The 18O of open-filling calcites range from -2.16‰ to +20.58‰VSMOW, while
13C values range from -11.23‰ to -0.16‰VPDB (Appendix C). The oxygen and carbon isotope compositions of open-filling calcites and marble lenses are show in Fig 3.4. The oxygen isotope compositions of marble lenses have constant values with distributed carbon isotope. Type A and type Others have smaller 18O with bigger 13C. Type B has similar carbon isotope with varied oxygen isotope.
30 Figure 3.4 The plot of stable isotopes of open-filling calcite and marble lenses from cores.
The carbon isotope values of carbonate powders range from -7.78‰ to -0.16‰ for type A (n=169); from -6.67‰ to -4.63‰ for type B (n=36); from -11.23‰ to -0.28‰ for type Others (n=86) and the 13C composition of marble lenses (n=49) range from -9.74‰
to -4.39‰ (Appendix C). The carbon isotope of type B has an average of
±‰VPDB (Table 3) which is almost constant with depth (Fig 3.5). The 13C of marble lenses ±‰VPDB (Table 3) also shows variation with depth. The 13C of fracture-filling carbonates do not have a trend with depth (Fig 3.5).
31 Table 3 Statistics of carbon and oxygen isotope compositions form of open-filling calcites and marble lenses from meta-granite cores.
Sample 13C (‰VPDB) 18O (‰VSMOW) n
Type A ± ±
Type B ± ±
Type Others ± ±
Marble lenses ± ±
Figure 3.5 The carbon isotope values with depth.
32 The oxygen isotope composition of calcite powders collected from meta-granite cores versus depth is shown in Fig 3.6. In detail, the 18O values of calcites range from -2.16‰ to 14.14‰VSMOW for type A, from -1.79‰ to 20.58‰VSMOW for type Others, from 4.44‰ to 19.23‰VSMOW for type B and from 10.18‰ to 11.53‰VSMOW for marble lenses (Appendix C). The oxygen compositions of marble lenses 18O(= 11.13 ± 0.38‰VSMOW) show little variation with depth compared with open-filling calcites (Table 3). The 18O of fracture-filling carbonates have no trend with depth (Fig 3.6).
Figure 3.6 The oxygen isotope values versus depth.
33 Table 4 Statistics of carbon and oxygen isotope compositions of marbles and marble lenses in outcrops.
Sample 13C (‰VPDB) 18O (‰VSMOW) n
Marble lenses ± ±
Marble (upstream) ± ±
Marble (downstream) ± ±
To investigate isotope signals of marbles and marble lenses in outcrops, 24 marbles were collected from both upstream and downstream of Hoping River and 2 marble lenses were collected in upstream. Their results are show in Table 4 the carbon and oxygen isotopes of marbles range from +0.23 to +4.28‰VPDB and from +10.36 to +24.28‰VSMOW, respectively (Appendix D). The 13C of marble in upstream has some variation from +0.23 to +3.86‰VPDB. Similarly, the carbon isotope values of marble in downstream oscillate between +2.20 and +4.28‰VPDB. Nevertheless, the oxygen isotope values of marble in downstream ±‰VSMOW are heavier than that of marble in upstream ±‰VSMOW(Table 4). Marbles in upstream and downstream have bigger 18O with smaller 13C. The carbon and oxygen isotopes of marble lenses in outcrops are similar to the oxygen and carbon isotope pattern of marble lenses in cores, the oxygen isotope of marble lenses in outcrops have constant values with distributed carbon isotope.
34 Figure 3.7 The carbon and oxygen isotope pattern of marbles and marble lenses from outcrops.
3.3 Fluid inclusion analysis
Each inclusion we measured 30 measurements, inclusion sizes generally vary from20 to 50 µm (Fig 3.8). Fluid inclusion analysis was performed in type A (location A42_2) and type other (sample O06 and location O19_2). Fig 3.9 shows histograms of homogenization temperatures (Th) of the fluid inclusions within the calcite crystal from 164 – 231°C for sample A42 at 464.66m depth; from 106 – 305 ℃ for sample O06 at 217.05m depth and 160 – 211°C for sample O19 at 426.19m depth. The highest homogenization temperature was recorded at 305°C and lowest at 106°C. Although, the average homogenization temperature of location A42_2 (Th =190.76 ± 16.31°C) is higher
35 than that of sample O06 (Th =184.77 ± 48.12°C) and location O19_2 (Th =181.08 ± 16.79°C) (Table 5), error bar of sample O06 is overlapped with sample A42 and O19.
