Formation of H2 and CH4 by weathering of olivine at temperatures between 30 and 70°C

Hydrocarbons such as CH4 are known to be formed through the Fischer-Tropsch or Sabatier type reactions in hydrothermal systems usually at temperatures above 100°C. Weathering of olivine is sometimes suggested to account for abiotic formation of CH4 through its redox lowering and water splitting properties. Knowledge about the CH4 and H2 formation processes at low temperatures is important for the research about the origin and cause of early Earth and Martian CH4 and for CO2 sequestration. We have conducted a series of low temperature, long-term weathering experiments in which we have tested the CH4 and H2 formation potential of forsteritic olivine

Experimental determination of natural carbonate rock dissolution rates with a focus on temperature dependency

The denudation of carbonate rocks at landscape scale is controlled by factors like mineral composition, temperature, precipitation, runoff, fracture spacing and vegetation cover. Knowledge on carbonate denudation is important in order to understand landscape development and long-term terrestrial/marine carbon transport, but there are few laboratory studies done on weathering rates of natural carbonate rocks under the low temperatures relevant for glacial-interglacial periods. To enhance the understanding of carbonate dissolution kinetics we studied low-temperature dissolution reactions of various natural Triassic carbonate rocks belonging to the Lower Muschelkalk in Germany. We conducted batch and flow-through experiments investigating the direct correlation of dissolution rates with temperature, and to establish whether the fine-grained carbonate rocks (micrite) are more reactive than the coarser-grained sparitic limestones. By increasing the temperature from 5 to 26 °C far-from-equilibrium dissolution rates of micritic and sparitic limestone samples increased from 2.42 × 10− 07 to 10.88 × 10− 07 and 4.19 × 10− 07 to 7.74 × 10− 07 mol m− 2 s− 1, respectively (Specific Surface Areas (SSA) of about 0.006–0.01 m2/g). The dissolution rates of dolomite rock samples varied only slightly from 1.06 × 10− 07 to 2.02 × 10− 07 mol m− 2 s− 1 (SSA approximately 0.002 m2/g) in the temperature range 5–25 °C at circum-neutral pH. The obtained apparent activation energies are in the range of earlier experiments done at higher temperatures, but there is a distinct difference between the calcite in the micrite (~ 51 kJ/mol) and sparitic (~ 20–22 kJ/mol) lithologies, indicating that the dissolution mechanisms are not the same. Using these activation energies in modelling of natural carbonate denudation we see that there is a clear effect of changing temperature, but this is mostly through the increased solubility at lower temperatures and not through the increasing far-from-equilibrium dissolution rates at higher temperatures. Formation of fluid pathways by preferential dissolution of framework calcite crystals is suggested to form infiltration pathways and affect denudation rates. The difference in crystal size between the micritic and sparitic limestones will affect the formation of such pathways (larger crystals may create fewer and larger conduits) and this is expected to be more important for the long-term denudation than the differences in activation energies

Tectonic processes in the Jan Mayen fracture zone based on earthquake occurrence and bathymetry

Jan Mayen is an active volcanic island situated along the mid-Atlantic Ridge north of Iceland. It is closely connected with the geodynamic processes associated with the interaction between the Jan Mayen Fracture Zone (JMFZ) and the slowly spreading Kolbeinsey and Mohns Ridges. Despite the significant tectonic activity expressed by the frequent occurrence of medium to large earthquakes, detailed correlation between individual events and the causative faults along the JMFZ has been lacking. Recently acquired detailed bathymetric data in the vicinity of Jan Mayen has allowed us to document such correlation for the first time. The earthquake of 14 April 2004 (Mw 6), which occurred along the JMFZ, was studied in detail and correlated with the bathymetry. Locations of aftershocks within the first 12 hours after the mainshock outline a 10-km-long fault plane. Interactions between various fault systems are demonstrated through locations of later aftershocks, which indicate that supposedly normal fault structures to the north of the ruptured fault, in the Jan Mayen Platform, have been reactivated. Correlation of the waveforms shows that events located on these structures are significantly different from activity at neighboring structures. Coulomb stress modeling gives an explanation to the locations of the aftershocks but cannot reveal any information about their mechanisms