scholarly journals Glasses in howardites: Impact melts or pyroclasts?

2013 ◽  
Vol 48 (5) ◽  
pp. 715-729 ◽  
Author(s):  
Sheryl A. Singerling ◽  
Harry Y. McSween ◽  
Larry A. Taylor
Keyword(s):  
Impact Melts

The Projectile of the Lappajärvi Impact Crater

1980 ◽  
Vol 35 (2) ◽  
pp. 197-203 ◽  
Author(s):  
Elke Göbel ◽  
Uwe Reimold ◽  
Hildegard Baddenhausen ◽  
Herbert Palme
Keyword(s):  
Impact Crater ◽  
Carbonaceous Chondrite ◽  
Volatile Elements ◽  
Rich Phase ◽  
Impact Melt ◽  
Siderophile Elements ◽  
High Concentrations ◽  
Impact Melts

Abstract Two impact melt samples from the Lappajärvi crater (Scandinavia) are highly enriched in siderophile elements, such as Ir, Re, and Os. This indicates the presence of a meteoritic component. The simultaneous enrichments of Ni, Co, Cr, and Se suggest a chondritic projectile. Because of the relatively large indigenous contributions to Ni, Co, and Cr, it is not possible to distinguish between a normal and a carbonaceous chondrite. The high concentrations of relatively volatile elements could point towards a volatile-rich projectile.The two melt samples have high Re/Ir ratios compared to chondritic ratios. Enrichment of Re relative to Ir is very unusual in terrestrial impact melts. Loss of Re, because of volatilisation under oxidizing conditions or by weathering is frequently observed.The high Re/Ir ratios and the high abundances of relatively volatile elements either indicate the presence of a volatile rich phase or they characterize a type of meteorite, which has not been sampled. Some lunar highland rocks have a pattern of meteoritic elements rather similar to that observed for the Lappajärvi meteorite.The Lappajärvi crater is, after Rocheehouart, the second European crater where a significant amount of meteoritic component has been found.A melt sample from the Lake St. Martin crater (Manitoba), did not show any enrichment in meteoritic elements.

Reclassification of four aubrites as enstatite chondrite impact melts: Potential geochemical analogs for Mercury

2019 ◽  
Vol 54 (4) ◽  
pp. 785-810 ◽  
Author(s):  
Arya Udry ◽  
Zoë E. Wilbur ◽  
Rachel R. Rahib ◽  
Francis M. McCubbin ◽  
Kathleen E. Vander Kaaden ◽  
...  
Keyword(s):  
Enstatite Chondrite ◽  
Impact Melts

Origin of Iron Meteorite Groups IAB and IIICD

1980 ◽  
Vol 35 (8) ◽  
pp. 781-795 ◽  
Author(s):  
John T. Wasson ◽  
John Willis ◽  
Chien M. Wai ◽  
Alfred Kracher
Keyword(s):  
Parent Body ◽  
Iron Meteorite ◽  
Iron Meteorites ◽  
Impact Melt ◽  
Equilibrium Crystallization ◽  
Ni Content ◽  
Oxide Phases ◽  
Host Metal ◽  
Impact Melts ◽  
The Impact

AbstractSeveral low-Ni iron meteorites previously assigned to group IAB are reclassified IIICD on the basis of lower Ge, Ga, W and Ir concentrations and higher As concentrations; the low-Ni extreme of IIICD is now 62 mg/g, that of IAB is 64 mg/g. The resulting fractionation patterns in the two groups are quite similar. It has long been established that, in contrast to the magmatic iron meteorite groups, IAB and IIICD did not form by fractional crystallization of a metallic magma. Other models have been proposed, but all have serious flaws. A new model is proposed involving the formation of each iron in small pools of impact melt on a parent body consisting of material similar to the chondritic inclusions found in some IAB and IIICD irons, but initially unequilibrated. These impact melts ranged in temperatures from ~ 1190 K to ~ 1350 K. The degree of equilibration between melt and unmelted solids ranged from minimal at the lowest temperature to moderate at the highest temperature. The lowest temperature melts were near the cotectic in the Fe-Ni-S system with Ni contents of ~ 12 atom %. Upon cooling, these precipitated metal having ~ 600 mg/g Ni by equilibrium crystallization. The Ni-rich melt resulted from the melting of Ni-rich sulfides and metal in the unequilibrated chondritic parent. Low-Ni irons formed in high temperature melts near the composition of the FeS-Fe eutectic or somewhat more metal rich. We suggest that the decreasing Ge, Ga and refractory abundances with increasing Ni concentration reflect the trapping of these elements in oxide phases in the unequilibrated chondritic material, and that very little entered the Ni-rich melt parental to the Oktibbeha County iron. The remaining elements tended to have element/Ni ratios in the melts that were more or less independent of temperature. The remarkable correlation between I-Xe age of the chondritic inclusions and Ni content of the host metal is explained by a detailed evolution of (mega)regolith in which these groups originated. The most Ni-rich melts could only be generated from an unequilibrated chondrite parent; as the continuing deposition of impact energy produced increasingly higher grades of metamorphism, the maximum Ni content of the impact melts (and their subsequently precipitated metal) gradually decreased.

