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Geochemical Characterization, Petrogenetic Modelling And Geochemical characterization, petrogenetic modelling and engineering behaviour of granitic rocks and basic dykes from the northern Indian plate in north-western Pakistan Muhammad Sajid Submitted to the University of Exeter as a thesis for the degree of Doctor of Philosophy in Geology in September 2016 This thesis is available for Library use on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. I certify that all material in this thesis which is not my own work has been identified and that no material has previously been submitted and approved for the award of a degree by this or any other University. Signature: ………………………………………………………….. September 2016 1 Abstract The pre-Himalayan magmatic events along the northern margin of Indian plate in north-western Pakistan have been investigated and correlated with analogous magmatism in other Himalayan and northern Gondwana regions. The samples from Utla and Mansehra regions of NW Pakistan are dominantly megacrystic two mica granites, strongly peraluminous (A/CNK > 1.1) and intruded by aplite dykes and quartz-rich veins. The high precision zircon U-Pb ages (471-479 Ma) show their emplacement in early Paleozoic. These granites are enriched in light rare- earth elements (LREEs) and show similar chondrite normalized REE patterns with negative Eu anomalies (Eu/Eu* = 0.07–0.73). The geochemical signature and REE based modelling indicate that the granites are derived mainly from the partial melting of pelitic source followed by the evolution of melt via fractional crystallization resulting in the formation of aplites. Tourmaline occurrences in distinct modes show post-magmatic alteration of these granites triggered by hydrothermal fluids from different sources. Enrichment of Sn in certain alteration zones and trace elements ratios suggests a strong mineralization potential for these granites. The analogous composition, source rock characteristics and geochronology represent their regional association with other Cambro- Ordovician granitoids from northern Gondwana. Due to these similarities, an early Paleozoic orogenic event has been anticipated for these granitoids initiated due to subduction of Proto-Tethys oceanic lithosphere beneath the northern Gondwana supercontinent. Dykes of basic composition that intrude these granites and other lithologies are divided into dolerites and amphibolites on the basis of their distinct mineralogical and geochemical composition. Major elements composition suggests alkaline to sub alkaline character of both dykes with intraplate tectonic setting, however, amphibolites (>3%) are markedly enriched in TiO2 relative to dolerites (<3%). Trace element ratios designates the origination of dolerites from subcontinental lithosphere with significant crustal contamination. They show analogous geochemical character to Panjal traps which represent a regional scale rift related basic magmatism in Himalayan terrane during Permian. The geochemical signature of amphibolites, however, show similarities to high-Ti Qiangtang dykes which originates from asthenospheric source via deep mantle plume. The sporadic distribution of both dykes in similar aged host rocks represent their 2 evolution from distinct sources in separate but synchronous magmatic pulses during extensional tectonism related to separation of Cimmeria from Gondwana. Granites with distinct petrographic features have been tested to examine the influence of textural characteristics on the variation of their respective strength. Comparison of petrographic observations before and after the strength tests and the relationship of fracture propagation with mineral boundaries specifies vital impact of textural variation in evaluating the mechanical behaviour of granites. The important textural features include average grain size of rock, grain boundary recrystallization, maximum grain size of major rock forming minerals, mean grain size of cleaved minerals, mineral exsolution and variation of grain size within a rock. The petrographic observations, however, are more effective to describe the strength variation of granites having analogous weathering grade as change in degree of weathering has a dominant effect on rock mechanics. 3 Table of Contents Abstract ……………………………………………………………………………… 2 Table of Contents …………………………………………………………………... 4 List of figures ………………………………………………………………………... 8 List of tables ………………………………………………………………………… 17 Acknowledgements ………………………………………………………………… 18 Dedication …………………………………………………………………………... 19 Chapter One Introduction ……………………..…………………………… 20 1.1 Project Statement ……………………………………………………….. 21 1.2 Major Objectives and Scope …………………………………………… 23 1.2.1. Geochemical aspects ……………………………………………. 