Relationship between 2.37 Ga Boninitic Dyke Swarms of Indian Shield: Evidence from the Central Bastar Craton and NE Dharwar Craton

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(1)33 國立臺灣師範大學理學院地球科學研究所碩士論文 Department of Earth Sciences College of Science. National Taiwan Normal University Master Thesis. Relationship between 2.37 Ga Boninitic Dyke Swarms of Indian Shield: Evidence from the Central Bastar Craton and NE Dharwar Craton. 廖倩儀 Chien-Yi Liao. 指導教授：. 謝奈特. 博士. Adviser : J. Gregory Shellnutt, Ph.D. July, 2018.

(2) Abstract The Indian Shield is cross-cut by a number of distinct Paleoproterozoic mafic dyke swarms. The density of mafic dyke swarms in the Dharwar and Bastar Cratons is amongst the highest on Earth. Globally, Proterozoic boninitic (high SiO2 and MgO, low TiO2) dyke swarms are rare compared to tholeiitic dyke swarms and yet they are common within the Southern Indian Shield. In this study, the geochronology and geochemical results were used to constrain the petrogenesis and relationship of the boninitic dyke in the central Bastar Craton and the NW Dharwar Craton. A single U-Pb baddeleyite age from a boninitic dyke near Bhanupratappur of the Central Bastar Craton yielded a weighted-mean 207Pb/206Pb age of 2365.6 ± 0.9 Ma and is within error of boninitic dykes (2368.5 ± 2.6 Ma; U-Pb, baddeleyite) near Karimnagar and further south near Bangalore (2365.4 ± 1.0 Ma to 2368.6 ± 1.3 Ma; U-Pb, baddeleyite) of the Dharwar Craton. Dykes in both Karimnagar and Bhanupratappur region have boninitic characteristic (SiO2 = 52.9 to 56.1 wt%, MgO = 5.9 to 19.0 wt%, and TiO2 = 0.31 wt% to 0.78 wt%). The Nd isotopes (εNd(t) = –6.4 to +4.5) of the Bhanupratappur dykes are more variable than Karimnagar dykes (εNd(t) = –0.7 to +0.6) but overlap. The variability Nd isotopes may be related to crustal contamination either during fractional crystallization or during emplacement. Rhyolite-MELTS modeling using the least contaminated sample (B/29) indicates that fractional crystallization may partly influence the geochemical variability of the boninitic dykes in these areas. The trace element modeling shows the primary melt may be derived from a pyroxenite mantle source near the spinel-garnet transition zone. The chemical and temporal similarities of the Bhanupratappur dykes with the dykes of the Dharwar Craton (Karimnagar, Dharwar) indicate they are all members of the same giant radiating dyke swarm. It is I.

(3) possible that the dyke swarm was related to a mantle plume which assisted in break-up of an unknown supercontinent. Furthermore, the results indicate that the Bastar and Dharwar Cratons were adjacent but likely had a different configuration before 2.37 Ga. Keyword:. Indian. Shield,. Boninitic. Dyke. Contamination, Paleoproterozoic.. II. Swarm,. Geochronology,. Crustal.

(4) Acknowledgement I am grateful to Professor Shellnutt for giving this chance to work on this project and learn from him. Thank you for always guide me with patience, and being the mentor of my thesis and my life. Thanks to Dr. Steven Denyszyn for teaching and helping me through the U-Pb baddeleyite dating; Dr. Kosiyathu R. Hari and Dr. Neeraj Vishwakarma for their assistance of the field work in India; Dr. Kuo-Long Wang and Dr. Typhoon Lee and their assistants Wen-Yu Hsu, Fu-Long Lin and Masako Usuki for all the help on the isotopic analysis; Dr. Huai-Jen Yang and Chia-Ju Chieh for the help on trace elements analysis; Dr. Yoshiyuki Iizuka and Yu-Hsiang Wang for all the help on the SEM and EPMA experiments. I would like to give my special thanks to my labmates (Carol, Wen-Yu, Ha, Thuy, Jen, Dieu, Chi, Andy and Sally) and classmates for the encouragement, happiness and all the support you gave me. Thanks to all my friends and their advice during the difficult times. A big thank you to my family for their patience and support during my studies and to Ping-Chen for always standing by me. Thanks everyone. . III.

(5) Table of Contents Abstract ............................................................................................................................ I Acknowledgement ......................................................................................................... III Table of Contents .......................................................................................................... IV List of Figures ............................................................................................................... VI List of Pictures ............................................................................................................ VII List of Tables .............................................................................................................. VIII Chapter 1 Introduction .................................................................................................. 1 1.1 Crustal evolution ............................................................................................. 1 1.2 Mafic dyke swarms of the Southern Indian Shield ......................................... 6 1.3 Purpose of this study ....................................................................................... 9 1.4 Geological background ................................................................................... 9 1.4.1 Indian Shield.............................................................................................. 9 1.4.2 Bastar Craton ............................................................................................11 1.4.3 Dharwar Craton ....................................................................................... 14 1.5 Sample location ............................................................................................ 18 1.5.1 Bhanupratappur area................................................................................ 18 1.5.2 Karimnagar area ...................................................................................... 18 Chapter 2 Petrography................................................................................................. 21 2.1 Dykes from the Bhanupratappur area ........................................................... 21 2.2 Karimnagar Dykes ........................................................................................ 22 Chapter 3 Research Methods ...................................................................................... 29 3.1 Baddeleyite U-Pb Dating .............................................................................. 29 3.2 Whole Rock Geochemistry ........................................................................... 32 3.2.1 Major Elements ....................................................................................... 32 3.2.2 Trace Elements ........................................................................................ 36 3.2.3 Sr, Nd Isotopes ........................................................................................ 40 IV.

(6) Chapter 4 Results.......................................................................................................... 47 4.1 Geochronology ............................................................................................. 47 4.2 Bhanupratappur area, Bastar Craton ............................................................. 50 4.2.1 Major Element ......................................................................................... 50 4.2.2 Trace Element .......................................................................................... 52 4.2.3 Sr-Nd Isotopes ......................................................................................... 56 4.3 Karimnagar area, Dharwar Craton ................................................................ 58 4.3.1 Major element.......................................................................................... 58 4.3.2 Trace element .......................................................................................... 59 4.3.3 Sr-Nd Isotopes ......................................................................................... 62 Chapter 5 Discussion .................................................................................................... 65 5.1 Geochemical correlation of the Bhanupratappur boninitic dykes ................ 65 5.1.1 Boninitic dyke swarms across the Bastar Craton .................................... 65 5.1.2 Paleoproterozoic (2.3 Ga) mafic dyke swarm across the Dharwar Craton69 5.2 Petrogenesis of the 2.3 Ga boninitic dykes ................................................... 74 5.2.1 Fractional crystallization ......................................................................... 74 5.2.2 Crustal contamination.............................................................................. 79 5.2.3 Heterogeneous mantle source .................................................................. 84 5.3 Emplacement model of the 2.3 Ga boninitic dykes ...................................... 87 5.4 Position of Bastar Craton in Paleoproterozoic.............................................. 89 5.4.1 The Bastar – Dharwar Craton connection ............................................... 89 5.4.2 Position of Indian Shield and Supercontinents........................................ 93 Chapter 6 Conclusion ................................................................................................... 95 References...................................................................................................................... 96 Appendixes .................................................................................................................. 104 Appendix 1: Results of Rhyolite MELTS modeling of the boninitic dykes. .... 104 Appendix 2: Mixing modeling results of Sr isotope and SiO2. ........................ 107. V.

(7) List of Figures Figure 1.1 Figure 1.2 Figure 1.3 Figure 1.4 Figure 1.5 Figure 1.6 Figure 1.7 Figure 3.1 Figure 3.2 Figure 3.3 Figure 3.4 Figure 3.5 Figure 4.1 Figure 4.2 Figure 4.3 Figure 5.1 Figure 5.2 Figure 5.3 Figure 5.4 Figure 5.5 Figure 5.6 Figure 5.7 Figure 5.8 Figure 5.9 Figure 5.10 Figure 5.11 Figure 5.12 Figure 5.13 Figure 5.14 Figure 5.15. Schematic rates of production of basalts, komatiites, norites, and boninites with respect to time, continental growth, and relative global heat production.................................................................................................... 8 Major Cratons and structural features of the Indian Shield ...................... 10 Simplified geological map of the Bastar craton ...................................... 133 Simplified geological map of the Dharwar craton .................................. 166 Geological map of east-central peninsular India ..................................... 199 Distribution of the mafic dyke swarm within Bhanupratappur region...... 20 Distribution of the mafic dyke swarm within Karimnagar region ............ 20 The analytical result of the standard (NBS987) of Sr isotope................... 44 The analytical result of the standard (JMC Nd) of Nd isotope. ................ 44 The elusion curve of the first column separation ...................................... 45 The elusion curve of the Sr column separation ......................................... 45 The elusion curve of the second (Nd) column separation ......................... 46 Concordia plot of baddeleyite U-Pb TIMS data for sample B-29. ............ 49 Trace element plot of the mafic dykes of the central Bastar Craton ......... 55 Trace element plot of the Karimnagar dykes .......................................... 661 Comparison of the major element compositions of the Bhanupratappur boninitic dykes from the southern and central Bastar Craton ................... 67 Trace element plot of the boninitic dykes of the central and southern Bastar Craton ............................................................................................. 68 Comparison of the major element compositions of the 2.3 Ga mafic dykes from the Dharwar Craton .......................................................................... 71 Trace element plot of the mafic dykes of the Dharwar Craton ................. 72 Comparasion of 2.3 Ga boninitic dykes between Karimnagar and Bhanupratappur region .............................................................................. 73 Rhyolite-MELTS modeling results ........................................................... 77 Th/Yb vs. Ta/Yb basalt tectonomagmatic discrimination diagrams ......... 81 Dy/Dy* vs. Dy/Yb diagram ...................................................................... 82 εNd(t) versus ISr of the dykes from the Bhanupratappur and Karimnagar region. ........................................................................................................ 82 Mixing modeling of a least contaminated dyke (B-29) and Archean basement rocks of the Bastar Craton ......................................................... 83 Trace elemental partial melting modeling ................................................. 86 Convergence model of the Western Dharwar Craton towards the Eastern Dharwar Craton ......................................................................................... 86 A schematic model for the genesis of the 2.37 Ga boninitic dykes of the Bastar and Dharwar Craton. ...................................................................... 88 Possible continental reconfiguration of Bastar and Dharwar Craton. ....... 91 Comparasion of 2.3 Ga dykes between Dharwar Craton and Bhanupratappur region .............................................................................. 92. VI.

