A Mátyás-hegyi feltolódás „fejlődéstörténete”

Abstract

The northern (upper) yard in the south-western quarry of the Mátyás Hill is considered as one of the classic sites which exposes the Triassic/Eocene contact. In the last century several, often contradictory descriptions were published
about the structural position of the outcropping Triassic dolomite. It was usually interpreted as a formation which thrust over the Eocene limestone; however, according to the different authors the place and direction of the tectonic surface are
different.
The source of the problems is that this part of the quarry was abandoned in the earliest stage and no descriptions are available from its one-time condition. The geological characteristics were damaged by the quarrying. Moreover, due to
the continuous collapse of the wall and the 6–10-m-high scree at the foot of the wall several features have been hidden. The matter is more complicated, because the features can be seen in a multiply broken-lined section; the average direction
of the section, in which the Triassic core of the fold is exposed in 10–190° direction, whereas the direction of the long wall towards the South is 130–310°. The breccia in the wall was interpreted by previous authors (SCHAFARZIK, PÁVAI, JASKÓ,
SCHRÉTER, etc.) as a friction breccia derived from the Triassic limestone (in fact dolomite) which stands out along the north-eastward dipping steep surface.
The breccia is of different genetics in FODOR's work; due to synsedimentary reverse faulting the emerging Triassic block has been broken into pieces and its other part has been shifted onto the abrasional debris at the foot of the wall.
Based on the latest studies the SE–NW fracture (described as a reverse fault in the literature) is situated within the Triassic dolomite; the Triassic-Eocene contact has not been moved by it, thus its pre-Late Eocene age can be reasonably assumed.
The Triassic block was in almost horizontal position; it had not been affected by considerable tilting in the Late Eocene. Its eroded (karstified) surface was covered with a thin layer of terrestrial sediments. Over time, after its subsidence, it became overlain by an approximately 1 km-thick Upper Eocene – Oligocene succession. Subsequently, the succession was folded forming parallel folds and, compared to the north-eastern limb, the south-western limb underwent flexure-like, 40–50 m bending down along a 120–300° axis. The steep, south-western limb of the fold is almost parallel to the Triassic-Eocene contact at the foot of the wall. Due to plastic deformation this part was located in a depth of at least 1 km under the well insulating cover; therefore the folding cannot be considered as older than End-Oligocene.
This type of fold is in connection with compressive forces; however, these forces have not led to regional folding because the blocks avoid it by uplift and subsidence (by faulting and reverse faulting in a wider sense); deformation
occurred only in narrow zones. Due to stronger compression these zones may be torn up forming an imbricate structure. The tilting of the area, characterized by south-eastward dipping, took place after the folding. For lack of appropriate
overlying sediments its exact age cannot be determined; nevertheless, it is older than the thermal water activity considered as Pleistocene.