La edad de las ilitas en areniscas pérmicas y triásicas de la Cordillera Ibérica mediante el método K/Ar: Implicaciones en la historia diagenética y evolución de la cuenca.

Abstract

A K/Ar studyof the fine-grainedauthigenicillite in the Permianand Triassicsandstonesof the Iberian Rangefrom a Sigiienzawell 44-3 core (near1000 m depth)wasperformed.The compositionof the sandstones rangefrom sublitharenitesto greywackesin the Permianand from arkosesto subarkosesin the Buntsandstein.Thesesandstoneshowpervasive authigenic illite which occurred during at least three episodesof cementationduring the burial history. This is indicatedby the compositional and morphological characteristicsof the illite and also by the generalsequenceof cementation. K/Ar age determinationsindicatethat the episodeof illitization range between202.8±4.4M.a. to 153.8±3.4M.a. duringHettangian-Sincmurian to the Callovian-Tithonian.Theseagescoincidewith theperiodof the most intensiveextensionaltectonicsin the basincoevalwith volcanicevents.Upwardflow of hot fluids from the basement andthe convectivefluids mouvementproducedthe fibrous illite growth. Constraintsplacedby vitrinite reflectancededucedtemperaturesfrom the associatedorganicmatter which suggestthat the diageneticillite formed at temperaturesbetween134.8 and 159.50Cfrom 3 800 to 450Cmin depth.Theseestimatesimply geothermal gradientssignificantly greaterthanthosethat could havebeendeducedfrom theburial historyreconstructionof the Permo-Triassicbasin.