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Morasko - The Largest Known Meteorite Strewnfield?
... Bartoschewitz and Spettel (2001) discovered that another iron from Germany, Tabarz, has a very similar composition. Because its location plots relatively close to a great circle passing through Morasko and Seel€ asgen, they suggested that it is also paired with these meteorites (Bartoschewitz 2001(Bartoschewitz , 2002Grossman and Zipfel 2001). However, its reported recovery location is 474 km from Morasko, a distance far greater than found in the largest strewn fields and very difficult to explain in terms of a plausible trajectory and atmospheric drag. ...
... The second variety of Morasko is cohenitefree, with wider kamacite bands that contain schreibersite in the form of irregular inclusions or as rhabdite crystals. This cohenite-free texture is also observed in Seel€ asgen and Tabarz (Bartoschewitz and Spettel 2001;Bartoschewitz 2001Bartoschewitz , 2002 and in the iron found in Jankowo Dolne. ...
Differences in texture and discovery location prompted us to analyze 16 irons from Morasko; one from Seeläsgen, known to have a similar composition; and a new mass found at Jankowo Dolne. These were analyzed in duplicate by instrumental neutron-activation analysis (INAA). The results show that all 18 samples have very similar compositions, distinct from all other IAB irons except Burgavli; we conclude that they are all from a single shower. Eight of the samples were from regions with large amounts of cohenite (but were largely free of inclusions) and six were from samples with very little cohenite; we could find no resolvable difference in composition between these sets, a fact that suggests that the C contents of the metal phases were similar in the two areas. Although Morasko has been classified into the IAB main group (IAB-MG), its Ir plots well outside the main group field on an Ir-Au diagram. We considered the possibility that the low Ir reflected contamination by a melt from a IAB region that ponded and experienced fractional crystallization; however, because Morasko has Pt, W, and Ga values that are the same as the highest values in IAB-MG, we rejected this model. We therefore conclude that Morasko formed from a different melt than the IAB-MG irons; the Morasko melt was produced by impact heating, but one or more of the main Ir carriers did not melt, leaving much of the Ir in the unmelted residue. Copper is the only element that shows resolvable differences among Morasko samples. Most (13 of 18) samples have 149 ± 4 μg g−1 Cu, but three have 213 ± 10 μg g−1; we interpret this to mean that the low-Cu samples have equilibrated with a Cu-rich phase, whereas there was none of the latter phase within a few diffusion lengths of the samples with high Cu contents.
Recent remote sensing analyses and field studies have shown that Bajada del Diablo, in Argentina, is a new crater-strewn field. Bajada del Diablo is located in a remote area of Chubut Province, Patagonia. This amazing strewn field contains more than 100 almost circular, crater-type structures with diameters ranging from 100 to 500 m in width and 30 to 50 m in depth. It is composed of three separated impact crater fields, which formed simultaneously. The impact was upon a Miocene basaltic plateau and Pliocene–Early Pleistocene pediments. The original crater field (60 km2) was later eroded by Late Pleistocene fluvial processes; thus, three major, separate areas were defined. Due to the erosional processes that have affected the area, it is difficult to determine yet if the crater field has a classic elliptical distribution. Crater structures are similar in target rocks, although showing different response and morphology in relation to rock type. They are simple rings, bowl-shaped with raised rimrock. Basaltic boulders have been deposited as a ring-shaped pile and the ejecta are found toward the NE flanks. The craters present a hummocky bottom, with dry ponds and lakes in the center, but they do not show raised central peaks. The rocks within the craters have strong and stable magnetic signature. No meteorite fragments or other diagnostic landmarks have been found yet. The craters have been partially filled in by debris flows from the rim and windblown sands in recent times. The origin of these crater fields may be related to multiple fragmentation of one asteroid that broke up before impact, perhaps traveling across the space as a rubble pile. Alternatively, multiple collisions of comet fragments could explain the formation of these crater fields. Based on field geological and geomorphological data, the age of this event is estimated to be bracketed between Early Pleistocene and Late Pleistocene (i.e., 0.78–0.13 Ma ago).
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