Proterozoic Newer Dolerite Dyke Swarm Magmatism in the Singhbhum Craton, Eastern India

Abstract

Precambrian mafic magmatism and its role in the evolution of Earth’s crust has been paid serious attention by researchers for the last four decades. The emplacement of mafic dyke swarms acts as an important time marker in geological terrains. Number of shield terrains throughout the world has been intruded by the Precambrian dyke swarms, hence the presence of these dykes are useful to understand the Proterozoic tectonics, magmatism, crustal growth and continental reconstruction. Likewise, the Protocontinents of Indian Shield e.g. Aravalli-Bundelkhand, Dharwar, Bastar, and Singhbhum Protocontinent had experienced the dyke swarm intrusions having different characteristics and orientations. In Singhbhum craton, an impressive set of mafic dyke swarm, called as Newer dolerite dyke swarm, had intruded the Precambrian Singhbhum granitoid complex through a wide geological period from 2800 to 1100 Ma. Present chapter focuses on the published results or conclusions of these dykes in terms of their mantle source characteristics, metasomatism of the mantle source, degree of crustal contamination and partial melting processes. Geochemical characteristics of these dykes particularly Ti/Y, Zr/Y, Th/Nb, Ba/Nb, La/Nb, (La/Sm)PM are similar to either MORB or subduction zone basalts that occur along the plate margin. The enriched LREE-LILE and depletion of HFSE especially Nb, P and Ti probably indicate generation of these dykes in a subduction zone setting.

1. Introduction

Precambrian mafic magmatism and its role in the evolution of Earth’s crust has received particular attention of the geoscientists during the last three decades because it has not only been influenced by progressive secular compositional variation and mantle sources/reservoirs but also by onset of plate tectonics. Study of dykes is useful for recognition of Large Igneous Provinces (LIP) and rebuilding of different continents which may have displaced through geological time [1]. All protocontinents of India such as Aravalli-Bundelkhand, Dharwar, Bastar and Singhbhum retain dykes of varied orientations, therefore, these dykes or dyke swarms represent a main thermal episode during the Proterozoic or Precambrain times [2]. Geochemical and isotope studies of these dykes offer an opportunity in understanding the geochemical evolution of mantle through space and time [3, 4].

Singhbhum Craton is a book that records complex geological and tectonic processes from Paleoarchean to Neoproterozoic [5, 6]. Several dykes of mafic to acidic compositions are intruding the Singhbhum Granitoid Complex, which are collectively referred to as the Newer dolerites dykes (NDD) in the geological literature [7, 8]. Being the latest magmatic episode of the Singhbhum Granitoid Complex, Newer dolerite dykes provide the path in understanding the Proterozoic geodynamic evolution of the Singhbhum Craton [9]. The present work contributes in understanding the mantle source characteristics and tectonic setting of the NDD.

2. General geology

Mahanadi Graben and Sukinda thrust borders the Eastern Indian shield in the west and granulite terrain of Eastern Ghats along with recent alluvium surrounds this shield in the south, whereas, Gangetic alluvium and Quaternary sediments of Bengal basin exist in north and east of this shield (Figure 1). The major divisions of this shield includes: Chotanagpur Granite Gneiss Complex, Singhbhum Mobile Belt and Singhbhum Craton. The general geological features of each of the above geological provinces are briefly discussed in the following sections.

Figure 1.

Simplified geological map of eastern Indian shield illustrating the three geological provinces viz. Chotanagpur granite gneiss complex (CGGC), Singhbhum Mobile Belt (SMB) and Singhbhum craton (SC). SSZ – Singhbhum shear zone [9].

2.1 Chotanagpur granite gneiss complex

Chotanagpur Granite Gneiss Complex (CGCC) exists in West Bengal and Jharkhand states of India and covers an area of about 80,000 km2 (Latitudes 23°00′N to 25°00′N; Longitudes 83°45′E to 87°45′E). It is mostly made of granites, granite-gneisses, migmatites, dolerite dykes and pegmatite, aplite and quartz veins From the structural patterns, worked out in different parts of the CGGC, it is clear that the region has undergone polyphase deformation producing distinctive folds and related linear fabrics [8].

