A geological and petrographical study has been made of the ophiolite complex and volcano-sedimentary cover of the eastern Taurus mountain belt NE of Malatya.
The paleozoic crystalline substratum of the ophiolite complex demonstrates paragenesis of the typical greenschist facies of the pelitic sequence. For the entire length of the region studied the basement is overthrust by an ophiolite mass. The latter forms a recumbent fold whose overturned limb fills a large portion of the map.
A younger volcano-sedimentary cover overlies the ophiolites with a transitional layer of volcanic breccias and agglomerates. The sedimentary series from bottom to top consists of red schists (argilites), greenschists containing more calcareous units, and finally a nummulitic limestone. Since the entire ophiolite volcano-sedimentary series lies in an inverted position, the latter occurs in thrust contact with the paleozoic basement.
In the Malatya region, thrusting in general has been southward in the southern part of the massif of Bitlis and northward in the northern part.
We propose the term "Lower Malatya Nappe" (Nappe de Malatya inférieure) for the abnormal superposition of the ophiolite complex and its volcano-sedimentary cover on the paleozoic substratum.
Lithologies of the ophiolitic sequence are described in separate chapters. Topics thus discussed include spilitic diabases, submarine lavas (sensu lato), pyroclastic products, albite syenites and various types of gabbros. The presence of epidote, pumpellyite and prehnite in these rocks is due to phenonena of deuteric alteration posterior to their emplacement.
Some examples of chemical reactions which are characteristic of both the deuteric late-magmatic processes and metamorphic processes are discussed in the chapter on metamorphism. Each of these reactions results in paragenesis of spilitic nature.
All of the units, from picritic basalt and olivine basalt to dacite and rhyolite, do not result from a "normal" magmatic evolution. Such a magmatic evolution probably exists to a certain extent. However, late-magmatic differentiation by fractional crystallization "in situ" followed by hydrothermal phases must have played a very important role. This would explain the great chemical diversity observed in these ophiolites.
The spilito-keratophyric series of Malatya is considered to represent the last products of differentiation of a tholeiitic magma of calcic-pacific type rich in aluminium and silica. The chemical composition of these ophiolites is analogous to that of many midocean ridge lavas.
