Discussion
Geochronological data correlated with specific magmatic and metamorphic imprints as described in the previous section allow us to visualize the evolution of the EGB in large canvass of ~1250 m.y. (~1.76-0.50 Ga), summarized in Table 1. It follows that the present configuration is a result of crustal growth in a phase-wise manner during this time span (Fig.2). We are excluding the ~2.8 Ga granulite metamorphism in Jeypore Province at this stage in the absence of compelling petrological and structural data.
Table 1. Global geological events during Paleo-Neoproterozoic supercontinental cycles vis-à-vis events in EGB, India (Compiled from Zhao et al, 2004, Li et. al., 2008 and references therein, events in EGB are referred in accordance with the text).
| Major Global Geological Events | Continents | Time Period |
|---|---|---|
| Earth’s existing continents began to collide and finally coalesced into a pre-Rodinian supercontinent named “Columbia” evident from matching patterns of two pairs of rifts in the Columbia River region of western North America and Eastern India. Global scale collisional orogens were recorded e.g. Trans-Hudson Orogens in N. America, Nagssugtoqidian Orogen in Greenland, Kola-Karelia, Volhyn-Central Russian and Pachelma Orogens in E. Europe, Transamazonian and Eburnean Orogens in S. America and W. Africa, Capricorn Orogeny in Australia, Creek Orogen in N. Australia, Central Indian Tectonic Zone in India and Trans-North China Orogen in N. China. | Pre-Rodinian Supercontinent “Columbia” | 2.1- 1.8 Ga |
| Growth of supercontinent Columbia | ||
| 1. Accretionary zone along the western margin of the Amazonia craton. | South America | 1.8-1.3 Ga |
| 2. An accretionery magmatic belt is extensively exposed as inliers surrounding the southern and eastern margins of the North Australian Craton and the eastern margin of the Gawler Craton, represented by the Arunta, Mt. Isa, Georgetown, Coen and Broken Hill Inliers. | Australia | 1.8-1.5 Ga |
| 3. An accretionery magmatic zone, called the Xiong’er belt (Group), extends along the southern margin of the North China Craton. | China | 1.5-1.3 Ga |
| 4.Granulite-grade metamorphism and magmatism in connection with probable accretionary orogeny in Krishna Province, EGB (Bose et al., 2008; Upadhyay et al., 2009), Banded Gneissic Complex, Aravalli (Buick et al., 2006; Sarkar et al., 1989), metamorphism and emplacement of felsic gneiss along the Napier-Rayner province boundary in E. Antarctica (Kelly et al., 2002), granulite-grade metamorphism in Bhopalpatnam granulite belt (Santosh et al., 2004) and Shillong Plateau Gneissic Complex (Chatterjee et al., 2007). | India | 1.76-1.6 Ga |
| Fragmentation and final break-up of Supercontinent Columbia | ||
| One of the most characteristic features of Mesoproterozoic geology is widespread continental rifting and anorogenic magmatism presumably due to mantle plume diapirism and asthenospheric upwelling. Continental rifting in Western Laurentia (1.6-1.2 Ga), Siberia (1.6-1.3 Ga), Northern China (1.8-1.4 Ga); Anorogenic magmatism in Baltica, Ural Mountains, Ukriane and Peninsular India (1.6-1.2 Ga), widespread alkaline ultrabasic rocks, represented by kimberlites, lamproites and carbonatites in West Africa, South Africa, India, South America and Western Australia (1.4-1.2 Ga). Major episode of plate-wide extension and rifting was marked by the intrusion of many mafic dike swarms and associated basaltic extrusions in North America Greenland, Baltica, north China, South America, East Antarctica, Western Australia and Central South Australia. Emplacement of alkaline rocks along the western margin of EGB and concomitant boundary shear zone (Biswal et al., 2001; Upadhyay et al., 2006). | ||
| Formation of supercontinent Rodinia (ca. 1100 – 900 Ma) | ||
| Collision of Yangtze craton with Laurentia at southern Cathaysia when Laurentia, Siberia, North China, Cathaysia (part of present day South China) and possibly Rio de la Plata were already together. King island, Tasmania, and the South Tasman Rise were close to the collision of Yangtze and Laurentia. Amalgamation of Australian craton and East Antarctica part of the Mawson craton occurred. | Growth of Rodinia | 1100 Ma |
| Formation of Rodinia | ||
| Kalahari collided with southern Laurentia and Continued collision of the Yangtze craton with western Laurentia. Development of convergent margins between most continents where oceanic lithosphere were consumed between them during assembly of supercontinent Rodinia. | 1050 Ma | |
