have adhered to all principles of academic honesty and integrity, and have ..... Winter JD (2009) : Principles of Igneous and Metamorphic petrology ( 2nd Edition)
Geochemistry of Lava flows from Kasara and Kalsubai section Submitted for partial fulfillment of the requirements of the degree of
Master of Science by
Vimal Pal 135060012 Supervisor Prof. Kanchan Pande
Department of Earth Sciences INDIAN INSTITUTE OF TECHNOLOGY BOMBAY
Mumbai: 400076 2015
Approval Sheet This dissertation entitled “ Geochemistry of Lava flows from Kasara and Kalsubai Section” submitted by Mr. Vimal Pal bearing Roll Number 135060012, is approved for the degree of Master of Science in Applied Geology.
Examiner
Supervisor
Date:
Place:
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DECLARATION I, Vimal Pal, hereby declare that this thesis represents my own ideas and words, and wherever I have used the ideas or words of others, I have duly cited and referenced the original sources. I have adhered to all principles of academic honesty and integrity, and have not misinterpreted, fabricated or falsified any information in my thesis, and I realise that doing so will result in disciplinary action from the institute or the sources which have not been properly cited or from whom adequate permission has not been taken.
( Vimal Pal ) Roll No.135060012
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Acknowledgements I would like to express my deepest gratitude to all those who helped me to complete this this dissertation project work. I am deeply indebted to my supervisor Prof. Kanchan Pande for his enthusiastic guidance and help during my field work, lab work and literature survey. He has shown me right path and enhanced my self-confidence. I would like to express my earnest thanks to Prof. G. Mohan ( Head of Department), Dr. Soumyajit Mukherjee (Faculty Advisor), Prof. T.N.Singh, Prof. G.N.Jadhav, Prof. S.C.Patel, Prof. G. Mathew, and Prof. S.Banerjee for providing me the best facilities to conduct the project work and their valuable suggestion during my project presentation. I would also like to thanks Ms. Trupti Gurav, Mr. Nilesh Borkar, Mr. Prem Verma, Mr. N. N. Vengurlekar and Mr. Sanjay for helping me during sample preparation. I am very grateful to Ms. Anjali Vijayan, Mr. Sharad Pal and Mr. Virinder Pal Singh for providing valuable literatures and accompanying me in the field respectively. At last but not the least I would like to convey my heartfelt thanks to my friends and family for their continuous encouragement and support.
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List of figures: Fig. 1.1 Range in composition for critical oxides and elements in each GPB in kalsubai Sub-group (Hooper et al., 1988)……………………………………………..…………………………...….02 Fig.2.1 Global distribution of large igneous provinces (in Red)……………………………………….....03 Fig. 2.2 Map showing distribution of Deccan lavas and associated intrusives in the Western and Central India(GSI)……………....……………………………………………………………………...…04 Fig 2.3 Deccan Trap lava Formations of the Western Ghats. ( Based on Bodas et al., 1985; Cox and Hawkesworth, 1985; Bean et al., 1986; Devey and Lightfoot, 1886)……………………............05 Fig 3.1 ( Map Showing different locations of collected samples for Kasara section )……………………08 Fig.3.2 Different locations of samples collected from field along road side……………………..………09 Fig. 3.3 Map showing different points of sample collection……………………………………………...10 Fig.3.4 Simple flow along Kasara-Khardi road side. These rocks are highly jointed and almost amygdales free………………………………………………………………….……………………...…… Fig.3.5 Compound flow near latifwadi. Here bottom, core and top of low was clearly observed. Elongation of vesicles suggest flow toward southern side………………….......………......……11 Fig.3.6 components of compound flow are defined. Base of flow has pipe basalt and inverted y. Core lacks vesicles . ………………………………….......………………………………...………….12 Fig. 3.7 Thalghat GPB near abandoned Tunnel ……………………………………………...………...…12 Fig.3.8 Zeolites and other cherty minerals have been observed at some locations………….…………..13 Fig. 3.9 Spectacular view from top of Bhasta valley. From there distinct horizontal flows can be observed………………………………….....