5:15 PM - 6:30 PM
[SCG44-P01] Intrusive and emplacement process of the Tono plutonic complex: Constraints from dating and isotopic analysis of zircons
Keywords:zircon, U-Pb age, Ti concentration, Hf isotope, Tono plutonic complex
Introduction
Tono plutonic complex (TPC), northeast Japan, consists of adakitic rocks (central facies) and calk-alkaline rocks (main facies and marginal facies) surrounding the central facies [1,2]. Some previous studies have reported TPC zircon U-Pb ages; 117.5 ± 2.4 Ma in the central facies; 118.9 ± 2.6 Ma and 118.0 ± 1.2 Ma in the main facies [3,4]. These ages are related to last stage of igneous activity in the Kitakami Mountains. Revealing the formation process of zonal granitic pluton such as TPC can constrain for the history of the Cretaceous igneous activities in the Kitakami Mountains. Although intrusive relations among the facies are estimated from field observations [5] and whole rock Nd and Sr isotopic compositions [6], there is no discussion regarding to zircon U-Pb ages associated with solidification temperature and origin of magma. Zircon collected from a granitic pluton provides its crystallization age and crystallization temperature [7] from zircon U-Pb dating and titanium (Ti) concentration analysis, respectively. The pairs of data enable to reveal the sequential formation process from intrusion through emplacement to crystallization/solidification of plutonic body [8]. Hafnium isotopic compositions of zircon provide us the information of their source of magma [4]. In this study, we estimated crystallization age and temperature of TPC zircons deduced from U-Pb isotopic analysis and quantitative analysis of Ti, respectively. Moreover, Hf isotopic analysis of TPC zircons are carried out to discuss their source magma.
Samples and methods
Zircons were separated from each rock samples of TPC three lithofacies, and observed through cathodoluminescence images using scanning electron microscope at Yamagata University to clarify the internal structures related to crystal growths. On the basis of the observation, we performed simultaneous determination of U-Pb age and Ti concentration by using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) [9] at Gakushuin University. Hf isotopic analysis are carried out at Tono Geoscience Center, Japan Atomic Energy Agency by using LA-ICP-MS.
Results and discussion
As the result of U-Pb isotopic analysis of zircons, age ranges of TPC three lithofacies overlap (Table 1). There are no significant age differences between core and rim of each zircon grain. Weighted means of U-Pb age are listed (Table 1). The zircon U-Pb age of central facies is older than reference age [3], whereas that of main facies is consistent with results of previous studies [3,4].
Ti concentrations have ranges between 1.96 ± 0.28 ppm and 4.74 ± 0.44 ppm for the central facies (9 grains, 23 spots), 4.07 ± 0.42 ppm and 13.61 ± 0.96 ppm for the main facies (12 grains, 32 spots), and 6.65 ± 0.59 ppm and 8.81 ± 0.71 ppm for the marginal facies (1 grain, 10 spots) (Table 1). Crystallization temperature estimated by Ti-in-zircon geothermometer (assuming both SiO2 activity and TiO2 activity were 1.0.) [10] range 613 ± 38 ℃ to 680 ± 39 ℃ for the central facies, 668 ± 39 ℃ to 775 ± 43 ℃ for the main facies, and 709 ± 40 ℃ to 734 ±41 ℃ for the marginal facies. Since these temperature conditions are close to solidus of granitic magma, zircon U-Pb age and crystallization temperature reflect the emplacement age and thermal condition in magma chamber, respectively. In future works, to make further consideration on intrusive and emplacement process of each TPC lithofacies, additional analysis and new perspective such as Hf isotope are required.
Acknowledgments
This study was carried out under a contract with the Ministry of Economy, Trade and Industry (METI), Japan, as part of its R&D supporting program titled “Establishment of Advanced Technology for Evaluating the Long-term Geosphere Stability (2020 Fy)”.
References
[1] Tsuchiya and Kanisawa, 1994, J. Geophysical Research, 99, 205 – 220. [2] Mikoshiba and Kanisawa, 2008, Earth Sci. (Chikyu Kagaku), 62, 183 – 201. (in Japanese with English abstract) [3] Tsuchiya et al., 2015, Japanese Magazine of Mineralogical and Petrological Sci., 44, 69 – 90. (in Japanese with English abstract) [4] Osozawa et al., 2019, J. Asian Earth Sci., 184, e103968. [5] Nishimura et al., 1999, The Memoirs of the Geological Society of Japan, 53, 177 – 188. (in Japanese with English abstract) [6] Tsuchiya et al., 2007, J. Volcanology and Geothermal Reseach, 167, 134 – 159. [7] Watson et al., 2006, Contribution to Mineralogy and Petrology, 151, 413 - 433. [8] Yuguchi et al., 2016, J. Mineralogical and Petrological Sci., 111, 9 – 34. [9] Yuguchi et al., 2020, Lithos, 372 – 373, e105682. [10] Ferry and Watson, 2007, Contribution to Mineralogy and Petrology, 154, 429 – 437.