(8) List of Pictures Picture 2.1 Picture 2.2 Picture 2.3 Picture 2.4 Picture 2.5 Picture 2.6 Picture 3.1 Picture 3.2 Picture 3.3 Picture 3.4 Picture 3.5. Optical microscope image of sample B/3 ................................................. 23 Optical microscope image of sample B/24 ............................................... 24 Optical microscope image of sample B/19 ............................................... 25 Optical microscope image of sample B/13 ............................................... 26 Optical microscope image of sample KN/1 .............................................. 27 Optical microscope image of sample KN/2 .............................................. 28 Triton T1 TIMS. ........................................................................................ 31 Wilfley table. ............................................................................................. 31 Panalytical AxiosmAX WDXRF. ................................................................. 33 Claisse M4 Fluxer...................................................................................... 35 Agilent 7500ce ICP-MS. ........................................................................... 37. VII.

(9) List of Tables Table 1.1 Table 1.2 Table 3.1 Table 3.2 Table 3.3 Table 4.1 Table 4.2 Table 4.3 Table 4.4 Table 4.5 Table 4.6 Table 4.7 Table 5.1. Paleoproterozoic LIP records of the Indian shield ......................................... 5 Geochronology results of the Paleoproterozoic mafic dykes from EDC .. 177 The analyzing result of the standard (SDC-1, BIR-1a) of major element ... 34 The analyzing result of the standard (BCR-2) of trace element. ................. 38 The analyzing result of the standard (BHVO) of trace element. ................. 39 U-Pb isotopic data for baddeleyite from the Bastar craton dyke (B/29). .... 48 Major elements analyses of the Bhanupratappur area, Bastar Craton. ........ 51 Trace elements concentration of the Bhanupratappur area, Bastar Craton.. 54 Sr-Nd isotopic ratio of Bhanupratappur area, central Bastar Craton. .......... 57 Major elements analyses of the Karimnagar area, Dharwar Craton. ........... 58 Trace elements concentration of the Karimnagar area, Dharwar Craton. ... 60 Sr-Nd isotopic ratio of Karimnagar area, Dharwar Craton.......................... 63 Temperature range in which different minerals crystallized in the RhyoliteMELTS modeling result............................................................................... 68. VIII.

(10) Chapter 1 Introduction 1.1 Crustal evolution The Earth’s crust is divided into simatic (Si+Mg) oceanic crust and sialic (Si+Al) continental crust. The oceanic crust is thin (~7 km on average), dense, composed of basaltic rocks less than 200 Ma in age, whereas the continental crust is thick (~35 - 40 km on average), buoyant, and has an average composition similar to andesite, and is up to 4.0 Ga. The continental crust extends laterally until the continental slope and vertically from the surface to the Mohorovicic discontinuity (Moho) (Cawood et al., 2013; Cogley, 1984; Rudnick and Gao, 2003). Modern continental crust probably did not exist in large volume during the Hadean or Paleoarchean, which was produced through a variety of processes that culminated in the development of plate tectonics (Rogers and Santosh, 2004). Although the precise timing of modern plate tectonics is debatable, there were inherent differences between thermal conditions of modern Earth and that of Archean Earth. During the Archean it is likely that the Earth had higher heat flow and that the crust was thin and rheologically weak, so collision/subduction zones might not able to develop (Rogers and Santosh, 2004; Smithies et al., 2004). Instead it is thought that proto-continental crust was produced mostly by vertical tectonic processes related to the diapiric upwelling (mantle plume) of the mantle (Cawood et al., 2006). Cratons are the stable parts of the continental crust that have undergone very little deformation (Bleeker and Ernst, 2006; Cawood et al., 2013; Davis et al., 2004; Rogers and Santosh, 2003). Almost every continent is comprised of a craton. Cratons can be described as shields and platforms, the former comprised of crystalline and. 1.

(11) metamorphic rocks, the latter are the basement rocks, which are covered by both lithified and unlithified sediments (Bleeker and Ernst, 2006; Cawood et al., 2013; Davis et al., 2004). Cratons are the continental nuclei involved in the supercontinent cycle, whereby rifting and break-up might be affected by mantle plume processes. A supercontinent is amalgamation of cratons into a single entity that encompasses the majority of continental crust (Aspler and Chiarenzelli, 1998; Bradley, 2011; Hoffman, 1999; Rogers, 1996; Rogers and Santosh, 2003; Salminen et al., 2009). Supercontinents experience a cyclical development, where they are in a constant state of consolidation and dissolution (Santosh et al., 2009; Bradley, 2011; Rogers and Santosh, 2004; Sankaran, 2003). The break-up of a supercontinent into smaller continental blocks is often accompanied by the eruption of rift-related flood basalt and widespread plutonism, which are comparatively easy to identify in the geological record (Ernst and Bleeker, 2010; Santosh et al., 2009). Understanding the assemblage of a supercontinent requires evidence using a variety of different techniques that utilize various disciplines of geoscience including: geology, paleontology, paleomagnetism, geochronology, and geochemistry (Belica et al., 2014; Zhao et al., 2004). Regarding the most recent supercontinent, Pangaea, there is sufficient evidence to support a reconstruction of high certainty due to the abundance of geologic data, fossil record, and paleoclimatic data, in addition to seafloor magnetic anomaly and paleomagnetic data (Belica et al., 2014; Salminen et al., 2009). The reconstruction of older supercontinents is more complex than the reconstruction of Pangaea. For example, the reconstruction of Paleoproterozoic supercontinents is more difficult due to the limited paleontological and paleoclimate evidence; thus the geological, paleomagnetic and geochronological data are relatively more important in reconstructing ancient 2.

(12) supercontinents (Aspler and Chiarenzelli, 1998; Belica et al., 2014; Bleeker and Ernst, 2006; Halls et al., 2007; Pesonen et al., 2003; Rogers and Santosh, 2003; Salminen et al., 2009). Large igneous provinces (LIPs) and their plumbing systems are one of the key tools for palinspastic reconstructions (Mahoney and Coffin, 1997; Coffin and Eldholm, 1991; Ernst and Srivastava, 2008; Bryan and Ernst, 2008). LIPs are volumetrically large ( 0.1 x 106 km3), have a short magmatic duration, and are typically associated with anorogenic tectonic settings (Bryan and Ernst, 2008; Coffin and Eldholm, 1991). Most LIPs are thought to be derived by mantle plumes, and some are associated with continental break-up. The eruption of continental flood basalts (CFB) and formation of passive margins are not the only evidence for mantle plume-related break-up events. Massive emplacement of dykes, which represent the magma conduits of CFB, can be used to recognize mantle plumes in the past (Ernst and Buchan, 1997). There are nonmantle plume-related LIPs, which are generated by plate-related tensional stress. This stress is thought to be caused by upper-mantle convection that thins the lithosphere and permits decompressional mantle melting (Hagstrum, 2005). LIPs are also useful in solving other geological problems, as they are often associated with mass extinctions, regional basin formation, regional uplift, and the formation of precious and base metal deposits (Bryan and Ernst, 2008; Ernst and Srivastava, 2008). Paleoproterozoic LIPs are generally identified by their feeder system of mafic dykes, large layered intrusions, and sill provinces, because the flood basalt remnants are mostly eroded or deformed (Bryan and Ernst, 2008). Consequently, mafic dyke swarms are increasingly important for the reconstruction of Paleoproterozoic supercontinents as they provide a record that can be used for 3.

(13) geochronology, geochemistry, and paleomagnetism (Bryan and Ernst, 2008; Ernst and Bleeker, 2010; Ernst and Buchan, 1997; Hou et al., 2008; Yale and Carpenter, 1998). The Indian Shield has one of the highest dyke densities on Earth, which makes it an ideal setting to investigate ancient large igneous provinces and temporally constrain ancient supercontinents (Meert and Pandit, 2015; Saha and Mazumder, 2012; Srivastava et al., 2008; Valdiya, 2015). There are four major Proterozoic mafic dyke swarms of the Southern Indian Shield that span from the western Dharwar Craton to the eastern Singhbhum Craton (Table 1.1).. 4.

(14) Table 1.1 Paleoproterozoic LIP records of the Indian shield (modified from Ernst and Srivastava, 2008). Name (Location). Age and method. References. A. 2366 Ma Bangalore LIP (Dharwar Craton) (Henur, near Mysore) (Near Bangalore) (West of the Cuddapah basin). 2366±1 Ma; U-Pb baddeleyite 2365±1.1 Ma; U-Pb baddeleyite 2454±100 Ma; Sm-Nd. Halls et al. (2007) French et al. (2004) Zachariah et al. (1995). B. 2180 Ma Mahbubnagar LIP (Dharwar craton) Mahbubnagar (Shimoga region) (NE Dharwar) Bijli (northern margin Dharwar). 2173±64 Ma; Sm-Nd 2180 Ma; U-Pb baddeleyite and zircon 2180 Ma; U-Pb baddeleyite and zircon 2180±25 Ma; Rb-Sr. Pandey et al. (1997) French et al. (2004) French et al. (2004) Divakara Rao et al. (2000). C. 1891-1882 Ma Southern Bastar – Cuddapah LIP. Pulivendla and Tadpatri (Cuddapah basin). 1882.4±1.5 Ma; U-Pb baddeleyite 1891.1±0.9 Ma; U-Pb baddeleyite 1883.0±1.4 Ma; U-Pb baddeleyite and zircon 1885.4±3.1 Ma; U-Pb baddeleyite 1899±20 Ma; Ar-Ar phlogopite. (West of the Cuddapah basin). 1894 Ma; U-Pb baddeleyite. Halls et al. (2007). (SW of Cuddapah basin). 1879±5 Ma; Ar-Ar. Chatterjee and Bhattacharya (2001). (Bhanupratappur, central Bastar) BD2 swarm (Dantewara, South Bastar) BD2 swarm (Bastanar, South Bastar) Pulivendla (Cuddapah basin). Shellnutt et al. (2018) French et al. (2008) French et al. (2008) French et al. (2008) Anand et al. (2003). D. 1600 Ma Dalma LIP (Singhbhum craton) Dalma. 1619±38 Ma; Rb-Sr. Roy et al. (2002). Base of the Semri Group. 1631±5 Ma; U-Pb zircon. Rasmussen et al. (2002). 5.

