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| Titel |
The co-genetic evolution of metamorphic core complexes and drainage systems |
| VerfasserIn |
Georg Trost, Franz Neubauer, Jörg Robl |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127135
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| Publikation (Nr.) |
 EGU/EGU2016-6972.pdf |
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| Zusammenfassung |
| Metamorphic core complexes (MCCs) are large scale geological features that globally occur
in high strain zones where rocks from lower crustal levels are rapidly exhumed along discrete
fault zones, basically ductile-low-angle normal faults recognizable by a metamorphic break
between the cool upper plate and hot lower plate. Standard methods, structural analysis and
geochronology, are applied to reveal the geodynamic setting of MCCs and to constrain timing
and rates of their exhumation. Exhumation is abundantly accompanied by spatially and
temporally variable vertical (uplift) and horizontal motions (lateral advection) representing
the tectonic driver of topography formation that forces drainage systems and related
hillslopes to adjust. The drainage pattern commonly develops in the final stage of exhumation
and contributes to the decay of the forming topography. Astonishingly, drainage
systems and their characteristic metrics (e.g. normalized steepness index) in regions
coined by MCCs have only been sparsely investigated to determine distinctions
between different MCC-types (A- and B-type MCCs according to Le Pourhiet et al.,
2012). They however, should significantly differ in their topographic expression that
evolves by the interplay of tectonic forcing and erosional surface processes. A-type
MCCs develop in an overall extensional regime and are bounded partly by strike-slip
faults showing transtensional or transpressional components. B-type MCCs are
influenced by extensional dynamics only. Here, we introduce C-type MCCs that are
updoming along oversteps of crustal-scale, often orogen-parallel strike-slip shear
zones.
In this study, we analyze drainage systems of several prominent MCCs, and compare their
drainage patterns and channel metrics to constrain their geodynamic setting. The Naxos MCC
represents an A-type MCC. The Dayman Dome located in Papua New Guinea a B-type
MCC, whereas MCCs of the Red River Shear Zone, the Diancang, Ailao-Shan and Day Nui
Con Voi complexes, show structural features of the C-type endmember. In the case
of the Diancang complex, the MCC is even superimposed by late stage B-type
dynamics. The Tauern window and Lepontine dome in the Alps are described as C-type
MCCs. We extracted drainage systems and basins and calculated Strahler orders to
explore asymmetries in the drainage pattern and to detect evidence for horizontal
advection of rivers and catchments. We computed longitudinal river profiles and
determined the normalized steepness indexes for channels to uncover regions of spatially
variable uplift rates and to constrain the state of landscape adjustment at active
MCCs. Furthermore, we analyzed the stability of watersheds by computing so called
χ-maps.
A-type MCCs show a drainage pattern, which is partly parallel to the stretching and
elongation direction, potentially developing from grooves of the detachment. The B-type
MCCs show preferences for a radial oriented drainage pattern along lateral terminations. The
radial morphology is overprinted by fault systems and neighboring uplifted domes beside the
investigation site. A clear preferred direction for further capturing of catchments can be
described along detachment zones. The results show an asymmetric alignment of the drainage
networks of C-type MCCs, caused by tilting and lateral offset of the streams. One side of the
valley shows short streams, whereas the other side is characterized by long, deeply
incised streams with a clear tendency to capture adjacent catchments. In C-type
MCCs, the drainage pattern develops perpendicular to the trunk streams, which are
subparallel to confining faults. The tributaries of the trunk valleys show often dragging in
shear direction of the confining fault. The drainage pattern along ductile low-angle
normal faults seemingly develops parallel to these faults and shows an asymmetry
due to tilting towards the hangingwall block. The analysis reveals that the three
types of MCCs can be distinguished by their drainage pattern. All three types have
a distinct central drainage divide in common, which is getting elongated in the
stretching direction in C-type MCCs and remains small in B-type MCCs. Further
early results of our analysis show the high potential of employing morphometric
tools in combination with methods from structural geology and low temperature
geochronology to determine the type of MCCs, to reveal timing and rates of uplift and
horizontal advection, and to constrain the state of landscape adjustment at active
MCCs. |
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