| © 2008 by SourceSink consortium - all rights reserved |
Problem statement: In several aspects the Apuseni Mountains are quite outstanding: they are rather circular in shape, they separate two large basins (Pannonian and Transylvanian) with very different characretistics and they are bordered by suture zones on either side.
The proposed project intends to address 1) the internal tectonometamorphic evolution of the Apuseni mountains from the emplacement of the South Apuseni ophiolites to the late-stage cooling and exhumation and 2) the tectonic interaction of the Apuseni Mountains with the surrounding basins.
Apart from the scientific aspects this IP also provides substantial information of social and economic interest. The economic evolution of the former eastern countries also involves the construction of new roads and railways. The outcomes of this project serve as inevitable prerequisites for such projects, especially with respect to tunnels. The Apuseni Mountains form an obvious obstacle to traffic and are currently only crossed by second order roads and railways which clearly ask for reconstruction in the nearer future.
Major tectonic units of the Alps, Carpathians and Dinarides (Schmid et al., 2008, Swiss Journal of Geosciences)
Aims and objectives: The circular shaped Apuseni Mountains are bordered by two basins of rather distinct character and evolution: the Miocene Pannonian basin in the west and north with a rather flat topography and the hilly Transsylvanian basin with its two-stage evolution. The northern part of the Apuseni mountains belongs to the the Tisza-unit, a microplate with mixed European and Adriatic affinity, which extends from NE Croatia into Romania and is mostly covered by the Neogene infill of the Pannonian basin. The Tisza unit presently forms a top to the NW-directed Turonian-age nappe stack which comprises from bottom to top the Mescek (only outcropping in southern Hungary), the Bihor (northern Croatia and Apuseni mountains) and the Codru (Apuseni Mountains) nappe systems. Most authors also attribute the tectonically highest Biharia nappe system (Bleahu et al., 1981; Balintoni, 1994) to the Tisza microplate (e.g. Csontos & Vörös, 2004). The Biharia nappe system itself is tectonically overlain by the South Apuseni ophiolites (or Transylvanides according to Sandulescu, 1984) defining the “Main Tethyan suture” between Tisza and Dacia which formed during mid-Cretaceous orogeny (Sandulescu, 1994). However, when combining surface information in the Apuseni Mountains (e.g. Balintoni, 1994) with subsurface information from the eastward located Transylvanian basin (Matenco et al., 2007) it becomes evident that the Biharia nappe is without interruption connected with the easterly located Bucovinian (or Getic/Supragetic) nappes of the Dacia unit. They form one and the same tectonic unit with takes the structurally highest position in the East Carpathian nappe stack. Although already partly formed during the late Jurassic, final east-directed emplacement of the Transylvanides occurred during the mid-Cretaceous. According to this correlation Turonian NW-directed thrusting led to a substantial offset of the former suture and thrusted Dacia-derived units (Biharia) against the Codru nappe system of Tisza with the western prolongation of the former suture buried underneath the Apuseni mountains.
While the southern continuation of the south Apuseni Mountains into the Eastern Vardar ophiolites is well accepted there is no clear answer in the north. Either the Eastern Vardar-South Apuseni ophiolites represent the remnants of a northerly ending branch of Neotethys (failed arm) or it has to be sutured between the continuously documented Biharia-Bucovinian nappes and the underlying Codru nappe system.
Based on these models and ideas concerning the tectonic evolution and paleogeographic correlation of the Apuseni Mountains the proposed study tries to address the following questions:
- Structural and metamorphic evolution of the different units outcropping in the Apuseni mountains
- Direction of thrusting and emplacement along first order contacts during the distinct events
- Cooling and exhumation history of the various units and formation of the present dome
Thus we expect to answer the following questions and contribute to the Source-Sink topic:
- Characterization of kinematics and activity of main tectonic contacts should allow for correlation with tectonic contacts in the wider Alpine Carpathian Dinaride context
- Characterization of the cooling and exhumation history of the Apuseni mountains, from when on did the area serve as a source region
- Was the exhumation of the Apuseni Mountains continuous or discontinuous both in space and in time?
- Were any pre-existing faults reactivated to allow for its exhumation?
- Is the exhumation of the Apuseni Mountains linked to the shortening in the Transylvanian basin?
- Are the Apuseni Mountains at least partly responsible for the distinct Tertiary tectonic evolution of the Pannonian and Transylvanian basin respectively?
Innovation: In the light of the newly proposed paleogeographic correlation (Biharia as part of Dacia, Schmid et al., submitted) the main tectonic contacts ask for re-examination and evaluation. Base on a detailed description of early (ductile?) faults their possible (brittle?) reactivation during the late stage evolution will be addressed. Existing zones of weakness exert a fundamental control on the ongoing tectonic evolution of mountain belts and thus allow for rather unexpected map patterns and features such as en echelon fault arrays, positive and negative flower structures, releasing and restraining bends etc.
A further aspect worth mentioning is the possibility to study the coupling of tectonic forces between “weak” basins and “strong” basement during extension and compression. Close collaboration with IP 02 (exchange of IP 02 post-Doc) focuses on the correlation of the tectonic evolution of the surrounding basin and the Apuseni Mountains.
Added value: The Apuseni Mountains “pop-up” exerts a fundamental control on the otherwise connected Pannonian and Transylvanian basins. Exact knowledge of its exhumation history is crucial for both, the drainage pattern as well as their further evolution in terms of erosion vs. deposition in the light of the tectonic evolution.
Methodologies/experiments: This strongly field based this study applies state of the art structural geology with respect to plastic and brittle deformation assisted by geochronology (Ar-Ar, Rb-Sr, Sm-Nd), low-temperature geochronology (fission track- and (U-Th)/He analyses) and thermobarometry. Shear sense indicators and microstructures/textures will be investigated in SL tectonites related to the ductile evolution of the working area. Apart from kinematic data this provides syndeformational temperature information further constrained by thermobarometry (PT estimates on mineral parageneses) and thermochronology (dating of syndeformationally grown minerals). Brittle deformation will be investigated by fault-plane analysis and elaboration of individual sub-sets in close collaboration with IP 09. The low cooling and exhumation history will be continuously documented by Ar/Ar analyses on feldspar (collaboration with VU Amsterdam) and fission-track analyses on zircon and apatite. This provides a continuous cooling path from peak metamorphic conditions down to about 60°C by application of thermal modelling of apatite fission-track data (track lengths in combination with apparent ages). Further insight in the cooling and exhumation history will be provided by integration of detrital ages (IP01) which bear information on the eroded part of the Apuseni mountains.
Deliverables and/or milestones: The project will generate coherent datasets on the tectonometamorphic evolution of the main units within the Apuseni Mountains. This not only allows for a better understanding of its internal evolution but also serves as an input parameter for 4D modelling approaches with clear constraints on the exhumation of this intra-basin barrier. Furthermore the generated in-situ fission-track cooling ages allow for better interpretation of age patterns derived from detrital samples. On the other hand data from detrital samples will help to further constrain the cooling history towards older ages.
|