……………………………………………….……..13 Fig.3.10 Spheroidal Weathering in Basalt………………………………………………………….……14 Fig.3.11 Comb Structure in Secondary filling………………………………………………………...….14 Fig. 3.12 Highly vesicular flow …………………………………………………………………………..14 Fig.3.13 In Kalsubai hill we can see perfectly horizontally spread simple flows………………….….…15 Fig. 3.14 bouldery outcrops of basalt (surface flow)…………………………………………………..….15 Fig.4.1 Porphyritic texture ( Near Khardi)…………………………………………………………….…17 Fig.4.2 Intergranular texture. Pyroxene is surrounded by plagioclase laths……………………………..17 Fig. 4.3 Ophitic and sub-ophitic texture…………………………………………………………………..17 Fig. 4.4 Giant Plagioclase basalt (GPB) from Thalghat…………………………………………………..17
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Fig.4.5 Porphyritic texture : Plagioclase as phenocryst present in matix. Notice matrix is containing pyroxene and also plagioclase has been changed as comparison with GPB…………...……...…18 Fig. 4.6 Trachitic or pilotaxitic texture : Lath shaped small plagioclase are strongly aligned…………...18 Fig.4.7
Olivine grains are clearly observed in S4 Sample from Kalsubai hill………………………..…19
Fig.4.8 Palagonite alteration near rim of secondary precipitated chert. The glassy material has been replaced by palagonite………………………………………………………………………………...…..19 Fig 4.9 Clinopyroxene in plagioclase matrix. Cpx shows inclined extinction……………………………20 Fig. 4.10 Zeolite filling (secondary) in vesicles…………………………………………………………..20 Fig.5.1 TAS diagram showing different samples collected along Kasara and Kasubai hill. All of them lie on basaltic field except one which is relatively richer in silica content……………………………….25 Fig.5.2 AFM diagram denoting variations in bulk rock composition of samples. All samples are in Tholeiitic basalt field………………………………………………………………………………….…..25 Fig.5.3 ACF diagram showing bulk rock composition of samples. This diagram is used to denote the relative enrichment of Fe+Mg, Ca and Al in samples. This is a useful indicator of the relative proportions………………………………………………………………………………………………..26 Fig 5.4 chondrite normalized values of trace elements for different samples……………………………27
List of Tables: Table 2
showing detailed description of Kalsubai Subgroup and major GPB litho-boundaries of different formations……………….……………………………………………………………..6
Table 5.1 Values of major, minor and trace elements in standards used for analysis…………….……...22 Table 5.2 Major oxides and trace elements geochemistry………………….…………………………….23 Table 5.3 showing observed and average values of different Formations in Kalsubai subgroup…….…..24
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Abstract This project work is concentrated on geochemical classification of collected samples from Kalsubai and Kasara sections, Maharasthra and put them in correct chemo-stratigraphic column. The main objective was to understand procedures of geochemical analysis of the lava flows and characterize their formation in Deccan stratigraphy. In the field first lava flow classification was done by using literature survey as simple or compound flow. Their characteristics are totally different. Compound flow has three major constituent as bottom, core and top based on their vesicles orientation. Characterization of GPB markers in field was also in priority as in Kalsubai Sub-Group GPBs plays an important role in identification of formations. The presence of these Giant Plagioclase Basalts (GPB) are proof of crystal fractionation within the magma chamber. After field work collected sample were analysed through thin section study as well as data obtained from geochemical studies. In thin section we have observed a gradual change in size of groundmass as we move from one formation to another and mineralogical characters also become changed. Phenocryst present in one formation is different from another formation. Harmonic results also observed in geochemical data as from one formation to other certain element shows significant changes in their concentration. Different graphs have been plotted to represent the data in easy way and chemical classification of collected samples was also done.
