**Abstract**

The chapter is devoted to petrogeochemical features of late Cenozoic collision volcanism of the Lesser Caucasus. It was determined that at the early and middle stages of crystallization of the rocks of the andesite-dacite-rhyolite association, amphibole fractionation played an important role in the formation of subsequent differentials. On the basis of computer modeling, it was found that when mixing andesite and rhyolite (taken as a contaminant) magma, it is possible to obtain a rock of dacitic composition. Under conditions of high water pressure, as a result of fractionation of olivine and pyroxene from primary high magnesian magma, high-alumina basalts are formed, which can be considered as the parent magma. Geochemical features of moderately alkaline olivine basalts indicate that the source of magma is metasomaticized, phlogopite-garnet-rutile containing lithospheric mantle. The evolution of moderately alkaline olivine basalts occurs due to changes in the composition of the main rock-forming and accessory minerals. Medium rock formations are formed by the assimilation of poorly differentiated primary magma by an acidic melt. The calculations have shown that proportion of melting rhyolitic melt separated from andesite substrate is close to 15%. After removal of the remaining melt, restite is entirely consistent with the composition of the lower earth crust.

**Keywords:** late Cenozoic collision volcanism, Lesser Caucasus, geochemical, petrological features, AFC – modeling

### **1. Introduction**

One of the pressing problems of collision zones of the study is to elucidate the evolution of magmatism occurring within them. Display magmatic associations, their petrochemical characteristics reflect the specificity of their manifestations, as well as the development of magmatism from magma generation to the evolution of magmatic melt in the Earth's crust. Materials on the distribution of rare and rare earth elements in different rock types, as well as other of their geochemical and petrological characteristics allow using the well-known models [1–8] to analyze some aspects of the processes of birth, evolution, and crystallization of deep magmatic melts.

In this sense, the study of the geochemical characteristics of mantle and crystal sources of magmatism that have come out in a collision like the continent – the continent is quite topical. Therefore, the study late collision volcanism of the Lesser Caucasus is a theoretical and practical interest.

Such, more than 10 geodynamic models have been proposed on the genesis of Cenozoic collision volcanism including the Eastern Anatolian-Caucasian zone. The most popular models are: (1) lateral upper mantle flow of plume material from the East African rifts [3, 6]; (2) break-off of a subduction slab at the early collision (inversion) stage and, as a result, formation of an asthenospheric uplift under the growing collision orogen directly below the Moho boundary [2, 4–6, 9–10]; (3) collision magmatism with a leading role of oxidation of deep fluids [1]; (4) Paleogene collision-riftogenic volcanoplutonic magmatism, which occurred from lateral compression of the lithosphere and uplift of a less compacted mantle substrate [11]; (5) relationship of late collision volcanism with longitudinal and latitudinal extension structures, which formed in the suture-collision zone during activation of an area along the junction zone [12]; and (6) collision-riftogenic origin of late collision volcanism with mantle metasomatosis playing a leading role [13].

convergence. According to Koronovsky and Demina [1] in the Caucasian segment of the Alpine-Himalayan orogen Late Cenozoic volcanism manifested itself in an atmosphere of NS compression in the region, led to an accelerated movement towards the north of the Arabian plate due to disclosure in the Late Miocene (about 11–10 million years ago) the Red Sea [1]. This collision stage is divided into the stage of mild collisions (late Middle Eocene – Middle Miocene) and the stage of hard collisions (with the Late Miocene to present). This fragmentation of rigid crust was accompanied by volcanism; mark the sites of local stretching of the

*Late Cenozoic Collisional Volcanism in the Central Part of the Lesser Caucasus (Azerbaijan)*

