Journal of African Earth Sciences 112 (2015) 213e233

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Journal of African Earth Sciences

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The potential of high heat generating granites as EGS source to generate power and reduce CO2 emissions, western Arabian shield, Saudi Arabia

* D. Chandrasekharam a, b, , A. Lashin c, d, e, f, N. Al Arifi b, A. Al Bassam b, f, M. El Alfy f, g, h, P.G. Ranjith i, C. Varun j, H.K. Singh a a Department of Earth Sciences, Indian Institute of Technology Bombay, 400076, India b College of Science, Geology and Geophysics Department, King Saud University, Riyadh 11451, Saudi Arabia c Faculty of Science, Geology Department, Benha University, Benha 13518, Egypt d College of Engineering, Petroleum and Natural Gas Engineering Department, King Saud University, Riyadh 11421, Saudi Arabia e Geothermal Resources Engineering Group, Sustainable Energy Technologies Centre, King Saud University, Saudi Arabia f Saudi Geological Survey (SGS) Research Chair, King Saud University, Riyadh, Saudi Arabia g CPSIPW, Prince Sultan Institute for Environmental, Water and Desert Research, King Saud University, Saudi Arabia h GeologyDepartment, Faculty of Science, Mansoura University, Egypt i Department of Civil Engineering, Monash University, Victoria 3800, Australia j GeoSyndicate Power Pvt. Ltd., Mumbai, India article info abstract

Article history: Saudi Arabia's dependence on oil and gas to generate electricity and to desalinate sea water is widely Received 10 August 2015 perceived to be economically and politically unsustainable. A recent business as usual simulation Received in revised form concluded that the Kingdom would become an oil importer by 2038. There is an opportunity for the 22 September 2015 country to over come this problem by using its geothermal energy resources. The heat flow and heat Accepted 23 September 2015 generation values of the granites spread over a cumulative area of 161,467 sq. km and the regional stress Available online 30 September 2015 regime over the western Saudi Arabian shield strongly suggest that this entire area is potential source of energy to support 1) electricity generation, 2) fresh water generation through desalination and 3) Keywords: extensive agricultural activity for the next two decades. The country can adopt a policy to harness this CO2 EGS vast untapped enhanced geothermal systems (EGS) to mitigate climate and fresh water related issues Radiogenic granites and increase the quantity of oil for export. The country has inherent expertise to develop this resource. Desalination © 2015 Elsevier Ltd. All rights reserved. Agriculture Arabian shield

1. Introduction these countries. According to the World Energy Outlook (WEO, 2014), for each barrel of oil saved in OECD countries, two barrels World primary energy is projected to increase by 36% in 2030 more are consumed in non OECD countries to meet the growing due to the increase in consumption, at the rate of 1.6% per year demand in the transport, electricity and water sectors. The demand between 2013 and 2030. Those countries that depend on oil im- is expected to grow to 104 million barrels per day (mb/d) in 2040 ports, especially non-OECD (Organization for Economic Coopera- from the current 90 mb/d (WEO, 2014). OPEC countries, on the tion and Development) countries, have to struggle to keep the other hand, have a different kind of problem, even though their oil supply demand gap narrow without compromising the economic and gas resources are in surplus. The growing demand in these and industrial growth. About 90% of the world's population lives in countries is for water, due to drastic fluctuations in the microcli- non-OECD countries and future energy demand centres around mate system that lead to an increase in air temperatures and anomalous rain fall patterns (Almazroui et al., 2012). Saudi Arabia consumes 275 L/d per capita of water which is being generated from desalination processes using 134 106 kWh of electricity * Corresponding author. Department of Earth Sciences, Indian Institute of Tech- (Chandarasekharam et al., 2014a, b). nology Bombay, 400076, India. E-mail address: [email protected] (D. Chandrasekharam). http://dx.doi.org/10.1016/j.jafrearsci.2015.09.021 1464-343X/© 2015 Elsevier Ltd. All rights reserved. 214 D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233

1.1. Desalination hydrothermal and enhanced geothermal systems (EGS). Nowadays, EGS is attracting attention around the world and will be the future With increase in population growth, the demand for fresh water green and renewable energy source of the future. While the po- from fossil fuel based desalination plants will grow at an alarming tential of hydrothermal systems is site specific and limited, EGS rate (Fig. 1). It has been reported that Saudi Arabia's reliance on sources are unlimited and have enormous potential to provide fossil fuels to generate electricity and generate fresh water through primary energy for electricity generation, for direct applications desalination using the same energy source is economically and like extracting gas from oil sands, green house cultivation and politically unsustainable, and if this trend continues Saudi Arabia dehydration of agricultural products and for the generation of fresh will become an oil importer in the next two decades (Ahmad and water for domestic and agricultural purposes (MIT, 2006; Xu Ramana, 2014), leading to destabilization of the global economy. et al., 2015; Hofmann et al., 2014; Paoletti et al., 2015; Zhang Although reverse osmosis is commonly adopted for desalination et al., 2014a, b). projects around the world, Saudi Arabia still uses the energy- intensive thermal multistage flash distillation process that re- 1.2. Heat mining quires ~10 to 12 TWh to desalinate 1 m3 sea water (Ghaffour et al., 2014). The net quantity of electricity co-generated through this Heat mining technology (also known as hot dry rock technology process is insignificant (Fig. 1) compared to the amount consumed or enhanced geothermal systems) is making considerable advances during desalination process. In addition, ultimately both desalina- and by 2040 this technology will enable countries to generate an tion processes result in significant emissions of CO2 (Ghaffour et al., oversupply of electricity. The USA has initiated the process to 2014). For countries like Saudi Arabia the most efficient and cost provide 100,000 MWe from EGS by 2050 (MIT, 2006; Cladouhos effective method to obtain fresh water through desalination pro- et al., 2012) and France and Australia have already mastered the cess is to adopt technology based on solar or geothermal energy technology. Several countries have initiated EGS projects that are sources (Ghaffour et al., 2014). Although the desalination plants under research and development (R & D) or in commercial stages generate electricity, the unit cost of the power is not cost effective for power production (Table 1) and also for other applications like compared to other energy sources that generate electricity (Ahmad processing oil sands in Canada (Zhang et al., 2014a, b; Xu et al., and Ramana, 2014). This is an alarming situation that should be 2015; Hofmann et al., 2014). An EGS technology feasibility study noted by policy makers. As discussed below, Saudi Arabia's food to generate electricity from abandoned horizontal oil wells is being security is also threatened due to the high cost of energy for the carried out in the Daqing Oil field, China (Zhang et al., 2014a, b). desalination process. The most suitable rocks for EGS are the granites and its co- In addition to its domestic and irrigation purposes, water is also genetic rocks because these rocks are capable of generating enor- required for energy production. The world energy sector consumed mous amounts of radiogenic heat due to the high content of about 583 billion cubic meters of water in 2010 and by 2030 con- radioactive elements like uranium, thorium and potassium. Con- sumption will increase by 85% (IEA, 2012). Demand is directly ditions suitable for EGS is that such rocks should generate tem- linked to population growth and the need to increase economic perature of the order of 150e500 C, and capable of maintaining a growth through industrial activities (IEA, 2012). The most signifi- fluid circulation flow rate of 265 L/s through a network of induced cant water consumers in the power sector are fossil fuel and nu- fractures over an area of 16 km2. The thermal capacity should be clear powered plants. Water is required to irrigate crops to support 250 MWth. The power that could be generated under such condi- biofuel based power plants. Solar photo voltaic (solar pv) plants tions will be about 50 MWe (Potter et al., 2013). Although Saudi need water to clean the panels to maintain output and efficiency in Arabia is currently the leader in oil and gas production and export, countries like Saudi Arabia (Segar, 2014). Solar pv desalination the country's major oil companies are considering options to in- plants operate at 20% efficiency and can generate 5000 cm3/day of crease the quantity of oil and gas exported by reducing the do- fresh water (Ahmad and Ramana, 2014). The water requirement of mestic demand through the use of renewable energy sources. In geothermal power plants is low and they can be use to generate addition the Saudi Government is exploring the possibilities of fresh water for consumption as well to support industrial and using renewable energies like nuclear and solar pv to mitigate agricultural activities. A geothermal source that is inherent to the current and future demand for fresh water for the growing popu- earth system is available in the form of well-established lation, live stock, agriculture and industry. At present Saudi Arabia consumes around 3 mb/day of oil to support its electricity demand that is expected to grow to 8 mb/d in a decade due to the 6% annual increase in population (OPEC, 2014; WEO, 2014). If corrective measures are not adopted by the country now to guarantee food and energy supplies to its population, the country is at risk of being an net energy importer by 2020 (Ahmad and Ramana, 2014). The western Saudi Arabia shield is a tectonically and thermally active region with high heat flow regime, active tectonic zones and wide spread occurrence of high heat generating granites. The growing demand for electricity and water and climate vagaries due to large CO2 emissions from fossil fuel based power plants may be mitigated by exploiting the country's huge geothermal (hydro- thermal and EGS) resources spread along the entire western shield margin.

2. Status of energy sources

2.1. Present energy consumption Fig. 1. Desalination trend using fossil fuels. The numbers denote the power co- generated by the desalination plants (modified after Ahmad and Ramana, 2014). The Kingdom of Saudi Arabia, with a land area of ~2 million sq. D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233 215

Table 1 R & D and commercial EGS projects of the world (MIT, 2006).

