The Ancient Environments of Venus as Recorded by Tessera Terrain
Abstract
Tessera terrain are the stratigraphically oldest materials on Venus, predating the volcanic plains that cover the majority of the planet. A revised estimate of the surface crater age of the tesserae may be as old as 1.75 Ga, which overlaps with models that predict a more clement Venus during the first 2-3 Ga of Venus history (Way et al., 2016); the formation age of the rocks in the tesserae may be much older. Thus, tesserae uniquely record extinct environmental and geodynamic conditions on Venus which are critical to understand how this Earth-sized planet evolved.
Tesserae reveal that ancient (pre-plains) Venus was different in the following ways: 1) The NIR emissivity of some tesserae is lower than the presumably basaltic plains in a way that is consistent with more felsic igneous compositions (Gilmore et al., 2015), which require liquid water and a plate recycling mechanism for their formation. 2) Analysis of the radar emissivity properties of tessera highlands indicates there are at least three different weathering styles of tessera rocks, indicating local differences in rock type, atmospheric composition and/or age. 3) The scale and style of deformation indicates that the tesserae were created during a time of enhanced surface strain and lithospheric thermal gradients relative to today (e.g., Brown and Grimm, 1997). 4) The tesserae were present prior to and during the emplacement of the global plains, and may preserve weathering reactions that recorded a climate perturbation spurred by this extensive volcanism. 5) The tesserae may serve as a sink for sediment on Venus (Whitten and Campbell, 2016). 6) The tesserae have different structural domains accreted together by collision. 7) Layering in the tesserae suggests the possibility of sedimentary rocks and erosion (Byrne et al., this conference). The tesserae are the remnants of early crust on a once habitable Earth-sized planet and contain evidence of several characteristics that are directly relevant to exoplanet modeling. The age and composition of tesserae indicates that they formed during a time when liquid water was stable on Venus. Their deformation, assembly and composition may require an era of plate recycling and continental crust formation. The rocks of the tesserae have been weathered under multiple climate regimes on Venus which may be recorded in the mineralogy.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P51G3445G
- Keywords:
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- 5205 Formation of stars and planets;
- PLANETARY SCIENCES: ASTROBIOLOGY;
- 6295 Venus;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6296 Extra-solar planets;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 5430 Interiors;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS