Petrologic features of mesoproterozoic lamprophyric dykes from Montevideo (Piedra Alta terrane, South Uruguay)

Mafic dykes of lamprophyric affinity cropping out along the coastal area Montevideo city are described. These trend N75º-85º and crosscut 2.1 Ga Paleoproterozoic metamorphic units Rio de la Plata craton. They show mainly porphyritic textures with phlogopite clinopyroxene macrocrysts in a groundmass composed carbonates, phlogopite, augite, feldspathoids. Ocellar structures filled by leucite, carbonates fibrous alkaline amphibole present. The mineralogical assembly allows their classification as lamprophyres (minettes), but according to chemical nature, they can be classified lamprophyres. A crystallization age 1.42 Ga, Ar-Ar method (on biotite/phlogopite) was obtained.