Porella : features, morphology, anatomy, reproduction etc.
Southern granulite
1. Precamdrian study on
southern granulite terrane
of pan-african rejuvenation
PRESENTED BY
SANDIP SAHA
DIPANKAR BURAGOHAIN
LISA KOLE
MEERA RAJAN
SOHINI BHATTACHARYA
MEHEBUB –a-ALAM
2. CONTENTS
1.Introduction : Geological Settings
2.Geological Attributes of the Granulites Blocks
3.Structural set up of SGT
4.Metamorphic history of SGT
5.Pandyan Mobile Belt
6.Models and Evolutions
7.Discussion
8.Intracratonic Purana Basins in Peninsular India
Cuddahpah Basin
Kaladgi Basin
Godavari Basin
Vindhyan Basin
3. Introduction: Geological Settings
The Southern Granulite Terrain(SGT) is known as Pandyan Mobile Belt ,
The name is given by Ramkrishnan(1993, 1988)
SGT is situated to the south of the E-W trending Palghat-Cauvery
Shear Zone(PCSZ).
According to Fermor(1936), this terrain is a part of the large
“”Charnockite Province”” located to the south of the Orthopyroxene-in
isograd,delineated along a line straddling the Join Mangalore-Mysore-
Bangalore-Chennai.
4.
5. India’s Southern Granulite Terrain Consists of three late Archean to
Neoproterozoic,high-grade Metamorphic blocks, joined together.
The whole terrain is divided into two distinct crustal blocks-
1.The Northern Granulite Terrain(NBSGT)
2.The Southern Granulite Terrain(SBSGT)
The Northern Block (also known as the Salem Block) of the Southern
Granulites consists of a granulite massif at the southern edge of the
Dharwar Craton. The block is located between the ‘Fermor line’ and the
Palghat-Cauvery Shear Zone . Lithologies present in the Salem include,
pyroxene-bearing granites(charnockites), granite gneisses, and
migmatites (Devaraju et al., 2007; Clark et al., 2009).
6. Geological Attributes of the
Granulites Blocks
This terrain is dissected by Proterozoic shear zones that separate the
Granulite rocks into four regions or blocks---
1.Madras Block
2.Nilgiri Block
3. Madurai Block
4.Trivandrum Block
8. Structural set up of SGT
The multiple deformations experienced by the Archaean-Proterozoic
rocks have affected them differently in different sectors.
According to the Geological Survey of India (Sugavanam and
Vidyadharan, 1988), the granulite terrain is characterized by isoclinal and
Asymmetrical F1 folds with NNE-SSW axial planes, observed in both
2.6–2.5 Ga old charnockites and supracrustals. The superposed F2 folds
with WNW-ESE trend affected migmatites, granulites and 2450 Ma old
granites. The F3 are shear folds with N-S trend.
According to Mukhopadhyay et al. (2003),
the superposition of F2 on F1 folds produced interference patterns in the
Gneisses and granulites.
The sheared rock
9. The major fault and fracture systems of Tamil Nadu are oriented in the
following directions-
1.Nearly E-W to WNW-ESE
2.NNE-SSW to NE-SW
3.ENE-WSW
4.N-S
5.NW-SE
Vijaya Rao and Prasad (2006) proposed southwardsubduction of Dharwar
Craton beneath the SGT and proposed collision along the MBSZ inthe late
Archaean followed by crustal delamination.
Sanjeev et al . (2009) considered both MBSZ and PCSZ as parts a suture
zone between the Dharwar Craton and the Madurai Block that formed in
the Neoproterozoic-Cambrian during which UHT granulites developed.
However, the available geochronological and structural data do not
support thisinterpretation.
10. Metamorphic history of SGT
The SGT, India represents a very unique opportunity to study crustal
process at depth(Newton and Hansen, 1986). Modern studies with
textural imprints, mineral chemistry have improved our understanding
of the metamorphic evolution of the SGT.
UHT metamorphism in the south block of the SGT (Madurai Block) is
shown by the occurrence of sapphirine bearing granulite enclaves
within the gneisses (Prakash et al., 2010).
Madurai Block shows high grade metamorphic features including
preservation of excellent texture textures.
Lal et al. (1984) reported enclaves of Mg-Al granulites within the gneisses.
In Madurai Block wide variations in mineral assemblages are found in
different granulites facies rocks, especially Mg-Al granulites
11. Tectonic map of Southern India,
simplified after Drury and Holt (1980)
showing the major metamorphic and
structural subdivisions
12. Pandyan Mobile Belt
The Pandyan mobile belt (PMB), according to Ramakrishnan (1993), is
the geological domain between the PCSZ in the north and the AKSZ in
the south.
Ramakrishnan (2003) divided the enlarged Pandyan Mobile Belt into
Three zones.These zones are: (1) Northern Marginal Zone (NMZ),
(2) Central Zone (CZ), and (3) Southern Zone (SZ).
The NMZ lies just north of the E-W trending Moyar-Bhavani Shear zone
(MBSZ).This zone is characterized by the charnockite massifs of Shevaroy,
Javada, BRHills and Nilgiri.
The Central Zone, CZ (2) is located between the MBSZ and Noyil-Cauvery
shear zone (i.e. PCSZ). This zone consists of mainly high-grade
relics of older greenstone (Sargur Group), namely Satyamangalam Group.
13. The area lying to the south of the PCSZ is the Southern Zone (SZ). It
Contains charnockite-khondalite rocks. The SZ of the PMB,
according to Ramakrishnan(2003), contains two sub-units on either
side of the AKSZ. First is the Kerala Khondalite Belt (KKB) to the south of
the AKSZ and is predominantly formed of khondalite-leptynite suite with
subordinate charnockite. Second sub-unit is the Madurai Block to the
north of the AKSZ. It consists of quartzo-feldspathic gneisses;and
Charnockites.
With the basic information given above, the two different
evolutionary models of the Pandyan Mobile Belt are discussed…..
1. Subduction-Collision Model (Ramakrishnan, 1993, 2003, 2004)
2. Accretion Model (Radhakrishna and Naqvi, 1986)
