**1. Introduction**

Volcano mentions as the magma and associated ingredients erupt to the surface from the vent and also refer to the landform formed by solidified lava and volcanic debris near the vent. Abundant volcanic rocks in the Earth's upper continental crust are broadly studied because they are closely related to with magmatic processes,

#### **Figure 1.**

*(A) Global map showing location of volcanoes and centers of valcanism on lithospheric plates and related to crustal evolution (modified after Encyclopedia Britannica, 2008). (B) Geological map of Nakora area, Western Rajasthan, India. (C) Aerial view of Nakora Ring Complex, Siwana Ring Complex and Luni lineament, Rajasthan, India.*

*Petrology and Geochemistry of Nakora Ring Complex with Emphasis on Tectonics… DOI: http://dx.doi.org/10.5772/intechopen.98609*

crustal evolution, tectonics and geodynamics [1]. Volcanoes are almost located where tectonic plates diverge or converge on Earth surface/subsurface, and the majority of them are found underwater. Volcanic vent were documented from diverse settings of the world and they are sketched with crustal provinces, platforms, shield areas and orogenic belts (**Figure 1**). The volcanoes such as Mid-Atlantic Ridge and Pacific Ring of Fire are superlative example of divergent and convergent tectonic plates respectively. Volcanoes can also found in the East African Rift, Rio Grande Rift (North America), Hawaii, Arizona, Iceland, Mount Fuji (Japan), Stromboli (Italy), Valles Caldera and Yellowstone National Park in New Mexico and Narcondam Island (India). As isolated magma bodies ascend from large magma source regions, small volcanic vents are discovered within the Tharsis Volcanic Province [2]. The cooling efficiency inside the parent fountain determines the pyroclastic products are generated by basaltic Hawaiian fountaining [3, 4]. Big Ben lavas identified in Heard Island (Subantartic volcanic) are dominated by basalt, basanite and trachybasaltic rocks and discharge rate of average magma is very truncated [5].

On survey of India topographic sheet no. 45C/1; Scale 1: 50000; 25°45<sup>0</sup> – 25°50<sup>0</sup> N; 72°05<sup>0</sup> –72°15<sup>0</sup> E Nakora Ring Complex is located in Western Rajasthan. NRC divided in many hills, i.e., Milara, Nakora, Dadawari, Variya, Sewadiya, Tikhi, Maini and Pabre which consists of granite, basalt, trachyte, rhyolite, tuff, gabbro and dolerite (**Figure 1B**). The NRC's rocks are related to the Malani Igneous Suite (MIS, Neoproterozoic) in the Trans Aravalli Block (TAB) of Indian Shield. The major period of anorogenic (A-type) is an exclusive event in the geological evolution of Indian Shield with the characteristics of bimodal in nature, high heat producing and Intraplate magmatism.

TAB consists of peralkaline, metaluminous to mildly peralkaline and peraluminous granites of Siwana, Jalor, Jhunjhunu and Tosham respectively with cogenetic association of acid volcanics [6–8]. MIS is India's largest anorogenic acid volcanism and the world's third largest with the characteristics of distinctive ring structures and radial dykes. It has a range of �55,000 sq. Km with a broad initial phase of felsic and mafic volcanism, accompanied by granitic plutonism. MIS owes its origin to hot spot tectonics and is governed in the TAB by NE–SW trend lineaments [9, 10]. The objective of this research is to provide a relation between magmatism and tectonism by using petrological and geochemical data in Nakora area of MIS.

### **2. Geological setting**

MIS (�780–750 Ma) spread in NW India which is a silicic large igneous province (Precambrian) and characterised by Pan-African thermo-tectonic event [11–13]. This event showed volcanic and plutonic igneous multiphase assemblages during the Neoproterozoic period that were operated by hot-spot tectonism. In NW India, TAB is leading with A-type magmatic felsic rocks having specific geochemical characteristics i.e., alkaline, peralkaline, metaluminous and peraluminous [7–9, 14]. In Tosham (Haryana), Siwana, Jalor, Jhunjhunu, Nakora, Mokalsar, Jodhpur, Sirohi (Rajasthan) and even in Nagar Parkar (Sind-Pakistan), Kirana Parkar (Kirana), they are well exposed (Lahore-Pakistan) [6, 9, 10, 15].

The tectonic, magmatic and geodynamic characteristics of NRC are enlightened on the basis of geological field mapping, petrography and major and trace elements chemical data. Different rocks are classified into different phases based on the field relationships of the region. They are categorizing as Extrusive phase (trachyte,

rhyolite, basalt, tuff, perlite, breccia, ash and agglomerate), Intrusive phase (granite and gabbro) and Dyke phase (basalt, dolerite, rhyolite and microgranite). In NRC, region first phase includes basic flows which is latter outpoured the acidic volcanic rocks and contains pyroclastic explosive rocks, acid lava flows and pyroclastic ash fall. Second phase having granite which is intruded the acid flows (plutons, ring dykes and bosses) and third phase consists of felsic and mafic dykes which cut the rocks of earlier phases [16, 17]. The NRC hill is located along the Luni River and the Luni River suddenly turns 'U' from West to South, reflecting the continental rift [18]. The Sukri lineaments are followed by NE–SW trend parallel lineaments of the Luni River and are called major Luni-Sukri lineaments (**Figure 1C**). These types of lineaments are caused by the release of stress after the orogenic cycles of Aravalli-Delhi and MIS magmatism, caused by mantle plume [19]. In TAB, the Luni rift is an important tectonic lineament [20]. This lineament is linked to significant continental rift model crustal dislocations for magma extrusions and intrusions [21]. Luni rift has therefore acted as the path for magma to rise through various major fractures, followed by anorogenic volcanism that may precede/follow the position of ring complexes. The NRC field, which is a small part of the NW continental block, a very significant element in explaining the petro-genetic, geodynamic evolution of MIS.
