Multiple thrust systems from the Southern Granulite Terrane, India: Insights on Precambrian convergent margin tectonics
Graphical abstract
Introduction
The Southern Granulite Terrane (SGT), southern India, represents a key Gondwana collisional orogenic belt. The geological and structural complexities of the SGT are increasingly recognized and our understanding is still evolving despite several international collaborative efforts. One of the fundamental approaches that helps in resolving some of the mysteries of the SGT is to construct structural cross sections, although a challenging task, which would provide significant insights in unraveling the evolution history. Reconstructing structural cross sections is essentially based on the field observations such as lithological characteristics and their mutual relationships, planar and tectonic fabrics that help in tectonic interpretations and 3D visualization of the present day structural architecture with a view to unravel their genesis and progressive development in terms of geodynamics. The tectonic models that are derived from such studies require modification and refinement as and when additional new data is available through further researches. However, new comprehensive geochronological and petrological data are vital in these models.
It is now well established that the SGT constitutes a collage of crustal/tectonic blocks exposing mid- to lower crustal rocks traversed by crustal - scale suture/ shear zones amongst which Cauvery Suture Zone (CSZ) and Achankovil Shear Zone (AKSZ) (Chetty, 2017, Chetty et al., 2006 and the references there in), which are significant tectonic belts in the reconstruction models of Gondwana (Fig. 1). However, the features such as lithological variations, existence of shear zones, variable deformation from massive to intense mylonitisation, a range of complex fold styles like recumbent, isoclinal, deformed sheath fold geometries of different scales, multiple periods of deformation, different events of progressive and retrogressive metamorphic events and their geodynamic models related to the evolution of the SGT are still being debated, Recent studies provided a range of geochonological events from Archaean to Cambrian periods often adding to debates and discussion. Inorder to resolve some of them, an attempt has been made here to reconstruct interpretative multi-scale structural cross sections along the selected critical corridors of tectonic significance across the SGT, which provide insights and some exciting possibilities in addressing some of the geological issues that were hither to remained as enigmas.
Our new results together with a framework of a simple model of collision related subduction tectonics and the mechanisms in the development of mega thrust –nappe structures apparently show a broad systematic pattern that aids in resolving some of the above complexities and provide guidance to future researches. In this contribution, we present here multi-scale structural observations that led to the construction of regional structural cross sections reflecting the existence of mega thrust-nappe structures with in the SGT, which are genetically related to subduction zone tectonics.
Section snippets
General geological setting
The Southern Granulite Terrane (SGT) is one of the largest exposed Precambrian orogenic belts of India, consisting of multiply deformed Archean to Neoproterozoic high grade metamorphic rocks (Fig. 1). The major rock types include high-grade granulite facies rocks comprising essentially Neoarchean charnockites and their variably retrograded assemblages, pyroxene granulites, metasedimentary assemblages, which were subsequently intruded by Cryogenian anorthositic rocks, alkaline plutons,
Tectonic blocks of the SGT
It is widely accepted that the SGT constitutes a collage of tectonic blocks exposing mid- to lower crustal rocks and separated by crustal- scale shear/suture zones (see Fig. 1). The block in the north is Neoarchaean Northern Granulite Block (NGB) that occurs to the north of the CSZ and comprising north verging frontal fold-thrust belt. The Neoproterozoic Madurai Granulite Block (MGB) is located in the central part of the SGT and is limited by the CSZ in the north and the AKSZ in the south. The
Structural cross sections
Six north–south trending critical corridors in different parts of the SGT were chosen for detailed study considering the structural architecture, lithological characteristics and tectonic significance. The details of each corridor and the derived interpretative structural cross sections are based on the author’s extensive experience in the field and a variety of tectonic models proposed for orogenic belts in the modern literature. In order to have a comprehensive examination, a distinct
Transpressional tectonics
The transpressional tectonics in CSZ are characterized by vertical extrusion, variations in the geometry and disposition of different shear zones with consistent dextral strike-slip displacements implying that the YZ sections of the CSZ are important in accommodating the shortening in obliquely convergent tectonics of the SGT. Typical features such as: high-grade metamorphism characterized by a clockwise P-T-t trajectory with a steep isothermal decompressive segment, ductile strike-slip
Conclusions
- 1.