Start date Project site Country Well depth m Rock type BHT C Flow rate L/s Remarks

1977 Rosemanowes UK 2600 Granite 100 15 R & D 1982 Ogachi Japan 1027 Granodiorite 230 Not known R & D 1987 Soultz France 5093 Ganite 200 3.5 Commercial 1989 Hijori Japan 2151 Volcanic 225 17 R & D 1999 Cooper Basin Australia 4325 Granite 250 13 Commercial 2005 Paralan Australia 4003 Granite 171 6 R & D 2009 Geneys, Hannover Germany 3900 Sandstone 160 7 R & D 2009 St Gallen Switzerland 4450 Shell Lst 150 Not known R & D 2010 Newberry USA 3066 Volcanic 315 Not known Commercial km is the richest country in the Middle East, with a population of other countries and in future net export has to increase to maintain ~29 million. The country's proven crude oil reserves are 266 billion stability in the global economy. The present thinking is that the barrels and the natural gas reserves are 8317 billion m3 (OPEC, country should save domestic consumption of oil using renewables 2014). This proven crude reserve will soon be revised once the sources and export the savings to maintain the Kingdom's profit. offshore Manifa field goes into its full production capacity of There is also a fear that if this situation continues, by 2020 Saudi 900 kb/d (WEO, 2014). Currently the domestic oil demand is 3 Arabia may be forced to import oil from other countries (Ahmad million barrels per day which is mostly consumed to generate and Ramana, 2014). A recent economic feasibility study of nuclear electricity. The current daily production of oil is 9 billion barrels energy and solar pv (Karaveli et al., 2015) reveals that although from about 3372 wells (OPEC, 2014). The total electricity generated nuclear energy has advantages over solar pv, the time taken from by Saudi Arabia is 271 TWh with 42% of this amount being supplied planning, construction and decommissioning period for nuclear by gas (Table 2). power plants is about 45e50 years and the environmental risk is Total energy consumption of 248 TWh does not include the too high. In fact, Saudi Arabia is currently tackling the problem of electricity utilized by the desalination plants located along the east high radiation levels in groundwater along the western coastal belt and west coasts. The per-capita consumption of water is about due to the high content of radioactive elements in the aquifer rocks 275 L/day, which consumes 134 106 kWh of electricity (Vincent, 2008). Solar power plants also have severe constraints, (Chandarasekharam et al., 2014a, b). With its scanty annual rainfall due to the prevailing weather conditions and the dust and the heat. and fluctuating climate conditions, Saudi Arabia's water demand Although the land required for solar plants is not an issue in Saudi will grow at an exponential rate by 2040. It is projected that the Arabia, the water required to clean the panels is a big challenge. The peak electricity demand in 2032 will be around 736 TWh, excluding land required to generate 1 MWe from solar pv is about 7 acres. the demand to meet fresh water supply through desalination pro- Furthermore, the efficiency of the solar pv systems falls due to cess. Therefore, with 6% annual growth in population, the per capita temperatures reaching >30 C during most of the year (Segar, 2014; electricity consumption will double by 2030 (Table 2), making a Chandarasekharam et al., 2014a; Karaveli et al., 2015). Even in the large impact on the per capita CO2 emissions (Table 2). case of solar based absorption cooling system the maximum cyclic cooling capacity reaches about 14 kW in places like Jeddah only on 2.2. Renewable energy status clear sunny days (El Sharkawy et al., 2014). Geothermal energy has several advantages over solar pv since Although new optimization models to balance energy demand, the land requirement and water requirement is far less compared to reduction of CO2 emissions and inducting renewable energy sour- solar pv. 1 MWe geothermal power plants need 1 acre of land and ces score over the existing models (such as MARKAL and MESSAGE the power plants can supply baseload electricity without additional Almansoori and Torcat, 2015), these models are targeted to UAE back-up facilities. The unit costs for power and the investment costs scenario. However, the application of such models to Saudi Arabia's for renewables compared with conventional fossil fuel-based and energy scenario can be examined while advocating the use of hydro electric power plants are shown in Table 3. EGS has the added renewable energy sources such as EGS for the above purposes, advantages of CO2 storage and recovery of heat from hot geological thereby saving domestic consumption of oil for export (Almansoori formation. It has been reported that the recoverable geothermal and Torcat, 2015). potential from hot rocks in China is about 431 MWh and the CO2 14 The country has an ambitious program of having 41 GW of solar storage is about 3.53 10 kg. Therefore CO2 injection for power by 2032 from CSP concentrated solar plants (CSP), solar pv geothermal production is more economical than pure CO2 storage with an investment of 109 billion USD. In addition, the country has in geological formations (Zhang et al., 2014a, b). the target of developing about 18 GWe from nuclear power plants (WNA, 2013; Ahmad and Ramana, 2014). Saudi Arabia's motivation 3. CO2 emission to rely on nuclear sources for future energy needs emerge from the fact that depending on fossil fuel based desalination system to 3.1. CO2 emission from electricity generation provide fresh water to millions is unsustainable and will only in- crease the cost and CO2 emissions. In a recent business-as-usual CO2 emission is a cause of concern due to its influence on macro simulation study (Ahmad and Ramana, 2014) the country will and micro climate changes. Since these are intimately related to the lose stability if it does not maintain a sustained supply of oil to electricity generated from fossil fuels and desalination, fossil fuel

Table 2

Power generation status and CO2 emissions by Saudi Arabia (IEA, 2014).

Oil (Mt) Gas (bcm) Electricity (TWh) Electricity TWh) Population TPES Electricity CO2 emission Mt Elec. consump CO2 emission production production from oil from gas million MtOe con. TWh of CO2 kWh/capita tCO2/capita 2011 544 95 142 112 28.1 187 227 458 8068 16.28 2013 540 84 150 121 28.3 200 248 459 8763 16.22 216 D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233

Table 3 exported (Farnoosh et al., 2014). Saudi Arabia has an excellent Average levalized costs (2011 $/MWh) for plants entering service in 2018 (modified renewable energy source, to mitigate CO2 emissions and control after Chandrasekharam et al., 2014a). micro-climate changes, in the form of hydrothermal systems and 12 3 4 5 6 EGS along the western margin (Hussein et al., 2013; Lashin and Al Conventional coal 85 65.7 4.1 29.2 1.2 10 Arifi, 2012; Lashin and Al Arifi, 2014; Chandarasekharam et al., Advanced coal 85 84.4 6.8 30.7 1.2 12.3 2014a, b; 2015a, b). Here we highlight the vast EGS resources Conventional combined cycle 87 15.8 1.7 48.4 1.2 6.7 available to the country for development and for the mitigation of Conventional combustion turbine 30 44.2 2.7 80.0 3.4 12 the issues described above. Advanced combustion turbine 30 30.4 2.6 68.2 3.4 10.4 Advanced nuclear 90 83.4 11.6 12.3 1.1 10.8 Geothermal 92 76.2 12.0 0.0 1.4 8.96 4. Geothermal systems of Saudi Arabia Biomass 83 53.2 14.3 42.3 1.2 11.1 Wind 34 70.3 13.1 0.0 3.2 8.66 4.1. Hydrothermal energy resources Solar PVa 25 130.4 9.9 0.0 4.0 14.4 Hydrob 52 78.1 4.1 6.1 2.0 9.03 The western Arabian shield evolved with the initiation of the & & 1. Capacity factor, 2. Levalized Capital cost, 3. Fixed O M, 4. Variable O M, 5. Afar plume that triggered volcanic activity over the shield giving Transmission investment, 6. Levelized cost US$c/kWh. “ ” a Costs are expressed in terms of net AC power available to the grid for the rise to volcanic centres known as the Harrats which extend over installed capacity. the entire western margin of the shield (Fig. 2). This plume activity b As modelled, hydro is assumed to have seasonal storage so that it can be dis- continued until the shield broke into two giving rise to the Nubian patched within a season, but overall operation is limited by resources available by and Arabian shields, separated by the Red Sea. The Red Sea opening site and season. started with the initiation of the rift from the south that propagated north with time and rotated the shield anti-clock wise. The uprising based power generation is being controlled around the world to plume that stretched the continental crust along the west coast reduce the effects of detrimental climate variation on human be- triggered dikes swarms parallel to the Red Sea rift axis at about e ings. Countries like Saudi Arabia, a major producer and consumer of 30 25 Ma. This was followed by a series of volcanic eruptions that oil and gas, is facing micro climate change. The ambient tempera- poured enormous volumes of lava. These Harrats covered all the ture over the past decade over Saudi Arabia has increased by 0.70 C pre-existing drainage and paleochannels resulting in the creation of (Almazroui et al., 2012). This is due to an increase in the con- boiling aquifers below the Harrats. Water vapour from the basaltic sumption of electricity for space cooling, especially in the summer magma and steam from the hot aquifers emerged on to the surface months (IEA, 2013). At present Saudi Arabia utilizes 80% of the as fumaroles (Chandarasekharam et al., 2014a, b; Coleman et al., 1983; Lashin et al., 2015). The volcanic activity continues to the electricity generated for space cooling. The country's CO2 emission from fuel combustion has increased from 252 Mt in 2000 to 459 Mt present with the intrusion of dikes and the appearance of magma at present with oil contributing 175 Mt and gas contributing 77 Mt chamber at about 8 km below the Harrat Lunayyir (Al-Zahrani et al., (IEA, 2012; Chandarasekharam et al., 2014b). The current per capita 2013; Duncan and Amri, 2013). These magmatic and tectonic ac- tivities gave rise to wet geothermal systems associated with the emission of CO2 has increased to 16 Mt from 12 Mt in 2000 (Table 2; Harrats. Chandarasekharam et al., 2014b). High emissions of CO2 from the building sector can be mitigated by appropriate design of struc- 4.2. EGS resources tures. According to the standard building code, the CO2 emitted by well designed building should be 0.685 kg CO2/kWh. However this code is not practiced by several builders in the country (Taleb and In addition to the volcanic and tectonic activity, crustal thinning, Sharples, 2011). In addition to electricity for lighting and space under-plating of the oceanic crust below thinned continental applications, countries like Saudi Arabia, with scanty rainfall and segment and attenuated crust at several places along the conti- lack of surface river systems, need fresh water to support the entire nental margin, like that observed around Al Lith and Jizan, gave rise fl e 2 socio-economic system. This support comes from the desalination to high heat ow of 110 209 mW/m (Gettings et al., 1986; Lashin fi of Red Sea water. At present, 33 desalination plants are in operation and Al Ari , 2012; Chandrasekharam et al., 2015b), supporting high in Saudi Arabia with a government subsidy of US$ 0.03/m3 of water temperature geothermal systems. While hydrothermal activity is generated which is much lower than other countries of the world commonly seen in association with Harrats, geothermal systems where the cost is US$ 6/m3 of water generated (Taleb and Sharples, are also present in areas dominated by high radiogenic granites. 2011). About 13 Mt of CO2 is emitted from desalination plants if oil 5. Radiogenic granites is the fuel and 3 Mt of CO2 if gas is the fuel source (Chandrasekharam et al., 2015b). If agricultural activity is included, the demand for fresh water escalates at an exponential rate. With 5.1. Evolution of the granites an annual population growth of 6% there will be tremendous stress on the power generation system to meet the demand for electricity The initial tectonic evolution of the Arabian shield followed the and water (see Section 1.1, Fig. 1). Phanerozoic plate tectonic regime. Between 900 and 631 Ma, plutonic activity was represented by diorite, quartz diorite, tonalite and trondhjemite formed under an island arc setting that was 3.2. Options to reduce CO2 emission terminated between 680 and 630 Ma. This collision changed the tectonic style from an arc to an orogenic tectonic regime facilitating The country is examining at energy options to mitigate this extensive plutonic activity represented by granites and granitic problem. Major oil companies like ARAMCO are encouraging the rocks with a peak activity between 660 and 610 Ma. The end stage development of renewable energy sources (Chandarasekharam of plutonism was represented by peraluminous and peralkaline et al., 2014a, b). Energy optimization models reveal that by using alkali feldspar granites, pegmatites and acid dikes. The Arabian a source mix of fossil based power and renewables, the country can shield occupies an area of 770,000 sq.km. Nearly 55% of this area is reduce the cost of power by 28% per year from 2030 onwards and occupied by felsic plutonic rocks and the rest by volcanic rocks can save about 0.5 Mb/day of oil equivalent from 2020 which can be represented by Harrats (Stoeser, 1986). Of this 55%, granitic rocks D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233 217

