臺灣東部和平地區開口充填方解石的液體來源之研究

Abstract

noneThe aim of this study is to evaluate whether the meteoric water can penetrate into the deep crust of Hoping area, eastern Taiwan. To test the hypothesis, this work investigated the fluid source of open-filling carbonates deposited on the fracture surfaces with various attitudes via Raman spectroscopy, stable isotope analysis, fluid inclusion and clumped isotope analysis. In details, Raman spectroscopy can identify the type of open-filling carbonates, analysis of oxygen and carbon stable isotopes of carbonate deposits can help to delineate the possible fluid sources. Fluid inclusion analysis can provide temperature information of open-filling carbonates. The clumped isotope of carbonates will further attain the absolute temperature for estimating the oxygen isotope of fluids. With Raman spectroscopy, calcite is identified in type A, B and Others deposits although their occurrences are quite different. Type A and Others is thick film and crystal types and is deposited on oblique-foliation fractures. Type B is thin membrane type and is deposited on parallel -foliation fractures. No dolomite is found in the carbonate deposit. Also quartz is identified in specific intervals. The carbon and oxygen isotopes of Type A, type B and type Others in meta-granite cores did not hold relationship with depth. Type A has smaller 18O with bigger 13C, while type B has similar carbon isotope with varied oxygen isotope. The oxygen isotope of marble lenses have constant values with scattered carbon isotope. The carbon and oxygen isotope pattern of marble lenses has a trend different from that of open- filling calcites. The 18O values of marble lenses from meta-granite cores are consistent with those of marble lenses from marble outcrops. Fluid inclusion analysis of calcite crystals was applied to measure the homogenization temperature (Th) of location A42_2, sample O06 and location O19_2. Their Th ranges 164 - 231 ℃, 106 - 305 ℃ and 160 - 211 ℃, respectively. Calcite was formed at 3 – 6 km below the surface with the geothermal gradient of 30–60°C/km. Assuming that the oxygen of open-filling calcites are equilibrium with that of fluid at Th, the calculated 𝛿18O fluid of location A42_2 and A42_3 ranges from -13.33 to -9.52‰VSMOW and -13.08 to -8.89‰VSMOW, respectively, indicative of meteoric water from 500 to 3000m elevation. The average δ18O fluid of sample O06 is -6.26 ± 2.62‰VSMOW indicate formation from meteoric water at elevation less than 4000m. These results show that meteoric waters dominate the fluid phase in open-filling calcites. However, the calculated 𝛿18O fluid of location O19_1 were mixed meteoric water with either magmatic sources or metamorphic water. The clumped-isotope temperature of sample A42 and O19 is 209℃ and 92℃, respectively. The calculated oxygen isotope fluid of sample A42 and O19 is similar with local meteoric water at 300m elevation.