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Retrogressive metamorphism in Central Bosnia dated by K/Ar and Ar/Ar methods on Hyalophane

The Mid-Bosnian Schits Mts. (MBSM) are the central part of the Inner Dinarides. The most widespread rocks of the MBSM are pre-Devonian metamorphics. Low-grade metamorphism affected them at 350-400°C and pressure of 3-5kbar. Permian is a time of intesive extrusions and intrusion of acid magmas building up huge masses of q-porphyries. The main phase of the Tethyan rifting was experienced during Ladinian. It brought about plutonic/hypabissal rocks of diorite, gabro, syenite and albite granite. Volcanics are basalts, spilites, andesites, keratophyres, dacites and pyroclastics. The opening of Tethyan Ocean took place during Upper Triassic and most of Jurassic and uplift of Dinarides during the Pyrenean phase. It was the time of commencement of retrogressive metamorphism and formation of Quartz-hyalophane Alpine veins in the already brittle metamorphic rocks. Fluid inclusion study on hyalophane determined (L(H20)+L(CO2)+V) type,with presence of N2 and CH4. Their P-T-t characteristics confirm origin from retrogressive metamorphic fluids developed during the Dinarides uplift. K/Ar age on hyalophane varies between 16.7+0.7 and 25.3+1.0 Ma, obviously affected by loss of Ar (suspected perthitization). Ar/Ar spectrum: a plateau age of 31.2+0.3 Ma has been obtained in the 731° to 1410°C temperature range, where 98.2% of Ar was released.

Mid-Bosnian Schits Mts; Dinarides; metamorphism; q-porphyries; Alpine veins; quartz; hyalophane; fluid inclusion; K/Ar; Ar/Ar; Bosnia

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