GONDWANALAND AND

TECTONISM

Presented by –Debasis Pal, Roll No. 414ER2020

Archchi Sarkar, Roll No. 414ER2024M.Sc. Applied Gelogy, 3rd Semester

National Institute of Technology, Rourkela

INTRODUCTION The continent of Gondwana or Gondwanaland was named by Austrian

scientist Eduard Suess, after the Gondwana region of central northern India (from Sanskrit gondavana - "forest of the Gonds“). The name had been used in a geological context, first by H.B. Medlicott in 1872, from which the Gondwana sedimentary sequences (Permian-Triassic) are also describe.

Gondwana formed prior to Pangaea, then became part of Pangaea, and finally drifted after the breakup of Pangaea.

Gondwana is believed to have sutured between about 570 and 510 Mya, thus joining East Gondwana to West Gondwana. It separated from Laurasia 200-180 Mya (the mid-Mesozoic era) during the breakup of Pangaea, drifting farther south after the split.

Span of Gondwanalandin GTS

Evidences that it existed…1. Paleoclimatic evidence - Ancient climatic zones match up when continents are moved back to their

past positions. • Glacial tillites • Glacial striations • Carbonate deposits • Evaporite deposits

2. Late paleozoic glaciation - Late Paleozoic glaciation patterns on southern continents are best explained

by their reconstruction into Gondwanaland

3. Fossil Evidence Supporting Plate Tectonics -

4. Paleomagnetism and Pole Locations

• Studies of rock magnetism allowed determination of magnetic pole locations (close to geographic poles) through time.

• Paleomagnetism uses magnetic mineral alignment direction and dip angle to determine the direction and distance to the magnetic pole. Steeper dip angles indicate rocks formed closer to the north magnetic pole.

• Rocks with increasing age point to pole locations increasingly far from today’s poles.

5. Fit of rock units and boundaries

• Improved fit results in rock units (and glacial ice flow directions) precisely matching up across continent margins.

Formation of Gondwanaland The assembly of Gondwana was a protracted process. Several orogenies led

to its final amalgamation 550–500 Mya at the end of the Ediacaran, and into the Cambrian. These include the Brasiliano Orogeny, the East African Orogeny, the Malagasy Orogeny, and the Kuunga Orogeny. The final stages of Gondwanan assembly overlapped with the opening of the Lapetus Ocean between Laurentia and western Gondwana. During this interval, the Cambrian explosion occurred.

Gondwana was formed from the following earlier continents and microcontinents, among others, colliding in different orogenies:

•Azania: much of central Madagascar, the Horn of Africa and parts of Yemen and Arabia (Named by Collins and Pisarevsky (2005): "Azania" was a Greek name for the East African coast.)

•The Congo–Tanzania–Bangweulu Block of central Africa;

•Neoproterozoic India: India, the Antongil Block in far eastern Madagascar, the Seychelles, and the Napier and Rayner Complexes in East Antarctica

•The Australia/Mawson continent: Australia, the west of Adelaide and a large extension into East Antarctica

•Other blocks which helped to form Argentina and some surrounding regions, including a piece transferred from Laurentia when the west edge of Gondwana scraped against southeast Laurentia in the Ordovician. This is the Famatinian block (named after Famatina in northwest Argentina) and it formerly continued the line of the Appalachians southwards.

Reconstruction showing final stages of assembly of Gondwana, at 550 Mya.

One of the major sites of Gondwanan amalgamation was the East African Orogeny (Stern, 1994) at 650–630 Mya, where these two major orogenies are superimposed. This orogeny affected a large part of Arabia, NE Africa, E Africa, and Madagascar. Collins and Windley (2002) propose that in this orogeny, Azania collided with the Congo–Tanzania–Bangweulu Block.

The later Malagasy orogeny at about 550–515 Mya affected Madagascar, eastern East Africa and southern India. In it, Neoproterozoic India collided with the already combined Azania and Congo–Tanzania–Bangweulu Block, suturing along the Mozambique Belt.

At the same time, in the Kuunga Orogeny Neoproterozoic India collided with the Australia/Mawson continent.

• Gondwana began to break up in the early Jurassic (about 184 Mya) accompanied by massive eruptions of basalt lava, as East Gondwana, comprising Antarctica, Madagascar, India, and Australia, began to separate from Africa. South America began to drift slowly westward from Africa as the South Atlantic Ocean opened, beginning about 130 Mya during the Early Cretaceous, and resulting in open marine conditions by 110 Mya. East Gondwana then began to separate about 120 Mya when India began to move northward.

• The Madagascar block, and a narrow remnant microcontinent presently occupied by the Seychelles Islands, were broken off India; elements of this breakup nearly coincide with the Cretaceous–Paleogene extinction event. The India–Madagascar–Seychelles separations appear to coincide with the eruption of the Deccan basalts, whose eruption site may survive as the Réunion hotspot.

• Australia began to separate from Antarctica at 80 Mya (Late Cretaceous), but sea-floor spreading between them became most active about 40 Mya during the Eocene epoch of the Paleogene Period.

• New Zealand probably separated from Antarctica between 130 and 85 Mya.

The break-up of Gondwanaland involves two major time periods – the Jurassic and the Early Cenozoic.

JURASSIC

Break-up and Drifting

• The continent of Australia-New Guinea began gradually to separate and move north at 55 Mya, rotating about its axis and thus retaining some connection with the remainder of Gondwana for about 10 million years.

• At ~45 Mya, Indian Plate collided with Asia, buckling the crust and forming the Himalayas. At about the same time, the southernmost part of Australia (modern Tasmania) finally separated from Antarctica, letting ocean currents flow between the two continents for the first time. Antarctica became cooler and Australia became drier because ocean currents circling Antarctica were no longer directed around northern Australia into the subtropics.

• The separation of South America from West Antarctica some time during the Oligocene, perhaps 30 Mya, also caused climate changes. Immediately before this separation, South America and East Antarctica were not connected directly.

• By about 15 Mya, the collision between New Guinea and the SW part of the Pacific Plate pushed up the New Guinea Highlands, causing a rain shadow effect which drastically changed weather patterns in Australia, drying it out.

• Later, South America was connected to North America via the Isthmus of Panama, cutting off a circulation of warm water and thereby making the Arctic colder, as well as allowing the Great American Faunal Interchange.

CENOZOIC

Dispersal of Gondwanaland

The relative positions of the continents at any time are determined by paleomagnetic measurements. Rocks formed at a certain time freeze in the local magnetic field. The direction of the field tells the distance to the magnetic pole (paleolatitude). Magnetic anomalies on the sea floor also provide a history of the opening of the ocean.

References • Wikipedia and many other internet sources

• Weddell Sea tectonics and Gondwana break-up: an introduction by E. C. KING, R. A. LIVERMORE & B. C. STOREY, British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK

• The Geological Society of America – Lyell Collection

That’s all, folks!