Indication of hydrogen and oxygen stable isotopes on the characteristics and circulation patterns of medium-low temperature geothermal resources in the Guanzhong Basin, China
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Abstract: Guanzhong Basin is a typical medium-low temperature geothermal field mainly controlled by geo-pressure in the west of China. The characteristics of hydrogen and oxygen isotopes were used to analyze the flow and storage modes of geothermal resources in the basin. In this paper, the basin was divided into six geotectonic units, where a total of 121 samples were collected from geothermal wells and surface water bodies for the analysis of hydrogen-oxygen isotopes. Analytical results show that the isotopic signatures of hydrogen and oxygen throughout Guanzhong Basin reveal a trend of gradual increase from the basin edge areas to the basin center. In terms of recharge systems, the area in the south edge belongs to the geothermal system of Qinling Mountain piedmont, while to the north of Weihe fault is the geothermal system of North mountain piedmont, where the atmospheric temperature is about 0.2℃-1.8℃ in the recharge areas. The main factors that affect the geothermal water δ18O drifting include the depth of geothermal reservoir and temperature of geothermal reservoir, lithological characteristics, water-rock interaction, geothermal reservoir environment and residence time. The δ18O-δD relation shows that the main source is the meteoric water, together with some sedimentary water, but there are no deep magmatic water and mantle water which recharge the geothermal water in the basin. Through examining the distribution pattern of hydrogen-oxygen isotopic signatures, the groundwater circulation model of this basin can be divided into open circulation type, semi-open type, closed type and sedimentary type. This provides some important information for rational exploitation of the geothermal resources.
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Key words:
- Guanzhong Basin /
- Hydrogen-oxygen isotopes /
- Storage characteristics /
- Circulation model
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Table 1. The result of hydrogen-oxygen stable isotopes in study area
Sample NO. Depth Temperature pH δD/‰ δ18O/‰ Sample NO. Depth Temperature pH δD/‰ δ18O/‰ Surface water q014 1 672.08 66 8.57 –79.42 –11.25 R001 - 17.5 7.63 –61.24 –8.87 q031 2 850 88 8.22 –84.63 –9.17 R005 - 17.5 7.38 –57.1 –8.28 q035 496.8 68.3 8.76 –84.93 –12.52 R007 - 17.5 7.83 –66.92 –9.14 q036 573 49.6 8.66 –82.57 –11.43 R008 - 17.5 7.53 –68.4 –9.28 q037 1 360 57 8.32 –80.02 –11.18 R009 - 17.5 7.47 –65.1 –9.05 q039 1 500 54 8.86 –84.01 –11.4 Outside basin q043 2 402 23.5 8.35 –87.71 –4.73 q008 580 45 8.23 –86.51 –12.9 q045 2 700 96 8.32 –83.28 –5.12 q041 250.27 58.2 8.02 –73.51 –10.61 q046 3 000 91 8.36 –78.1 –8.72 q042 530 43 8.31 –78.92 –11.38 q048 1 750 69 8.15 –82.36 –7.27 q056 648.08 33.7 8.34 –78.44 –11.51 q057 2 685.3 80 7.9 –79.57 –9.44 Baoji bulging(BJ) q058 2 905.3 86 7.88 –81.62 –9.84 q006 28.9 7.55 –71.46 –10.62 q060 1 450 55 7.94 –83.89 –11.46 q009 1 462 46 8.39 –82.24 –11.9 q075 1 650 85 8.88 –85.02 –11.92 q015 2 470 53 