(15) 1.2 Mafic dyke swarms of the Southern Indian Shield A mafic dyke is a sheet-like, tensional stress-related structure that intrudes bedrock and has a basaltic composition (Ernst et al., 1995; Ernst and Buchan, 1997). A dyke swarm is comprised of numerous dykes of similar age, composition, and orientation (Ernst et al., 1995; Ernst and Buchan, 1997). Mafic dyke swarms can be classified into three geometric types: (1) parallel dyke swarm, (2) small radiating dyke swarm, and (3) giant radiating dyke swarm (Ernst et al., 1995; Ernst and Buchan, 1997; Hou, 2012). The parallel dyke swarms are usually related to regional tensional plate stress. The small radiating dyke swarms are highly-localized feeder systems of individual volcanic edifices. The giant radiating dyke swarms are typically related to the breakup of a supercontinent and a mantle plume (Ernst et al., 1995; Hou, 2012; Yale and Carpenter, 1998). Mafic dyke swarms can be used to identify paleo-stress fields, locate mantle plume centres, produce deformation maps, and reconstruct ancient supercontinent (Ernst et al., 1995; Halls, 1982; Srivastava et al., 2008). Mafic dyke swarms are conspicuous in the Indian Shield (Ernst and Srivastava, 2008; Srivastava et al., 2008). They range in age from the Paleoproterozoic (2.37 Ga) to Eocene and are primarily found in the Dharwar, Bastar, and Singhbhum Cratons (Belica et al., 2014; French and Heaman, 2010; French et al., 2008; Kumar et al., 2012; Srivastava et al., 2015). The Indian Shield has one of the highest dyke densities, as it is cross-cut by at least four known Paleoproterozoic mafic dyke swarms (Ernst and Srivastava, 2008; Halls, 1982; Halls et al., 2007). The dykes range in composition from basaltic, mostly tholeiitic, to boninitic compositions (Demirer, 2012; French and Heaman, 2010; French et al., 2008; Halls et al., 2007; Kumar et al., 2012; Murthy et al., 1985; Srivastava and Gautam, 2012; Srivastava and Gautam, 2015; Srivastava et 6.

(16) al., 2008). Table 1.1 shows four Paleoproterozoic dyke swarms. The 2.36 Ga dyke swarms in the Eastern Dharwar Craton is known as Dharwar giant dyke swarm, broadly E-W trending, and they are iron-rich tholeiites. The 2.18 Ga Mahbubnagar dykes in the Dharwar Craton are northwest trending, and they are tholeiitic and subalkalic in composition. The 1.89 Ga dyke swarm located in the southern Bastar Craton and Cuddapah basin in the Dharwar Craton and are NW-SE trending dolerite, which may be related to a mantle plume event. The 1.6 Ga Dalma dyke swarm is located in the Singhbhum Craton however much less is known about this swarm. Neoarchean to Paleoproterozoic dyke swarms of the Indian Shield have boninitic (higher SiO2 and higher MgO content) characteristics (Halls et al., 2007; Srivastava, 2008; Srivastava and Gautam, 2012). Boninite and boninitic rocks are mafic igneous rocks that have MgO > 8 wt%, SiO2 > 52 wt% and TiO2 < 0.5 wt% (Le Bas, 2000). Boninitic rocks tend to have high LILE concentrations with low Gd/Yb and high La/Gd compared to primitive mantle compositions (Smithies, 2002; Smithies et al., 2004). Modern boninites are mostly reported from the Phanerozoic subduction-related settings, the classic example of modern boninite resides in the Bonin Islands (Crawford et al., 1989; Hickey and Frey, 1982; Smithies et al., 2004; Taylor et al., 1994). Smithies et al. (2004) suggested that Archean to Paleoproterozoic boninites have different petrogenesis than their Phanerozoic counterparts. Figure 1.1 shows that komatiite magmatism gives way to boninite/norite magmatism by the end of the Archean and is thought to be related to crustal thickening (Hall and Hughes, 1993). Ancient boninites are subdivided into two petrogenetic groups. The Whundo type boninite is similar to the petrogenesis of modern boninite (i.e. oceanic arcs), whereas the Whitney type may be derived by plume-induced melting of refractory mantle (Smithies et al., 2004). 7.

(17) Figure 1.1 Schematic rates of production of basalts, komatiites, norites, and boninites with respect to time, continental growth (dotted line), and relative global heat production (dashed-dotted line). Model from Hall and Hughes (1993).. 8.

(18) 1.3 Purpose of this study There are a significant amount of dykes and dykes swarms in the Indian Shield that have yet to be identified, due to a dearth of geological investigations (Meert and Pandit, 2015; Saha and Mazumder, 2012; Srivastava et al., 2008). Thus, the investigation of mafic dykes throughout the Indian Shield will help to evaluate the veracity of palinspastic reconstructions, and help to constrain the petrogenetic processes that produce large volumes of mafic magma and their chemical diversity. Dykes in both Dharwar and Bastar Craton have boninitic characteristics, our aim is to use the geochronology, geochemistry result and isotope ratios to constrain the petrogenesis of the boninitic dykes and the relationship between Dharwar and Bastar Craton.. 1.4 Geological background 1.4.1 Indian Shield The Indian Shield, as shown in Figure 1.2, is comprised of cratons that formed and stabilized during the Archean to Paleoproterozoic and Meso- to Neoproterozoic mobile belts (Meert and Pandit, 2015; Saha and Mazumder, 2012; Srivastava, 2008; Valdiya, 2015). There are four cratons: the Dharwar Craton in southern India, the Bastar Craton in central India, the Singhbhum Craton in eastern India, and the Aravalli-Bundelkhand Craton in northern India. All of these cratons are demarcated by rifts or mobile belts (Meert and Pandit, 2015; Saha and Mazumder, 2012; Valdiya, 2015). The Aravalli-Bundelkhand Craton is separated from the southern cratons by the Central Indian Tectonic Zone (CITZ), whereas the Dharwar and Bastar Craton are separated by the Godavari rift. The boundary between the Bastar and Singhbhum. 9.

(19) Craton is the Mahanadi rift.. Figure 1.2 Major Cratons and structural features of the Indian Shield (modified from Srivastava, 2008).. 10.

(20) 1.4.2 Bastar Craton Located in central India, the Bastar Craton is bound by the Godavari rift in the SW, the Mahanadi rift in the NE, the Narmada–Son rift in the north, and the Eastern Ghats Mobile Belt in the SE (Figure 1.3). The basement rocks of the Bastar Craton are 2.5 - 2.6 Ga Gneissic Complex and are comprised of tonalite–trondhjemite gneisses and greenstone belts (e.g. the Sonakhan belt) (Ramakrishnan, 1990; Sarkar et al., 1993; Valdiya, 2015). The oldest age reported of the basement rocks are from 3.6 Ga tonalitic enclaves (Ghosh, 2004) and a 3.51 Ga xenocrystic zircon within a gneiss (Sarkar et al., 1993). The Bastar Craton contains at least three major supracrustal sequences, oldest to youngest: the Dongargarh Supergroup, the Sakoli Group and the Sausar Group, respectively. The Dongargarh Supergroup consists of Dongargarh Granite and rhyolite, the Sakoli Group contains of low-grade metamorphic rocks such as slates and phyllites, and the Sausar Group consists of metasediments and manganese-bearing ores (Meert and Pandit, 2015; Naqvi and Rogers, 1987; Saha and Mazumder, 2012; Valdiya, 2015). The sedimentary basins of the Bastar Craton are the Chhattisgarh Basin and the Indravati Basin, along with four minor basins. Mafic dyke swarms are widespread in the Bastar Craton, have a variety of ages and compositions, and they mainly intrude Archean basement rocks (French et al., 2008; Srivastava and Gautam, 2009; Srivastava and Gautam, 2015). Many of the dykes are NW-SE to WNW-ESE trending and generally 20 to 30 m wide, but can be up to 200 m in width. Srivastava (2008) documented three groups of mafic dyke swarms in the southern Bastar Craton: the Meso-Neoarchean sub-alkaline mafic dykes (BD1), Neoarchean to Paleoproterozoic boninite-norite dykes (BN), and Paleoproterozoic subalkaline mafic dykes (BD2) (French et al., 2008; Sarkar et al., 1993; Srivastava, 1999; 11.

(21) Srivastava, 2006; Srivastava et al., 2016; Srivastava and Singh, 2003). The only dated dykes in the southern Bastar Craton are members of the BD2 dykes, which have weighted-mean zircon or baddeleyite U-Pb ages of 1883.0 ± 1.4 Ma, 1883.5 ± 4.4 Ma, 1891.1 ± 0.9 Ma (French et al., 2008). On the other hand, NWSE to WNW-ESE trending mafic dyke swarms exposed in the central Bastar craton are poorly studied. Ramachandra et al. (1995) noted a suite of mafic dykes in Bhanupratappur and Keskal region, located in south of the Chattisgarh basin, and categorized the dykes as sub-alkaline basalts. The dykes are considered to be correlative to either the BD1 or BN swarms in the southern Bastar Craton (Srivastava and Gautam, 2012). The dyke swarm in Bhanupratappur was dated by Shellnutt et al. (2018) using baddeleyite U-Pb TIMS method and discovered that it is the same age (1882.4 ± 1.5 Ma) as the Paleoproterozoic dykes from the southern Bastar Craton. The BN dykes from the central Bastar Craton have yet to be investigated. Mafic dyke swarms in the northern Bastar Craton are exposed in south of the Chattisgarh basin, and trend in ENE-WSW (Srivastava and Gautam, 2015).. 12.

(22) Figure 1.3 Simplified geological map of the Bastar craton (modified after Srivastava et al. 2015).. 13.

(23) 1.4.3 Dharwar Craton The Dharwar craton (Figure 1.4) is bound by the Deccan volcanic province to the north, the Godavari Rift and the Eastern Ghats mobile belt to the east, the Southern Granulite Terrane to the south and the Arabian Sea to the west (Naqvi and Rogers, 1987; Ramakrishnan and Vaidyanadhan, 2008). The Dharwar Craton is comprised of four major units: the Peninsular gneisses forming a typical Archean TTG gneiss terrain, the supracrustal belts (i.e. greenstone belts), the Proterozoic metasedimentary basins and the late potassic granites, such as the Closepet granite. The Dharwar Craton was divided into two distinct cratonic domains: (1) Western Dharwar craton (WDC, c.a. 3.3 – 2.7 Ga) and (2) Eastern Dharwar craton (EDC, c.a. 3.0 – 2.5 Ga). The NW-SE trending Chitradurga schist belt is in the middle of WDC and EDC. The emplacement of the Closepet Granite next to the Chitradurga schist belt represents the amalgamation of WDC and EDC during ~ 2.5 Ga (Chadwick et al., 2000; Meert and Pandit, 2015; Naqvi and Rogers, 1987; Saha and Mazumder, 2012). Mafic dyke swarms are widespread in the Dharwar craton, but the dyke distribution in the WDC is comparatively less than EDC (Demirer, 2012; Halls, 1982; Halls et al., 2007; Srivastava et al., 2015). Previous studies have classified the dykes in the Dharwar Craton into at least four discrete mafic dyke swarms by their orientation, geochemistry and U-Pb geochronology results (Chatterjee and Bhattacharji, 2001; Demirer, 2012; French and Heaman, 2010; Halls et al., 2007; Kumar et al., 2012; Pandey et al., 1997; Srivastava et al., 2014; Srivastava et al., 2015). The largest dyke swarm is the 2.37 Ga, WNW-ESE Dharwar dyke swarm. It is very extensive, as it is scattered across the Dharwar Craton and is comprised of the Bangalore dykes in the south and central parts of the Dharwar Craton and the Karimnagar dykes in the NE 14.

