Shear zones geometry in the Paraíba do Sul belt, southeastern Brazil, delineates a NE-trending fan-like structure. Shear zones dip towards SE in the northern limb, and towards NW in the southern one. This geometry has been interpreted either due to transpression or to late folding of flat-lying thrust surfaces. Stretching lineation plunges to ENE-ESE in the northern limb and towards NNE-NE in the southern one. Structural data in the southern limb of the divergent fan suggest a two stage kinematic evolution in high-temperature conditions: an earlier stage with top-to-SSW/SW sinistral thrusting and orogenic-parallel tangential motion, and a later stage with top-down to NNE/NE transtensional deformation. We propose a heterogeneous deformation model to explain the observed shear reversal, and suggest that the imposed transpressional displacement gradient may change during progressive deformation due to transient rheological inhomogeneities in bulk pure shear strain. In the earlier stage, the partially molten material could easily accommodate the imposed strain rates, giving rise fi rstly to the SW-directed shearing. As the thermal disturbance tended to vanish and the convergence increased, the NNE-directed transtensional shearing developed. We propose that the transtensional deformation characterized in this paper could be related to extrusion processes during regional transpressional strain.

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EXTENSIONAL OBLIQUE TECTONICS IN AN AREA SOUTHWEST OF THE CITY OF CAJATY, SOUTHERN SÃO PAU-LOSTATE Thegeologicalrnapping(scale:1:50.000)undertakensouthwestofCajatiCity,southofSãoPauloState,revealedthattheseveral lithological associations suffered an intense deformation, r'esponsible for a pelvasive mylonitization of all lithologies. The stretching Iineations and thé shear sense iudicators associated to this mylonitizâtion, such as S-C foliation planes, asymmetric porfiroclasts and boudins, suggest arl extensional tectonics fol this deformation, with extensional component to ESE, associated to sinistral strike-slip motion. Sheath folds and synmylonitic folds, with axes parallel to the stretching lineation indicate that the uon-coaxial deformation reached h-igh values of shear strain. This deformation occured in aniphibotite to greenschist facies conditions, and nicrostluctures suggest the rnylonitic fabric postdates the ¡reak of the metalìtorphisln. The transfotmation of kyanite to sillinranite suggest a decrease in pressure duling progressive metamorphism. Undel the presence òf tlre kyanite indicate a prcvious compressive history. Latel on, at a shallow stluctural level, clenulatiolt and asyrnmetric north-v-elgent iolds associated io discrete luptilð-ductile disciet thlusts, cornplete the stluctural evolution of the investigated area. The tectonic significance ofthis structural pattenr, in Blasiliano OÍogeny scenery in this crustal segment, needs ofmot'e detailed studies.RESUMO O mapearnento geológico na escala l:50.000 de urna ár'ea a sudoeste da cidade de Cajati, sul do Estado de São Paulo, tevelol que as divetsas associafões litológicas ldentificadas sofreram urna deforrnação intensa, res¡ronsável por utna milonitização pervasiva eln todos os litotipos. As lineaç-ões de estiral.nento e as estruturas indicadoras do sentido de cisalhanento associadas a esta milonitização, corno pales de foliaiOes S-C, poliiloclastos do tipo o e boud.itts assirnétricos, sugereln urna cillemática transtlacional Pala esta d.efotmação, com componeute extelisionâl de iopo para ESE asso'ciada à urna componente direcional sinistral. Dobras em bainha e dobras sin-milcníticas, com eixos palalelos à lineação de estiralireuto, indicam que a deformação não-coaxial atiugiu elevados valores de sheu'.ltruin. Esta defolmação ocolleu elncolìdições'r¡etanrór'hcas de fácies anfibõlito a xisto-vèr'de, co¡n as microestrutulas sugerindo que a trama nilonítica foi iurplantada após o ápice mótamó¡:fico. A plesença restrita de cianita, sempre instável pala sillirnanita, sugere decréscitno de ptessão dutante o ¡netamorfìsmo ptogres-¡ível est¡utural relativárnente nlais i'aso, crenulações e dobras assimétricas com velgência pal'a notte, associadas a discletas zouas de cisalha¡Iento r'úpteis-dúcteis de empurrão, courpletain a evolução estl utul al da área investigada. O signihcado tectônico deste padr'ão estrutural, no cenário da Ologênese Blasilianã ueste segmento c[ustal, encontla-se na dependência de estudos mais detalhados.Pul¿u,rus-chuve: tectônica ex...

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