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Index
Chapter 1: Introduction and Objectives …………………………………01
Chapter 2: Literature Survey
…………………………………03
Chapter 3: Field Observations
…………………………………07
Chapter 4: Thin Section Study
………………………………….16
Chapter 5: Geochemical Studies
………………………………….. 21
Chapter 6: Discussion and Conclusion ………………………………… 28
References
…………………………………….29
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Chapter 1: Introduction and Objectives 1.1 Definition of Problem The project is entitled as “Geochemistry of Lava flows from Kasara and Kalsubai section” seeks to characterize the geochemical properties of lava flows along Kasara and Kalsubai hill. Kasara ghat includes lower part of Kalsubai subgroup as Jawhar and Igatpuri formations. Giant plagioclase basalt ( GPB) is found from Thalghat area. Different flows are also indentified in Kasara section. Pipe basalt is seen at bottom of flow. Phyric and aphyric both type of flows are observed. Phenocryst of plagioclase as well as partial altered olivine is seen in field area. Kalsubai hill includes upper part of Kalsubai subgroup i.e. Thakurvadi and Bhimashankar formations. Based on petrography of collected samples as well as using geochemical analysis we can reform the chemostratigraphy of Kalsubai Subgroup.
Based on earlier studies, the basalt flows in Western Ghats of the Deccan have been divided into compound flows and simple (compact) flows (Walker, 1972; Marathe et al., 1981). Compound flows are massive, poorly jointed and amygdaloidal. Each compound flow includes many separate flow units of lava toes which are a few centimeters to a few meter thick, laterally discontinuous and are often defined by thin oxidized surfaces with pipe vesicles above their base and ropy structures developed in their upper parts. Simple flows in contrast are essentially nonamygdaloidal except for the clearly vesicular and oxidized flow tops or flow top breccia and they have joints perpendicular to their lower contacts. Ghodke (1978) has shown that individual flows of both types can be mapped over many square kilometers. For the field identification of individual flows or closely related flow sequences as well as for grouping them into recognizable stratigraphic units, the above criterion have been used. Further, the lava sequence is divided into individual flows based mainly on textural characters (aphyric-microphyric to porphyritic), phenocryst assemblage (feldspar, mafics) and characteristic geomorphic features. 1.2 Chemical Type A chemical type is defined as one or more members having the same chemical composition, regardless of stratigraphic position (Wright et al. 1973). In defining a chemical type those elements
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less indicate to vary with weathering and other alteration processes are most useful. Thus MgO, CaO, TiO2, P2O5, Zr, Y, Nb etc are typically stable during alteration and are very useful than such ‘mobile’ elements as K2O, Ba, Rb etc. Within each chemical type there are few samples, which fall outside the normal chemical range, making the definition of a chemical type less rigid. While most part of the definition each chemical type tends to be characterized by its own set of megascopic characters. 1.3 GPB: Giant Plagioclase Basalts are valuable markers for mapping the stratigraphy of the Kalsubai Sub-group. The GPBs are among the most evolved flows (largest abundances of the incompatible elements, smallest Mg* values) found in Western Ghats. Their mineralogical and chemical composition contrast sharply changes with the overlying/underlying more primitive flows and their usefulness as markers in the field is well recognized.
Fig.1.1
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Chapter 2: Literature Survey 2.1 Background Today, the DVP (Deccan Volcanic Provinces) occupies an area of over 5,00,000 sq. km however, original estimates of the extent of the lava pile prior to erosion and possible downthrow on the western side into the Arabian Sea are of the order of 1 to 1.5 million sq km. The lava pile has a maximum thickness of over 1.5 km in the western parts of India and it reduces to few tens of meters near exposed margins of the province. Kalsubai, a prominent peak in the western parts of Ahamadnagar district bordering Thane district of Maharashtra is the tallest peak of the province (>1640m).
Fig.2.1 Global distribution of large igneous provinces (in Red)
The DVP is largely made of basaltic lava flows with subordinate volumes of intrusive bodies and relatively trivial proportion of pyroclastics. The lava flows are nearly horizontal over vast regions of the province but they assume measurable dips in the western parts of the province 3|Page
(near Mumbai) and in Satpura ranges. The average thickness of the individual lava flows is around 20 m and they can be traced for few to nearly hundred kilometers. As far as the rock sequences hidden beneath the Deccan lavas are concerned, direct evidences are provided by the localities where the Deccan lavas are seen resting over these sequences.