2.2 Singhbhum mobile belt

The formations occurring in between the Singhbhum Granitoid Complex (SGC) and CGGC are collectively recognized either as the Singhbhum Mobile Belt (SMB) or Singhbhum Group. The SMB (Figure 2), has been divided into five litho-stratigraphic domains from north to south [11, 12] like (a) volcano-sedimentary belt, (b) Dalma metavolcanic belt, (c) Chaibasa and Dhalbhum Formations, (d) the rocks occurring in the SSZ and (e) Dhanjori and/or the Ongarbira metavolcanic rocks.

Figure 2.

Simplified geological map of the Singhbhum craton [10].

2.3 Singhbhum craton

The Singhbhum Craton (SC) records a long history of crustal evolution from Mesoarchaean to Mesoproterozoic. It is an extensive terrain of granite and gneissic complex with subordinate metabasic and minor metasedimentary rocks (Figure 2). Some important geological units are briefed below:

2.3.1 Older metamorphic group

Older Metamorphic Group (OMG) occurs near Champua (Latitudes 22°04′N: Longitudes 85°40′E) and as enclaves in the SGC. This group had experienced amphibolite facies metamorphism and is made of pelitic schists, garnetiferous quartzite, calc-magnesian metasediments and sill like mafic rocks [5]. Goswami et al. [13] and Mishra [14], have dated detrital zircons and recognized an older limit of 3.5Ga age for these supra-crustals. On the bases of Pb/Pb whole rock dating, Moorbath and Taylor [15] has established 3378 ± 98 Ma age for these supra-crustals. This age matches with Sm/Nd (TDM model) ages of 3.41, 3.39 and 3.35 Ga [15]. Sharma et al. [16], however, pointed out that protoliths of OMG amphibolites are 3305 ± 60 Ma old and therefore OMTG which intrude OMG cannot be older than 3300 Ma. The younger 3.40, 3.35 and 3.20 Ga ages have been interpreted as metamorphic events [17, 18].

2.3.2 Singhbhum granitoid complex

It has been suggested that SGC (Latitudes 21°00′ and 22°45′ N: Longitudes 85°30′ and 86°30′E) is composed of 12 distinct units that were emplaced in three successive magmatic phases [5]. The K-poor, granodiorite trondhjemite early (phase I) has been dated as 3.25 ± 0.05 Ga [19]. The II and III phases are made of granodiorite that grade to monzogranite and granite and these phases are dated as 3.06 Ga (Pb/Pb whole rock) and 2.9 Ga (Rb/Sr. whole rock) respectively [5]. The other granitic bodies that occur in SC show ages similar to that of SGC, for example, Bonai granites (3369 ± 57 Ma) [20] and Katipada tonalite (3275 ± 81 Ma) [21]. Recent U–Pb zircon studies have revealed that rocks of the SG batholith were emplaced between ~3.45 Ga and ~ 3.32 Ga [22].

2.3.3 Banded iron formations

BIF is considered to have been deposited in three interconnected basins [5]. These basins are: (i) Noamundi (Latitudes 22°09′N: Longitudes 85°31′E) – Koira (Latitudes 21°54′N: Longitudes 85°15′E) basin of west Singhbhum district and Keonjhar, (ii) Gorumahisani (Latitudes 22°18′30′N: Longitudes 86°17′E) – Badampahar (Latitudes 22°04′N: Longitudes 86°07′E) basin along the eastern border of the Singhbhum Granitoid Complex and (iii) Daitari-Tomka basin in the southern parts of the Singhbhum Craton. In the Noamundi– Koira BIF, rocks are made up of shale, phyllite, the middle formation of banded hematite jasper and an upper formation of magniferous shale, chert, manganese formation and shale. A granite body intruding BIF near Sulaipat has been dated as 3.12 ± 0.01 Ga [23]. Some mafic and ultramafic rocks referred to as Gorumahisani Greenstones are associated with this Gorumahisani-Badampahar BIF sequence [24].

2.3.4 Bonai volcanic suite

Bonai volcanics show sub-aerial and sub-marine features in the west and east parts of its extension respectively [24, 25]. These volcanics are made of mafic rocks, tuffs and subordinate silica volcanic clastic interbeds. It has been inferred that these volcanics show island arc basalt characteristics [24].

2.3.5 Jagannathpur volcanic suite

These volcanics are exposed around Noamundi upto Jagannathpur and are younger than BIF of Noamundi-Koira belt [24]. Significantly, NDD are not cutting across the Jagannathpur Suite. It, therefore, appears that it is either equivalent in age or younger than the NDD. Alvi and Raza [26] found these to be calc-alkaline basalts and suggested that these lava flows represent an early arc volcanism. The Jagannathpur lavas have been dated around 1629 ± 30 Ma by K/Ar method [5] and 2250 ± 81 Ma by Pb/Pb whole rock isochron method [27].