Therefore, homogenization temperatures of three samples did not significantly change with depth (Fig 3.9), suggested that the local geothermal gradient was very low 30°C - 60°C/km during calcite precipitation (Lin, 2000, p.193).
Table 5 Statistics of homogenization temperatures (Th), temperature of first ice melting (Te) and last ice melting (Tm ) of sample A42; O19 and O06.
No Th (°C) Te (°C) Tm (°C)
A42 ±16.31 ±3.35 ±0.27
O06 ± ± ±0.43
O19 ±16.79 ± ±0.23
36 Figure 3.8 Inclusion size of location A42_2 and O19_2.
37 Figure 3.9 Homogenization temperature vs depth for location A42_2, O19_2 and O06.
Error bars of Th is 1 standard deviation.
Freezing measurements for temperature of first ice melting (Te) and last ice melting (Tm) were made in aqueous saline inclusions. Te ranges from -49°C to -27°C for sample A42; from -40°C to -28°C for sample O19 and from -56°C to -32°C for sample O06. Tm for these fluid inclusions ranges from −1.02 °C to +0.3°C (Fig 3.10).
38
39 3.4 Clumped isotope analysis
The results of clumped isotopic compositions, 47 value and temperatures derived from sample A42 and O19 are shown in Table 6. The 47value of sample A42 collected at a depth of 464 m is 0.415‰andsample O19 collected at 426 m is 0.547‰. The calculated precipitation temperatures based on the 47-T calibration line from Kluge et al., (2015) are 209°C for A42 and 92°C for O19, respectively. As shown in Table 6, although the calculated temperatures of clumped-isotope analysis are increased with depth, it is very difficult to give reasonable interpretation by only two samples.
Table 6 Clumped-isotope compositions and depth of A42 and O19 Experiment
40 Figure 3.11 The carbon isotope value of sample A42 and O19 verus depth for clumped-isotope.
The 13C values of clumped-isotope are -1.83‰ and -6.11‰ for location A42_2 and O19_2, respectively (Table 6). The carbon clumped-isotope values of location A42_2 and O19_2 are increased with depth (Fig 3.11). The oxygen clumped-isotope values of location A42_2 and O19_2 are 1.03‰ and 10.6‰VSMOW, respectively (Table 6). The
18O values are decreased with depth (Fig 3.12), opposite with the 13C pattern.
Comparison with the carbon and oxygen isotope values, those of clumped-isotope of A42 and O19 have a trend with depth. In this study, because only two powders were analyzed for clumped-isotope analysis, it is very difficult to give reasonable interpretation. For the temperature result, the clumped temperature of sample A42 is similar with homogenization
41 temperature of fluid inclusion, but homogenization temperature of sample O19 is larger than clumped temperature of clumped-isotope.
Figure 3.12 The 18O value of sample A42 and O19 versus depth for clumped-isotope.
42
Chapter 4. Discussion
4.1. 18O and 13C compositions of open-filling calcite
In the section 2.2, we descripted that each sample was drilled three locations and each location was took three powders with different depths if possible (Fig 2.3). Thus, more or less nine calcite powders were collected per sample. As results, 18O values of open-filling calcites in all samples range from -2.16‰ to +20.58‰VSMOW and 13C values range from -11.23‰ to -0.16‰VPDB. In details, in fig 4.1, the carbon isotope of foliation-oblique samples have variable value, however foliation-parallel samples have consistent value even considering measurement errors. For example, the carbon isotopes of sample A42 within location 1 are similar and values of location 2 are similar with that of location 3 (Fig 4.1a). However, the carbon isotope values of sample O19 are consistent with location 1&2 but different to location 3 (Fig 4.1b). The carbon isotope compositions of sample B13 have similar values for different depths (Fig 4.1c). Nevertheless, in Fig.3.6 the oxygen isotopes have inconstant values for all samples (no matter foliation -parallel and foliation - oblique open-filling calcites). For instance, the oxygen isotope values of sample A42 range for +5.52 to +6.89‰VSMOW at location 1 (3 powders) and similar from 1.85 to -0.37‰VSMOW at location 2 and 3 (6 powders) (Fig 4.1e). For sample O19 (Fig 4.1f) and B13 (Fig 4.1g), 18O values fluctuate from +5.26 to +15.16‰VSMOW at all 3 locations (9 powders) per sample. Since the oxygen compositions of open-filling calcites for each sample were different, it suggested that the different oxygen isotopes of calcites might come from different 18O fluid, we will discuss more details in section 4.3.
