Química mineral e evolução petrológica do magmatismo alcalino neoproterozóico do maciço São José de Campestre (Rn-Pb), extremo NE da Província Borborema

摘要: The southern portion of the Sao Jose de Campestre massif (NE Borborema Province) comprises a number granitic rocks alkaline affinity, associated with ductile shear zones Neoproterozoic age. These bodies are constituted by very similar petrographic and textural features. They consist essentially hololeucocratic, white to pink alkali-feldspar granites equigranular fine- medium-grained texture. Feldspar (microcline albite) quartz, moke up about 90 weight %. main mafic phase is clinopyroxene types aegirineaugite or hedenbergite, in addition accessory amounts garnet, sphene, allanite, zircon, apatite magnetite. Microprobe analyses corroborate distinction clinopyroxenes into two types. In garnet bearing rocks, pyroxene whereas no aegirine-augite. Garnet andradite rich (88-82 mol%), subordinate grossular, spessartine almandine components. Plagioclase shows remarkable uniformity composition ranging from 0 9 mol% anortite, more calcium individuals found garnet. oxides always Tipoor Chemically, studied show similarities high silica (>70%) alkali granites. metaluminous slighly peraluminous, Na 2 O+K O higher than 8%, values Fe (Fe#=64-100) on agpaitic index less 1,0. geochemical features typical classical suites. On other hand, low Nb, Ga, Y, Rb Zr, as well Sr, total rare earth elements positive Eu anomalies (Eu/Eu*=1,5-2,9) not compatible traditional magmas. integration data suggests fractional crystallization petrogenetic process. Some mass balance calculations trace element modeling point 10% fractionation, cumulate composed clinopyroxene, plagioclase, magnetite zircon.