Evolution of Tethys Ocean and

Collision of INDIAN PLATE WITH

EURASIAN PLATE

By Mukhtiar Ghani

mukhtiarghani@upesh.edu.pk

Introduction The collision of Indian and Eurasian plates has significantly changed the

surface of the earth

Producing one of the most spectacular orogenic mountain ranges called the

Himalayas.

Contains some of the highest mountains on earth.

Triggering ice ages.

Evolution of Tethys Ocean

A super continent Pangea was formed about 300 My ago

It existed during late Paleozoic and early Mesozoic era

Covering much of the southern hemisphere unlike today

Pangea had two distinct divisions i.e. Laurasia and Gondwanaland

The Pangea was surrounded by a super ocean called Panthalassa

Smaller ocean called paleo Tethys ocean occupied an area between Laurasia

and Gondwanaland

It was narrow in the west and extremely wide in the east forming a gulf

290 Ma

The India-Asia collision is a part of a long accretion history of small

sized microcontinents

Originated from the break-up of Gondwanaland in the Paleozoic

(Bond et al., 1984).

progressively accreted from then on

contributed to the growth of the Asian margin southwards (Matte et

al., 1996).

These were accreted in three episodes:

(1) Variscan

(2) Cimmerian

(3) Alpine

The Cimmerian episode corresponds to the break-up of the

Cimmerian continent from the Gondwana margin.

Began in the Late Permian and was complete during the Triassic

(Sengör et al., 1988).

The closure of the Paleo-Tethys Ocean, and saturation of the

Cimmerian Continents occurred between Middle Triassic (Zanchi et

al., 2000).

Panjal trap volcanism and Peshawar plain alkaline igneous complex

are associated with opening of the Neo-Tethys Ocean (Honnegger et

al., 1982).

250 Ma

The Kohistan Ladakh terrain is characterized by intra oceanic arc

magmatic rocks,

Formed during Middle Cretaceous times (110 to 90 Ma)(Honegger

et al.)

These oceanic terrains are mainly remnants of arc-series reflecting

intra-oceanic subduction of the Neo-Tethys in the north.

The central part of the Karakoram terrain is comprised of the NW-

SE striking composite calc-alkaline Karakoram Batholith

Emplaced between 120 and 88 Ma in response to northwards

subduction of Tethyan oceanic crust (Debon et al., 1987)

These terrains were subsequently accreted to the Asian margin

during the Late Cretaceous (80 to 88 Ma)(Weinberg et al., 2000),

along the Shyok suture zone.

Gondwanaland split into two parts at about 210 Ma i.e. East

Gondwana and West Gondwana.

The Indian plate became a part of East Gondwana together with

Australia and Antarctica

In early cretaceous at about 130 million years ago India separated

from the other continents

Started rapid movement towards north covering a distance of 6000

km.

This happened because of formation of Indian ocean in the south

due to rifting

Ocean-ocean subduction in the northern margin of Tethys.

Finally the Tethys Ocean closed and India collided with Eurasia.

100 Ma

Collisional EventsThe exact time of collision of India with Eurasia is always debated

Estimated to have happened in range of 70 to 25 Ma.

Since 55 million years ago, India has steadily rotated counterclockwise

Coupled with Arabia's separation from Africa about 20 million years ago.

This rotation caused convergence in Baluchistan, closure of some of the

smaller basins (Seistan, Katawaz), collision of various crustal blocks in

Iran-Afghanistan region and formation of the Baluchistan fold-and-thrust

belt.

The India-Eurasia collision produced the spectacular Himalayas along

uplifted and deformed 2,500 km long Indo-Pakistan plate margin.

*Between 65 and 55 Ma, the Kohistan Ladakh Arcs were obducted

onto the Indian margin along the Main Mantle Thrust (MMT,

Tahirkheli et al., 1979).

*Magnetic studies have evidenced an abrupt decrease in

convergence rate, from 18-19.5 cm.y-1 to 4.5 cm.y-1, at ~ 50 Ma for

Patriat & Achache (1984)

*This drop in convergence rate coincides with a reduction in the

spreading rate of SW and central Mid-Indian Ocean ridge at 56 – 50

Ma (Molnar & Tapponnier, 1975)

The timing of the collision is constrained by extensive emplacement of

ophiolites along the Indus- Tsango Suture Zone, in Waziristan, Zhob

Valley and Lasbela area.

Along suture zones the youngest marine sediments are lower Eocene.

At places Indus molasse overlies Early Eocene limestone and contains

debris both of Eurasian and Indian terrains.

Compressional tectonic began after deposition of Early Eocene

Nummulitic limestone.

Thanks