The pressure character of the Inda Ad metamorphism (Northern Somalia)

The Inda Ad Complex represents the metasedimentary cover of the crystalline basement of the Northern Somalia. It mainly consists of Upper Proterozoic or Cambrian sandstones, siltstones and shales, which only underwent a low-grade metamorphic event, of late Pan-African age. The aim of this work is to estimate the baric character of metamorphism recorded in this Complex. The method used is based on the measure of the 6d(33-1,060) cell dimension of K-white micas in metapelites. This parameter varies as a function of the metamorphic pressure, significantly at least within the greenschist facies and for metapelites having a specific Al-rich bulk composition. Therefore it has been necessary to define the petrographic characters of the rock samples utilized. The analytical results support the following conclusions: 1)The Inda Ad metamorphism took place under low pressure conditions; 2)Correlating the average value of the 6d(33-1,060) parameter to the metamorphic temperature recorded in these rocks (deduced from the mineral assemblages), it has been possible to estimate a thermal gradient of ca. 20#C/km for the Inda Ad metamorphic event.