of South American Earth Sciences | 2005 | 15 Pages |
Abstract
The Boa Vista Basin (BVB) is located approximately 60Â km southwest of Campina Grande, ParaÃba, northeastern Brazil. It has a half-graben geometry controlled by dip-slip normal faults striking NE-SW. From the base to the top, the BVB is composed of (1) a lower volcanic unit of altered basalts and basaltic andesites overlying Precambrian basement rocks, (2) an intermediate unit of bentonitic shales that pass upward to medium- to coarse-grained sandstones and conglomerates and downward to sandstones and siltstones, and (3) an upper volcanic unit of massive to vesiculated basaltic flows grading to pillowed or autobrecciated basalts. These basalts show porphyritic (olivine and augite microphenocrysts), glomeroporphyritic, intersetal, pilotaxitic, and variolitic textures. They are medium-K, Fe-rich tholeiites with SiO2 of 50.2-53.3Â wt%, magnesium number of 50.54-60.21Â wt%, total alkali of 2.15-3.92Â wt%, and TiO2 of 1.8-1.9Â wt% and are related by low-pressure fractionation of olivine, plagioclase, magnetite, ilmenite, and apatite. They are LREE-enriched (LaN/YbN=8.54-44.14) with no significant europium anomaly. Trace element modeling suggests a garnet-bearing metasomatised lherzolite as their source. The geological context and geochemistry of the basalts suggest a close connection between reactivated deep-rooted Precambrian shear zones, which channeled mantle-derived Tertiary tholeiitic magmas, and continental rifting in northeastern Brazil.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Earth and Planetary Sciences (General)
Authors
Zorano Sérgio de Souza, Marcos Antonio Leite do Nascimento, Rogério Vidal Nunes Barbosa, Luis Gustavo da Silveira Dias,