Original paper

Deformation-enhanced mineralogical changes in igneous quartz-feldspar rocks from a semi-brittle shear zone, Southern Iberian Massif, SE Spain

Jiménez-Millán, Juan; Abad, Isabel; Vázquez, Mercedes; Velilla, Nicolás


Two stages of crystallization at greenschist and sub-greenschist facies were identified in leucocratic dikes and granodioritic rocks in a shear zone on the southern border of the Santa Elena intrusion in the southern Iberian Massif near Jaén (SE Spain). Protoliths containing quartz+plagioclase+K-feldspar±muscovite±biotite experienced intense fracturing, fluid infiltration and metasomatism replacing the primary assemblage by muscovite and biotite interlayered with kaolinite, K-feldspar and albite, partly developing a myrmekitic texture. The mineral paragenesis and microcline-low-albite solvus thermometry suggest upper greenschist facies temperatures during a prograde process comprising an initial synkinematic stage and a postkinematic metasomatic replacement. Deformation of porphyroclasts indicates a combination of brittle to plastic shearing which is consistent with this temperature. The synkinematic mica formation caused strain softening. A final retrograde postkinematical stage of shear zone development at high amounts of fluid at lower temperature is reflected by the presence of kaolinite formed mainly by the replacement of mica and plagioclase in veins.


semtemsoftening reactionsfeldspars solvus thermometrycentral-iberian granodioritesfluid-rock interaction