Homogeneous impact melts produced by a heterogeneous target?

2003 ◽  
Vol 67 (4) ◽  
pp. 733-750 ◽  
Author(s):  
B Kettrup ◽  
A Deutsch ◽  
V.L Masaitis
Keyword(s):  
Impact Melts

Dissemination and fractionation of projectile materials in the impact melts from Wabar Crater, Saudi Arabia

Meteoritics ◽  
1992 ◽  
Vol 27 (4) ◽  
pp. 361-370 ◽  
Author(s):  
David W. Mittlefehldt ◽  
Thomas H. See ◽  
Friedrich Hörz
Keyword(s):  
Saudi Arabia ◽  
Impact Melts ◽  
The Impact

scholarly journals Initial observations of lunar impact melts and ejecta flows with the Mini-RF radar

2012 ◽  
Vol 117 (E12) ◽  
pp. n/a-n/a ◽  
Author(s):  
Lynn M. Carter ◽  
Catherine D. Neish ◽  
D. B. J. Bussey ◽  
Paul D. Spudis ◽  
G. Wesley Patterson ◽  
...  
Keyword(s):  
Lunar Impact ◽  
Impact Melts

scholarly journals GEOLOGICAL MAPPING OF LUNAR CRATER LALANDE: TOPOGRAPHIC CONFIGURATION, MORPHOLOGY AND CRATERING PROCESS

2017 ◽  
Vol XLII-3/W1 ◽  
pp. 77-83
Author(s):  
B. Li ◽  
Z.C. Ling ◽  
J. Zhang ◽  
J. Chen ◽  
C. Q. Liu ◽  
...  
Keyword(s):  
Volcanic Eruptions ◽  
Central Peak ◽  
Geological Mapping ◽  
Crater Floor ◽  
Linear Features ◽  
Melt Ponds ◽  
Volcanic Source ◽  
Interior Walls ◽  
Impact Melts ◽  
Geological Units

Highland crater Lalande (4.45° S, 8.63° W; D = 23.4 km) is located on the PKT area of the lunar near side, southeast of Mare Insularum. It is a complex crater in Copernican era and has three distinguishing features: high silicic anomaly, highest Th abundance and special landforms on its floor. There are some low-relief bulges on the left of crater floor with regular circle or ellipse shapes. They are ~ 250 to 680 m wide and ~ 30 to 91 m high with maximum flank slopes > 20°. There are two possible scenarios for the formation of these low-relief bulges which are impact melt products or young silicic volcanic eruptions. According to the absolute model ages of ejecta, melt ponds and hummocky floor, the ratio of diameter and depth, similar bugle features within other Copernican-aged craters and lack of volcanic source vents, we hypothesized that these low-relief bulges were most consistent with an origin of impact melts during the crater formation instead of small and young volcanic activities occurring on the crater floor. Based on Kaguya TC ortho-mosaic and DTM data produced by TC imagery in stereo, geological units and some linear features on the floor and wall of Lalande have been mapped. Eight geological units are organized by crater floor units: hummocky floor, central peak and low-relief bulges; and crater wall units: terraced walls, channeled and veneered walls, interior walls, mass wasting areas, blocky areas, and melt ponds. These geological units and linear features at Lalande provided us a chance to understand some details of the cratering process and elevation differences on the floor. We evaluated several possibilities to understand the potential causes for the observed elevation differences on the Lalande's floor. We proposed that late-stage wall collapse and subsidence due to melt cooling could be the possible causes of observed elevation differences on the floor.

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