Changes in submarine hydrothermal 3He/heat ratios as an indicator of magmatic/tectonic activity

来自 EBSCO

阅读量：

作者：

展开

摘要：

AN important question in submarine hydrothermal research concerns the connection between hydrothermal discharge from a spreading centre and variations in local magmatic and tectonic activity. Because it is likely that tectonic stretching and concomitant shallow magmatic activity triggered the cataclysmic venting that created the Juan de Fuca Ridge 'megaplumes', we have for three years monitored the He concentration and temperature anomaly of the underlying steady-state plume at the site of the original megaplume. We report here that the apparent He/heat ratio in the steady-state plume has progressively decreased from 4.4 to 2.4 to 1.3 x 10cmSTP calchanging from a uniquely high ratio to one characteristic of established vent fields on other ridge segments. We propose that the initially high He/heat ratio, sampled within days of the megaplume eruption, resulted from magma degassing into a hydrothermal circulation system of high permeability and short fluid residence time. Thus, high He/heat ratios may indicate venting created or profoundly perturbed by a magmatic-tectonic event, and lower ratios may typify systems at equilibrium.

展开

关键词：

Experimental/ Earth composition geochemistry helium isotope relative abundance oceanic crust oceanographic regions seawater tectonics terrestrial heat volcanology/ Juan de Fuca hydrothermal plume midocean ridge seawater 3He content ocean spreading centre permeable seafloor hydrothermal system AD 1986 to 1988 hydrothermal vent fields ocean chemistry NE Pacific Ocean submarine hydrothermal 3He/heat ratios magmatic/tectonic activity tectonic stretching shallow magmatic activity cataclysmic venting Juan de Fuca Ridge `megaplumes' temperature anomaly steady-state plume megaplume eruption magma degassing hydrothermal circulation system fluid residence time magmatic-tectonic event 1.8 to 2.3 km 3He concentration mantle 3He outgassing / A9150E Seafloor processes A9135D Terrestrial heat A9135L Geochemistry A9330P Pacific Ocean A9210B Physical properties of seawater A9220C Chemistry of the oceans/ depth 1.8E+03 to 2.3E+03 m/ He/el He/el