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| Titel |
Sill intrusion driven fluid flow and vent formation in volcanic basins: Modeling rates of volatile release and paleoclimate effects |
| VerfasserIn |
Karthik Iyer, Daniel Schmid |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127664
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| Publikation (Nr.) |
 EGU/EGU2016-7565.pdf |
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| Zusammenfassung |
| Evidence of mass extinction events in conjunction with climate change occur throughout the
geological record and may be accompanied by pronounced negative carbon isotope
excursions. The processes that trigger such globally destructive changes are still under
considerable debate. These include mechanisms such as poisoning from trace metals released
during large volcanic eruptions (Vogt, 1972), CO2 released from lava degassing during the
formation of Large Igneous Provinces (LIPs) (Courtillot and Renne, 2003) and CH4
release during the destabilization of sub-seafloor methane (Dickens et al., 1995), to
name a few. Thermogenic methane derived from contact metamorphism associated
with magma emplacement and cooling in sedimentary basins has been recently
gaining considerable attention as a potential mechanism that may have triggered
global climate events in the past (e.g. Svensen and Jamtveit, 2010). The discovery of
hydrothermal vent complexes that are spatially associated with such basins also
supports the discharge of greenhouse gases into the atmosphere (e.g. Jamtveit et al.,
2004; Planke et al., 2005; Svensen et al., 2006). A previous study that investigated
this process using a fluid flow model (Iyer et al., 2013) suggested that although
hydrothermal plume formation resulting from sill emplacement may indeed release large
quantities of methane at the surface, the rate at which this methane is released into the
atmosphere is too slow to trigger, by itself, some of the negative δ13C excursions
observed in the fossil record over short time scales observed in the fossil record.
Here, we reinvestigate the rates of gas release during sill emplacement in a case
study from the Harstad Basin off-shore Norway with a special emphasis on vent
formation.
The presented study is based on a seismic line that crosses multiple sill structures
emplaced around 55 Ma within the Lower Cretaceous sediments. A single well-defined vent
complex is interpreted above the termination of the main sill in the region. We use a 2D,
hybrid FEM/FVM model that solves for fully compressible fluid flow to quantify the
thermogenic release and transport of methane and to evaluate flow patterns within these
systems. Additionally, vent formation in the model is implemented by simple fracture criteria
that modify the permeability structure when the fluid pressure exceeds a threshold
determined by the lithostatic pressure. The model with fracture formation is able to
reproduce a single vent complex at the observed location above the main sill tip.
This is very different from hydrothermal plume formation elsewhere in the region
and occurs over short time scales (hundreds of years) and results in fluid focusing
in that region. The rate of degassing and the resulting negative δ13C excursion
from the vent model is then compared to models where only hydrothermal plume
formation results in gas transportation. Lastly, variations in the amount of gas liberated
in the system are investigated based on kerogen type and other mineral reactions
such as limestone decarbonation and halite breakdown in the affected source rock. |
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