Siberian gas venting and the end-Permian environmental crisis

Hydrothermal venting of greenhouse gases triggering Early Jurassic global warming

On the causes of mass extinctions

Rapid magma emplacement in the Karoo Large Igneous Province

How Large Igneous Provinces affect global climate, sometimes cause mass extinctions, and represent natural markers in the geological record

The Karoo large igneous province, formed at c . 183 Ma, is characterized by the presence of voluminous basaltic intrusive complexes within the Karoo Basin, extrusive lava sequences and hydrothermal vent complexes. These last are pipe-like structures, up to several hundred metres in diameter, piercing the horizontally stratified sediments of the basin. Detailed mapping of two sediment-dominated hydrothermal vent complexes shows that they are composed of sediment breccias and sandstone. The breccias cut and intrude tilted host rocks, and are composed of mudstone and sandstone fragments with rare dolerite boulders. Sandstone clasts in the breccias are locally cemented by zeolite, which represents the only hydrothermal mineral in the vent complexes. Our data document that the hydrothermal vent complexes were formed by one or a few phreatic events, leading to the collapse of the surrounding sedimentary strata. We propose a model in which hydrothermal vent complexes originate in contact metamorphic aureoles around sill intrusions. Heating and expansion of host rock pore fluids resulted in rapid pore pressure build-up and phreatic eruptions. The hydrothermal vent complexes represent conduits for gases and fluids produced in contact metamorphic aureoles, slightly predating the onset of the main phase of flood volcanism.

Structure and evolution of hydrothermal vent complexes in the Karoo Basin, South Africa

[1] Magmatic sill intrusions develop saucer-like geometries in layered sedimentary basins intruded by large volumes of magma. Saucer-shaped sill emplacement models are based on the analysis of the intrusion geometry and their spatial relationships with potential feeders, not on magma flow pattern. The Karoo Basin of South Africa hosts hundreds of saucer-shaped sills. Among these, the Golden Valley Sill is well exposed and displays connections with adjacent and nested saucers. A combination of detailed field observations and anisotropy of magnetic susceptibility measurements (AMS) were used to identify strain markers that can be interpreted in terms of magma flow directions. A total of 113 localities (six specimens per site), mostly including pairs of opposite sill margins, were sampled for anisotropy of magnetic susceptibility analyses. The magnetic properties were determined by measuring hysteresis loops and K-T curves. The majority of the localities display well-defined magnetic foliations that consistently dip outward from the center of the Golden Valley Sill. This orientation of the magnetic foliation most likely represents inflation/deflation cycles of the intruding sill that interacts with nonstatic enclosing walls. In addition, magma channels and ropy flow structures were identified and display an imbrication of the magnetic foliation indicating an outward magma flow direction. The observed magma flow geometries derived from macroscopic flow indicators and the AMS data correlate well and constrain an emplacement model for the Golden Valley Sill Complex. Our emplacement model integrates our observations with dynamic emplacement processes characterized by inflation and deflation cycles.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2008JB005620

How are saucer‐shaped sills emplaced? Constraints from the Golden Valley Sill, South Africa

Fracturing of doleritic intrusions and associated contact zones: Implications for fluid flow in volcanic basins

https://www.lehigh.edu/~geb0/SvensenKarooBasinGCA08.pdf

Luc Chevallier

Papers

Hydrothermal venting of greenhouse gases triggering Early Jurassic global warming

Structure and evolution of hydrothermal vent complexes in the Karoo Basin, South Africa

How are saucer‐shaped sills emplaced? Constraints from the Golden Valley Sill, South Africa

Fracturing of doleritic intrusions and associated contact zones: Implications for fluid flow in volcanic basins

Nitrogen geochemistry as a tracer of fluid flow in a hydrothermal vent complex in the Karoo Basin, South Africa