| All continents assembled to be joined with Laurentia except India, Australia–East Antarctica and Tarim. The Yangtze craton was still suturing to Cathaysia part of Laurentia. The transpressional movement between Greater India and Western Australia advanced. | 1000 Ma | |
| All major continental blocks aggregated to form supercontinent Rodinia. | 900 Ma | |
| Orogenic events during this period: | ||
| 1) Arc volcanics and ophiolite obduction in the eastern Sibao Orogen of South China | South China | 920–880 Ma |
| 2) Arc volcanics along the northern margin of the Yangtze craton | Yangtze craton | 950–900 Ma |
| 3) High-grade metamorphic events in both the Eastern Ghats Belt of India and the corresponding Rayner Province in East Antarctica | India and East Antarctica | 990–900 Ma |
| 4) The Corn Creek Orogeny sometime | Northwestern Laurentia | between 1033 Ma and 750 Ma |
| 5) Southern Capricorn Orogen | West Australian craton | 900 Ma |
| 6) King Leopold Orogen | North Australian craton | 900 Ma |
| Break-up of Rodinia | ||
| Superplume events and continental rifting: | ||
| Beginning of Rodinia break-up is represented by first sign of a Rodinia superplume, a small number of 870–850 Ma intrusions such as those in South China and Africa. Ca. 845 Ma and 870 Ma bimodal intrusions are reported from the Scandinavian Caledonides and the Scottish promontory of Laurentia. | ca. 860 – 570 Ma | |
| Magmatism like mafic dyke swarms, intra-continental mafic–ultramafic intrusions, and felsic intrusions (resulting from crustal melt or magma differentiation) is commonly found in the polar end of Rodinia only, including Australia, South China, Tarim, India, Kalahari, and the Arabian–Nubian terranes. Felsic magmatism and metamorphism in Chilka domain of EGB (Simmat and Raith, 2008; Upadhyay et al., 2008; Bose et al., 2008) and anorthosite (?) magmatism (Dobmeir and Simmat, 2002). Ca. 800 Ma felsic magmatism (Shaw et al., 1997) is reported from domain boundary shear zone (NVSZ, Fig. 1). | 825 Ma | |
| Origin of Gondwanaland | 600–530 Ma | |
| The Rodinia supercontinent fragmented around Laurentia with continental pieces that was moving away from Laurentia and colliding to form Gondwanaland. West Gondwana was largely together by ca. 600 Ma. By ca. 550 Ma India moved closer to its Gondwanaland position along the western margin of Australia along the Pinjarra Orogen. Kalahari started to collide with Congo and Rio de la Plata, thus closing the Neoproterozoic Adamastor Ocean between them. North China separated from Laurentia–Siberia after ca. 650 Ma was drifted toward Australia at that time. Final thrusting of EGB with Bastar craton on west and Singbhum craton on north ~550 Ma, granulite-grade metamorphism in Chilka domain of EGB (Bose et al., 2008), Rengali province (Dobmeir and Raith, 2003). | ||
| Finally Gondwanaland amalgamated by ca. 540–530 Ma. | ||
| Major orogenic events during this period | ||
| The Malagasy Orogeny in the East African Orogen | ||
| India tied up to Australia–East Antarctica along the Pinjarra Orogen. |
Figure 2. Supercontinental cycles in India-Antarctica sector
Correlation of events related to supercontinental cycles in India-Antarctica sector during Precambrian time (modified after Harley, 2003). Chronology of events are followed after Harley (2003) and references cited in the present study. Domains and abbreviations are as the appear in figure 1.
The earliest high-grade metamorphism under UHT condition in the Krishna Province (Ongole Domain) occurred at ~1.76 Ga and it was soon followed by magmatism during ~1.72 - 1.70 Ga. Documentation of these events in the EGB has important consequences for the growth history of the supercontinent Columbia (ca. 2.1-1.8 Ga) (Rogers and Santosh, 2002; Zhao et al., 2002, 2004). Columbia is postulated to have undergone long-lived subduction-related growth via accretion at key continental margins for nearly 500 Ma. This history is shared by major accretionary belts surrounding cratonic blocks of Laurentia, Antarctica, South Africa and Australia. Traces of tectonothermal activity of similar age are recorded from the Aravalli Craton of northwestern India, where granulite-grade metamorphism and emplacement of orthopyroxene-bearing TTG suite of rocks took place at ~1.72 Ga (Sarkar et al., 1989; Buick et al., 2006). It is likely that the ~1.76 - 1.70 Ga growth history of Columbia encompassed the southern part of EGB.