(24) (Demirer, 2012; French and Heaman, 2010; Halls et al., 2007; Kumar et al., 2012). The 2.21 Ga Kunigal dyke swarm is thought to be related to Pan-Dharwar LIP, with mostly NNW-SSE to N-S orientations. The 2.18 Ga Mahbubnagar dyke swarm is generally NW-SE to WNW-ESE-trending. There are 1.88 Ga mafic dykes and sills in the Cuddapah Basin that are correlated to the dykes of the Southern Bastar Craton (i.e. Southern Bastar-Cuddapah LIP) and mostly trend E-W to ENE-WSW (Belica et al., 2014).. 15.

(25) Figure 1.4 Simplified geological map of the Dharwar craton (modified after Srivastava et al. 2015), showing the distribution of the Proterozoic mafic dykes that has been dated, detailed age and trend are shown in Table 1.2. The black dashed line represents the Chitradurga Fault, the boundary of EDC and WDC (after Mahadevan, 2008). The dated mafic dykes are classified into four groups and marked in different colors: ~2.37 Ga Bangalore swarm (green), ~2.21 Ga swarm (red), ~2.18 Ga swarm (cyan), and ~1.89 Ga swarm (purple).. 16.

(26) Table 1.2 Geochronology results of the Paleoproterozoic mafic dykes from the eastern Dharwar Craton, India (after Srivastava et al. 2015). No.. Location. Age and method. Reference. 1. Henur, near Mysore. 2366 ± 1 Ma; U-Pb baddeleyite. Halls et al. (2007). 2. Harohalli. 2365.4 ± 1.0 Ma; U-Pb baddeleyite. French and Heaman (2010). 3. Penukonda. 2365.9 ± 1.5 Ma; U-Pb baddeleyite. French and Heaman (2010). 4. Chennekottapalle. 2368.6 ± 1.3 Ma; U-Pb baddeleyite. French and Heaman (2010). 5. Hyderabad. 2367.1 ± 3.1 Ma; U-Pb baddeleyite. Kumar et al. (2012a). 6. Karimnagar. 2368.5 ± 2.6 Ma; U-Pb baddeleyite. Kumar et al. (2012a). 7. Somala. 2209.3 ± 2.8 Ma; U-Pb baddeleyite. French and Heaman (2010). 8. Kandlamadugu. 2220.5 ± 4.9 Ma; U-Pb baddeleyite. French and Heaman (2010). 9. Close to Closepet granite. 2215.2 ± 2.0 Ma; U-Pb baddeleyite. Srivastava et al. (2014). 10. Close to Closepet granite. 2211.7 ± 0.9 Ma; U-Pb baddeleyite Srivastava. Srivastava et al. (2014). 11. Mahbubnagar. 2173 ± 64 Ma; Sm-Nd whole-rock and minerals. Pandey et al. (1997). 12. Bandepalem. 2176.5 ± 3.7 Ma; U-Pb baddeleyite and zircon. French and Heaman (2010). 13. Dandeli (western Dharwar Craton). 2180.8 ± 0.9 Ma; U-Pb baddeleyite. French and Heaman (2010). 14. SW of Cuddapah basin. 1879 ± 5 Ma; Ar-Ar whole-rock. Chatterjee and Bhattacharji (2001). 15. Hampi. 1894 Ma; U-Pb baddeleyite. Halls et al. (2007). 16. Pulivendla (Cuddapah basin). 1885.4 ± 3.1 Ma; U-Pb baddeleyite. French et al. (2008). 17.

(27) 1.5 Sample location Samples were collected from the Karimnagar area in the northeast Dharwar Craton and the Bhanupratappur area of central Bastar Craton; the locations are shown in Figure 1.5. The dykes typically form forested ridges that can be easily identified using topographic maps or satellite images. Specific dykes were selected based on their accessibility, orientation, and mineralogy/composition. 1.5.1 Bhanupratappur area Boninitic dykes that trend NW-SE to WNW-ESE from Bhanupratappur area of the Bastar Craton are parallel to the Godavari and Mahanadi Rift and transect the Bengpal and Bailadila Groups. The length of the dyke swarm is around 50 km; 11 samples were collected for this study. The distribution of dykes and the sample location are shown in Figure 1.6. Most dykes were collected from ridges, however some were collected from road side exposures. 1.5.2 Karimnagar area Seven NE-SW-trending dykes were collected from the Karimnagar area. The darker-colored dykes were relatively easy to identify, compared to the lighter-colored Archean gneiss country rock (~2.9 Ga, Friend and Nutman, 1991). The distribution and sample locations of the dykes are shown in Figure 1.7.. 18.

(28) Figure 1.5 Geological map of east-central peninsular India (modified after French et al. 2008), yellow dots showing two sample locations in north-east Dharwar Craton and central Bastar Craton.. 19.

(29) Figure 1.6 Distribution of the mafic dyke swarm within Bhanupratappur region, the central Bastar Craton. Red circles represent the sample location.. Figure 1.7 Distribution of the mafic dyke swarm within Karimnagar region, the northeast Dharwar Craton. Red circles indicate the sample location.. 20.

(30) Chapter 2 Petrography The polished section preparation was conducted at the Yu-Neng Rock and Mineral Separation Co., Lanfang, Hubei province, China. The sections were used to check the alteration level and choose the least-altered samples for Sr, Nd isotopes and baddeleyite U-Pb dating experiments. A Carl Zeiss Axioplan 7082 polarizing optical microscope was used for the observation of the thin sections at the Department of Earth Science, National Taiwan Normal University.. 2.1 Dykes from the Bhanupratappur area Eleven mafic dykes were collected from the Bhanupratappur region. The rocks have doleritic texture and only some of them preserve the original mineralogy. Sample B/3 and B/24 are the least altered, 4 samples are moderate to highly altered (B/19, B/28b, B/29, B/33), and 5 samples highly altered (B/13, B/15, B/16, B/17 and B/20). The least-altered samples (Picture 2.1 and Picture 2.2) are ophitic to sub-ophitic, contain orthopyroxene (~40%), plagioclase (~25%), secondary amphibole (~25%), quartz (~5%), and euhedral Fe-Ti oxides (~5%). Plagioclase are euhedral and are typically 0.5 – 1.0 mm in length. Quartz and iron oxides are anhedral and ~ 0.1 mm length. The moderate to highly-altered samples (Picture 2.3) contain minerals with grain size between 0.5 –1.0 mm but the original igneous texture (ophitic) is retained. There are uralite (~70%) and amphibole (~15%) which likely replaced pyroxene and plagioclase. Subhedral to euhedral opaque iron oxides (~10%) and anhedral quartz (5%) are also present. The original igneous texture of the highly altered samples (Picture 2.4) cannot be ascertained as well as the original mineralogy. The altered rocks are comprised of amphibole (50%), clay minerals (saussurite) with the lath shape of. 21.

(31) plagioclase (40%), anhedral opaque iron oxides (5%), and anhedral quartz (5%).. 2.2 Karimnagar Dykes Samples for the Karimnagar dykes include 6 dolerites (KN/1, KN/3, KN/4, KN/5, KN/6 and KN/7) and gabbro (KN/2). The dolerites sample (Picture 2.5) are comprised of plagioclase (~40%), pyroxene (~40%), opaque Fe-Ti oxides (5–10%), quartz (~5%), and have ophitic to sub-ophitic texture. The plagioclase crystals are euhedral and ~0.5 mm in length. There are two types of pyroxenes, subhedral orthopyroxene and euhedral clinopyroxene. The grain size is smaller than 0.5 mm with columnar shape. The Fe-Ti oxides and quartz are anhedral and small grain size (i.e. < 0.5 mm), the FeTi oxides grow within other minerals and the quartz has a graphic texture. Sample KN/2 (Picture 2.6) is moderate to highly altered, coarse-grained gabbro that comprised of uralite (~30%), saussurite (~30%), chlorite (~20%), anhedral pyroxene (~10%), FeTi oxides (<5%) and quartz (<5%).. 22.

(32) (a) Plag. Opq Amp. (b) Plag. Opq Amp. Picture 2.1 Optical microscope image of sample B/3. (a) Plane polarized and (b) crosspolarized light.. 23.

(33) (a). Px. Plag. Opq. (b). Px. Plag. Opq. Picture 2.2 Optical microscope image of sample B/24. (a) Plane polarized and (b) crosspolarized light.. 24.

(34) (a). Px. Qtz Opq. Plag. (b). Amp. Px Qtz Opq. Plag. Amp. Picture 2.3 Optical microscope image of sample B/19. (a) Plane polarized and (b) crosspolarized light.. 25.

(35) (a). Qtz. Opq. (b). Qtz. Opq. Picture 2.4 Optical microscope image of sample B/13. (a) Plane polarized and (b) crosspolarized light.. 26.

(36) (a). Plag. Qtz. Px. Qtz. Px. Opq Px. (b). Plag Opq Px. Picture 2.5 Optical microscope image of sample KN/1, less altered dolerite. (a) Plane polarized and (b) cross-polarized light.. 27.

(37) (a) Px. Amp. Opq. (b) Px. Amp. Opq. Picture 2.6 Optical microscope image of sample KN/2, moderate to highly altered gabbro. (a) Plane polarized and (b) cross-polarized light.. 28.

