 |
| Titel |
Fabric Analysis in the Koppal Granitoid (Southern India) using AMS and its significance in understanding the structural evolution of Dharwar Craton |
| VerfasserIn |
Sandeep Bhatt, Manish A. Mamtani, Virendra Rana |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250131050
|
| Publikation (Nr.) |
 EGU/EGU2016-11403.pdf |
|
|
|
|
|
| Zusammenfassung |
| The Dharwar Craton in southern India is known to have formed by the accretion of East
Dharwar Craton (EDC) and West Dharwar Craton (WDC) at ca. 2500 Ma. This
accretion occurred along the Chitradurga Boundary Fault (CBF), which is considered
to demarcate the WDC from the EDC (Chadwick et al., 2003). In recent years,
several structural studies integrating field, anisotropy of magnetic susceptibility
(AMS) and paleostress analyses have been carried out on metabasalts and granite
(Mulgund Granite) in the vicinity of Gadag town that lie in WDC, i.e., west of CBF
(Mondal and Mamtani, 2013; 2014; 2016). These have established the following: (a)
Rocks around Gadag have undergone three deformation events – D1/ D2 was due to
NE-SW compression that led to the development of NW-SE fabric elements in the
metabasalts and granitic rocks; the latter is manifested in the magnetic foliation recorded
from AMS. D3 was on account of NW-SE compression that led to doubly plunging
magnetic lineations. (b) The metabasalts are replete with quartz veins many of which
are gold bearing. These dominantly strike in NW-SE direction and formed due to
dilation during D3. (c) Strain partitioning took place at the contacts between the
Mulgund Granite and surround rocks resulted in development of oblique-slip normal
faults within the granite during late stages of D3. In comparison to such in-depth
knowledge of the WDC, structural evolution of the rocks of EDC has remained to be
poorly understood. Therefore, in the present study, the authors have focused on
rocks of the Koppal region that lie to the east of CBF in EDC. The objectives of the
research are to evaluate the deformation fabric in the region and compare the results
with those of the WDC (cited above) to understand the kinematics associated with
formation of the Dharwar Craton. To fulfill this objective, the authors have investigated
Peninsular Gneisses and granitoids (Koppal Granitoid) around Koppal town (61 km
east of Gadag). The field fabric recorded in the gneisses is having an orientation
varying from NW-NNW. In some parts of the Koppal Granitoid, a foliation with
NE-NNE orientation is recorded; however several parts of this granitoid do not
show a clear foliation. Therefore, to analyse the fabric in the granitoid, the authors
have carried out AMS analysis, and it is found that the mean orientation of the
magnetic foliation is NNE (20˚ /64˚ /110˚ ). These initial results indicate that whilst
the host rock (gneiss) has NW-SE fabric, the Koppal granitoid is dominated by
NE-SW planar fabric. This indicates that the granitoid fabric developed during
regional D3 deformation that was on account of NW-SE compression, which is in
contrast to the granitoids of WDC (Mulgund Granitoid). It is envisaged that further
integration of microstructural studies with the above information will enhance the
existing knowledge of the accretionary processes and kinematic evolution of Dharwar
craton.
References
Chadwick et al., 2003 B. Chadwick, V.N. Vasudev, G.V. Hedge The Chitradurga schist
belt and its adjacent plutonic rocks NW of Tungabhadra: Karnataka: a duplex in the late
Archean convergent setting of the Dharwar craton Journal of the Geological Society of India,
v.61, pp. 611–613.
Mondal, T.K., Mamtani, M.A. (2013). 3-D Mohr circle construction using vein
orientation data from Gadag (southern India) Implications to recognize fluid pressure
fluctuation. Journal of Structural Geology, v. 56, pp.45-56.
Mondal, T.K. and Mamtani, M.A., 2014. Fabric analysis in rocks of the Gadag region
(southern India)—Implications for time relationship between regional deformation and gold
mineralization. Tectonophysics, v. 629, pp.238-249.
Mondal, T.K. and Mamtani, M.A., 2016. Palaeostress analysis of normal faults in
granite–implications for interpreting Riedel shearing related to regional deformation. Journal
of the Geological Society, v.173 (1), pp.216-227. |
|
|
|
|
|
|