K [sbnd]Ar ages of clay-size concentrates from the mineralisation of the Pedroches Batholith, Spain, and evidence for Mesozoic hydrothermal activity associated with the break up of Pangaea

Abstract

The K Ar ages of 32 clay concentrates extracted from samples of ore, gangue and wallrock associated with mineralisation in the Pedroches Batholith lie in the range 119–285 Ma. Although some of the mineralisation is of Permian age more than half of the ages lie between 210 and 230 Ma and indicate a hydrothermal event at this (Triassic) time. A comparison with age data for mineralisation and certain anorogenic magmatism in other areas of the North Atlantic reveals a consistent pattern of a major event at ca. 210–230 Ma and a minor event at ca 160 Ma with little Cretaceous or Tertiary activity. It is proposed that the ca. 210–230 Ma event was related to an initial rapid fracturing of the crust associated with the break up of Pangaea, which was related with an increase in the geothermal gradient and penetration of the deep crust by surface waters which returned via both new and rejuvenated fissure systems.