Paleomagnétism and geochronology of mafic dikes from the regions of Salvador, Olivença and Uauá, São Francisco Craton, Brazil: present stage of the USP/Princeton University collaboration

Th!!purposeortheUSP/Princetonlhi~ers1tycollaboratJonproJect isapalecma~t1c and geochronological study 01' PrecrO:lrlanmetamorphlc '-"1ts and anorogenic Proterozoic intrusi~es from selected areas in Brazll.lhe Instituto Astrormlco e GeofIslco of the lhl~ersld<1de de SlIo Paulo has been carrylng out th!! paleornaç;netic analyse s whereas geochronological determinations usinç th!! 40Arr9Armett"()(j are being made at PrirlCeton lhi~ers1ty dth th!! collaboration of th!! Instituto de Geociências of USP.A total of 799orientedrockS8ll{lleshasbeencollected frOOl Jrl!tamorphosed and l.rfIIetano:JrpOOsed dikesandalsofrOOlthetlaserentrockslnthereglonsofuau.á(131s~les), Salvador (200 satl"l)les)andllhéus-Oliverça-ltaJudoCOlOnia(341s~les)in the 5tate of BahIa andwestof'Belotbrizonte(107sa.;:>les),StateofMinasGerals(Fig.1).ihe presentstatusofthepaletlllilg"letiCandgeochronologicalstudiesofth!!serocks lspresentedhere, includingresultsootained~tonowaodananalysisof'paleogeographicand geotectonicimpl1cations.Regia"! West of Reli:> Ibrizcntelhe paleO'llaç;netic analysls of dlkes frOOl t1:"o1s reg10n re~eals a~lexlllapticbeha~iour-..hensutmittedtolaboratorytreatments.san.:>les from th!! same dike often show stable directions which, howe~er, lIre oot coherent.ih1s tias probably beencausedbytheCOlf\)lexthenno-tectonlchistoryofthisregionin which several theIlJlll e~ents (frOll lrl!l1s_Amazonian to Brasiliano) have been recorded.Sa/IJlles from th!! few dikes which presentconerent paleOlllag""leticdirections are being prepared for 40Ar/39Ar age determinations.Uaui Regicn -Sa~les fram 20 dikes (two of them llletamorphosed) collected ncar the townoflJ&uápresentedgoodmaç;neticstabilitytoalternatingrield(AF)andthermaltreatment and yielded directions with declination arowd 13' and positi~e inclination (Fig. 2a).Some ofthesesamplesarebeir,gprepared for 40 Arp9 Ar age determinations.