2.3.6 Gorumahisani volcanic suite

It is associated with Gorumahisani-Badampahar BIF along the eastern border of SBGC. The rocks of this volcanic suite are intruded by Kumhardubi (Latitude 22° 17′N: Longitude 86°19′30″) - Dublarbera (Latitude 22°29′30″ N: Longitude 86°17′E) gabbro- anorthosite, Rangamatia (Latitude 22°29′15″N: Longitude 86°17′30″E) Leucotonalite, Katupith (Latitude 22°18′N: Longitude 86°17′30′′E) Leucogranite and NDD swarm.

2.3.7 Simlipal complex

Recently Kar et al. [28] suggested that the circular shape of Simlipal complex is only a topography controlled rather than an existence of alternate bands of mafic volcanic and quartzites. Further, they suggested that the Simlipal complex overlies the weakly metamorphosed basement heterolith unit (Lulung Formation) which is overlain by Barehipani Formation and Jurunda Formation. Paleoproterozoic age for this complex has been given by Saha [5]. Further, Iyengar et al. [29] suggested 2084 ± 70 Ma age for Similipal complex by following the Rb-Sr whole rock method.

2.3.8 Kolhan group

This group exists on the western margin of the SBC and its length is around 100 km with a width of about 12 km. Saha [5] correlated Chaniakpur-Keonjhargarh, Mankarchua and Sarpalli-Kamakhyanagar formations with Kolhan Group. The Singhbhum granite Basement, Dongoaposi (Jagannathpur) lavas and the Iron Group surround Kolhan basin on the NE, S-SE and west respectively [30]. The Kolhan shales north of Hat Gamaria are intruded by three parallel sills of the NDD. South west of Jagannathpur, flat lying Kolhan shales overlie the Jagannathpur lava.

3. Petrography

NDD have experienced low grade regional metamorphism in the vicinity of Singhbhum Shear Zone, however they are fresh to least effected in the western and central parts of the Singhbhum Granitiod Complex. NNE–SSW trending ultramafic-mafic dyke exposed near Keshargaria is medium to coarse grained rock with green to dark green color. The ultramafic dykes which consist of olivine (25–52%) and pyroxenes (45–65%) are present. Mafic dykes are mainly massive, sometimes coarse grained and their color varies from black to greenish gray. The essential constituents of dolerite type of dykes includes pyroxenes, plagioclases and quartz with little amphiboles. Clinopyroxene is mainly augite in the form of euhedral to subhedral prismatic phenocrysts and also as granular aggregates in the groundmass. Rarely, clinopyroxene shows alteration to pale-green amphibole and/or biotite around the grain boundaries. Quartz (0.5 to 3%) is present as subhedral to anhedral crystals. Accessory minerals are opaques, apatite, and rutile. Opaque minerals (0.5 to 5%) include magnetite and Cr-Spinel. Norite samples consist dominantly orthopyroxene (hypersthene) and plagioclase (labradorite) together with subordinate diopsidic augite and small amounts of quartz. In Quartz dolerites relatively greater proportion of anhedral quartz is noticed. The major constituents in quartz dolerite are calcic plagioclase, clinopyroxene (diopside-augite) and subordinate amount of orthopyroxene (hypersthene, enstatite). Coarse grained gabbroic variety of the NDD is mostly coarse grained dark colored. Under microscope, they show overall hypidiomorphic texture with local development of subophitic texture. They show subhedral laths of labradorite plagioclase and augite. Orthopyroxene is rarely found within this petrographic variant.

4. Geochemistry

While observing geochemical characteristics, NDD have been classified as (i) ultramafic dykes {having MgO >30.0 wt. %, SiO₂ < 45.0 wt. %, Al₂O₃ < 5.0 wt. % and alkalies <1.0 wt. %; (ii) Group I dykes {having MgO 12–22 wt. %, SiO₂ 45–53 wt. %, Al₂O₃ < 11.0% and total alkalies <3.0%; (iii) Group II dykes {having MgO 7.0–19.0 wt.%, SiO₂ 51–60 wt. %, Al₂O₃ 10–12 wt. % and alkalies 1.0–3.50 wt. %; (iv) Group III {having MgO 6.0–12 wt. %, SiO₂ 51.0–70.0 wt. %, Al₂O₃ 10.0–12.5 wt. % and total alkalies 2.0–4.5 wt. %. Group I dykes contain lower MgO and MnO and higher SiO₂, TiO₂, Al₂O₃, P₂O₅ and alkalies as compared to Ultramafic dykes. Group II contains high TiO₂, Fe₂O₃, MgO and P₂O₅ contents and lower SiO₂ and Alkalies relative to group III dykes. In Total Alkali-Silica relationships the NDD show chemical variation from ultramafic to dacite through basalt and basaltic andesite (Figure not shown). Some samples show chemical features like MgO > 8%, SiO₂ > 52%, TiO₂ ≤ 0.5% and CaO/Al₂O₃ < 1 similar to that found in boninitic rocks [31, 32, 33, 34].