Tono plutonic complex (TPC), northeast Japan, consists of adakitic rocks (central facies) and calk-alkaline rocks (main facies and marginal facies) surrounding the central facies [1,2]. Some previous studies have reported TPC zircon U-Pb ages; 117.5 ± 2.4 Ma in the central facies; 118.9 ± 2.6 Ma and 118.0 ± 1.2 Ma in the main facies [3,4]. These ages are related to last stage of igneous activity in the Kitakami Mountains. Revealing the formation process of zonal granitic pluton such as TPC can constrain for the history of the Cretaceous igneous activities in the Kitakami Mountains. Although intrusive relations among the facies are estimated from field observations [5] and whole rock Nd and Sr isotopic compositions [6], there is no discussion regarding to zircon U-Pb ages associated with solidification temperature and origin of magma. Zircon collected from a granitic pluton provides its crystallization age and crystallization temperature [7] from zircon U-Pb dating and titanium (Ti) concentration analysis, respectively. The pairs of data enable to reveal the sequential formation process from intrusion through emplacement to crystallization/solidification of plutonic body [8]. Hafnium isotopic compositions of zircon provide us the information of their source of magma [4]. In this study, we estimated crystallization age and temperature of TPC zircons deduced from U-Pb isotopic analysis and quantitative analysis of Ti, respectively. Moreover, Hf isotopic analysis of TPC zircons are carried out to discuss their source magma.
Samples and methods
Zircons were separated from each rock samples of TPC three lithofacies, and observed through cathodoluminescence images using scanning electron microscope at Yamagata University to clarify the internal structures related to crystal growths. On the basis of the observation, we performed simultaneous determination of U-Pb age and Ti concentration by using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) [9] at Gakushuin University. Hf isotopic analysis are carried out at Tono Geoscience Center, Japan Atomic Energy Agency by using LA-ICP-MS.
Results and discussion
As the result of U-Pb isotopic analysis of zircons, age ranges of TPC three lithofacies overlap (Table 1). There are no significant age differences between core and rim of each zircon grain. Weighted means of U-Pb age are listed (Table 1). The zircon U-Pb age of central facies is older than reference age [3], whereas that of main facies is consistent with results of previous studies [3,4].
Ti concentrations have ranges between 1.96 ± 0.28 ppm and 4.74 ± 0.44 ppm for the central facies (9 grains, 23 spots), 4.07 ± 0.42 ppm and 13.61 ± 0.96 ppm for the main facies (12 grains, 32 spots), and 6.65 ± 0.59 ppm and 8.81 ± 0.71 ppm for the marginal facies (1 grain, 10 spots) (Table 1). Crystallization temperature estimated by Ti-in-zircon geothermometer (assuming both SiO2 activity and TiO2 activity were 1.0.) [10] range 613 ± 38 ℃ to 680 ± 39 ℃ for the central facies, 668 ± 39 ℃ to 775 ± 43 ℃ for the main facies, and 709 ± 40 ℃ to 734 ±41 ℃ for the marginal facies. Since these temperature conditions are close to solidus of granitic magma, zircon U-Pb age and crystallization temperature reflect the emplacement age and thermal condition in magma chamber, respectively. In future works, to make further consideration on intrusive and emplacement process of each TPC lithofacies, additional analysis and new perspective such as Hf isotope are required.
Acknowledgments
This study was carried out under a contract with the Ministry of Economy, Trade and Industry (METI), Japan, as part of its R&D supporting program titled “Establishment of Advanced Technology for Evaluating the Long-term Geosphere Stability (2020 Fy)”.
References
[1] Tsuchiya and Kanisawa, 1994, J. Geophysical Research, 99, 205 – 220. [2] Mikoshiba and Kanisawa, 2008, Earth Sci. (Chikyu Kagaku), 62, 183 – 201. (in Japanese with English abstract) [3] Tsuchiya et al., 2015, Japanese Magazine of Mineralogical and Petrological Sci., 44, 69 – 90. (in Japanese with English abstract) [4] Osozawa et al., 2019, J. Asian Earth Sci., 184, e103968. [5] Nishimura et al., 1999, The Memoirs of the Geological Society of Japan, 53, 177 – 188. (in Japanese with English abstract) [6] Tsuchiya et al., 2007, J. Volcanology and Geothermal Reseach, 167, 134 – 159. [7] Watson et al., 2006, Contribution to Mineralogy and Petrology, 151, 413 - 433. [8] Yuguchi et al., 2016, J. Mineralogical and Petrological Sci., 111, 9 – 34. [9] Yuguchi et al., 2020, Lithos, 372 – 373, e105682. [10] Ferry and Watson, 2007, Contribution to Mineralogy and Petrology, 154, 429 – 437.