Fig. 2. Plume initiated volcanic centres along the western Arabian shield (modified after Bosworth et al., 2005). constitute 63%. The distribution of granites and volcanic rocks is These radioactive mineral deposits with its high concentration of shown in Fig. 3. The absolute area occupied by the granitic rocks is radioactive elements make these granites very unusual. The ura- 161,467 sq. km (Stoeser, 1986; Chandarasekharam et al., 2014a, b) nium, thorium and potassium content in some of the granites and and the area occupied by volcanic flows or the Harrats is 90,000 sq. the heat generated by them are shown in Table 5 and their location km (Coleman et al., 1983). After the tectonic transformation from is shown in Fig. 2. The heat flow values are similar to the heat flow arc to collation type, the arc tectonic fabric was imprinted as paleo- values of 175 mW/m2 reported from bore hole measurement from suture zones that divided the shield into five plates or terranes the Precambrian basement along the western margin of the Red Sea bounded by these paleo-suture zones (Stoeser and Camp, 1985; in Egypt (Morgan and Swanberg, 1978) and over the geothermal Milkereit and Fluh, 1985; Mooney et al., 1985; Prodehl, 1985). sites along the eastern margin of the Gulf of Suez (Zaher et al., These terranes and paleo-suture zones are shown in Fig. 4. The 2012). The geothermal gradient measured in the bore holes dril- areal exposure of various rocks of granitic composition occurring in led within the Precambrian crystalline complex and Paleocene different terranes is shown in Table 4. varies from 40 to >80 C/km. Numerical simulation of temperature distribution with depth at the Hammam Faraun geothermal site 5.2. Radioactive property of the granites gave value of 170e180 C at 2 km depth (Morgan and Swanberg, 1978). In fact some of the geothermal systems located in granites These paleo-suture zones are the loci of uranium-bearing min- (i.e. at Al Lith, Lashin et al., 2014 and at Jizan, Chandrasekharam erals that were mobilized from the granite plutons shown in Table 4 et al., 2015a, b) are driven by such radiogenic granites. The (Stoeser, 1986; Stern and Johnson, 2010; Du Bray, 1986; Elliott, tritium content in the thermal waters from the above sites indicates 1983; Bokhari et al., 1986; Agar, 1992; Dawood et al., 2010). These long circulation time (>600 years, for Al Lith, Lashin et al., 2014, and minerals in the granites and associated pegmatites gave rise to high 12e32 K years for Jizan, Chandrasekharam et al., 2015a, b) within temperature geothermal systems along the western Arabian shield the granites indicating prolonged water rock interaction giving rise and maintain a high geothermal gradient and high heat flow value. to high chloride content (Al Lith: 1594 ppm, Lashin et al., 2014; 218 D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233

Fig. 3. General geological map showing the distribution of geothermal provinces, Harrats and granites and related intrusives (modified after Chandrasekharam et al., 2015a, b). The numbers indicate heat generated by the granites in mW/m3 calculated based on U, Th and K values (see Table 5). Only locations with heat generation >3 mW/m3 are shown in the figure. The complete heat generation values of the granites are shown in Table 5.

Jizan 1934 ppm, Hussein and Loni, 2011) in the thermal waters. shortening. The D2 deformation was represented by W-WSW thrust together with EeW compression that gave rise to the WadiYiba shear zone (Hamimi et al., 2013). During the last phase (D3), the 6. Regional stress over the Arabian shield stress regime changed from EeWtoNeS compression. Therefore, the shield was subjected to both EeW and NeS compression within 6.1. Deformation stresses the period extending from 786 to 630 Ma (Hamimi et al., 2013). The EeW compression regime recorded by the D1 deformation stage in The western shield of Saudi Arabia has been subjected to several the Wadi Yiba shear zone (Ablah Group, western shield) was also episodes of stress pattern since 630 Ma (Hamimi et al., 2013). The imprinted in the 689 Ma old EeW elongated ellipsoidal Mizil crystalline basement rocks of Saudi Arabia exposed along the granitic gneiss dome in the eastern Arabian shield indicating the western margin appears to be the largest tract of juvenile Neo- general EeW compression experienced by the entire shield region proterozoic continental crust on earth (Patchett and Chase, 2002). (Al Saleh and Kassem, 2012). The initial three regional deformations (D1,D2 and D3)(Hamimi et al., 2013) printed over the oldest lithological units (gneisses, syn-post tectonic granitoids, metavolcanics and metal clastics of 6.2. Regional stresses Ablah Group (Hamimi et al., 2013)) reveal the initial stress condi- tions of the ANS. The D1 deformation resulted due to EeW Between 600 and 540 Ma extensive left lateral faulting along the D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233 219

Fig. 4. Paleo suture zones and terranes, western shield, Saudi Arabia (modified after Lashin et al., 2014).

NWeSE trending Najd fault system cut across the Arabian shield. It was reported that the Najd fault system represents a set of trans- Table 4 form faults resulting from the rift basin in NE Egypt (Stem, 1985). In Percent of granitic rock types exposed in five terrane located adjacent to the Red Sea the western part of the shield evoporite rift basins developed coast. bounded by NW trending faults that are parallel to the Najd fault MH J A Afsystem. Therefore, all the EeW trending stress parameters related to collision tectonics terminated between 640 and 600 Ma and the Alkali felspar granite 14 10 1 2 4 e Granite 45 31 34 23 48 shield subsequently experienced NW SE directed crustal exten- Granodiorite 11 19 20 13 24 sion related to continental, breakup (Husseini, 1988). The stress Tonolitic rocks 15 15 17 35 8 regime in 30 Ma changed due to the rotation of Arabia with respect Dioritic 9 14 20 18 12 to Africa as a consequence of the opening of the Red Sea and Gulf of Gabbroic rocks 6 9 8 8 3 Syenitic rocks 2 1 1 Aden. The break up of the continents was sharp and the total Red Total granite rocks 70 60 55 38 76 Sea floor and the Gulf of Aden were made of entirely ocean floor Total intermediate rocks 30 40 45 62 24 (McKenzie et al., 1970; Bohannon, 1986; Le Pichon and Gaulier, M: Midyan terrane, H: Hijaz terrane, J: Jiddah terrane, A: Asir terrane, Af: Asif 1988). The initial movement at around 30 Ma started at the rate terrane, (modified after Stoeser, 1986; Chandrasekharam et al., 2014a, b). of 9 mm/year and during the last 5 Ma this rate increased to 9 mm/y 220 D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233

Table 5 Uranium, thorium and potassium in certain granites from Saudi Arabia (U, Th and K data from 1 to 5: Struckless et al., 1986, 1987;2:Al Saleh and Al Berzan, 2007;3:Harris and Marriner, 1980;4:Elliot, 1983;6:Harris et al., 1980;7:Pallister, 1986).

Sample no. Location Lat (N) Long (E) U (ppm) Th (ppm) K (wt%) RHP (mW/m3) HF (10 k) Ref.

