On the formation of hydrothermal vents and cold seeps in the Guaymas Basin, Gulf of California

Sonja Geilert,Mechthild Doll,Longhui Deng,Sudipta Sarkar,Stefan Schloemer,Chih-Chieh Su,Volker Liebetrau,Christian Hensen,Florian Scholz,Annika Fiskal,Mark Schmidt,Christian Berndt,Mark A Lever,Volker Thiel

doi:10.5194/bg-15-5715-2018

Abstract

Abstract. Magmatic sill intrusions into organic-rich sediments cause the release of thermogenic CH4 and CO2. Pore fluids from the Guaymas Basin (Gulf of California), a sedimentary basin with recent magmatic activity, were investigated to constrain the link between sill intrusions and fluid seepage as well as the timing of sill-induced hydrothermal activity. Sampling sites were close to a hydrothermal vent field at the northern rift axis and at cold seeps located up to 30 km away from the rift. Pore fluids close to the active hydrothermal vent field showed a slight imprint by hydrothermal fluids and indicated a shallow circulation system transporting seawater to the hydrothermal catchment area. Geochemical data of pore fluids at cold seeps showed a mainly ambient diagenetic fluid composition without any imprint related to high temperature processes at greater depth. Seep communities at the seafloor were mainly sustained by microbial methane, which rose along pathways formed earlier by hydrothermal activity, driving the anaerobic oxidation of methane (AOM) and the formation of authigenic carbonates. Overall, our data from the cold seep sites suggest that at present, sill-induced hydrothermalism is not active away from the ridge axis, and the vigorous venting of hydrothermal fluids is restricted to the ridge axis. Using the sediment thickness above extinct conduits and carbonate dating, we calculated that deep fluid and thermogenic gas flow ceased 28 to 7 kyr ago. These findings imply a short lifetime of hydrothermal systems, limiting the time of unhindered carbon release as suggested in previous modeling studies. Consequently, activation and deactivation mechanisms of these systems need to be better constrained for the use in climate modeling approaches.

Highlights

Abrupt climate change events in Earth’s history have been partly related to the injection of large amounts of greenhouse gases into the atmosphere (e.g., Svensen et al, 2004; Gutjahr et al, 2017)
Seep communities at the seafloor were mainly sustained by microbial methane, which rose along pathways formed earlier by hydrothermal activity, driving the anaerobic oxidation of methane (AOM) and the formation of authigenic carbonates
Seismic images suggest that massive disturbance of sediments and vertical pipe structures are related to channeled fluid and/or gas advection caused by sill intrusions (Fig. 2)

Summary

Introduction

Abrupt climate change events in Earth’s history have been partly related to the injection of large amounts of greenhouse gases into the atmosphere (e.g., Svensen et al, 2004; Gutjahr et al, 2017). Among the most prominent of these events was the Paleocene–Eocene Thermal Maximum (PETM) during which the Earth’s atmosphere warmed by about 8 ◦C in less than 10 000 years (Zachos et al, 2003). The PETM was possibly triggered by the emission of about 2000 Gt of carbon (Dickens, 2003; Zachos et al, 2003). The processes discussed regarding the release of these large amounts of carbon in a relatively short time are gas hydrate dissociation, volcanic eruptions as well as igneous intrusions into organicrich sediments, triggering the release of carbon during con-. Geilert et al.: On the formation of hydrothermal vents and cold seeps tact metamorphism (Svensen et al, 2004; Aarnes et al, 2010; Gutjahr et al, 2017)

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