geographia - Studia

I. MAC, N. HODOR, MARIA HOSU
The Oaş Mountains stretch from the Huta Pass (587 m) and the western slopes of
the Igniş Massif to the South, up to the large Tisa Valley at North and Northwest. Towards
West and Southwest, because of the interference of the volcanic structures with the Western
Plain sedimentary ones, the bounder follows a sinuous course along, the hummocks and the
volcanic ridges alternating with gulf depressions. However, the line linking the localities
Seini, Medieş-Vii, Turlung-Vii şi Halmeu-Vii may be considered as the limit between the
two tectono-structural units.
The volcanic structures cover around 178 km 2 , among which 97 km 2 represent
lava flows, 41 km 2 rooted bodies and 40 km 2 pyroclastic accumulations. This situation is
unusual for a „pacific type” volcanic area, but it may be explained through the vigorous and
long erosion that determined a drastic reduction of the pyroclastic formations and lava flows.
3. SPECIFIC GEOLOGIC AND GEOMORPHOLOGIC FEATURES
In comparison to the other volcanic mountains in the Eastern Carpathians, Oaş
Mountains are individualized by some specific features:
a) petrographic diversity: rhyiolites, dacites, microgranodiorites, microdiorites,
andesites (pyroxenic, amphybolic, quartzite, basaltic, with a prevalence of the pyroxenic ones);
b) polycyclic magmatism, the most evident cycles being the Badenian –
Bassarabian, the Pannonian and the Pontian-Romanian;
c) structural variety: intrusive bodies (laccolites, dykes, necks), effusive volcanic
forms with central eruption, associated volcanic bodies, volcanic cupolas, isolated volcanic
bodies, rooted bodies etc;
d) differentiation in the way the volcanic structures fit up into the region’s
geologic system:
− subvolcanic bodies developed on the Pannonian sedimentary structures through
secondary uplifting mechanisms (of diapir type – Geamăna Massif);
− volcanic bodies sized through negative isostasic movements (postvolcanic
collapse - the Cămârzana caldera, developed between Geamăna, CetăŃeaua Mică and
Holmurile Hummocks);
− volcanic bodies at the intersection of several faults (magmatic nuclei);
− isolated (singular) magmatic bodies, as the western hummocks or the Măguriciu
one, near Bixad;
e) high degree of fragmentation and prevalence of the negative landforms -
depressions, corridors, differential erosion saddles. The lowest areas follow the main river
channels:
− Oaşului Depression, developed on the crustal fracture that separates the
Pannonian domain from the Carpathian one (Tur River inferior course);
− TârşolŃ channel – on a graben;
− Lechincioara – Cămârzana passage channel;
− Tămăşeni– Bătarci – Bocicău passage channel.
Positive morphostructures with various genetic conditions and preservation
degrees stretch between the above mentioned river channels and depressions:
− Călineşti-Fraşin tectono-magmatic horst (SSV – NNE);
− Sirlău – Dealul Viilor – Oul – Târlung-Vii knolls microhorst;
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