Publication details
Three phases activity of the Clay Fault (Barrandian)
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| Year of publication | 2015 |
| Type | Conference abstract |
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| Description | The Clay Fault was recognized in mines of the Příbram and Bohutín ore district and named by ancient miners. The dip varies from 70° to NW to nearly vertical. Havlíček classified this structure as an overturned synsedimentary normal fault. He deduced the Cambrian age of the fault base on his geological map, where lower Paleozoic basalt dike cross-cuts the fault surface. Deformation zone near Clay Fault is by observation of Březové Hory mines powerful up to 60 m. It is possible to distinguish three distinct phases of fault activity. There is mylonite zone with distinct (two) types of mylonites of different ages – the older mylonite with slickenside in the dip direction and the younger mylonite with subhorizontal slickenside. Last fault activity is documented by the youngest tectonic clay (several centimeters powerful in core Clay Fault) that gave the name to the structure. This tectonic clay crosses also variscan Bohutín tonalite, unlike older mylonites. This indicates that the last movement at this break must occur after its intrusion. The fact, that the clay is still in slippery, incoherent form proofs its very young, Neogene age probably. It seems from the course of Clay Fault that it is crosscutting by younger oblique faults corresponding roughly to the direction of NS because the shift is indicated also by the shift in the other structures (lithological body, discordance surface). This geometry of deformations shows that the last movement on Clay Fault was along the dip direction of the fault plane. The last phase belongs to the “dip-slip” faults group, but it is not possible to clearly determine its sense of movement. The older mylonites (mostly external) of Clay Fault have distinct striations on foliation surfaces oriented along the dip direction. There are microscopically observed deformations with S-C structures and asymmetric pressure shadows around clasts. Macroscopically visible interlayer slips shows postsedimental character of deformations already in hard rock. Senses of movements, direction of lineation and distribution/partition of deformations in the Příbram syncline indicate a logical conclusion about the reverse fault clay character during the earliest phases of movements. Příbram Syncline is by its foundation the consequence of deformation of Clay Fault. N-W wall was dragged along the Clay Fault. Possible compression and reverse fault can be considered only in the Middle Devonian. This movement can be placed in the time between Frasnian and Westphalian. The middle phase of activity corresponds to sinistral strike-slip displacement with a slight rotation and can be classified by the intrusions of Blatná granodiorite on the edge of Tournaisian and Visean. At this time Clay Fault and Závist Fault were the same fault structure. Besides the kinematics of sinistral strike slip fault the rotation is applied (Knížek & Melichar, 2014). |