184385 Al Bara bat ho I it h 23 28 52 41 20 15 4.07 14.0 3.93 2.4 63.8 1 184412 Al Maslukah 24 28 26 44 13 53 3.46 18.0 3.76 2.5 64.9 1 889494 Baid al Jimalah 25 8 55 42 41 15 13.30 35.2 3.87 6.2 102.2 1 893039 Baid al Jimalah 25 8 55 42 41 15 11.80 24.4 3.74 5.1 90.7 1 893159 Baid al Jimalah 25 8 55 42 41 15 11.30 29.6 4.68 5.4 93.9 1 893235 Baid al Jimalah 25 8 55 42 41 15 10.30 28.9 3.96 5.0 90.2 1 184122 Dukhnah 24 46 44 43 18 42 4.77 14.0 3.99 2.6 65.7 1 184127 Dukhnah 24 55 38 43 9 50 6.55 20.3 3.92 3.5 74.6 1 184241 Dukhnah 24 48 30 43 9 7 1.53 7.8 4.41 1.3 53.5 1 184431 Dukhnah 24 50 52 43 9 43 7.05 13.2 4.15 3.1 71.1 1 1 84432 Dukhnah 24 52 26 43 12 56 4.46 10.3 4.18 2.3 62.5 1 184154 Gharnaq Pluton 23 36 54 40 32 45 5.46 12.5 3.74 2.6 66.2 1 184154A Gharnaq Pluton 23 36 54 40 32 45 5.49 11.5 3.83 2.6 65.7 1 184155 Gharnaq Pluton 23 35 54 40 33 39 4.49 9.5 3.45 2.1 61.4 1 184156 Gharnaq Pluton 23 32 54 40 33 58 3.54 11.5 3.43 2.0 60.3 1 184382 Gharnaq Pluton 23 35 29 40 33 19 4.80 11.6 3.38 2.4 63.5 1 184383 Jabal Ramram 23 27 33 40 41 15 2.33 5.6 2.58 1.2 52.3 1 184004 Hadb ad Dayahin 23 32 34 41 10 2 2.81 2.7 3.49 1.2 52.4 1 184171 Hadb ad Dayahin 23 35 19 41 11 18 13.70 28.5 2.39 5.7 97.2 1 184180 Hadb ad Dayahin 23 34 15 41 13 37 5.50 4.1 3.28 2.0 60.1 1 184184 Hadb ad Dayahin 23 31 1 41 13 43 5.18 4.2 3.14 1.9 59.2 1 184381 Hadb ad Dayahin 23 30 32 41 12 57 2.77 8.2 3.91 1.6 56.5 1 184415 Hadbat Tayma 24 8 28 41 13 31 8.47 26.7 4.16 4.4 84.1 1 184384 Hudayb al Jidar 23 22 10 41 10 34 5.52 12.2 3.28 2.6 65.7 1 184014 Jabal Abha 24 24 19 40 41 15 6.89 20.8 3.30 3.5 75.2 1 184015 Jabal Abha 24 23 43 40 41 06 8.48 22.1 2.75 4.0 79.7 1 184018 Jabal Abha 24 23 14 40 46 09 9.12 29.8 3.40 4.7 87.2 1 184374 Jabal Abha 24 21 26 40 40 41 0.54 2.0 0.54 0.3 43.3 1 184375 Jabal Abha 24 22 38 40 40 09 7.72 25.6 3.29 4.1 80.6 1 184019 Jabal Aj i r 24 58 57 41 06 56 2.82 9.6 3.93 1.8 57.6 1 184021 Jabal Aj i r 24 58 25 41 08 30 2.59 7.7 4.06 1.6 55.8 1 184023 Jabal Aj i r 24 51 48 41 10 13 3.66 9.1 3.98 1.9 59.4 1 184089 Jabal Dhuray 24 13 04 43 43 12 15.80 35.2 3.74 6.8 108.5 1 184414 Jabal Dhuray 24 13 03 43 42 57 4.40 13.0 2.96 2.3 63.1 1 184031 Jabal Furqayn (north) 24 49 13 41 40 49 3.26 6.9 3.93 1.7 56.8 1 184036 Jabal Furqayn (north) 24 54 15 41 36 17 2.12 6.5 3.74 1.3 53.5 1 184038 Jabal Furqayn (north) 24 55 59 41 40 53 2.12 7.5 3.90 1.4 54.3 1 184377 Jabal Furqayn (north) 24 52 45 41 32 40 2.31 6.1 3.88 1.4 53.8 1 184378 Jabal Furqayn (north) 24 54 37 41 39 48 2.62 7.4 3.96 1.6 55.6 1 184040 Jabal Furqayn (south) 24 3 29 41 15 6 7.63 21.3 3.82 3.8 77.9 1 184379 Jabal Habhab al Jissu 24 31 24 41 36 50 8.01 15.0 3.80 3.5 74.5 1 184380 Jabal Habhab al Jissu 24 27 25 41 35 40 12.70 28.5 3.69 5.6 95.8 1 184009 Jabal Hadb ash Sharar 23 48 48 40 58 19 8.11 21.9 3.17 3.9 79.0 1 184056 Jabal Hadb ash Sharar 23 46 20 40 58 53 7.16 12.3 3.14 3.0 69.9 1 184396 Jabal Hadb ash Sharar 23 47 22 40 59 19 0.69 2.0 0.96 0.4 44.1 1 184087 Jabal Jabalah 24 46 41 43 53 19 4.19 10.1 3.98 2.1 61.5 1 184088 Jabal Jabalah 24 48 9 43 53 26 6.79 15.6 3.94 3.2 71.9 1 184269 Jabal Jabalah 24 46 53 43 51 44 7.96 8.5 4.10 3.0 70.2 1 184070 Jabal Haslah 23 48 57 42 03 12 2.42 7.6 3.87 1.5 55.1 1 184177 Jabal Haslah 23 49 42 42 00 28 2.55 8.0 4.00 1.6 55.8 1 184388 Jabal Haslah 23 51 42 42 00 07 4.35 15.8 4.03 2.6 65.9 1 184389 Jabal Haslah 23 49 42 42 00 02 2.98 9.3 3.83 1.8 57.7 1 184390 Jabal Haslah 23 49 41 42 00 03 3.27 11.5 3.54 2.0 59.7 1 184329 Jabal Khazaz 25 25 20 43 33 59 6.27 27.5 4.28 3.9 79.1 1 184334 Jabal Khazaz 25 22 30 43 33 17 3.87 28.6 3.89 3.3 73.4 1 114337 Jabal Khazaz 25 19 29 43 36 16 6.24 21.9 3.47 3.4 74.4 1 184338 Jabal Khazaz 25 19 54 43 35 50 9.07 25.5 3.64 4.4 84.4 1 184433 Jabal Khazaz 25 25 25 43 33 54 3.83 17.4 4.23 2.6 65.8 1 184434 Jabal Khazaz 25 23 05 43 34 59 3.24 18.7 4.17 2.5 65.2 1 184435 Jabal Khazaz 25 19 58 43 36 14 7.43 13.9 3.56 3.2 72.1 1 184419 Jabal Khurs 23 34 42 44 41 40 7.57 19.7 3.92 3.7 76.8 1 184077 Jabal Khinzir 23 10 11 43 49 27 30.30 8.3 3.49 8.7 126.9 1 184079 Jabal Khinzir 23 08 57 43 50 09 20.00 22.8 3.51 7.0 110.5 1 184080 Jabal Khinzir 23 08 17 43 52 13 9.81 27.1 3.63 4.7 87.4 1 184129 Jabal Khinzir 23 09 41 43 51 48 10.30 21.6 4.28 4.5 85.4 1 184130 Jabal Khinzir 23 09 11 43 50 48 10.60 24.2 4.03 4.8 87.8 1 184420 Jabal Khinzir 23 09 19 43 47 08 12.20 12.3 3.41 4.3 83.1 1 184421 Jabal Khinzir 23 08 56 43 48 30 12.20 26.8 3.98 5.4 93.6 1 184422 Jabal Khinzir 23 08 03 43 53 42 2.27 4.8 2.70 1.2 51.7 1 184117 Jabal Minya 24 59 11 43 24 01 16.10 24.1 4.38 6.2 102.2 1 184359 Jabal Minya 24 59 15 43 23 06 14.20 37.4 3.81 6.6 105.9 1 184373 Jabal Minya 24 59 18 43 23 28 23.70 38.5 3.66 9.1 131.0 1 184423 Jabal Minya 24 57 55 43 20 56 11.20 27.2 4.07 5.1 91.4 1 D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233 221

Table 5 (continued )

Sample no. Location Lat (N) Long (E) U (ppm) Th (ppm) K (wt%) RHP (mW/m3) HF (10 k) Ref.

184424 Jabal Minya 24 57 55 43 20 57 13.70 27.1 4.21 5.8 97.9 1 184425 Jabal Minya 24 57 31 43 19 45 11.60 15.9 2.91 4.4 83.5 1 184376 Jabal Sanaa 24 43 54 41 17 28 3.30 8.3 3.83 1.8 57.8 1 184439 Jabal Shiib 24 05 02 42 31 30 7.08 42.1 3.91 5.1 91.0 1 184440 Jabal Shiib 24 09 35 42 26 20 13.80 47.1 3.94 7.2 111.7 1 184440A Jabal Shiib 24 09 35 42 26 20 14.60 44.0 3.99 7.2 111.7 1 184441 Jabal Shiib 24 04 41 42 25 16 7.62 17.0 4.18 3.5 75.3 1 184061 Jabal Saqrah 23 04 31 42 50 57 1.78 20.1 5.37 2.4 63.5 1 184063 Jabal Saqrah 23 03 43 42 52 20 1.78 8.6 5.65 1.6 55.8 1 184064 Jabal Saqrah 23 01 07 42 58 25 1.41 7.7 4.44 1.3 53.1 1 184065 Jabal Saqrah 23 03 32 43 01 53 2.63 13.5 4.62 2.0 60.4 1 184301 Jabal Saqrah 23 06 16 42 58 19 3.56 12.4 4.09 2.2 61.6 1 184302 Jabal Saqrah 23 04 59 42 58 57 1.69 6.5 4.11 1.3 52.7 1 184402 Jabal Saqrah 23 04 16 42 49 11 1.83 24.0 5.52 2.6 66.5 1 184403 Jabal Saqrah 23 06 05 42 56 30 5.57 32.0 4.45 4.1 80.6 1 184404 Jabal Saqrah 23 06 04 42 56 30 26.30 49.8 4.05 10.6 145.8 1 184405 Jabal Saqrah 23 03 18 43 00 00 3.57 20.7 3.87 2.7 67.1 1 184406 Jabal Saqrah 23 02 00 43 01 00 3.96 14.1 3.48 2.3 63.2 1 181859 Jabal Si Isl lah 26 05 41 42 39 11 12.10 36.1 3.59 5.9 99.4 1 181871 Jabal Si Isl lah 26 05 16 42 39 47 8.39 33.9 3.54 4.8 88.3 1 181872 Jabal Si Isl lah 26 04 39 42 39 44 13.80 22.3 2.86 5.4 93.6 1 181964 Jabal Si Isl lah 26 06 13 42 38 48 6.28 21.7 4.00 3.5 74.9 1 184392 Jabat Tukhfah 23 53 03 42 09 51 9.86 25.0 3.65 4.6 86.1 1 184393 Jabat Tukhfah 23 56 14 42 07 29 7.48 25.2 4.14 4.1 80.5 1 184394 Jabat Tukhfah 23 56 14 42 07 31 7.91 25.4 4.02 4.2 81.7 1 184391 Jabal Umm Adban 23 50 27 42 07 31 2.15 7.1 3.98 1.4 54.2 1 184417 Jabal Za'abah 23 48 24 44 46 06 3.85 11.5 3.69 2.1 61.3 1 184418 Jabal Za'abah 23 46 18 44 45 55 5.60 17.5 4.30 3.1 70.5 1 184444 Jabal al Mudayh 24 24 30 42 12 30 8.21 38.4 4.22 5.2 91.6 1 184445 Jabal al Mudayh 24 26 58 42 12 00 7.55 24.9 4.09 4.0 80.5 1 184397 Jabal al Yanufi 23 25 59 43 04 23 4.57 13.1 3.72 2.4 64.3 1 184398 Jabal al Yanufi 23 27 9 43 04 22 2.84 14.3 3.69 2.1 60.7 1 184399 Jabal al Yanufi 23 24 20 43 04 58 2.80 15.4 3.87 2.1 61.5 1 184058 Jabal at Safuah 23 08 23 42 17 13 3.25 13.1 3.82 2.1 61.0 1 184059 Jabal at Safuah 23 07 43 42 17 32 5.32 15.8 4.08 2.8 68.4 1 184395 Jabal at Safuah 23 07 24 42 16 05 8.08 20.2 3.84 3.8 78.3 1 184339 Ha lik Granite 25 10 23 43 39 03 1.64 25.3 4.28 2.6 65.7 1 184342 Ha lik Granite 25 7 50 43 47 06 3.31 18.7 4.78 2.6 65.9 1 184344 Ha lik Granite 25 10 39 43 44 19 3.83 28.9 4.07 3.4 73.6 1 184149 Hiskah 1 24 36 57 42 56 30 5.88 18.9 4.08 3.2 72.0 1 184426 Hiskah 1 24 41 4 42 51 00 7.60 24.4 4.39 4.1 80.5 1 184242 Hiskah 1 24 35 16 43 05 01 9.51 29.0 4.25 4.8 88.5 1 184368 Hiskah 2 24 48 56 42 54 11 0.44 14.6 5.91 1.7 56.8 1 184427 Hiskah 2 24 54 46 42 48 12 7.21 16.5 4.06 3.4 73.8 1 184446 Hiskah 2 24 55 35 42 34 24 12.40 25.8 3.81 5.3 93.3 1 184447 Hiskah 2 24 56 5 42 35 41 11.80 19.5 4.13 4.8 87.7 1 184152 Hiskan 3 24 35 31 43 10 05 3.03 9.2 3.96 1.8 57.9 1 184428 Hiskan 3 24 35 27 43 10 07 2.56 12.9 4.53 2.0 59.8 1 184429 Hiskan 3 24 34 50 43 12 55 2.03 8.4 4.33 1.5 55.1 1 184430 Hiskan 3 24 35 27 43 10 07 2.41 8.3 4.22 1.6 55.9 1 184409 Najirah 24 14 0 44 25 31 4.61 18.9 4.39 2.9 69.0 1 184410 Najirah 24 14 1 44 26 28 5.06 16.1 4.28 2.8 68.2 1 184411 Najirah 24 15 45 44 26 39 4.56 17.2 4.28 2.8 67.6 1 184436 Suva j 25 11 57 43 17 16 11.90 24.2 3.90 5.1 91.0 1 184437 Suva j 25 11 57 43 17 16 9.81 19.2 4.37 4.3 82.6 1 184438 Suva j 25 10 58 43 16 57 7.86 21.2 4.30 3.9 78.9 1 184274A Unnamed 1 24 9 0 43 52 32 3.67 19.3 4.06 2.7 66.6 1 184275 Unnamed 1 24 11 58 43 55 20 3.57 15.6 4.17 2.4 63.9 1 184413 Unnamed 1 24 9 26 43 55 34 8.32 19.9 4.23 3.9 79.1 1 184400 Unnamed 2 23 27 40 42 40 44 2.98 17.9 4.17 2.4 64.0 1 184442 Unnamed 3 24 21 8 42 26 5 1.72 7.7 6.39 1.6 55.7 1 184443 Unnamed 3 24 21 8 42 26 6 12.40 19.3 3.84 4.9 88.8 1 G-1 Salmon 4.26 10.3 4.80 2.3 62.6 2 G-2 Bianco sardo 7.67 12.1 4.45 3.2 72.3 2 G-3 Sweet gold 0.15 0.1 0.04 0.1 40.5 2 G-4 Najran brown 0.01 0.0 0.00 0.0 40.0 2 G-5 Saudi brown 0.01 0.1 0.00 0.0 40.1 2 G-6 Saudi green 0.00 0.0 0.00 0.0 40.0 2 G-7 Royal gold 0.00 0.0 0.00 0.0 40.0 2 G-8 Spring green 0.00 0.0 0.00 0.0 40.0 2 1 Midian Granite 5.00 11.0 4.12 2.4 64.3 3 2 Midian Granite 5.00 1.0 3.84 1.7 57.1 3 3 Midian Granite 1.00 2.0 3.53 0.7 47.3 3 4 Ghurayyah Granite 104.00 625.0 2.59 70.2 741.8 3 (continued on next page) 222 D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233

