METAMORPHOSED PRECAMBRIAN MAFIC ROCKS FROM THE SOUTH CARPATHIANS - ISLAND-ARC REMNANTS - A GEOCHEMICAL CHARACTERIZATION OF AMPHIBOLITES FROM THE FAGARAS MOUNTAINS, ROMANIA

This work describes general geochemical features of the Precambrian ma fic rocks, mainly amphibolites which occur extensively in two metamorp hic formations of the Cumpana Group, an important tectonic block incor porated in the Carpathian Belt. Direct and inverse approaches relate t he behavior of major and 29 minor, incompatible and compatible element s with the geological environment. The statistical regression of the m ajor element concentrations confirmed the two models according to whic h most of the amphibolites have originated from basaltic magmas, but a t the same time a part of them were derived from mechanical mixtures o f a similar igneous component and crustal sediments. The compositions of the possible parental liquids of the least fractionated sample, cor rected for olivine crystallization,were in equilibrium with mantle bet ween 15 and 22 kb. The REE modeling requires around 5% partial melting of a depleted mantle, initiated in the garnet stability field, possib le to exist in hydrous conditions. Furthermore, 20-90% fractional crys tallization of a clinopyroxene rich solid and its partial remelting ca n determine the observed REE abundances and chondrite normalized patte rns. The HFSE elemental ratios are characteristic of tholeiitic basalt s. On the average, the amphibolites are depleted in Nb and Zr, which i s a geochemical feature of continental or island are tectonic settings . The distribution of transition metal abundances is consistent with t he assumption that some parts of the stratigraphic sequence are potent ial hosts for terrigenous mixing processes. The strato-volcanic struct ure identified in the lithostratigraphic Group of Cumpana can be relat ed with the presence of an incipient island are.