Skip to content
Home
About Us
Resources
Profiles Metrics
Authors Directory
Institutions Directory
Top Authors
Top Institutions
Top Sponsors
AI Digest
Contact Us
Menu
Home
About Us
Resources
Profiles Metrics
Authors Directory
Institutions Directory
Top Authors
Top Institutions
Top Sponsors
AI Digest
Contact Us
Home
About Us
Resources
Profiles Metrics
Authors Directory
Institutions Directory
Top Authors
Top Institutions
Top Sponsors
AI Digest
Contact Us
Menu
Home
About Us
Resources
Profiles Metrics
Authors Directory
Institutions Directory
Top Authors
Top Institutions
Top Sponsors
AI Digest
Contact Us
Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
Nitrogen geochemistry as a tracer of fluid flow in a hydrothermal vent complex in the Karoo Basin, South Africa
Geochimica et Cosmochimica Acta, Volume 72, No. 20, Year 2008
Notification
URL copied to clipboard!
Description
We have investigated the N geochemistry of minerals and rocks from contact metamorphic aureoles and hydrothermal vent complexes (HVC) in the Karoo Basin in South Africa. The HVC formed during phreatic eruptions associated with rapid devolatilization and pressure build-up in contact aureoles around early Jurassic sill intrusions. By combining outcrop data from a HVC and core data from contact aureoles, we investigate the relationship between light element release during metamorphism and vertical fluid migration. Sandstone and breccia from the HVC contain early-diagenetic ammonium NH4+-bearing feldspar (buddingtonite) and illite. Ammonium occupies up to 95% of the A site in feldspar, corresponding to concentrations up to 5.2 wt% N. Bulk-rock N isotope data for rocks from inside and outside the hydrothermal vent complex fall into two distinct groups. Background samples have δ15Nair between +1.5‰ and +4.9‰, whereas minerals from the vent complex have δ15N in the range +7.5 to +10.6‰. The N geochemistry of contact metamorphic shale from the lower stratigraphic units of the Karoo Basin shows that the vitrinite reflectance and δ15N values are positively correlated. Shale with reflectivity values >4%Ro are enriched in 15N, with δ15N values between +6‰ and +14‰, implying the release of isotopically light N into metamorphic fluids (probably as N2). We suggest that the relatively high δ15N values of the early-diagenetic buddingtonite in the HVC reflect exchange of buddingtonite with N-bearing fluids ascending from greater depth after their release during contact metamorphism and dehydration. We present a qualitative model whereby hydrothermal vent complexes represent fluid flow structures after their formation, focusing N-bearing metamorphic fluids sourced in deeper levels of the basin. The release of organic N from sediments at depth in volcanic basins could play a role in the geochemical cycle of N, becoming particularly important during periods of intense volcanic activity. © 2008 Elsevier Ltd. All rights reserved.
Authors & Co-Authors
Svensen, Henrik Hovland
Norway, Oslo
Universitetet I Oslo
Bebout, Gray E.
United States, Bethlehem
Lehigh University
Kronz, Andreas
Germany, Gottingen
Georg-august-universität Göttingen
Li, Long
United States, Bethlehem
Lehigh University
Planke, Sverre
Norway, Oslo
Universitetet I Oslo
Norway, Oslo
Volcanic Basin Petroleum Research as
Chevallier, Luc P.
South Africa, Pretoria
Council for Geoscience
Jamtveit, Bjørn Rn
Norway, Oslo
Universitetet I Oslo
Statistics
Citations: 52
Authors: 7
Affiliations: 5
Identifiers
Doi:
10.1016/j.gca.2008.07.023
ISSN:
00167037
Study Approach
Qualitative
Study Locations
South Africa