Garnet-bearing amphibolites as indicators of metamorphic conditions in the Krivaja-Konjuh ultramafic massif

Jugoistočno područje Krivajsko-konjuškog ultramafitnog masiva karakteriziraju zone metamorfnih stijena uključujući i stijene amfibolitnog metamorfnog facijesa. Istraživani granatski amfiboliti s područja Duboštice i Tribije pokazuju raznolikost u strukutrno-teksturnim karakteristikama. P–T putevi metamorfizma uzoraka napravljeni su uz pomoću cijelostijenske geokemije, geokemije minerala granata, rendgenskim mapiranjem granata te računalnim modeliranjem uz pomoć Perple_X-a. P–T putevi svih uzoraka odgovaraju clockwise modelu koji indiciraju retrogradne uvjete metamorfizma. Uzorci iz Tribije pokazuju varijabilnost u P–T uvjetima formiranja stijena. Jedan od njih je je dao uvjete formiranja jezgre granata pri tlaku od 21,25 kbar i temperaturi 1050°C karakteristično za P–T raspon granulitnog facijesa, dok su za rub determinirani tlakovi od 10,5 kbar i temperatura 840°C. Drugi uzorak iz Tribije daje uvjete formiranja jezgre pri 4 kbara i 575°C, a onaj iz Duboštice formiranje jezgre pri 4 kbara i 550°C. Uzorak iz Tribije s većim uvjetima formiranja nastao je dublje a protolit mu je bazalt N–MORBA, dok su ostala dva nastala iz bazalta plićih oceanskih područja. Sve stijene pripadaju intraoceanskom subdukcijskom okolišu.In the South-eastern part of Krivaja-Konjuh ultramfic masiff exist zones of metamorfic rocks which contain variates of amphibolites. Investigated amphibolites from Duboštica and Tribija show structural and textural petrografic variabilities. P–T paths of samples were reconstructed using whole rock composition, cemical composition of garnets, X-ray mapping of garnets, and thermodynamic and graphic results made by Perple_X. All of samples contain P–T results of isopleths of garnets that show clockwise model. That indicates retrograde conditions of metamorphism. One of the samples from Tribija shows heigher P–T conditions of garnets. It includes forming of garnet's core, implying, pressure of 21,25 kbar and temperature of 1050°C, while its rim includes pressure about 10,5 kbar and temperature about 840°C. It can suggest deeper origin of that sample which can belong to granulitic facies. Its protolith is basalt of N-MORB. Other sample from Tribija gave P-T conditions of forming garnet's core. Calculated pressure is 4 kbar and temperature of 575°C, as similar as, sample from Duboštica which includes P–T conditions of 4 kbar and 550°C. They were derived of basalt from shallower oceanic areas. All of samples belong to intraoceanic subduction environment