New age data for Mid‐Atlantic Ridge hydrothermal sites: TAG and Snakepit chronology revisited

Abstract

The chronologies of TAG and Snakepit hydrothermal fields have been established using 210Pb/Pb, 230Th/234U and 14C dating. At the TAG field, a Mn‐oxide record, indicative of low temperature events, began at least 125,000 years and possibly 140,000 years ago with maximum intensities at 15,000, 7000 and 4000 years before present. High temperature events, giving rise to sulfide deposits, began about 100,000 years ago and have been intermittent to the present day. A presently active site has experienced intermittent pulses of activity every 4000 to 6000 years over the past 20,000 years. Decrease in activity is often marked by low temperature aragonite precipitation in chimney conduits at 4000, 7000 and 9000 years ago. After a period of quiescence lasting about 4000 years this site was reactivated about 50 years ago. The Snakepit field is much younger and no sulfides older than 4000 years have been recovered. Relict sulfide deposits are dated between 2000 and 4000 years old indicating this site was active during a quiescent period at TAG. Reactivation of Snakepit. took place about 80 years ago, and is presently concurrent with that of TAG. Comparison with hydrothermal sites on the East Pacific Rise suggests that on slow spreading ridges the major fracture systems focussing the hydrothermal discharge can be reactivated at intervals and new deposits precipitated on top of older ones, while on faster spreading ridges each pulse of activity is separated in space and time resulting in discrete deposits.

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

“…The ages of 270 sulfides from other mid-oceanic ridge(MOR) sites range from \10 yrs to 200 kyrs. The majority of older sulfides (with ages greater than *10 kyrs) are from the SWIR (Münch et al 2001), CIR (Lalou et al 1998a, b;Wang et al 2012), MAR Cherkashov et al 2010;Lalou et al 1993Lalou et al , 1996Shilov et al 2012) (Table 2; Fig. 7).…”

“…The 230 Th/ 238 U dating method was widely applied to determine the age of seafloor hydrothermal sulfides (Lalou et al 1985(Lalou et al , 1993(Lalou et al , 1995(Lalou et al , 1998a. This method is usually used for dating samples aged between 5 and 350 kyrs (Lalou et al 1993;Lalou and Brichet 1987).…”

“…This method is usually used for dating samples aged between 5 and 350 kyrs (Lalou et al 1993;Lalou and Brichet 1987). The development of analytic techniques has greatly improved the dating precision in the age range from 10 to 600 kyrs by multi-collector inductively coupled plasma mass (MC-ICP-MS) Shen et al 2008Shen et al , 2013Ludwig et al 2011;Andersen et al 2008).…”

The Trans-Atlantic Geotraverse hydrothermal field: A hydrothermal system on an active detachment fault

“…The chronologic framework of the sulfides extends back to 140,000 years and includes periods when multiple discharge zones were active (Lalou et al, 1986(Lalou et al, , 1990(Lalou et al, , 1993(Lalou et al, , 1995You and Bickle, 1998).…”

“…High-temperature activity began ~100 ka followed by a major thermal event at 50 ka that continued episodically until ~ 0.6 ka (Lalou et al, 1993(Lalou et al, , 1995. High heat-flow values in the Mir Zone indicate that this area continues to be thermally active, and suggests that hydrothermal activity may have ceased only recently .…”