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| Titel |
Crustal flow in western Yunnan, China, and along the Mogok belt, Myanmar |
| VerfasserIn |
Benita-Lisette Sonntag, Myo Min, Eva Enkelmann, Daniela Kornfeld, Lothar Ratschbacher, Jörg Pfänder, Raymond Jonckheere, István Dunkl |
| 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 |
250074834
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| Zusammenfassung |
| Keywords: crustal flow, Yunnan, Myanmar, fission track, cooling history
The mode of deformation along the eastern boundary of the northward moving Indian
block during the Cenozoic is still controversial. Models considered are: (i) southward lateral
extrusion of a single crustal block bounded by the right lateral Sagaing fault in Myanmar and
the left-lateral Aialo-Shan shear zone (ASSZ) in Yunnan; (ii) southward lateral extrusion of at
least two different crustal blocks between the right-lateral S(W)-striking Gaoligong Shan
shear zone (GSSZ), the NW-trending Chong Shan shear zone (CSSZ), and the ASSZ. We
present a radically different new model: the GSSZ and CSSZ constitute a folded
sub-horizontal detachment separating the brittle upper crust from the middle-lower crust
represented by the Mogok igneous and metamorphic belt. The kinematics of flow along the
detachment was dominantly top-to-S. Folding of the detachment was coeval with and
followed top-to-S flow. In the brittle crust, ~E-W shortening is expressed by a
fold-thrust belt, and in the ductile crust by L>S tectonites. The deformation pattern is
preliminary interpreted as reflecting gravitationally driven flow of upper crustal
material from Tibet towards SE-Asia, reminiscent to what is observed by GPS geodesy
today.
New Mogok-belt granitoid U-Pb zircon dates span the Early to Late Cretaceous
(peaks at ~125; 115; 90, and 65 Ma) and tie the Mogok belt to the Gangdese arc
of the Lhasa block. New Tertiary magmatic and metamorphic U-Pb zircon dates
are 40-30 Ma, similar to magmatism observed across SE-Asia and similar to the
monazite age of dikes that we interpret as pre-tectonic along CSSZ [1]. Published and
new 40Ar/39Ar dates show that rapid cooling, that we relate to onset of high-strain
deformation along the shear zones, started at 20-15 Ma [2, 3]. Fission-track and
(U-Th)/He thermochronology indicates that its activity continued at least to 6-3
Ma.
References:
[1] Akciz, S., Burchfiel, B. C., Crowley, J. L., Jiyun, Y., and Liangzhong, C.
(2008): Geometry, kinematics, and regional significance of the Chong Shan shear
zone, Eastern Himalayan Syntaxis, Yunnan, China: Geosphere, Febr. 2008, v. 4, p.
292-314.
[2] Lin, T.-H., Lo, S.-L., Hsu, F.-J., Yeh, M.-W., Lee, T.-Y., Ji, J.-Q., Wang, Y.-Z., and
Liu, D. (2009): 40Ar/39Ar dating of the Jiali and Gaoligong shear zones: Implications for
crustal deformation around the Eastern Himalayan Syntaxis: Journal of Asian Earth Science,
v. 34, p. 674-685.
[3] Zhang, B., Zhang, J, Zhong, D., Yang, L., Yue, Y., and Yan, S. (2012): Polystage
deformation of the Gaoligong metamorphic zone: Structures, 40Ar/39Ar mica ages, and
tectonic implications: Journal of Structural Geology v. 37, p. 1-18. |
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