Petrochemical characteristics of Precambrian amphibolites from the northern parts of the Central Rhodopes

Abstract

Ortho- and paraamphibolites in the northern part of the Central Rhodope Mts. are metamorphosed into amphibolite facies showing no traces of migmatization. This study is an analysis of the major and trace elements, REE included. Part of the orthoamphibolites represented by amphibolized metabasalts and garnet amphibolites are products of a subvolcanic autochthonous magmatism of tholeiitic affinities. Geochemically, they are comparable to the island-arc igneous rocks. The mrtabasalts show high alumina contents, varying iron and titanium contents and a tholeiite-like REE distribution. The garnet amphibolites are characterized by high iron and titanium contents. The predominating role of garnet in these rocks is reflected in the marked prevalence of HREE among REE and in the negative europium anomaly. Some bedded amphibolites of unknown origin show similar geochemical characteristics combining the features of island-arc and of ocean-floor tholeiites. The paraamphibolites differ sharply from the typical orthoamphibolites in their much lower iron, titanium and vanadium contents and higher calcium, aluminium, zirconium and LREE contents. Fe, Ti, Mg. V, Cr, Ni, Zr, Hf and REE are relatively immobile elements during metamorphism and their ratios can be reliably used to distinguish, characterize and determine the primary features of the amphibolite rock groups.