『Abstract
The knowledge of how and why marine 87Sr/86Sr
ratios changed helps understand the impacts of many processes
on the global biogeochemical cycle in the geological past. Here
we examine the possible influence of global cooling on the evolution
of marine 87Sr/86Sr curve by a kinetic approach.
The importance of mica weathering is emphasized due to its high
content of radiogenic strontium and low activation energy in weathering
reaction. Since the activation energy determines the sensitivity
of weathering rate in response to temperature changes, global
cooling will increase the 87Sr/86Sr ratio
of continental flux by relatively preferential weathering of mica.
Based on the average strontium contents and 87Sr/86Sr
ratios of the mica minerals in the exposed upper continental crust,
a kinetic model is established to survey the response of riverine
87Sr/86Sr to the changes of global temperatures.
The model result indicates that the increase of riverine 87Sr/86Sr
caused by global cooling can solely account for most of the increase
in seawater 87Sr/86Sr since 3.4 Myr B.P.
This finding emphasizes that the weathering kinetics is an important
mechanism relating the global climate change to marine 87Sr/86Sr
curve; and the marine 87Sr/86Sr curve should
be used with great care in the climate-weathering-tectonic connections.
Keywords: climate; marine 87Sr/86Sr; mica;
geochemical cycle; kinetics』
1. Introduction
2. Mica weathering to river flux
3. Preferential weathering of mica
4. Riverine 87Sr/86Sr response to cooling
5. Marine 87Sr/86Sr response to cooling
6. Conclusions
Acknowledgement
References