The Cretaceous-Paleocene Andean basin system of central-western South America, comprises northwestern Argentina and southwestern Bolivia. It is situated between 62 o -68 o W and 18 o -27 o S, but extends westward to northern Chile and northward to Bolivia and Peru. These basins have been interpreted as an aborted foreland rift. In a general sense, it may be possible to relate this rift to the opening of the South Atlantic Ocean, however it was directly associated, in a backarc position, with the subduction of the Nazca Plate below the South American Plate. Three main magmatic episodes were recognized: the pre-rift stage (130-120 Ma) which is characterized by an early phase of anorogenic plutonism, with subalkaline and alkaline granitic intrusives; the syn-rift volcanic episode which started with a mainly alkaline volcanic activity (110-100) in which alkaline rocks prevail; a second more voluminous volcanic episode (80-75 Ma) which is characterized by an alkaline suite represented by basanites and tephriphonolites; and the last volcanic episode (65-60 Ma) which consists of lamproitic sills and basic K rich lava flows. Petrography, chemistry and chronology of the Cretaceous plutonic bodies indicate anorogenic pre-rift related A-type granite complexes closely related to the further evolution of the Cretaceous rift basin. The petrology and geochemistry of the Cretaceous volcanic rocks show strong alkaline affinities and suggest a similar rift-related origin. The geochemical and isotopic characteristics of the alkaline basalts suggest that they originated through low degrees of partial melting of a depleted mantle subcontinental lithosphere which was previously enriched by processes such as the introduction of veins rich in amphibole, high Ti phlogopite, and apatite. Cretaceous plutonic and volcanic rocks from central-southwestern South America are related to an intracontinental rift environment and although their ages are correlative with those of the Parana volcanic province, their petrology, geochemistry and isotopic compositions reveal different source regions and petrogenetic processes.El Sistema de cuencas cretacicas-paleocenas de la zona centro-oeste de Sudamerica comprende el noroeste de Argentina y las cuencas andinas del sur de Bolivia. Este sistema esta situado entre los 62 o y 68 o W y los 28 o y 27 o S y se extiende hacia el norte hasta Bolivia y Peru y hacia el oeste hasta las cuencas cretacicas del norte de Chile. Estas cuencas han sido interpretadas como un rift de trasarco abortado. En sentido general es posible relacionar el regimen extensional de rift a la apertura del oceano Atlantico Sur, sin embargo se asocia su evolucion a una extension de trasarco debido a la subduccion de la Placa de Nazca en el margen Pacfico de Sudamerica. Fueron reconocidos tres episodios magmaticos diferentes relacionados a distintas etapas de evolucion del rift. El estadio de prerift (130-120 Ma) caracterizado por una fase de plutonismo anorogenico de composicion grantica alcalina a subalcalina. El estadio sin-rift comenzo con actividad volcanica alcalina entre los 110 y 100 Ma. y siguio con un segundo pulso volcanico (80-75 Ma) que esta representado por una suite alcalina de basanitas y tefrifonolitas. La ultima fase volcanica (65-60 Ma) consiste de sills lamproticos y flujos de lavas basicas ricas en potasio. Las caractersticas geoqumicas e isotopicas de los basaltos alcalinos sugieren que los mismos fueron originados por bajos grados de fusion parcial de un manto litosferico empobrecido, enriquecido en LREE por diferentes procesos entre ellos el metsomatismo producido por la intrusion de venas ricas en anfbol, flogopita y apatita. Si bien las rocas plutonicas y volcanicas cretacicas del centro-sudoeste de Sudamerica estan relacionadas a un ambiente geotectonico de rift de antepas y sus edades son coincidentes con las efusiones de la Provincia volcanica de Parana, su geoqumica sugiere una diferente fuente de generacion de los magmas y distintos procesos petrogeneticos.