Table 5 (continued )

Sample no. Location Lat (N) Long (E) U (ppm) Th (ppm) K (wt%) RHP (mW/m3) HF (10 k) Ref.

5 88.00 160.0 2.63 33.9 379.3 3 6 Vain 363.00 590.0 1.65 134.2 1382.4 3 7 Precursor granites 8.00 30.0 4.23 4.5 85.3 4 8 Precursor granites 6.00 30.0 4.07 4.0 80.0 4 11 Tin-bearing granites 12.00 48.0 3.24 6.7 107.1 4 14 Tin-bearing granites 4.00 26.0 3.59 3.2 71.6 4 15 Tin-bearing granites 12.00 34.0 3.36 5.8 97.5 4 155575 Jabal Nis 20 02 49 41 13 12 3.45 13.5 3.30 2.1 61.3 5 155576 Jabal Nis 2003 22 41 13 01 3.54 9.3 3.90 1.9 59.2 5 155577 Jabal Nis 20 03 07 41 13 23 4.33 14.1 3.64 2.4 64.3 5 155578 Jabal Shada 19 50 31 41 18 47 3.51 9.1 3.55 1.9 58.7 5 155579 Jabal Shada 19 50 31 41 18 47 3.75 7.0 3.67 1.8 57.9 5 155587 Jabal Shada 19 51 04 41 19 19 1.90 10.1 2.89 1.5 54.6 5 155588 Jabal Shada 19 51 04 41 19 19 1.44 6.5 2.01 1.0 50.1 5 155589 Jabal Shada 19 51 18 41 19 55 3.61 12.0 3.91 2.1 61.2 5 155580 Jabal Dugayna 18 46 08 42 16 26 4.93 12.8 4.23 2.5 65.5 5 155581 J. Dugayna 18 46 08 42 16 26 5.13 15.3 4.57 2.8 68.1 5 155582 J. Dugayna 18 46 44 42 17 49 3.74 12.7 4.42 2.3 62.5 5 155583 J. Barquq 18 48 14 42 11 28 1.05 6.1 4.23 1.1 50.9 5 155584 J. Barquq 18 47 46 42 11 42 6.44 6.6 3.83 2.5 64.7 5 155585 J. Barquq 18 47 46 42 11 42 5.64 13.4 4.05 2.8 67.6 5 155586 J. Barquq 18 47 28 42 12 00 1.36 1.8 3.75 0.8 48.3 5 155591 Al Ajarda 19 10 19 41 58 19 0.78 3.3 4.28 0.8 48.3 5 155592 Al Ajarda 19 10 19 41 58 19 0.96 3.1 3.60 0.8 48.0 5 155593 Al Ajarda 19 07 23 41 57 18 0.05 0.4 4.58 0.5 44.7 5 155594 Al Ajarda 19 07 23 41 57 18 0.05 0.5 4.44 0.5 44.6 5 155595 Al Ajarda 19 06 29 41 59 49 0.29 0.6 2.06 0.3 43.1 5 155596 J. Fuqa'ah 19 03 04 41 26 13 4.00 7.1 3.75 1.9 58.7 5 155597 Par al Jabal 19 50 38 41 32 38 0.97 2.2 1.57 0.5 45.5 5 155598 Par al Jabal 19 50 28 41 32 56 1.04 0.8 1.48 0.5 44.6 5 155598I Par al Jabal 19 50 28 41 32 56 0.32 0.8 1.67 0.3 42.9 5 155599 J. Duqayna 19 43 26 41 37 44 10.20 2.0 3.79 3.1 71.2 5 155600 J. Duqayna 19 42 32 41 40 05 6.10 13.4 3.88 2.9 68.6 5 155601 J. Raft 20 27 47 41 58 05 4.00 7.3 3.37 1.9 58.5 5 155502 J. Raft 20 29 35 42 0 36 4.43 5.4 2.81 1.8 57.8 5 155603 J. Raft 20 30 29 42 01 08 3.69 4.3 2.80 1.5 55.1 5 155604 J. Raft 20 30 11 41 55 30 5.40 8.8 3.34 2.3 63.1 5 155605 J. Raft 20 28 41 41 55 48 5.15 5.2 3.24 2.0 59.9 5 155536 J. Raft 20 26 24 42 00 29 2.64 2.7 0.70 0.9 49.3 5 155607 Al Mu'taridah 20 18 25 42 12 40 11.70 2.2 2.19 3.4 73.6 5 155608 Al Mu'taridah 20 18 25 42 12 40 1.26 0.9 0.93 0.5 44.7 5 155609 Al Mu'taridah 20 14 06 42 14 24 8.90 12.1 3.67 3.5 74.7 5 155510 Al Mu'taridah 20 12 58 42 11 35 8.07 13.5 3.80 3.4 73.6 5 155611 Al Mu'taridah 20 12 50 42 12 32 14.00 19.8 3.53 5.3 93.0 5 155612 J. Balas 19 48 25 41 52 26 10.10 17.8 3.99 4.2 82.0 5 155613 J. Balas 19 48 47 41 53 24 6.36 18.0 4.06 3.3 72.6 5 155514 J. Balas 19 51 29 41 53 28 7.07 18.0 3.98 3.4 74.4 5 155615 Wadi Shumms 19 53 42 41 51 32 6.91 19.2 4.33 3.5 75.1 5 155516 Wadi Shumms 19 53 28 41 55 05 2.43 8.8 4.00 1.6 56.1 5 155517 Wadi Shumms 19 57 11 41 52 59 1.15 4.2 4.28 1.0 49.9 5 155518 J. Abu Sadi 20 25 16 40 00 22 3.71 12.8 3.87 2.2 62.0 5 155619 J. Abu Sadi 20 25 55 40 00 47 5.72 10.5 4.11 2.6 65.8 5 155620 J. Abu Sadi 20 26 49 40 01 05 2.89 11.8 3.72 1.9 59.1 5 155621 J. Abu Sadi 20 24 50 40 02 10 3.87 14.0 3.98 2.3 63.4 5 155622 Adan Pluton 20 23 24 40 52 19 1.32 6.7 2.33 1.0 50.2 5 155523 Adan Pluton 20 23 24 40 52 19 1.41 6.7 3.81 1.2 51.8 5 155624 Adan Pluton 20 23 24 40 52 19 0.78 5.6 2.69 0.8 48.4 5 155625 Adan Pluton 20 24 11 40 55 44 2.30 7.6 3.54 1.5 54.5 5 155626 Adan Pluton 20 24 11 40 55 44 1.78 7.0 3.83 1.3 53.0 5 155627 J. Ibrahan 20 26 35 41 09 58 1.44 3.6 3.58 1.0 49.6 5 155626 J. Ibrahan 20 26 35 41 09 58 1.12 4.4 3.41 0.9 49.1 5 155629 J. Ibrahan 20 25 55 41 08 13 1.24 6.9 3.55 1.1 51.3 5 155530 J. Ibrahan 20 24 54 41 07 59 1.19 4.5 3.42 0.9 49.4 5 155631 J. Ibrahan 20 24 36 41 09 04 1.98 6.0 3.09 1.2 52.1 5 155632 Hawil 20 57 36 41 21 50 2.24 9.3 4.18 1.6 56.1 5 155633 Hawil 20 55 48 41 21 32 1.47 4.9 3.47 1.0 50.4 5 155634 Hawil 20 54 36 41 20 49 1.41 4.5 5.96 1.2 52.3 5 155635 Hawil 20 51 29 41 17 28 1.44 4.3 4.17 1.1 50.6 5 155641 Hawil 20 52 34 41 19 30 1.42 5.4 4.57 1.2 51.7 5 155636 J An 21 17 28 41 10 23 2.24 9.3 4.29 1.6 56.2 5 155537 J An 21 17 38 41 10 30 1.47 4.9 4.11 1.1 51.0 5 155638 J An 21 17 17 41 10 59 1.41 4.5 4.14 1.1 50.6 5 155639 J An 21 17 17 41 10 59 1.44 4.0 4.18 1.0 50.4 5 155640 J An 21 17 28 41 10 41 1.42 5.4 4.21 1.1 51.3 5 155542 J. Ounnah 21 04 16 41 09 07 6.24 19.6 3.48 3.3 72.9 5 D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233 223