Within the Lesser Caucasus Late Cenozoic volcanism covers part of the Transcaucasian transverse uplift (Akhalkalaki volcanic region, Kechut, Aragats volcanostructural sub-zones) and the eastern volcanic zone (Gegham, Vardenis, Syunik, Kaphan – in Armenia, Karabakh, Kelbajar, Nakhchivan in Azerbaijan) (**Figure 1**). Since the Middle Miocene, in these zones formed a high volcanic terrain, located on 2–3 km above sea level. Their association corresponds to the Caucasian age of folding, when the intense collision of the Arabian and Eurasian plates. Due to volcanic activity, there were formed many relatively large volcano-tectonic structures, such as Aragats, Ishygly, and others, erupting volcanoes of the central,

Products of the Late Cenozoic volcanism in the Azerbaijan distributions upper river Terter and Akera are characterized by lava flows and pyroclastics varied

Neogene volcanism in the Lesser Caucasus is mainly manifested itself, starting from the upper Sarmatian, Meotis-Ponte to the Upper Pliocene. However, Rustamov in the south-western part of Lesser Caucasus to carry a Molasse basin (Nakhchivan, Karadag) trachyandesite-teschenite and analcite alkaline basalt-trachyandesite, with the absolute age of 14–15 million years, volcanic fissure and concludes that the Neogene stage of volcanism in the region did not begin in the upper Sarmatians and in the Middle Miocene (based on determining the age of rocks with the K-Ar method,

In the central part of the Lesser Caucasus upper-volcanogenic complex with a capacity of 200 m in the literature described as Agdzhagyz suite and submitted dacite, rhyolite, pyroclastic rhyodacites and their derivatives – dacite and rhyolite tuffs. The layers of fine-sedimentary rocks – carbonaceous shales, lignites are

Volcanic complex with a thickness of 1150 m Meotis-Pont age first isolated as

trachyandesite, and latites (**Figure 2**). This complex with the angular and azimuthally unconformity lies at Agdzhagyz suite and places, Eocene and Cretaceous sediments. They overlap with an angular unconformity Upper Pliocene and Quaternary

These volcanic complexes are distinguished in the differentiated andesite-daciterhyolite association [13]. Based on geological data, the age of association is defined as the Late Miocene-Low Pliocene. Volcanics of close age are also known in other regions of the Lesser Caucasus. For example, an Early Pliocene andesite-dacite association is developed within the Miskhan-Zangezur and Yerevan-Ordubad zones. Similar rocks are found within the Gegham and Vardenis highlands in Armenia.

Basarkechar suite [14] and submitted dacite-trachydasite, andesite and

**2. The late Cenozoic volcanism of the Lesser Caucasus**

and by the stratigraphic position of the studied rocks) [11].

volcanic rocks in the volcanic highlands (**Figure 2**).

lithosphere.

composition.

**45**

**2.1 Neogene volcanism**

present between the volcanic rocks.

central-type fracture (**Figure 1**).

*DOI: http://dx.doi.org/10.5772/intechopen.93334*

Some of these models do not contradict each other and, as noted by Koronovskii and Demina [1], differ in the heat sources necessary for melting and mechanisms by which sources of late collision volcanism melt. On the basis of seismic tomographic, geological-petrochemical, and geophysical data, we have developed a geodynamic model that relates the geodynamic processes and magmatism at the late collision stage of the evolution of the Lesser Caucasus. We also used seismic and seismic tomographic data for the Lesser Caucasus and adjacent collision regions (Eastern Anatolia, northwestern Iran). Having developed the model and analyzed previous models, we tried to assess the role of lithospheric mantle and asthenosphere in the Late Cenozoic collision volcanism of the Lesser Caucasus.

Late Cenozoic geodynamics of the Alpine-Himalayan belt is defined sector of the Mediterranean collision of Eurasian and the Afro-Arabian megaplate [1]. According to modern concepts, folded structures of the Caucasus emerged as a result of their

**Figure 1.** *The distribution of Neogene-Quaternary volcanoes in Eastern Anatolia, the Caucasus, North-West Iran.*

*Late Cenozoic Collisional Volcanism in the Central Part of the Lesser Caucasus (Azerbaijan) DOI: http://dx.doi.org/10.5772/intechopen.93334*

convergence. According to Koronovsky and Demina [1] in the Caucasian segment of the Alpine-Himalayan orogen Late Cenozoic volcanism manifested itself in an atmosphere of NS compression in the region, led to an accelerated movement towards the north of the Arabian plate due to disclosure in the Late Miocene (about 11–10 million years ago) the Red Sea [1]. This collision stage is divided into the stage of mild collisions (late Middle Eocene – Middle Miocene) and the stage of hard collisions (with the Late Miocene to present). This fragmentation of rigid crust was accompanied by volcanism; mark the sites of local stretching of the lithosphere.