Fig. 2.2 Map showing distribution of Deccan lavas and associated intrusives in the Western and Central India (GSI)
If continuation of the older sequences is assumed beneath the Deccan Trap then, a variety of rock types including granitic rocks, sedimentary rocks as well as metamorphic rocks of Achaean to Jurassic age can be presumed to underlie the DVP. Further, crustal fragments brought up by dykes also provide a ready-made window to peep into the rocks that underlie the DVP. The overall composition of the Deccan Basalts is tholeiitic-quartz and olivine tholeiites, olivine rich basalts and alkali olivine basalts. The lower traps are similar to the primary effusives during the Deccan magmatism and are therefore undifferentiated. Many areas has been found showing uniformity in the chemical composition of the lower traps. In contrast to the uniformity of lower traps, upper traps show heterogeneity in chemical composition. (Ghose, 1976)
2.2 Stratigraphy of Deccan Basalt: Combination of field mapping with petrochemical and isotopic studies permit division of the basalt stack of Western Ghats into twelve formations which fall in three sub-groups 1) Kaksubai Sub-Group 2) Lonavala Sub-Group 3) Wai Sub-Group
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Fig 2.3 Deccan Trap lava Formations of the Western Ghats. ( Based on Bodas et al., 1985; Cox and Hawkesworth, 1985; Bean et al., 1986; Devey and Lightfoot, 1886)
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Table 2 showing detailed description of Kalsubai Subgroup and major GPB litho-boundaries of different formations
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Chapter 3: Field Observations 3.1 Objective of Field work To collect the samples from different formations for future study of petrography and geochemical analysis. 3.2 Plan of Field Work Field work is carried out in two different traverse1)- Along Khardi- Kasara-Thalghat 2)- Along Bari- Kalsubai Based on literature survey samples from different formation are collected. 3.3 Traverse 1 : Khardi-Kasara-Thalghat (Along Mumbai-Nashik Highway) 3.3(a) Location : Toposheet 47 E/6, 47 E/9 & 47 E/10 (on survey of India) Along this section we have found compound flow along road side, Giant plagioclase Basalt (GPB), zeolites, phyric and aphyric flow. 3.3(b) Description of stops ( From Kasara Section ) : S.N. 1 2 3 4 5 6
Stop Sample NameCodeSample Code Stop 1 K1 Stop 2 K2 Stop 3 K3 Stop 4 K4 Stop 5 K5 Stop 6 K6
Latitude N19˚37.107’ N19˚37.576’ N19˚40.552’ N19˚41.412’ N19˚41.778’ N19˚41.803’
Longitude E73˚24.959’ E73˚27.642’ E73˚30.087’ E73˚29.759’ E73˚29.854’ E73˚31.273’
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3.4 Traverse 2 : Bari-Kalsubai section 3.4(a) Location: Toposheet 47 E/10 ( on survey of India) Along this section we collected samples of Thakurvadi and Bhimashankar formations. Kalsubai is designated as the type section of the Thakurvadi formation with a maximum thickness of 650 m. The boundary between Bhimashankar and Khandala formations is marked by the presence of Giravali GPB exposed at 1480 m. 3.4(b) Description of stops ( From Kasara Section ) : S.N. 1 2 3 4 5 6 7
Stop Name Stop 1 Stop 2 Stop 3 Stop 4 Stop 5 Stop 6 Stop 7
Sample Code S1 S2 S3 S4 S5 S6 S7
Latitude N19˚36.45’ N19˚36.157’ N19˚36.16’ N19˚36.12’ N19˚36.045’ N19˚36.071’ N19˚36.0812’
Longitude E73˚43.29’ E73˚43.029’ E73˚43.02’ E73˚43.01’ E73˚42.889’ E73˚42.801’ E73˚42.75’
Fig 3.1 ( Map Showing different locations of collected samples for Kasara section ) 8|Page
Fig.3.2 Different locations of samples collected from field along road side
Traverse 2: Bari- Kalsubai hill section
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Fig. 3.3
During this whole field work different flows were identified and samples from different horizons were collected for further thin section studies and geochemical analysis. Thalghat is heavily travelled truck route between Kasara and Nasik via Igatpuri. Area between Khardi and Kasara has shown exposures of alternate sequences of simple, plagioclase phyric and compound aphyric, amygdaloidal flows. The simple flows typically have amygdale free, well jointed (block joints) lower parts and amygdaloidal flow tops. The compound flows on the other hand have amygdales throughout the individual unit and exhibit pipe amygdales and inverted ‘Y’ structures only at the bases of different units.
