VARIATIONS IN STRONTIUM ISOTOPIC COMPOSITION OF PARANA BASIN VOLCANIC ROCKS OF BRAZIL

Abstract

Tot al Rb a nd total Sr co ntents, as well as Sr isotopi c r atios, were a nalysed O il seven ba sa ltic rocks of the Paran a Basin , co llec ted in the sta les of Sa nta Ca tari na a nd R io Grande do Sui, Brazi l. 'I' ll(' res u lts ind ica te t hat th e rocks arc not ch e m icall y a nd iso top ica lly ho mogeneous. The va-ria tious seem to correla te with ti me of ext r usion , and with the co m posit ion of the base m e nt cr usta l rocks. So me relative ly high Sr Il 7 j Sr 8 (; ra t ios (more than 0 .7 14) wen: obtained, co m ing fro m t he high ly differ enti ated rocks which occ ur :. 11 th e uppermosl p ari of the b asaltic section in Rio Grande do Sui Stall'. These ra tios a re consid ered III Ilt' dll t' 10 la rge sea le conta mina t ion of th e ma gmas 1,,-crusta l m aterial curic-lu-rl ill l'ad itl ~ t ' l1i (" vuumi um. RESUM O A11 ,\ Iises q uimi ras cit, Rb tot al t-Sr tot a l, t· a ualis cs isot o p ica s de cstron cio fora m o bti das em sere a mos tras de rochas basah icas da Bacia do Pa rana, provcnicnr cs do s cstados m cri dio ua is bra sih-iros. Os resultados indicam que as roc has sao quimicamentc hct erogcncas em rclacao a tai s elem en tos. As va ria cocs pan'cem ser corrcla cio na vcis com () tempo de cxt ru sao d os ba saltos c co rn a co mposicao d as roc hes do c m ba sa mc n to (cro sta do tipo co n tine n ta l]. A lg uns re sult ados clevados d a l'a zao isot opica Sr fl 7 jSr fl fi (sup criores a 0 ,714) foram o htid os lias a m ostras d e roch as altam on te difercuci ad as q lle o co r rc m na part e su perior do platrou ha saltico, no Rio C:rall < h~ do S u I. Ta is rel acoes iso topicas sao co nsid cra d as dcvidas a co ntamina cao em la rga csca la dos magma s, pil I' mat eri al crustal euriqucr-ido r-m es t ro n cio rudiogenico.