TectÃnica e litogeoquÃmica de rochas supracruciais e ortognaisses a norte e a sul da zona de cisalhamento congo-cruzeiro do nordeste (ParaÃba): um teste da hipÃtese de terrenos no domÃnio central da provÃncia Borborema

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The area around Aroeiras, ParaÃba, includes quartz- monzodioritic orthogneisses of paleoproterozoic ages and alkali-feldspar granitic to tonalitic orthogneisses of uncertain ages; metasedimentary sequences and intrusive rocks. The studied lithologies were separated according to its occurrence north or south of the Congo-Cruzeiro do Nordeste Shear Zone (CCNSZ), which is defined as the limit between the Alto Moxotà and Rio Capibaribe terranes. The CCNSZ and others shear zones (dextral and sinistral) have caused milonitization of the rocks lying along their extension. Quartz-feldspar paragnaisses to biotite paragneisses are the most abundant rocks, lying within the Surubim, SertÃnia and Vertentes complexes according to the geological map of ParaÃba. The protholits were probably arcosean arenites that went through little transport and have some contribution from more pelitic sediments. Typical schists are locally intercalated with quartzites. In some places, migmatization occurs, with variable intensity. Some differences were observed between rocks situated north and south of the CCNSZ, but they are not enough to decide if they belong to distinct units or are part of the same litostratigraphic unit. Four generations of folds affected the region: the first one is not easily found anymore. The second one produced overturned folds with SW-NEstriking axial planes and NW vergence. This generation was affected by upright folds with E-W-trending axes, generally plunging to the E. The fourth generation has affected the area in a less intense way. The folds are open, with NW-SEstrinking axial planes. The CCNSZ is a sinistral shear zone, consisting of two NE- to ENE-striking branches that join westward and then with the E-W-striking dextral Coxixola shear zone. These shear zones cut across the north portion of the area, acting as a conduct for two granitic plutons. Another shear zone (SÃo Bento) cuts the E/SE portion of the Ãrea, and has a dextral shear sense. A smaller sinistral shear zone was also found within the W-SW potion of the area. Metasedimentary rocks and orthogneisses were submitted to chemical analyses. The orthogneisses are characterized as arc volcanic calc-alkaline rocks. The RRE diagrams for orthogneisses and metasedimentary rocks are nearly parallel, although the latter are somewhat poorer in REE, suggesting that the orthogneisses may have been one of the main sources for the sedimentary precursors of the paragneisses. Taking into account the geochemical similarities between metasedimentary rocks and orthogneisses in different places of the area, it seems to be no differences between terranes situated north and south of the CCNSZ.

ASSUNTO(S)

terreno alto moxotà metasediments litogeoquÃmica limit between terrenes limite entre terrenos orthogneisses ortognaisses alto moxotà terrane provÃncia borborema metassedimentos rio capibaribe terrane geociencias borborema province lithogeochemistry terreno rio capibaribe

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