(38) Chapter 3 Research Methods 3.1. Baddeleyite U-Pb Dating The baddeleyite U-Pb dating analytical work was carried out at University of. Western Australia (Picture 3.1), in peak-jumping mode using a secondary electron multiplier. Uranium was measured as an oxide (UO2). Fractionation and dead time were monitored using SRM 981 and SRM 982. Mass fractionation was 0.03 ± 0.06 %/amu. Data were reduced and plotted using the software packages Tripoli (from CIRDLES.org) and Isoplot 4.15 (Ludwig, 2011). All uncertainties are reported at 2σ. Baddeleyite were separated using a method modified after Söderlund and Johansson (2002). The details of the mineral separation procedures are list below. The size of baddeleyite grains are very small therefore no pre-treatment methods were used beyond cleaning the grains with concentrated distilled HNO3 and HCl, and no chemical separation methods were required. For ID-TIMS analysis, the samples were spiked with an in-house. 205. Pb-235U tracer solution, which has been calibrated against. SRM 981, SRM 982 (for Pb), and CRM 115 (for U), as well as an externally-calibrated U-Pb solution (the JMM solution from the Earth Time consortium). This tracer is regularly checked using “synthetic zircon” solutions that yield U-Pb ages of 500 Ma and 2000 Ma, provided by D. Condon (BGS). The weights of the baddeleyite crystals were calculated from measurements of photomicrographs and estimates of the third dimension. The weights are used to determine U concentration and do not contribute to the age calculation, and an uncertainty of 50% may be attributed to the concentration estimate. 1.. Separation procedures: 29.

(39) (1) The samples were crunched and milled to ca. 250-micron size in order to liberate individual baddeleyite grains. (2) The coarse sample powder was mixed with soap and water, and was passed over the Wilfley table (Picture 3.2) to create a concentrate of dense, flat minerals. (3) The flattened grains were hand-picked under the ethanol using a binocular microscope to isolate baddeleyite. 2.. Dissolution procedures: (1) Baddeleyite crystals were dissolved using Teflon microcapsules with vapor transfer of HF in a Parr pressure vessel placed in a 200oC oven for six days. (2) The resulting residue was re-dissolved in HCl and H3PO4. (3) The residue was placed on an outgassed, zone-refined rhenium single filament with 5 µL of silicic acid gel.. 30.

(40) Picture 3.1 Triton T1 TIMS hosted at University of Western Australia.. Picture 3.2 Wilfley table hosted at University of Western Australia.. 31.

(41) 3.2. Whole Rock Geochemistry The weathered outer crust of each sample was removed, and the rocks were cut. into smaller pieces and washed before further processing. The rock chips were pulverized for whole rock and trace elemental data, and isotope analyses at the YuNeng Rock and Mineral Separation Co., Lanfang, Hubei province, China. The major elements were analyzed at the XRF Laboratory, Department of Earth Sciences, National Taiwan Normal University. The trace elements were analyzed at Inorganic Geochemistry Laboratory, Department of Earth Sciences, National Cheng Kung University, and the Sr and Nd isotope were analyzed at the Mass Spectrometer Lab, Institute of Earth Science, Academia Sinica. 3.2.1. Major Elements. X-Ray Fluorescence Spectrometry (XRF) was used to determine the major elements, the model of the XRF is Panalytical AxiosmAX WDXRF (Picture 3.3), and ten major oxides were measured, including: SiO2, TiO2, Al2O3, Fe2O3t, MnO, MgO, CaO, Na2O, K2O, and P2O5. During the analysis, SDC-1 and BIR-1a were used as the standard after every five samples to detect the accuracy and stability of the instrument. The measured standard reference materials results are listed in Table 3.1. The preparation methods are as follows: 1.. Loss on ignition (L.O.I.) measurement: (1) Approximately 3 grams of sample powder was heated at 105oC in ceramic crucibles for 3 hours to release ambient water. Sample mass was recorded for the loss of water after being heated at 105oC.. 32.

(42) (2) The temperature was increased from room temperature to 900oC for 5 ~ 6 hours. The sample was oxidized and freed of molecular water. The sample was removed from the oven and cooled in room temperature air. Sample mass was recorded again for the loss of water after being heated at 900oC. 2.. Glass bead preparation: (1) 0.6000 ± 0.0005 grams of dry powder was mixed with 6.0000 ± 0.0005 grams of lithium borate with lithium bromide flux (49.75% Li2B4O7, 49.75% LiBO2 with 0.5% LiBr). (2) Fused at ~1200oC in platinum crucibles to make a glass bead using an M4 Fluxer (Picture 3.4).. Picture 3.3 Panalytical AxiosmAX WDXRF hosted at NTNU.. 33.

(43) Table 3.1 The analyzing result of the standard (SDC-1 and BIR-1a) of major element. Sample name BIR-1a BIR-1a BIR-1a BIR-1a BIR-1a BIR-1a BIR-1a BIR-1a BIR-1a BIR-1a BIR-1a BIR-1a BIR-1a BIR-1a BIR-1a R.V Accuracy (%) Precision (%) SDC-1 SDC-1 SDC-1 SDC-1 SDC-1 SDC-1 SDC-1 SDC-1 SDC-1 SDC-1 SDC-1 SDC-1 SDC-1 SDC-1 SDC-1 R.V Accuracy (%) Precision (%). SiO2. TiO2. Al2O3. Fe2O3. MnO. MgO. CaO. Na2O. K2O. P2O5. LOI. TOTAL. (%) 48.12 48.16 48.14 48.21 48.16 48.20 48.26 48.27 48.23 48.28 48.15 48.18 48.20 48.20 48.23 47.96. (%) 0.88 0.88 0.89 0.90 0.90 0.94 0.94 0.94 0.94 0.94 0.93 0.93 0.93 0.93 0.93 0.96. (%) 15.71 15.70 15.71 15.71 15.70 15.70 15.73 15.72 15.72 15.72 15.67 15.67 15.67 15.68 15.68 15.5. (%) 11.18 11.19 11.18 11.18 11.19 11.20 11.19 11.19 11.20 11.19 11.18 11.18 11.18 11.18 11.18 11.3. (%) 0.16 0.16 0.16 0.16 0.16 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.175. (%) 9.64 9.69 9.70 9.69 9.70 9.76 9.78 9.77 9.79 9.80 9.63 9.63 9.61 9.63 9.62 9.7. (%) 13.33 13.33 13.33 13.32 13.32 13.34 13.34 13.36 13.35 13.34 13.32 13.28 13.30 13.30 13.29 13.3. (%) 1.79 1.80 1.80 1.81 1.82 1.85 1.86 1.86 1.86 1.87 1.80 1.81 1.81 1.80 1.81 1.82. (%) 0.03 0.03 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.03 0.03 0.03 0.03 0.03 0.03. (%) 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.021. (%) -0.24 -0.24 -0.24 -0.24 -0.24 -0.24 -0.24 -0.24 -0.24 -0.24 -0.24 -0.24 -0.24 -0.24 -0.24 -. (%) 100.62 100.72 100.73 100.78 100.75 100.96 101.06 101.08 101.06 101.11 100.66 100.65 100.67 100.69 100.71 -. 0.50. 4.30. 1.28. 1.01. 5.57. 0.03. 0.17. 0.17. 18.70. 15.68. -. -. 0.10. 2.42. 0.13. 0.07. 0.96. 0.70. 0.17. 1.52. 8.05. 3.45. -. -. 66.53 66.56 66.63 66.62 66.61 66.65 66.70 66.72 66.66 66.74 66.60 66.58 66.66 66.56 66.61 65.8. 0.92 0.92 0.92 0.93 0.93 0.97 0.97 0.98 0.98 0.97 0.96 0.96 0.96 0.96 0.96 1.01. 16.17 16.21 16.23 16.21 16.18 16.20 16.20 16.24 16.23 16.22 16.14 16.15 16.15 16.10 16.11 15.8. 6.80 6.77 6.76 6.75 6.76 6.76 6.77 6.77 6.76 6.76 6.78 6.78 6.79 6.80 6.78 6.32. 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 -. 1.69 1.68 1.69 1.70 1.69 1.73 1.74 1.74 1.74 1.74 1.71 1.71 1.70 1.71 1.71 1.69. 1.37 1.37 1.38 1.38 1.42 1.42 1.41 1.45 1.42 1.44 1.41 1.41 1.40 1.42 1.43 1.4. 2.06 2.07 2.09 2.08 2.09 2.14 2.14 2.15 2.14 2.15 2.09 2.09 2.08 2.09 2.10 2.05. 3.13 2.79 2.70 2.61 2.64 2.67 2.70 2.77 2.65 2.71 3.00 3.06 3.09 3.22 2.99 3.28. 0.14 0.14 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.14 0.14 0.14 0.14 0.14 0.16. 1.41 1.41 1.41 1.41 1.41 1.41 1.41 1.41 1.41 1.41 1.41 1.41 1.41 1.41 1.41 -. 100.33 100.05 100.07 99.95 100.00 100.22 100.30 100.48 100.27 100.41 100.35 100.42 100.49 100.52 100.35 -. 1.26. 5.73. 2.43. 7.17. -. 1.30. 0.66. 2.60. 13.18. 8.47. -. -. 0.09. 2.14. 0.29. 0.23. -. 1.13. 1.75. 1.46. 6.32. 1.89. -. -. 34.

(44) Picture 3.4 Claisse M4 Fluxer hosted at NTNU.. 35.

(45) 3.2.2. Trace Elements. An Agilent 7500ce Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used (Picture 3.5) with collision/reaction cell that provides high sensitivity of ca. 150 million counts per second (cps/ppm) for mono-isotopic heavy elements (atomic mass > 89) in standard solution mode. A typical round commenced with two analyses of NIST SRM 610 standard, followed by two analyses of other geological standards (e.g. BCR, BHVO, BIR) to ensure advanced control on reproducibility and accuracy. Then, 8 to 10 unknowns were analyzed, followed by two analyses of other geological standards and two analyses of NIST SRM 610. In short, for most elements, relative deviation of average concentrations in BHVO-2G and BCR-2G obtained in this study, from reference values of Gao et al. (2002), are ±5 %. The analyzing results of the standards are listed in Table 3.2 and Table 3.3. The preparation procedures are list below: 1.. About 100 mg whole rock sample powder was used and decomposed with 0.5 mL concentrated HNO3 and 1.5 mL concentrated HF in the Teflon beaker and was then dried.. 2.. The remnants were dissolved with 0.25 mL 7N HNO3 and 2 mL concentrated HF at 90oC for 2 nights and was dried.. 3.. 5 mL of 6N HCl was added, heated for 12 hours, and then dried.. 4.. 3 mL of 7N HNO3 was added and dried. Then, 1 mL of mill-Q water and 0.25 ml of concentrated HNO3 were added.. 5.. Centrifuge for 5 minutes.. 6.. Dilute the liquid to a concentration of 1/5000.. 36.

