Deep-water Seep-related Carbonate Mounds: Implications for Seawater and Vent Fluid Geochemistry in the Mesoproterozoic Borden Basin, Nunavut
Previously Published Material: A government summary of activities summarizes geochemical results but very little interpretation. (Canada-Nunavut Geoscience Office Summary of Activities, 2014).Early versions of interpretations and results have been presented at GAC-MAC (2014-Fredericton) and GSA (Vancouver-2014).Most interpretations presented in this paper are new and have not been presented.
Abstract ID#: 36826
Detritus-corrected REE+Y patterns show binary mixing of marine and seep fluids. The seawater-dominated end-member has a positive slope in shale normalization, indicating a marine heritage, and a +ve Ce anomaly, indicating deposition below a redoxcline. REE+Y patterns show a strong local runoff influence and hence basin restriction. The seep-dominated end-member has flat REE+Y patterns, no Ce anomaly, and a -ve Eu anomaly. Carbon isotope values are typical for Mesoproterozoic seawater (~3.5‰). The absence of a +ve Eu anomaly suggests that seep fluids were <300°C and not influenced by an anomalous heat source (intrusion). The lack of light δ13C in mound dolostone indicates that methane was not a major component of seep fluid. Seep fluids may have originated as seawater-derived brines that became concentrated evaporatively and sank to interact with basement rocks where their REE pattern was modified, before being vented as high-Mg/Ca, <300°fluids. Although trace elements indicate a marine basin water heritage, the Borden basin was epicratonic, its geochemistry influenced by local weathering, and redox-stratified. Such conditions are common in Mesoproterozoic basins, complicate understanding global seawater conditions, and imply that controls on Phanerozoic carbonate mineralogy may not adequately explain Mesoproterozoic carbonates.