Abstract-We analyzed noble gases from 18 samples of weathering products ("iddingsite") from the Lafayette meteorite. Potassium-argon ages of 12 samples range from near zero to 670 * 91 Ma. These ages confirm the martian origin of the iddingsite, but it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration or incorporation of martian atmospheric 40Ar. In any case, because iddingsite formation requires liquid water, this data requires the presence of liquid water near the surface of Mars at least as recently as 1300 Ma ago, and probably as recently as 650 Ma ago. Krypton and Xe analysis of a single 34 p g sample indicates the presence of fractionated martian atmosphere within the iddingsite. This also confirms the martian origin of the iddingsite. The mechanism of incorporation could either be through interaction with liquid water during iddingsite formation or a result of shock implantation of adsorbed atmospheric gas.

The major‐ and minor‐element abundances were determined by electron microprobe in 1039 glasses from regoliths and regolith breccias to define the compositional topology of lunar glasses at the Apollo 16 landing site in the central highlands of the Moon. While impact glasses with chemical compositions similar to local materials (i.e., Apollo 16 rocks and regoliths) are abundant, glasses with exotic compositions (i.e., transported from other areas of the Moon) account for up to ˜30% of the population. A higher proportion of compositionally exotic, angular glass fragments exists when compared to compositionally exotic glass spherules. Ratios of non‐volatile lithophile elements (i.e., Al, Ti, Mg) have been used to constrain the original source materials of the impact glasses. This approach is immune to the effects of open‐system losses of volatile elements (e.g., Si, Na, K). Four impact glasses from one compositionally exotic group (low‐Mg high‐K Fra Mauro; lmHKFM) were selected for 40Ar/39 Ar dating. The individual fragments of lmHKFM glass all yielded ages of ˜3750 ± 50 Ma for the time of the impact event. Based on the petrography of these individual glasses, we conclude that the likely age of the impact event that formed these 4 glasses, as well as the possible time of their ballistic arrival at the Apollo 16 site from a large and distant cratering event (perhaps in the Procellarum KREEP terrain) (Zeigler et al. 2004), is 3730 ± 40 Ma, close to the accepted age for Imbrium.

No abstract

Abstract-20-25 mg whole rock samples of the nakhlites Lafayette and Nakhla have been analyzed via the 40 Ar-39 Ar technique, in part to verify their formation ages, but primarily, in an attempt to determine the timing of aqueous alteration in these martian meteorites. As in previous studies, plateaus in apparent age are observed at about 1300 Ma (1322 ± 10 for Lafayette, 1332 ± 10 and 1323 ± 11 for Nakhla), presumably corresponding to crystallization ages. The plateaus are not entirely flat, perhaps reflecting the effects of recoil during creation of 39 Ar in the nuclear irradiation.The first 5-20% of the K-derived Ar released from all three samples give apparent ages <1300 Ma. Coupled with the fact that chronometric isotopic studies of nakhlites typically show some disturbance, we believe the low temperature pattern represents more recent (than 1300 Ma) formation of martian aqueous alteration products such as iddingsite. No low temperature plateaus are observed. This is consistent with petrographic evidence for multiple formation events, although the lack of low temperature plateaus is far from conclusive. On the other hand, if there was a single time of alteration, we believe that it will be difficult, if not impossible, to determine it using the K-Ar system.

Barrier-EIFS (exterior insulation and finish system) refers to EIFS with no internal drainage plane or through-wall flashings to collect and drain water that bypasses the EIFS’s surface barrier. EIFS’s surface barrier consists of a thin lamina and exposed joint sealants at transitions to elements such as windows, projecting decks, and intersecting parapets to prevent water infiltration through the surface barrier. Breaches in the surface barrier, however, can cause water leakage into the wall and building interior. In some cases reasonable reduction of leakage and preservation of the exterior walls may be accomplished by reducing barrier-EIFS’s over-reliance on sealants, and by introducing watertight through-wall flashings at leakage-prone transitions and penetrations. The authors refer to this approach—providing flashings and localized drainage immediately around transitions and penetrations of wall elements while maintaining or improving the existing barrier-EIFS system away from such details—as “hybrid repairs.” A case study of repairs on an existing high-rise barrier-EIFS-clad building shows the in-service performance of the hybrid repair methodology. The subject building had experienced water leakage at intersections of the EIFS and other building envelope elements, including windows, doors, balcony deck-to-wall transitions, and intersecting parapets. Repairs to correct water leakage focused on creating reliable concealed flashings at these details, along with more common barrier-enhancement repairs over the original EIFS, which was generally left in place. To help evaluate the hybrid repairs’ effectiveness, the authors surveyed typical exterior repairs in place for 2–1/2 to 5–1/2 years and interior finishes in the areas of the repairs. The Authors interviewed residents in some units that had experienced chronic water intrusion prior to the repairs; residents commented that they have seen no water intrusion since the repairs. The survey and interviews with residents revealed no evidence or reports of reoccurring water intrusion, supporting the general effectiveness of the hybrid repairs on the subject building.