The ~1.60 Ga tectonothermal event in southern EGB (Ongole Domain) is often correlated with the juxtaposition of Napier Complex of east Antarctica with Eastern Dharwar Craton (Harley, 2003; Dobmeier and Raith, 2003; Upadhyay et al., 2009). Identification of similar ~1.60 Ga tectonothermal imprints from other mobile belts surrounding cratonic blocks of India (Shillong Plateau Gneissic Complex by Chatterjee et al., 2007; Bhopalpatnam Granulite Belt by Santosh et al., 2004) are also encouraging. In a different viewpoint, this event was responsible for suturing the cratonic blocks of northern and southern India through the Central Indian Tectonic Zone (CITZ). Combining all the evidenc, we may postulate that the geographical span of this event was a result of the (more far-fetched) assembly of cratonic blocks of India and east Antarctica. The ~1.76 – 1.60 Ga history of the EGB thus can be correlated with the growth of the supercontinent Columbia.
Alkaline rock complexes of the EGB were intruded during ~1.50 – 1.30 Ma (Upadhyay, 2008 and references therein) and metamorphosed by Grenvillian and Pan-African events (Upadhyay et al., 2006). These rocks are interpreted to form in rift-related tectonic setting during break up of Columbia (Upadhyay, 2008). Evidence of rift-related magmatism is widespread along the margins and interior of Columbia (Zhao et al., 2004 and references therein). However, regional structural analysis suggests development of a fold-thrust belt at the north-western part of EGB (Biswal et al., 2001) with concomitant formation of terrain boundary shear zone and synkinematic alkali magmatism at ca. 1400 Ma (Biswal et al., 2001; Upadhyay, 2008). The tectonic framework is inconclusive as the geochemical affinity of these alkaline suites indicates extension related magmatism (Upadhyay et al., 2006).
The UHT metamorphism in the Eastern Ghats Province (~1.25-1.10 Ga?) was followed by a separate pervasive granulite grade metamorphism and associated deformation during ~950-900 Ma. This latter part of the history has a strong resemblance to the evolutionary history of Rayner Complex of east Antarctica (Kelly et al., 2002; Harley, 2003 and references therein). This led most of the researchers to conceive that the Eastern Ghats-Rayner belt amalgamated Indian and Antarctic cratons during the assembly of the next supercontinent Rodinia (Veevers, 2009 and references therein). Absence of younger pervasive granulite-grade events in this composite belt demonstrates that it was cratonized with India during ~900 Ma.
Strong presence of ~800-700 Ma tectonothermal activities in the granulites of Chilka Domain and lower grade rocks of Rengali Province is diagnostic. Thermal activities during this time frame are documented from Aravalli Craton (Malani Igneous Suite, Torsvik et al., 2001), Cauvery Shear zone (Bhaskar Rao et al., 1996), parts of Prydz Bay (Kelsey et al., 2008; Wang et al., 2008), Western Rayner Complex (Shiraishi et al., 2008), south China (Zhao et al., 2002) and Leeuwin Complex (Collins, 2003). In all these occurrences, this broad time frame witnessed the disintegration of Rodinia. Magmatic and metamorphic signatures in most of such occurrences show rift-related setting (reviewed in Li et al., 2008) for which little analogous data exists in the EGB (~800 Ma granite emplacement in the Rayagada by Shaw et al., 1997).
The ~550-500 Ma granulite-grade events in the Chilka Domain and amphibolite-grade events in the Rengali Province trace the Pan-African signatures in the EGB. Available geochronological data suggest that the Pan-African front swap through the northern part of the EGB. This event left its strong presence in south India, Madagascar, east Africa, Sri Lanka, east Antarctica, Australia and south America (Li et al., 2008 and references therein). It caused the final docking of India with east Antarctica and Australia during the assembly of the third supercontinent Gondwana. The present configuration of the EGB was finally achieved when its northern segment was thrust over the Singhbhum Craton with a westward vergence (Dobmeier and Raith, 2003). Discrete segments of EGB thus recorded three time-punctuated courses of development (Fig. 2). The amazing fact is, all these events and their interkinematic gaps coincided with the assembly and demise of three extinct supercontinents.