Within the Lesser Caucasus Late Cenozoic volcanism covers part of the Transcaucasian transverse uplift (Akhalkalaki volcanic region, Kechut, Aragats volcanostructural sub-zones) and the eastern volcanic zone (Gegham, Vardenis, Syunik, Kaphan – in Armenia, Karabakh, Kelbajar, Nakhchivan in Azerbaijan) (**Figure 1**).

Since the Middle Miocene, in these zones formed a high volcanic terrain, located on 2–3 km above sea level. Their association corresponds to the Caucasian age of folding, when the intense collision of the Arabian and Eurasian plates. Due to volcanic activity, there were formed many relatively large volcano-tectonic structures, such as Aragats, Ishygly, and others, erupting volcanoes of the central, central-type fracture (**Figure 1**).

Products of the Late Cenozoic volcanism in the Azerbaijan distributions upper river Terter and Akera are characterized by lava flows and pyroclastics varied composition.

## **2. The late Cenozoic volcanism of the Lesser Caucasus**

### **2.1 Neogene volcanism**

Such, more than 10 geodynamic models have been proposed on the genesis of Cenozoic collision volcanism including the Eastern Anatolian-Caucasian zone. The most popular models are: (1) lateral upper mantle flow of plume material from the East African rifts [3, 6]; (2) break-off of a subduction slab at the early collision (inversion) stage and, as a result, formation of an asthenospheric uplift under the growing collision orogen directly below the Moho boundary [2, 4–6, 9–10]; (3) collision magmatism with a leading role of oxidation of deep fluids [1]; (4) Paleogene collision-riftogenic volcanoplutonic magmatism, which occurred from lateral compression of the lithosphere and uplift of a less compacted mantle substrate [11]; (5) relationship of late collision volcanism with longitudinal and latitudinal extension structures, which formed in the suture-collision zone during activation of an area along the junction zone [12]; and (6) collision-riftogenic origin of late collision

Some of these models do not contradict each other and, as noted by Koronovskii and Demina [1], differ in the heat sources necessary for melting and mechanisms by which sources of late collision volcanism melt. On the basis of seismic tomographic, geological-petrochemical, and geophysical data, we have developed a geodynamic model that relates the geodynamic processes and magmatism at the late collision stage of the evolution of the Lesser Caucasus. We also used seismic and seismic tomographic data for the Lesser Caucasus and adjacent collision regions (Eastern Anatolia, northwestern Iran). Having developed the model and analyzed previous models, we tried to assess the role of lithospheric mantle and asthenosphere in the

Late Cenozoic geodynamics of the Alpine-Himalayan belt is defined sector of the Mediterranean collision of Eurasian and the Afro-Arabian megaplate [1]. According to modern concepts, folded structures of the Caucasus emerged as a result of their

*The distribution of Neogene-Quaternary volcanoes in Eastern Anatolia, the Caucasus, North-West Iran.*

volcanism with mantle metasomatosis playing a leading role [13].

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

Late Cenozoic collision volcanism of the Lesser Caucasus.

**Figure 1.**

**44**

Neogene volcanism in the Lesser Caucasus is mainly manifested itself, starting from the upper Sarmatian, Meotis-Ponte to the Upper Pliocene. However, Rustamov in the south-western part of Lesser Caucasus to carry a Molasse basin (Nakhchivan, Karadag) trachyandesite-teschenite and analcite alkaline basalt-trachyandesite, with the absolute age of 14–15 million years, volcanic fissure and concludes that the Neogene stage of volcanism in the region did not begin in the upper Sarmatians and in the Middle Miocene (based on determining the age of rocks with the K-Ar method, and by the stratigraphic position of the studied rocks) [11].