43 Figure 4.1 The carbon and oxygen isotope of open-filling calcites of sample A42, O19, B13 and VC11 for each location (1.1, 1.2, 1.3 ……..3.2, 3.3 are drilled references in fig 2.4).
44 Figure 4.2 The carbon and oxygen of vein calcite with depth in TCDP work (Wang et al., 2010).
In order to know which cause might not be reasonable, we will check with previous work with similar situation first. In the previous study (Wang et al., 2010, p.252), the oxygen isotope values of fracture-filling carbonates ranged from 10‰ to 20‰VSMOW generally increased with depth. The carbonate isotope values of vein increased from -10‰
to -2‰VPDB at the depth from 400 to 1290m, and then decreased to -12.5‰ below 1290m (Fig. 4.2). They assumed that the fluid isotope balanced with the vein carbonate isotope, then they used to the equilibrium equation to calculate the oxygen of fluid by the equation of Õ Neil et al., (1969) based on the temperature inferred by the high local geothermal gradient obtained from the well-logging (22–25oC/km). Contrary to their work, the oxygen and carbon isotope of open-filling calcites in this study range from -11.23 to -0.16‰VBDP
45 and -2.16 to 20.58‰VSMOW, respectively (Figure 3.5 & 3.6). These results showed that the carbon and oxygen isotope do not have trend with depth, it probably did not be strongly influenced by geothermal gradient (gentle slope = -0.007) if geothermal gradient was constant (Fig 4.3). There will be more discussion for fluid origin in section 4.5.
Figure 4.3 Homogenization temperature (Th) versus depth of open-filling calcite showing a gentle slope.
46 4.2 The compositions of marble
The stable isotopes of oxygen and carbon of marble lenses in core samples range from 10.18‰ to 11.93‰VSMOWand -9.74‰ to -4.17‰VPDB (Fig 3.4), respectively. To compare with these isotope compositions, we collected 26 marble samples from outcrop included 2 marble lenses. The 18O and 13C of marble lenses values in outcrop samples ranged from +10.08‰ to +10.68‰VSMOW and -2.2 to 0.79‰VPDB, respectively (Fig 4.4). As results, the oxygen isotopes of marble lenses in core samples are similar to the oxygen isotopes of marble lenses in outcrop samples. Nonetheless, the carbon isotopes of marble lenses have fluctuated value for core and outcrop samples.
Figure 4.4 The compositions of carbon and oxygen isotope in Hoping core and outcrop samples from previous study (Wang Lee and Teng, 1986) and our data.
47 Analyses of marble in outcrop yielded that 18O values ranging from +17.52‰ to +24.28‰VSMOW for upstream samples and +15.67‰ to +23.01‰VSMOW for downstream samples (Fig 4.4). The 13C values in upstream and downstream samples range from +0.23‰ to 3.83‰VPDB and +2.31‰ to +4.28‰VPDB, respectively (Fig 4.4). A former research of marble outcrops in Hoping to Tailuko area (Wang Lee and Teng, 1986) showed that the 18O and 13C values ranged from +12.0‰ to +25.2‰VSMOW and +0.1‰ to 4.0‰VPDB, respectively, which is similar to our results. For investigating the possible causes of stable isotope composition from marble to marble lenses, the isotope compositions the boundary between marble and meta-granite (Fig 4.7).
To calculate distance between marble and meta-granite along the profile, we plotted sample orientation by steoreonet, we determined mean pole of sample orientation (Fig 4.5).
Then, the profile was drew perpendicular to mean strike (Fig 4.6). The horizontal created with the profile an angle Distance between marbles and meta-granites (l) is determined by projection of sample location onto the profile, which is parallel to strike orientation.
These results were listed in Appendix B.
