Dating of Sulfide Chimneys in the Longqi-1 Hydrothermal Field, Southwest Indian Ridge

Hydrothermal activity is usually accompanied by the accumulation of hydrothermal precipitation, while the formation of massive sulfide mounds is usually required by the periodic long accumulation process. The study on the hydrothermal product dating, on the one hand, can explain the evolution history of hydrothermal activity, and the U-series disequilibrium methods have been widely used to determine the formation time of modern sulfide deposits. Dating of modern oceanic sulfides will provide information for the reconstruction of tectono-magmatic processes as a whole and hydrothermal venting and SMS accumulation (Lalou et al., 1990; Johns et al., 2014). On the other hand, it can be helpful for estimating the metallogenic scale of the hydrothermal field (Ditchburn et al., 2004) and even can be used for resource estimation (Cherkashov et al., 2017). The hydrothermal mineralization of the Southwest Indian Ridge (SWIR) within the segment between 49° and 51°E has been studied by geologists during numerous cruises (Tao et al., 2014). The Longqi-1 hydrothermal Field at 49 ̊39’E, 37 ̊47’S, pre-called Dragon Flag Field (DFF), was the first active vent field documented along ultra-slow spreading Ridge, and is mainly composed of two ulfide mineralization zone of 'S’ and ‘M’ zone (Tao et al., 2012). During the Chinese Dayang Cruise (CDC) 35, the first time of submersible observation was conducted by “Jiaolong” at Longqi-1 field. The highest vent fluid temperature was measured at of 379°C (Tao et al., 2016), at the DFF6 site of M zone. It was indicated that the scale of Longqi-1 vent system is *