In the central part of the Lesser Caucasus upper-volcanogenic complex with a capacity of 200 m in the literature described as Agdzhagyz suite and submitted dacite, rhyolite, pyroclastic rhyodacites and their derivatives – dacite and rhyolite tuffs. The layers of fine-sedimentary rocks – carbonaceous shales, lignites are present between the volcanic rocks.

Volcanic complex with a thickness of 1150 m Meotis-Pont age first isolated as Basarkechar suite [14] and submitted dacite-trachydasite, andesite and trachyandesite, and latites (**Figure 2**). This complex with the angular and azimuthally unconformity lies at Agdzhagyz suite and places, Eocene and Cretaceous sediments. They overlap with an angular unconformity Upper Pliocene and Quaternary volcanic rocks in the volcanic highlands (**Figure 2**).

These volcanic complexes are distinguished in the differentiated andesite-daciterhyolite association [13]. Based on geological data, the age of association is defined as the Late Miocene-Low Pliocene. Volcanics of close age are also known in other regions of the Lesser Caucasus. For example, an Early Pliocene andesite-dacite association is developed within the Miskhan-Zangezur and Yerevan-Ordubad zones. Similar rocks are found within the Gegham and Vardenis highlands in Armenia.

series and cover Geghama, Vardenis and Syunik, Karabakh, Kelbajar highlands. In Armenia Kaphan zone has recently been formed basanite-tephrite-picro-bazaltic

*Late Cenozoic Collisional Volcanism in the Central Part of the Lesser Caucasus (Azerbaijan)*

This chapter used data from the Neogene-Quaternary volcanism of the Azerbaijan part of Lesser Caucasus based on the authors. Chemical analysis of rocks was determined by the Institute of Geology of Azerbaijan Academy of Sciences X-ray fluorescence method. Rare and rare-earth elements are in Geological and Geochemical Bronitsk expeditions in Russia. Microprobe analysis of mineral composition written in Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Moscow and Russian Geological Research Institute (VSEGEI), St. Petersburg. Measuring the isotopic composition of He performed in Geochemistry Institute of Academy of Sciences Russia, also used the data Sr and Nd [17, 18] performed on the material of Armenia and Georgia.

**4. Petrography characteristics of the Late Cenozoic volcanic rocks**

The rocks of the *andesite-dacite-rhyolite associations* form thin flows and subvolcanic body in the form of dikes, extrusions and other recent distributed along the Tartar, Lachin-Bashlybel, Istibulag-Agyatak deep faults (**Figure 2**). Texture of porphyritic rocks, with high (25–30%) content of phenocrysts. In andesites, trachyandesites, latites phenocrysts are plagioclase, feldspar, clinopyroxene, and amphibole. In the more acidic varieties (dacites, rhyodacites, rhyolites their varieties), the proportion of dark-colored minerals decreases, leucocratic minerals also increased to 10%, there is quartz, biotite. The bulk of these rocks have hyalopilitic,

The compositions of plagioclase in the rocks have *An30–<sup>40</sup>* and are paragenesis with amphibole, biotite, clinopyroxene, and feldspar. Plagioclases second generation are relatively acid composition (*An20–30*), crystallized on its own effusive stage. Feldspar in the rocks present in quartz latites, trachyandesites. The composition ranges from *Or55.3Ab26.3An0.3* to *Or73.4Ab44.0 An3.4* (**Table 1**). They belong to an intermediate structural-optical type and are monoclinic, but not homogeneous and presented albite and orthoclase phases. Composition of clinopyroxene varies from medium to acid rocks and the proportion of the component increases Fs: *Wo37.1–41.4 En43.9–40.0 Fs19–19.6* (for andesites), *Wo40.0–44.4 En45.4–44.8 Fs15.2–11.2* (for quartz latites), and *Wo41.7–42.7 En36.3–34.6 Fs22–22.7* (for dacites) (**Table 1**) [13, 19]. The compositions of amphiboles in the classification of B.E. Like [20] are responsible