Field observations together with structural cross sections in critical segments suggest that the rocks of the SGT must have evolved through thrust-nappe tectonic processes resulting from convergent margin tectonics at the southern margin of the Dharwar craton.
- 2.
The pre-existing subhorizontal compositional banding and subparallel metamorphic gneissic foliation in charnockite massifs are completely overprinted through shearing giving rise to mylonitic fabrics and other complex structures at the
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Much of the work was carried out during my international collaborative programmes of INSA-JSPS and Indo-Australia in addition to DST-sponsored projects during my service at CSIR-NGRI. I owe my gratitude to all the organisations and my collaborators (Profs.Santosh, Alan Collins, Tsunogae and Bhaskar Rao) in the field as well as in the lab who encouraged and supported my interest and enthusiasm in pursuing my researches in understanding the evolution history of Proterozoic orogens of India.
References (78)
- et al.
Recumbent folds: key structural elements in orogenic belt
Earth-Sci. Rev.
(2014) - et al.
Kinematics, strain pattern and geochronology of the Salem-Attur shear zone: Tectonic implications for the multiple sheared Salem-Namakkal blocks of the Southern Granulite terrane, India
Precambr. Res.
(2019) Pan-African granitic magmatism in the Kerala Khondalite Belt, southern India
J. Asian Earth Sci.
(2006)- et al.
Petrology and U-Th-Pb geochronology of the sapphirine-quartz-bearing metapelites from Rajapalayam, Madurai Block, Southern India: Evidence for polyphase Neoproterozoic high-grade metamorphism
Chem. Geol.
(2007) - et al.
Crustal evolution of the Southern Granulite Terrane, South India: New geochronological and geochemical data for felsic orthogneisses and granites
Precambr. Res.
(2014) - et al.
Constrictive deformation in transpressional regime: field evidence from the Cauvery Shear Zone, Southern Granulite Terrain, India
J. Struct. Geol.
(2006) - et al.
Strain pattern and deformational history in the eastern part of the Cauvery shear zone, southern India
J. Asian Earth Sci.
(2006) - et al.
Proterozoic orogens in southern Peninsular India: Contiguities and complexities
J. Asian Earth Sci.
(2013) - et al.
Crustal architecture and tectonic evolution of the Cauvery Suture Zone, southern India
J. Asian Earth Sci.
(2016) - et al.
Crustal structure and tectonic evolution of the Southern Granulite Terrain, India: Introduction
Gondwana Res.
(2006)
SHRIMP U-Pb age constraints on the age of charnockite magmatism and metamorphism in the Salem Block, southern India
Gondwana Res.
Age and sedimentary provenance of the Southern Granulites, South India: U-Th-Pb SHRIMP secondary ion mass spectrometry
Precambr. Res.
Prograde and Retrograde Growth: An example from the Nagercoil Block, southern India
Geosci. Front.
Palaeoproterozoic ancestry of Pan-African high-grade granitoids in southernmost India: Implications for Gondwana reconstructions
Gondwana Res.
Zircion ages and Hf Isotopic Systematics reveal Vestiges of Mesoproterozoic to Archean crust with in late Neo proterozoic-cambrain high grade terrain of Southern most India
Gondwana Res.
A Pan-African thermal event in southern India
J. SE Asian Earth Sci.
The Cambrian collisional suture of Gondwana in southern India: a geophysical appraisal
J. Geodyn.
Lu-Hf isotope evidence for Paleoproterozoic metamorphism and deformation of Archean oceanic crust along the Dharwar Craton margin, Southern India
Precambr. Res.