In under investigated samples Mg# (Mg # = molar 100 Mg/Mg + Fetotal) show variation like 89–85, 79–64, 80–43 and 74–49 in ultramafic dykes, group I, II and III dykes respectively. Such a change in Mg# is consistent with the fractional crystallization of ferromagnesian minerals [35]. The presence of normative quartz content in studied dolerite samples (excluding ultramafic samples) having Mg# >70 may indicate their derivation from multiple parental magmas. Mir and Alvi, [36] have suggested more investigation in terms of isotope geochemistry and radiometric data of ultramafic dykes from Keshergarya village, Singhbhum craton. They suspect their relationship with the mafic members of the NDD. Tholeiite and calc-alkaline trends are commonly based on AFM ternary plot (A = Na2O + K2O, FeO* = total iron as FeO, and M = MgO) [37]. In AFM diagram the NDD show tholeiitic trend. Ultramafic dykes concentrate towards MgO corner of AFM diagram (Figure 3).

Figure 3.

K₂O + Na₂O-Fe₂O₃^t-MgO (AFM) diagram showing theoleiitic trend of NDD. Field lines are after Kuno [37] and Irvine and Baragar [38].

During the partial melting or fractional crystallization the transitional elements like Nickel (Ni) and Cobalt (Co) are compatible with olivine whereas Scandium (Sc), Chromium (Cr) and Vanadium (V) are compatible with clinopyroxene [39], hence these elements are important in petrogenetic studies of basic rocks. These elements are useful to demarcate the primary nature of magma as it has been noted that primary mid ocean ridge basalt (MORB) magmas retain high concentration of Ni (> 250–400 ppm), Cr (> 600 ppm) and Mg # > 70 [35]. Mg#, Ni & Cr varies like {(85–89, 150–304 & 560–2458), (64–79, 45–145 & 255–733), (43–80, 9–73 & 31–524), (49–74, 17–43 & 42–226)} respectively in concern ultramafic dykes, group I, II and III mafic dykes. Such geochemical observations infer that the samples with low Mg #, Cr and Ni values may have evolved through fractional crystallization of olivine and pyroxene [35]. Further, it has been suggested that some dyke samples having similar Mg# with distinct Ni and Cr contents and some samples having distinct Mg# with similar Ni and Cr contents indicates that either the diverse extents of partial melting of the same source or heterogeneous mantle sources are responsible for the generation of different phases of the Newer dolerite dykes. Ti/V values ranging from 20 to 50 indicates the low oxygen fugacity ( ƒO2) i.e. reduced condition of magma generation like MORB setting whereas Ti/V values ranging from 10 to 20 are markers of high ƒO2 i.e. oxidizing condition of magma generation like subduction zones or supra-subduction zones settings [40]. In concern Newer dolerite dykes, Ti/V values range from 14 to 30, 9–29, 10–34 and 14–32 in ultramafic dykes, group I, II and III dykes respectively which indicates generation of melts for these dykes had occurred under varied oxidizing conditions.

Mafic intrusions in subduction environments are important for deciphering interaction between subduction slabs and mantle. Such interactions usually result in the mantle wedge being enriched in LILE by introduction of fluids and /melts from the converging lithosphere [41]. Both fluids and melts can be introduced at different depths above a subduction zone [41]. Thus, mafic rocks across subduction zone environments may record variable degrees of mantle source modification by slab derived components [41].

