Abstract
Geological, petrographic, rock and mineral chemistry data of two gabbroic ocurrences, from the mountain region of Rio de Janeiro State, are presented in this article. The larger one corresponds to a gabbroic lense of almost 3 Km 2 outcropping area. It is surrounded by granitic rocks and intrudes migmatitic gneisses of the Ribeira Belt. Small lenses of melanogabbro are enclosed in metasediments and occur 15 Km west far from the gabbro.The gabbro essentially contains plagioclase An 45-47´ Opx (En 35-45 ) Cpx (diopsidic augite), porphyritic amphibole and biotite. Locally, quartzgabbro is found in the contact zone of gabbro andgranitic rocks. The neighbouring granitic rocks are quartzdiorite, granodiorite and leucogranite. The gabbro shows tholeiitic signature and develops trends with the calc-alkalic granitic rocks in variation diagrams.The melanogabbro contains olivine (Fo 63 ) and plagioclase (An 97 ). These minerais react to form coronas of Opx (En 70 ) amphibole and spinel/amphibole simplectites around the olivine. The melanogabbro is mterpreted as a cumulatic rock enriched in Mg, Ca, Sr and incompatible elements.A cogenetical link and contemporaneous intrusion for the gabbro, quartzgabbro and quartzdiorite is suggested based on contact relationships and geochemical signature. Such intrusion may nave been empiaced during or late the high grade regional metamorphism.A geochemical relation between the gabbro and the melanogabbro is not well stablished. Although they show similar REE patterns.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
