The Indian Keystone of Gondwana: Protolith Affiliation, Age and Significance of Metamorphism of the Southern Granulite Terrane of India

Project Investigators

Project Collaborators

Professor M. Santosh (Kochi University)

Doctor Christopher Clark (Curtin University)

Project Details

The Cambrian biotic explosion (~600-500 Ma) occurred in a world dominated by vast mountain ranges that linked Australia to Antarctica, India and East Africa (Fig. 1). These ranges formed by the agglomeration of much of the planet's continents to form the super-continent Gondwana (Fig. 1). The roots of these ranges (known as orogenic belts) today form a time capsule preserving evidence of the geography of the time, the nature of the collisions between the constituent plates of Gondwana, the timing of these collisions and a record of the dynamic processes that occurred at this key period of Earth history.

This project aims to resolve a key outstanding problem in the timing and nature of the Gondwana-forming collision by integrating fieldwork in southern India with state-of-the-art geochronology. The timing and nature of the amalgamation of Gondwana is a hot topic in geodynamics with recent work transforming the traditional view of a 'simple' collision of two mega-continents - East Gondwana (Australia, India and Antarctica) and West Gondwana (Africa and South America) - to one of piecemeal amalgamation of Australia-scale continental blocks throughout the Neoproterozoic (1000-543 Ma - million years before present) (Fitzsimons, 2000; Powell and Pisarevsky, 2002; Boger and Miller, 2004) . The nature and timing of these Gondwana-forming collisions, and even their locations are the subject of considerable controversy (Fig. 1). In one popular model, India collided with East Africa at ~630 Ma along the East African Orogen (Fig. 1), whereas a subsequent ~550 Ma orogen, known as the Kuunga or Pinjarra Orogen, resulted from the collision of Australia, Antarctica and Southern Africa with the previously amalgamated India and East Africa (Fig. 1) (Meert and Van der Voo, 1997; Meert, 2003) . A second current model is that individual continental blocks progressively collided with the East African margin, with collisions younging eastward (Kröner et al., 2000) . A third view is that India acted as a wedge, colliding at ~550 Ma with both Western Australia and East Africa (Collins et al., 2004a; Collins et al., 2004b).

Fig. 1: Reconstruction of Gondwana at 530 Ma (after Reeves and de Wit, 2000) showing the interpreted sites of the East African and Kuunga/Pinjarra Orogens (Meert, 2003) . Az = Azania, a metacraton consisting of much of central Madagascar, east Ethiopia, Somalia and part of Arabia (Collins et al., 2004a) . RP = Rio Plata, SF = Sao Franciso, Sah = Sahara metacraton, WA = West Africa, Ru = Ruker Terrane, Maw = Mawson craton, Aus = Australia.

Southern India lies in the key position to resolve these models: at the junction of the proposed Kuunga and East African Orogens in the first model; within a young collision zone in the second model, and; at the leading edge of an indenting India in the third model. To significantly contribute to resolving these models with the available resources and within the available time, the aims are to:

• Undertake focussed field studies of key locations in Neoproterozoic/Cambrian orogenic belt of Southern India to investigate the structural setting of geochronological sample.
• Date the protoliths of meta-granitoids and meta-sedimentary gneisses by analysing zircon on the Perth Sensitive High-mass Resolution Ion MicroProbe (SHRIMP), to a) investigate granitoid protolith ages to test whether the rocks are related to Indian rocks further north, or share closer affiliations with other continental units in Gondwana; b) to examine the metasedimentary age provenance record to investigate possible source terranes of these rocks.
• Date the zircon metamorphic rims using the SHRIMP to tie down the age of high-grade metamorphism in this region.

Indian keystone sub-projects

Age, origin and tectonic significance of mafic gneisses in the Palghat-Cauvery shear zone system.

Northern Madurai Block: tectonic evolution.