Analyses of rock-forming minerals were carried out at the analytical laboratories of the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Moscow State University; Moscow and Russian Geological Research Institute (VSEGEI), St. Petersburg on a Camebax microprobe. Magnetite was analyzed by conventional chemical techniques at Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy

The rocks of the *rhyolite association* of petrographic composition and structural

and textural features are divided into crystallized – rhyolites, trachyrhyolites, rhyodacites and glass – obsidians and perlites. Phenocrysts crystallized rocks are

of Sciences. Analysts A.I. Tsepin, V.K. Garanin, and V.S. Pavshukov.

series.

**3. Research methods**

*DOI: http://dx.doi.org/10.5772/intechopen.93334*

glass texture (**Figure 3**).

**47**

chermakit-, pargasit- and magnesian hornblendes.

### **Figure 2.**

*Geological map of Late Cenozoic volcanic associations in the central part of the Lesser Caucasus (Azerbaijan), scale 1:100,000. Compiled by Imamverdiyev [13].* Volcanic association: Quaternary: 1 – *trachybasalts, basaltic trachyandesites, and trachyandesites; 2 – tuffs, volcanic ashes, tuff breccias;* 3 *– rhyolites, perlite, and obsidian;* Upper Pliocene-Low Quaternary: 4 – *trachybasalts, basaltic trachyandesites, and trachyandesites;* Upper Miocene-Low Pliocene: *5 – dacites, rhyodacites, rhyolites; 6 – andesites, trachyandesites, quartz latites, dacites, trachydacites (Basarkechar formation) 7 – dacites, trachydacites, rhyodacites and rhyolites (Ajagz formation); 8 – diorites, granodiorites, syenites;* Upper Oligocene-Low Miocene: *9 – granodiorites, granites, monsonites, quartz syenites;* Eocene: 10 – *andesites, trachyandesites and their tuffs; 11 – granodiorites, monsonites, quartz diorites;* Base rocks (Cretaceous): *12 – ophiolites; 13 – flysch; limestone's, sandstone's, tuffs; 14 – faults; 15 – Terter deep fault; 16 - largest centers of volcano eruption; 17 – rivers; 18 – lakes.*

### **2.2 Late Pliocene-quaternary acidic volcanic associations**

Late Pliocene-quaternary acidic volcanic associations as independent volcanism are widely developed within the Caucasian segment of the Mediterranean belt. Within Azerbaijan, they are confined Kelbajar and Karabakh uplands and form a dome-shaped volcanoes, and a number of small extrusive domes (Kechaldag, Devegezy) with their lava flows composed of rhyolite, rhyodacites their subalkaline varieties, as well as obsidian and perlite (**Figure 2**).

The age of acidic volcanic rocks of the Lesser Caucasus in the studied region based on their stratigraphic position was considered late Pliocene-Akchagyl-Absheron [15]. This is confirmed by the absolute age. Thus, according to [16] age of rhyolite volcanic rocks Devegezy identified 0.61 million years, Kechaldagh 0.7 million years. Based on these data, the age of acidic volcanic rocks can be considered Quaternary.

*Upper Pliocene-Quaternary volcanic associations* with a more basic and medium composition, cover the entire Lesser Caucasus, form vast volcanic plateaus and large volcanoes and occupies about 5000 km<sup>2</sup> of surface area. These volcanic associations in the eastern area of Armenia and Azerbaijan within the differentiated form a continuous trachybasalt-basaltic trachyandesite-trachyandesite-trachyte

*Late Cenozoic Collisional Volcanism in the Central Part of the Lesser Caucasus (Azerbaijan) DOI: http://dx.doi.org/10.5772/intechopen.93334*

series and cover Geghama, Vardenis and Syunik, Karabakh, Kelbajar highlands. In Armenia Kaphan zone has recently been formed basanite-tephrite-picro-bazaltic series.