7.85 –85.23 –11.47 q077 2 000.2 65 8.26 –84.48 –9.34 q028 1 602.6 51.2 8.56 –85.54 –11.65 q078 2 731.86 80 8.11 –84.74 –6.85 q029 350.5 72 8.39 –86.34 –12.06 q079 3 479.35 112 8.39 –85.29 –3.48 q033 450.5 64 8.87 –86.2 –12.65 q083 3 000 93 8.58 –85.64 –5.89 q034 282 68 8.77 –88.06 –12.82 q084 3 015.9 98 8.68 –83.19 –8.05 q071 - 29 8.27 –81.88 –11.85 q090 1 601.9 65 7.77 –84.38 –7.22 S001 1 450 29 8.32 –70.4 –8.1 q091 1 958 69.5 8.41 –77.24 –8.81 S002 1 114.35 39.2 8.27 –76.8 –11.5 q092 3 558 94 7.65 –84.07 –2.3 S003 400.18 41.5 8.16 –81.8 –11.1 q094 3 355 102 7.81 –87.3 –3.48 S004 400 41.5 8.32 –72.3 –10.6 q095 2 658 92 8.3 –81.41 –8.56 S005 Spring 30 8.36 –69 –9.6 q096 2 003.17 52 8.64 –83.5 –11.44 S015 1253 47 8.25 –70.8 –9.2 q097 2 211.8 81 8.15 –84.45 –10.22 Xianli fault-step(XL) q098 2 651.7 99 8.46 –85.17 –3.65 q030 3 050 90 7.98 –82.6 –8.08 q099 2 500 8.47 –83.5 –9.18 q080 2 700 70 7.83 –85 –7.8 S014 1 450 40 8.23 –76.6 –11.611 q086 2 800 90 8.28 –85.95 –10.41 Pucheng bulging(PC) q087 2 105.8 65 7.96 –85.07 –10.3 q016 169 29.5 8.2 –74.92 –9.79 q088 1 901.68 53 7.65 –76.45 –10.24 q017 160 27.5 8.17 –73.22 –9.72 q093 2 975 90 7.71 –83.9 –2.85 q018 150 27.8 8.08 –73.16 –9.77 S008 2 787 71 8.03 –68.1 –6.7 q019 210 28.6 8.16 –72.66 –10 S020 1 751 72 8.14 –71.6 –6 q020 300 41 7.79 –75.6 –10.25 S022 2 471 90 7.95 –66.3 –3.8 q021 520 27 8.1 –74.16 –10.01 S023 3 553 94 7.89 –70.6 –4.5 q022 2 000 63 8.23 –87.78 –9.87 S024 2 000 74 8.31 –69.3 –4.4 q023 651.8 25.5 8.33 –69.47 –9.37 S025 2 818 89 8.03 –66 –3.7 q024 270 26 8.32 –69.12 –9.72 S028 3 500.3 120 7.96 –71 –5.3 q025 430 28 7.68 –73.06 –10.14 S029 2 905.3 86 7.88 –71.5 –9.34 q026 2 452 75 8.16 –83.59 –7.98 S030 2 013 80 8.15 –70.8 –9.07 q049 651.5 28 8.22 –74.11 –10.23 Linlan bulging(LL) q050 1 050 33 8.13 –77.17 –11.26 q027 2 625.5 63 8.34 –81.22 –9.75 q051 778.3 42 8.16 –75.99 –10.86 q032 1 500 56 8.81 –85.01 –12.03 q073 2 600 105 7.3 –68.23 –3.69 q038 1 772 56 8.78 –84.58 –11.61 q085 2 857.8 96 8.64 –84.09 –9.36 q040 2 060 79 8.41 –85.85 –11.6 q089 800 35 7.74 –76.81 –10.2 q052 854.3 49 8.68 –78.74 –11.36 Gushi depression(GS) q053 10.7 44.6 8.33 –72.36 –10.46 q001 2 470 71 8.41 –85.23 –7.23 q055 2 136.9 52 8.34 –81.48 –10.54 q002 2 403 78 7.98 –85.93 –7.32 q061 455.9 54.5 8.76 –76.4 –10.94 q003 2 341 68 8.13 –85.4 –7.67 q062 652.8 58 8.92 –82.27 –11.74 q004 2 790 80 7.31 –72.37 –7.25 q072 1 012.6 53 8.73 –83.25 –11.99 q007 22.1 8.16 –69.68 –10 q076 1 985 55 8.56 –81.65 –11.34 q044 2 870 100 8 –75.41 –3.96 q100 3 230 81 8.05 –85.14 –5.53 q059 1 669.7 61.5 8.76 –87.02 –11.92 S006 Spring 11 - –71.3 –10.1 q069 3 258.7 63 7.94 –85.06 –7.66 S007 Spring 43 - –69.1 –9.8 q070 3 200 101 7.5 –84.45 –2.3 S018 460 55 - –72.9 –10.8 S009 3 008.9 100 - –54.5 –1.7 S019 1 550 50 - –76.2 –11 S010 2451 92 - –56.4 –2.7 Xi’an Depression(XA) S011 2600 105 - –61.1 –3.21 q005 2100 35.2 8.83 –85.01 –11.68 S012 854 49.5 - –71.9 –10.4 q010 3 258.7 92 8.63 –85.37 –8.41 S013 1 500.3 55 - –68.9 –9.5 q011 2 096 81.5 8 –85.43 –10.99 Qinling(QL) q012 2 436.5 52 8.6 –84.32 –10.94 S041 0 16 7.83 –71 –9.9 q013 3 005 80 8.53 –83.08 –9.4 S042 0 16 7.52 –81 –11.4 -
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