Vesicular basalt

Sahagian D.L., Proussevitch A.A., and Carlson W.D. (2002) Analysis of vesicular basalts and lava emplacement processes for application as a paleobarometer/paleoaltimeter. 

Sahagian D, Proussevitch A (2007) Paleoelevation measurement on the basis of vesicular basalts. Rev Mineral Geochem 66 195-213... 

We applied this technique to make an initial estimate of the timing and extent of Cenozoic uplift of the Colorado Plateau (Sahagian et al. 2002a). Because the technique measures paleoatmospheric pressure, it is not subject to uncertainties stemming from the use of proxies that depend on environmental factors other than elevation alone. Vesicular lavas preserve a record of paleopressure at the time and place of lava emplacement because the difference in internal pressure in bubbles at the base and top of a lava flow depends on atmospheric pressure and lava flow thickness. The modal size of the vesicle (bubble) population is larger at the top than at the bottom. This leads directly to paleoatmospheric pressure and thus elevation because the thickness of the flow can easily be measured in the field, and the vesicle sizes can be measured in the lab. All proxies have their limitations and hence are not applicable in all places and at all times. Vesicular basalts are no exception. For a lava flow to record atmospheric pressure, the flow thickness must remain constant between the time the upper and lower crusts (10-20 cm) form, and the time of complete solidification of the flow. 

Figure 1. Diagram of methodology for determining paleoelevation from vesicular basalts (vesicular basalt paleoaltimeter) (Sahagian et al. 2002b).

Figure 3. Typical outcrop of vesicular basalt. Note upper and lower vesicular zones, and massive vesicle free region in the interior of this 2.5 m flow.

Figure 4. Vesicular basalt sample (Sahagian et al. 2002b).

Figure 11. Uplift history of Colorado Plateau based on vesicular basalt paleoaltimeter (Sahagian et al. 2002a).

The process of pressure-porosity diffusion, the fourth solution mentioned in Section 7, requires solid-fluid coupling to exist. If the pore liquid cannot flow, as is likely in the case of ductile smectitic shales (Dusseault 2003), or if the liquid is present as a fully occluded phase so that it is in the form of liquid bubbles in the solid mineral, as in a vesicular basalt, the wave cannot exist. This also... 

The thickness of the Exposure Formation varies locally between 10 and 150 m. It is composed of breccia containing clasts of altered basalt, vesicular basalt, dolerite, sandstone, and beds of lapiUi tuff, tuff, and tuffaceous ripple-marked sandstone (Elliot et al. 1986a Wbmer 1992 Roland and Wbmer 1996). 

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