23 1.2.2. Geotechnical aspects ……………………………………………. 25 1.3 Structure of thesis ……………………………………………………….. 25 Chapter Two Regional Geology …………………………………………… 27 2.1 Tectonic division of Himalayas …………………………………………. 28 2.2 Geology and tectonic setup of NW Pakistan …………………………. 31 2.2.1. Early Paleozoic magmatism in the northern Indian plate ……. 34 2.2.2. The Permian rifting event in the northern Indian plate ……….. 36 2.2.3. Precambrian and Paleozoic stratigraphy of study area ……… 38 2.3 The Panjal Traps ………………………………………………………… 40 2.3.1. Panjal Traps in NW Pakistan …………………………………… 41 Chapter Three Implications of Rock Textures to Rock Mechanics ...…. 43 3.1 Rocks Textures as a Controlling Factor ………………………………. 45 3.1.1. Concentration of minerals ……………………………………….. 45 3.1.2. Textural description of rock ……………………………………... 47 3.2 Weathering effects and Classification …………………………………. 48 3.3 Scope of the current investigation ……………………………………... 53 Chapter Four Geochemical characterization, petrogenesis and mineralization potential of the Utla and Mansehra 55 Granites, North-West Pakistan……….……………………. 4.1 Introduction ………………………………………………………………. 56 4 4.2 Regional Geology ……………………………………………………….. 58 4.3 Methodology ……………………………………………………………… 60 4.4 Field features …………………………………………………………….. 61 4.5 Petrography and mineral chemistry …………………………………… 61 4.5.1. Feldspars …………………………………………………………. 63 4.5.2. Micas ……………………………………………………………… 65 4.5.3. Tourmaline ……………………………………………………….. 66 4.5.4. Epidote ……………………………………………………………. 70 4.5.5. Garnet …………………………………………………………….. 70 4.6 Whole rock major and trace elements geochemistry ………………... 73 4.7 Discussion ………………………………………………………………... 82 4.7.1. Evidence of fractional crystallization …………………………... 82 4.7.2. Source rock characteristics and partial melting ……………… 83 4.7.3. Significance of tourmaline chemistry ………………………….. 87 4.7.4. Epidote as a magmatic phase in Utla Granitoids ……………. 88 4.7.5. Garnet zonation ………………………………………………….. 89 4.7.6. Mineralization potential of Utla Granitoids ……………………. 91 4.7.7. Comparison with other granitic suites …………………………. 93 4.8 Conclusions ………………………………………………………………. 94 Chapter Five Petrogenesis and tectonic association of rift-related basic Panjal dykes from northern Indian Plate, NW Pakistan: evidence of High-Ti basalts analogous to dykes from Tibet …………………………………………….. 96 5.1 Introduction ………………………………………………………………. 97 5.2 Geological Setting ……………………………………………………….. 98 5.3 Analytical methods ………………………………………………………. 100 5.3.1 Mineral chemistry (Electron probe and QEMSCAN) ………….. 100 5.3.2. Whole rock geochemistry (XRF and ICP Mass Spectrometry) 102 5.4 Petrography and Mineral Chemistry …………………………………… 102 5.4.1. Dolerites ………………………………………………………….. 102 5.4.2. Amphibolites ……………………………………………………… 103 5.5 Major and trace elements geochemistry ……………………………… 112 5.6 Petrogenetic Discussion ………………………………………………… 113 5 5.6.1. Evidence of magmatic fractionation in dolerites ……………… 113 5.6.2. Partial melting of mantle source ………………………………... 119 5.6.3. Prospects of crustal contribution ……………………………… 120 5.6.4. Comparison with Panjal Traps from other locations ……….... 124 5.6.5. Tectonic implications ……………………………………………. 125 5.7 Conclusions ………………………………………………………………. 129 Chapter Six Geochronology ……………………………………………… 130 6.1 Introduction and Sample Description ………………………………….. 131 6.2 Methods Description …………………………………………………….. 132 6.2.1 Zircon Separation …………………………………………………. 132 6.2.2. SIMS analysis …………………………………………………….. 133 6.2.3. Zircon Morphology ……………………………………………….. 135 6.3 Results ……………………………………………………………………. 137 6.3.1. Utla Granite (MPG) ………………………………………………. 137 6.3.2. Utla Granite (AMG) ………………………………………………. 143 6.3.3. Mansehra Granite ………………………………………………... 147 6.3.4. Dolerite dykes …………………………………………………….. 152 6.4 Interpretations ……………………………………………………………. 154 6.5 Discussion ………………………………………………………………... 156 Chapter Seven Petrographic features as an effective indicator for the variation in strength of granites ………………………….. 160 7.1 Introduction ………………………………………………………………. 161 7.2 Geology of Studied granites ……………………………………………. 163 7.3 Methodology ……………………………………………………………… 164 7.4 Petrographic characteristics of studied granites ……………………... 165 7.4.1. Utla Granites (UG) …………………………………………….. 165 7.4.2. Mansehra Granite (MG) ………………………………………. 165 7.4.3. Ambela Granite (AG) ………………………………………….. 166 7.4.4. Malakand Granite (SG) ……………………………………….. 166 7.5 Alteration grade of studied granites …………………………………… 171 7.6 Mechanical behaviour of studied granites ……………………………. 174 7.7 Discussion ………………………………………………………………... 177 6 7.8 Conclusions ………………………………………………………………. 185 Chapter Eight Discussion …………………………………………………… 187 8.1 The Utla granites ………………………………………………………… 188 8.1.1. Research Outcomes and Evaluation ………………………….. 188 8.1.2. Tectono-magmatic
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