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Natasha Artemieva

2010 Research Report

Natasha Artemieva worked on a number of researcher projects in 2010:

 

1.     Chicxulub Impact Plume and ejecta re-distribution (PGG grant, LPSC abstract, paper in preparation).

The K-P boundary is widely recognized as a global ejecta layer formed by a large meteorite impact 65 million years ago. The discovery of an iridium anomaly, shocked quartz grains, and the Chicxulub crater provided the strongest confirmation of the impact hypothesis. However, 30 years later the mechanism for transporting the impact ejecta world-wide is still unclear, and atmospheric disturbances may play a crucial role in ejecta re-distribution. With this in mind we model the Chicxulub ejecta starting from impact and ending with the deposition of the ejecta (shocked quartz and spherules) around the globe. To solve this problem we have to deal with extremely different time and spacial scales: from seconds to days, and from microns to thousands of km.

Up to distances of 1000 km from the crater ejecta are deposited ballistically within the first 20 minutes. At larger distances interaction of ejecta with the atmosphere play an important role: ejecta density currents are formed (although they never reach the surface as they disappear during descent), fine ejecta are thrown back upwards to the rarified atmosphere, and strong atmospheric shock waves disperse ejecta in all directions. Two hours after the impact 99% of ejecta have been deposited. The remaining particles (still in the atmosphere) have sizes from 1 mm (1.5 % of the total non-deposited mass), 10 mm (18%), and 100 mm (80%). These long-lasting ejecta contain particles from all target units (i.e. shocked quartz grains from the basement, sulfur aerosols from the sedimentary cover) and plenty of the projectile material (which was partially vaporized during the impact). On average, smaller particles are further from the crater, at higher altitude, and have higher velocities (horizontally and vertically). Whereas the upper atmosphere (above ~50 km) is still strongly disturbed (horizontal velocities reach a couple of km/s, i.e. much bigger than any hurricanes), the lower atmosphere is almost quiet.

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2.     Interaction of impact melt with water (partially published in M&PS, another two paper – in preparation) 

The idea of an intensive impact melt interaction with water in terrestrial craters becomes widely accepted (one paper has been published, another one is ready for submission, also we have a very good feedback from our colleagues).

The Ries crater study (in collaboration with my German colleagues from the Natural History Museum in Berlin) showed that no one hypothesis of suevite genesis (plume ejecta, melt or pyroclastic flow from the crater central uplift) works from the viewpoint of physics. Instead, we suggested the post-impact modification of intra-crater melt pool by interaction with an external source of water. While the source of hot (up to melting) rocks) is quite obvious (at least 15 km3 of melt has been created upon the impact), possible sources of water are still not clear and may include: 1) condensates from the impact plume; 2) water in sediments around the crater; 3) rivers or lakes which feed into the Ries basin within a few thousand years after the impact.

 

Similar process happened in much older (and much bigger) Sudbury crater in Canada. The existence of 1.5-km-thick “fallback” breccias (Onaping Formation) overlying the Sudbury melt pool (Sudbury Igneous Complex, SIC) was absolutely inconsistent with physics (and still is the fact). The relative thickness, internal stratigraphic and lithological character, and the relative chronology of depositional units indicate multiple processes were involved over some time in the formation of the Onaping. The Sudbury structure formed in a foreland basin and water played an essential role in the evolution of the Onaping, as indicated by a major hydrothermal system generated during its formation. Taken together, observations and interpretations of the Onaping suggest a working hypothesis for the origin of the Onaping that includes not only impact but also the interaction of sea water with the impact melt, resulting in repeated explosive interactions involving proto-SIC materials and mixing with pre-existing lithologies.

 

3.     Intra-crater melt pool at Sudbury (published in GSA Special Paper) 

The integration of numerical modeling results and their application to the observed geophysical and current topographic data provides new insights into the early evolution of the deeply eroded Sudbury Structure. The modeling shows a maximum depth of melting of 30–40 km (depending on impact angle and impact velocity). However, melt from upper target layers (< 10 km) is mainly ejected during the excavation stage of crater formation, and the remaining melt is strongly biased to melt derived from lower crustal material. Two-dimensional thermal evolution modeling with various granophyre/norite thickness ratios shows that irrespective of the granophyre/norite thickness ratio, the hottest part of the Sudbury Igneous Complex (SIC) was near the crater center at the melt-pool bottom and within the crater floor, which supports precipitation of sulfides toward the crater floor. The 2D cooling models give compelling evidence for longevity of melt at the bottom of the SIC and partial remelting of the crater floor. The numerical model results are compared with observed topographic, seismic and magnetic data and provide important constraints on their interpretation. 

 

4.     Impact ejecta on the Moon and on Earth (recently funded  LASER project).

To start this project, I currently work on the modification of my numerical code: 1) implement spherical geometry into the code – to model global distribution of ejecta; 2). adopt a well-tested porosity model – to model lunar ejecta in small-scale impacts.

 

Papers 

1.     Grieve R.A.R., Ames D.E., Morgan J.V., Artemieva N. (2010) The evolution of the Onaping formation at the Sudbury impact structure. Meteoritics and Planetary Science 45, p. 759-782. 

2.     Milkereit B., Artemieva N., Ugalde H. (2010) Fracturing, thermal evolution and geophysical signature of the crater floor of a large impact structure: The case of the Sudbury Structure, Canada. GSA Special Paper 465, 115-131. 

 

Abstracts 

1.     Wünnemann K., Artemieva N., Collins G. (2010) Modeling the Ries impact: the role of water and porosity for crater formation and ejecta deposition. Nordlingen 2010: The Ries crater, the Moon and the future of human space exploration (invited).

2.     Artemieva N. (2010) Meteoritic strikes and  liquid water pool on Titan. COSPAR meeting Bremen, Germany, July 2010 (invited)

3.     Artemieva N., Pierazzo E. (2010) Projectile material in Meteor Crater (oral). European Planetary Science Congress, Rome, Italy, September 2010.

4.     Artemieva N. (2010) Magic of an Impact Plume — Insight from Numerical Modeling (poster). LPSC-41, abstract 1968.

5.     Lunine J., Artemieva N., Tobie G. (2010) Impact Cratering on Titan: Hydrocarbons Versus Water (poster). LPSC-41, abstract 1537.

Research Year: 
2010
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