The studied NDD have low K/Rb ratios up to 320 perhaps suggesting the source region of the Newer Dolerites experienced fluid modification [41, 42]. The ratios of elements such as Barium (Ba), Thorium (Th), Zirconium (Zr) and Niobium (Nb) are useful to know about the subduction zone related metasomatism of mantle, hence the values of Ba/Th, Ba/Zr & Ba/Nb in ultramafic dykes, group I, II and III dykes range like {(59–197, 3–6 & 38–119), (35–365; 1–5 & 18–195), (34–231, 1–6 & 10–76) and (37–228, 2–14 & 20–106)} respectively. Such values are higher than that of the average values of the continental crust which in turn points towards the subduction zone related metasomatism of mantle source of these rocks [42]. Two alternative processes could explain the negative Nb anomaly (Figure 4) observed in the NDD: (i) metasomatic enrichment of lithospheric mantle [44] and (ii) chemical interaction between lithospheric mantle and asthenosphere-derived magma having incompatible elements but little Nb [45]. However, high La/Nb and La/Ta of Newer dolerite dykes supports the metasomatic enrichment of lithospheric mantle as a reason for Nb anomalies. Hence, the negative anomalies of Nb and Ti on primitive mantle normalized patterns (Figure 4) [42], abundance of light rare earth elements (LREE) (Figure not shown), nearly flat sub-parallel pattern of heavy rare earth elements (HREE) (Figure not shown), chondrite normalized ratio of Lanthanum to Ytterbium (La/Yb_N < 12.0) and chondrite normalized ratio of Lanthanum to Samarium (La/Sm_N < 4.0) of concern NDD supports their affiliation with arc or subduction zone setting [46].

Figure 4.

Primitive mantle normalized multi-element spider diagram of NDD. Normalized values are after Sun and McDonald [43]. CLM- continental lithospheric mantle; E-MORB-enriched mid ocean ridge basalts; N-MORB-Normal mid ocean ridge basalts; OIB-Ocean island basalts.

5. Petrogenesis

The petrogenesis of mantle derived magmatic rocks can commonly be traced by their geochemical and isotopic data. The mafic magmatic activity in the form of dykes at intervals throughout the Proterozoic provides a useful window to monitor mantle evolution [47, 48].

From the mentioned geochemical characteristics, it may be inferred that the NDD having Mg# <60 are evolved members that have been formed through fractional crystallization of Mg-rich minerals like olivine and/or pyroxene [49]. On TiO₂ vs. Al₂O₃/TiO₂ (Figure 5a) and CaO/TiO₂ diagrams (Figure 5b) NDD plot in MORB, low TiO₂ boninite & high-Mg andesite fields which suggests the compatibility of Ti and retention of Al and Ca in residual phases like pyroxenes, garnet, plagioclase and spinel [50]. Further, these relationships indicate that low TiO₂ samples were derived from relatively more hydrously fractionated magmas and high TiO₂ samples were derived from least hydrously fractionated magmas [51].

Figure 5.

(a) TiO₂ vs. Al₂O₃/TiO₂ and (b) TiO₂ vs. CaO/TiO₂ binary diagrams for NDD. HMA-high Mg Andesites and MORB-Mid Ocean ridge basalts.

Fractional crystallization associated with crustal contamination (AFC) is an important process during magma evolution that may modify both elemental and isotopic compositions [52]. As we know that the concentration of Rubidium (Rb), Barium (Ba), Potassium (K), Sodium (Na) etc. is rich in crustal materials whereas P₂O₅ and TiO₂ is poor in these materials. Hence, any crustal contamination of mafic magma changes the primary geochemistry of magma accordingly [41]. However, in concern samples the low content and range of K₂O and NaO₂ are indications of least crustal contamination in these rocks. In addition to this, the ratio of Cerium to Lead (Ce/Pb) and Niobium to Uranium (Nb/U) are not changed due to partial melting, hence, these ratios can be applied to know about the effects of alteration or crustal contamination of mafic rocks. In concern samples these ratios are higher than that of upper continental crust (Ce/Pb = 3.2) and (Nb/U = 9) [53]. Therefore, it is suggested that the investigated NDD have least or no contamination of crustal materials.

Trace element ratios, such as La/Yb, Th/Yb, Ba/La and La/Nb are widely used to identify the metasomatic agents and estimate the flux from the subducted slab [54]. All these ratios in case of NDD imply varying inputs of sediment and fluid components from the subducting slab in their formation.

