The Importance of Impact Melts

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2 The Importance of Impact Melts Constrain bombardment histories [Chapman et al. (2007)] Ar-Ar age dating [e.g. Norman et al. (2006)] Identify type of impactor Highly Siderophile Elements (HSE) [e.g. Puchtel et al. (2006)] Whole-rock and individual crystal chemistry Target material Composition of crust and (potentially) interior Melt sheet differentiation [e.g. Warren et al. (1996)] Crater scaling laws [Cintala & Grieve (1994); Cintala & Grieve (1998); Grieve & Cintala (1992); Grieve & Cintala (1997)] Remote Sensing [Tompkins & Pieters (2010)] Chapman C.R. et al. (2007) Icarus 189, ; Norman M.D. et al. (2006) GCA 70, ; Puchtel I.S. et al. (2006) LPSC 37 th, 1428; Warren P.H. et al. (1996) GSA Spec. Pap. 307, ; Cintala M. & R. Grieve (1994) GSA Spec. Pap. 293, 51-59; Cintala M. & R. Grieve (1998) MPS 33, ; Grieve R. & M. Cintala (1992), Meteoritics 27, ; Grieve R. & M. Cintala (1997) Adv. Space Res. 20, ; Tompkins S. and C. M. Pieters (2010) MPS 45,

3 Location, Location, Location Transient crater cavity Estimate size and melt volume [Spudis P. (1993); Warren P.H. et al. (1996); Grieve R. & M. Cintala (1992)] Spudis P. (1993) The Geology of Multi-Ring Impact Basins; Warren P.H. et al. (1996) GSA Spec. Pap. 307, ; Grieve R. & M. Cintala (1992), Meteoritics 27, French, B.M. (1998) Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures. LPI Cont. 954.

4 Location, Location, Location: King Crater Melt pools on wall terraces or outside crater Melt flows [Campbell B.A. et al. (2010); Bray V.J. et al. (2010)] Apollo 16 metric camera image AS16-M-0891 Blue- ejecta blanket Brown-distal ejecta blanket Yellow- faulted crater walls Green- slumped crater walls Grey-central peak Red-melt ponds Ashley et al. (2011), this conference; Campbell B.A. et al. (2010), Icarus 208, ; Bray V.J. et al. (2010), GRL 37, L21202.

5 N Giordano Bruno impact melt flow ~200m LROC image M RC

6 LRO-NAC image M R Giordano Bruno Bray et al Orientale ~100 km The Moon Issues and Considerations Mare Basalt Can obscure impact melt Distinguishing between can be difficult Site selection Large enough to have substantial impact melt Little or no mare basalt fill Mare basalt clearly distinct from impact melt Advantages Samples available on the surface Abundant remote sensing data LROC WAC mosaic

7 Mars: Science Priorities and impact melt #4: constrain absolute ages of major Martian crustal geologic processes including cratering #9: for present day surface and accessible shallow subsurface environments, determine preservation potential for chemical signatures of extant life and prebiotic chemistry by evaluating state of oxidation MEPAG ND-SAG (2008). Portion of HiRISE image of Tooting Crater s southern rim: Mouginis-Mark et al. (2007) 7th Conf. Mars, #1353

8 ~1 km ~10 km MOC red wide-angle M Schultz, P.H. and J.K. Mustard (2004), Impact melts and glasses on Mars, J. Geophys. Res., 109, E01001, doi: /2002JE MOC narrowangle M

9 Hale Crater 35.7 S, E ~1 km ~10 km MOC wide-angle M Schultz, P.H. and J.K. Mustard (2004), Impact melts and glasses on Mars, J. Geophys. Res., 109, E01001, doi: /2002JE MOC narrowangle M

10 Hale Crater 35.7 S, E ~1 km Issues and Considerations Atmospheric interference Drill cores? Site selection Large enough to have substantial impact melt Few dunes obscuring crater floor Advantages No in situ impact melt yet!!!! ~10 km MOC wide-angle M Schultz, P.H. and J.K. Mustard (2004), Impact melts and glasses on Mars, J. Geophys. Res., 109, E01001, doi: /2002JE MOC narrowangle M

11 Mercury- peak ring basins N Occur at smaller diameters than the Moon and Mars Impact velocity accelerated by Sun s gravity [16] Depth of melting ~ depth of transient crater [5-8, 16] Sample lower crust composition? Sample within peak ring MESSENGER NAC mosaic; credit :NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington ~100 km

12 Mercury- peak ring basins Smooth Plains Origin: Volcanic? [Prockter et al., 2009] Impact Melt? [Martellato et al., 2010] Image credit: Prockter, L.M. et al. (2009) LPSC, 40th, abstract #1758

13 Mercury-Caloris Basin Stratigraphic marker ( by)- Calorian Epoch MESSENGER enhanced-color image Nervo Formation [Fasset C.I. et al. (2009) EPSL 285, ] Impact melt or fallback ejecta Smooth plains Draped over and burying Caloris Montes First mapped based on Mariner 10 images Unambiguous exposures absent from MESSENGER Image produced by NASA/Johns Hopkins University Applied Physics Laboratory/Arizona State University/Carnegie Institution of Washington. Image reproduced courtesy of Science/AAAS

14 Mercury-Caloris Basin Issues Stratigraphic and Considerations marker ( Samples by)- Calorian directly Epoch from surface Site selection Nervo Formation [Fasset Large C.I. enough et al. (2009) to have EPSL substantial 285, impact ] melt Impact melt or fallback ejecta Peak ring basins Smooth plains Draped over and burying No Caloris in situ Montes impact melt yet!!!! First mapped based on Mariner 10 images Unambiguous exposures absent from MESSENGER Advantages MESSENGER enhanced-color image Image produced by NASA/Johns Hopkins University Applied Physics Laboratory/Arizona State University/Carnegie Institution of Washington. Image reproduced courtesy of Science/AAAS

15 Precursor Missions Detailed remote sensing studies Spectral instruments such as Moon Mineralogy Mapper (M 3 ) Digital Elevation Models (DEMs) High-Resolution imagery LROC, HiRISE Better criteria to distinguish impact melts from primary basalts Remotely and hand sample

16 Final Thoughts Impact Melt or Basalt? Tuesday Poster Session Fagan & Neal, Distinguishing between Apollo 14 high-alumina basalts and olivine vitrophyres: textural and chemical analyses of olivines, abstract #2149 Neal et al., Using quantitative petrography to distinguish between pristine basalts and impact melts from the Moon, abstract #2668 Special thanks to the SSSR workshop for funding this opportunity!!!