1 ULTRAMAFIC K-ALKALINE AND CARBONATITIC ROCKS FROM PLANALTO DA SERRA, MATO GROSSO, BRAZIL A. De Min1, P. Comin-Chiaramonti1*, C.B. Gomes2., .A.V. Girardi2, F. Slejko1, E. Ruberti2 1Mathematics and Geosciences Department, Trieste University: Via Weiss 8. I-34127 Trieste, Italy. 2Instituto de Geociências, University of Sao Paulo, Cidade Universitária, Rua do Lago, 562, 05508-900 São Paulo, Brazil. *Corresponding author: e-mail:
[email protected] ABSTRACT The Planalto da Serra lithotypes are represented by 600 Ma plugs and necks of glimmerites and carbonatites. Phlogopite and/ or tetraphlogopite are the most abundant minerals of the glimmerites. Carbonatites comprise granular hypidiomorphic alvikites and brecciod beforsites. Diopside and melanitic garnet are restricted to the glimmerites, whereas pyroclore occur only in carbonatites. Perovskite, tremolite, magnetite, pyrite, apatite, titanite, chlorite and serpentine are common accessories of both lithologies. Under high CO2 and H2O activity glimmerites and carbonatites gave rise to hydrotermalites, in which chlorite and serpentine are the predominant minerals (up to 70%).They derived from tremolite, diopside and sometimes from olivine. Pyrite is a common accessory. Glimmerites, alvikitic dykes and hydrotermalites have kamafugitic affinity. Sr-Nd isotopes and incompatible trace-element data, characterized high LREE/HREE fractionation suggest that the K-ultramafic alkaline and carbonatite rocks originated from a varied metasomatized source mantle, characterized by Sr radiogenic enrichment. Crustal