2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 9
Presentation Time: 10:00 AM

The Relationship Between 87Sr/86Sr and Seawater Chemistry

RASBURY, Troy, HOLT, William E., FRODSHAM, Aaeron, EKSTROM, Brittany and WILSON, Janette, Geosciences, Stony Brook University, Stony Brook, NY 11794, troy.rasbury@stonybrook.edu

When compared with sea level curves, which are thought to reflect changes in the volume of mid-ocean ridge spreading (through increased rates or increased length), there is a notable offset with 87Sr/86Sr. By understanding this offset we should be able to better understand how plate tectonics has controlled ocean chemistry through time. To first order, marine 87Sr/86Sr is high when Mg concentrations are high and low when Mg concentrations are low. This is consistent with radiogenic 87Sr/86Sr's and Mg concentrations being derived from continental weathering, whereas hydrothermal alteration produces unradiogenic 87Sr/86Sr and is a significant sink for Mg. Moreover, Sr and Ca concentrations are high when 87Sr/86Sr is high and low when 87Sr/86Sr is low. Ca is derived from continental weathering and has a significant contribution from hydrothermal alteration of ocean crust; Sr appears to be derived solely from the continents (based on the observation that [Sr] in hydrothermal fluids are unchanged from seawater). We use the differences in sources and sinks of Mg, Ca, and Sr, as well as constraints imposed by the 87Sr/86Sr ratios, to investigate the relative roles of continental run-off versus hydrothermal alteration of ocean basalts in affecting seawater chemistry through time.