Vitrinite reflectance and thermal modelling of the Late Cretaceous magmatic intrusion at Ponta das Ferrarias (Praia da Luz): implications for the regional maturation of the Algarve Basin
At Ponta das Ferrarias, Praia da Luz, Lower Cretaceous Luz Mudstones are intruded by a ca. 150 m thick igneous dyke of Upper Cretaceous age. In order to assess the effect of this intrusion on the regional organic maturation, vitrinite reflectance (VR) and 1D thermal modelling was measured and performed, respectively. Samples for VR were collected at increasing distance from the intrusion wall. At the contact with the intrusion, VR reaches a maximum value of 1.68 %Rr. decreasing to 1.1 %Rr at 30 cm away from the contact wall. Further out, VR values gradually decrease away from the intrusion. Equilibrium with the regional background VR (0.66%Rr) was obtained at a distance 2 km away from the intrusion.
1D modelling results show that between 20 and 1000 years after the intrusion, the temperature in the centre of the intrusion decreased from ca. 500 °C to ca. 200 °C, whereas, in the margins of the intrusion the temperature decreased from ca. 275 °C to 190 °C. During the same period of time, the country rock temperatures at the intrusion wall increased from 100 °C (peak temperature attained by the rocks during burial) to near 275 °C. The temperature at the contact after 10 000 years was 30°C above the background temperature. After 0.1 Ma the temperature at the contact was only 10°C above the background temperature and at 1 Ma the temperature had equilibrated with the regional background temperature. The results indicate that peak temperatures associated with the burial stage were attained before the intrusion and the thermal effect of the intrusion was restricted to a maximum distance of ca. 2 km away from the intrusive contact, during a period of maximum 1 Ma. This implies that Late Cretaceous igneous activity did not have a major role on the organic maturation and thermal history of the Algarve Basin.
AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015