Table 5 (continued )

Sample no. Location Lat (N) Long (E) U (ppm) Th (ppm) K (wt%) RHP (mW/m3) HF (10 k) Ref.

155643 J. Ounnah 21 02 53 41 07 05 0.07 0.1 0.15 0.0 40.4 5 155644 J. Ounnah 21 02 53 41 07 05 0.07 0.1 0.16 0.0 40.4 5 155645 Al Mahdan 20 56 38 40 53 02 1.95 8.5 2.81 1.4 53.5 5 155646 Al Mahdan 20 53 28 40 52 34 1.25 7.3 4.09 1.2 52.1 5 155647 Al Mahdan 20 53 46 40 51 50 0.68 0.8 4.77 0.7 46.8 5 155648 J. Bargatinah 20 47 56 39 51 18 1.51 5.6 3.41 1.1 51.0 5 155649 J. Bargatinah 20 47 56 39 51 18 2.17 6.4 3.24 1.3 53.0 5 155650 J. Bargatinah 20 47 56 39 51 18 2.52 6.4 3.57 1.4 54.3 5 155651 J. Bargatinah 20 47 28 39 51 14 1.68 4.1 2.61 1.0 49.6 5 155652 Unnaaed 21 09 29 39 57 29 2.79 6.8 4.46 1.6 56.1 5 155653 Unnaaed 21 09 11 39 57 07 2.57 9.6 3.54 1.7 56.6 5 155654 Unnaaed 21 09 43 39 58 23 3.54 5.5 3.57 1.6 56.3 5 155655 Unnaaed 21 10 59 39 59 02 2.00 5.1 3.19 1.2 51.7 5 155656 Unnaaed 21 10 59 39 59 02 3.28 6.7 4.01 1.7 56.8 5 155657 Unnaaed 21 10 59 39 59 02 2.92 8.5 3.82 1.7 57.0 5 155558 Judayrah 21 23 28 40 25 25 5.05 55.2 4.54 5.5 95.4 5 155659 Judayrah 21 26 49 40 25 59 2.81 13.3 4.71 2.1 60.8 5 155660 J. Sha'ir 21 19 08 40 17 56 4.99 12.2 3.97 2.5 65.0 5 155661 Unnaned 21 10 23 40 05 53 1.08 6.2 2.87 1.0 49.8 5 155662 Unnaned 21 10 01 40 09 07 3.73 7.0 3.40 1.8 57.6 5 155663 J. Abu Sibal 21 19 55 39 37 30 1.34 3.9 2.63 0.9 48.6 5 155664 J. Abu Sibal 21 19 52 39 37 34 1.85 3.7 2.31 0.9 49.5 5 155665 J. Abu Sibal 21 19 52 39 37 34 1.62 3.6 2.15 0.9 48.7 5 155666 J. Abu Sibal 21 19 44 39 37 41 1.76 4.0 2.35 0.9 49.5 5 155667 Unnaned 21 05 35 40 00 04 2.52 7.6 4.08 1.6 55.6 5 155668 Unnaned 21 05 35 40 00 04 2.65 10.7 3.39 1.7 57.4 5 155669 Unnaned 21 05 35 45 05 56 1.71 11.7 3.87 1.6 56.1 5 155670 J. Savdah 20 47 56 40 13 01 1.73 12.1 4.45 1.7 57.0 5 155571 J. Savdah 20 47 56 40 13 01 1.23 3.0 3.90 0.9 48.9 5 155672 J. Savdah 20 47 24 40 14 13 1.49 10.0 4.29 1.5 54.8 5 155673 J. Savdah 20 47 24 40 14 13 1.95 9.3 2.73 1.4 54.0 5 155674 J. Alonsa 20 29 35 40 40 08 0.56 1.6 1.79 0.4 44.2 5 155675 J. Alonsa 20 29 35 40 40 08 0.45 1.7 1.69 0.4 43.9 5 155676 Unnmmed 20 32 24 40 57 40 3.59 9.5 3.95 2.0 59.5 5 155677 Unnmmed 20 32 24 40 57 40 3.18 15.7 4.25 2.3 63.0 5 155578 J. Majiah 20 16 12 42 41 46 3.79 12.7 4.12 2.2 62.4 5 155679 J. Majiah 20 16 59 42 38 46 2.32 11.6 5.39 1.9 59.0 5 155660 J. Majiah 20 16 34 42 37 23 2.33 7.2 4.40 1.5 55.1 5 155661 J. Majiah 20 16 34 42 37 23 2.07 7.3 5.10 1.5 55.1 5 155682 Sha'ib Dahthami 20 24 54 41 24 22 2.65 7.0 3.09 1.5 54.5 5 155683 Sha'ib Dahthami 20 25 44 41 22 05 1.74 3.8 3.60 1.0 50.5 5 155684 J. Suliy 20 28 12 41 30 54 6.79 15.9 4.56 3.3 72.7 5 155665 J. Suliy 20 58 41 42 30 07 6.37 16.1 4.63 3.2 71.9 5 155686 J. Suliy 20 58 41 42 30 07 5.29 17.2 4.66 3.0 69.9 5 155687 J. Suliy 20 57 56 42 31 30 3.03 7.7 4.11 1.7 57.0 5 155588 J. Kor 20 59 28 42 45 14 5.14 8.6 2.91 2.2 61.9 5 155669 J. Kor 20 58 59 42 48 36 6.50 13.4 4.31 3.0 70.0 5 155690 J. Kor 20 56 52 42 50 42 6.11 20.2 4.34 3.4 73.7 5 155691 J. Kor 20 58 52 42 50 42 6.31 10.8 4.11 2.8 67.5 5 155692 J. Taweel 20 54 7 42 54 25 0.98 2.4 3.88 0.8 47.8 5 155693 J. Taweel 20 50 17 42 55 19 1.78 5.7 4.20 1.2 52.5 5 155694 J. Taweel 20 49 44 52 56 46 2.62 5.5 4.07 1.4 54.4 5 155695 J. Taweel 20 46 34 42 57 25 2.88 4.3 3.99 1.4 54.1 5 155696 J. Taweel 20 43 30 42 56 38 1.93 3.8 3.92 1.1 51.3 5 155697 J. Bafdeh 19 33 22 42 57 00 18.30 21.1 3.44 6.5 104.9 5 155698 J. Bafdeh 19 33 14 42 55 37 4.61 14.5 3.65 2.5 65.3 5 155699 J. Bafdeh 19 32 17 42 53 28 3.25 9.8 3.70 1.9 58.6 5 155700 Unnaaed 19 18 4 42 54 07 0.80 0.6 1.64 0.4 44.0 5 155701 Jazirah 19 02 49 42 54 25 1.63 4.0 4.23 1.1 50.9 5 155702 Jazirah 19 01 05 42 55 26 0.50 0.5 4.78 0.6 46.1 5 155703 Jazirah 19 01 05 42 56 46 0.40 0.5 0.56 0.2 41.9 5 155704 Jazirah 19 02 35 42 57 22 0.44 0.5 5.61 0.7 46.7 5 155705 J. Marub 19 6 36 42 35 53 2.79 10.2 3.04 1.7 57.1 5 155706 J. Marub 19 7 52 42 36 40 2.32 8.9 3.36 1.5 55.3 5 155707 Unnaned 19 19 48 42 37 16 17.20 2.4 3.18 4.9 88.9 5 155708 Unnaned 19 20 42 42 34 52 5.69 16.9 4.04 3.0 70.1 5 155709 Unnaned 19 20 42 42 34 52 7.00 15.5 3.80 3.2 72.3 5 155710 Unnaned 19 21 32 42 37 01 25.90 3.1 2.99 7.2 111.5 5 155711 Unnaned 19 21 32 42 37 01 23.60 3.2 3.26 6.6 105.9 5 155712 Madmbiyah Pluton 19 24 22 42 37 16 2.76 8.3 4.22 1.7 56.8 5 155713 Madmbiyah Pluton 19 29 17 42 39 43 5.94 19.3 3.92 3.2 72.3 5 155711 Gslalah Dome 19 33 22 42 39 58 0.86 5.5 4.01 1.0 49.8 5 155715 Gslalah Dome 19 33 54 42 40 48 1.43 3.3 3.99 1.0 49.7 5 155716 Gslalah Dome 19 37 57 42 42 00 6.17 19.1 3.57 3.2 72.4 5 (continued on next page) 224 D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233

Table 5 (continued )

Sample no. Location Lat (N) Long (E) U (ppm) Th (ppm) K (wt%) RHP (mW/m3) HF (10 k) Ref.