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Fig.3.4 Simple flow along Kasara-Khardi road side. These rocks are highly jointed and
almost amygdales free. Near Latifwadi location compound, aphyric, amygdaloidal flow is exposed. It marks the base of the progressively coarsening upward sequence of upper parts of Jawhar formation.
Fig.3.5 Compound flow near latifwadi. Here bottom, core and top of low was clearly observed. Elongation of vesicles suggest flow toward southern side.
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Fig.3.6 components of compound flow are defined. Base of flow has pipe basalt and inverted y. Core lacks vesicles .
Near abandoned tunnel on Thalghat road typical Giant Plagioclase Basalt can be traced along road side. This is the type locality for the Thalghat GPB which marks the top of the Jawhar formation. The flow is characterized by 2-3 cm long phenocrysts laths of plagioclase which is found in medium to fine grained ground mass.
Fig 3.7 12 | P a g e
In Kasara-Nasik road lot of secondary alteration are observed. Zeolite, chert and other secondary minerals have been precipitated at these sites.
Fig.3.8 Zeolites and other cherty minerals have been observed at some locations
At the top of Bhatsa Valley (Top of Thalghat) offers a panoramic view of Jawhar and Igatpuri formations. Here we seen simple flow that was devoid of vesicles. Rocks were jointed there.
Fig. 3.9
Spectacular view from top of Bhasta valley. From there distinct horizontal flows can be observed.
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Kalsubai has the thickest lava pile ( ̴ 1000 m) and is the highest peak in the Deccan. Kalsubai hill is designated as the type section of the Thakurvadi formation with a maximum thickness of 650 m.
Fig.3.10 Spheroidal Weathering in Basalt
Fig.3.11 Comb Structure in Secondary filling.
Crystals in a vein grow perpendicular to vein wall Indicates infilling of an open fracture
Fig. Highly vesicular flow near Kalsubai Fig. 3.12
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Simple flow
Fig.3.13 In Kalsubai hill we can see perfectly horizontally spread simple flows.
Fig. 3.14 15 | P a g e
Chapter 4: Thin Section Study Total 8 thin sections were prepared to study petrography of obtained samples from field. Thin section study was aimed to know1) Understand the mineralogy of the rocks 2) Study the alteration (if any) of the minerals that would help in interpretation of geochemical data
Here I will discuss some general petrographical observations during thin section study. The samples prepared from Kasara and Khardi area shows distinctly porphyritic texture with phenocrysts of plagioclase feldspar, altered olivine and occasional clinopyroxene. The ground mass is fine grained with granular to sub-ophitic texture. GPB found near abandoned tunnel on Thalghat road is type locality for Thalghat GPB which marks the top of Jawhar formation. The flow is characterized by the presence of phenocrysts of plagioclase feldspar in a fine to medium grained, altered groundmass. In thin sections we observed a distinctly porphyritic texture with large phenocrysts of plagioclase as well as microphenocrysts of clinopyroxene and altered olivine. The ground mass is distinctly medium grained, hypocrystalline with patches of altered glass. Lying above the Thalghat GPB a plagioclase phyric, amygdaloidal flow exposed at this (S-4) locality forms a part of the typical Igatpuri formation which is petrographically distinct as the presence of olivine in both the phenocryst assemblage and the ground mass of this flow as against the restricted occurrence of olivine only as microphenocrysts in the plagioclase phyric flows of Jawhar formation. Samples collected from top of thalghat shows mafic flow which is distinctly porphyriric with abundant glomerocrysts of clinopyroxene and olivine.
