Rare Earth Element and Trace Metal Composition of Pore Fluids in the Nankai Trough as Relates to the Lithostratigraphy and Deep Biosphere.
Abstract
One of the primary scientific objectives of the NanTroSEIZE expeditions is to test the hypothesis that the earthquake cycle results in systematic changes in the chemical alteration of pore fluids and sediments through which they flow (Tobin and Kinoshita, 2006). Trace elements, particularly the rare earth elements (REE) are sensitive to subtle changes in temperature, pressure and host lithologies, making them excellent monitors of fluid movement along fault zones. However, because of the difficulty in properly extracting and analyzing REE, compounded with limited sample volume that is typically recovered from squeezing deep sediments, REE are poorly constrained in many sub-surface environments. We measured REE, Y and Cd in pore fluids recovered from six sites that were drilled during IODP Exp 315 and 316, using a modified extraction-HR-ICP-MS technique for low sample volumes (5 ml). These extractions were conducted by an automated system utilizing an 8-hydroxy-quinoline column that selectively immobilizes transition metals and REEs while allowing alkali and alkali earth metals and anions to pass through the column. Results of these analyses indicate that concentrations of REE vary by an order of magnitude throughout the sediment column at each site, one of which (C0002) sampled sediments at depths of 1043 meters below the seafloor. These results suggest that variations in pore fluid compositions result from diagenetic reactions with differing lithologies. On the basis of the REE data, there is no indication of present- day fluid flow and no indication of a deep-sourced fluid even though the sediment section bisected a variety of faults including splay faults and the decollement. There are, however, variations in REE concentrations associated with changes in redox conditions caused by microbial activity in the upper 30-50 m of the sediment column.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.T31B2001H
- Keywords:
-
- 0461 Metals;
- 0489 Trace element cycling (4875);
- 1031 Subduction zone processes (3060;
- 3613;
- 8170;
- 8413);
- 1060 Planetary geochemistry (5405;
- 5410;
- 5704;
- 5709;
- 6005;
- 6008);
- 8170 Subduction zone processes (1031;
- 3060;
- 3613;
- 8413)