155717 Gslalah Dome 19 37 52 42 42 00 15.10 16.2 2.07 5.2 92.0 5 155718 Al Hideb 19 41 06 42 47 49 3.69 10.3 4.20 2.1 60.6 5 155719 Al Hideb 19 43 12 42 47 53 6.85 15.4 4.14 3.2 72.1 5 155720 Al Hideb 19 43 12 42 47 53 5.96 11.8 4.07 2.7 67.3 5 155721 J. Munireh 20 36 07 42 46 37 2.27 4.9 4.32 1.3 53.3 5 155722 J. Munireh 20 36 07 42 46 37 1.42 3.5 4.45 1.0 50.3 5 155724 J. Munireh 20 33 25 42 42 37 3.74 9.3 4.13 2.0 59.9 5 155724 J. Munireh 20 30 45 42 42 29 6.75 8.6 3.97 2.7 67.0 5 155725 J. al Jafar 20 30 50 42 47 10 7.69 2.2 4.17 2.5 65.2 5 155726 20 30 35 42 46 59 7.26 7.8 4.14 2.8 67.9 5 155726A 20 39 35 42 46 59 8.71 2.4 4.20 2.8 68.0 5 155727 20 27 18 42 46 44 4.24 13.3 4.25 2.4 64.1 5 155728 J. al Fu'ad 20 59 06 43 47 17 5.99 16.5 4.22 3.1 70.8 5 155729 20 59 06 43 47 17 5.72 23.6 3.81 3.5 74.6 5 155730 20 57 00 43 49 48 5.12 14.1 4.25 2.7 66.9 5 155731 20 55 34 43 51 14 4.61 15.3 4.12 2.6 66.3 5 155732 J. al Qarah 20 16 01 43 12 43 1.63 7.6 3.64 1.3 52.9 5 155733 20 16 01 43 12 43 4.54 8.6 3.92 2.1 61.3 5 155734 20 13 16 43 13 59 4.91 9.8 3.95 2.3 63.1 5 155735 Bnni Shawhatah 20 05 54 43 27 00 3.45 10.4 3.98 2.0 59.8 5 155736 20 02 31 43 27 22 3.14 10.4 4.13 1.9 59.1 5 155737 Unnaned 19 43 55 42 34 30 5.81 15.0 3.99 2.9 69.1 5 155738 Wadi al Khanaq 19 45 47 42 46 05 12.40 26.4 3.86 5.4 93.7 5 155739 Sirat Rishah 19 52 37 42 42 00 3.42 13.8 3.43 2.2 61.6 5 155742 J. Asbah 20 09 11 41 56 46 0.70 4.5 4.96 1.0 49.5 5 155743 20 06 11 41 54 58 2.16 5.1 4.08 1.3 52.9 5 155744 J. Amoudah 20 04 52 42 47 49 4.78 10.6 4.06 2.3 63.4 5 155745 20 07 48 42 47 24 3.83 9.6 4.17 2.0 60.4 5 155746 20 12 54 42 47 28 1.70 3.9 4.15 1.1 51.0 5 155747 J. Khashaadheed 20 15 04 42 52 52 4.31 11.5 4.12 2.3 62.9 5 155748 20 19 25 42 53 28 13.00 20.0 4.03 5.1 91.0 5 155749 20 19 26 42 53 28 6.86 15.7 4.10 3.2 72.3 5 155750 J Umm Hashiyah 20 01 01 42 55 01 3.63 13.3 3.08 2.1 61.4 5 155751 19 58 52 42 57 43 4.93 10.6 3.05 2.3 62.9 5 155752 19 58 52 42 57 43 2.46 8.2 3.11 1.5 54.9 5 155753 19 58 52 42 57 43 4.21 8.5 4.38 2.1 60.8 5 155754 19 58 52 42 57 43 4.10 9.8 2.91 2.0 60.1 5 3b Peralkaline granite 16.00 40.0 33.20 7.2 111.9 6 1 3.00 2.0 1.66 1.2 52.1 6 12a 4.00 4.0 3.32 1.6 56.1 6 16c 14.00 39.0 32.37 6.5 105.4 6 5a Monzogranite 3.00 14.0 11.62 2.1 61.4 6 20 3.00 21.0 17.43 2.6 65.8 6 22 3.00 19.0 15.77 2.4 64.4 6 39a 7.00 20.0 16.60 3.6 75.8 6 4 Red granite 11.00 35.0 29.05 5.6 96.4 6 31 12.00 24.0 19.92 5.1 90.8 6 38 49.00 117.0 97.12 21.1 250.9 6 3a Dumah granodiorite 1.00 3.0 2.49 0.6 45.9 6 165006 Hawaiite 20 43.6 39 41.5 1.20 3.3 2.74 0.6 46.4 7 175764 Gabbro 20 28 40 12.2 0.70 3.1 2.57 0.5 44.6 7 175776 Diabase 19 23 41 15 0.20 1.7 1.41 0.2 42.1 7 175785 Diorite 20 54.4 39 53.2 2.10 7.8 6.47 1.2 52.5 7 165574 Qz.diorite 20 47.7 39 51.3 1.60 3.6 2.99 0.8 48.1 7 165546 Rhyolite 20 44.3 39 53.4 13.80 40.6 33.70 6.7 106.6 7 165571 Basalt 20 47.7 39 51.3 0.30 1.4 1.16 0.3 42.6 7 165627 Cooendite 20 48.6 39 54.0 5.20 17.0 14.11 2.8 68.3 7 165661 Diabase 20 56.8 39 40.5 0.90 2.7 2.24 0.5 45.1 7 165881 Basalt 20 52.4 39 56.5 0.80 3.3 2.74 0.6 45.6 7 165882 Hawaiite 20 54.2 39 53.8 0.59 1.2 1.00 0.3 43.2 7 175780 Diabase 20 48.8 39 52.9 0.40 1.7 1.41 0.3 42.8 7 165714 Perlite 20 44.5 39 38 3.60 7.9 6.56 1.8 58.0 7 165767 Alk.basalt 20 57.5 39 37.2 0.40 1.2 1.00 0.2 42.0 7 6.68 16.9 4.41

1. Stuckless et al., 1986.2.Al Saleh and Al Berzan 2007.3.Harris and Marriner 1980.4.Elliot, 1983.5.Stuckless et al., 1987.6.Harris et al., 1986.7.Pallister, 1986.

(Bayer et al., 1988) along the EeW and SWeNE directions. The alkaline at about 30e32 Ma magmatism along a narrow linear zone plume based separation of the Nubian-Arabian shield (see Fig. 2; in the shield, b) rotational and detachment faulting at 25 Ma, c) Bosworth et al., 2005) that eventually gave rise to the Red Sea gabbro and diorite intrusive and acid volcanic phase between 20 spreading axis was discounted by Bohannon et al. (1989) based on and 25 Ma with simultaneous non marine sedimentation in the extensive field and fission track dates on apatites from the Prote- initial rift, d) deposition of marine sediments and subsidence of rozoic rocks. The sequence of formation of the Red Sea was a) initial shelf in the Miocene and e) uplift of adjoining continental area D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233 225 subsidence of the shelf between 13 and 5 Ma. The above sequence direction with respect to Africa at a rate of 1 cm/y (Girdler, 1966; of processes was caused by lithospheric extension that is linked to Garson and Krs, 1976). Whatever the process of evolution of the the collision of India and Eurasia. Due to this collision, the Owens Red Sea (Bosworth et al., 2005; Bohannon et al., 1989) and the fracture zone north of the Carlsberg Ridge became rigid forcing the changes of stress directions that the shield has undergone since 700 Arab plate to rotate along with India and move away from the Af- Ma (Makris and Rihm, 1991) the high heat generating granites of rican plate. As a result, the Arabian shield was under extension the western shield are under a compressional regime along the regime while the eastern margin was under compression due to the NEeSW to EeW direction. collision with the Iranian plate. This initial extension regime must have caused intrusion of dike swarms parallel to the coast before the evolution of the Harrats (Chandarasekharam et al., 2014a, b; 7. Heat flow and subsurface temperature of the Arabian 2015a, b). Makris and Rihm (1991) proposed pull apart model for shield the evolution of the Red Sea based on seismic, gravity and magnetic anomaly investigations. According to this model, the breakup of the 7.1. Radioactive heat production and heat flow African and Arabian shields was initiated by strike-slip faulting, a similar process advocated by Bohannon et al. (1989) described The radioactive heat production (RHP in mW/m3) by granites has above. The strike slip model advocates early oceanisation of the Red been calculated using the heat generation constant (amount of heat Sea due to the on-set-of pull apart basins and extensive intrusive released per gram of U, Th, and K in per unit time) and the uranium, (dike) activity along the eastern coast of the Red Sea. The strike-slip thorium and potassium concentrations CU, CTh and CK (Table 5) process was facilitated by the inherent weakness (e.g. Najd shear using the equation suggested by Rybach (1976) and Cermak et al. system) developed by the shield during 600 Ma Pan-African (1982): orogeny (Makris and Rihm, 1991). The initial faults and linea- ments that developed due to the pull apart structural regime were ¼ rð : þ : þ : Þ 5 RHP 9 52CU 2 56CTh 3 48CK 10 reactivated subsequently during the Oligocene and resulted in 3 extensive magmatic activity that continues in recent times. An where, r is the density of rock in kg/m ; CU and CTh are the con- fi insitu eld stress investigation at the Mudhiq dam site in the Taif centration of U and Th in mg/kg respectively and CK is the con- region, western Saudi Arabia (Giraud et al., 1986) in conjunction centration of K in weight percentage in the granites. Th heat with studies of earthquake focal mechanism, fracture pattern, and generation values by the granites over the western shield region are topography demonstrated that the major stress field of the shield is shown in Fig. 2 (values >3 mW/m3 only are shown). oriented along the NEeSW to EeW direction with the Arabian plate The surface heat flow values were calculated using the following as demonstrated earlier, rotating at an angle of 6 in anticlockwise equation of Lachenbruch (1968).

Fig. 5. Subsurface temperature (C) at 2 and 3 km depth (See Section 7). 226 D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233

Fig. 6. Gamma ray and gamma ray spectrometry logs of Well 1, Arabian shield-Saudi Arabia (for location see Fig. 5). D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233 227

Fig. 7. Gamma ray and gamma ray spectrometry logs of Well 2, Arabian shield-Saudi Arabia (for location see Fig. 5). 228 D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233

Fig. 8. Gamma ray and gamma ray spectrometry logs of Well 3, Arabian shield-Saudi Arabia (for location see Fig. 5). D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233 229

Q ¼ Q0 þ D A where Q is the heat flow at the surface, Q0 is an initial value of heat flow unrelated to the specify decay of radioactive element at certain time, D is the thickness of rock over which the distribution of radioactive element is more or less homogeneous, and A is the radioactive heat production. Since the Moho depth along the western Arabian coast varies from 18 to 25 km (Park et al., 2008) the background heat flow (Q0) value along the shelf is considered as 250 mW/m2 and along the coastal region (between the shore line and the escarpment) the value is taken as 100 mW/m2 (Girdler and Evans, 1977). The heat flow values thus calculated over the shield are listed in Table 5. Based on the heat flow values (Table 5) the subsurface temperature has been calculated using the following relation (Vernekar, 1975)

Q ¼ kðdT=dZÞ where, k is the thermal conductivity of the rock and dT/dZ is the thermal gradient. The subsurface temperature has been calculated by taking the average surface temperature as about 30 C (Vernekar, 1975) and thermal conductivity of the rock (i.e. granite) as 3.98 W m 1 C 1. The estimated subsurface temperatures of the Arabian shield at 2 km and 3 km depths were calculated and the results are shown in Fig. 5.

