Structure and Geochronology of the Wayanad Schist Belt, Western Dharwar
Craton, Southern India
Abstract
The Wayanad Schist Belt (WSB) located along the southern margin of the
Western Dharwar Craton (WDC) is a small discontinuous schistose belt
occur as pockets and patches within basement gneisses. WSB is oriented
parallel to the E-W trending Moyar Shear Zone (MSZ) separating the WDC
and Southern Granulite Terrane (SGT). The major rock types include
metapelitic schists, metamafic schists, banded magnetite quartzite,
pyroxene granulite, amphibolite, metapyroxenite, mylonite,
hornblende-biotite schist/gneiss, micaceous quartzite etc. The fabrics
in schistose rocks are defined mostly by the orientation of
shape-preferred aggregates of biotite-chlorite-muscovite-sillimanite (in
metapelites) and tremolite-talc-chlorite-actinolite (in metamafites).
Whereas the gneissic fabric is defined by the quartz-plagioclase rich
leucocratic layers and biotite-garnet-amphibole-pyroxene rich
melanocratic layers. The WSB has undergone at least three phases of
deformation. The most prominent fabric in WSB is the E-W to ESE-WNW
trending sub-vertical foliations developed during the D3 deformation.
Poles to the steep-dipping S3 foliations are WNW-ESE trending and the F3
folds are steeply plunging in nature. At the low strain domains of D3
deformation the early foliations are preserved. The N-S to NNW-SSE
trending sub-vertical S2 fabric developed axial planar to moderately
tight to open (F2) folds during D2 deformation. The early S1 foliations
are rarely preserved in the interfolial domains of S2 foliation. In the
regional scale, the poles to S1 fabrics lie on a well-defined girdle
with NE-SW trending upright asymmetric folds. The U-Th-total Pb dating
of texturally controlled monazites from WSB has yielded prominent age
populations at around 700-850 Ma and 500-600 Ma with minor age peaks at
2.2-2.3 Ga, 2.4-2.6 Ga. The structural and chronological data suggest
that, the deformation events in WSB are similar to that reported from
the WDC. However, the D3 deformation is more prominent and all the
earlier fabrics are truncated or brought into parallelism with the S3
fabric during D3 deformation. The 700-850 Ma and 500-600 Ma monazite
growths post-tectonic with respect to the D3 deformation indicates that
the Neoproterozoic accretionary events affected the whole SGT must have
recrystallized the monazites present in the MSZ.