48 Figure 4.5 Mean pole of sample orientation in upstream and downstream
49 Figure 4.6 Projection of marble and meta-granite in outcrops.
50 Figure 4.7 The carbon and oxygen isotope with distance relationship between marble and meta-granite in outcrops
We assumed that the 18O fluid values of marble lenses are equilibrium with 18O fluid values of metamorphic waters, therefore the temperature was calculated based on Eq.7.
The inferred temperature of marble lenses range from 137.19°C to 11516.68°C (Appendix G). The clumped isotope temperature of marble collected from the Backbone Range of Taiwan ranges from 95°C to 329°C, (Lasker et al., 2016), the clumped isotope temperature of calcite veins in Chingshui area range from 136°C to 264°C (Lu et al., 2017), the temperature of calcite hosted in Carrara marbles is 250°C (Vaselli, et al., 2012) and the clumped-isotope of carbonate veins from the SAFOD ranges from 110°C to 115°C (Luetkemeyer et al., 2016) (yellow square in fig. 4.8). Based on previous work, the higher temperature from 480°C to 1050°C will made crystal broken and lower temperature below 95°C, inclusion size is very small. In next work, we expected that the temperature from higher than 95°C and less than 480°C.
51 Figure 4.8 The 18O fluid of marble lenses and expected temperature.
52 Figure 4.9 The 13C and 18O values of fresh-water carbonates and marine limestones by Keith and Weber (1964). The comparison between the carbon and oxygen isotopes of open-filling calcites and marbles in this study and marbles in previous works.
Fig 4.9 shows the 13C and 18O values from marine limestone (cyan square ) and fresh-water carbonates (orange square) based on Kieth and Weber, (1964) (table 1 & 2, p.
1795-1796). The oxygen isotope value of fresh-water carbonate and marine limestones ranges from 20.3 to 26.3‰VSMOW and 20.8 to 29.6‰VSMOW, respectively. The carbon isotope value of marine limestone and freshwater carbonates ranged from -0.07‰ to 1.96‰VPDB and -6.64‰ to -2.24‰VPDB, respectively. The distribution the 13C and
18O values of marbles from previous study (Lee et al., 1986, table 1, p.37) range from 0.14 to 3.58‰VPDB and from 14.38 to 25.16‰VSMOW, respectively (purple square in Fig
53 4.9). These results were overlapped with most of marbles in upstream and downstream of Hoping area. Based on the conclusions of Keith and Weber, (1964), the isotope composition of oxygen and/or carbon of calcite can be changed due to exchange between calcite and fluid. Although all the carbon composition of marble in upstream lie within the region indicative of a marine limestone, a substantial number of the oxygen isotope values do not conform to this trend (pale yellow in Fig 4.9). The carbon isotope compositions clearly demonstrate that the marble studied are probably of marine origin.
54 4.3 Calculated δ18O fluid
Figure 4.10 Summary plot of stable isotopes and temperatures of sample A42, O06 and O19 and clumped isotope temperature (sample A42_2 and O19_2 are the location where were made thin sections for fluid inclusion and clumped isotope analysis).
After resulting δ18O value of open-filling calcites in section 3.2 and related forming temperature in section 3.3 and 3.4, the δ18O of fluid will be evaluated in this section. Here, the δ18O fluid was calculated using the calcite-water oxygen isotope fractionation equation (O’Neil et.al., 1969, p.5547) (Eq.7):
T(℃) = √𝛿18𝑂 2.78×106
𝑐𝑎𝑙−𝛿18𝑂𝑓𝑙𝑢𝑖𝑑+2.89− 273.15 (Eq.7)
55 Cause of variations in δ18O fluid can either be from changes in temperatures, fluid composition, or both of them (Zheng and Hoefs, 1993). 30 measurements of homogenization temperatures were conducted for location A42_2 and O19_2 from one thin section and 18 measurements for O06 from 5 thin sections. The average homogenization temperature of sample A42, O06 and O19 is 191±16℃, 187±46℃ and 185±17℃, respectively (Fig 4.9). The oxygen fluid values were calculated based on Eq.7, because temperature measurements were not conducted on all location for isotope analysis, the assumption that temperature was the same for all isotope compositions of open-filling calcites were made. In details, 9 isotope compositions of sample A42 (blue in Fig 4.10) and 30 homogenization measurements at location A42_2 were used to calculate δ18O fluid (red triangle in Fig 4.11). Total, 270 values δ18O fluid at location A42_2 were calculated. The δ18O fluid value at location A42_2 range from -13.75 to -10.22‰VSMOW (red bar in Fig 4.12a); from -6.27 to -1.63‰ and -13.50 to -8.89‰VSMOW at location A42_1 and A42_3, respectively (black and red bar in Fig 4.12a). Fig 4.10 show that location A42_1 have bigger δ18O and smaller δ13C than location A42_2 and location A42_3 and the calculated oxygen fluid values at location A42_2 and A42_3 is similar, but different with that of A42_1, it suggested that the δ18O fluid at location A42_1 is not reliable. For sample O06, it was made five thin sections from different location of the whole sample. The δ18O fluid was calculated by 6 oxygen isotope values time with 18 homogenization temperatures.