Delineating crustal domains in Peninsular India: age and chemistry of orthopyroxene-bearing felsic gneisses in the Madurai Block
Precambr. Res.
Structure and tectonics of the Achankovil Shear Zone, southern India
Gondwana Res.
High-Mg low-Ni olivine cumulates from a Pan-African accretionary belt in southern India: implications for the genesis of volatile-rich high-Mg melts in suprasubduction setting.
Precambrian Res.
Retrogressed eclogite (20 kbar, 1020 °C) from the Neoproterozoic Palghat-Cauvery suture zone, southern India
Precambr. Res.
Anatomy of a Cambrian suture in Gondwana: pacific-type orogeny in southern India?
Gondwana Res.
Neoarchean suprasubduction zone ophiolite from Agali hill, southern India: petrology, zircon SHRIMP U-Pb geochronology, geochemistry and tectonic implications
Precambr. Res.
Cryogenian alkaline magmatism in the Southern Granulite Terrane, India: petrology, geochemistry, zircon U-Pb ages and Lu-Hf isotopes
Lithos
Subduction-accretion-collision history along the Gondwana suture in southern India; A laser ablation ICP-MS study on zircon chronology
J. Asian Earth Sci.
Cryogenian (~830Ma) mafic magmatism and metamorphism in the northern Madurai Block, Southern India: a magamtic link between Sri Lanka and Madagascar
J. Asian Earth Sci.
Charnockite genesis across the Archaean-Proterozoic terrane boundary in the South Indian Granulite Terrain: Constraints from major-trace element geochemistry and Sm-Nd isotopic systematics
Gondwana Res.
Manamedu complex: Geochemical constraints on Neoproterozoic suprasubduction zone ophiolite formation within Gondwana suture in southern India
J. Geodyn.
High-pressure granulites at the dawn of the Proterozoic
Geology
The application of single zircon evaporation and model Nd ages to the interpretation of polymetamorphic terrains: an example from the Proterozoic mobile belt of south India
Contrib. Miner. Petrol.
Sm-Nd and Rb-Sr ages and P-T history of the archean-sittampundi and bhavani layered meta-anorthosite complexes in cauvery shear zone, South-India - evidence for neoproterozoic reworking of archean crust
Contrib. Miner. Petrol.
Sm-Nd model ages and Rb–Sr isotope systematics of charnockites and gneisses across the Cauvery Shear Zone, southern India: implications for the Archaean-Neoproterozoic boundary in the Southern Granulite Terrain
Geological Society of India, Memoir
Electron microprobe dating of monazite from the Chittikara granulite, South India: evidence for polymetamorphic events
J. Geosci. Osaka City Univ.
The cauvery suture zone: map of structural architecture and recent advances
J. Geol. Soc. India
Proterozoic orogens of India: A critical window to Gondwana
Elsevier
Behaviour of stretching lineations in the Salem-Attur shear belt, southern Granulite Terrane, South India
J. Geol. Soc. India
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2022, Earth-Science ReviewsCitation Excerpt :The MBSZ (Moyar-Bhawani Shear Zone, Fig. 2d) and Chennimalai Noyil Shear Zone (CNZ Fig. 2d), equivalent to the PCSZ of Drury et al. (1984) mark the northern and southern boundaries of the CSZ, respectively (Fig. 2d). The CSZ is shown to be dominated by Archean granulites near the MBSZ, whereas proximal to the southern boundary, the rocks of Neoproterozoic age are more prevalent (Chetty et al., 2011; Chetty et al., 2016; Chetty, 2021). The ‘Northern Granulite Block’, CSZ and the ‘Madurai Granulite Block’, according to Chetty et al. (2011, 2016), constitute the ‘Southern Granulite Terrane’ (SGT, Fig. 2d).
Rb–Sr and Sm–Nd ages of the basement from Cauvery Basin: Crustal linkage to the Madurai Block, Peninsular India
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