Geochemical tracers of processes affecting the formation of seafloor hydrothermal fluids and deposits in the Manus back-arc basin

dc.contributor.author Craddock, Paul R.
dc.coverage.spatial Eastern Manus Basin
dc.coverage.spatial Manus Spreading Center
dc.date.accessioned 2008-12-26T15:32:46Z
dc.date.available 2008-12-26T15:32:46Z
dc.date.issued 2009-02
dc.description Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2009 en
dc.description.abstract Systematic differences in trace element compositions (rare earth element (REE), heavy metal, metalloid concentrations) of seafloor vent fluids and related deposits from hydrothermal systems in the Manus back–arc basin (Eastern Manus Basin, EMB and Manus Spreading Center, MSC) are used to investigate processes that affect their formation. Processes responsible for observed differences in fluids and deposits from distinct geologic settings include (a) fluid–rock interaction (with temperature, pressure and crustal composition as variables), (b) magmatic acid volatile input and, (c) local seawater entrainment and mixing with hydrothermal fluids, coupled with sulfide precipitation and metal remobilization. REE distributions in vent fluids in the Manus Basin exhibit a wide range of chondrite-normalized patterns that contrast with the relatively uniform distributions observed in mid-ocean ridge vent fluids. This heterogeneity is attributed to marked differences in fluid pH and fluoride and sulfate concentrations that significantly affect REE solubility. The data indicate that REEs can be used as indicators of the styles of magmatic acid volatile input in back-arc hydrothermal systems. Anhydrite in deposits record the same range of REE patterns, suggesting that REE distributions preserved in anhydrite can be used as indicators of past magmatic acid volatile input. Vent fluid heavy metal and metalloid concentrations also exhibit considerable differences. High metal concentrations in EMB versus MSC vent fluids reflect low pH, largely from input of magmatic acid volatiles (indicated by fluoride concentrations greater than seawater). In EMB, metal concentrations are locally affected by dissolution of previously deposited sulfide owing to low pH conditions affected by magmatic acid volatile input or seawater entrainment and mixing with hydrothermal fluid that leads to sulfide precipitation and secondary acidity generation. Massive sulfide deposits in the Manus Basin exhibit a wide range of mineral compositions and heavy metal enrichments. The formation of Zn-rich (sphalerite/wurtzite) deposits in the MSC and of Cu-Fe and Cu-As-rich (chalcopyrite, tennantite) deposits in the EMB reflects differences in the conditions of sulfide precipitation (temperature, pH) and in metal concentrations. The data suggest that heavy metal and metalloid distributions in massive sulfide deposits can be used as indicators of the conditions of vent deposit formation. en
dc.description.sponsorship The thesis research presented herein was funded by the National Science Foundation through grants OCE-0327448 (to W. Bach and M.K. Tivey) and OCE- 0441796 (to M.K. Tivey) and by support to P.R. Craddock from the MIT Presidential Fellowship and Ocean Drilling Program Schlanger Fellowship, as well by WHOI Academic Programs Office. en
dc.format.mimetype application/pdf
dc.identifier.citation Craddock, P. R. (2009). Geochemical tracers of processes affecting the formation of seafloor hydrothermal fluids and deposits in the Manus back-arc basin [Doctoral thesis, Massachusetts Institute of Technology and Woods Hole Oceanographic Institution]. Woods Hole Open Access Server. https://doi.org/10.1575/1912/2609
dc.identifier.doi 10.1575/1912/2609
dc.identifier.uri https://hdl.handle.net/1912/2609
dc.language.iso en_US en
dc.publisher Massachusetts Institute of Technology and Woods Hole Oceanographic Institution en
dc.relation.ispartofseries WHOI Theses en
dc.subject Hydrothermal vents en_US
dc.subject Sea-floor spreading en_US
dc.subject Melville (Ship) Cruise MGLN06MV en_US
dc.title Geochemical tracers of processes affecting the formation of seafloor hydrothermal fluids and deposits in the Manus back-arc basin en
dc.type Thesis en
dspace.entity.type Publication
relation.isAuthorOfPublication 4cc15b86-52be-4e13-9bb1-32f51258882e
relation.isAuthorOfPublication.latestForDiscovery 4cc15b86-52be-4e13-9bb1-32f51258882e
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