Presenter : Omer M. Ahmed University of Kerala, India, 2015.

b The name ophiolite derived from Greek root which means b Ophio : snake or serpent Litho : Stone  The green colour, structure and texture of sheared ultramafic rocks is similar to some serpents

 The term ophiolite was initially given to dark green shiny outcrops which composed of serpentines (serpentinite rocks)  later on become used not only to a single rock, but also to an association of related rock types which are found as a consistent of upper mantle rocks and oceanic crust. Ophiolite

Ophiolite Sequence  Sediments  Pillow Lavas  sheeted Dykes  Gabbros  Layered Gabbro  Layered Peridotite  Upper mantle Robin Gil 2010

 The above sequences has been emplaced on subduction zone.  and subsequently pushed up on to continents by thrusting a long narrow belts or it can extend more than 1000 km.  Depends on thrust angle either moving al members () or missing some other members (  Depends on thrust angle either moving al members ( Allochthonous or intact ophiolite ) or missing some other members ( autochthonous ophiolite ). Ophiolite

 These metamorphic rocks represent upper mantle.  They shows sharp contact with cumulates.  With variable size in some outcrops over thousands of square kilometers.  The ranges from lherzolite ( CPX, OPX, Olivine and MG spinel ) to harzburgite ( OPX and olivine ) and dunite ( olivine ).  These components of ophiolite are generally the most prominent because they record mantle history of subduction zone. Metamorphic Peridotite

 Many ophiolites occurring within the folded mountain belts have repeated deformation and metamorphism which transforms the layered fragments into tectonic mixture or Mélange.  It can be interpreted as a remnant of an ancient subduction zone during emplacement of ophiolite.  Transitional zone between the oceanic crust and mantle. Mélange

o They are represent oceanic crust and usually occurred as deformed, sheared, and highly serpentinized. o Consist of Peridotites (), pyroxenites and layered gabbros. o Consist of Peridotites ( olivine, CPX ± plagioclase ), pyroxenites and layered gabbros. o The layering is maybe result of crystal settling (by density) during the crystallization, which allowed accumulation or a segregation process related to the chemical stability of minerals. o The cumulate complexes are made of four minerals OPX, CPX, Olivine, and plagioclase (dominant in layered), with important amounts of chromite. Cumulates

ROM/Sudum/Sudum_layering.html

 The occurrence of leucocratic rocks in ophiolites known as plagiogranites.  It is late-stage of magmatic products in formation of the main ophiolitic crust.  These plagiogranites consist mainly of quartz and plagioclase with only minor amounts of ferromagnesian minerals. plagiogranites

They occur as minor dykes They occur as minor dykes Within the upper part of some ophiolite sequences with variable thickness. Within the upper part of some ophiolite sequences with variable thickness. They formed by continuous injection of basaltic liquid along the extension zones it could be mid oceanic ridge, marginal basin, or small restricted ocean basin like Red Sea. They formed by continuous injection of basaltic liquid along the extension zones it could be mid oceanic ridge, marginal basin, or small restricted ocean basin like Red Sea. The chemistry of the dykes indicates derivation from a differentiating mafic magma. The chemistry of the dykes indicates derivation from a differentiating mafic magma. Minerals are plagioclase (zoned), CPX, magnetite or ilmenite and accessory hornblende, these minerals show fine to medium grains with ophitic texture. Minerals are plagioclase (zoned), CPX, magnetite or ilmenite and accessory hornblende, these minerals show fine to medium grains with ophitic texture. Sheeted Dykes

geochemistry/ocean-ridge-hydrothermal-fluxes

o Include pillow lavas, massive lavas and pillow breccia. o generally dismembered by several thrust faults, shear zones and overturned folds. o Pillow lavas provide direct evidence that they developed in the water. o There are some intrusive rocks associated with pillows: sills, dykes and sometime irregular masses. The volcanic sequences The volcanic sequences

Pillow lava o Pillow lavas show chilled margins and glassy material o Pillow lavas show chilled margins and glassy material. o The most common crystallites in the chilled margin are Plagioclase ( sometime zoned ), CPX and phenocrysts of olivine. o It shows sub-ophitic texture away from the chilled margins. o Pillow lavas have normative hypersthene and quartz. o pillow lava and sheeted dykes are characteristic of ophiolite

 The deep oceanic sediments deposited on oceanic crust have provided us information about materials resting directly on the oceanic crust and interlayered with the pillow lavas.  Cherts, greywackes and shales are the most common types of these sediments.  They contain organic remnants like radiolaria, that clearly demonstrate their deep ocean origin. Sediment

Relation between lava and sediments ( Robert G. Coleman 1977). 1- pillow lava. 3- fragment of pillow lava. 2- sand. 4- radiolarian chert 5- sediment.

Geochemistry  The ophiolite consist of variable rocks types: mafic, ultramafic, acidic, metamorphic and fossiliferous sediments.  These association show a wide range of chemical composition.  Rajesh K. Srivastava has done a geochemistry analysis for three samples in Naga Hills ophiolite.  Bulk compositions of basalt and felsic rocks (Granitoids and Plagiogranite) for major oxides and trace elements.

Major oxides Rajesh K. Srivastava (2011)) Major oxides ( Rajesh K. Srivastava (2011)) basalt Granitoid Plagiogranite

Trace elements

Ophiolites are recognized in many areas around the world.  Oman (s )  Sudan (Nubba mountains)  Cyprus (Troodos island)  Albania (Mirdita )  Northern California Occurrences of Ophiolites in the world

 Naga Hills in North east India  An important feature at Naga Hills is the occurrence of late-granitoids.  presence of two feldspars plagioclase and potash feldspar, and amphibole.  Mineralization base-metal and sulfide. Occurrences of ophiolite in India

 Massive Sulphide It founded within pillow lava most of massive Sulphide associated in Ophiolites have well developed Gossans (bright colored iron oxide, hydroxides, and sulfides) which is very rich in gold.  Chromite Stratiform (be tabular or pencil shape) or podiform (irregular shape) within ultra-mafic rocks. Other deposits are developed on serpentinite peridotite  Laterites (nickel and iron)  Asbestos  Talc  Magenesite Economic value

 Ophiolites are association of mafic and ultra mafic rocks within mantle and oceanic crust.  With relation between Metamorphic, Igneous and Sedimentary rocks.  Involved several tectonic process  Ophiolites are key to detecting old subduction zones, gives clues of earth history.  Minerals wealth. Conclusion

References  Coleman R G (1977), Ophiolite, Springer-Verlag Berlin Heidelberg New York, 229 P.  DILEK,Y and ROBINSON, R T (2003), ophiolites in Earth History, Published by the Geological Society London, 700P.  Gill, R (2010), Igneous Rocks and Processes A Practical Guide, John Wiley & Sons Ltd, 428 P.  Gupta A K.Alok (1998),Igneous rocks, Allied Publishers Limited 690 P.  Srivastava R K (2011), Dyke Swarms: Keys for Geodynamic Interpretation, Springer-Verlag Berlin Heidelberg, 605 P.