Results show that the δ18O fluid value of sample O06 range from -12.08 to -0.53‰ (Fig 4.12b). For sample O06, the calculated oxygen fluid range from -12.08 to -0.53‰VSMOW, from -13.54 to -2.01‰VSMOW and from -11.93 to -0.91‰VSMOW at location O06_1, O06_2 and O06_3, respectively. The δ18O fluid values of whole sample O06 are overlapped together. For sample O19, the δ18O fluid values also calculated similar to sample A42 with
56 30 homogenization temperatures and 9 oxygen isotope values. The δ18O fluid of location O19_2 range from 6.67 to 4.09‰ (blue bar in Fig 4.12b); from 3.86 to 6.24‰ and from -6.67 to 0.8‰ at location O19_1 and O19_3, respectively (black and red bar in Fig 4.12b).
Two oxygen isotope powders of A42_2 and O19_2 are used for clumped-isotope analysis. The δ18O of location A42_2 and O19_2 are 1.03‰ and 10.6‰VSMOW, respectively. The clumped isotope temperatures of open-filling calcites of A42 and O19 powders are 209 and 92℃, respectively (Fig 4.12). Based on Eq.7, the δ18O fluid were calculated by the oxygen isotope values with clumped isotopes are -8.04‰ and -7.36‰ for location A42_2 and O19_2, respectively(red line in Fig 4.12 a & c).
57 Figure 4.11 The calculated oxygen isotope fluid of open-filling calcites vs Th. Black, blue and red rectangle represents the 18O fluid at location 1, location 2 and location 3, respectively.
58 Figure 4.12 The calculated oxygen isotope fluid of open-filling calcites. Black, blue and red rectangle represents the 18O fluid at location 1, location 2 and location 3, respectively. Red line represents the 18O fluid of clumped-isotope.
59 4.4 Meteoric water
The meteoric water have a wide range of oxygen and hydrogen isotope, like meteoric waters come from all areas in the world (Craig, 1961). In order to evaluate whether fluid of open-filling calcites come from meteoric water, we plotted δ18O with elevation range from 0m to 4000m in Fig.4.7 following previous work (Shieh, et.al, 1983, p.130):
The δ18O values of meteoric water in Taiwan were calculated based on Eq.8 and Eq.9 at the elevations ranged from 0m to 4000m height (Table 7). The oxygen isotope of local meteoric water is lighter with high elevations (Fig 4.13).
Elevation (m) δ18O(‰VSMOW) Elevation (m) δ18O(‰VSMOW)
60 Figure 4.13 Plot of 18O value with elevation in Taiwan. These values were calculated based on previous study by Shieh, 1983.
57.6mg crystal CaCO3 of location O19_2 was used the oxygen and hydrogen of fluid inclusion analysis (Uemura et al., 2015). The 18O and D compositions are -9.6‰
and -58.6‰, respectively (Figure 4.13). This result covered meteoric water at 564m elevation. The calculated temperature is 57°C, 114°C and 72°C based on Eq.7 with 18O calcite value from stable isotope analysis for location O19_2 (3 location).
61 Figure 4.14 Plot of D and 18O compositions of location O19_2
As results in section 4.3, the oxygen isotope fluid at location A42_2 (blue bar in Fig 4.15a) is as the same as that of A42_3 (red bar Fig 4.15a), range from -13.75‰ to -8.4‰.
