ARC RELATED JURASSIC IGNEOUS AND META-IGNEOUS ROCKS IN THE COASTAL CORDILLERA OF NORTHERN CHILE REGION ANTOFAGASTA

A deep section of the Jurassic, 200-150 Ma old magmatic arc is exposed in the Coastal Cordillera south of Antofagasta in northern Chile. The chemical compositions of metabasic and plutonic rocks from the deep l evel are compared with those of Jurassic volcanic rocks and almost-equ al-to 150 Ma old dykes. The metabasites, most of the plutonic rocks, a nd the dykes have calc-alkaline characteristics. However, small postme tamorphic gabbro plutons are tholeiitic. The composition of the volcan ic rocks is not related to the plutonic rocks, metabasites and dykes. All igneous and meta-igneous rocks of the arc are derived from a simil ar source in the upper mantle and evolved without major crustal contam ination. The general tectonic setting was dominated by extension, and Pre-Jurassic crust is extremely thinned or absent in the area. Details of the tectonic, magmatic and metamorphic development remain still a matter of speculation.