Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p43c1698m&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P43C-1698
Mathematics
Logic
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties
Scientific paper
Impact craters are the dominant geological landform on the Moon; however, relationships between specific lunar craters and their impactites are typically poorly constrained. With limited lunar samples, planetary scientists look to terrestrial craters as lunar analogues. The Mistastin Lake impact structure, located in northern Labrador, Canada (55°53'N; 63°18'W) offers a unique opportunity to study preserved impactites of similar lunar mineralogy and outcrop characteristics, and to understand the origin and emplacement of lunar impact ejecta. The Mistastin Lake impact structure is an intermediate-size, complex crater (28 km apparent crater diameter) formed by a meteorite impact ~36 million years ago. It is comparable to many of the larger impact craters on the Moon (150-200 km in diameter) when scaled for gravity differences. The original crater has been differentially eroded; however, a subdued rim and distinct central uplift are still observed [1]. The inner portion of the structure is covered by the Mistastin Lake and the surrounding area is locally covered by soil/glacial deposits and vegetation. The crystalline target rocks of the Mistastin Lake region are dominated by anorthosite, granodiorite, and mangerite. Locally, allochthonous impactite units including impact melt and various types of breccias are unevenly distributed around the lake and on Horseshoe Island (interpreted as the remains of a central uplift). Previous studies of the Mistastin Lake impactites have primarily focussed on the melt rocks (e.g., [1], [2]). This project builds on these studies and further evaluates the suite of impactite rocks in terms of their context within the crater structure and origin of their components. Based on field mapping over three field seasons, the Mistastin Lake is interpreted as the outer edge of the collapsed transient crater of the Mistastin Lake impact structure and the plateaus extending up to 5 km away from the edge of the water are interpreted as terraces formed by collapse during the modification stage of crater formation. Exposed impactite units in this region, define a consistent stratigraphy, from bottom to top: autochthonous to parachthonous lithic (monomict) breccias, allochthonous lithic (polymict) breccias, and allochthonous impact melt. Impact melt and breccia deposits in the terraced rim are interpreted as proximal ejecta deposits. These units may be analogous to impact melt ponds that overlie the blocky continuous ejecta blanket [3]. Field relationships between Mistastin breccias and overlying melt units exhibit evidence of flow and are not consistent with an airborne mode of origin for either impactite type. Sharp contacts between these units suggest that there is a time gap between their depositions, and are consistent with a multi-stage impact ejecta emplacement process [4].
Mader Matthias
Osinski Gordon R.
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