230Th/238U dating of hydrothermal sulfides from Duanqiao hydrothermal field, Southwest Indian Ridge

Duanqiao hydrothermal field is located between the Indomed and Gallieni fracture zonesat the central volcano, at 50°28′E in the ultraslow-spreading Southwest Indian Ridge (SWIR). Twenty-eight subsamples from a relict chimneyand massive sulfideswere dated using the 230Th/238U method. Four main episodes of hydrothermal activity were determined according to the restricted results: 68.9–84.3, 43.9–48.4, 25.3–34.8, and 0.7–17.3 kyrs. Hydrothermal activity of Duanqiao probably started about 84.3 (±0.5) kyrs ago and ceased about 0.737 (±0.023) kyrs ago. The periodic character of hydrothermal activity may be related to the heat source provided by the interaction of local magmatism and tectonism. The estimated mean growth rate of the sulfide chimneyis <0.02 mm/yr. This study is the first to estimate the growth rate of chimneysin the SWIR. The maximum age of the relict chimneyin Duanqiao hydrothermal filed is close to that of the chimneysfrom Mt. Jourdanne (70 kyrs). The hydrothermal activity in Dragon Flag fieldis much more recent than that of Duanqiao or Mt. Jourdanne fields. The massive sulfidesare younger than the sulfidesfrom other hydrothermal fields such as Rainbow, Sonneand Ashadze-2. The preliminarily estimated reserves of sulfideores of Duanqiao are approximately 0.5–2.9 million tons.