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Fig.4.1 Porphyritic texture ( Near Khardi) road)
Fig. 4.3 Ophitic and sub-ophitic texture
Fig.4.2 Intergranular texture. Pyroxene is surrounded by plagioclase laths
Fig. 4.4 Giant Plagioclase basalt (GPB) from Thalghat
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Fig.4.5 Porphyritic texture : Plagioclase as phenocryst present in matix. Notice matrix is containing pyroxene and also plagioclase has been changed as comparison with GPB
Fig. 4.6 Trachitic or pilotaxitic texture : Lath shaped small plagioclase are strongly aligned
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Fig.4.7
Olivine grains are clearly observed in S4 Sample from Kalsubai hill. Olivine crystals are not altered so it suggests that sample is not suffered weathering on much amount
Fig.4.8
Palagonite alteration near rim of secondary precipitated chert. The glassy material has been replaced by palagonite. 19 | P a g e
Fig. 4.9
Fig. 4.10 20 | P a g e
Chapter 5: Geochemical Studies 5.1 General Introduction ICP-AES is an emission spectrophotometric technique, exploiting the fact that excited electrons emit energy at a given wavelength as they return to ground state. The fundamental characteristic of this process is that each element emits energy at specific wavelengths peculiar to its chemical character. Although each element emits energy at multiple wavelengths, in the ICP-AES technique it is most common to select a single wavelength (or a very few) for a given element. The intensity of the energy emitted at the chosen wavelength is proportional to the amount (concentration) of that element in the analyzed sample. Thus, by determining which wavelengths are emitted by a sample and by determining their intensities, the analyst can quantify the elemental composition of the given sample relative to a reference standard.
5.2METHODOLOGY The 9 samples were broken into small chips and crushed into fine ( 200 micron or 75 mesh) powder using a mechanical rock crusher. The crushing vessel and its metallic rings were cleaned with water and isopropyl alcohol at each stage. 0.25 g of the sample powder was then fused with 0.75 g of lithium metaborate (LiM) and 0.50 g of lithium tetraborate (LiT) in platinum crucibles, following which they were dissolved in 1N HCl (Freshly Prepared), and the solutions were made to 100 ml using the same solvent. Similar solutions were also prepared for two standards and one blank. After this, the solutions were further diluted with distilled water in the ratio of 1:5, and were analysed using ICP-AES for major, minor and trace elements. Loss on ignition for each sample was also measured, by heating 1 g of the powdered sample to 950˚C for 20-30 mins. LOI was calculated as the percentage loss in weight after heating. We used 5 standards for calibration of our samples that are attached in next sheet. The obtained data was represented graphically using Petrograph which is open source software for analysis of rocks. For some graphs Microsoft Excel was also used.
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Table 5.1 Values of major, minor and trace elements in standards used for analysis
Rock type
Dolerite (DNC-1)
Basalt (BHVO-2)
Oxides
SiO2 TiO2 Al2O3 FeO Fe2O3 Fe2O3T MnO MgO CaO Na2O K2O P2O5 Elements Sc V Cr Co Ni Cu Zn Sr Y Zr Nb Ba
47.15 0.48 18.34 7.32 1.79 9.97 0.15 10.13 11.49 1.89 0.234 0.07
49.9 2.73 13.5
12.3 0.166 7.23 11.4 2.22 0.52 0.27
31 148 270 57 247 100 70 144 18 38 2 118
32 317 280 45 119 127 103 389 26 172 18 130
Andesite (AGV-2)
Wt. (%) 59.3 1.05 16.91
6.69 0.099 1.79 5.20 4.19 2.88 0.48 ppm 13 120 17 16 19 53 86 658 20 230 15 1140
Quartz Latite (QLO-1)
Granodiorite (GSP-2)
65.6 0.62 16.2 2.97 1.02 4.35
66.6 0.66 14.9
1.00 3.17 4.20 3.60 0.25
54 3.2 7.2 29 61 340 24 185 10 1370
4.90 0.041 0.96 2.10 2.78 5.38 0.29 6.3 52 20 7.3 17 43 120 240 28 550 27 1340
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Table 5.2. Major oxides and trace elements geochemistry (determined using ICP-AES at SAIF IIT Bombay)
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(Average values taken from Bean et al. 1986, Subbarao et al, 2000)
Table 5.3 showing observed and average values of different Formations in Kalsubai subgroup
Fig.5.1 TAS diagram showing different samples collected along Kasara and Kasubai hill. All of them lie on basaltic field except one which is relatively richer in silica content.
