 |
| Titel |
Structures, microfabrics, fractal analysis and temperature-pressure estimation of the Mesozoic Xingcheng-Taili ductile shear zone in the North China craton |
| VerfasserIn |
Chenyue Liang, Franz Neubauer, Yongjiang Liu, Wei Jin, Zuoxun Zeng, Manfred Bernroider, Weimin Li, Quanbo Wen, Guoqing Han, Yingli Zhao |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088707
|
| Publikation (Nr.) |
 EGU/EGU2014-2849.pdf |
|
|
|
|
|
| Zusammenfassung |
| The ductile shear zone in Xingcheng-Taili area (western Liaoning Province in China) is
tectonically located in the eastern section of the northern margin of the North China craton,
and dominantly comprises deformed granitic rocks of Neoarchean and Triassic to Late
Jurassic age, which were affected by shearing within middle- to low-grade metamorphic
conditions. Because a high-temperature metamorphic overprint is lacking, microstructures
attesting to low-temperature ductile deformation are well preserved. However, the rocks and
its structures have not been previously analyzed in detail except by U-Pb zircon dating and
some geochemistry. Here, we describe the deformation characteristics and tectonic
evolution of the Xingcheng-Taili ductile shear zone, in order to understand the
mode of lithosphericscale reactivation, extension and thinning of the North China
craton.
The ductile deformation history comprises four successive deformation phases: (1) In the
Neoarchean granitic rocks, a steep gneissosity and banded structures trend nearly E–W (D1).
(2) A NE-striking sinistral structure of Upper Triassic rocks may indicate a deformation event
(D2) in Late Triassic times, which ductile deformation structures superimposed on
Neoarchean granitic rocks. (3) A gneissose structure with S-C fabrics as well as an
ENE-trending sinistral strike-slip characteristic (D3) developed in Upper Jurassic biotite
adamellite and show the deformation characteristics of a shallow crustal level and generated
mylonitic fabrics superimposed on previous structures. (4) Late granitic dykes show different
deformational behavior, and shortening with D4 folds. The attitude of the foliation S and
mineral stretching lineation of three main types of rocks shows remarkable differences in
orientation.
The shapes of recrystallized quartz grains from three main types of granitic rocks
with their jagged and indented boundaries were natural records of deformation
conditions (D1to D3). Crystal preferred orientation of quartz determined by electron
back scatter diffraction (EBSD) suggest sinistral strike-slip displacement within a
temperature at about 400 to 500°C. Quartz mainly shows low-temperature fabrics with
dominant {0001}-slip system. As the deformed rocks show obvious deformation
overprint, we have estimated flow stresses from dynamically recrystallized grain sizes of
quartz separately. But coincident fractal analysis showed that the boundaries of
recrystallized grains had statistically self similarities with the numbers of fractal
dimension from 1.153 to 1.196 with the range of deformation temperatures from 500 to
600°C, which is corresponding to upper greenschist to lower amphibolite facies
conditions. Together with published flow laws to estimated deformation rates between
the region of 10-11 - 10-13 S-1depending on the temperature 500 °C, and the
paleo-stress was calculated with grain size of recrystallized quartz to be at 5.0 to 32.3
MPa. Even though the deformation history and kinematics are different, progressive
microstructures and texture analysis indicate an overprint by the low-temperature
deformation (D3).
Typical regional-dynamic metamorphic conditions ere deduced by mineral pair
hornblende-plagioclase and phengite barometry identified within the ductile shear zone. The
hornblende-plagioclase pair of porphyritic granitic gneiss gives metamorphic conditions of
T =450–500 °C and p=0.39 GPa, which indicate a metamorphic grade of lower-amphibolite
facies conditions and a depth of around 13 km estimated following a normal lithostatic
pressure.
All of the structural characteristics indicate that the Xingcheng-Taili ductile
shear zone represents a mainly ENE-striking sinistral ductile strike-slip zone, which
formed after intrusion of the Upper Jurassic biotite adamellite and transformed and
superimposed previous deformation structures. This deformation event might have
occurred in Early Cretaceous times and was related to the lithospheric thinning and
extension, due to roll-back of the Pacific plate beneath the eastern North China craton. |
|
|
|
|
|
|