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| Titel |
3D and 2D inversion of magnetotelluric data from the continental collision zone in the Pamirs and Tien Shan, Central Asia |
| VerfasserIn |
Paul Sass, Oliver Ritter, Anatolii Rybin, Vladislav Batalev |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250072900
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| Zusammenfassung |
| Many geodynamic processes governing intra-continental collisional orogeny are largely
unexplained and controversial. A key question is the state and dynamic behaviour of the
lithosphere at middle and lower crustal levels while continental collision progresses. The
Pamir – Tien Shan region in Central Asia may be the best location on Earth to study such
lithospheric deformation processes in situ. The mountain ranges and high plateaus formed at
the tip of the north-western Indian promontory through the Cenozoic experienced rates of
shortening similar to the adjacent Himalaya-Tibet system. Today, the Pamir – Tien Shan
orogenic belt hosts some of the deepest active intra-continental subduction zones on Earth
and absorbs the highest strain rate over the shortest distance that is manifested in the
India–Asia collision zone. The multi-disciplinary Tien Shan – Pamir Geodynamic
Program (TIPAGE) was designed to address some of the geodynamic key questions in
this region. A magnetotelluric (MT) survey was carried out in concert with other
geophysical and geological observations in Kyrgyzstan and Tajikistan, predominantly
along a 350 km long and 50 km wide corridor from southern Tajikistan to Osh in
Kyrgyzstan across the Pamir Plateau and southern Tien Shan mountain ranges. In total we
recorded MT data at 178 stations, 26 of them combine long-period and broad band
recordings. We present and compare 2D and 3D MT inversion results. Strike analysis
of the data revealed an overall mean geo-electric strike direction consistent with
the predominant tectonic trends. 2D inversion yields a reasonable data fit, with
exception of some sites which exhibit phases above 90 degrees. 3D inversion was
carried out with the ModEM package. We inverted for all four impedance tensor
components and the vertical magnetic transfer functions. Topography was also included.
The 3D models are generally in agreement with the 2D results but achieve a better
data fit, particularly phases which could not be fitted with 2D inversion. The MT
inversions reveal an upper crust of the Pamirs, which is generally resistive, with
embedded conductive parts correlating to suture zones. Several distinct zones of high
conductivity appear beneath the southern Pamirs and the central/northern Pamir
at mid crustal levels, possibly reaching mantle depths. We interpret the southern
mid-crust conductor as hot and partially molten, viscous felsic material. To the
north, the conductor is bound by a resistive block which correlates with the miocene
gneiss of the Muskol dome. The second conductive zone north of the Muskol dome
could originate from brittle and fractured crust. Faults and old deformation zones
can form pathways for aqueous fluids in the crust. When highly mineralized fluids
penetrate fractured brittle areas, the entire region can become conductive. Further
north, the seismically active Main Pamir Thrust which separates the Pamir from the
Tien Shan corresponds to a sharp, south-dipping conductivity contrast between
resistive upper crust in the Pamirs and conductive crust beneath the Alai valley. |
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