Shock and Impactor Signatures in Rio Cuarto Impactites, Argentina

Details Shock and Impactor Signatures in Rio Cuarto Impactites, Argentina Shock and Impactor Signatures in Rio Cuarto Impactites, Argentina

Jul 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28r.432s&link_type=abstract

Meteoritics, vol. 28, no. 3, volume 28, page 432

Computer Science

Impact Fractionation, Oblique Impacts, Rio Cuarto

Scientific paper

Glasses recovered from the Rio Cuarto (RC) Crater Field, Argentina [1] exhibit clear evidence for high-grade shock metamoIphism with inferred pressures exceeding 50 Gpa: decomposition of zircon to baddeleyite + SiO2, diaplectic and monomineralic phases, lechatelierite, sphene rimmed by ilmenite and minor pseudobrookite, and quenched skeletal remains of magnetite/titanomagnetite grains [2]. The large degree of heterogeneity and evidence for intense heating with rapid quenching are unlike naturally occurring glasses. Consequently the thermal history of the RC glasses are inconsistent with the suggestion that they are simply the result of brush fires [3]. Laboratory experiments using the NASA Ames Vertical Gun have been used to examine the products of impacted loess and possible fractionation of the impactor signature. Aluminum spheres and chondrite slugs (0.635 cm diameter) were impacted into loess at 15 degrees under vacuum and atmosphenc (argon) conditions. Ropy glasses produced in this experiment exhibited significant enhancement of MgO and CaO and depleted K2O and Na2O relative to the bulk target, whereas blocky fused products more closely resembled volcanic glass shards comprising the smallest fractions in the loess. Hollow glass spherules produced by the chondritic impactor exhibited not only enhanced MgO and CaO (and depleted K2O and Na2O) but also significant enhancements in Mn and Cr (factor of 15-20) without enhancement of Fe or Ni. Similar patterns can be documented within RC glasses as well as green glasses found at much larger distances. In such cases, Mn and Cr are directly proportional with levels ranging from those of bulk loess (<0.1% and 27 ppm, respectively) to levels (5-7% and 2000 ppm, respectively) approaching chondritic values. These preliminary experimental and sample analyses reinforce previous studies indicating severe fractionation of siderophiles from iron impactors [4,5]. Our results, however, document that the Cr/Ni ratio can significantly change during impact by a chondritic projectile and that the suspected chondritic impactor in the RC impact glasses is better represented by the lithophile trace elements, Cr and Mn. References: [1] Schultz P. H. and Lianza R. (1992) Nature, 355, 234-237. [2] Schultz P. H. et al. (1993) LPSC XIV, 1259-1260. [3] Bloom A. (1992) Geol. Soc. Am. Abs., 24, A136-A137. [4] Attrep M., Jr. el al. (1992) Proc. LPSC, Vol. 22, 39-40. [5] Mittlefehldt D. W. et al. (1992) Meteoritics, 27, 361-370.

Affiliated with

Also associated with

No associations

Rating

Shock and Impactor Signatures in Rio Cuarto Impactites, Argentina does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Shock and Impactor Signatures in Rio Cuarto Impactites, Argentina, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Shock and Impactor Signatures in Rio Cuarto Impactites, Argentina will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1073103