The Darnó Unit within the Zagorje-Mid-Transdanubian Megaunit is an allochtonous part
of Dinarides in NE-Hungary and represents a relict of the Neotethyan accretionary
complex. It contains blocks of submarine basalts of Triassic age in turbiditic sediments
(olistrostrome) of Jurassic age. The lava clogged in the lime mud at the original
site ofvolcanism and developed closely packed pillow, pillow fragment hyaloclastite
breccia, and peperite facies. Interaction between the lava and the sea water produced
mostly chloritic alteration of basalt and precipitation of hydrothermal calcite in
amygdales, feeding channels of lava lobes and hyaloclastite breccia cements. Calcite
is associated with chlorite, epidote, hematite and pyrite. Fluid inclusions in calcite
infillings record conditions of fluid/rock interaction. Salinities of fluid inclusions
(3.2-5.6 wt.%. NaCl equiv. wt.%.) are close to the salinity of recent sea water and
their homogenization temperatures are in the range of 80-150°C. Fluid inclusion data
support interpretation that volcanic fades represent rapidly cooled distal zones away
from the submarine volcanic centre. This is also confirmed by the comparison to the
volcanic and hydrothermal alteration facies of the submarine basalt lava-flow complex
and associated pillow lava formation of Triassic age in the Hruškovec quarry in the
Kalnik Mts., NW-Croatia. The obtained data contribute to understanding of the early
history of Neotethyan evolution, i.e. dilemma about rifting or oceanization in Triassic
time and offer new aspects of correlation between units of Dinaridic origin which
had been displaced from their original setting by large scale Tertiary tectonic processes.