(46) Picture 3.5 Agilent 7500ce ICP-MS hosted at NCKU.. 37.

(47) Table 3.2 The analyzing result of the standard (BCR-2) of trace element.. Sc Ti V Cr Co Ni Rb Sr Y Zr Nb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Pb Th U. Recommended value. BCR-2. 33.00 1.35 416.00 18.00 37.00 48.00 346.00 37.00 188.00 1.10 683.00 25.00 53.00 6.80 28.00 6.70 2.00 6.80 1.07 1.33 0.54 3.50 0.51 4.80 11.00 6.20 1.69. 33.75 1.36 418.11 14.45 37.56 12.73 46.95 341.11 34.74 191.79 11.85 0.96 687.63 25.34 54.05 6.94 29.28 6.73 2.04 4.50 1.13 6.46 1.35 3.76 0.54 3.41 0.51 4.91 13.28 5.95 1.71. Precision (%) 1.93 0.82 1.17 4.40 1.33 4.16 0.51 1.19 0.58 0.76 0.92 1.27 1.08 0.72 0.53 0.96 0.72 1.36 1.48 1.19 1.72 0.94 0.86 1.06 1.64 0.93 1.71 1.21 1.46 0.83 1.39. 38. Accuracy (%) 2.27 0.93 0.51 19.73 1.50 2.18 1.41 6.09 2.02 12.85 0.68 1.38 1.98 2.04 4.58 0.50 2.23 33.78 5.49 1.46 0.61 2.50 0.53 2.31 20.75 4.04 1.40.

(48) Table 3.3 The analyzing result of the standard (BHVO) of trace element.. Sc Ti V Cr Co Ni Rb Sr Y Zr Nb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Pb Th U. Recommended value. BHVO-2. 32.00 1.63 317.00 280.00 45.00 119.00 9.80 389.00 26.00 172.00 130.00 15.00 38.00 25.00 6.20 6.30 0.90 1.04 2.00 0.28 4.10 1.20 -. 32.50 1.64 318.40 293.01 45.21 119.86 9.16 387.97 28.02 171.66 16.44 0.09 127.83 14.98 37.09 5.26 24.35 6.03 2.07 6.30 0.98 5.21 0.99 2.53 0.33 1.97 0.27 4.33 2.07 1.20 0.40. RSD (%) 1.55 0.72 0.24 1.25 1.68 0.42 0.23 0.79 0.34 0.82 0.28 3.77 4.10 0.11 0.37 0.88 1.03 0.54 0.54 1.93 0.68 1.21 0.94 1.00 3.29 1.68 1.47 1.00 3.09 1.99 2.20. 39. Accuracy 1.56 0.37 0.44 4.65 0.47 0.72 6.49 0.26 7.78 0.20 1.67 0.12 2.39 2.61 2.71 0.03 8.59 4.65 1.41 3.24 5.59 0.08 -.

(49) 3.2.3. Sr, Nd Isotopes. A Finnigan MAT262Q thermal ionization mass spectrometer (TIMS) was used for Sr isotope analysis, and a Thermo Fisher Scientific Triton Plus multicollector thermal ionization mass spectrometer was used for Nd isotope analysis. The standard used to measure the stability of Sr is NBS987 Sr, which was measured 118 times between 2006 and 2017. JMC Nd was the standard of the Nd experiment, which was measured 127 times between 2006 and 2016. The standard measured results are shown below (Figure 3.1 and Figure 3.2). In order to isolate Sr and Nd from all other elements, chemical column separation methods were used. The first column was used to isolate Sr and rare-earth elements (REEs), a 2.5 ml Bio-Rad AG50W-X8 cation exchange resin bed was used, the grain size is 100 to 200 meshes from the sample matrix. The Sr column is used to further separate Sr, a 1 ml resin bed of AG 50W-X8 was used, and the grain size is 100 to 200 meshes. The second column (Nd column) is used to separate Nd from other REEs, 8 ml column was used with a 1 ml resin bed of Eichrom Ln (100-150 μ) which was covered on top by a 0.1 ml of anion exchange resin bed (Dowex 1-X8, 100-200 mesh). The column separation procedures and chromatograms (Figure 3.3, Figure 3.4 and Figure 3.5) were created by Masako Usuki at IES, Academia Sinica. The preparation procedures are list below: 1.. Preprocessing procedure: (1) Sample powder was weighted; the amount of powder is based on the concentration of Sr and Nd, usually around 100 mg. (2) The sample powder was added into a Teflon beaker with 50 drops concentrated HNO3 and concentrated HF respectively, heat at 100oC for 2 nights and dry it. 40.

(50) (3) 2 mL of 6N HCl was added, and dry it. (4) 2 mL of 6N HCl was added, and dry it, cooling 10 minutes. (5) 2 mL of 1N HCl was added, centrifuge for 10 minutes and congregating supernatant to a new Teflon beaker for the following column chemistry steps. (6) (If there still residual precipitate in the beakers, dissolve the precipitate again follow the step 2 to step 5, and collect the supernatant to the same beaker.) 2.. Column chemistry - First column separation (1) The resin bed was equilibrated by 8 mL of 2N HCl. (2) The supernatant of sample (2 mL of 1N HCl) was carefully loaded by a glass pipette into the resin without disturbing the resin bed. (3) 1 mL of 2N HCl was added to the beaker and the liquid was loaded into the resin bed by a digital pipette, repeat 3 times to wash potential sample solution from the walls of the column. (4) 30 mL of 2N HCl was used as eluent and added to the column carefully, the liquid was collected from 19th mL to 30th mL to a new beaker, and dried. 1 mL of 2N HCl was added to the beaker, this will be used for the second column separation to collect strontium. (5) 16 mL of 2N HCl was used as eluent and added to the column carefully, the liquid was collected from 4th mL to 16th mL to a new beaker, and dried. 0.1 mL of H2O was added to the beaker, this will be used for the Nd column separation to collect neodymium. (6) The resin bed was washed by filling full column of 6N HCl twice and full column 41.

(51) of Mill-Q water. 3.. Column chemistry - Sr column separation (1) The resin bed was equilibrated by full column of 2N HCl. (2) The supernatant of sample (1 mL of 2N HCl) was carefully loaded by a digital pipette into the resin without disturbing the resin bed. (3) 1 mL of 2N HCl was added to the beaker and the liquid was loaded into the resin bed by a digital pipette, repeat 2 times to wash potential sample solution from the walls of the column. (4) 14 mL of 2N HCl was used as eluent and added to the column carefully, the liquid was collected from 5th mL to 14th mL to a new Teflon beaker. (5) The solution was dried in the new beaker, 1 drop of HCl and 1 drop of HNO3 was added to the solution and dried, repeat this step for 3 times. (6) The resin bed was then washed by filling full column of 6N HCl twice and full column of Mill-Q water once.. 4.. Column chemistry - Second column separation (1) The resin bed was equilibrated by 6 mL of 0.2N HCl. (2) The sample supernatant (0.1 mL of H2O) was carefully added by a digital pipette into the resin without disturbing the resin bed. (3) 0.1 mL of 0.2N HCl was added to the beaker and the liquid was loaded into the resin bed by a digital pipette, repeat 2 times to wash potential sample solution from the walls of the column. (4) 12.8 mL of 2N HCl was used as eluent and added to the column carefully, the 42.

(52) liquid was collected from 8.9th mL to 12.8th mL to a new Teflon beaker. (5) The solution was then dried in a new beaker, 1 drop of HCl and 1 drop of HNO3 was added to the solution and dried, repeat this step for 3 times. (6) The resin bed was washed by fill full column of 6N HCl, full column of 2N HCl, and full column of Mill-Q water. 5.. Loading sample (1) 0.6 mA current was chosen to load 1 drop of H3PO4 on the middle of the Re filament. (2) 0.8 – 1.0 mA current was chosen to load sample liquid on the Re filament.. 43.

(53) Figure 3.1 The analytical result of the standard (NBS987) of Sr isotope.. Figure 3.2 The analytical result of the standard (JMC Nd) of Nd isotope.. 44.

(54) Figure 3.3 The elusion curve of the first column separation. CPS = counts per second.. Figure 3.4 The elusion curve of the Sr column separation. CPS = counts per second.. 45.

(55) Figure 3.5 The elusion curve of the second (Nd) column separation. CPS = counts per second.. 46.

(56) Chapter 4 Results 4.1 Geochronology Four baddeleyite crystals were analyzed for U-Pb geochronology (Table 4.1, Figure 4.1). Two smaller, apparently fresher grains with calculated weights of 0.1 µg, and two larger grains with calculated weights of 0.3 µg were analyzed, without any apparent correlation with age or degree of discordance. Calculated U concentrations are apparently lower in the smaller grains, ca. 60 ppm, with the larger grains containing ca. 260 ppm. Th/U ratios are low, typical of baddeleyite, between 0.07 and 0.19. The data are variably discordant (Figure 4.1), between 0 – 2%, indicating some small degree of Pb loss. The coherence of the. 207. Pb/206Pb ages of all data indicates any Pb loss was recent, and. supports our interpretation of the weighted-mean. 207. Pb/206Pb age representing the. magmatic crystallization age of the dyke. The weighted-mean analyses is 2365.6 ± 0.9 Ma (2σ, MSWD = 0.17, N = 4).. 47. 207. Pb/206Pb age of all four.

(57) Table 4.1 U-Pb isotopic data for baddeleyite from the Bastar Craton dyke (B/29). Sample. 1 2 3 4. wt. (μg) 0.1 0.1 0.3 0.3. U (ppm) 66 29 287 259. 206Pb Pbc mol% Th 204Pb (pg) Pb* U B29: 1 crystal per fraction 0.3 92 0.07 535 0.3 83 0.14 239 3.0 93 0.13 792 1.2 97 0.19 1718. 207Pb. ± (%). 207Pb. 206Pb. 235U. ± (%). 0.15172 0.15176 0.15181 0.15174. 0.07 0.13 0.14 0.13. 9.2365 9.0819 9.2855 9.1564. 0.30 0.65 0.23 0.19. ± (%). ρ. 238U. 0.44152 0.43403 0.44362 0.43765. 0.28 0.63 0.14 0.09. .98 .98 .79 .82. 206Pb. 206Pb/238U. Age (Ma) 2357.4 2323.9 2366.8 2340.1. ± (Ma) 6.7 14.5 3.4 2.1. 207Pb/206Pb. Age (Ma) 2365.4 2365.8 2366.4 2365.6. ± (Ma) 1.1 2.3 2.4 2.1. Sample weights are calculated from crystal dimensions and are associated with as much as 50% uncertainty (estimated) Pbc = Total common Pb including analytical blank (0.8±0.3 pg per analysis). Blank composition is: 206Pb/204Pb = 18.55 ± 0.63, 207Pb/204Pb = 15.50 ± 0.55, 208Pb/204Pb = 38.07 ± 1.56 (all 2σ), and a 206Pb/204Pb – 207Pb/204Pb correlation of 0.9. Th/U calculated from radiogenic 208Pb/206Pb and age. Measured isotopic ratios corrected for tracer contribution and mass fractionation (0.03 ± 0.06 %/amu). ρ = error correlation coefficient of radiogenic 207Pb/235U vs. 206Pb/238U. All uncertainties given at 2σ Ratios involving 206Pb are corrected for initial disequilibrium in 230Th/238U using Th/U = 4 in the crystallization environment.. 48.

