Rare Earth Elements and Sr-Nd-Pb Isotopic Analyses of the Arima Hot Spring Waters, Southwest Japan: Implications for Origin of the Arima-type Brine

Multivariate statistical analyses of rare earth element compositions of spring waters from the Arima and Kii areas, Southwest Japan

“…5a). This is consistent with the δ 18 O-δD and Sr-Nd-Pb isotopic ratios of Kinsen, which suggests its slab-fluid origin from the subducted Philippine Sea slab (Kusuda et al, 2014;Nakamura et al, 2014).…”

“…8c), suggesting significant involvement of mantle-derived component (Masuda et al, 1985;Kusuda et al, 2014). Kusuda et al (2014) and Nakamura et al (2014Nakamura et al ( , 2016 argued that the brine could have originated from the subducted Philippine Sea slab, based on the calculated slab-fluid compositions for δ 18 O and δD (grayish kinked thick line in Fig. 8a) and REE concentrations (broken lines in Fig.…”

“…1). These spring waters involves the Arima-type brines (Matsubaya et al, 1973;Sakai and Matsubaya, 1976) and several interesting features: (1) In spite of their occurrence in the non-volcanic areas, the Arima-type brines exhibit geochemical characteristics indicative of water-rock reactions at high temperatures at depths (Matsubaya et al, 1973;Tanaka et al, 1984;Masuda et al, 1985) and were argued to have originated from the subducted Philippine Sea slab (Kusuda et al, 2014;Nakamura et al, 2014Nakamura et al, , 2015, which may provide key information for the origin of deep-seated fluids, (2) in spatially close association with the Arima-type brine, different types of spring waters such as a carbonated water occur (Masuda et al, 1985;Nakamura et al, 2015Nakamura et al, , 2016Morikawa et al, 2016), (3) the high-dimensional data, including major solutes, rare earth elements (REEs), and helium isotopic ratio, are available and suitable for multivariate analyses. Within this context, based on the previously published data, this study aims at extracting essential geochemical features of the spring waters to infer their origin and processes beneath the areas.…”

Arima hot spring waters as a deep-seated brine from subducting slab

“…The estimated solute concentrations in the Arima deep brine (e.g., 42,000 ppm Cl; 3,700 ppm K; 84 ppm Br; Br/Cl~2.0 × 10 −3 ) are consistent with the recent knowledge on slab-derived fluids, e.g., 12,000 to 240,000 ppm Cl, 600 to 3,700 ppm for K, Br/Cl~1.0 to 3.7 × 10 −3 for fluids derived from subducted serpentinite (Kendrick et al 2011), and 5.1 wt% NaCl (approximately 30,000 ppm Cl) for fluid inclusions in the mantle xenoliths (Kawamoto et al 2013). On the contrary, the Philippine Sea slab-derived fluid compositions estimated from volcanic rocks in central Japan (Nakamura and Iwamori 2013) have higher concentrations for K and Sr (64,000 and 268 ppm, respectively), possibly reflecting different dehydration conditions of higher pressure and temperature beneath the volcanic region compared with those in the forearc region in southwestern Japan (Nakamura et al 2014). It is also noted that during deep processes of dehydration and melting in subduction zones, Cl and F are reported to behave very differently (Straub and Layne 2003), which may explain the poor correlation between the major solute including Cl and F (Figure 2).…”