Fig.5.2 AFM diagram denoting variations in bulk rock composition of samples. All samples are in Tholeiitic basalt field.
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Fig.5.3 ACF diagram showing bulk rock composition of samples. This diagram is used to denote the relative enrichment of Fe+Mg, Ca and Al in samples. This is a useful indicator of the relative proportions
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Sample/ chondrite Fig.5.4
The above graph is showing chondrite normalized values of trace elements for different samples. It is observed that at P we are having low value. Possible explanation of this can be given as Apatite rich in Phosphorous went out of melt. P being compatible in apatite restrict itself in Apatite and resulting decrease in concentration of P in melt. ( plotting based on Wood et al. (1979))
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Chapter 6: Discussion and Conclusion From the results obtained from geochemistry of sample are plotted in TAS (Total Alkali Silica) diagram to check which rock type we were dealing with. Almost all the samples fall on Basalt field except one. More Sr content in trace elemental alanysis favors the obtained result as it was expected. Sr is compatible to plagioclase feldspar and thin section studies confirms the presence of good amount of plagioclase phenocrysts. Triangular AFM diagram shows that the samples fall on Tholeiitic basalt field. It is also found during plotting of trace elemental data against chondrite normalized sample values that significant low value of P can be explained by apatite removal from melt. As P is compatible with Apatite so its absence in melt made it depleted in P concentration. Chemostratigraphy of samples is done using elements that are least susceptible to weathering. We compared the values of samples from earlier work carried out in our area and found that values are matching closely. By this way we categorized our samples in different formations. Major and minor elements analysis are in sync with the values already provided in the chemostratigraphic classification which enabled to interpret their positions.
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References
Bean JE, Turner CA, Hooper PR, Subbarao KV and Walsh JN, (1986) : Stratigraphy, composition and form of the Deccan Basalts, Western Ghats, India, Bull Volcano 48, 6183
Bodas MS, Khadri SFR, Subbarao KV (1988) Stratigraphy of the Jawhar and Igatpuri Formations, Western Ghat lava pile, India. In: Subbarao KV (eds) Deccan flood basalts. Memoir of the Geological Society of India 10:235–252
Bose, M.K. (1972): Deccan Basalts. Lithos 5 , 131-45
Ghose, N.C.(1976) composition and origin of Deccan basalts, Lithos 9, 65-73
Higgins MD, Chandrasekharam D (2007) Nature of Sub-volcanic magma chambers, Deccan Province, India: evidence from quantitative textural analysis of plagioclase megacrysts in the giant plagioclase Basalts. J Petrol 48:885–900
K.V. Subbarao, M.S.Bodas, S.F.R.Khadri and J.E. Beane Penrose Deccan 2000, Field Excursion Guide to The Western Deccan Basalt Povince, Geo. Soci. Of India
Potts PJ, Handbook of Rock Analysis
Sheth, H. C., Ray, J. S., Senthil Kumar, P., Duraiswami, R. A.,Chatterjee, R. N., Gurav,T., 2011 Recycling of flow-top breccia crusts into molten interiors of flood basalt lava flows: Field and geochemical evidence from the Deccan Traps. In: Ray, J., Sen, G., Ghosh, B. (Editors), Topics in Igneous Petrology, pp.161-180. Springer.
Winter JD (2009) : Principles of Igneous and Metamorphic petrology ( 2nd Edition)
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