(58) Figure 4.1 Concordia plot of baddeleyite U-Pb TIMS data for sample B-29.. 49.

(59) 4.2 Bhanupratappur area, Bastar Craton 4.2.1 Major Element Samples from the Bhanupratappur area have SiO2 in the range of 51.5 to 55.7 wt% and 0.7 to 2.4 wt% of Na2O, 0.5 to 4.5 wt% of K2O, they are sub-alkaline basaltic-andesite (Table 4.2, Figure 5.1). The Mg# range of the samples is between 50 and 79, MgO range from 5.8 to 18.7 wt%. The Mg# is calculated by the following equation:. Mg# =. 𝑀𝑔2+ × 100 𝐹𝑒 2+ + 𝑀𝑔2+. These dykes have higher SiO2, higher MgO, and are broadly boninitic. Boninite and boninitic rocks are mafic igneous rock with high magnesium (MgO > 8 wt%) and high silica (SiO2 > 52 wt%) and low titanium (TiO2 < 0.5 wt%) (Le Bas, 2000). The TiO2 ranges from 0.30 wt% to 0.77 wt%, thus we use ‘boninitic dykes’ to describe the mafic dykes in this study. Two of the samples in the study are compositionally different. Compare to the other dykes, sample B/3 has highest SiO2 (55.6 wt%) and K2O (4.5 wt%), B/24 has highest MgO (18.7 wt%) while the average of other dykes is ~9 wt%.. 50.

(60) Table 4.2 Major elements analyses of the Bhanupratappur area, Bastar Craton. Sample name. B/3. B/13. B/15. B/16. B/17. B/19. B/20. B/24. B/28B. B/29. B/33. SiO2. 55.66. 53.81. 54.41. 52.84. 51.54. 53.46. 53.59. 53.32. 53.84. 53.57. 53.51. TiO2. 0.37. 0.59. 0.77. 0.52. 0.75. 0.63. 0.69. 0.30. 0.54. 0.55. 0.60. Al2O3. 7.96. 14.46. 14.14. 12.05. 11.04. 12.24. 11.32. 7.73. 10.91. 12.73. 13.25. Fe2O3. 8.31. 9.98. 11.63. 9.75. 11.75. 9.29. 11.21. 9.74. 10.50. 10.10. 10.18. MnO. 0.18. 0.16. 0.18. 0.15. 0.16. 0.13. 0.17. 0.18. 0.17. 0.16. 0.16. MgO. 8.44. 6.52. 5.78. 10.38. 10.85. 10.36. 9.18. 18.67. 10.76. 8.82. 7.64. CaO. 12.46. 9.65. 8.68. 8.67. 8.49. 7.86. 8.45. 6.74. 9.57. 10.40. 10.47. Na2O. 1.21. 2.38. 1.96. 1.90. 1.65. 2.01. 1.78. 0.73. 1.37. 1.62. 1.62. K2O. 4.45. 0.80. 1.12. 1.24. 1.02. 1.47. 1.26. 0.48. 0.56. 0.53. 0.65. P2O5. 0.20. 0.07. 0.10. 0.08. 0.14. 0.12. 0.10. 0.03. 0.07. 0.07. 0.07. LOI. 0.67. 1.86. 1.64. 2.20. 2.25. 2.42. 2.26. 1.34. 1.41. 1.80. 1.71. TOTAL. 99.05. 98.27. 98.59. 97.43. 97.22. 97.45. 97.58. 97.74. 98.11. 98.39. 98.00. Mg #. 66.80. 56.40. 49.60. 67.80. 64.70. 68.90. 61.90. 79.20. 67.00. 63.40. 59.80. 51.

(61) 4.2.2 Trace Element The concentration of transition metals range from tens of ppm (e.g. Sc = 8–37, Co = 30–60 ppm) to hundreds of ppm (V = 111–223, Cr = 34–2105, Ni = 78–320 ppm), the transition metals are less variable except Cr which has the highest coefficient of variation. The concentration of high field strength (HFSE) elements are listed below: Zr = 21–99, Nb = 1.0–8.3, Hf = 0.61–2.51, Ta = 0.09–0.51, Th = 0.64–7.33, U = 0.28–1.89 ppm. The large ion lithophile (LILE) elements (Cs = 0.19–2.72, Rb = 23–137, Ba = 79–740, Sr = 70–296 ppm) are most variable. Compare with other samples, sample B/24 has highest concentration of Cr (2105 ppm) and lowest concentration of Sc (8 ppm). Sample B/3 has lowest concentration of V (111 ppm) and Co (30 ppm) but has the highest concentration of REEs. The incompatible trace elemental data are normalized to the primative mantle values of Sun and McDonough (1989). Most of the samples exhibit large-ion lithophile elements (Cs, Rb, Ba and K) enrichment and high-field-strength element (Nb, Ta and Ti) depletion whereas sample B/3 shows Cs depletion but is enriched in Rb and Ba. The rare earth elemental data (Table 4.3, Figure 4.2) are normalized to the chondrite values of Sun and McDonough (1989). REEs data in Bhanupratappur area exhibit light rare earth element enrichment (La/YbN = 2.5 to 10.4) and no heavy rare earth element depletion (Gd/ YbN = 1.0 to 2.1) with 30 to 100 times chondrite concentration. Sample B/24 is anomalous as it shows 10 times chondrite concentration. Sample B/3 has the highest concentration of the REEs compare with other samples and exhibits a distinct negative Eu anomaly (Eu/Eu* = 0.58) whereas other samples do not have a significant anomaly (Eu/Eu*  0.9). 52.

(62) The Eu anomaly is calculated by the following equation: 𝐸𝑢 𝐸𝑢𝑁 = 2 × (𝑆𝑚𝑁 + 𝐺𝑑𝑁 ) 𝐸𝑢∗. 53.

(63) Table 4.3 Concentration of trace element of the Bhanupratappur dykes, Bastar Craton. Sample name. B/3. B/13. B/15. B/16. B/17. B/19. B/20. B/24. B/28B. B/29. B/33. Sc. 24.09. 34.26. 36.07. 28.92. 26.26. 23.09. 30.46. 7.55. 33.21. 36.70. 37.26. V. 110.94. 203.97. 222.96. 176.97. 190.54. 162.46. 199.57. 145.03. 199.59. 213.86. 220.92. 677.42 2104.67. (ppm). Cr. 275.86. 161.07. 34.20. 742.18. 924.50. 940.90. 697.36. 472.02. 346.82. Co. 30.21. 41.14. 42.60. 46.81. 54.60. 46.62. 46.23. 59.98. 50.56. 48.26. 43.62. Ni. 102.03. 96.87. 78.42. 212.53. 252.78. 318.23. 141.54. 319.77. 171.99. 131.04. 129.30. Rb. 136.57. 42.03. 48.57. 90.50. 58.51. 63.59. 77.15. 38.64. 22.59. 22.65. 26.56. Sr. 296.15. 144.25. 113.92. 170.11. 225.63. 239.49. 170.37. 69.71. 111.48. 121.04. 122.66. Y. 26.14. 16.82. 22.21. 12.25. 15.21. 16.70. 15.54. 7.35. 13.87. 15.75. 17.74. Zr. 21.01. 64.09. 95.69. 64.51. 75.17. 99.35. 68.37. 22.29. 56.87. 53.44. 65.91. Nb. 8.29. 3.36. 6.07. 2.73. 3.62. 5.94. 3.33. 1.03. 2.94. 2.82. 3.42. Cs. 0.19. 0.64. 0.74. 0.90. 1.65. 2.13. 1.38. 2.72. 2.20. 1.13. 2.04. Ba. 739.96. 194.16. 306.2. 337.93. 634.06. 459.64. 250.69. 79.11. 153.00. 137.51. 171.56. La. 23.04. 9.30. 16.83. 8.71. 11.59. 21.24. 9.04. 2.81. 9.07. 7.88. 9.62. Ce. 66.84. 18.97. 34.26. 18.07. 24.80. 41.13. 19.19. 6.00. 18.45. 16.2. 19.50. Pr. 9.83. 2.20. 3.91. 2.13. 3.030. 4.55. 2.33. 0.74. 2.15. 1.95. 2.27. Nd. 42.05. 8.60. 15.01. 8.36. 12.25. 16.70. 9.43. 3.06. 8.46. 7.82. 9.06. Sm. 7.91. 2.03. 3.25. 1.87. 2.72. 3.31. 2.20. 0.81. 1.93. 1.84. 2.14. Eu. 1.34. 0.65. 0.89. 0.64. 0.89. 0.93. 0.71. 0.29. 0.58. 0.62. 0.65. Gd. 5.90. 2.34. 3.33. 2.00. 2.74. 3.11. 2.47. 1.03. 2.13. 2.20. 2.52. Tb. 0.88. 0.42. 0.58. 0.35. 0.46. 0.51. 0.42. 0.19. 0.37. 0.39. 0.44. Dy. 4.45. 2.60. 3.48. 2.00. 2.58. 2.86. 2.52. 1.19. 2.25. 2.43. 2.79. Ho. 0.88. 0.59. 0.77. 0.43. 0.54. 0.59. 0.54. 0.27. 0.49. 0.53. 0.62. Er. 2.41. 1.75. 2.25. 1.24. 1.51. 1.63. 1.57. 0.82. 1.43. 1.57. 1.81. Tm. 0.35. 0.26. 0.34. 0.18. 0.21. 0.23. 0.23. 0.12. 0.21. 0.23. 0.28. Yb. 2.28. 1.72. 2.19. 1.18. 1.36. 1.47. 1.50. 0.81. 1.36. 1.51. 1.78. Lu. 0.35. 0.26. 0.34. 0.18. 0.20. 0.22. 0.23. 0.13. 0.21. 0.23. 0.27. Hf. 0.86. 1.67. 2.51. 1.42. 1.89. 2.49. 1.72. 0.61. 1.45. 1.40. 1.65. Ta. 0.44. 0.27. 0.51. 0.21. 0.24. 0.44. 0.26. 0.09. 0.22. -. 0.29. Th. 3.40. 3.00. 6.33. 2.44. 1.75. 7.33. 2.48. 0.64. 3.09. 2.60. 3.04. U. 1.12. 0.78. 1.89. 0.60. 0.41. 1.60. 0.72. 0.28. 0.77. 0.68. 0.81. Eu/Eu*. 0.58. 0.91. 0.82. 1.01. 0.99. 0.87. 0.93. 0.95. 0.87. 0.94. 0.86. (La/Yb)N. 7.30. 3.90. 5.50. 5.30. 6.10. 10.40. 4.30. 2.50. 4.80. 3.70. 3.90. 54.