7.2. Gamma ray logs in bore wells

The natural gamma ray log (API) together with the resistivity, thorium, uranium and potassium content and lithology recorded in 5 bore wells drilled within or near the western Arabian shield area are shown in Figs. 6e10. The locations of the bore wells are shown in Fig. 5. The heat generated by the lithology along the bore holes was calculated using the relationship suggested by Bucker and Rybach (1996) as given below

RHP ¼ aðGR½APIÞ±b

Where A is the rate of radiogenic heat production (mW/m3), and a and b are empirical constants. In general, the lithology shows a thin sedimentary cover (detrital sandstone) overlying the hard crystalline basement granites (Figs. 6, 7 and 9). In borehole 4, located towards the SE periphery of the shield, thin carbonate rocks are present at near surface depth (see Fig. 9 for well 4). It is interesting to note that the high level gamma ray signature, with a heat generation value of 2e4 mW/m3, is recorded within the detrital sandstone with high content of thorium (Figs. 6, 7 and 9). The high radioactivity in the detrital sandstone appears to be due to the washout of detrital material from the granitic rocks. The high caliper log response (20e25inch)atthecontactbetweenthe detrital sandstone and the underlying granite rocks indicates thehighly-fracturednatureoftheuppersurfaceofthegranitic rocks (Figs. 6 and 7). High radiogenic heat generation (RHP>5 mW/m3) associated with high gamma ray response is recorded in the middle (see Fig. 6 for well 1) and lowermost part of the granitic rocks (Fig. 9 for well 4). Low heat generation (1e2 mW/m3) is represented by the thin basaltic sheets which are frequently interbedded with the detrital shallow sandstone (Fig. 7). Very high heat generation is recorded where the granitic rocks are exposed at the surface as seen in well 5 (Fig. 10). The well is a shallow one, drilled at the extreme northern borders of the Arabian shield (very close to Haal Fig. 9. Gamma ray and gamma ray spectrometry logs of Well 4, Arabian shield-Saudi province) and tapping a granitic section of 35 m. High heat Arabia (for location see Fig. 5). 230 D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233

Fig. 10. Gamma ray and gamma ray spectrometry logs of Well 5, Arabian shield-Saudi Arabia (for location see Fig. 5). generating values in the order of 10e15 mW/m3 are estimated. The 8. Discussion abnormal high response of the caliper log (>20 inch) in the middle of the granite section indicates the highly fractured state of the Following the successful demonstration and implementation of granite. The heat flow values recorded in the bore holes and that EGS projects in France and Australia (Vigneressel et al., 1987; calculated using the radioactive elements in the outcropping Genter et al., 2010; Chen, 2010; Gareth et al., 2010; Zhang et al., granites are similar. 2014a, b), and the nearing completion of the New Berry volcano D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233 231

EGS project (Table 1), it is apparent that high heat generating domain fracture network using finite volume based ANSYS/CFX granites are the future focus of energy source in the world (MIT, demonstrates that this efficiency can be improved for industrial 2006). The EGS system has the dual advantage of CO2 storage and scale EGS reservoirs (Xu et al., 2015). Several such reserves sites are recovery of heat from hot granites through CO2 circulation (Zhang available (Fig. 4) along the entire western shield that can be et al., 2014a, b; Mohan et al., 2015). Besides power, EGS is being exploited for power generation as well as for desalination. Some of used to generate hot water to recover oil from oil sands in Canada the geothermal sites that are located in Al Lith and Jizan (Lashin (Hofmann et al., 2014). et al., 2014; Chandrasekharam et al., 2015a) with the granites are The peralkaline granite plutons that contain the highest content driven by such high radiogenic granites and the reservoir temper- of uranium, thorium and potassium (Table 5) are over seventy in atures estimated using cation geothermometers for these site vary number and the largest number of plutons ever recorded in the from 200 to 220 C. At present the per capita water demand of world (Drysdall et al., 1977; Jackson et al., 1984; Ramsay, 1982; 275 L/day is generated using 134 106 kWh of electricity and in Ramsay et al., 1986; Chandarasekharam et al., 2014a, b). 1 km3 of future this demand will increase by 20%. In addition to drinking such granite can generate 79 106 kWh of electricity for a period of water produced through desalination, the country needs water for 30 years (Somerville et al., 1994). Considering the area of high agricultural activities, especially for producing staple food like radiogenic granites exposed in the western Saudi Arabian shield wheat and barley. Due to severe water scarcity, the country has (161,467 sq. km), and the prevailing NEeSW compressional stress adopted a policy to phase out the production of wheat by 2016. acting on these granites, these rocks are an excellent resource for Wheat is an important item in the Saudi food diet, consumed initiating EGS projects for power generation. In fact, according to commonly in the form of pita. Average per-capita consumption is the MIT report on EGS (MIT, 2006), radiogenic granites will be the 241 gm per day or 88 kg annually. The total wheat consumption in main source of energy in the 21st Century in USA, anticipated to Saudi Arabia in MY 2013e2014 was 3.25 million metric tones. Due generate 100,000 MWe of baseload electricity by 2050. The Midyan to the new government policy, wheat imports are expected to reach granites of the western shield appear to provide the most fertile 3.03 million metric tones in MY 2013e2014 compared to 1.92 granite generating temperature above 200 C at 2 km depth. A million metric tones in 2012e2013 (USDA, 2013). Such water schematic cross section showing the temperature and stress stressed situation related to food crop can be mitigated if only the deduced from the data discussed in Sections 6 and 7 above is shown country realizes this situation and develops its huge untapped in Fig. 11. geothermal energy resources. The technology is available and can Assuming 2% of heat recovery from such a granite body, the be bought off the shelf for implementation. Since the country is the Midyan granites alone can generate about 160 1012 kWh of leader in oil exploration and production, it should implement a electricity (Chandrasekharam et al., 2015b). Modelling of fluid flow policy for exploiting geothermal resources to mitigate CO climate and heat transfer under coupled conditions and validation of this and water related issues both in the agricultural and socio- against detailed prediction of fluid flow and heat transfer in a public economic development sectors. It is detrimental for countries to reply on imported food supplies when viable energy sources are available at hand.

9. Conclusions

Although Saudi Arabia has large oil and gas resources, the amount of CO2 that the country is generating is growing at an exponential rate and soon the country will have the dubious distinction of being at the top of the list of countries emitting large amount of CO2. The country is currently emitting 446000 Gg of CO2 by generating 240 TW h of electricity and this is already affecting the country's weather pattern (Almazroui et al., 2012). Nearly 80% of this electricity is used for space cooling, resulting in the emission of 900 Gg of CO2. Besides this, the demand for freshwater is growing due to 6% increase in annual population growth. Agricul- tural produce is being affected due to the scarcity of fresh water. In future the country will be burning several million barrels of oil to meet the growing demand for drinking water. Unless mitigation strategies are adopted and renewable energy policies are enacted, the country's future energy security will be at risk. Saudi Arabia has the advantage of being located along a tectonically active zone with a constant heat sources along its west coast. Although nuclear and solar pv are advocated as the best options for sustained growth with low CO2 emissions, analyses indicate that nuclear power plants are not appropriate as renewable energy sources in Saudi Arabia because of the high unit cost of electricity (Ahmad and Ramana, 2014; WNA, 2013) while solar pv has inherent problems related to the efficiency and base load electricity supply (Segar, 2014; El Sharkawy et al., 2014). Using geothermal energy as a source mix, the country can i) extend the life of its oil reservoirs, ii) retain supremacy in the world oil production iii) rely on indigenous agricultural produce rather than importing staple food grains like Fig. 11. Schematic cross section of Mydian granite at 2 km depth (Heat generation and wheat and barley and iv) support the production of wheat and temperature are taken from Table 5 and Fig. 5 respectively). barley through irrigation for several decades. Energy optimization 232 D. Chandrasekharam et al. / Journal of African Earth Sciences 112 (2015) 213e233 models reveal that by using a source mix (fossil fuel and renew- Chandrasekharam, D., Lashin, A., Al Arifi, N., Al Bassam, A., Ranjith, P.G., Varun, C., ables) the country can reduce the cost of power by 28% per year Singh, H.K., 2015a. Geothermal energy resources of Jizan, SW Saudi Arabia. J. Afr. Earth Sci. 109, 55e67. from 2030 onwards and can save about 0.5 Mb/day of oil equivalent Chandrasekharam, D., Lashin, A., Al Arifi, N., Varun, C., Al Bassam, A., 2015b. In: High from 2020 onwards which can be exported (Hussein et al., 2013). Heat Generating Granites of Western Saudi Arabian Shield. Proceedings, World Desalination plants benefit most in Saudi Arabia if the geothermal Geothermal Congress. Melbourne (CD). Chen, D., 2010. In: Concepts of a Basic EGS Model for the Cooper Basin, Australia. sources are used for this purpose. An economic analysis for a Proceed. World Geothermal Congress, Bali. 3 20,000 m /day Vacuum Membrane Distillation (VMD) plant reveals Cladouhos, T.T., Osborn, W.L., Petty, S., Bour, D., Inovenitti, J., Callahan, O., Nordin, Y., that the production cost of fresh water generated with geothermal Perry, D., Stern, P.L., Jan 30-Feb 2012. In: New Berry Volcano EGS Demonstra- 3 tion: Phase I Results. Proceed. 37th Workshop on Geothermal Res. Engg. energy is US$ 0.53/m while the cost of water generated using Stanford Univ, p. 1. 3 conventional energy source is US$ 1.22/m (Sarbatly and Chiam, Coleman, R.G., Gregory, R.T., Brown, G.F., 1983. Cenozoic Volcanic Rocks of Saudi 2013). There are no technical barriers to develop the geothermal Arabia. 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