EDIACARAN (~600 MA) ROSETTA GABBRO FROM THE NORTHERNMOST ARABIAN-NUBIAN SHIELD, SOUTH JORDAN: MINERALOGY, GEOCHEMISTRY AND PETROGENESIS

The Rosetta Gabbro has a unique "dandelion" spherical texture that consists of amphibole cores from which large plagioclase euhedra radiate. This rock is exposed as small outcrops in south Jordan (max 200x200 meters) tht could be magma pipes in surrounding granitic rocks, and is part of the ~600 Ma granitic complex exposed in SW Jordan. The 3D flower-like texture is similar is to “Chrysanthemum Stone”, which is a diagenetic growth in much softer sedimentary rock. The “amphibole-plagioclase flowers” range continuously in diameter from aggregates that are essentially groundmass to spheres of a few mm up to a maximum of 30 mm; all central sections of the flower have an amphibole core. Tabular radiating plagioclase typically are complexly twinned, with broad lamellae and show no optical zoning.

Amphibole occurs in two forms: 1) large grains which are riddled with opaques; the areas of high opaque concentrations are more Mg-rich, leached light green areas with relict brown amphiboles. Some diopside relics are included in amphibole. The cores of the flowers have amphiboles that are in most cases transformed into granular and angular; and 2) acicular mass of yellowish-light green actinolitic amphibole. Scattered flakes of phlogopitic mica also occur.

The groundmass of this rock contains amphibole and plagioclase in proportions that are roughly 2:1. Furthermore, the groundmass contains smaller spheres with an amphibole core and a plagioclase rim though the flower texture is not well developed as in the larger ones.

It is hoped to get a better understanding of how this rock has formed with the help of rock and mineral chemistry that’s now being carried out.