(64) (a) Rock/Chondrites. 100. 10. 1 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 1000. (b) Rock/Primitive Mantle. 100. 10. 1. .1. Cs Rb Ba Th U Nb Ta K La Ce Pb Pr Sr P Nd Zr Sm Eu Ti Dy Y Yb Lu. Figure 4.2 (a) Chondrite normalized rare earth element plot and (b) primitive mantle normalized incompatible element plot of the mafic dykes of the central Bastar Craton. Samples normalized to the values of Sun and McDonough (1989).. 55.

(65) 4.2.3 Sr-Nd Isotopes Four samples from Bhanupratappur were analyzed for the Sr, Nd isotopes (Table 4.4). The analyses are calculated using the U–Pb baddeleyite age of 2365.6 ± 0.9 Ma in this study. The initial 143. 87. Sr/86Sr ratios (ISr) range from 0.692638 to 0.704468. The initial. Nd/144Nd ratio ranges from 0.509246 to 0.509800 with corresponding εNd(t) values from. –6.4 to +4.5 using a CHURtoday value of 0.512638. The initial 143Nd/144Nd is calculated by the following equation: 143 143 147 𝑁𝑑 𝑁𝑑 𝑆𝑚 ( 144 ) = ( 144 ) − ( 144 ) × (𝑒 𝜆𝑡 − 1) 𝑁𝑑 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑁𝑑 𝑚𝑒𝑎𝑠𝑢𝑟𝑒 𝑁𝑑. The initial 87Sr/86Sr is calculated by the following equation: 87. 87 87 𝑆𝑟 𝑆𝑟 𝑅𝑏 ( 86 ) = ( 86 ) + ( 86 ) × (𝑒 𝜆𝑡 − 1) 𝑆𝑟 𝑚𝑒𝑎𝑠𝑢𝑟𝑒 𝑆𝑟 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑆𝑟. The εNd(t) is calculated by the following equation: 143𝑁𝑑. εNd(t) = [. ( 144. )𝑠𝑎𝑚𝑝𝑙𝑒,t. 𝑁𝑑 143𝑁𝑑. (144. 𝑁𝑑. )𝐶𝐻𝑈𝑅,t. 56. − 1] ∗ 104.

(66) Table 4.4 Sr-Nd isotopic ratio of Bhanupratappur area, central Bastar Craton.. Sample. Sm. Nd. 7.91 0.81 2.14 1.84. 42.1000 3.1000 9.1000 7.8200. (147Sm/144Nd)m. (143Nd/144Nd)m. 2σ. (143Nd/144Nd)i. 0.1136 0.1580 0.1422 0.1422. 0.511017 0.511737 0.511668 0.512017. 5 6 6 5. 0.509246 0.509274 0.509451 0.509800. εNd (2365). Rb. Sr. 13700 3900 2700 2300. 29600 7000 12300 12100. (87Rb/86Sr)m. (87Sr/86Sr)m. 2σ. (87Sr/86Sr)I 2365. 1.345 1.619 0.636 0.542. 0.747389 0.747943 0.726212 0.720842. 8 8 6 7. 0.701448 0.692638 0.704468 0.702316. Age: 2365.6 Ma B/ 3 B/24 B/33 B/29. 57. -6.400 -5.800 -2.400 +4.500.

(67) 4.3 Karimnagar area, Dharwar Craton 4.3.1 Major element Samples from the Karimnagar area have SiO2 in the range of 52.9 to 54.2 wt%, the total alkalis (Na2O+K2O) range from 1.9 wt% to 2.4 wt%, and they classify as sub-alkaline basaltic-andesite (Table 4.5, Figure 5.3). The Mg# of these samples is between 60 and 64, with 8.0 to 9.6 wt% of MgO, 10.3 to 10.6 wt% of Fe2O3(t), and ~0.57 wt% TiO2. The dykes have boninitic chemical characteristics (MgO > 8%, SiO2 > 52% and TiO2 < 0.5%).. Table 4.5 Major elements analyses of the Karimnagar area, Dharwar Craton. Sample name. KN/1. KN/2. KN/3. KN/4. KN/5. KN/6. KN/7. SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 LOI TOTAL Mg #. 53.66 0.55 13.70 10.40 0.17 8.68 10.97 1.69 0.37 0.07 0.25 100.11 62.30. 52.93 0.57 13.20 10.34 0.17 8.58 10.13 1.55 0.79 0.07 1.41 98.17 62.20. 53.62 0.54 12.64 10.53 0.17 9.61 10.81 1.56 0.35 0.06 0.35 99.74 64.40. 53.79 0.59 14.08 10.52 0.17 8.05 11.07 1.75 0.43 0.07 0.18 100.35 60.20. 53.58 0.57 13.94 10.38 0.17 8.30 11.07 1.73 0.40 0.07 0.28 100.05 61.30. 53.51 0.58 13.73 10.61 0.17 8.17 10.95 1.71 0.41 0.07 0.49 99.74 60.40. 54.21 0.59 13.82 10.58 0.17 8.53 11.11 1.71 0.40 0.07 0.17 101.02 61.50. 58.

(68) 4.3.2 Trace element The trace element concentrations of the dykes in the Karimnagar region are more uniform compare with dykes in Bhanupratappur region. The average coefficient of variation (C.V.) of transition metals is 5.5%, with Sc = 36–38, V = 215–225, Cr = 363–556, Co = 46– 49, Ni = 120–144 ppm. The high field strength (HFSE) elements (Zr = 45–52, Nb = 2.1–2.4, Hf = 1.21–1.36, Ta = 0.17–0.22, Th = 1.44–1.67, U = 0.28–1.89 ppm) are uniform with the average C.V. of 5.4%. The large ion lithophile (LILE) elements (Cs = 0.42–0.54, Rb = 15– 31, Ba = 112–186, Sr = 110–136 ppm) are generally uniform (average C.V. of 15.8%) except Rb (C.V. = 31.58%). The incompatible trace elemental data are normalized to the primitive mantle values of Sun and McDonough (1989), and all the samples exhibit large ion lithophile elements (Rb, Ba and K) enrichment and high-field-strength elements (Nb, Ta and Ti) depletion. The rare earth elemental data (Table 4.6, Figure 4.3) are normalized to the chondrite values of Sun and McDonough (1989); REEs data in Karimnagar area show light rare earth element enrichment (La/YbN = 2.8), and no heavy rare earth element depletion. The concentration of REEs is 10 to 30 times chondrite concentration.. 59.

(69) Table 4.6 Concentration of trace element of the Karimnagar dykes, Dharwar Craton. Sample name (ppm) Sc V Cr Co Ni Rb Sr Y Zr Nb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Th U Eu/Eu* (La/Yb)N. 00KN/1. 37.37 224.28 459.68 48.89 132.99 14.79 120.52 15.26 48.46 2.23 0.53 130.32 6.06 12.99 1.62 6.78 1.74 0.60 2.14 0.39 2.39 0.54 1.58 0.23 1.54 0.23 1.30 0.18 1.57 0.43 0.96 2.80. 00KN/2. 38.21 225.25 467.43 48.15 131.57 30.90 135.60 15.84 50.59 2.37 0.48 185.82 6.31 13.76 1.70 7.18 1.80 0.63 2.23 0.40 2.51 0.56 1.64 0.24 1.58 0.24 1.36 0.19 1.67 0.45 0.96 2.90. 00KN/3. 00KN/4. 37.95 218.62 556.21 48.97 144.15 14.71 109.65 14.31 45.06 2.07 0.48 111.76 5.54 11.96 1.48 6.35 1.61 0.56 1.98 0.36 2.27 0.50 1.49 0.22 1.46 0.22 1.21 0.17 1.44 0.40 0.95 2.70. 37.81 221.26 362.70 46.73 119.86 17.24 123.61 15.91 50.36 2.32 0.54 139.59 6.25 13.58 1.69 7.07 1.78 0.62 2.21 0.40 2.48 0.56 1.65 0.25 1.59 0.24 1.33 0.22 1.61 0.44 0.96 2.80. 60. 00KN/5. 38.01 221.91 440.39 47.89 128.65 16.69 124.62 15.65 50.17 2.30 0.50 133.00 6.21 13.44 1.67 7.01 1.78 0.62 2.22 0.40 2.45 0.55 1.62 0.24 1.58 0.23 1.34 0.18 1.60 0.44 0.95 2.80. 00KN/6. 38.28 225.24 371.64 48.80 125.36 17.03 124.04 16.08 51.98 2.36 0.42 138.59 6.24 13.6 1.69 7.19 1.84 0.63 2.20 0.41 2.52 0.56 1.67 0.25 1.62 0.24 1.34 0.18 1.61 0.45 0.95 2.80. 00KN/7. 36.02 214.55 404.85 46.11 122.82 15.73 114.79 15.08 48.41 2.18 0.46 130.78 5.93 12.88 1.59 6.70 1.72 0.60 2.10 0.38 2.36 0.53 1.57 0.23 1.53 0.23 1.26 0.17 1.52 0.42 0.96 2.80.

(70) (a) Rock/Chondrites. 100. 10. 1 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 1000. (b) Rock/Primitive Mantle. 100. 10. 1. .1. Cs Rb Ba Th U Nb Ta K La Ce Pb Pr Sr P Nd Zr Sm Eu Ti Dy Y Yb Lu. Figure 4.3 (a) Chondrite normalized rare earth element profiles of the Karimnagar dykes. (b) Primitive mantle normalized incompatible element plot of the Karimnagar dykes. Samples normalized to values of Sun and McDonough (1989). 61.