These values show that the 18O values of fluid at location A42_2 and location A42_3 lie in a wide range of elevations from 3000m to 0m. The average of calculated oxygen isotope fluid at location A42_2 is -11.76 ± 0.91‰VSMOW, it shows that the 18O values of fluid at location A42_2 is at elevation about 2000m. In much the same way with location A42_2, the average of calculated fluid at location A42_3 is -10.91 ± 0.91‰VSMOW, it shows that the 18O values of fluid of location A42_2 is at elevation about 1000m. However, the 18O fluid at location A42_1 (black bar in Fig 4.15a) range from -6.1‰ to -1.13‰ is bigger than that of location A42_2 and A42_3. Consequently, they do not lie in these line, suggesting that the fluid of A42_1 calcite did not come from meteoric water. Similarly, for sample
62 O06, the calculated oxygen values of fluid of location O06_1, O06_2 and O06_ 3 (black, blue and red bar in Fig 4.15b) are similar, range from -13.54 to -0.54‰. Figure 4.8b shows that the calculated oxygen values of a part of location O06_1 and O06_2 lie in a wide range of elevation from 0 to 2000m and that of location O06_ 3 lie in elevation from 0 to 3000m.
The calculated oxygen isotope of fluid of location O19_3 (red bar in Fig 4.15c) was covered that of local meteoric water at elevation from 0 to 100m high. However, the 18O values of fluid of location O19_1 and O19_2 (blue & red bar in Fig 4.15c) is heavier than the 18O values of meteoric water in Taiwan with elevation range from 0 to 3000m (Fig 4.15c). It indicates that the calculated oxygen fluid did not come from meteoric water.
For clumped isotope analysis, the 18O values of fluid of sample A42 and O19 were showed in section 4.3, the computed δ18Ofluid of sample A42 is -8.04‰VSMOW and that of sample O19 is -7.36‰VSMOW (red line in Fig 4.15a &c). As a consequence, the oxygen isotope of fluid of A42 and O19 are overlapped with δ18O values of the meteoric water in drainage divides of 300m to 400m and 100m to 200m, respectively.
63 Figure 4.15 The O fluid of sample A42, O06 and O19 vs different elevation in Taiwan.
Black, blue and red rectangle represents location 1, location 2 and location 3, respectively.
64 4.5 Fluid sources
In figure 4.16a (red & blue rectangle), it shows that the δ18O fluid of location A42_2 and A42_3 were covered that of meteoric water at elevation from 500 to 3000m and 400 to 3000m, respectively. The δ18O fluid of location A42_2 and A42_3 implied that meteoric water could play an important role of forming open-filling calcites. Similar to the δ18O fluid of sample A42, those of sample O06 are within the range of meteoric water (Fig 4.16b). In details, the calculated δ18O fluid of location O06_1, O06_2 and O06_3 (black, red & blue rectangle in Fig 4.16b, respectively) were covered that of local meteoric water at different altitudes from 3000m to 0m. The δ18O fluid of location O06_1 is similar with that of location O06_2, which is covered in meteoric water source from 0 to approximately 2000m height, while that of location O06_3 is covered from 0 to 3000m height. The calculated δ18O fluid of location O06_1, O06_2 and O06_3 imply that meteoric water might play an important role of forming open-filling calcites. However, the oxygen isotopes of the shaded area in Fig 4.11b are below sea level and it is located at the range between meteoric and
In figure 4.16a (red & blue rectangle), it shows that the δ18O fluid of location A42_2 and A42_3 were covered that of meteoric water at elevation from 500 to 3000m and 400 to 3000m, respectively. The δ18O fluid of location A42_2 and A42_3 implied that meteoric water could play an important role of forming open-filling calcites. Similar to the δ18O fluid of sample A42, those of sample O06 are within the range of meteoric water (Fig 4.16b). In details, the calculated δ18O fluid of location O06_1, O06_2 and O06_3 (black, red & blue rectangle in Fig 4.16b, respectively) were covered that of local meteoric water at different altitudes from 3000m to 0m. The δ18O fluid of location O06_1 is similar with that of location O06_2, which is covered in meteoric water source from 0 to approximately 2000m height, while that of location O06_3 is covered from 0 to 3000m height. The calculated δ18O fluid of location O06_1, O06_2 and O06_3 imply that meteoric water might play an important role of forming open-filling calcites. However, the oxygen isotopes of the shaded area in Fig 4.11b are below sea level and it is located at the range between meteoric and