1. Presented By :-
Ajoy Saikia
M.Sc. Sem.-1, 2013
Dept of Earth & Environmental Science
KSKV Kachchh University

2.  What are Ophiolites ???
 Ophiolites are techtonicaly emplaced
successions of mafic and ultramafic rocks that
are considered to represent fragments of
oceanic or back-arc basin crust.

3.  An ideal ophiolite includes from bottom to top the
following units :
1. Ultramafic tectonite (generally harzburgites)
2. Layered cumulate gabbros and ultramafic
rocks
3. Non-cumulate gabbros, diorites and
plagiogranites
4. Sheeted diabase dykes
5. Pillowed basalts

4. An idealized
ophiolite succession compared
with various exposedophiolites. Modified after Moores
(1982).

5.  Ophiolites have been described from three
oceanic tectonic settings :
Mid ocean ridges
Back-arc basins
Immature island arcs
( in some instances )

6.  Ophiolites are emplaced in arcs or collisional oregenes
by three major mechanisms.
I. Obduction or thrusting of oceanic lithosphere onto a
passive continental margin during continental
collision

7. II. Splitting on the upper part of a descending slab
and obduction of a thrust sheet onto a former arc

8. III. An addition of a slab of oceanic crust to
accretionary prism in an arc system.

9. Continue…
 The metamorphic complex at the base of
ophiolites may play a major role in ophiolite
emplacement.
 These metamorphic soles, as they are often
called, have many features in common:
1. Thickness generally range from 10-500 m
2. They extend laterally for tens to hundreds of
kilometers
3. Most show a sharp decrease in metamorphic
grade from top to bottom

10. 4. They are highly deformed and have a pronounced
tectonic foliation
5. They are composed of mixed mafic
volcanics, serpentine, and metasediments.
 These data are consistent with an origin for soles
of successive underplating and welding onto the
base of an ophiolite as it moves from the upper
mantle to the surface.

11. Ophiolite
Subduction
realated
ophiolites
Subduction
unrealated
ophiolites

12.  Subduction related ophiolite include
suprasubduction zone and volcanic arc types.
 Whose evolution is governed by slab
dehydration and accompanying metasomatism of
the mantle.
 Melting of the subducting sediments repeated
episodes of partial melting of metasomatised
peridotites

13.  It include continental margin mid-ocean ridge and
plume type ophiolites.
 That generally have MORB composition.
 Its developed during the closure of the ocean
basin whereas involved during rift drift and sea
floor spreading

14.  The density of the oceanic crust is low as
compare to the ophiolite sequence
 Ophiolites do not have any contrast thickness.
They may have even more or less thickness while
oceanic crust have 5-7 km thickness.
 Ophiolite lavas are dominated by arc tholeiites,
back arc basalt, andesite etc which are different
from oceanic crust lavas

15. Semail Ophiolite in Oman
 One of the best of the exposed ophiolite sequences
in the world.
 600 km long, 100-150 km wide.
 Tethysian oceanic lithosphere obduted on the
Arabian continental margin.

16.  Naga hills ophiolites
at the India-Burma
plate boundary.
 It’s a convergent plate
boundary.
 India plate boundary
had subducted
eastward below the
Burma micro plate at
early cretaceous.

17.  Ophiolites are slabs of ancient oceanic crust
obducted/preseved onto the continental crust/earth
surface.
 They are located in collisional boundaries.
 Their compostion is sediments, lavas, sheeted
dikes, gabbros, and ultramafic rocks.
 Have similarity with oceanic crust.

18. Reference :
• Plate tectonics and crustal evolution
(kent c. condie)
And from many website.