The high (La/Yb)N and (Gd/Yb)N in combination with relatively low HREE abundance of the NDD suggest that they may have formed by low degrees of partial melting of a garnet bearing source. Asthenospheric or deep or plume and lithospheric or shallow or non-plume derived mafic melts or basalts can be differentiated or evaluated by geochemical ratios like Lanthanum (La) /Tantalum (Ta) and La/Nb. Thompson and Morrison [55] suggested that values of La/Ta =10–12 and La/Ta >30 indicates that basaltic rocks may have been derived from asthenospheric mantle and lithospheric mantle respectively. Further, Wang et al. [56] used La/Nb ratio to discriminate asthenospheric mantle and lithospheric mantle sources. They suggested La/Nb <1.5 for asthenospheric mantle derived mafic rocks and La/Nb >1.5 for lithospheric mantle derived mafic rocks. In majority of NDD it has been seen that La/Ta is greater than 30 and La/Nb is greater than 1.5 that reveals their derivation may be from lithospheric mantle source. Moreover, on primitive mantle-normalized multi-element diagram (Figure 4), NDD show patterns differed from that of normal mid ocean ridge basalts, enriched mid ocean ridge basalts, ocean island basalts and continental lithospheric mantle and show depletion of Ba, Nb, Sr., P, Ti and richness of Zr. Such geochemical characteristics are similar to that found in arc or back-arc extension basalts [57, 58].

6. Tectonic setting

Keeping in view the importance of dykes or dyke swarms in identification of large igneous provinces, reconstruction of continents, continental rifting and continental-continental collision events [59], the geochemical studies on NDD may have potential in understanding the geodynamic evolution of Singhbhum craton in Precambrian times. The association of mafic dykes with the initiation of sedimentary basins and their geochemistry retaining long term memories of subduction processes in the lithosphere mantle are too well known [60]. Origin of NDD has been either related to arc/back-arc tectonic setting i.e. non-plume source [42, 61, 62, 63, 64, 65, 66] or plume source [5, 67]. In addition, Boss [68] suggested both depleted and enriched mantle source for Newer dolerite dykes. However, mantle plume model faces some issues in evaluation of origin of the NDD due to following reasons (i) age of NDD varying from 2800 to 1000 Ma [5, 69, 70] suggests that it is hard to tap a uniform magma source for such a long time interval, (ii) absence of large scale mafic lavas in Singhbhum craton having intraplate setting/geochemistry and (iii) further, the occurrence of voluminous hydrous lithospheric mantle across the cratons developed during the Archaean (~3 Ga) and its role in the Proterozoic magmas [48].

7. Conclusions

Reported age of newer dolerite dykes vary from 900 Ma to 2800 Ma and traverse a number of rock types in some regular sets like NNE–SSW and NW-SE trends. Variations in major elements, particularly SiO₂, Al₂O₃, CaO, TiO₂ contents, and CaO/TiO₂ and Al₂O₃/TiO₂ ratios in these dykes indicates that their Ca and Al are held in the residual mantle phases such as clinopyroxene, plagioclase, spinal and garnet. The overall low Mg #, Cr and Ni values in studied NDD indicate their evolution through fractional crystallization of olivine and pyroxene. A few dyke samples having similar Mg# with distinct Ni and Cr contents and some samples having distinct Mg# with similar Ni and Cr contents indicates that either the diverse extents of partial melting of the same source or heterogeneous mantle sources are responsible for the generation of different phases of the Newer dolerite dykes. In studied NDD low content and narrow range of K₂O and NaO₂ in addition to higher values of Ce/Pb and Nb/U than that of upper continental crust are indications of least crustal contamination in these rocks.

Values of Ba/Th, Ba/Zr & Ba/Nb in NDD are higher than that of the average values of the continental crust which in turn points towards the subduction zone related metasomatism of mantle source of these rocks. Further, the enriched LREE and flat sub-parallel pattern of HREE along with La/YbN <12.0 and La/SmN <4.0 of concern NDD supports their affiliation with arc or subduction zone setting. Moreover, their primitive mantle-normalized multi-element patterns differed from that of normal mid ocean ridge basalts, enriched mid ocean ridge basalts, ocean island basalts and continental lithospheric mantle and show depletion of Ba, Nb, Sr., P, Ti and richness of Zr. Such geochemical characteristics are similar to that found in arc or back-arc extension basalts.

Acknowledgments

Author is sincerely thankful to the Director, Leh Campus Taru, University of Ladakh for providing facilities in preparation of this book chapter. Author pays thanks to Dr. Malik Zubair A. and Dr. Farooq A. Dar for their valuable suggestions during write up of this book chapter. Constructive comments and valuable suggestions from anonymous reviewers are duly acknowledged.